Thermal insulation

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The term thermal insulation can refer either to materials used to reduce the rate of heat transfer, or the methods and processes used to reduce heat transfer. Heat energy can be transferred by conduction, convection, radiation. Thermal insulation prevents heat from escaping a container or from entering a container. In other words, thermal insulation can keep an enclosed area such as a building warm, or it can keep the inside of a container cold. Insulators are used to minimize that transfer of heat energy. In home insulation, the R-value is an indication of how well a material insulates. The flow of heat can be reduced by addressing one or more of the three mechanisms of heat transfer and is dependent on the physical properties of the material employed to do this.

Contents

Factors that compromise insulation

Moisture

Calculating requirements

Industry standards are often "rules of thumb" developed over many years, that offset many conflicting goals: what people will pay for, manufacturing cost, local climate, traditional building practices, and varying standards of comfort. Both heat-transfer and layer analyses can be performed in large industrial applications, but in household situations (appliances and building insulation), airtightness is the key in reducing heat transfer due to air leakage (forced or natural convection). Once airtightness is achieved, it has often been sufficient to choose the thickness of the insulative layer based on rules of thumb. Diminishing returns are achieved with each successive doubling of the insulative layer. It can be shown that for some systems, there is a minimum insulation thickness required for an improvement to be realized.[1]

Applications

Clothing

Clothing is chosen to maintain the temperature of the human body.

To offset high ambient heat, clothing must enable sweat to evaporate (cooling by evaporation). When we anticipate high temperatures and physical exertion, the billowing of fabric during movement creates air currents that increase evaporation and cooling. A layer of fabric insulates slightly and keeps skin temperatures cooler than otherwise.

To combat cold, evacuating skin humidity is still essential while several layers may be necessary to simultaneously achieve this goal while matching one's internal heat production to heat losses due to wind, ambient temperature, and radiation of heat into space. Also, crucial for footwear, is insulation against conduction of heat into solid materials.

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