Experimental analysis of freezing process of stationary food samples inside a hydrofluidisation freezing chamber

Food freezing technologies are one of the most important methods commonly used for food preservation and shelf life extension. In addition to the process effectiveness, modern food freezing techniques should guarantee the high quality of the products after freezing. The hydrofluidisation freezing (HF) is a promising technology that offers short freezing times and high energy efficiency. The heat transfer coefficient (HTC) typical for that method significantly exceeds the HTCs for similar immersion freezing (IF) or popular air-blast freezing. On the other hand, the literature focused on the experimental investigation of the HF is fairly limited. Therefore, the experimental investigation of the laboratory scale HF unit is presented in this paper. The experimental campaign was conducted for the various stationary samples immersed in the HF chamber. A copper sample was used to evaluate the HTC for the investigated system. According to the gathered results the HTC achieved for the investigated HF was equal to 2 941 W· m⁻²K⁻¹. In addition, the freezing time for cocktail tomato, blueberry, potato and plum was experimentally determined. The potato samples of various sizes were used to analyse the freezing time for the IF and HF methods. The results of that analysis showed that the freezing time for the HF setup was almost two times shorter for all considered sample sizes. Nevertheless, the freezing time reduction related to the HF employment decreased with the increase of the sample sizes.