Simulation of Food Freezing: Effects of Air Temperature and Velocity

Abstract

Freezing is one of the most popular methods for long term preservation of foods. Air-blast freezingis one which is commonly used in food freezing industry. The major problems of a large scale spiralair-blast freezer were non-uniformity of both air temperature and velocity distributions. Therefore, thiswork was aimed to simulate the effects of air temperature (-20 to -50°C) and velocity (0.1 to 5.0 m/s) onfreezing times of model foods (slab of 0.02 m in thick, cylinder and sphere of 0.02 m in diameter) in thespiral air-blast freezing. The result would be used as guidance on an improvement of an air-blast freezer.One-dimensional numerical analysis using finite difference method (Crank-Nicholson scheme) wasdeveloped and written in FORTRAN code. The simulated results showed that the ambient temperatureaffected the freezing time, especially during the phase change period. To obtain the moderate freezing ratewith stable operation, the suitable air velocities were 1.6 to 1.8, 2.0 to 2.2 and 2.0 to 2.1 m/s in equivalencewith Nusselt numbers of 23.5 to 24.5, 20.8 to 21.0 and 24.0 to 26.0 and the corresponding freezing timeswould be 38, 21 and 12 minutes for slab, cylindrical and spherical shapes, respectively.

Keywords : Air Blast Freezing / Simulation / Air Velocity / Nusselt Number