Application of experimental data to model local fouling resistances

Abstract

Fouling is a problem that varies in space and time, but a fouling situation is commonly quantified using the integral thermal fouling resistance based on the integral heat balance and an area-averaged heat transfer assessment. However, current modeling does not take into consideration the local differences, such as constrictions, that can affect the integral fluid dynamic behavior. This work shows experimental and analytical results of local investigations of a fouled counterflow double-pipe heat exchanger. The determined local parameters are used to calculate different local fouling resistances as part of a holistic modeling approach with the aim of modeling and linking local and integral fouling resistances as well as the thermal and the mass based approaches. Therefore, mass based parameters are utilized to recalculate the obtained local thermal fouling resistances as a way to account for the heat transfer increases caused by local surface roughness and/or local constrictions. The aim of this procedure is to explain and eliminate apparent negative fouling resistances on a local basis. The local thermal fouling resistances are determined by measuring the local temperatures and then used for quantification of the local overall heat transfer coefficients. Modeling of the local mass based fouling resistances requires knowledge of the density and thermal conductivity of the local material, as well as the local layer thickness and/or the local fouling mass. The local thermal fouling resistances are recalculated using the local friction coefficients and local flow velocities resulting from local constrictions. All experimental and theoretical approaches are merged into the model presented here for the determination of local fouling resistances.