Experimental investigation and performance evaluation of a mixed-flow air to air membrane enthalpy exchanger with different configurations

This paper presents an experimental investigation and performance evaluation of a mixed-flow air to air membrane enthalpy exchanger with different flow configurations. The moisture diffusivity, water contact angle and elastic modulus of five porous membranes were first experimentally determined using a wet cup test method, a contact angle meter and the tensile test, respectively. The five porous membranes investigated consisted of two Polyvinylidene difluoride membranes with the mean pore diameters of 0.22 mu m (PVDF22) and 0.45 mu m (PVDF45) respectively, two Nylon membranes with 0.1 mu m and 0.45 mu m pore sizes respectively and one Polyethersulfone (PES) membrane with a 0.1 mu m pore size. The optimal membrane was then identified and used to fabricate an enthalpy exchanger. Lastly, the performance of the enthalpy exchanger with different mixed-flow configurations was experimentally investigated. The results showed that the PVDF45 membrane offered the highest moisture diffusivity (1.91 x 10(-6) +/- 2A2 x 10(-8) m(2)/s) with hydrophilic surface and a relatively high elastic modulus (4.97 x 10(8) +/- 3.86 x 10(7) Pa). It was shown that the enthalpy exchanger with Z-shape flow of the supply air stream and H-shape flow of the exhaust air stream at an entrance ratio of 0.25 offered the best thermal performance as the sensible, latent and total effectiveness increased by 12.3%, 15.1% and 14.6% respectively, when the flow rate was 0.3 l/s, as compared to that of the pure cross flow. The same flow configuration was able to recover the highest energy among all configurations investigated.