Coefficient of Thermal conductivity

In summary, the equation for calculating heat transfer through conduction is Q = KA(t2-t1)/thickness, where K is the coefficient of thermal conductivity. This value depends on temperature and can vary for different materials. When solving for Q, it is important to use the appropriate K value for the given temperature range. If the K value is not constant, numerical methods can be used to solve for Q. Another method is the heat conduction equation Q = -kA(dT/dx), which can be integrated to find Q.
  • #1
imselva
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TL;DR Summary
K depends on temperature. K varies with temperature. For all the materials we have a tabular data of K for different temperatures.
While calculating Q for which temperature K value has to be taken?
Which K value is valid?
We know that,

Conduction Heat Transfer Q = KA(t2-t1)/thickness

K is the coefficient of thermal conductivity. If T2 = 1020°C and T1= 22°C also consider we know A and thickness value.

K depends on temperature. K varies with temperature. For all the materials we have a tabular data of K for different temperatures.
While calculating Q for which temperature K value has to be taken?
Which K value is valid?
 
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  • #2
The equation Q = KA(t2-t1)/thickness is only valid in case the coefficient of thermal conductivity can be assumed to be about constant in the given temperature range.
 
  • #3
If it is not constant, how to calculate it analytically?
Is there any other relation to calculate Q
 
  • #4
Heat conduction problems with temperature dependent material properties are preferentially solved using numerical methods.
 
  • #5
$$Q=-kA\frac{dT}{dx}$$so $$Q\Delta x=-A\int_{T_1}^{T_2}{kdT}$$
 
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1. What is the coefficient of thermal conductivity?

The coefficient of thermal conductivity is a measure of how well a material conducts heat. It is the rate at which heat flows through a material per unit area, per unit thickness, per unit temperature difference. It is denoted by the symbol k and has units of watts per meter per Kelvin (W/mK).

2. How is the coefficient of thermal conductivity determined?

The coefficient of thermal conductivity is determined through experiments and measurements. A sample of the material is placed between two surfaces with different temperatures, and the rate of heat flow is measured. This value is then divided by the cross-sectional area of the material and the temperature difference to obtain the coefficient of thermal conductivity.

3. What factors affect the coefficient of thermal conductivity?

The coefficient of thermal conductivity is affected by several factors including the type of material, its density, and its temperature. Generally, materials with higher densities and lower temperatures have higher thermal conductivity. The presence of impurities, voids, and other defects can also affect the coefficient of thermal conductivity.

4. How does the coefficient of thermal conductivity relate to insulation?

The coefficient of thermal conductivity is inversely related to insulation. Materials with lower thermal conductivity are better insulators, as they do not allow heat to flow through them easily. This is why materials such as fiberglass and foam are commonly used as insulation, as they have low thermal conductivity values.

5. Can the coefficient of thermal conductivity change over time?

Yes, the coefficient of thermal conductivity can change over time due to factors such as aging, exposure to extreme temperatures, and physical changes in the material. It is important to consider these potential changes when selecting materials for long-term use, as the thermal conductivity can affect the overall performance and efficiency of a system.

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