13.21 Consider coaxial, parallel, black disks separated a dis-tance of 0.20 m. The lower disk of diameter 0.40 mis maintained at 500 K and the surroundings are at300 K. What temperature will the upper disk of diame-ter 0.20 m achieve if electrical power of 17.5 W issupplied to the heater on the back side of the disk?-Нeaterjo.20 m-0.20 m500 K-0.40 m-

Answered: Image /qna-images/answer/775b991d-b479-4b90-bf4a-edcfcca9a262.jpg

Answered: 13.21 Consider coaxial, parallel, black…

Elements Of Electromagnetics

7th Edition

ISBN:9780190698614

Author:Sadiku, Matthew N. O.

Publisher:Sadiku, Matthew N. O.

ChapterMA: Math Assessment

Section: Chapter Questions

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PROBLEM 4: A black thermocouple is inside a chamber with black walls. If the air around the thermocouple is at 20°C, the walls are at 100-C, and the heat transfer coefficient between the thermocouple and the air is 75 W/m²K, what temperature will the thermocouple read?
Consider a silicon wafer positioned in a furnace that is zone-heated on the top section and cooled on the lower section. The wafer is placed such that the top and bottom surfaces of the wafer exchange radiation with the hot and cold zones respectively of the furnace. The zone temperatures are Tsur,h = 1050 K and Tsur.e = 330 K. The emissivity and thickness of the wafer are e = 0.65 and d = 0.78 mm, respectively. With the ambient gas at T. = 700 K, convection heat transfer coefficients at the upper and lower surfaces of the wafer are 8 and 4 W/m²-K. Find the steady-state temperature of the wafer, in K. Tw i K
Determine the heat loss by radiation from an oven wall to the wall of a room to which the oven wall is directly facing. Assume that no heat flows through the adjacent walls, which are coated with a reradiating material. The oven wall is square, 4 ft on one side, and is 2 ft from the room wall and parallel to it. The oven wall is steel sheet and is at 400°F, and the wall is at 80°F and is of asbestos board.
A spherical satellite of 2m diameter circles the earth at an altitude of 600 miles. Assuming all surfaces are black, calculate the equilibrium temperature of the satellite on the 'dark' side and on the 'bright' side of the earth. Assume the earth has a radius of 4,000 miles and a temperature of 200C. The suns temperature can be taken to be 6,700K and it has a radius of 433,000 miles. The distance between the sun and the earth is 93,000,000 miles. View factor of a small sphere to a much larger one: S→L Where R = '2 ri is the radius of the large sphere and x is the separation distance between the spheres.
5. A horizontal uninsulated steam pipe passes through a large room whose wall and ambient air are at 300 K. The air in the room is quiescent. The pipe of 150-mm diameter has an emissivity of 0.85 and an outer surface temperature of 400 K. Calculate the heat loss per unit length from the pipe.
A manufacturing facility located at 32° N latitude has a glazing area of 60 m² facing west that consists of double pane windows made of clear glass (SHGC = 0.766). To reduce the solar heat gain in summer, a reflective film that will reduce the SHGC to 0.35 is considered. The cooling season consists of June, July, August, and September, and the heating season, October through April. The average daily solar heat fluxes incident on the west side at this latitude are 2.35, 3.03, 3.62, 4.00, 4.20, 4.24, 4.16, 3.93, 3.48, 2.94, 2.33, and 2.07 kWh/day · m² for January through December, respectively. Also, the unit costs of electricity and natural gas are $0.09/kWh and $0.45/therm., respectively. If the coefficient of performance of the cooling system is 3.2 and the efficiency of the furnace is 0.90, determine the net annual cost savings due to installing reflective coating on the windows. Also, determine the simple payback period if the installation cost of reflective film is $20/m². Answers:…
A long, thin-walled horizontal tube 10.0cm in diameter with an emissivity of 0.80 is maintained at 120.0°C by the passage of pressurized steam inside the tube. To reduce radiation heat transfer losses, a round, tubular radiation shield with an emissivity of 0.10 is installed surrounding the heated tube, with a gap of 1.00cm between the outside of the tube and the radiation shield. At steady-state operating conditions, the temperature of the radiation shield is measured to be 35.0°C. Calculate the total heat transfer rate per meter length assuming that the gap between the pipe and heat shield is now filled with air at a pressure of 1.00 atm.
3. A star has a surface temperature of 5,500K. Determine the radiative heat transfer received by planet Z in Petawatts with diameter of 2100 km, temperature of surface of 300K and mean absorptivity of 0.8. Radiative energy loss due to radiation dispersion on outer space is 99%.
2. A heater is a thin vertical panel 1.0m long and 0.7m high and is used in a warehouse to keep workers warm. The heater has air circulating on each side. Assume the maximum temperature of the panel is 60°C (already above the board line that is safe for human hands to touch briefly without getting hurt). Assume the room air temperature is 18°C but the warehouse wall temperature is 5°C. Model the surface with an emittance of 0.9 and Vair = 1.57x105 m²/s. a. Determine the maximum power rating for the heater. b. Now if you run the heat by standing on its side (it will be 1.0 m high and 0.7 m long), determine the surface temperature. c. Compare case a and b and explain any differences you see.
Compute the heat gain for a window facing southeast at 32° north latitude at 10 A.M. central daylight time on August 21. The window is regular double glass with a 13-mm air space. The glass and inside draperies have a combined shading coefficient of 0.45. The indoor design temperature is 25° C, and the outdoor tempera ture is 37°C. Window dimensions are 2 m wide and 1.5m high.
The tungsten filament of an incandescent light bulb has a temperature of approximately 3000 K. The emissivity of tungsten is approximately 1/3, and you may assume that it is independent of wavelength. To increase the efficiency of an incandescent bulb, would you want to raise or lower the temperature? (Some incandescent bulbs do attain slightly higher efficiency by using a different temperature.)
. Calculate the heat transfer rate per m² area by radiation between the surfaces of two long cylinders having radii 100 mm and 50 mm respectively. The smaller cylinder being in the larger cylinder. The axes of the cylinders are parallel to each other and separated by a distance of 20 mm. The surfaces of inner and outer cylinders are maintained at 127°C and 27°C respectively. The emissivity of both the surfaces is 0.5.

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