Question

As part of your summer job as an engineering intern at an insulation manufacturer, you are...

As part of your summer job as an engineering intern at an insulation manufacturer, you are asked to determine the R factor of insulating material. This particular material comes in 1/2 in sheets. Using this material, you construct a hollow cube that has 15 in long edges. You place a thermometer and a 85 W heater inside the box. After thermal equilibrium has been attained, the temperature inside the box is 90°C when the temperature outside the box is 20°C. Determine the R factor of the material. F°· ft2· h/Btu

Homework Answers

Answer #1

Given, Power of the heater or heat supplied by heater, Q = 85 W = 290.032 Btu/hr

The hollow cube has side length, l = 15 in = 1.25 ft

Total surface area of the cube, S = 6l2 = 6 (1.25)2 = 9.375 ft2

Temperature difference, = (90 - 20) oC = 126 oF

Let R factor of material be denoted by "R"

At thermal equilibrium,

Thus, the R factor of the material is 4.073 oF ft2 h/Btu

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