Thermal Insulation - Resistance - Conduction Coefficient
Controlling high temperature is a difficult task and often requires professional support. Thermal insulation made by taking into account parameters such as variable heat conduction coefficient, surface area, surface form, ambient temperature, ambient wind intensity will provide optimum efficiency, otherwise it will result in low efficiency and high cost.
In this article, high We will examine three concepts that are often confused with each other in the fight against heat, but are very different from each other.
Heat resistance, heat insulation and heat transmission coefficient.
Heat resistance
The term heat resistance has many sub-categories within itself. It is a term that can be divided into groups. We will examine two important subgroups that are frequently mentioned in technical textiles;
Continuous heat resistance
The maximum temperature at which the mechanical performance values of the material at room temperature remain constant regardless of time represents its value. For example, for E-glass glass fiber, this value is approximately 550 'C.
Instantaneous heat resistance
The mechanical performance values of the material at room temperature depend on time. It refers to the maximum temperature value at which it remains constant, and the time it can withstand this temperature is also stated along with the temperature value. For example, for E-glass glass fiber, this value is approximately 650'C and 1 minute.
It is a variable independent of the physical properties of the material. Heat resistance will not change as the material thickness increases.
For example, wrapping two or more layers of E-glass glass fiber with a temperature resistance of 550'C on the surface at a temperature of 1,000'C will bring nothing but loss of time and money, E -glass will result in the glass fiber melting. (Unfortunately, this has happened.) The material to be used will be Silicate fiber with a temperature of 1,100'C or Ceramic fiber with a temperature of 1,200'C.
We can roughly express the phenomenon of heat resistance in this way.
Thermal conduction coefficient
It is defined as the amount of heat transmitted from the unit surface area of a material of unit thickness, at unit temperature difference and in unit time. Its unit is W/m2K. This value varies depending on the molecular structure of the material. Materials with high density and tight molecular structure, such as metal, have a high heat conduction coefficient.
As the material density decreases, the heat conduction coefficient will also decrease as the amount of energy transmission between molecules will decrease. This is the reason why woven fabrics provide lower insulation than needled mattresses (felt, wool).
In materials exposed to high temperatures, some of the heat energy turns into molecular motion energy and the amount of movement of molecules increases, therefore, as the temperature increases, the heat energy of the materials increases. The conduction coefficient increases.
Insulation materials such as ceramic wool, rock wool, glass wool, silica wool or airgel are insulation materials with low heat conduction coefficient that are frequently used today.
Thermal insulation
It is a phenomenon related to variables such as insulation geometry and environmental factors, especially the heat conduction coefficient of the material and material thickness.
Providing high thermal insulation The following factors ensure optimum thermal insulation:
1) Low thermal conductivity coefficient
2) Selection of materials with sufficient heat resistance
2) Sufficient material thickness
3) Geometry free of sharp corners
4) Isolation from external environmental conditions or minimum exposure (wind, rain, etc. .)
To summarize, since we have examined the concepts of heat resistance, heat insulation and heat transmission coefficient separately;
“To ensure high thermal insulation, materials with high heat resistance and low heat conduction coefficient should be selected.”
Optimum thermal insulation In order to achieve efficiency, it is necessary to use Heat Flow Simulation programs where parameters such as variable heat conduction coefficient, heat resistance, thickness, material geometry and environmental factors are evaluated together.