Air-Side Heat Transfer Augmentation of a Refrigerator Evaporator Using Vortex Generation

In air-cooling applications with frost production, heat exchanger performance is often air-side limited, because the two-phase flow of the refrigerant provides excellent heat transfer coefficients, and because designers typically use a large air-side fin spacing for frost tolerance. The large fin spacing prolongs operation of the heat exchanger by mitigating the effect of the accumulating frost, but it does not allow for a very high air-side heat transfer coefficient. Longitudinal vortex generation is a proven and effective technique for thinning the thermal boundary layer and enhancing heat transfer, but its efficacy in a frosting environment is essentially unknown. In this study, an array of delta-wing vortex generators is applied to a plain fin-and-tube heat exchanger with a fin spacing of 8.5 mm. Heat transfer and pressure drop performance are measured to determine the effectiveness of the vortex generator under frosting conditions. For Reynolds numbers between 500 and 1200, a reduction of 35.0% to 42.1% is observed in the air-side thermal resistance. Correspondingly, the heat transfer coefficient is observed to be between 33-53 W/m-K for the enhanced heat exchanger and between 18-26 W/m-K for the baseline heat exchanger. A modified volumegoodness parameter is also calculated and shows that the enhanced exchanger outperforms the baseline specimen for the range of Reynolds numbers examined.