ANALYSIS OF LOCAL HEAT TRANSFER IN PLATE HEAT EXCHANGERS FOR FLOW PATTERN OPTIMISATION

Plate heat exchangers are already very effective and successful in liquid to liquid heat transfer. Nevertheless there is still room for improvement if more details about flow maldistribution and specifically about the coupling between flow interactions and heat transfer mechanisms on a local scale would be accessible. The relation between surface corrugation of the plates and thermal effectiveness is known, if at all, to the manufactors only. This contribution will report on an experimental study of local heat transfer within corrugated plate heat exchangers. The resolution of the experimental procedure is better than 0.5 x 0.5 mm. The measurements are performed using the Temperature Oscillation Infra Red Thermography (TOIRT) method, which can resolve a local heat transfer coefficient behind a surface with an uncertainty of less than 10 % if the flow is turbulent. The outer surface is periodically heated by means of sinodial laser radiation, the temperature response of the plate surface to this excitement is recorded by a lockin IR-camera. The phase shift between heat flux excitement and temperature response as seen by the IR camera is depending, among other parameters, on the heat transfer coefficient on the back side of the plate. This can be extracted using a numerical model based signal evaluation, thus enabling an intrusion free measurement. Plates with different corrugation angles and different flow fields have been analysed in detail. The result of this analysis gives rise to an understanding of the distribution of the local heat transfer coefficient as a function of topology of the plate and as a function of flow parameters. These results will be discussed on behalf of improvement potential for corrugated plates.