Method to delay frost formation under high relative humidity by choosing proper heat exchange temperature difference and air velocity

Abstract

At frozen storage conditions, it is benefit to delay frost formation and maintain high relative humidity, by reducing temperature difference between cold surface and wet air. This study aimed to investigate the quantification of smallertemperature difference on frost formation characteristics, refrigerating capacity and water removal of an tube-fin evaporator, at the temperature of -18 oC, relative humidity of 85% and velocity from 2 to 5 m/s. With limited fins space, frost growth was insufficient and easily to be destroyed, so three stages of frost thickness, "rapid growth stage", "stable stage" and "slow reduction stage", were found. Smaller temperature difference provided smaller heat exchange but illustrated good ability to stop sharp decline of refrigerating capacity. With temperature difference changing from 7 to 3 ℃, the removal of water content in the air by passing through the evaporator decreased by 3 ~ 5 times. Ratios of heat exchange for frost formation were also calculated. The combined results showed that for a special evaporator, smaller temperature difference and larger air velocity was a useful guideline to forbid frost formation and maintain stable high refrigerating capacity and relative humidity. This was essential for practical applications.