Freezing and thawing of foods – computation methods and thermal properties correlation

Abstract

Correlations are derived for local water activities, aw, unfrozen water contents, nw, ice contents, nI, effective heat capacities, C, thermal conductivities, k, and specific enthalpies, H, as functions of temperature, T , in foods at subfreezing conditions.The validity of the correlations has been demonstrated for many foods. The correlations can be used to provide thermal properties data for freezing and thawing calculations, including numerical solution of partial differential equations (PDEs) describing heat transfer during freezing and thawing. Finite element and finite difference methods for solving such PDEs are described, particularly enthalpy step methods. Local T versus time, t, histories for food freezing and thawing obtained by the use of these methods are presented. 1 Engineering calculations Food process engineers often have to calculate heat transfer loads for freezing and thawing, how fast such heat can be transferred, how changing product or process variables affects transfer rapidity, how freezing rates and T differ in different parts of a product, and how T rises in frozen food exposed to abusive conditions. Thermal property correlations and computational methods presented here can be used for such calculations.