Fault detection of heat exchangers

Abstract

Heat exchangers transfer heat between two or more media. They exist in a large variety of types in the chemical and power industries, in buildings and vehicles. Typical faults in these heat exchangers are leaks, e.g. by corrosion and the contamination by dirt and dissolved or suspended matter. The growth of deposits is called fouling and leads to a reduction of heat transfer. Therefore heat exchangers are usually designed with excess heat transfer surfaces of about 35% average, [10.16]. This excess design increases costs, space and weight. Remedies against fouling are chemical or mechanical mitigation techniques like filtration, additives, higher velocities, lower surface temperatures, polished surfaces. However, fouling cannot usually be avoided completely and therefore periodic cleaning will still be necessary. For more details see, e.g. [10.19], part Oc 1 and [10.17]. The detection of leaks in heat exchangers may be based on mass balances and methods described in Chapter 7. Fouling increases mainly the heat transfer coefficients, respectively the heat transfer resistance and to a minor extent the flow resistance of the media. The following sections describe some methods to detect changes of the heat transfer and some experimental results for steam-heated tubular heat exchangers with linear and parameter variable models.