Performance evaluation of shell-and-tube heat exchangers: a numerical approach.

Abstract

Performance evaluation of heat exchangers is generally based on a number of idealized assumptions. In this work, an attempt has been made to investigate the effect of neglecting the presence of nonideal conditions on heat exchanger rating, testing and performance projections. Representative nonideal conditions such as the variation of fouling resistance along and across the tubes, maldistribution of flow, temperature dependent variation of fluid properties and plugged tubes are simulated on a one-pass, counterflow shell-and-tube heat exchanger using a numerical method of solution. The apparent nature of the test fouling resistance is demonstrated and an estimate of the errors introduced on using it for performance projections is made. An analysis of the uncertainty involved in heat exchanger rating, testing and performance projections is conducted and the characteristics of apparent fouling resistance are studied in the context of the overall uncertainty. The effect of typical input variable uncertainties on the uncertainty of key performance parameters such as heat transfer rate, terminal temperatures and fouling resistance is evaluated. Principal uncertainty contributors are identified and methods of reducing the overall uncertainty are discussed.