Heat transfer equipment

Shell-Side Heat Transfer and Pressure Drop (Single Phase) Condensers 

Reboilers and Vaporizers Piate Heat Exchangers Direct-Contact Heat Exchangers Finned Tubes 

The transfer of heat to and from process fluids is an essential part of most chemical processes. The most commonly used type of heat transfer equipment is the ubiquitous shell and tube heat exchanger, the design of which is the main subject of this chapter. 

The fundamentals of heat transfer theory are covered in many other textbooks see Holman (2002), Ozisik (1985), Rohsenow et al. (1998), Kreith and Bohn (2000), and Incropera and Dewitt (2001). 

The principal types of heat exchangers used in the chemical process and allied industries, which will be discussed in this chapter, are as follows  

Double-pipe exchanger the simplest type, used for cooling and heating. 

Plate and frame exchangers (plate heat exchangers) used for heating and cooling. 

As a minimum, a distillation assembly consists of a tower, reboiler, condenser, and overhead accumulator. The bottom of the tower serves as accumulator for the bottoms product. The assembly must be controlled as a whole. Almost invariably, the pressure at either the top or bottom is maintained constant at the top at such a value that the necessary reflux can be condensed with the available coolant at the bottom in order to keep the boiling temperature low enough to prevent product degradation or low enough for the available HTM, and definitely well below the critical pressure of the bottom composition. There still remain a relatively large number of variables so that care must be taken to avoid overspecifying the number and kinds of controls. For instance, it is not possihle to control the flow rates of the feed and the top and bottom products under perturbed conditions without upsetting holdup in the system. 

On temperature control of the vapor leaving the reboiler or at some point in the tower, 

On control of composition or some physical property of the bottom product. 

Although only one of these methods can be shown clearly on a particular sketch, others often are usable in combination with the other controls that are necessary for completeness. In some cases the HTM shown is condensing vapor and in other cases it is hot oil, but the particular flowsketches are not necessarily restricted to one or the other HTM. The sketches are shown with and without pumps 

Flow control of reflux is most common. It is desirable in at least these situations  

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Even if the reactor temperature is controlled within acceptable limits, the reactor effluent may need to be cooled rapidly, or quenched, to stop the reaction quickly to prevent excessive byproduct formation. This quench can be accomplished by indirect heat transfer using conventional heat transfer equipment or by direct heat transfer by mixing with another fluid. A commonly encountered situation is... 

Use heat transfer equipment which requires a low inventory, such as plate heat exchangers. 

George W. Gassman, Paul J. Schajhuch, Thomas J. McAvoy, Dale E. Seborg Process Economics F. A. Holland, J. K Wilkinson Transport and Storage of Fluids Meherwan P. Boyce Heat-Transfer Equipment Richard L. Shilling, Kenneth J. Bell,... 

Kenneth J. Bell, Ph.D., P.E., Regents Professor Emeritus, School of Chemical Engineering, Oklalioma State University Member, American Institute of Chemical Engineers (Section 11, Heat-Transfer Equipment)... 

Overall Coefficient of Heat Transfer In testing commercial heat-transfer equipment, it is not convenient to measure tube temperatures (t,3 or t4 in Fig. 5-6), and hence the overall performance is expressed as an overall coefficient of heat transfer U based on a convenient area dA, which may be dAi, oi an average of dAi and dA whence, by definition,... 

Because heat-transfer equipment for solids is generally an adaptation of a primarily material-handhng device, the area of heat transfer is often small in relation to the overall size of the equipment. Also pecuhar to sohds heat transfer is that the At varies for the different heat-transfer mechanisms. With a knowledge of these mechanisms, the At term generally is readily estimated from temperature hmita-tions imposed by the burden characteristics and/or the construc tion. 

Conauctive Heat Transfer Heat-transfer equipment in which heat is transferred by conduction is so constructed that the solids load (burden) is separated from the heating medium by a wall. 

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