"This comprehensive reference covers all the important aspects of heat exchangers (HEs)--their design and modes of operation--and practical. Kuppan Thulukkanam. SECOND International Standard Book Number (eBook - PDF) my parents, S. Thulukkanam and T. Senthamarai, Chapter 1 Heat Exchangers: Introduction, Classification, and Selection. Heat Exchanger Design Handbook S E C O N D E D I T I O N-Kuppan Sorry, this document isn't available for viewing at this time. In the meantime, you can download the document by clicking the 'Download' button above. Download pdf.
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The higher the pressure, the greater will be the required thickness of the pressure-retaining membranes and the more advantage there is to placing the high-pressure fluid on the tubeside.
The pressure level of the fluids has a significant effect on the type of unit selected [ 181. At low pressures, the vapor-phase volumetric flow rate is high and the low allowable pressure drops may require a design that maximizes the area available for flow, such as crossflow or split flow with multiple nozzles.
At high pressures, the vapor-phase volumetric flow rates are lower and allowable pressure drops are greater. These lead to more compact units.
In general, higher heat-transfer rates are obtained by placing the low-pressure gas on the outside of tubular surfaces. Operating pressures of the gasketed plate heat exchangers and spiral plate heat exchangers are limited because of the difficulty in pressing the required plate thickness, and by the gasket materials in the case of PHEs.
The floating nature of floating-head shell and tube heat exchangers and lamella heat exchangers limits the operating pressure. Design Temperature. This parameter is important as it indicates whether a material at the design temperature can withstand the operating pressure and various loads imposed on the component.
For low-temperature and cryogenic applications toughness is a prime requirement, and for high-temperature applications the material has to exhibit creep resistance. Temperature Program.
Temperature program in both a single pass and multipass shell and tube heat exchanger decides 1 the mean metal temperatures of various components like shell, tube bundle, and tubesheet, and 2 the possibility of temperature cross.
The mean metal temperatures affect the integrity and capability of heat exchangers and thermal stresses induced in various components.
Heat Exchanger Design Handbook
Temperature Driving Force. The effective temperature driving force is a measure of the actual potential for heat transfer that exists at the design conditions. With a counterflow arrangement, the effective temperature difference is defined by the log mean temperature difference LMTD. For flow arrangements other than counterflow arrangement, the LMTD must be corrected by a correction factor, F. The F factor can be determined analytically for each flow arrangement but is usually presented graphically in terms of the thermal effectiveness P and the heat capacity ratio R for each flow arrangement.
The influence of operating pressure and temperature on selection of shell and tube Heat Exchangers 23 heat exchanger, compact heat exchanger, gasketed plate heat exchanger, and spiral exchanger is discussed next. Shell and Tube Heat Exchanger. Shell and tube heat exchanger units can be designed for almost any combination of pressure and temperature.
In extreme cases, high pressure may impose limitations by fabrication problems associated with material thickness, and by the weight of the finished unit.
Differential thermal expansion under steady conditions can induce severe thermal stresses either in the tube bundle or in the shell. Damage due to flow-induced vibration on the shellside is well known.
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In heat-exchanger applications where high heattransfer effectiveness close approach temperature is required, the standard shell and tube design may require a very large amount of heat transfer surface [ 191. Depending on the fluids and operating conditions, other types of heat-exchanger design should be investigated.
Compact Heat Exchanger.
Compact heat exchangers are constructed from thinner materials; they are manufactured by mechanical bonding, soldering, brazing, welding, etc. Therefore, they are limited in operating pressures and temperatures.
Gasketed plate heat exchangers and spiral exchangers are limited by pressure and temperature, wherein the limitations are imposed by the capability of the gaskets.
Flow Rate Flow rate determines the flow area: the higher the flow rate, the higher will be the crossflow area. Higher flow area is required to limit the flow velocity through the conduits and flow passages, and the higher velocity is limited by pressure drop, impingement, erosion, and, in the case of shell and tube exchanger, by shell-side flow-induced vibration.
Sometimes a minimum flow velocity is necessary to improve heat transfer, to eliminate stagnant areas, and to minimize fouling. For example, the pharmaceutical, dairy, and food industries require quick access to internal components for frequent cleaning. Since some of the heat exchanger types offer great variations in design, this must be kept in mind when designing for a certain application.
For instance, consider inspection and manual cleaning. Spiral plate exchangers can be made with both sides open at one edge, or with one side open and one closed. They can be made with channels between 5 mm and 25 mm wide, with or without studs. The shell and tube heat exchanger can be made with fixed tubesheets or with a removable tube bundle, with small- or large-diameter tubes, or small or wide pitch.
A lamella heat exchanger bundle is removable and thus fairly easy to clean on the shellside. Inside the lamella, however, cannot be drilled to remove the hard fouling deposits.
Gasketed plate heat exchangers PHEs are easy to open, especially when all nozzles are located on the stationary end-plate side. The plate arrangement can be changed for other duties within the frame and nozzle capacity. Repair of some of the shell and tube exchanger components is possible, but the repair of expansion joint is very difficult. Tubes can be renewed or plugged. Repair of compact heat exchangers of tube-fin type is very difficult except by plugging of the tube.
Repair of the platefin exchanger is generally very difficult.
For these two types of heat exchangers, extension of units for higher thermal duties is generally not possible. All these drawbacks are easily overcome in a PHE. It can be easily repaired, and plates and other parts can be easily replaced. Due to modular construction, PHEs possess the flexibility of enhancing or reducing the heat transfer surface area, modifying the pass arrangement, and addition of more than one duty according to the heat-transfer requirements at a future date.
Overall Economy There are two major costs to consider in designing a heat exchanger: the manufacturing cost and the operating costs, including maintenance costs. In general, the less the heat-transfer surface area and less the complexity of the design, the lower is the manufacturing cost. The operating cost is the pumping cost due to pumping devices such as fans, blowers, pumps, etc.
The maintenance costs include costs of spares that require frequent renewal due to corrosion, and costs due to corrosioxdfouling prevention and control.
Therefore, the heat exchanger design requires a proper balance between thermal sizing and pressure drop.
They are the major factors in the initial cost and to a large extent influence the integrity, service life, and ease of maintenance of the finished heat exchanger . For example, shell and tube units are mostly fabricated by welding, plate-fin heat exchangers and automobile aluminum radiators by brazing, copper-brass radiators by soldering, most of the circular tube-fin exchangers by mechanical assembling, etc.
Choice of Unit Type for Intended Applications According to the intended applications, the selection of heat exchangers will follow the guidelines given in Table 2. PHE will require the smallest surface area.
PHE offers the advantages of good flow distribution, and will involve the smallest surface area. For extreme viscosities, the SPHE is preferred.
Heat Exchanger Design Handbook
Use STHE with removable tube bundle. Use PHE if easy access is of importance.
SPHE offers the best characteristics. Extended surface types.
Use STHE with extended surface on the gas side or brazed plate-fin exchanger. Evaluating plate heat exchangers[ edit ] Partially dismantled exchanger, with visible plates and gaskets All plate heat exchangers look similar on the outside. The difference lies on the inside, in the details of the plate design and the sealing technologies used.
Hence, when evaluating a plate heat exchanger, it is very important not only to explore the details of the product being supplied but also to analyze the level of research and development carried out by the manufacturer and the post-commissioning service and spare parts availability. An important aspect to take into account when evaluating a heat exchanger are the forms of corrugation within the heat exchanger. There are two types: intermating and chevron corrugations.
In general, greater heat transfer enhancement is produced from chevrons for a given increase in pressure drop and are more commonly used than intermating corrugations. In plate heat exchangers due to presence of corrugated plate, there is a significant resistance to flow with high friction loss. Thus to design plate heat exchangers, one should consider both factors.
For various range of Reynolds numbers, many correlations and chevron angles for plate heat exchangers exist. The plate geometry is one of the most important factor in heat transfer and pressure drop in plate heat exchangers, however such a feature is not accurately prescribed. In the corrugated plate heat exchangers, because of narrow path between the plates, there is a large pressure capacity and the flow becomes turbulent along the path.Fouling Tendencies Fouling is defined as the formation on heat exchanger surfaces of undesirable deposits that impede the heat transfer and increase the resistance to fluid flow, resulting in higher pressure drop.
For flow arrangements other than counterflow arrangement, the LMTD must be corrected by a correction factor, F. Shell and tube heat exchanger units can be designed for almost any combination of pressure and temperature. A lamella heat exchanger bundle is removable and thus fairly easy to clean on the shellside. Operating pressures of the gasketed plate heat exchangers and spiral plate heat exchangers are limited because of the difficulty in pressing the required plate thickness, and by the gasket materials in the case of PHEs.
The plate geometry is one of the most important factor in heat transfer and pressure drop in plate heat exchangers, however such a feature is not accurately prescribed.
The plates are pressed to form troughs at right angles to the direction of flow of the liquid which runs through the channels in the heat exchanger.