CFD Simulation of Energy Transfer within a Membrane Heat Exchanger under Turbulent Flow

Abstract

Air-to-air fixed plate enthalpy membrane exchanger is considered one of the equipment used in energy recovery services. Thermal performance of air-to-air energy recovery ventilator is examined numerically using a 3D CFD simulation. Air flow inside the exchanger is tested using four numerical turbulence models: Standard k-ε, k-ε renormalization group (RNG), k-ε realizable and k-ω shear-stress transport (SST) models. The adopted heat and mass exchange element within the ventilator (membrane) is a thin 98 µm porous 60 gsm Kraft paper. A user defined function (UDF) has been developed to enable the CFD model to estimate amounts of mass exchanged between the two sides of the membrane. Grid dependency study is conducted and results have shown that a perpendicular distance of 50  m or less from the membrane surface would result in a negligible variation in the ERV thermal effectiveness. The validated CFD model and UDF code against experimental measurement resulted in a maximum difference in thermal effectiveness of 3.6%. Results have shown that the SST k-ω turbulence models under enhanced wall treatment showed more sensitivity to flow at all Re values when compared with the k-ε simulated models.