Numerical investigation on the effect of area ratio on an adjustable ejector for heat pump dryer based on dynamic mesh

Adjustable ejector is considered as a promising device to recover the expansion work and enhance the performances of refrigeration or heat pump system. To investigate the impacts of area ratio (AR) of mixing chamber throat to nozzle throat, a dynamic mesh based numerical model of an adjustable ejector for the heat pump dryer was established. The area of nozzle throat could be modified by adjusting the position of needle. The movement of needle was simulated by using the dynamic mesh method. The effects of the nozzle throat area and the mixing chamber throat area on the ejector performances were investigated. Further, the optimal values of dimensionless parameter AR under the different structure parameters of ejector were estimated. The numerical model was validated by the experimental results, and the k-ε standard turbulence model was proved to predict the ejector performances well. The numerical results indicated the optimal AR to obtain the maximum entrainment ratio of ejector ranged from 2.65 to 4.87 at the given working condition. Among the structure parameters of ejector, the length of constant-area mixing section has the greatest influence on the optimal AR. These numerical results provided the guidance for structure optimization of adjustable ejectors in heat pump dryer.