Fundamentals of heat exchanger design / Ramesh K. Shah, Dusˇan P. Sekulic´. p . cm. Includes index. ISBN 1. Heat exchangers–Design and. Fundamentals of Heat Exchanger Design. Author(s). Ramesh K. Heat Exchanger Design Procedures (Pages: ) · Summary · PDF. This research paper explains the basics of heat exchangers, covering such topics as: classification; design methods; pressure drop; analysis of.
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Common metals used are carbon steel and stainless steel. Other materials used include titanium. Other metals include titanium. A spiral plate exchanger has a relatively large diameter because of the spiral turns. Carbon steel and stainless steel are common materials. The largest exchanger has a maximum surface area of about m2 ft2 for a maximum shell diameter of 1. It is preferred especially for applications having very viscous liquids.
Mechanical cleaning is also possible with removal of the end covers.
Heat Exchanger Design and Operations
For con- densation or vaporization applications. This exchanger is well suited as a condenser or reboiler. If the passage starts fouling. The fouling rate is very low compared to that of a shell-and-tube unit. The advantages of this exchanger are as follows: It can handle viscous. The maximum operating pressure ranges from 0. The disadvantages of this exchanger are as follows: As noted above.
When there is a pressure drop constraint on one side. The maximum operating temperature is limited to C F with compressed asbestos gaskets. It is more amenable to chemical. A lamella heat exchanger consists of an outer tubular shell surrounding an inside bundle of heat transfer elements.
These elements. It is also used in the treatment of bauxite suspensions and mash liquors in the alcohol industry. The inside opening of the lamella ranges from 3 to 10 mm 0. Lamellas are stacked close to each other to form narrow channels on the shell side. In a small exchanger.
This exchanger is used for heat recovery in the pulp and paper industry. This exchanger shown in Fig. A lamella exchanger is capable of pressures up to 3. The large units have surface areas up to m2 A lamella exchanger weighs less than a shell-and-tube exchanger having the same duty.
The exchan- ger thus has a single pass. This sheet is then stacked with another plain sheet without stopweld material on it. In the spot-weld process. In the die- stamping process. High surface area densities. In a roll-bond process.
Having a small channel size. The channel depth is 0. Examples are shown in Fig. It has been used successfully with relatively clean gases. The basic elements of this exchanger are called panelcoils. The two plates are joined by electric resistance welding of the metal sheets. The most commonly used materials for panelcoils are carbon steel. After annealing the panelcoil. The panelcoil sheet metal gauges range between 1. A variety of materials. On one of the metal sheets.
An example is shown in Fig. The sheets are then heated and immediately hot-rolled under high pressure to provide a metallurgical bond. When both sheets are stamped. Subsequent cold rolling follows to provide an appropriate increase in length.
The panelcoil serves as a heat sink or a heat source. Several blocks are welded together for large heat duty applications. The maximum operating pressure ranges from 1. One of the most common methods to increase the surface area and exchanger. Panelcoil heat exchangers are relatively inexpensive and can be made into desired shapes and thicknesses for heat sinks and heat sources under varied operating conditions.
This results in a large heat transfer surface area require- ment. In some applications. Courtesy of Tranter PHE. Flow area is increased by the use of thin- gauge material and sizing the core properly. The resulting exchanger is referred to as an extended surface exchanger.
In Europe. In the cryogenics industry. Fins may be used on both sides in gas-to-gas heat exchangers. Courtesy of Delphi Harrison Thermal Systems. Fins are also sometimes used for pressure containment and rigidity. Fins are die or roll formed and are attached to the plates by brazing. In gas-to-liquid applications. Such exchangers have been made from metals for temperatures up to about C F and made from ceramic materials for temperatures up to about C F with a peak temperature of C F.
For ventilation applications i.
In a gas-to-liquid exchanger. Fin heights may range from 2 to 25 mm 0. Conventional Tube-Fin Exchangers. Fins are generally used on the outside. They are now used widely in electric power plants gas turbine. The highest temperature is again limited by the type of bonding. Fins on the inside of the tubes are of two types: Noranda Metal Industries. Heat Pipe Heat Exchangers. Courtesy of Forged-Fin Division. As shown in Fig. Heat is transferred from the hot gas to the evaporation section of the heat pipe by convection.
In a properly designed heat pipe. The condensed liquid may also be pumped back to the evaporator section by the capillary force or by the force of gravity if the heat pipe is inclined and the condensation section is above the evaporator section.
The HPHE has a splitter plate that is used primarily to prevent mixing between the two gas streams. The tube bundle may be horizontal or vertical with the evaporator sections below the condenser sections. The heat applied at the evaporator section tries to dry the wick surface through evaporation. A heat pipe heat exchanger HPHE. Since the splitter plate is thin. Small units have a face size of 0. The tube rows are normally staggered with the number of tube rows typically between 4 and This feature can be used to regulate the performance of a.
The wick is what makes the heat pipe unique. Because of this sensitivity. When heat is applied at the evaporator by an external source. This pressure is responsible for transporting the condensed liquid back to the evaporator section. The inner surfaces of a heat pipe are usually lined with a capillary wick a porous lining.
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The vapor condenses in the condenser section of the pipe. In a gas-to-gas HPHE. In the case of gas-to- liquid heat exchangers. Heat pipe heat exchangers are generally used in gas-to-gas heat transfer applications. They are used primarily in many industrial and consumer product—oriented waste heat recovery applications.
The heat transfer surface or elements are usually referred to as a matrix in the regenerator. For further details on the design of a HPHE. To have continuous operation.. It should be noted that at very low temperatures. Here again. For a rotary regenerator. For some applications. This Rothemuhle regenerator is used as an air preheater in some power- generating plants. Since the basic thermal design theory of all types of regenerators is the same. Courtesy of Andco Industries.
Regenerators have been made from metals. Rotating drives also pose a challenging mechanical design problem. The cost of manufacturing such a compact regenerator surface per unit of heat transfer area is usually substantially lower than that for the equivalent recuperator. New Orleans. A much more compact sur- face may be employed than in a recuperator. Courtesy of Babcock and Wilcox. Major advantages of the regenerators are the following.
The major reason for having a much more compact surface for a regenerator is that the hot and cold gas streams are separated by radial seals or valves. The design Reynolds number range with these types of surfaces is to Depending on the applications.
The matrix surface has self- cleaning characteristics. Rotary regenerators are shown in Figs. The matrix in the regenerator is rotated by a hub shaft or a peripheral ring gear drive. Munter wheel. In a rotary regenerator. Every matrix element is passed periodically from the hot to the cold stream and back again.
In this exchanger. Two examples of rotary regenerator surfaces are shown in Fig. For the annular sector—shaped seals shown in Fig.
For regenerators with seals of equal area but arbitrary shape. Metal rotary regenerators have been designed for continuous operating inlet temperatures up to about C F. For higher-temperature applications. Two common shapes are shown in Fig. For the uniform-width seals in Fig. They can employ thinner stock material.
A typical cycle time is between 1 and 3 h. For continuous operation. Fixed-matrix regenerators have two types of heat transfer elements: Cowper stoves are very large with an approximate height of 35 m ft and diameter of 7. In air-conditioning and industrial process heat recovery applications. For this reason. Rotary regenera- tors are also used in chemical plants and in preheating combustion air in electricity generation plants for waste heat utilization.
Checkerwork or thin-plate cellular structure are of two major categories: The regen- erator. To minimize the temperature swing. In the series parallel arrangement of Fig. Ceramic regenerators are used for high- temperature incinerators and the vehicular gas turbine power plant. Even paper. Vehicular regenerators have diameters up to 0.
Typical power plant regenerators have a rotor diameter up to 10 m 33 ft and rotational speeds in the range 0. Ljungstrom air preheaters for thermal power plants. Air-ventilating regenerators have rotors with diameters of 0.
Since the stove cools as the blast is blown through it. In a Cowper stove. The surface geometries used for packed beds are quartz pebbles.
The amount of blast through the hot stove is constantly increased while that through the cool stove is decreased by the same amount to maintain the hot blast air temperature approximately constant. In the staggered parallel arrangement of Fig..
Heat transfer surface area densities of In this arrangement. At the end of one-half period. At this point.
If the exchanger of Fig. To illustrate the concept. As shown later. Some header arrangements are shown in Fig. This does not corre- spond to a single-pass exchanger of the unfolded exchanger height. An additional degree of freedom is introduced by unfolding.
Fluid temperature variations. The symbol T is used for temperature. In such a case. It provides early initiation of nucleate boiling for boiling applications. This may eliminate or minimize the problems of fouling. In this type of exchanger. Note that when the number of tube rows is reduced to one. For the cases of Fig. Fluids 1 and 2 in Fig.
Fluid 1 in Fig. In this case within the exchanger. In reality. As will be shown in Section Even though the truly unmixed and truly mixed cases are the extreme idealized conditions of a real situation in which some mixing exists. When the number of tube rows is reduced to one. This case is practically less important. In this exchanger as shown in Fig. For the same surface area. Each module in Fig. These are shown in Fig. This arrangement is the most common for extended surface exchangers. In a series-coupled multipass exchanger.
In the series coupling of n passes. There are a large number of combinations of the foregoing basic multipass arrangements yielding com- pound multipass arrangements. Now let us introduce additional basic terminology for series-coupled multipass exchangers.
In both cases a and b. Cases c and d are symbolic representations of cases a and b. S1 in Fig. For high-temperature applications approximately above C or F. In either Fig. Figures 1. Special metals such as stainless steel and super- alloys may be used in passes having high operating temperatures. Since the liquid is evaporating on the shell side in the K shell as a kettle reboiler application. For illustrative purposes. A heat exchanger with this arrangement is also simply referred to as a conventional 1—2 heat exchanger by industry and in this book.
When the number of tube passes is greater than one. The dashed lines are the pass partitions on the other end of the tube bundle. In this case. Common tube-side multipass arrangements are shown in Fig. As the tubes are rigidly mounted only at one end. Increasing the even number of tube passes of a 1—2n exchanger from two to four.
The solid lines indicate pass ribs in the front header. Typical temperature distribution is shown in Fig. Split-Flow Exchanger. Divided-Flow Exchanger. In a plate exchanger. It is a variant of the conventional 1—2 exchanger.
Possible arrangements are 1 pass — 1 pass. Some of them are shown in Fig. Looped patterns are most commonly used. G shell. Multipass arrangements: This eliminates the need for disconnecting pipework for maintenance and cleaning purposes. Table 3. It is used for very close temperature approaches..
Looped or single-pass arrangements: American Society of Mechanical Engineers.
Radiation heat transfer is a primary mode in fossil-fuel power plant boilers. New York. In most pasteurizers. Gas Turbine Regenerators. A summary is provided in Fig.
Radiant heat transfer combined with convective heat transfer plays a role in liquid metal heat exchangers and high-temperature waste heat recovery exchangers.
Single-phase convection on one side and two-phase convection on the other side with or without desuperheating or superheating. The major emphasis in this chapter is placed on introducing the terminology and concepts associated with a broad spectrum of commonly used industrial heat exchangers many specialized heat exchan- gers are not covered in this chapter.
Multicomponent two-phase convection occurs in condensation of mixed vapors in distillation of hydrocarbons. Rules for Construction of Pressure Vessels.. Developments in shell-and-tube heat exchangers.
Design and Construction. Heat exchangers. Hemisphere Publishing. Hemisphere Publish- ing. Chapter Compact Heat Exchangers: Techniques for Size Reduction. The Netherlands. Foumeny and P. Compact and enhanced heat exchangers. Tubular Exchanger Manufacturers Association. Unit Operations II.. Krieger Publish- ing. Standards of TEMA. Plate heat exchangers and their design theory. Compact Heat Exchangers. Thermal-Hydraulic Funda- mentals and Design.
Rohsenow and J. Hemisphere Publishing.. Industrial Heat Exchangers: A Basic Guide. Heat Exchangers: Heat pipe heat exchanger design theory. Ellis Horwood. VCH Publishers. Heat exchange. Learning from Experiences with Compact Heat Exchangers.. Bisio and S. Lecture Series No. Industrial heat exchangers—functions and types. Heat Mass Transfer. Theory and Practice. Compact heat exchanger technology and applications. Life- cycle design assumes considerations organized in the following stages.
Concept development selection of workable designs. Based on this analysis. If the problem is clearly formulated. Most of these considerations are dependent on each other and should be considered simultaneously to arrive iteratively at the optimum exchanger design based on an optimum system design approach.
Utilization considerations operation. Problem formulation including interaction with a consumer. From the formulation of the scope of this activity. Detailed exchanger design design calculations and other pertinent considerations. This must be based on a good understanding of customer needs. Various quantitative and qualitative design aspects and their interaction and interdepen- dence are discussed.
This activity leads to a proposed design solution. A methodology for designing a new single heat exchanger is illustrated in Fig. The overall design methodology is quite complex because of the many quali- tative judgments. Refer to appropriate blocks and boxes in Fig. Major design considerations include: The issues related to startups. Manufacturing considerations and cost.
In the following. This design procedure may be characterized as a case study one case at a time method. Within the framework of these activities. Mechanical design. Thermal and hydraulic design. Taborek Through consideration of these steps.
For shell-and-tube exchangers.
The orientation of the heat exchanger. There are several quantitative and qualitative criteria for surface selection. The core geometry such as shell type. The qualitative criteria for surface selection are the operating temperature and pressure. For shell-and- tube exchangers. Some of these are discussed in Section Some of the qualitative and quantitative criteria for compact heat exchanger surfaces are discussed in Sections Example 2.
Analysis and Discussion: This means that only shell-and-tube and double-pipe heat exchangers are feasible candidates. For welded and gasketed plate heat exchangers. Only information regarding some selected operating conditions is available a situation often encountered in practice. The liquid stream has the inlet temperature of C. More precisely. These criteria include the required heat exchanger. A spiral heat exchanger can operate at much higher temperatures up to C. The gas stream has to change its temperature from C to C.
Consider the following heat exchanger types: Both shell-and-tube and double-pipe heat exchangers see Sections 1. A study of various designs see Chapter 1 leads to the conclusion that lamella. All the information regarding various heat exchanger types under consideration shell-and-tube. A stream of a liquid hydrocarbon is available to be used as a coolant. Is it possible. See Example 2. Heat transfer rate equation or simply the rate equation [see also the equality on the left-hand side in Eq.
This block is the heart of this book. Only two important relationships constitute the entire thermal design procedure. Due to the fact that the heat exchanger should accommodate both a gas and a liquid. For a relatively small heat load i. These are: Equation 2.
It is discussed in Section 3. Solving a design problem means either determining A or UA of a heat exchanger to satisfy the required terminal values of some variables the sizing problem.
Note that the seven variables on the right-hand side of Eqs. In a broad sense. Nusselt number. Two of the simplest and most important problems are referred to as the rating and sizing problems. The sizing problem is a subset of the compre- hensive design process outlined in Fig.
Sizing Problem. Inputs to the sizing problem are surface geometries including their dimensionless heat transfer and pressure drop characteristics. For a plate exchanger. Rating Problem. Fanning friction factor. Based on the number of vari- ables associated with the analysis of a heat exchanger. The rating problem is also sometimes referred to as the performance or simulation problem. From the quantitative analysis point of view.
The sizing problem is also referred to as the design problem. Inputs to the rating problem are the heat exchanger construction. To avoid confusion with the term design problem.
Colburn factor. Reynolds number. MTD correction factor. On the shell side of a shell-and-tube heat exchanger. Theoretical solutions and experimental results for a variety of exchanger heat transfer surfaces are presented in Chapter 7 together with the description of experimental techniques for their determina- tions. These procedures are presented in Chapter 9. Depending on the choice of dimensionless groups. The basic methods for recuperators are presented in Chapter 3 and for regenerators in Chapter 5.
Advanced auxiliary methods for recup- erators are presented in Chapter 4. Due to the complexity of the calculations. For heat transfer and pressure drop analyses. Hydraulic design or pressure drop analyses are presented in Chapter 6. This is achieved by employing mathematical optimization techniques after initial sizing to optimize the heat exchanger design objective function within the framework of imposed implicit and explicit constraints. For thermal and hydraulic design.
From the viewpoint of a computer code. Since there are many geometrical and operating condition—related variables and parameters associated with the sizing problem.
Accurate and reliable surface basic characteristics are a key input for exchanger thermal and hydraulic design. For the wall. Some information on the thermophysical properties is provided in Appendix A.
A heat exchanger optimization procedure is outlined in Section 9. Solution procedures for rating and sizing problems are of an analytical or numerical nature. These methods include "-NTU. These quantities are computed from the basic dimen- sions of the core and heat transfer surface. Procedures to com- pute these quantities for some surface geometries are presented in Chapter 8.
Assume the validity of both Eqs. With these quite general assump- tions. A heat exchanger is considered as a black box that changes the set of inlet temperatures Tj.. The heat exchanger is adiabatic. So in this problem.. This means that these three equations can be reduced to two equalities by eliminating heat transfer rate q. How many of the seven variables listed must be known to be able to deter- mine all the variables involved in Eqs.
Note that the left- hand sides of these equalities are equal to the same heat transfer rate. Note that Eq. Using the two equations. A complete set of design problems including both the sizing and rating problems. Refer to the third dashed-line block from the top in Fig. The heat exchanger core is designed for the desired structural strength based on the operating pressures.
The remaining two problem types presented in Table E2. Exactly the same reasoning can be applied to devise a total of 15 rating problems in each of these problems. As mentioned in the beginning of Chapter 1. Unknown variable. Discussion and Comments: Among the six types of sizing problems.. A proper selection of the material and the method of bonding such as brazing. Although some aspects of mechanical design are considered upfront before the thermal design.
Thermal stress and fatigue calculations are performed to ensure the durability and desired life of the exchanger for expected startup and shutdown periods and for part-load operating conditions. At this stage. Many mechanical design criteria should be considered simultaneously or iteratively with thermal design. In addition to the heat exchanger core.
The structural support for the heat exchan- ger needs to be designed properly with proper tabs. Field experience. These bonding methods are usually decided upon before conducting the thermal-hydraulic analysis. Adequate provisions are also made for thermal expansion. In the mechanical design. Every heat exchanger must comply with applicable local. Structural design would include thermal stresses. TEMA standards. Section Flow velocities are checked to eliminate or minimize erosion.
Fouling and corrosion are covered in Chapter Enlist the important missing data to perform the stress analysis.
The loads include: The application of the heat exchanger is known. These are mechanical. TEMA designation. The missing set of data necessary for performing the stress analysis of the heat exchanger described in the example formulation. Allowable stress limits and fatigue life data are determined. The designer addresses. All data regarding allowable stress limits and fatigue life requirements for the materials used are known.
Vibration can be assessed. The following is the available information: Information about environmental and seismic conditions is available. Inspection of the data indicates that most of the information needed for stress analysis is available: The overall total cost.
Installation of the exchanger on the site can be as high as the capital cost for some shell-and-tube and plate heat exchangers. Other evaluation criteria include the shop workload. This example emphasizes a need for a thorough study of the input data. Mechanical loads caused by pressure and gravity forces. Manufacturing considerations may be sub- divided into manufacturing equipment considerations. The capital total installed cost includes the costs associated with design.
Processing considerations are related to how individual parts and components of a heat exchanger are manufactured and eventually assembled. This is the case not only when a mechanical design is considered. An engineer must identify the minimum required data set to start the analysis.
Not only the manufacturing equipment but also the complete processing considerations are evaluated upfront nowa- days when a new design of a heat exchanger is being considered. Operating loads under transient conditions such as startup and shutdown opera- tion. This illustrates why two engineers will never provide two exactly equal designs.
Superimposed loads caused by piping connections to nozzles these loads may cause axial. The heat exchanger type for a given performance. In Table E2. The cost of heat exchangers vs. Discuss how this decision changes with a change in the heat exchanger perfor- mance level. Because there are no available data for the performance level required. The analysis should be based on data provided in Table E2.
From the empirical data available. Idealize the dependence of the unit cost vs. This interpolation must be logarithmic. Schematics of heat exchanger types selected are given in Figs.
From the available empirical data. From a preliminary analysis. Table E2. For higher performance levels. Data presented are based on an approximate costing method developed by Hewitt et al.
From Table E2. The most economical is the plate-and-frame heat exchanger. The following conclusions can be formulated. For large duties.
Application of temperature controller
The double- pipe heat exchanger is more economical than the shell-and-tube type only for small performance values. The numbers in Table E2. Now we. These may be developed to weigh quantitatively the relative costs of pressure drop. Consider a shell-and-tube exchanger design with heavy fouling. But in reality. The dashed line from the bottom to top near the left-hand margin of Fig.
For a conventional exchanger. If the heat exchanger is one component of a system or a thermodynamic cycle. Let us review two examples to illustrate this point. For exchangers with new designs. During mechanical design. Because of a large number of qualitative judgments.
The application will dictate the choice of material as stainless steel or more exotic materials. Also the selection of the core geometry or heat transfer surface should be such that it either minimizes fouling or provides easy cleaning. Heat exchanger design is a complex endeavor and involves not only a determination of one or more feasible solution s but also the best possible or nearly optimal design solution.
Heat Exchangers for Sustainable Development. High-temperature operation means that a special brazing technique will be required. June 14— In the chapters that follow. During thermal—hydraulic design. The cost and thermal performance considerations will dictate the selection of material with respect to the desired life of the exchanger.
Most probably. Approximate design and costing methods for heat exchangers. So there are many interdependent factors that must be considered while designing and optimizing this exchanger. Only a part of the total design process consists of quantitative analytical evaluation. The decision should be made up front in terms of what type of cleaning technique and maintenance schedule should be employed: Heat transfer equipment. Advances in compact heat exchanger technology and design theory.
Heat Transfer Conf.. Institution of Chemical Engineers. Strategy of heat exchanger design. Heat Trans- fer Kluwer Academic Publishers. Thermal- Hydraulic Fundamentals and Design.
From a study of the design methodology chart presented in Fig. List the criteria as many as you can to be used to select the heat exchanger type that will suit the imposed requirements impose your own requirements. Can he or she determine these three variables using the data available? In this chapter the thermal design theory of recuperators is presented. The -P and P1 -P2 graphical presentation methods. The following are the contents of this chapter: An analogy between thermal.
It is shown in Section 3. In such cases. Considering seven variables of the heat exchanger design problem. The "-NTU method is introduced in Section 3. In a heat exchanger. Heat exchanger variables and the ther- mal circuit are presented in Section 3.The UT75A temperature controllers employ an easy-to-read, segment large color LCD display, along with navigation keys, thus greatly increasing the monitoring and operating capabilities. In order to exemplify the usage of a fuzzy logic system, consider a temperature control system controlled by a fuzzy logic controller.
Figure 1 Temperature control system of heating furnace Temperature control is a process in which change of temperature of a space and objects collectively there within , or of a substance, is measured or otherwise detected, and the passage of heat energy into or out of the space or substance is adjusted to achieve a desired temperature. How to cite this paper: Atarashi, T. Pressure Drop.
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