This chapter is written primarily for the plant engineer faced with the many problems involved in the operation of heat exchangers of the kinds described in previous sections. These problems are of four types:

1. Inadequate thermal effectiveness,

2. Excessive pressure drop,

3. Failure of materials, leading to leaks of fluid,

4. Nuisances (noise and fog).

The heat exchangers will have been supplied by the company's engineering department or by an external engineering contractor or manufacturer. The plant engineer should guard against as many as possible of the likely troubles, by checking the proposed designs very carefully, as described in Section 288. The failure of one beat exchanger may lead to the shut down of a complex process plant, with considerable financial losses.

Many problems arise from changes in the operating conditions. Heat exchangers are designed to specification sheets, as described in Section 250, but they never operate at precisely the conditions specified. The flow rates and inlet temperatures of the fluids may differ significantly from those specified. Moreover the fouling resistance will differ from the value assumed in design; when the exchanger is new, or recently cleaned, there will be little or no fouling, but the fouling resistance will build up gradually, during days or months of operation, and may exceed the specified value before the exchanger is cleaned.

Section 368, Section 369, Section 370 and Section 371 describe the special problems that relate to air-cooled heat exchanger, condensers, vaporisers, and water cooling towers respectively.