Impact of manifold design on heat exchanger efficiency

The impact of manifold design on single-phase heat exchanger effectiveness is studied using the NTU-effectiveness method. Manifolds are devices that redistribute the internal flow stream of a heat exchanger from one to several passages. Two manifold types are identified; collector box and direct split designs. A general enhancement analysis is performed which covers four different combinations of performance and objective criteria. Three cases involve increasing the heat exchanger effectiveness while constraining either the internal flow head loss, the internal mass flow rate, or their product. The other case involves reducing the required heat exchanger flow length while constraining the heat transfer rate. Familiar convection correlations are then incorporated into the enhancement analysis to predict general trends and behavior when the main tube is split into several smaller tubes. Analytical estimates are presented of improved effectiveness for three operating conditions of an actual heat exchanger which possesses a manifold. Experimental data acquired from the gas-to-gas heat exchanger is compared to numerical predictions of its performance without a manifold, (baseline design). The analytical equations developed correctly estimate an improvement in heat exchanger effectiveness.