IMPACT OF MANIFOLD DESIGN ON HEAT-EXCHANGER EFFICIENCY

The impact of manifold design on single-phase hear exchanger effective ness is studied using the NTU-Effectiveness method. Manifolds are devi ces that redistribute the internal flow stream of a heat exchanger fro m one to several passages. Two manifold types are identified: collecto r box and direct split designs. The particular application considered is that of a gas fired forced air heating system. A general enhancemen t analysis is performed which covers four different combinations of pe rformance and objective criteria. Three cases involve increasing the h eat exchanger effectiveness while constraining either the internal flo w head loss, the internal mass flow rate, or their product. The other case involves reducing the required heat exchanger flow length while c onstraining the heat transfer rate. Familiar convection correlations a re then incorporated into the enhancement analysis to predict general trends and behavior when the main tribe is split into several smaller tubes. Analytical estimates of improved effectiveness are presented fo r three operating conditions of an actual heat exchanger which possess es a manifold. Experimental data acquired from the gas-to-gas heat exc hanger are compared to numerical predictions of its performance withou t a manifold (baseline design). The analytical equations developed clo sely predict the improvement in heat exchanger effectiveness.