FOOD PROCESSING PRINCIPLES FOOD REFRIGERATION ASSIGNMENT
Q1. (i) Compare the refrigerant properties of ammonia and Rf134a, by means of a summary table and some brief notes explaining the advantages of each.
(ii) Explain the terms "cooling load" and "cooling capacity". Use your definitions to explain how a cool room design for a static load might fail in practise.
(iii) What is an immersion refrigeration system? Use diagrams and notes to explain. What products is it suited best for?
Q2. Calculate the specific heat of a food product which consists of 70% water (of which 30% is frozen), and 30% dry solids (specific heat of 1.35 kJ/kg.K).
Q3. A food storage chamber requires a refrigeration system of 8.5 ton capacity when operating at an evaporator temperature of -15°C and a condenser temperature of 40°C. Refrigerant R134a is used. Determine:
(i) the system C.O.P.
(ii) the required refrigerant flow-rate
(iii) the rate of heat removal by the condenser
(iv) choose an appropriate motor size (assume efficiency c=0.85).
(v) attach a diagram showing your workings.
Q4. A 4 cm thick beef-steak is being frozen in a cold room at -18°C. The product has 73% moisture content, a density of 970 kg/m-3, and a thermal conductivity (frozen) of 1.1 W/m.K. Estimate the freezing time using Planck's equation. The product has an initial freezing temperature of -1.75°C, and the movement of air in the room provides a convective heat-transfer coefficient of 7 W/m2.K.