Numerical investigation on the effect of varying the number of flow dividers on Z-shaped membrane heat exchanger performance

Abstract

To reduce building energy consumption and to improve indoor air quality, it is necessary the use heat recovery such as air-to-air fixed-plates enthalpy heat exchanger in mechanical ventilation. Prediction of enthalpy performance by utilizing CFD simulation is challenging since most commercial software do not simulate moisture transfer. In this research, a Z-shaped membrane heat exchanger which is used for building energy recovery systems was modeled by using commercial CFD software (FLUENT). Kraft paper of 45 gsm was used as the heat exchanger heat and moisture transfer surface. A User Define Function (UDF) code was developed and incorporated in the CFD software to enable the software to model moisture transfer through the membrane. This model is used to investigate the performance of Z-Shaped heat exchanger when the number of flow dividers within the heat exchanger is varied. It was found that a 21 % increase in the effectiveness was achieved when the number of ribs was increased from no ribs to 5 ribs. However, increasing the number of ribs from 5 to 11 only demonstrates minor effect. Therefore, no significant improvement is noticed when the number of ribs is increased beyond 5 which is attributed to air flow distribution which because more uniform when number of ribs is increased. However, the flow is already uniform when 5 ribs where used, hence increasing the ribs to 11 will not improve the flow distribution further.