The relaxation processes calculation of fish dehydrated surface layer during drying and smoking

Abstract

Abstract In this work the methods of study of relaxation processes that are applicable during fish dehydration based on the influence of the chemical composition, geometric size of the processing object and regime parameters of the dehydration processes are developed. The numerical methods of calculation on the basis of solution of the second-order differential equation with boundary conditions of the third type allow with sufficient for engineering practice accuracy to model the various conditions of the dehydration process conducting with periodic restoration of hydraulic conductivity properties of dehydrating objects. The proposed calculation methods applicable to dehydration processes consisting of a continuous initial period and the following combined periods of drying fish and surface layer relaxation of the object of dehydration. The importance of applying the relaxation is determined by the firming the upper layers which have lost part of the moisture during dehydration. The size of capillaries for the moisture pathway through the upper surfaces reduce. Thus, near the upper layer a free of major moisture mass zone appears, which also has low diffusion properties. As a result, the dehydration process of the entire object slows down. Applying the relaxation enables the hydraulic conductivity features of fish upper layer. During the relaxation the supply of electric power to the heating elements stops. The rate of circulation of the drying agent slows down. The drying installation is supplied with air of lower temperature and higher relative humidity than the drying agent. In the drier such conditions are created that constrain external mass transfer and enables moisture redistribution in the thickness of the fish. During the relaxation the moisture is gradually shifting from the central layers where dehydration has not yet come to the dehydrated surface layers.