Effects of Secondary Variables on Infiltration Rate of Open Refrigerated Vertical Display Cases with Single-band Air Curtain

Recently the authors of this work reported the effects of several primary variables that can affect the performance of a circulated air curtain in protecting open refrigerated vertical display cases against infiltration of outside warm air. Those variables were either associated with the dynamics of the air curtain flow or were geometrical variables. There were a few other variables that were thought to have lesser impact on infiltration or relatively much harder to manage and vary; therefore, they were categorized as, so-called, secondary variables and decided to be studied separately in a complimentary investigation. These variables were not included in the permutations of the primary variables as they would drastically increase the number of experiments in the published primary-variables study. Due to using a few simplified assumptions or ideal conditions in the primary study, the secondary variables’ effects were incorporated as several correction functions to modify the infiltration rate obtained from the primary study. The four secondary variables studied here are turbulence intensity of the air curtain jet at its discharge nozzle, average percentage of the space between the shelves that was filled with food products, difference between the temperatures of ambient air and the jet at the discharge nozzle, as well as the relative humidity between the aforementioned locations. For the ranges of the variables commonly used in typical medium-temperature display cases, it was found that the temperature and relative humidity changes are of little or no importance, while the turbulence intensity changes infiltration rate almost linearly and the food level varies it in a nonlinear manner.