Question

Liquid nitrogen and carbon dioxide can be used as a refrigerant in many food freezing applications. You are assigned by the project manager to investigate and report on the suitability of both liquid nitrogen and carbon dioxide in chilling meat products for the new frozen meat production line. In your report.

Explain the thermodynamics properties that allow nitrogen and carbon dioxide to function as a refrigerant in food freezing applications.

Answer 1

Freezing process is the most widely used process for the preservation of various food items which includes fruits,vegetables,meat etc.Because in the freezing process the taste,calories and texture of the items may not be changed.

There are several mechanisms for the freezing process.The major thermodynamic parameters for the freezing proces are

1. Thermal Conductivity
2. Change in Enthalpy
3. Heat Transfer medium
4. Dimensions of the product

Also there are various types in freezing process.That are immersion freezing,Cryogenic Freezing etc.

Carbondioxide is usually used in solid form known as dry ice and the liquid nitrogen are used extensively in Cryogenic type of Freezing.The term cryogenic refers to high negative temperatures.The thermodynamic properties of these components are as follows:

Dry ice at atmospheric pressure sublimes at -79⁰C and absorbs 575 kJ/kg of heat.While liquid nitrogen boils at -195⁰C and absorbs 198 kJ/kg of heat during vapourization.During the freezing process,the food items are kept over a conveyor belt and passed into the chamber consisting of dry ice or liquid nitrogen.During the passage of the items through the chamber,due to the high temperature difference the heat gets transferred from the items to the surrounding medium and gets frozen at a faster rate.The specific heats of the food items are usually reduced when compared with the fresh products.Likewise the major thermodynamic parameter,heat transfer coefficient also plays a keyrole in the freezing process.