Thermodynamic Properties

An important consideration in all designs of food processing involving heat exchange is the thermal properties of the food products to be handled in the system. The variable composition and structure of foods influence those properties. During storage the chemical and physical properties, the time, and the temperatures are the most important factors. The composition of the food product varies with species, growth condition, age, feed, harvest, slaughter, catch, handling, and processing, as well as storage conditions. All of these factors influence the thermal properties.

For these reasons it is easily understood that the values of thermal properties are not exact values but most often estimates. The more detailed a description of the food product measured the more accurate the values given. Another important consideration when using experimentally found thermal properties is the difference in the methods of measurement, which may place limitations on the value of the data (4). Computer programs have been developed to estimate the thermal physical properties from the knowledge of the specifications of the products, such as chemical composition, temperature, and density.

Values of specific heat and latent heat of fusion are often calculated directly from the water content of the product. This is the case for the values given in Table 1.

The values of water content in Table 1 are averaged for the product. The water content for fruit and vegetables

Table 1. Thermal and Related Properties of Food and Food Materials

Food or food material

Highest freezing point, ope

Specific heat6

Below freezing, kJ/kg °C

Latent heat of fusion"* kJ/kg

Table 1. Thermal and Related Properties of Food and Food Materials

Food or food material

Highest freezing point, ope

Below freezing, kJ/kg °C

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