Thermal influence of non-uniform inlet flow conditions for a commercial plate fin heat exchanger

Abstract

Paper presented to the 10th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Florida, 14-16 July 2014.

In this study, a commercially available plate heat exchanger with wavy fins is experimentally characterized under uniform and three non-uniform flow conditions. The heat exchanger is 275 mm wide and 295 mm high and has a distance in-between the plates of 3 mm and the wavy fins are 11 mm high. Internally, the heat exchanger is finned with offset strip fins. Hot water at 55°C is sent through the plates and the waterside mass flow rate is kept high in order to minimize the internal thermal resistance. For the internal convection coefficient, a correlation from literature is used. The airside mass flow rate is varied by adjusting the fan speed. In case of uniform flow conditions, the frontal air velocity varies between 1.7 and 7.6 m/s. The airside velocity is measured over a nozzle and the uniformity of the wind tunnel is verified by hot wire measurements. Three non-uniformities are placed 10 cm upstream of the heat exchanger: the first one covers the right-hand side of the heat exchanger, the second one covers the top half of the heat exchanger and the last (and most severe) non-uniformity consists of a circular hole of 150 mm diameter in the middle of a plate. Only the third non-uniformity has a significant influence on the heat transfer rate: up to 25% higher for the external convective resistance in comparison with the uniform case.