1. Heat units

2. Specific heat
Specific heat is the quantity of heat that must be supplied or removed from a gram of substance to bring about change in temp of 1⁰C.

3. Thermal conductivity
The rate of heat transfer depends on the co-efficient of thermal conductivity of the substance which is defined as thermal conductivity of medium in which a unit of heat (calorie) flows through a unit surface area of unit thickness at a temperature gradient of 1 unit.

4. Thermal diffusivity
Thermal diffusivity of any substance is directly proportional to its thermal conductivity and inversely proportional to specific heat and density of the substance.

5. Latent Heat
The quantity of heat required to change the state or condition or phase under which a substance exists without change in temperature.

6. Principle of freezing
Even at -30⁰C, approximately 10% of the water remains unfrozen.
To lower the temperature of 1g of water by 1⁰C, at temperatures above 0⁰C to ice at 0 ⁰C, 80 calories must be removed for each g of water. Specific heat of ice at temperatures below 0 ⁰C is 0.5.
Under ideal conditions, fish should be frozen to -0 ⁰C in 2 hours.
Fish should pass through the thermal arrest period as quickly as possible.