Modelling Heat Exchangers for Domestic Boilers

Abstract

In the present paper the thermal behaviour of fin-tube heat exchangers is modeled. Particular attention has been given to the plate fins. The heat fluxes in the fins are described using a finite volume technique to discretize the energy equation. The thermal interactions with the water in the tubes and the surrounding air are treated as external boundaries, using appropriate relationships for forced convection in pipes and flat plates. The numerical results are presented in terms of dimensionless numbers (Fourier, Biot and geometric ratios) which are found to be representative for this particular geometry. Furthermore, the effect of thermal gradients along the fin surface upon the fin efficiency is investigated. Based on a differential model for the heat balances, design charts have been developed for the thermal analysis of heat exchangers.