Chapter 2, Problem 2.23P

One end of a 0.3-m-long steel rod is connected to a wall at 204C. The other end is connected to a wall that is maintained at 93C. Air is blown across the rod so that a heat transfer coefficient of 17W/m2 K is maintained over the entire surface. If the diameter of the rod is 5 cm and the temperature of the air is 38C, what is the net rate of heat loss to the air?

Both ends of a 0.6-cm copper U-shaped rod are rigidly affixed to a vertical wall as shown in the accompanying sketch. The temperature of the wall is maintained at 93C. The developed length of the rod is 0.6 m, and it is exposed to air at 38C. The combined radiation and convection heat transfer coefficient for this system is 34W/m2K. (a) Calculate the temperature of the midpoint of the rod. (b) What will the rate of heat transfer from the rod be?

Consider a 0.6 m X 0.6 m epoxy laminate (k = 0.2 W/m-k) whose thickness is 5 mm. In order to reduce the thermal resistance across the thickness, cylindrical copper fillings (k = 380 W/m-k) of 2 mm diameter are evenly implanted in throughout the laminate with a spacing of 6 mm (center to center) between the fillings.  a) Determine the thermal resistance of the laminate with and without the copper fillings. b) Assuming the temperature difference across the laminate is 20°C, calculate the total heat transfer rates with and without the fillings.

A 1.0-mm-diameter wire is maintained at a temperature of 400°C and exposed to aconvection environment at 40·C with h=120 W/㎡2.C. Calculate the thermal conductivitythat will just cause an insulation thickness of 0.2 mm to produce a “critical radius."How much of this insulation must be added to reduce the heat transfer by 75 percent from thatwhich would be experienced by the bare wire?

A heat-conducting rod, that is wrapped in insulation, is constructed with a 0.15-m length of alloy A and a 0.40-m length of alloy B, joined end-to-end. Both pieces have a cross-sectional area of 0.0020 m2. The thermal conductivity of alloy B is known to be 1.8 times as great as that of alloy A. The end of the rod in alloy A is maintained at a temperature of 10 degrees Celcius, and the other end of the rod is maintained at an unknown temperature. When the steady-state flow has been established, the temperature at the junction of the alloys is measured to be 40 degrees Celcius, and the rate of heat flow in the rod is measured at 56 W. What is the temperature of the end of the rod in alloy B.

A brick wall, plastered on one face, has a thermal conductance of 0.36 m2 K/W, an inside surface resistance of 0.4 m2K/W, and an outside surface resistance of 0.075 m2K/W. Calculate the total heat resistance.

You are designing a PCB laid horizontally on the ground.  The PCB surface temperature can’t exceed 85℃ and has a size of 96mm x 90mm. Tinfinity = 45oC.  "p" is the perimeter of the plate a) Calculate the Rayleigh number. b) If the PCB is laid hot-side UP, what is the Nusselt number and heat transfer coefficient? c) If the PCB is laid hot-side DOWN, what is the Nusselt number and heat transfer coefficient? d) Given your results from b and c, which one has better heat transfer?  In that case, what is the maximum power dissipation the board can put out? Properties of Air:k = 0.025 W/mkPr = 0.72v = 1.847 x 10−5u = 16.84 x10−6p = 1.2 kg/m3B =1/ Tf (idwal gass)

Example 3: The thermal contact conductance hc at the interface is 11,000 W/m2·°C. Determine the thickness of the aluminum plate whose thermal resistance is equal to the thermal resistance of the interface between the plates. (kaluminum=237 W/m.K

Question 1: A glass window of width W = 1 m and height H = 2m is 5 mm thick and has a thermal conductivity of kg =1.4 W/m.K. If the inner and outer surface temperatures of the glass are 15 °C and -20 C, respectively, on a cold winter day, what is the rate of heat loss through the glass? To reduce heat loss through windows, it is customary to use a double pane construction in which adjoining panes are separated by an air space. If the spacing is 10 mm and the glass surfaces in contact with the air have temperatures of (last two digit of your Registration number) °C and -15 °C, what is the rate of heat loss from a 1 mx2mwindow? The thermal conductivity of air is ka = 0.024 W/m.K.