Calculation of the process duration of thermo-moisture treatment of semi-finished products based on animal and vegetable raw materials

Abstract

Calculation of the parameters of studied systems heat treatment (the process duration, temperature distribution inside the product and in its mass change) is complicated both by external and internal moisture transfer. In this regard, a strict mathematical description of moisture and heat transfer between the surface of the semi-finished product, which must be considered as a capillary-porous body, and the surrounding medium should be based on a joint solution of hydrodynamics equations and convective heat- and mass transfer, taking into account the normal component of the mass flow on the body surface, which complicates the task. Consideration of such a task with regard to moisture transfer under the action of water content gradients, temperature and pressure is possible if the driving forces of transfer processes do not consider these potential gradients on the surface of a capillary-porous body, but the differences between potentials averaged over the surface and volume of the body. This theory successful application for widespread use in practical problems solving is complicated by the absence of a systematized database on the hygro- and hydro-mechanical equilibrium of treated semi-finished products with technological media. On the other hand, even in the presence of experimental data on hydro- and hygroscopic equilibrium, in this case there are not fields of transfer potentials, but only their average volume and mean surface values, which in principle does not allow calculating of heat treatment duration as the time to reach the required temperature in the middle of the product. Meat and fish products are treated at not too high temperatures and as a result gradients of transfer potentials inside capillary-porous bodies are not too great, therefore it can be considered that the internal moisture transfer does not change the temperature field inside meat and fish products significantly. Resource-saving modes of thermo-moisture treatment of combined products were justified: frying at t = 200 ° C, without humidification, duration - 5 min; baking at 180 ° C, water consumption for humidification (4.0-4.3)10-6 m3 / s with 10-15 minutes duration, providing a reduction in process losses of the finished product weight from 18% to 5-7%