Question

In: Mechanical Engineering

A new material has a measured thermal conductivity k of 200 BTU-in/hr-ft2 -°F. Is this material...

A new material has a measured thermal conductivity k of 200 BTU-in/hr-ft2 -°F. Is this material a thermal insulator or a conductor? Calculate the R and U values for a block of this material that is 3 inches thick. Now sandwich this block of material between two sheets of R-0.8 fiberboard. What is the new effective U value?

Expert Solution

A thermal insulator is a material which provides a large resistance to heat flow through it. Consider a well known thermal insulator - wood.

Oak wood has a thermal conductivity of 1.178 Btu-in/hr-ft² - ^oF.

Compare this with the given material. It becomes clear that the given material is a thermal conductor given the large difference in thermal conductivity.

R value is nothing but the thermal resistance per unit area provided by the material.

It is given as follows:

Where, t = thickness

K = thermal conductivity

U factor is just the reciprocal of resistance and indicates how well heat can be transferred across it.

After the block of this material is sandwiched between two fiberboard sheets, all the thermal resistances will be in series and total resistance will be the sum of all.

Thus the U value is given as,

Any feedback is appreciated.

samet mamat answered 2 years ago

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