Dynamic study on operation conditions for the higher sublimation rate during freezing drying of cooked beef slice

The operation conditions for the higher sublimation rate during freeze drying of cooked beef slice were studied. Mathematical models were established for sublimation layer thickness(δis), sublimation time（tis）and sample surface temperature (Tis) suited for the higher sublimation rate when the temperature of frozen sample is Ti during the sublimation. When the terminal freeing temperatures were –30, –29, –28, –26 and –24℃, respectively, The suitable sample thickness were 18, 15, 12, 8 and 6mm, respectively under the higher sublimation rate and the moisture rate and surface temperature of the sample were calculated. Moreover, the moisture ratio, center and surface temperature changing with time were forecast. The validation experiments were conducted, in which chamber pressure was 10 Pa, and shelf temperatures were controlled according to predictive temperature of sample surface. The results show that the comparative errors between forecast and measured moisture ratio are lower than 10%, and absolute errors between forecast and measured centre temperature of drying sample are lower than 5℃. It can be concluded that the predictive model of surface temperature can be applied in shelf temperature control during sublimation drying of frozen cooked beef slice with the thickness of 6～15 mm. Comparing average sublimation rate and energy consumption for dehydrating water from different samples with the thickness are 6, 8,12 and 15 mm, the highest sublimation rate and the lowest energy consumption are obtained when sample thickness is 6 mm.