Shell-and-tube heat exchangers are commonly used in chemical processes due to their advantages over other heat exchangers. They consist of tubes bundled together in a shell. Fluids can flow through either the tubes or shell. Pressure and temperature changes can be accommodated, materials can be selected to resist corrosion, and cleaning is straightforward by dismantling. Heat transfer is calculated based on fluid properties and flow configurations through the tubes and shell. Pressure drops through the tubes and shell are also estimated based on flow properties.
This document evaluates the performance of an air heater that was installed at a power plant as part of an efficiency improvement project. It describes the standard ASME method for evaluating air heater performance and discusses issues with applying that method in practice. The document then presents a new method for applying the vendor's performance curves to evaluate the air heater performance according to the ASME standard. It derives equations to calculate temperature correction factors needed for the evaluation and discusses estimating the uncertainty of the results.
This document summarizes an aerothermodynamic study of a generic flap configuration with an open gap conducted by researchers at the German Aerospace Center. The study used computational fluid dynamics simulations and experiments in a high enthalpy shock tunnel to better understand flap efficiency and heating effects. Experiments were performed using the shock tunnel at Mach numbers representative of the planned re-entry trajectory of the EXPERT spacecraft. Pressure and temperature measurements on the flap and body surfaces were taken to validate the CFD simulations.
This document outlines the objectives and content of a lecture on analyzing complete vapor compression refrigeration systems. The key points are:
1. It will discuss the importance of analyzing full systems and the graphical and analytical methods used.
2. It will cover the performance characteristics of compressors, condensers, evaporators, and expansion valves.
3. It will examine how to determine the balance point of a complete system by matching the characteristics of its individual components.
List of Detectable Gasses and Vapors by CAS-Number 2015Flow-Tech, Inc.
The CAS-number is a worldwide used code to identify a chemical substance non-ambiguously. This number is issued by the Chemical Abstracts Service and is the easiest way to characterize a chemical substance. Knowing the CAS-No. means to be able to get comprehensive information and links from internet and search engines.
This document is a gas list from Dräger that provides information on detectable gases and vapors. It includes three search indexes to find substances by name, CAS number, or sum formula. The main part of the list includes 17 columns with details on each substance such as molecular weight, density, boiling point, flash point, LEL levels, autoignition temperature, and toxic limit values. It also indicates which Dräger gas detection instruments are suitable for detecting each substance.
5.good practice & hr imp activitiesRavi Shankar
The document provides guidance on good practices for collecting and maintaining important technical information about a power plant's equipment and operations. It recommends assembling a thermal kit from the turbine supplier with performance curves, as well as collecting heat balance diagrams, pump/fan curves, piping diagrams, specifications for heat exchangers and flow elements, and historical operating data. Maintaining this information in a centralized location helps engineers properly evaluate equipment performance and potential improvement projects.
This document describes a CFD analysis of fluid flow through tube banks in heat recovery steam generators (HRSGs). The authors developed a new procedure to define porous medium parameters like loss coefficients starting from 3D simulations of flow through tube banks. Both finned and bare tube banks were considered. The analysis was performed using the commercial CFD code Fluent to simulate flow through a single tube row and investigate the effects of Reynolds number, inlet yaw angle, and inlet pitch angle on pressure drop and outlet flow angles. Results were compared to experimental data for a real fired HRSG to validate the proposed porous media modeling approach.
P&w tables of compressible flow functionsJulio Banks
Compressible-flow Mach Functionas
Page 5 - Nomenclature
Pages 6 & 7 - Mach Functions
Recommendaitons: Used Equations on Pp. 6 & 7 to
generate any of the results from the table as functions
of specific heat ration, Gamma = Cp/Cv.
Enjoy it as one would enjoy their favorite music.
This document evaluates the performance of an air heater that was installed at a power plant as part of an efficiency improvement project. It describes the standard ASME method for evaluating air heater performance and discusses issues with applying that method in practice. The document then presents a new method for applying the vendor's performance curves to evaluate the air heater performance according to the ASME standard. It derives equations to calculate temperature correction factors needed for the evaluation and discusses estimating the uncertainty of the results.
This document summarizes an aerothermodynamic study of a generic flap configuration with an open gap conducted by researchers at the German Aerospace Center. The study used computational fluid dynamics simulations and experiments in a high enthalpy shock tunnel to better understand flap efficiency and heating effects. Experiments were performed using the shock tunnel at Mach numbers representative of the planned re-entry trajectory of the EXPERT spacecraft. Pressure and temperature measurements on the flap and body surfaces were taken to validate the CFD simulations.
This document outlines the objectives and content of a lecture on analyzing complete vapor compression refrigeration systems. The key points are:
1. It will discuss the importance of analyzing full systems and the graphical and analytical methods used.
2. It will cover the performance characteristics of compressors, condensers, evaporators, and expansion valves.
3. It will examine how to determine the balance point of a complete system by matching the characteristics of its individual components.
List of Detectable Gasses and Vapors by CAS-Number 2015Flow-Tech, Inc.
The CAS-number is a worldwide used code to identify a chemical substance non-ambiguously. This number is issued by the Chemical Abstracts Service and is the easiest way to characterize a chemical substance. Knowing the CAS-No. means to be able to get comprehensive information and links from internet and search engines.
This document is a gas list from Dräger that provides information on detectable gases and vapors. It includes three search indexes to find substances by name, CAS number, or sum formula. The main part of the list includes 17 columns with details on each substance such as molecular weight, density, boiling point, flash point, LEL levels, autoignition temperature, and toxic limit values. It also indicates which Dräger gas detection instruments are suitable for detecting each substance.
5.good practice & hr imp activitiesRavi Shankar
The document provides guidance on good practices for collecting and maintaining important technical information about a power plant's equipment and operations. It recommends assembling a thermal kit from the turbine supplier with performance curves, as well as collecting heat balance diagrams, pump/fan curves, piping diagrams, specifications for heat exchangers and flow elements, and historical operating data. Maintaining this information in a centralized location helps engineers properly evaluate equipment performance and potential improvement projects.
This document describes a CFD analysis of fluid flow through tube banks in heat recovery steam generators (HRSGs). The authors developed a new procedure to define porous medium parameters like loss coefficients starting from 3D simulations of flow through tube banks. Both finned and bare tube banks were considered. The analysis was performed using the commercial CFD code Fluent to simulate flow through a single tube row and investigate the effects of Reynolds number, inlet yaw angle, and inlet pitch angle on pressure drop and outlet flow angles. Results were compared to experimental data for a real fired HRSG to validate the proposed porous media modeling approach.
P&w tables of compressible flow functionsJulio Banks
Compressible-flow Mach Functionas
Page 5 - Nomenclature
Pages 6 & 7 - Mach Functions
Recommendaitons: Used Equations on Pp. 6 & 7 to
generate any of the results from the table as functions
of specific heat ration, Gamma = Cp/Cv.
Enjoy it as one would enjoy their favorite music.
The document provides details on the design and construction of shell and tube heat exchangers. It describes the key components of a shell and tube heat exchanger including the shell, tubes, tube sheets, bonnet, channel, pass partition plates, nozzles, baffles, tie rods, and flanges. It also explains the functions of each component and provides examples of different types of components like baffles, joints between tubes and tube sheets, and impingement plates.
This document discusses heat exchangers and includes the following key points:
- It describes different types of heat exchangers including concentric-tube, cross-flow, shell-and-tube, and compact heat exchangers.
- It discusses the overall heat transfer coefficient and factors that influence it such as convection, conduction, fins, and fouling.
- It introduces the log mean temperature difference (LMTD) method for calculating heat transfer in heat exchangers and how LMTD is evaluated for different flow configurations.
- It provides an example problem demonstrating how to determine the overall heat transfer coefficient and heat transfer rate for a heat recovery device.
This document summarizes different types of heat exchangers and heat transfer concepts. It discusses four main types of heat exchangers: double pipe, shell and tube, plate, and cross flow. It also covers key heat transfer equations like log mean temperature difference (LMTD) and heat exchanger effectiveness. Important heat exchanger design parameters like number of transfer units (NTU), heat capacity ratio, and fouling factors are defined. Tables of typical fouling coefficients and overall heat transfer coefficients are also included.
This document discusses heat exchangers and calculating the log mean temperature difference (LMTD). It describes different types of heat exchangers including double-pipe, shell and tube with various shell and tube passes. It explains how to calculate the LMTD for countercurrent and co-current flow and introduces correction factors for multi-pass exchangers. An example problem demonstrates calculating the LMTD, heat transfer rate, and area required for a given problem.
A heat exchanger facilitates heat transfer between two fluids without mixing them. Heat is transferred via convection within each fluid and conduction through the separating wall. There are several types of heat exchangers including counter-flow, parallel flow, and cross-flow designs. The overall heat transfer coefficient accounts for conductive and convective resistances and determines the heat exchanger size required to achieve a given temperature change in one of the fluids.
applications of the principles of heat transfer to design of heat exchangersKathiresan Nadar
This file contain a very good description for the processes design of heat ex changer. the file courtesy is Prof. Anand Patwardhan ICT Mumbai (Deemed University)
FEEMSSD presentation on shell and tube heat exchanger75 .pptxAdarshPandey510683
The document describes the design of a shell and tube heat exchanger. It discusses the components of a shell and tube heat exchanger including the shell, tubes, tube bundle, tubesheet, expansion joint, flanges, gaskets, nozzles, and baffles. It also outlines the objectives of designing a shell and tube heat exchanger for an industry application. The thermal design process involves selecting fluids for the tube and shell sides based on properties, calculating the heat transfer area, tube dimensions, and other parameters. The results of the design case study showed that using recommended design ranges from literature led to an optimal design that met design specifications.
Heat exchangers transfer thermal energy between two or more fluids at different temperatures. They are classified based on their transfer process, geometry, heat transfer mechanism, and flow arrangement. Shell-and-tube heat exchangers consist of a set of tubes in a shell container and are the most important type, used across many industries. Their design involves calculating the heat transfer rate, selecting appropriate materials and geometry, and ensuring optimal fluid velocities and pressure drops within design limits.
heat exchanger is a device that transfers heat between two or more fluids. The fluids may be separated by a solid wall to prevent mixing or they may be in direct contact. Heat exchangers are widely used in a variety of applications, including:
Heating and cooling systems
Power plants
Chemical processing
Food processing
Refrigeration
Air conditioning
Numerical Modeling and Simulation of a Double Tube Heat Exchanger Adopting a ...IJERA Editor
This document presents a numerical model and simulation of a double tube heat exchanger using a "black box" approach. It first uses commercial CFD software to simulate the heat exchanger and generate outlet temperature results. It then develops a linear model to predict the outlet temperatures based on governing equations, considering the heat exchanger a black box. The linear model assumes steady state, constant properties, and approximates the logarithmic mean temperature difference with an arithmetic mean. Results from both methods are generated and compared to experimental data to validate the linear approximation. Comparisons show the linear model agrees well with experiments, justifying its use to analyze double tube heat exchangers.
Shell & tube heat exchanger single fluid flow heat transferVikram Sharma
This article was produced to highlight the fundamentals of single-phase heat exchanger rating using Kern's method. The content is strictly academic with no reference to industrial best practices.
This presentation summarizes paddle heat exchangers (PHEs). PHEs are indirect heating equipment that uses rotating surfaces to heat materials. There are two main types - vertical and horizontal PHEs. The presentation discusses the applications of PHEs in drying processes and industrial heating. It also describes the different types of paddles - solid, closed hollow, and open hollow - and analyzes their heat transfer performance. The presentation concludes by examining heat transfer analysis and dynamic start-up processes in PHEs.
The document outlines key thermal relationships and physical properties for tubular heat exchangers. It discusses the overall heat transfer coefficient calculation and factors that influence fouling resistance like fluid properties and heat exchanger geometry. It also covers fluid temperature relationships, including logarithmic mean temperature difference and corrections for multipass flow. Physical properties covered include density, specific heat, thermal conductivity, and viscosity for various liquids and gases.
Heat Transfer Analysis of Refrigerant Flow in an Evaporator TubeIJMER
the paper aim is to presenting the heat transfer analysis of refrigerant flow in an evaporator
tube is done. The main objective of this paper is to find the length of the evaporator tube for a pre-defined
refrigerant inlet state such that the refrigerant at the tube outlet is superheated. The problem involves
refrigerant flowing inside a straight, horizontal copper tube over which water is in cross flow. Inlet
condition of the both fluids and evaporator tube detail except its length are specified. here pressure and
enthalpy at discrete points along the tube are calculated by using two-phase frictional pressure drop model.
Predicted values were compared using another different pressure drop model. A computer-code using
Turbo C has been developed for performing the entire calculation
IRJET- Analysis of Shell and Tube Heat ExchangersIRJET Journal
The document analyzes the design and performance of shell and tube heat exchangers. It discusses the components of shell and tube heat exchangers including tubes, tube sheets, baffles, and nozzles. It also describes three common types of shell and tube exchangers: fixed tube sheet, U-tube, and floating head. The document then analyzes the performance of a shell and tube heat exchanger model made of brass with and without baffles using structural and thermal simulations. The results show that heat transfer rate and stresses are lower for the model with baffles compared to without baffles. Brass is also found to have lower stresses than other materials like carbon steel and stainless steel.
This document provides an overview of gasketed plate heat exchangers. It describes their construction using metal plates separated by gaskets to transfer heat between two fluids without mixing. The fluids flow in alternating passages formed between packed plates in a corrugated pattern that induces turbulence to enhance heat transfer. Key design considerations discussed include mean flow gap, hydraulic diameter, heat transfer coefficient, mass velocity, pressure drop, overall heat transfer coefficient, and heat transfer surface area.
Type of heat exchanger. Which is mainly used in food industries, like dairy plant, for the pasturization, heat treatment of the beavrages or liquid raw material.
This document provides an overview of a gasketed plate heat exchanger. It describes the construction of a plate heat exchanger using metal plates and gaskets to transfer heat between two fluids without mixing. It discusses key design considerations like flow pattern, plate materials, mean flow gap, heat transfer coefficient, pressure drop, and heat transfer area. The document highlights advantages of plate heat exchangers like minimizing leakage risk, flexibility in design, efficient heat transfer due to turbulence, compact size, and low fouling characteristics.
The document contains answers to frequently asked questions about heat transfer, listing the three main modes of heat transfer as conduction, convection, and radiation. It also provides explanations of key heat transfer terms and concepts such as baffles in shell and tube heat exchangers, factors that influence heat transfer rates, and equations that describe heat transfer mechanisms like Fourier's law of heat conduction.
This document discusses heat exchangers, including their types, performance parameters, and design methodologies. It introduces the log mean temperature difference method for relating heat transfer rate to inlet/outlet temperatures. It also describes the effectiveness-NTU method, where effectiveness is defined as the ratio of actual to maximum possible heat transfer, and NTU is the number of transfer units. Sample problems demonstrate the use of these methods to determine required surface areas, heat transfer rates, and outlet temperatures for given heat exchanger configurations and operating conditions.
The document provides details on the design and construction of shell and tube heat exchangers. It describes the key components of a shell and tube heat exchanger including the shell, tubes, tube sheets, bonnet, channel, pass partition plates, nozzles, baffles, tie rods, and flanges. It also explains the functions of each component and provides examples of different types of components like baffles, joints between tubes and tube sheets, and impingement plates.
This document discusses heat exchangers and includes the following key points:
- It describes different types of heat exchangers including concentric-tube, cross-flow, shell-and-tube, and compact heat exchangers.
- It discusses the overall heat transfer coefficient and factors that influence it such as convection, conduction, fins, and fouling.
- It introduces the log mean temperature difference (LMTD) method for calculating heat transfer in heat exchangers and how LMTD is evaluated for different flow configurations.
- It provides an example problem demonstrating how to determine the overall heat transfer coefficient and heat transfer rate for a heat recovery device.
This document summarizes different types of heat exchangers and heat transfer concepts. It discusses four main types of heat exchangers: double pipe, shell and tube, plate, and cross flow. It also covers key heat transfer equations like log mean temperature difference (LMTD) and heat exchanger effectiveness. Important heat exchanger design parameters like number of transfer units (NTU), heat capacity ratio, and fouling factors are defined. Tables of typical fouling coefficients and overall heat transfer coefficients are also included.
This document discusses heat exchangers and calculating the log mean temperature difference (LMTD). It describes different types of heat exchangers including double-pipe, shell and tube with various shell and tube passes. It explains how to calculate the LMTD for countercurrent and co-current flow and introduces correction factors for multi-pass exchangers. An example problem demonstrates calculating the LMTD, heat transfer rate, and area required for a given problem.
A heat exchanger facilitates heat transfer between two fluids without mixing them. Heat is transferred via convection within each fluid and conduction through the separating wall. There are several types of heat exchangers including counter-flow, parallel flow, and cross-flow designs. The overall heat transfer coefficient accounts for conductive and convective resistances and determines the heat exchanger size required to achieve a given temperature change in one of the fluids.
applications of the principles of heat transfer to design of heat exchangersKathiresan Nadar
This file contain a very good description for the processes design of heat ex changer. the file courtesy is Prof. Anand Patwardhan ICT Mumbai (Deemed University)
FEEMSSD presentation on shell and tube heat exchanger75 .pptxAdarshPandey510683
The document describes the design of a shell and tube heat exchanger. It discusses the components of a shell and tube heat exchanger including the shell, tubes, tube bundle, tubesheet, expansion joint, flanges, gaskets, nozzles, and baffles. It also outlines the objectives of designing a shell and tube heat exchanger for an industry application. The thermal design process involves selecting fluids for the tube and shell sides based on properties, calculating the heat transfer area, tube dimensions, and other parameters. The results of the design case study showed that using recommended design ranges from literature led to an optimal design that met design specifications.
Heat exchangers transfer thermal energy between two or more fluids at different temperatures. They are classified based on their transfer process, geometry, heat transfer mechanism, and flow arrangement. Shell-and-tube heat exchangers consist of a set of tubes in a shell container and are the most important type, used across many industries. Their design involves calculating the heat transfer rate, selecting appropriate materials and geometry, and ensuring optimal fluid velocities and pressure drops within design limits.
heat exchanger is a device that transfers heat between two or more fluids. The fluids may be separated by a solid wall to prevent mixing or they may be in direct contact. Heat exchangers are widely used in a variety of applications, including:
Heating and cooling systems
Power plants
Chemical processing
Food processing
Refrigeration
Air conditioning
Numerical Modeling and Simulation of a Double Tube Heat Exchanger Adopting a ...IJERA Editor
This document presents a numerical model and simulation of a double tube heat exchanger using a "black box" approach. It first uses commercial CFD software to simulate the heat exchanger and generate outlet temperature results. It then develops a linear model to predict the outlet temperatures based on governing equations, considering the heat exchanger a black box. The linear model assumes steady state, constant properties, and approximates the logarithmic mean temperature difference with an arithmetic mean. Results from both methods are generated and compared to experimental data to validate the linear approximation. Comparisons show the linear model agrees well with experiments, justifying its use to analyze double tube heat exchangers.
Shell & tube heat exchanger single fluid flow heat transferVikram Sharma
This article was produced to highlight the fundamentals of single-phase heat exchanger rating using Kern's method. The content is strictly academic with no reference to industrial best practices.
This presentation summarizes paddle heat exchangers (PHEs). PHEs are indirect heating equipment that uses rotating surfaces to heat materials. There are two main types - vertical and horizontal PHEs. The presentation discusses the applications of PHEs in drying processes and industrial heating. It also describes the different types of paddles - solid, closed hollow, and open hollow - and analyzes their heat transfer performance. The presentation concludes by examining heat transfer analysis and dynamic start-up processes in PHEs.
The document outlines key thermal relationships and physical properties for tubular heat exchangers. It discusses the overall heat transfer coefficient calculation and factors that influence fouling resistance like fluid properties and heat exchanger geometry. It also covers fluid temperature relationships, including logarithmic mean temperature difference and corrections for multipass flow. Physical properties covered include density, specific heat, thermal conductivity, and viscosity for various liquids and gases.
Heat Transfer Analysis of Refrigerant Flow in an Evaporator TubeIJMER
the paper aim is to presenting the heat transfer analysis of refrigerant flow in an evaporator
tube is done. The main objective of this paper is to find the length of the evaporator tube for a pre-defined
refrigerant inlet state such that the refrigerant at the tube outlet is superheated. The problem involves
refrigerant flowing inside a straight, horizontal copper tube over which water is in cross flow. Inlet
condition of the both fluids and evaporator tube detail except its length are specified. here pressure and
enthalpy at discrete points along the tube are calculated by using two-phase frictional pressure drop model.
Predicted values were compared using another different pressure drop model. A computer-code using
Turbo C has been developed for performing the entire calculation
IRJET- Analysis of Shell and Tube Heat ExchangersIRJET Journal
The document analyzes the design and performance of shell and tube heat exchangers. It discusses the components of shell and tube heat exchangers including tubes, tube sheets, baffles, and nozzles. It also describes three common types of shell and tube exchangers: fixed tube sheet, U-tube, and floating head. The document then analyzes the performance of a shell and tube heat exchanger model made of brass with and without baffles using structural and thermal simulations. The results show that heat transfer rate and stresses are lower for the model with baffles compared to without baffles. Brass is also found to have lower stresses than other materials like carbon steel and stainless steel.
This document provides an overview of gasketed plate heat exchangers. It describes their construction using metal plates separated by gaskets to transfer heat between two fluids without mixing. The fluids flow in alternating passages formed between packed plates in a corrugated pattern that induces turbulence to enhance heat transfer. Key design considerations discussed include mean flow gap, hydraulic diameter, heat transfer coefficient, mass velocity, pressure drop, overall heat transfer coefficient, and heat transfer surface area.
Type of heat exchanger. Which is mainly used in food industries, like dairy plant, for the pasturization, heat treatment of the beavrages or liquid raw material.
This document provides an overview of a gasketed plate heat exchanger. It describes the construction of a plate heat exchanger using metal plates and gaskets to transfer heat between two fluids without mixing. It discusses key design considerations like flow pattern, plate materials, mean flow gap, heat transfer coefficient, pressure drop, and heat transfer area. The document highlights advantages of plate heat exchangers like minimizing leakage risk, flexibility in design, efficient heat transfer due to turbulence, compact size, and low fouling characteristics.
The document contains answers to frequently asked questions about heat transfer, listing the three main modes of heat transfer as conduction, convection, and radiation. It also provides explanations of key heat transfer terms and concepts such as baffles in shell and tube heat exchangers, factors that influence heat transfer rates, and equations that describe heat transfer mechanisms like Fourier's law of heat conduction.
This document discusses heat exchangers, including their types, performance parameters, and design methodologies. It introduces the log mean temperature difference method for relating heat transfer rate to inlet/outlet temperatures. It also describes the effectiveness-NTU method, where effectiveness is defined as the ratio of actual to maximum possible heat transfer, and NTU is the number of transfer units. Sample problems demonstrate the use of these methods to determine required surface areas, heat transfer rates, and outlet temperatures for given heat exchanger configurations and operating conditions.
1. Shell-and-Tube Heat Exchangers
R. Shankar Subramanian
Shell-and-tube heat exchangers are used widely in the chemical process industries, especially in
refineries, because of the numerous advantages they offer over other types of heat exchangers. A
lot of information is available regarding their design and construction. The present notes are
intended only to serve as a brief introduction.
For detailed information about analyzing and designing shell-and-tube heat exchangers, consult
“The Chemical Engineers’ Handbook” (http://www.knovel.com/knovel2/Toc.jsp?BookID=48 )
(Chapter 11) or any of a variety of sources on heat exchanger design. Mechanical standards for
shell-and-tube heat exchangers are set by TEMA (Tubular Exchangers Manufacturers
Association) and these supplement the ASME code for such heat exchangers. API (American
Petroleum Institute) Standard 660 supplements both of these standards, and chemical and
petroleum companies also have their own internal standards in addition.
Advantages
Here are the main advantages of shell-and-tube heat exchangers (Thanks to Professor Ross
Taylor for this list).
1. Condensation or boiling heat transfer can be accommodated in either the tubes or the shell,
and the orientation can be horizontal or vertical. You may want to check out the orientation of
the heat exchanger in our laboratory. Of course, single phases can be handled as well.
2. The pressures and pressure drops can be varied over a wide range.
3. Thermal stresses can be accommodated inexpensively.
4. There is substantial flexibility regarding materials of construction to accommodate corrosion
and other concerns. The shell and the tubes can be made of different materials.
5. Extended heat transfer surfaces (fins) can be used to enhance heat transfer.
6. Cleaning and repair are relatively straightforward, because the equipment can be dismantled
for this purpose.
Basic considerations
The tube side is used for the fluid that is more likely to foul the walls, or more corrosive, or for
the fluid with the higher pressure (less costly). Cleaning of the inside of the tubes is easier than
cleaning the outside. When a gas or vapor is used as a heat exchange fluid, it is typically
introduced on the shell side. Also, high viscosity liquids, for which the pressure drop for flow
through the tubes might be prohibitively large, can be introduced on the shell side.
1
2. The most common material of construction is carbon steel. Other materials such as stainless
steel or copper are used when needed, and the choice is dictated by corrosion concerns as well as
mechanical strength requirements. Expansion joints are used to accommodate differential
thermal expansion of dissimilar materials.
Heat transfer aspects
The starting point of any heat transfer calculation is the overall energy balance and the rate
equation. Assuming only sensible heat is transferred, we can write the heat duty Q as follows.
= mhot C p ,hot (Thot ,in − Thot ,out )
Q = mcold C p ,cold (Tcold ,out − Tcold ,in )
= UA F ∆Tlm
Q
The various symbols in these equations have their usual meanings. The new symbol F stands
for a correction factor that must be used with the log mean temperature difference for a
countercurrent heat exchanger to accommodate the fact that the flow of the two streams here
is more complicated than simple countercurrent or cocurrent flow. Consider the simplest
possible shell-and-tube heat exchanger, called 1-1, which means that there is a single shell “pass”
and a single tube “pass.” The sketch schematically illustrates this concept in plan view. Note
that the contact is not really countercurrent, because the shell fluid flows across the bank of
tubes, and there are baffles on the shell side to assure that the fluid does not bypass the tube
bank. The entire bundle of tubes (typically in the hundreds) is illustrated by a single line in the
sketch. The baffle cuts are aligned vertically to permit dirt particles settling out of the shell side
fluid to be washed away.
T1
Baffle
t1 t2
T2
2
3. The convention in shell-and-tube heat exchangers is as follows:
T1 : inlet temperature of the shell-side (or hot) fluid
T2 : exit temperature of the shell-side (or hot) fluid
t1 : inlet temperature of the tube-side (or cold) fluid
t2 : exit temperature of the tube-side (or cold) fluid
Thus,
∆Tlm = 2
(T1 − t ) − (T2 − t1 )
T − t
ln 1 2
T2 − t1
The fraction of the circular area that is open in a baffle is identified by a “percentage cut” and we
refer to the types of baffles shown as “segmented” baffles. For the shell side, in evaluating the
Reynolds number, we must find the cross-flow velocity across a bundle of tubes that occurs
between a pair of baffles, and determine the value of this velocity where the space for the flow of
the fluid is the smallest (maximum velocity). For the length scale, the tube outside diameter is
employed.
Most shell-and-tube heat exchangers have multiple “passes” to enhance the heat transfer. Here
is an example of a 1-2 (1 shell pass and 2 tube passes) heat exchanger.
T1
Baffle
t1
t2
T2
As you can see, in a 1-2 heat exchanger, the tube-side fluid flows the entire length of the shell,
turns around and flows all the way back. It is possible to have more than two tube passes.
Multiple shell passes also are possible, but involve fabrication that is more complex and is
usually avoided, if possible.
Correction factors to be used in the rate equation have been worked out by analysis, subject to a
set of simplifying assumptions, for a variety of situations. In the olden days, the formulae for
3
4. them were considered too cumbersome to use. Therefore graphs were prepared plotting
t −t T −T
F ( P, R ) , where P = 2 1 and R = 1 2 are parameters on which F depends. Figures C4.a-
T1 − t1 t2 − t1
d in Appendix C of the textbook by Mills display such graphs. Nowadays, one can compute these
factors quickly with a pocket calculator. Given next are the two common factors.
R2 + 1 1 − P
ln
R − 1 1 − PR
F1− 2 =
A + R2 + 1
ln
A − R +1
2
R2 + 1 1 − P
ln
2 ( R − 1) 1 − PR
F2− 4 =
A + B + R2 + 1
ln
A + B − R +1
2
2 2
where A = −1− R , B= (1 − P )(1 − PR )
P P
The first and second subscripts on the factor F correspond to the number of shell and tube
passes, respectively. The simplifying assumptions mentioned in the previous paragraph, given
in Perry’s Handbook, are as follows.
1. The heat exchanger is at steady state.
2. The specific heat of each stream remains constant throughout the exchanger.
3. The overall heat transfer coefficient U is constant.
4. All elements of a given fluid stream experience the same thermal history as they pass through
the heat exchanger (see footnote in Perry for a discussion regarding the violation of this
assumption in shell-and-tube heat exchangers).
5. Heat losses are negligible.
The formula given above for F1− 2 also applies for one shell pass and 2, 4, (or any multiple of 2)
tube passes. Likewise, the formula for F2− 4 also applies for two shell passes and 4, 8, (or any
multiple of 4) tube passes.
In designing heat exchangers, one should avoid the steep portion of the curves of F versus P ,
because small errors in estimating P can cause large changes in the value of F . A misleading
rule of thumb is that F ≥ 0.8 , but the correct idea is that the region of steep fall-off in the curves
should be avoided.
4
5. Heat Transfer Coefficients
The evaluation of the overall heat transfer coefficient is an important part of the thermal design
and analysis of a heat exchanger. You’ll find several tables of typical overall heat transfer
coefficients in shell-and-tube heat exchangers in Chapter 11 of Perry’s Handbook. The following
generic result can be written for the overall heat transfer coefficient U o based on the outside
surface area of the tubes, which is the heat transfer surface.
1 1 ∆ r Ao 1 Ao
= + + + R f ,0 + R f ,i
U o ho k Alm hi Ai
In the above equation, ho is the heat transfer coefficient for the fluid flowing in the shell, hi is
the heat transfer coefficient for the fluid flowing through the tubes, Ai and Ao are the inside and
outside surface areas of a tube, respectively, and Alm is their log mean. The fouling resistances
on a unit area basis are R f ,0 for the shell side, and R f ,i for the tube side. Accumulated
information on fouling resistances can be found in the Standards published by TEMA.
The inside heat transfer coefficient hi can be evaluated using the standard approach for
predicting heat transfer in flow through tubes, including applying a viscosity correction where
possible. Typically, turbulent flow can be expected, and a good design would aim to arrange for
turbulent flow, because of the substantial enhancement in heat transfer provided by eddy
transport. Predicting the shell-side heat transfer coefficient ho is more involved, because the
flow passage is not simple, even in the absence of baffles. The presence of baffles needs to be
taken into account in calculating the fluid velocity across the tube bank. Heat transfer
correlations for flow through tube banks are used, such as those given in the book by Holman
(1). These correlations assume flow normal to the long axes of a set of tubes placed in a
geometrical array. The correlation given in Holman’s book is
ho Do
=
Nu = C Re n Pr1/ 3
k
DoVmax ρ
The Reynolds number Re = , where Do is the outside diameter of a tube. Vmax is the
µ
“maximum” velocity of the fluid through the tube bank. To find it, first, the cross-flow area
clearance
must be evaluated. This is given as Cross flow area =ID × Baffle spacing ×
Shell
pitch
where the clearance l and pitch S n (normal to the flow direction) are illustrated in the sketch on
the next page for tubes in a square pitch.
5
6. Flow direction
clearance
l
pitch
Do Tube
OD
Sn
pitch S p
The clearance = S n − Do . When the volumetric flow rate of the shell-side fluid is divided by
l
the cross-flow area defined here, it yields the “maximum velocity” through the tube bank, Vmax .
The symbols k , ρ , and µ represent the thermal conductivity, density, and viscosity of the shell-
side fluid, respectively, and all the properties should be evaluated at the arithmetic average
temperature of that fluid between the two end temperatures. The symbol Pr stands for the
Prandtl number of the shell-side fluid. The exponent n and the multiplicative constant C
depend on the pitch to tube OD ratio, and are given in a table provided in Holman’s book. An
excerpt from the table for tubes on a rectangular pitch (in-line tube rows) is given below.
Values of the constant C
S n / Do 1.25 1.5 2.0 3.0
S p / Do
1.25 0.386 0.305 0.111 0.0703
1.5 0.407 0.278 0.112 0.0753
2.0 0.464 0.332 0.254 0.220
3.0 0.322 0.396 0.415 0.317
6
7. Values of the constant n
S n / Do 1.25 1.5 2.0 3.0
S p / Do
1.25 0.592 0.608 0.704 0.752
1.5 0.586 0.620 0.702 0.744
2.0 0.570 0.602 0.632 0.648
3.0 0.601 0.584 0.581 0.608
As an alternative, one can use the procedure outlined in Section 4.5.1 of the book by Mills. For
the shell-side heat transfer coefficient, the Nusselt number calculated from correlations using
properties at the arithmetic average of the inlet and exit temperatures is usually sufficient.
The actual flow patterns are more involved, because the flow entering the shell has to distribute
itself into the space in which the tubes are located, and then the flow has to turn around each
baffle. At the exit, the flow again has to converge toward the exit pipe from the shell. In
addition, corrections need to be applied for leakage around the baffles, for by-pass of tube
bundles, and other less important non-idealities. As a rough rule of thumb, because of these
various corrections, the ideal heat transfer coefficient ho for flow across the tube bank
calculated using a suitable correlation is multiplied by a conservative correction factor of
0.6 in the end.
Pressure Drop
Tube-Side Pressure Drop
In designing heat exchangers, pressure drop considerations are usually quite important.
Typically, a design constraint might be ∆P ≤ N psi , where the number N is specified, and such
constraints may apply on both the tube side and the shell side. Calculation of the tube-side
pressure drop is made by first estimating the (Darcy) friction factor for flow through the tubes
from the value of the Reynolds number and the relative roughness, and applying the viscosity
correction we discussed in class. Then, this friction factor is used to evaluate the pressure drop
for flow through the tubes from
L 1 2
=∆P f corrected ρV × Number of tube passes
D 2
where L is the length of the tubes, D is the ID of the tubes, ρ is the density of the tube-side
fluid, and V is the average flow velocity through a single tube. To this, we must add ∆Pr , the
return pressure loss. This accounts for the pressure drop associated with fluid entry into the tube
bundle, fluid leaving the bundle, and fluid flowing around bends.
7
8. G2
∆Pr = 4 × Number of tube passes × t
2ρ
Here, Gt = ρ V is the mass velocity and is defined as
Mass flow rate m
Gt =
Total flow area available per pass At
and
Total number of tubes × Cross - sectional area of a tube
At =
Number of passes
Shell-Side Pressure Drop
There are several ways to estimate the pressure drop for the flow of the shell-side fluid in a shell-
and-tube heat exchanger. A reasonable estimate can be obtained by the relatively simple
approach described below, which is given in a book by Peters, Timmerhaus, and West (2). This
book also provides much valuable information on the design of such heat exchangers, including
more sophisticated methods of estimating the pressure drop.
The pressure drop on the shell-side is calculated using
2 f Gs2 Ds ( N B + 1)
∆Pshell = 0.14
µ
ρ De
µs
In this equation, f is a Fanning friction factor for flow on the shell side given in Figure 14-44 of
reference (2), Gs is the mass velocity on the shell side, Ds is the inside diameter of the shell,
N B is the number of baffles, ρ is the density of the shell-side fluid, and De is an equivalent
diameter. The mass velocity Gs = m / S m , where m is the mass flow rate of the fluid, and S m is
the crossflow area measured close to the central symmetry plane of the shell containing its axis.
This area is defined as
clearance
Cross flow = Ds LB ×
area
pitch
where LB is the baffle spacing, and the clearance and pitch are defined in the notes on shell-and-
tube heat exchangers. The equivalent diameter is defined as follows.
8
9. π D02
4 C p Sn −
2
De =
4
π D0
Here, D0 is the outside diameter of the tubes, and S n is the pitch (center-to-center distance) of
the tube assembly. The constant C p = 1 for a square pitch, and C p = 0.86 for a triangular pitch.
The friction factor f is given in Figure 14-44 of the book as a function of the Reynolds number
based on the equivalent diameter (Note the difference from the Reynolds number that we use for
the heat transfer coefficient from Holman, which uses D0 as the length scale). For the friction
factor graph, we must use the Reynolds number Re defined as
DeGs
Re =
µ
where µ is the viscosity of the shell-side fluid. A scanned image of Figure 14-44 from Peters et
al. (2) is available for your use at the course web site.
An alternative approach to estimating the shell-side pressure drop is given on pages 11-10 to 11-
11 from Perry’s Handbook; the notation is explained in pages 11-7 and 11-8. But, it is
recommended that you use the simple approach given in Peters et al. (2).
Cost
Cost is always an important consideration in designing any process equipment. Cost can be
broken into two principal components – capital cost and operating cost. In addition, maintenance
costs are incurred during operation, but they tend to be more or less independent of the size of
the heat exchanger, so long as the size is within a reasonable range.
The capital cost for heat exchangers increases with increase in the heat transfer area, and is
evaluated by using values known from 1957-1959, and applying a multiplicative factor known as
the “Cost Index.” This index is published in each issue of Chemical Engineering, and uses 100 a
the basis for the cost in 1957-1959. To find the cost for the equipment in 1957-59, consult the
nomogram in Figure 11-41 and Tables 11-13 and 11-14 from Perry’s Handbook.
Operating cost is primarily pumping cost. The pumps must provide work to overcome the
pressure drop on the tube side and that on the shell side. The shaft work per unit mass of fluid is
∆P / ρ , and this must be multiplied by the mass flow rate of the stream to obtain the shaft work
per unit time or shaft power. Then, this must be divided by the overall pump efficiency to obtain
the actual power needed. It is typical to conservatively assume the overall pump efficiency to be
0.6. The yearly pumping power cost can be calculated if one knows the cost per KWH (kilowatt-
hour). You can assume operation 24 hours per day for 350 days a year (the remaining days
being nominal maintenance shutdown days).
9
10. By writing off the capital costs over a certain length of time, the total cost per year can be
worked out. This is then minimized by making a suitable choice of heat exchanger, a job that
requires examining several designs using software to perform the tedious computations.
References
1. J.P. Holman, Heat Transfer, 9th Edition, McGraw-Hill, 2002.
2. Peters, M.S., Timmerhaus, K.D., and West, R.E., Plant Design and Economics for Chemical
Engineers, McGraw-Hill, New York, 2003.
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