Problem 59a
A carpenter builds an exterior house wall with a layer of wood cm thick on the outside and a layer of Styrofoam insulation cm thick on the inside wall surface. The wood has , and the Styrofoam has . The interior surface temperature is °C, and the exterior surface temperature is °C. What is the temperature at the plane where the wood meets the Styrofoam?
Problem 59b
A carpenter builds an exterior house wall with a layer of wood cm thick on the outside and a layer of Styrofoam insulation cm thick on the inside wall surface. The wood has , and the Styrofoam has . The interior surface temperature is °C, and the exterior surface temperature is °C. What is the rate of heat flow per square meter through this wall?
Problem 60a
An electric kitchen range has a total wall area of m2 and is insulated with a layer of fiberglass cm thick. The inside surface of the fiberglass has a temperature of °C, and its outside surface is at °C. The fiberglass has a thermal conductivity of . What is the heat current through the insulation, assuming it may be treated as a flat slab with an area of m2 ?
Problem 61
The blood plays an important role in removing heat from the body by bringing this energy directly to the surface where it can radiate away. Nevertheless, this heat must still travel through the skin before it can radiate away. Assume that the blood is brought to the bottom layer of skin at °C and that the outer surface of the skin is at °C. Skin varies in thickness from mm to a few millimeters on the palms and soles, so assume an average thickness of mm. A -lb, -ft-tall person has a surface area of about m2 and loses heat at a net rate of W while resting. On the basis of our assumptions, what is the thermal conductivity of this person's skin?
Problem 67
A spherical pot contains L of hot coffee (essentially water) at an initial temperature of °C. The pot has an emissivity of , and the surroundings are at °C. Calculate the coffee's rate of heat loss by radiation.
Problem 68
The emissivity of tungsten is . A tungsten sphere with radius cm is suspended within a large evacuated enclosure whose walls are at K. What power input is required to maintain the sphere at K if heat conduction along the supports is ignored?
Ch 17: Temperature and Heat