Refrigeration & Equipment Engineering

Unit 4 - Refrigerants

4.3.1.Properties of insulating materials

Thermal properties
Thermal conductivity is the ability of material which retards the flow of heat. It is a property of a homogeneous material which changes with the variation of density. The compressible material such as glass wool is better insulation if loosely packed. Furnace insulations must have low thermal capacity for quick response to temperature changes required. The other thermal properties are specific heat capacity, thermal diffusivity and coefficient of thermal expansion. Heat capacity is known as the product of specific heat and density. Thermal diffusivity is the ratio of thermal conductivity and heat capacity. It is a measure of the rate of progression of temperature rise in an insulating material when certain heat energy is available at one of its surface.

Mechanical properties
The mechanical properties of the insulating material depend upon the type and use of insulating material. These mechanical properties are strength of compression, tension shear and impact. Important mechanical properties required generally are high abrasion resistance and hardness, good compressive strength.

Physical properties
The physical properties of insulating material include conventional properties like density, porosity, coefficient of thermal expansion, surface tension, hygroscopicity and compactness. It should resist the moisture and should not absorb the moisture and should not absorb the moisture from the humid space. Insulating material should odor less and should not pickup odor of other article placed in the refrigerated space. Its density should be low to reduce its weight. It should be safe to health and its vapor and loose particles should not be dangerous to the health of the people. It should be fire proof.