841 Introduction

It is necessary to completely specify all of the operating parameters as well as the heat exchange capacity for the proper design of a heat exchanger, or for the selection of an off-the-shelf item. These specifications will determine the construction parameters and thus the cost of the heat exchanger. The final design will be a compromise among pressure drop (which fixes pump or fan capital and operating costs), maintainability (which strongly affects maintenance costs), heat exchanger effectiveness, and life-cycle cost. Additional features, such as the on-site use of exotic materials or special designs for enhanced maintainability, may add to the initial cost. That design will balance the costs of operation and maintenance with the fixed costs in order to minimize the life-cycle costs. Advice on selection and design of heat exchangers is available from manufacturers and from T.E.M.A.* Industrial Heat Exchangers(17) is an excellent guide to heat exchanger selection and includes a directory of heat exchanger manufacturers.

The essential parameters that should be known and specified in order to make an optimum choice of waste-heat recovery devices are:

Temperature of waste-heat fluid

Flow rate of waste-heat fluid

Chemical composition of waste-heat fluid

Minimum allowable temperature of waste-heat fluid

Amount and type of contaminants in the waste-heat fluid

Figure 8.17. Shell and tube heat exchanger.

*Tubular Equipment Manufacturers Association, New York, NY

Figure 8.17. Shell and tube heat exchanger.

Allowable pressure drop for the waste-heat fluid Temperature of heated fluid Chemical composition of heated fluid Maximum allowable temperature of heated fluid Allowable pressure drop in the heated fluid Control temperature, if control required

In the remainder of this section, some common types of commercially available waste-heat recovery devices are discussed in detail.

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