presentation on heat exchangers

Heat Transfer/Heat Exchanger

• How is the heat transfer?
• Mechanism of Convection
• Applications .
• Mean fluid Velocity and Boundary and their effect on the rate of heat transfer.
• Fundamental equation of heat transfer
• Logarithmic-mean temperature difference.
• Heat transfer Coefficients.
• Heat flux and Nusselt correlation
• Simulation program for Heat Exchanger

How is the heat transfer?�

• Heat can transfer between the surface of a solid conductor and the surrounding medium whenever temperature gradient exists.

Natural convection

Forced Convection

Natural and forced Convection

• Natural convection occurs whenever heat flows between a solid and fluid, or between fluid layers.
• As a result of heat exchange

Change in density of effective fluid layers taken place, which causes upward flow of heated fluid.

If this motion is associated with heat transfer mechanism only, then it is called Natural Convection

• If this motion is associated by mechanical means such as pumps, gravity or fans, the movement of the fluid is enforced.
• And in this case, we then speak of Forced convection .

Heat Exchangers�

• A device whose primary purpose is the transfer of energy between two fluids is named a Heat Exchanger.

Applications of Heat Exchangers

Heat Exchangers prevent car engine overheating and increase efficiency

Heat exchangers are used in Industry for heat transfer

Heat exchangers are used in AC and furnaces

• The closed-type exchanger is the most popular one.
• One example of this type is the Double pipe exchanger.
• In this type, the hot and cold fluid streams do not come into direct contact with each other. They are separated by a tube wall or flat plate.

Principle of Heat Exchanger

• First Law of Thermodynamic: “Energy is conserved.”
• Control Volume

Cross Section Area

Thermal Boundary Layer

Region I : Hot Liquid-Solid Convection

NEWTON’S LAW OF CCOLING

Region II : Conduction Across Copper Wall

FOURIER’S LAW

Region III: Solid – Cold Liquid Convection

BOUNDARY LAYER

Energy moves from hot fluid to a surface by convection, through the wall by conduction, and then by convection from the surface to the cold fluid.

• Velocity distribution and boundary layer

When fluid flow through a circular tube of uniform cross-suction and fully developed,

The velocity distribution depend on the type of the flow.

In laminar flow the volumetric flowrate is a function of the radius.

V = volumetric flowrate

u = average mean velocity

• In turbulent flow, there is no such distribution.
• The molecule of the flowing fluid which adjacent to the surface have zero velocity because of mass-attractive forces. Other fluid particles in the vicinity of this layer, when attempting to slid over it, are slow down by viscous forces.

Boundary layer

• Accordingly the temperature gradient is larger at the wall and through the viscous sub-layer, and small in the turbulent core.
• The reason for this is

1) Heat must transfer through the boundary layer by conduction.

2) Most of the fluid have a low thermal conductivity (k)

3) While in the turbulent core there are a rapid moving eddies, which they are equalizing the temperature.

Region I : Hot Liquid – Solid Convection

Region III : Solid – Cold Liquid Convection

U = The Overall Heat Transfer Coefficient [W/m.K]

Calculating U using Log Mean Temperature

Hot Stream :

Cold Stream:

Log Mean Temperature

CON CURRENT FLOW

COUNTER CURRENT FLOW

Log Mean Temperature evaluation

DIMENSIONLESS ANALYSIS TO CHARACTERIZE A HEAT EXCHANGER

• Further Simplification:

Can Be Obtained from 2 set of experiments

One set, run for constant Pr

And second set, run for constant Re

• For laminar flow

Nu = 1.62 (Re*Pr*L/D)

• Empirical Correlation
• Good To Predict within 20%
• Conditions: L/D > 10

0.6 < Pr < 16,700

Re > 20,000

• For turbulent flow

Experimental

• Two copper concentric pipes
• Inner pipe (ID = 7.9 mm, OD = 9.5 mm, L = 1.05 m)
• Outer pipe (ID = 11.1 mm, OD = 12.7 mm)
• Thermocouples placed at 10 locations along exchanger, T1 through T10

Hot Flow Rotameters

Temperature

Cold Flow rotameter

Heat Controller

Switch for concurrent and countercurrent flow

Temperature Controller

Examples of Exp. Results

Theoretical trend

y = 0.8002 x – 3.0841

Experimental trend

y = 0.7966 x – 3.5415

y = 0.3317 x + 4.2533

y = 0.4622 x – 3.8097

y = 0.026 x

y = 0.0175 x – 4.049

Experimental Nu = 0.0175Re 0.7966 Pr 0.4622

Theoretical Nu = 0.026Re 0.8 Pr 0.33

Effect of core tube velocity on the local and over all Heat Transfer coefficients

Understanding Heat Exchangers: A Guide

Learn how heat exchangers transfer heat between fluids in diverse applications, enhancing efficiency and conservation in engineering systems.

Heat exchangers are devices that facilitate the transfer of heat from one fluid to another without mixing them. Common in many industrial, commercial, and residential applications, these systems play a critical role in energy conservation and efficiency. This article explores the basic principles of heat exchangers, their various types, and real-world applications.

Basic Principles of Heat Exchange

At its core, a heat exchanger transfers heat energy through conductive and convective processes. The effectiveness of a heat exchanger is determined by factors such as the surface area of the heat exchange components, the temperature difference between the fluids, and the thermal conductivity of the materials involved. The general heat transfer equation used is:

Q = U * A * ΔT

• Q is the rate of heat transfer (in watts or joules per second).
• U stands for the overall heat transfer coefficient (in watts per square meter per kelvin).
• A is the heat transfer surface area (in square meters).
• ΔT is the temperature difference between the fluids (in kelvin).

Efficiency in a heat exchanger is enhanced by increasing the surface area in contact with the fluids or by maximizing turbulence, often by using fins or corrugations in the components’ designs.

Types of Heat Exchangers

Heat exchangers come in various designs, each suited to specific applications and fluid properties:

• Shell and Tube Heat Exchangers: These consist of a series of tubes, one set carrying the hot fluid and the other the cold fluid. Typically used in large-scale industrial applications where pressures are high.
• Plate Heat Exchangers: Constructed with corrugated plates arranged to form channels through which the fluids flow. They offer high heat transfer efficiency and are compact, making them ideal for use in food, beverage, and pharmaceutical industries.
• Air Cooled Heat Exchangers: Used primarily for cooling fluids with air, these are common in vehicle radiators and HVAC systems. They rely on fans to blow air across a network of tubes carrying the hot fluid.

Applications of Heat Exchangers

Heat exchangers are pivotal in numerous sectors:

• Power Generation: Used extensively in power plants, heat exchangers recover waste heat from exhaust gases to improve overall plant efficiency.
• Refrigeration and Air Conditioning: Heat exchangers are essential components of refrigerators and air conditioners, where they absorb and dissipate heat to regulate temperature.
• Chemical Processing: Chemical reactors often use heat exchangers to control the temperature of reactants, affecting the rate and yield of chemical reactions.
• Automotive: Cars use heat exchangers in the form of radiators and oil coolers to maintain engine temperature and prevent overheating.

Understanding the basic principles and applications of heat exchangers can significantly impact the design and operation of various systems in engineering. This knowledge assists engineers and technicians in selecting the most appropriate heat exchanger type, enhancing system efficiency and energy conservation.

Related Posts

• How heat exchangers recover waste heat
• Microchannel heat exchangers
• Advanced materials for heat exchangers

• Terminology
• Radiant Heat Transfer

Heat Exchangers

• Boiling Heat Transfer
• Heat Generation
• Continuity Equation
• Laminar/Turbulent Flow
• Bernoulli's Equation
• Natural Circulation
• Two-Phase Fluid Flow
• Centrifugal Pumps
• Unit Systems
• Force and Motion
• Newton's Laws
• Energy, Work, and Power
• Structure of Metals
• Properties of Metals
• Material Selection
• Thermal Stress
• Brittle Fracture

Check out these structural calculators :   • Beam Analysis     • Bolted Joints     • Lug Analysis   • Column Buckling

This page provides the chapter on heat exchangers from the "DOE Fundamentals Handbook: Thermodynamics, Heat Transfer, and Fluid Flow," DOE-HDBK-1012/2-92 , U.S. Department of Energy, June 1992.

Other related chapters from the "DOE Fundamentals Handbook: Thermodynamics, Heat Transfer, and Fluid Flow" can be seen to the right.

• Heat Transfer Terminology
• Conduction Heat Transfer
• Convection Heat Transfer

Heat exchangers are devices that are used to transfer thermal energy from one fluid to another without mixing the two fluids.

The transfer of thermal energy between fluids is one of the most important and frequently used processes in engineering. The transfer of heat is usually accomplished by means of a device known as a heat exchanger. Common applications of heat exchangers in the nuclear field include boilers, fan coolers, cooling water heat exchangers, and condensers.

The basic design of a heat exchanger normally has two fluids of different temperatures separated by some conducting medium. The most common design has one fluid flowing through metal tubes and the other fluid flowing around the tubes. On either side of the tube, heat is transferred by convection. Heat is transferred through the tube wall by conduction.

Heat exchangers may be divided into several categories or classifications. In the most commonly used type of heat exchanger, two fluids of different temperature flow in spaces separated by a tube wall. They transfer heat by convection and by conduction through the wall. This type is referred to as an "ordinary heat exchanger," as compared to the other two types classified as "regenerators" and "cooling towers."

An ordinary heat exchanger is single-phase or two-phase. In a single-phase heat exchanger, both of the fluids (cooled and heated) remain in their initial gaseous or liquid states. In two-phase exchangers, either of the fluids may change its phase during the heat exchange process. The steam generator and main condenser of nuclear facilities are of the two-phase, ordinary heat exchanger classification.

Single-phase heat exchangers are usually of the tube-and-shell type; that is, the exchanger consists of a set of tubes in a container called a shell (Figure 8). At the ends of the heat exchanger, the tube-side fluid is separated from the shell-side fluid by a tube sheet. The design of two-phase exchangers is essentially the same as that of single-phase exchangers.

Parallel and Counter-Flow Designs

Although ordinary heat exchangers may be extremely different in design and construction and may be of the single- or two-phase type, their modes of operation and effectiveness are largely determined by the direction of the fluid flow within the exchanger.

The most common arrangements for flow paths within a heat exchanger are counter-flow and parallel flow. A counter-flow heat exchanger is one in which the direction of the flow of one of the working fluids is opposite to the direction to the flow of the other fluid. In a parallel flow exchanger, both fluids in the heat exchanger flow in the same direction.

Figure 9 represents the directions of fluid flow in the parallel and counter-flow exchangers. Under comparable conditions, more heat is transferred in a counter-flow arrangement than in a parallel flow heat exchanger.

The temperature profiles of the two heat exchangers indicate two major disadvantages in the parallel-flow design. First, the large temperature difference at the ends (Figure 10) causes large thermal stresses. The opposing expansion and contraction of the construction materials due to diverse fluid temperatures can lead to eventual material failure. Second, the temperature of the cold fluid exiting the heat exchanger never exceeds the lowest temperature of the hot fluid. This relationship is a distinct disadvantage if the design purpose is to raise the temperature of the cold fluid.

The design of a parallel flow heat exchanger is advantageous when two fluids are required to be brought to nearly the same temperature.

The counter-flow heat exchanger has three significant advantages over the parallel flow design. First, the more uniform temperature difference between the two fluids minimizes the thermal stresses throughout the exchanger. Second, the outlet temperature of the cold fluid can approach the highest temperature of the hot fluid (the inlet temperature). Third, the more uniform temperature difference produces a more uniform rate of heat transfer throughout the heat exchanger.

Whether parallel or counter-flow, heat transfer within the heat exchanger involves both conduction and convection. One fluid (hot) convectively transfers heat to the tube wall where conduction takes place across the tube to the opposite wall. The heat is then convectively transferred to the second fluid. Because this process takes place over the entire length of the exchanger, the temperature of the fluids as they flow through the exchanger is not generally constant, but varies over the entire length, as indicated in Figure 10. The rate of heat transfer varies along the length of the exchanger tubes because its value depends upon the temperature difference between the hot and the cold fluid at the point being viewed.

Non-Regenerative Heat Exchanger

Applications of heat exchangers may be classified as either regenerative or non-regenerative. The non-regenerative application is the most frequent and involves two separate fluids. One fluid cools or heats the other with no interconnection between the two fluids. Heat that is removed from the hotter fluid is usually rejected to the environment or some other heat sink (Figure 11).

Regenerative Heat Exchanger

A regenerative heat exchanger typically uses the fluid from a different area of the same system for both the hot and cold fluids. An example of both regenerative and non-regenerative heat exchangers working in conjunction is commonly found in the purification system of a reactor facility. The primary coolant to be purified is drawn out of the primary system, passed through a regenerative heat exchanger, non-regenerative heat exchanger, demineralizer, back through the regenerative heat exchanger, and returned to the primary system (Figure 12).

In the regenerative heat exchanger, the water returning to the primary system is pre-heated by the water entering the purification system. This accomplishes two objectives. The first is to minimize the thermal stress in the primary system piping due to the cold temperature of the purified coolant being returned to the primary system.

The second is to reduce the temperature of the water entering the purification system prior to reaching the non-regenerative heat exchanger, allowing use of a smaller heat exchanger to achieve the desired temperature for purification. The primary advantage of a regenerative heat exchanger application is conservation of system energy (that is, less loss of system energy due to the cooling of the fluid).

Cooling Towers

The typical function of a cooling tower is to cool the water of a steam power plant by air that is brought into direct contact with the water. The water is mixed with vapor that diffuses from the condensate into the air. The formation of the vapor requires a considerable removal of internal energy from the water; the internal energy becomes "latent heat" of the vapor. Heat and mass exchange are coupled in this process, which is a steady-state process like the heat exchange in the ordinary heat exchanger.

Wooden cooling towers are sometimes employed in nuclear facilities and in factories of various industries. They generally consists of large chambers loosely filled with trays or similar wooden elements of construction. The water to be cooled is pumped to the top of the tower where it is distributed by spray or wooden troughs. It then falls through the tower, splashing down from deck to deck. A part of it evaporates into the air that passes through the tower. The enthalpy needed for the evaporation is taken from the water and transferred to the air, which is heated while the water cools. The air flow is either horizontal due to wind currents (cross flow) or vertically upward in counter-flow to the falling water. The counter-flow is caused by the chimney effect of the warm humid air in the tower or by fans at the bottom (forced draft) or at the top (induced flow) of the tower. Mechanical draft towers are more economical to construct and smaller in size than natural-convection towers of the same cooling capacity.

Log Mean Temperature Difference Application To Heat Exchangers

In order to solve certain heat exchanger problems, a log mean temperature difference (LMTD or ΔT lm ) must be evaluated before the heat removal from the heat exchanger is determined. The following example demonstrates such a calculation.

A liquid-to-liquid counterflow heat exchanger is used as part of an auxiliary system at a nuclear facility. The heat exchanger is used to heat a cold fluid from 120°F to 310°F. Assuming that the hot fluid enters at 500°F and leaves at 400°F, calculate the LMTD for the exchanger.

ΔT 2 = 400°F − 120°F = 280°F

ΔT 1 = 500°F − 310°F = 190°F

The solution to the heat exchanger problem may be simple enough to be represented by a straight-forward overall balance or may be so detailed as to require integral calculus. A steam generator, for example, can be analyzed by an overall energy balance from the feedwater inlet to the steam outlet in which the amount of heat transferred can be expressed simply as \( \dot{Q} = \dot{m} ~\Delta h \), where \( \dot{m} \) is the mass flow rate of the secondary coolant and Δh is the change in enthalpy of the fluid. The same steam generator can also be analyzed by an energy balance on the primary flow stream with the equation \( \dot{Q} = \dot{m} ~c_p ~\Delta T \), where \( \dot{m} \), c p , and ΔT are the mass flow rate, specific heat capacity, and temperature change of the primary coolant. The heat transfer rate of the steam generator can also be determined by comparing the temperatures on the primary and secondary sides with the heat transfer characteristics of the steam generator using the equation \( \dot{Q} = U_o ~A_o ~\Delta T_{lm} \).

Condensers are also examples of components found in nuclear facilities where the concept of LMTD is needed to address certain problems. When the steam enters the condenser, it gives up its latent heat of vaporization to the circulating water and changes phase to a liquid. Because condensation is taking place, it is appropriate to term this the latent heat of condensation. After the steam condenses, the saturated liquid will continue to transfer some heat to the circulating water system as it continues to fall to the bottom (hotwell) of the condenser. This continued cooling is called subcooling and is necessary to prevent cavitation in the condensate pumps.

The solution to condenser problems is approached in the same manner as those for steam generators, as shown in the following example.

Overall Heat Transfer Coefficient

When dealing with heat transfer across heat exchanger tubes, an overall heat transfer coefficient , U o , must be calculated. Earlier in this module we looked at a method for calculating U o for both rectangular and cylindrical coordinates. Since the thickness of a condenser tube wall is so small and the cross-sectional area for heat transfer is relatively constant, we can use Equation 2-11 to calculate U o .

Referring to the convection section of this manual , calculate the heat rate per foot of tube from a condenser under the following conditions. ΔT lm = 232°F. The outer diameter of the copper condenser tube is 0.75 in. with a wall thickness of 0.1 in. Assume the inner convective heat transfer coefficient is 2000 Btu/hr-ft 2 -°F, and the thermal conductivity of copper is 200 Btu/hr-ft-°F. The outer convective heat transfer coefficient is 1500 Btu/hr-ft 2 -°F.

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A Heat Exchanger is a device designed to transfer heat between two or more fluids (liquid, vapor, or gas) of different temperatures. On the basis of the heat exchanger, the heat transferring process can be gas-to-gas, liquid-to-gas, or liquid-to-liquid. The fluids are not in direct contact, unlike the distillation column.

This article focuses on the heat exchanger types, application, working, design codes, and exploring the various design considerations.

Table of Contents

Types of Heat Exchanger

There are mainly five types of heat exchanger used in the process industry-

• Double Pipe Type
• Shell and Tube Type
• Spiral Type
• Fin-fan or Air Cooler

Double Pipe Type Heat Exchanger

The double pipe type heat exchanger is one of the simplest types of heat exchangers. It is called a double pipe type heat exchanger because one fluid flows inside a pipe and the other fluid flows over that pipe and inside of another pipe that surrounds the first pipe.

The construction of Double Pipe Type Heat Exchanger is a concentric tube type. The fluid flow in a double-pipe heat exchanger can be co-current or counter-current.

There are mainly two types of fluid flow patterns: co-current flow pattern is when the flow of the two fluid streams is in the same direction, counter-current is when the flow of the fluid streams is in opposite directions.

As the conditions (inlet temperatures, flow rates, fluid properties, fluid composition, etc.) in the pipes change, the amount of heat transferred also changes. This transient behavior of the fluid leads to a change in the process temperatures, which will push to a point where the temperature distribution becomes steady.

When the heat starts to be transferred, as a result, the temperature of the fluids changes until the temperatures reach a steady-state (means equal temperature in both fluids). Their transient behavior is dependent on time.

In the double pipe type heat exchanger, a hot process fluid (coming from the process equipment) flows inside the inner pipe and transfers its heat to cooling water flowing in the outer pipe. The heat transfer is kept going until conditions change, such as flow rate or inlet temperature.

The new steady-state will be observed once the inlet and outlet temperatures of the hot and cool fluid become stable. In practice, the temperatures will never be completely stable, but with major changes in inlet temperatures, a relatively steady-state can be observed.

Note: Double pipe type heat exchangers can be paired in series or in parallel to increase the heat transfer rate for a system without complication.

Fluid allocation in the inner pipe or outer pipe.

• Corrosive fluids are generally flowing through inner pipes, as if they flow through the outer pipe, they will corrode both the pipes.
• The steam is usually passed through outer pipes and cooling water in the inner pipes.
• If both liquids are equally corrosive or non- corrosive in nature, cold fluid is passed through outer pipes in order to reduce the heat losses.
• It is one of the simplest and cheapest types of heat exchanger.
• It can be used for high temperature, high pressure, and highly viscous fluid services.
• It can be designed with longitudinal fins attached to the inner pipe to increase the heat transfer rate.

Limitations

• It provides less heat transfer area per unit length of the pipes as compared to other type heat exchangers.
• It can not bear the turbulency in the fluid flow through the pipes.

Application

• Polymer Industry
• Dairy Industry
• Chemical Industry

Before moving to other types of heat exchangers, let’s first understand the flow arrangement or pattern of the fluid in the heat exchanger.

Flow Arrangement or Pattern in the Heat Exchanger

Flow Arrangement, also known as the flow pattern, of a heat exchanger, refers to the direction of movement of the fluids within the heat exchanger in relation to each other. There are four types of flow patterns-

• Co-current flow
• Counter-current flow
• Hybrid-flow

Co-current Flow

Co-current flow also known as parallel-flow is the flow arrangement in which the fluids move parallel to each other and in the same direction. Although this flow pattern typically results in lower efficiencies than a counter-flow arrangement.

Counter-current Flow

Counter-current flow also known as counter-flow is the flow arrangement in which the fluids move anti-parallel (means parallel but in opposite directions) to each other within the heat exchanger. This is the most commonly used flow pattern in the heat exchanger.

A counter-flow arrangement typically performs the highest efficiencies, as it allows for the greatest amount of heat transfer rate between the two fluids.

In cross-flow arrangement, the fluids flow perpendicular to one another. The efficiency of this flow pattern type heat exchanger falls between the counter-current and co-current heat exchangers.

Hybrid Flow

In the Hybrid flow pattern, some combination of the above-mentioned flow arrangement is used. These types of flow patterned heat exchangers are typically used to accommodate the limitations of an application, such as space, budget, or temperature, and pressure requirements.

Figure 3, below, illustrates the various flow arrangement types-

Now, I hope you got an idea about the flow pattern or arrangement within the heat exchanger. Let’s move again to the other types of heat exchangers-

Shell and Tube Type Heat Exchanger

Out of all the types of heat exchangers, shell and tube type heat exchangers are the most versatile. A shell and tube type heat exchanger is designed with a number of tubes fixed on the tube-sheet placed inside a cylindrical shell.

The design of this type of heat exchanger allows flexibility to a wide range of pressures and temperatures. If we need to cool or heat a large amount of fluids or gases, the application of the shell and tube heat exchanger is an option to consider first.

A shell and tube type heat exchanger consists of a shell, tube bundle, tube sheet, baffle, tie rod, and two heads or caps at both ends of the shell. By selecting different design of these basic parts, we can have different types of heat exchanger as per TEMA .

Shell and Tube type heat exchangers are further classified on the basis of their design. There are mainly Four types-

• Fixed Shell and Tube Type
• U Tube Type
• Floating Head Type
• Kettle Type

Fixed Shell and Tube Type Heat Exchanger

A fixed shell and tube type heat exchanger has straight tubes fixed on the tube sheet and welded at both ends to the shell.

Fixed tube Sheet heat exchangers are the ones that are very much used in process industries, as there is absolutely no chance for intermixing of the two fluids.

Main components of a Shell and Tube Type Heat Exchanger

The main components of a shell and tube heat exchangers are as follow:

• Tube bundle : The tube bundle is the set of tubes that provide the heat transfer area between the two fluids that circulate inside the tubes and the fluid that circulates inside the shell.
• Tube sheet : The tube sheet is a metal plate with a drilled hole, where the tubes are housed, which are fixed by expansion or welding.
• Baffles: The baffles are used to control the general direction of flow inside the shell and also provides supports to the tubes.
• Tie Rod: It is used to separate the two baffles.
• Shell and connections : The shell is the cylindrical envelope of the second fluid. The shell is generally made of a steel plate shaped cylindrical and longitudinally welded. The shell has nozzle connections for the inlet and outlet of the secondary fluid.
• Removable heads : The removable heads are connected to the tubular plates at both ends of the heat exchanger whose objective is to provide the circulation of the product through the tubular beam.

Applications

• The fixed shell and tube type heat exchanger is applicable to all services where the temperature difference between the shell and tube is small.
• It can be installed vertically and horizontally both ways.
• The tubes can be cleaned mechanically after the removal of the bonnet.
• A wire brush can be used to clean the tube from inside.
• Rare leakage.
• Simple Construction
• The tube bundle is fixed to the shell and cannot be removed.
• The shell can not be cleaned mechanically, need to clean with the chemical.
• Limited to the lower temperature.

U Tube Type Heat Exchanger

As the name suggests, In this type of heat exchanger, the tube bundle is of “U” shaped . There is only one tube sheet as the tube is opened from one side only. All the tubes start from the upper half of this tube sheet and end within the lower half of the tube sheet, which makes a U-turn or U shape in the shell as shown in Figure 5, below-

• Expansion of shell and tube is independent hence used for high-temperature services.
• It is possible to clean the shell from the inside by removing the tube bundle.
• Tube bundle cleaning is possible from the outside.
• Cost-effective, as expansion joints are not needed and the tube bundle is free to expand or contract.
• Tube cleaning using the wire brush is not possible, as tubes are not straight.
• Removing the tube from the tube bundle is difficult.
• Installed only horizontally

Floating Head Type Heat Exchanger

In this type of shell and tube type heat exchanger, one end of the tubes is kept fixed in a tube sheet, while the other end of the tubes is free to expand or kept floating inside the shell.

A floating head type heat exchanger is one of the most used heat exchangers. Generally, both the shell and tube bundle are free of expansion or contraction, which causes no thermal stress production between the shell and tube bundle, if the temperature difference between the two fluid is large.

• Inspection is easy
• Expansion of tube and shell is not a problem
• Ease of Cleaning
• Accepted for the high-temperature application
• Suitable for the dirty fluid application, due to ease of cleaning
• High reliability and wide adaptability
• Tubes are straight, individual tubes can be replaced or cleaned without removing the tube bundle
• It overs comes the demerits of U tube type heat exchangers
• There is no limit for the number of tubes passes
• It is costly compare to the other heat exchangers
• A large number of gasket joints
• Leakage may be a problem, unlike the U tube type heat exchanger due to floating head.

Kettle Type Heat Exchanger or Reboiler

Kettle type heat exchanger mainly known as reboilers are used in the refineries within the distillation column assembly. It may require pumping of the distillation column bottoms liquid into the kettle, or there may be sufficient liquid head to deliver the liquid into the reboiler due to pressure head difference.

In this reboiler type heat exchanger, steam flows through the tube bundle and exits after getting condensate. The liquid from the bottom of the tower, commonly called the bottoms or bottom product flows through the shell side.

Kettle reboilers are reliable enough that they can handle high vaporization of up to 80% and are easy to maintain this level. It produces chemical vapor. The bundle of kettle type reboiler may of U tube type or floating head type.

Difference Between Reboiler and Boiler

Plate type heat exchanger.

A plate type heat exchanger is made of a series of parallel plates that are placed above the other plate (alternatively) so as to allow the formation of a series of channels for fluids to flow between them.

The gap between two adjacent plates creates the channel in which the fluid flows. You can increase or decrease the capacity of the heat exchanger by adding or removing the plates whenever required.

Inlet and outlet holes at the corners of the plates allow hot and cold fluids to flow through alternate channels in the exchanger so that a plate is always in contact on one side with the hot fluid and the other with the cold fluid.

The size range of a plate is recommended from a 100 mm x 300 mm up to 1000 mm x 2500 mm. The minimum number of plates is recommended in a single exchanger is 10 and the maximum can be several hundred.

The below figure shows the flow of fluids inside the plate type exchanger. Fluids are divided into several parallel streams and can produce a perfect counter-current flow.

• High Heat Transfer area and rate
• Compact Design and lower floor space requirement
• By increasing the number of plates, the heat transfer area can be increased
• Suitable for lower flow rate and heat-sensitive substances
• Lower liquid volume required
• Lower heat losses
• Ease of maintenance
• Limited to 150°C (for low-temperature application) and 300 psi pressure
• Leakage is more as compared to other types of heat exchangers
• Not suitable for high viscosity application
• The sump is required to collect the liquid between the plates
• The gasket used between the plates can not handle corrosive fluid
• Pressure drop is higher

Spiral Type Heat Exchanger

The spiral type heat exchanger is manufactured by rolling two metal plates around a central core to generate two concentric spiral flow passages, one for each fluid.  The plate edges are welded in a manner so that each fluid stays within its own passage and there is no bypass flow or intermixing of both fluids.

Channel plate width and the gap between plates are optimized for the specified duty, maximum heat transfer rate, and ease of access.  The plate gap is maintained by a welded spacer, although some exchanger do not require them.

Due to its circular design and large surface area to volume ratio, the spiral heat exchanger offers unique advantages over other types of heat exchangers.

• Higher Thermal Efficiency
• Self-Cleaning capacity for Passages
• Counter-current or Co-current flow pattern
• Less space required
• Less maintenance required
• Longer Operation duration is possible

Air Cooler or Fin-fan Cooler

The Air Cooled Heat Exchangers also known as Fin fan Cooler is nothing but the traditional name of Air Cooler. For example a radiator in the car. Although the Fins are used in the Cooler, it increases the residual time, which further increase the efficiency of the system. In this type of heat exchanger the ambient air used as the cooling medium.

• Used in overhead line of distillation column for cooling of the top product
• Used in a chiller to remove heat from condenser
• Mounted on pipe rack or may be on platform or structure

Fin Fan Cooler further classified in two types-

• Induced Draft
• Forced Draft

Difference Between Induced and Forced Draft Heat Exchanger

Refer below figure for better understanding

Heat Exchanger Selection Considerations

There are a wide range of heat exchangers available in the market or can be manufactured, the suitability of its type and design in transferring heat between fluids is dependent upon the specifications and requirements of the application. The calculation is done for the sizing of heat exchanger per the heat transfer rate requirement and some other consideration is taken for the selection of heat exchangers.

Some of the factors that the respective professionals should keep in mind while designing and choosing a heat exchanger-

• Type of fluids, stream, and their properties
• The required thermal outputs
• The availability of space
• Temperature range
• Project Budget
• Vendors availability
• Statutory Requirement
• Design code
• Application, etc.

Design Code Associated with the Heat Exchanger

The design code used for manufacturing heat exchanger is mentioned below-

TEMA (Tubular Exchanger Manufacturing Association)

TEMA is further categories on the application basis of heat exchangers-

• TEMA-R: If the heat exchanger is used in petrochemical, refineries or hydrocarbon industry
• TEMA-C: If the heat exchanger is used in general services
• TEMA-B: If the heat exchanger is used in chemical services

ASME (American Society of Mechanical Engineers)

• ASME Section II
• ASME Section V
• ASME Section VIII

You can watch the below video to feel the object

Few Related Posts Some Important Piping Codes and Standards Miter Bend Calculations For Fabrication Purpose Pipe Welding Positions: 1G, 2G, 5G, and 6G Pipe Thickness Calculation for Internal Pressure

References www.enggcyclopedia.com www.thomasnet.com Heat Exchangers: Selection, Rating, and Thermal Design Book by Anchasa Pramuanjaroenkij, Hongtan Liu, and S. Kakaç Heat Exchanger Design Handbook Book by Kuppan Thulukkanam www.onda-it.com unitedcoolingtower.com www.chartindustries.com

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Heat Exchanger – Types, Diagram, Working, Applications , Advantages

Table of Contents

Introduction to Heat Exchanger

A heat exchanger is a device, which transfers thermal energy between two fluids at different temperatures. In most of the thermal engineering applications, both of the fluids are in motion and the main mode of heat transfer is convection. Examples are automobile radiators, condenser coil in the refrigerator, air conditioner, solar water heater, chemical industries, domestic boilers, oil coolers in a heat engine, milk chillers in pasteurizing plant.

Classification of heat exchangers:

1. Classification according to construction:

• Tubular heat exchangers.
• Plate heat exchangers.
• Extended surface heat exchangers.
• Regenerative heat exchangers.

2. Classification according to the transfer process:

• Indirect contact heat exchangers.
• Direct contact heat exchangers.

3. Classification according to flow arrangement:

• Parallel flow exchangers.
• Counter flow heat exchangers.
• Cross flow heat exchangers.

4. Classification according to pass arrangement:

• Single pass arrangement.
• Multi-pass arrangement.

5. Classification according to surface compactness:

• Gas to liquid
• compact (β ≥ 700 m2/m3)
• non compact (β ≤ 700 m2/m3)
• Liquid to liquid and phase change
• compact (β ≥ 400 m2/m3)
• non compact (β ≤ 400 m2/m3)

6. Classification according to a number of fluids:

• Two fluids.
• Three fluids.

7. Classification according to the phase of the fluid.

• Gas- liquid.
• Liquid-liquid.

Materials for heat exchanger:

1. Aluminum 2. Stainless steel 3. Copper

Pipe in pipe heat exchangers:

Hairpin heat exchangers (often also referred to as “double pipes”) are characterized by a construction form which imparts a U shaped appearance to the heat exchanger. In its classical sense, the term double pipe refers to a heat exchanger consisting of a pipe within a pipe, usually of a straight-leg construction with no bends. However, due to the need for removable bundle construction and the ability to handle differential thermal expansion while avoiding the use of expansion joints (often the weak point of the exchanger), the current U-shaped configuration has become the standard in the industry.

Working: A double pipe heat exchanger, in its simplest form, is just one pipe inside another larger pipe. One fluid flows through the inside pipe and the other flows through the annulus between the two pipes. The wall of the inner pipe is the heat transfer surface. The pipes are usually doubled back multiple times as shown in the diagram at the left, in order to make the overall unit more compact. The term ‘hairpin heat exchanger’ is also used for a heat exchanger of the configuration in the diagram. A hairpin heat exchanger may have only one inside the pipe, or it may have multiple inside tubes, but it will always have the doubling back feature. Some heat exchanger advertises the availability of finned tubes in a hairpin or double pipe heat exchanger. These would always be longitudinal fins, rather than the more common radial fins used in a cross-flow finned tube heat exchanger. In a double pipe heat exchanger design, an important factor is the type of flow pattern in the heat exchanger. A double pipe heat exchanger will typically be either counterflow or parallel flow. Crossflow just doesn’t work for a double pipe heat exchanger. The flow pattern and the required heat exchange duty allow calculation of the log mean temperature difference. That together with an estimated overall heat transfer coefficient allows calculation of the required heat transfer surface area. Then pipe sizes, pipe lengths, and a number of bends can be determined.

Plate type heat exchanger

Construction and working of Plate type heat exchanger.

It consists of a series of closely spaced parallel plates with fins held in between. The plates separate the two fluids which flow through passages alternately formed between the plates. It also has fins attached over the primary heat transfer surface so as to increase the heat transfer area. This improves the effectiveness of the heat exchanger. Fins from the individual flow passages for single fluid. A typical cross-flow, both fluids unmixed arranged is shown below, in which heat is transferred between fluid “A” and fluid “B”. The counter flow or parallel flow arrangement can also be possible. The fins may be plain fin (Straight or corrugated) or interrupted and are attached to the plate by brazing or soldering. They are more suitable for gas to gas applications. Plate fin type heat exchanger is as shown in figure

Applications of plate type heat exchanger: a. Milk chilling plants b. Radiator in automobile c. Air conditioning d. Food industries

Shell and tube type heat exchanger

Shell and tube heat exchanger consists of a bundle of round tubes placed inside the cylindrical shell. The tube axis parallels to that of the shell. One fluid inside the tubes while the other over the tubes.

The main components of this type of heat exchanger are: i. Shell ii. Tube bundle iii. Front and rear headers of shell iv. baffles

The baffles provide the support to tubes and also deflect the fluid flow approximately normal to tubes. This increases the turbulence of shell-side fluid and improves heat transfer. The various types of baffles are existing and their type, spacing, shape, will depend on the flow rate, shell side pressure drop, required tube support, flow vibrations, etc.

The fluid combination may be : 1 Liquid to liquid 2 Liquid to gas 3 Gas to gas

Advantages of shell and tube type heat exchanger : 

• Less expensive as compared to Plate type coolers
• Can be used in systems with higher operating temperatures and pressures
• Pressure drop across a tube cooler is less
• Tube leaks are easily located and plugged since pressure test is comparatively easy
• Tubular coolers in the refrigeration system can act as a receiver also.
• Using sacrificial anodes protects the whole cooling system against corrosion
• Tube coolers may be preferred for lubricating oil cooling because of the pressure differential

Disadvantages of shell and tube heat exchanger : 

• Heat transfer efficiency is less compared to plate type cooler
• Cleaning and maintenance is difficult since a tube cooler requires enough clearance at one end to remove the tube nest
• Capacity of tube cooler cannot be increased.
• Requires more space in comparison to plate coolers

Shell and Coil type of heat exchanger

Construction of Shell and Coil Heat Exchanger 1. Shell and coil type heat exchanger consists of a helical coil. 2. The helical coil is compact in the shell. 3. The cooling medium is passed through the coil and liquid to be cooled is passed from the top of the shell. 4. The cooled liquid is taken out from the bottom of the shell. 5. Generally in this type of heat exchanger, the counter-flow arrangement is used.

Spiral Plate Heat Exchanger

It is a form of a plate heat exchanger usually made of stainless steel. It is often used in cellulose industries where the heat exchanger is subjected to severe fouling and corrosion. The plates of this type of heat exchanger are very long and thickness of passage between the plates must be rather small so that after the sheets forming the upper and lower surfaces are welded together, the unit can be wrapped into a spiral form. That’s why it is called as a spiral heat exchanger.

The technical features of this type of heat exchanger are : (a) Flow rates are relatively low (b) Pure counterflow heat exchanger (c) Highly compact (more than 700 m2/ m3) (d) Can withstand pressure up to 10 bar only

Regenerator

Heat exchangers in which there is an intermittent flow of heat from hot to cold fluid via heat storage and heat rejection through the exchanger surface or matrix are referred to as indirect or storage type heat exchanger or regenerator. The regenerative type heat exchangers are either static or dynamic.

Static Type Regenerator (a) No moving parts. (b) Consists of a porous medium (balls, pebbles, powders, etc.) through which hot and cold fluid pass alternatively. (c) A flow switching device regulates the periodic flow of the two fluids. (d) Compact for use in refrigeration and Stirling Engines. (e) Non-compact in high temperature (900 – 1500oC) applications. (f) Low cost and ruggedness are essential for the stationary type.

Storage Type or Regenerative Heat exchanger

The storage type or regenerative heat exchanger is shown in Figure 14.6. In this heat exchanger energy is stored periodically. Medium is heated or cooled alternatively. The heating period and cooling period constitute 1 (one) cycle.

Features (a) Periodic heat transfer-conduction. (b) Heat transfer fluid can be a liquid, phase changing, non-phase changing. (c) Solid storage medium is called matrix. (d) Matrix may be stationary or rotating

Classical Applications of Regenerator :  (a) Gas turbine regenerators: Heating the compressed air by the gas turbine exhaust before the air goes to the combustor. (b) Reversed Stirling engine for liquefaction of air-Philips refrigeration machine.

Applications of heat exchangers.

1. Food and beverages. 2. Petroleum/chemical processing. 3. Hydrocarbon processing. 4. Polymers. 5. Pharmaceuticals. 6. Industrial. 7. Energy and power.

Some Questions and Answers : 

1. Suggest the type of heat exchangers for following applications –

(i) A dairy plant (Milk Chilling Plant) (ii) The condenser of the refrigeration system. (Household system) Justify your answers

Answers: Types of Heat Exchanger Used for

1) Dairy Plant (Milk Chilling Plant)- Plate Type Heat Exchanger Because It is made up of an aluminum alloy which provides a higher rate of heat transfer. Due to larger surface area, It has more heat transfer as compared to other heat exchangers which is useful for dairy plants. It is lighter in weight.

2) The condenser of Refrigeration System:- Counter Flow tube type heat exchanger

Because High performance due to large surface area Compact and light in weight In tubes generally, turbulent flow is developed which reduces scale deposition. Less installation and maintenance cost.

2. Suggest the type of heat exchangers for following applications –

1) Mills Chiller Plant:- Plate type heat exchanger Justification:- a) Non-reactive material. b) Leakproof joints c) No mixing of two fluids d) Non-toxic material e) Non- corrosive material

2) The radiator of an Automobile:- Plate and tube type Heat Exchanger (Air Water Convective Radiator)

Justification:- a) it is used to cool the engine of an automobile b) Water flows through jacket along with engine and carried away heat by convection c) This water enter into the radiator where it gives its heat to the air of the atmosphere which is passed over water tubes. Though plates.

3. Classification of the heat exchanger and their applications

1. Nature of heat exchange process Heat exchangers, on the basis of nature of the heat exchange process, are classified as follows : (a) (i) Direct contact (or open) heat exchangers:- Examples : (i) Cooling towers ; (ii) Jet condensers ; (iii) Direct contact (ii) Indirect contact heat exchangers. (a) Regenerators:- Examples : (i) I.C. engines and gas turbines ; (ii) Open hearth and glass melting furnaces ; (iii) Air heaters of blast furnaces. (b) Recuperators Examples : (i) Automobile radiators, (ii) Oil coolers, intercoolers, air preheaters, economizers, superheaters, condensers and surface feed heaters of a steam power plant, (iii) Milk chiller of pasteurizing plant, (iv) Evaporator of an ice plant

2. The relative direction of fluid motion

According to the relative directions of two fluid streams the heat exchangers are classified into the following three categories (i) Parallel-flow or unidirectional flow :-: Examples: Oil coolers, oil heaters, water heaters etc. (ii) Counter-flow:- Examples: The cooling unit of refrigeration system etc. (iii) Cross-flow. Examples:- Automobile radiator etc.

3. Design and constructional features

On the basis of design and constructional features, the heat exchangers are classified as under : (i) Concentric tubes. (ii) Shell and tube (iii) Multiple shell and tube passes. (iv) Compact heat exchangers:- Example: Plate-fin, flattened fin tube exchangers, etc.

4. The physical state of fluids Depending upon the physical state of fluids the heat exchangers are classified as follows: Condensers (ii) Evaporators

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Sachin Thorat

Sachin is a B-TECH graduate in Mechanical Engineering from a reputed Engineering college. Currently, he is working in the sheet metal industry as a designer. Additionally, he has interested in Product Design, Animation, and Project design. He also likes to write articles related to the mechanical engineering field and tries to motivate other mechanical engineering students by his innovative project ideas, design, models and videos.

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This material is well explanatory and loaded. Keep good work up.

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Heat Exchanger Design - PowerPoint PPT Presentation

Heat Exchanger Design

Heat exchanger design anand v p gurumoorthy associate professor chemical engineering division school of mechanical & building sciences vit university – powerpoint ppt presentation.

• Anand V P Gurumoorthy
• Associate Professor
• Chemical Engineering Division
• School of Mechanical Building Sciences
• VIT University
• Vellore, India
• Recuperative
• Cold and hot fluid flow through the unit without mixing with each other. The transfer of heat occurs through the metal wall.
• Regenerative
• Same heating surface is alternately exposed to hot and cold fluid. Heat from hot fluid is stored by packings or solids this heat is passed over to the cold fluid.
• Direct contact
• Hot and cold fluids are in direct contact and mixing occurs among them mass transfer and heat transfer occur simultaneously.
• British Standard BS-3274
• TEMA standards are universally used.
• TEMA standards cover following classes of exchangers
• Class R designates severe requirements of petroleum and other related processing applications
• Class C moderate requirements of commercial and general process applications
• Class B specifies design and fabrication for chemical process service.
• Most commonly used type of heat transfer equipment in the chemical and allied industries.
• The configuration gives a large surface area in a small volume.
• Good mechanical layout a good shape for pressure operation.
• Uses well-established fabrication techniques.
• Can be constructed from a wide range of materials.
• Easily cleaned.
• Well established design procedures.
• Fixed tube design
• Simplest and cheapest type.
• Tube bundle cannot be removed for cleaning.
• No provision for differential expansion of shell and tubes.
• Use of this type limited to temperature difference upto 800C.
• Floating head design
• More versatile than fixed head exchangers.
• Suitable for higher temperature differentials.
• Bundles can be removed and cleaned (fouling liquids)
• Kern method
• Does not take into account bypass and leakage streams.
• Simple to apply and accurate enough for preliminary design calculations.
• Restricted to a fixed baffle cut (25).
• Bell-Delaware method
• Most widely used.
• Takes into account
• Leakage through the gaps between tubes and baffles and the baffles and shell.
• Bypassing of flow around the gap between tube bundle and shell.
• Stream Analysis method (by Tinker)
• More rigorous and generic.
• Best suited for computer calculations basis for most commercial computer codes.
• Tube diameters in the range 5/8 inch (16 mm) to 2 inch (50 mm).
• Smaller diameters (5/8 to 1 inch) preferred since this gives compact and cheap heat exchangers.
• Larger tubes for heavily fouling fluids.
• Steel tubes BS 3606 Other tubes BS 3274.
• Preferred tube lengths are 6 ft, 8 ft, 12 ft, 16 ft, 20 ft and 24 ft optimum tube length to shell diameter ratio 5 10.
• ¾ in (19 mm) is a good starting trial tube diameter.
• Tubes usually arranged in equilateral triangular, square or rotated square patterns.
• Tube pitch, Pt, is 1.25 times OD.
• Shell should be a close fit to the tube bundle to reduce bypassing.
• Shell-bundle clearance will depend on type of heat exchanger.
• Bundle diameter depends not only on number of tubes but also number of tube passes.
• Nt is the number of tubes
• Db is the bundle diameter (mm)
• D0 is tube outside diameter (mm)
• n1 and K1 are constants
• Baffles are used
• To direct the fluid stream across the tubes
• To increase the fluid velocity
• To improve the rate of transfer
• Most commonly used baffle is the single segmental baffle.
• Optimal baffle cut 20-25
• General equation for heat transfer is
• where Q is the rate of heat transfer (duty),
• U is the overall heat transfer coefficient,
• A is the area for heat transfer
• ?Tm is the mean temperature difference
• We are not doing a mechanical design, only a thermal design.
• Overall coefficient given by
• h0 (hi) is outside (inside) film coefficient
• hod (hid) is outside (inside) dirt coefficient
• kw is the tube wall conductivity
• do (di) is outside (inside) tube diameters
• Magnitude of individual coefficients will depend on
• Nature of transfer processes (conduction, convection, radiation, etc.)
• Physical properties of fluids
• Fluid flow rates
• Physical layout of heat transfer surface
• Physical layout cannot be determined until area is known hence design is a trial-and-error procedure.
• Difficult to predict and usually based on past experience
• To determine A, ?Tm must be estimated
• True counter-current flow logarithmic temperature difference (LMTD)
• LMTD is given by
• where T1 is the hot fluid temperature, inlet
• T2 is the hot fluid temperature, outlet
• t1 is the cold fluid temperature, inlet
• t2 is the cold fluid temperature, outlet
• Obtained from LMTD using a correction factor
• ?Tm is the true temperature difference
• Ft is the correction factor
• Ft is related to two dimensionless ratios
• Temperature correction factor, one shell pass, two or more even tube passes
• Fluid temperatures
• Operating pressures
• Pressure drop
• Stream flow rates
• High velocities give high heat-transfer coefficients but also high pressure drop.
• Velocity must be high enough to prevent settling of solids, but not so high as to cause erosion.
• High velocities will reduce fouling
• For liquids, the velocities should be as follows
• Tube side Process liquid 1-2m/s
• Maximum 4m/s if required to reduce fouling
• Water 1.5 2.5 m/s
• Shell side 0.3 1 m/s
• As the process fluids move through the heat exchanger there is associated pressure drop.
• For liquids viscosity lt 1mNs/m2 35kN/m2
• Viscosity 1 10 mNs/m2 50-70kN/m2
• For turbulent flow inside conduits of uniform cross-section, Sieder-Tate equation is applicable
• C0.021 for gases
• 0.023 for low viscosity liquids
• 0.027 for viscous liquids
• µ fluid viscosity at bulk fluid temperature
• µwfluid viscosity at the wall
• Butterworth equation
• For laminar flow (Relt2000)
• If Nu given by above equation is less than 3.5, it should be taken as 3.5
• j factor similar to friction factor used for pressure drop
• This equation is valid for both laminar and turbulent flows.
• Many equations for hi have developed specifically for water. One such equation is
• where hi is the inside coefficient (W/m2 0C)
• t is the water temperature (0C)
• ut is water velocity (m/s)
• dt is tube inside diameter (mm)
• where ?P is tube-side pressure drop (N/m2)
• Np is number of tube-side passes
• ut is tube-side velocity (m/s)
• L is the length of one tube
• m is 0.25 for laminar and 0.14 for turbulent
• jf is dimensionless friction factor for heat exchanger tubes
• Kerns method
• Bells method
• Calculate area for cross-flow As for the hypothetical row of tubes in the shell equator.
• pt is the tube pitch
• d0 is the tube outside diameter
• Ds is the shell inside diameter
• lB is the baffle spacing, m.
• Calculate shell-side mass velocity Gs and linear velocity, us.
• where Ws is the fluid mass flow rate in the shell in kg/s
• Calculate the shell side equivalent diameter (hydraulic diameter).
• For a square pitch arrangement
• For a triangular pitch arrangement
• The shell-side Reynolds number is given by
• The coefficient hs is given by
• where jh is given by the following chart
• The shell-side pressure drop is given by
• where jf is the friction factor given by following chart.
• In Bells method, the heat transfer coefficient and pressure drop are estimated from correlations for flow over ideal tube banks.
• The effects of leakage, by-passing, and flow in the window zone are allowed for by applying correction factors.
• where hoc is heat transfer coeff for cross flow over ideal tube banks
• Fn is correction factor to allow for no. of vertical tube rows
• Fw is window effect correction factor
• Fb is bypass stream correction factor
• FL is leakage correction factor
• The Re for cross-flow through the tube bank is given by
• Gs is the mass flow rate per unit area
• d0 is tube OD
• Heat transfer coefficient is given by
• For Regt2100, Fn is obtained as a function of Ncv (no. of tubes between baffle tips) from the chart below
• For Re 100ltRelt2100, Fn1.0
• For Relt100,
• Fw, the window correction factor is obtained from the following chart
• where Rw is the ratio of bundle cross-sectional area in the window zone to the tube bundle cross-sectional area (obtained from simple formulae).
• Clearance area between the bundle and the shell
• For the case of no sealing strips, Fb as a function of Ab/As can be obtained from the following chart
• For sealing strips, for NsltNcv/2 (Ns is the number of baffle strips)
• where a1.5 for Relt100 and a1.35 for Regt100.
• Tube-baffle clearance area Atb is given by
• Shell-baffle clearance area Asb is given by
• where Cs is baffle to shell clearance and ?b is the angle subtended by baffle chord
• where ßL is a factor obtained from following chart
• Involves three components
• Pressure drop in cross-flow zone
• Pressure drop in window zone
• Pressure drop in end zone
• where ?Pi pressure drop calculated for an equivalent ideal tube bank
• Fb is bypass correction factor
• where jf is given by the following chart
• Ncv is number of tube rows crossed
• us is shell-side velocity
• a is 5.0 for laminar flow, Relt100
• 4.0 for transitional and turbulent flow, Regt100
• Ab is the clearance area between the bundle and shell
• Ns is the number of sealing strips encountered by bypass stream
• Ncv is the number of tube rows encountered in the cross- flow section
• where Atb is the tube to baffle clearance area
• Asb is the shell to baffle clearance area
• AL is total leakage area AtbAsb
• ßL is factor obtained from following chart
• where us is the geometric mean velocity
• uw is the velocity in the window zone
• Ws is the shell-side fluid mass flow
• Nwv is number of restrictions for cross-flow in window zone, approximately equal to the number of tube rows.
• Ncv is the number of tube rows encountered in the cross-flow section
• Above calculation assumes clean tubes
• Effect of fouling on pressure drop is given by table above
• Construction of a condenser is similar to other shell and tube heat exchangers, but with a wider baffle spacing
• Four condenser configurations
• Horizontal, with condensation in the shell
• Horizontal, with condensation in the tubes
• Vertical, with condensation in the shell
• Vertical, with condensation in the tubes
• Horizontal shell-side and vertical tube-side are the most commonly used types of condenser.
• Filmwise condensation
• Normal mechanism for heat transfer in commercial condensers
• Dropwise condensation
• Will give higher heat transfer coefficients but is unpredictable
• Not yet considered a practical proposition for the design of condensers
• In the Nusselt model of condensation laminar flow is assumed in the film, and heat transfer is assumed to take place entirely by conduction through the film.
• Nusselt model strictly applied only at low liquid and vapor rates when the film is undisturbed.
• At higher rates, turbulence is induced in the liquid film increasing the rate of heat transfer over that predicted by Nusselt model.
• where (hc)1 is the mean condensation film coefficient, for a single tube
• kL is the condensate thermal conductivity
• ?L is the condensate density
• ?v is the vapour density
• µL is the condensate viscosity
• g is the gravitational acceleration
• G is the tube loading, the condensate flow per unit length of tube.
• If there are Nr tubes in a vertical row and the condensate is assumed to flow smoothly from row to row, and if the flow is laminar, the top tube film coefficient is given by
• In practice, condensate will not flow smoothly from tube to tube.
• Kerns estimate of mean coefficient for a tube bundle is given by
• L is the tube length
• Wc is the total condensate flow
• Nt is the total number of tubes in the bundle
• Nr is the average number of tubes in a vertical tube row
• For low-viscosity condensates the correction for the number of tube rows is generally ignored.
• For condensation inside and outside vertical tubes the Nusselt model gives
• where (hc)v is the mean condensation coefficient
• Gv is the vertical tube loading, condensate per unit tube perimeter
• Above equation applicable for Relt30
• For higher Re the above equation gives a conservative (safe) estimate.
• For Regt2000, turbulent flow situation analyzed by Colburn and results in following chart.
• A correlation for shear-controlled condensation in tubes simple to use.
• The correlation gives mean coefficient between two points at which vapor quality, x, (mass fraction of vapour) is known.
• 1,2 refer to inlet and outlet conditions respectively
• In a condenser, the inlet stream will normally be saturated vapour and vapour will be totally condensed. For these conditions
• When the vapor flows up the tube, tubes should not flood.
• Flooding should not occur if the following condition is satisfied
• where uv and uL are velocities of vapor and liquid and di is in metres.
• The critical condition will occur at the bottom of the tube, so vapor and liquid velocities should be evaluated at this point.
• When condensation occurs, the heat transfer coefficient at any point along the tube will depend on the flow pattern at that point.
• No general satisfactory method exists that will give accurate predictions over a wide flow range.
• Two flow models
• Stratified flow
• Limiting condition at low condensate and vapor rates
• Annular flow
• Limiting condition at high vapor and low condensate rates
• For stratified flow, the condensate film coefficient can be estimated as
• Condensation of steam
• For air-free steam a coefficient of 8000 W/m2-0C should be used.
• Mean Temperature Difference
• A pure, saturated, vapor will condense at a constant temperature, at constant pressure.
• For an isothermal process such as this, the LMTD is given by
• where Tsat is saturation temperature of vapor
• t1 (t2) is the inlet (outlet) coolant temperature
• No correction factor for multiple passes is needed.

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CLASSIFICATION OF HEAT EXCHANGERS

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HEAT EXCHANGER

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HEAT EXCHANGER. * Heat exchanger used to transfer thermal energy from one medium to another for the purpose of cooling and heating.*. *Types of heat exchangers -Air Cooled -Double Pipe -Spiral Plate and Tube -Shell and Tube.

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* Heat exchanger used to transfer thermal energy from one medium to another for the purpose of cooling and heating.*

*Types of heat exchangers -Air Cooled -Double Pipe -Spiral Plate and Tube -Shell and Tube

The media may be separated by a solid wall, so that they never mix, or they may be in direct contact. They are widely used in space heating, refrigeration, air conditioning, power plants, chemical plants, petrochemical plants, petroleum refineries, natural gas processing, and sewage treatment. One common example of a heat exchanger is the radiator in a car, in which the heat source, being a hot engine-cooling fluid, water, transfers heat to air flowing through the radiator.

One common example of a heat exchanger is the radiator in a car, in which the heat source, being a hot engine-cooling fluid, water, transfers heat to air flowing through the radiator.

Radiator Diagram

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HEAT EXCHANGER. By Farhan Ahmad Department of Chemical Engineering, University of Engineering &amp; Technology Lahore . Criteria for the selection of heat exchanger.

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Heat Exchanger Selection

Lecture series. Introduction to heat exchangersSelection of the best type for a given applicationSelection of right shell and tubeDesign of shell and tube. Q = U A ?T. The steps.

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Heat Exchanger Design

Problem Statement. Design a heat exchanger that cools a corrosive chemical with water properties from 45 C to 25 C with a mass flow rate of 220,000 kg/hr using city water at 22 C with variable mass flow rate.. Design Requirements. Heat Exchanger Length is less than 7 mHeat Exchanger

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Objective. To design a heat exchanger than meets the following criteria:Cools liquid from 45 C to 25 CMust be less than 7 meters in lengthShell diameter is less than 2 metersMinimize weight of the tube and shellMinimize pressure dropHeat transfer ratio of 1. Design Parameters.

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Heat Exchanger Design. ME 414 – Team #1 Jennifer Hacker Jesse Kendall Christopher Rogers Brandon Rodriguez Alek Vanluchene. Problem Statement.

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Heat Exchanger Correlations

COUNTER FLOW. PARALLEL FLOW. C min = min (C H ,C C ). T. T. HOT FLUID. D T 1. D T H. D T H. HOT FLUID. D T. D T max. D T 1. D T LM. D T LM. D T. D T 2. D T C. D T 2. D T C. COLD FLUID. COLD FLUID. d A. d A. A. A. Heat Exchanger Correlations.

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Heat Exchanger Design. Logan Schafer David McGown Mahmoud Abdelrazzaq Malhar Dave. Fixed Variables. Factors to be Considered using DOE. DOE 1 Comparison of 4 Variables. DOE 1 Factorial Design Analysis. Weight. DP_shell. DP_tube. Q_calc. Optimization of DOE 1.

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oil heat exchanger

2. 2. P. P. 5. 3. 3. hydraulic heat exchanger. oil heat exchanger. 1. 1. F. inflow. outflow. Venturi bilge uplift. F. exhaust heat exchanger. 4. deck wash. 6. Engine cooling heat exchanger. engine. P. F. aft bilge. f’wd bilge 1. f’wd bilge 2. inflow. filter. pump.

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HEAT EXCHANGER. GUIDED BY: PREPARED BY: Prof. S.C. Sharma Aayush Toshniwal Harsh Chudgar Nikhil Lele. FOULING FACTOR.

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Heat Exchanger Stall

Heat Exchanger Stall. Condensate Return. Hotter boiler feed water temperatures Minimizes the amount of chemicals required to treat boiler feed water Eliminates environmental concerns Minimizes water usage which is critical in some areas

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Heat Transfer/Heat Exchanger

Heat Transfer/Heat Exchanger. How is the heat transfer? Mechanism of Convection Applications . Mean fluid Velocity and Boundary and their effect on the rate of heat transfer. Fundamental equation of heat transfer Logarithmic-mean temperature difference. Heat transfer Coefficients.

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Heat Exchanger Design. ME 414- Fluid Systems Design Professor: John Toksoy Spring 2009 team Tyler Laughlin Denis Shkurapet Ethan Sneed Matt Tolentino Tyler Turk. Objective. To design a heat exchanger than meets the following criteria: Cools liquid from 45 C to 25 C

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PLATE HEAT EXCHANGER

PLATE HEAT EXCHANGER. GROUP MEMBERS. Nadeem Akhtar (2006-chem-22) Matloob Ahmed (2006-chem-26) Zohaib Atiq Khan (2006-chem-40). Introduction to PHE. Second abundantly used HEX after STHE. Fall in the category of compact heat exchangers.

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Heat Exchanger Design. Fall 2005 December 13, 2005. ME 414 Thermal / Fluid System Design William Donelson Josh Fosso Laurie Klank Jonathan Moore. Professor: John Toksoy. Problem. Cool a Fluid From 35 ºC to 25ºC Mass Flow 80,000 kg/hr Fluid is Corrosive

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HEAT EXCHANGER. By Farhan Ahmad Department of Chemical Engineering, University of Engineering &amp; Technology Lahore. Criteria for the selection of heat exchanger. Suitable on the grounds of operating pressure and temperature, fluid-material compatibility, handling, extreme thermal conditions

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Heat Exchanger

Heat Exchanger. Heat exchangers can be described as: they include all devices that are designed for exchanging heat. Only heat exchangers that are meant to exchange heat between two fluids are taken into account.

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Tubular Heat Exchanger

We offer Tabular Heat Exchanger that comes under the category of Heat Transfer Lab Equipment. It is used to study the fundamental concepts of heat exchanger.

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Heat Exchanger Manufacturer

We are involved in the manufacture and supply of all types of heat exchanger. Our heat exchangers are made of high quality steel and have a high structural strength and a longer service life. Know more about heat exchangers at: http://www.galaxyprocess.in/

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Heat Exchanger Tubes

TitaniumMetal is one of the leading manufacturers, Supplier and exporters of high quality Heat Exchanger Tubes, Stainless Steel 316Ti Round Bars, Inconel, Incoloy, 6Al4V titanium, Hastelloy, Steel 316Ti Round bar Supplier in Malaysia. Visit us:- https://titaniummetal.com.my/2016/09/26/heat-exchanger-tubes-seamless-welded/

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