**33. ssm A solid cylinder is radiating power. It has a length that is ten timesits radius. It is cut into a number of smaller cylinders, each of which has thesame length. Each small cylinder has the same temperature as the originalcylinder. The total radiant power emitted by the pieces is twice that emittedby the original cylinder. How many smaller cylinders are there?

Given data: The radius of cylinder is, r. The length of the cylinder is, l = 10r. The initial…

Answered: **33. ssm A solid cylinder is radiating…

Elements Of Electromagnetics

7th Edition

ISBN:9780190698614

Author:Sadiku, Matthew N. O.

Publisher:Sadiku, Matthew N. O.

ChapterMA: Math Assessment

Section: Chapter Questions

Problem 1.1MA

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Earth absorbs solar energy and radiates infrared energy. The intensity of the solar radiation incident on earth is J = 1350 Wm-2, also known as the solar constant. Assume earth’s surface (ground) temperature to be uniform at Ts, and that the ground and atmosphere are black (emissivity = 1) for infrared radiation. The radius of the earth is 6.378 x 106 m. The diagram shows the ground at the surface temperature Ts and the atmosphere, represented as a thin black layer, at temperature Ta . Suppose the atmosphere absorbs 100% of the infrared radiation emitted by the ground. Assume that the ground absorbs 47.5% of the incident solar energy, and that the atmosphere absorbs 17.5% of the incident solar energy (for a total of 65% absorbed by the planet). Calculate the "steady state” numerical values of the earth’s ground temperature Ts and the atmospheric temperature Ta taking into account the “greenhouse effect” of atmospheric infrared absorption and emission described above.
A quartz radiant heater has two cylindrical tubes 40 cm long and 1 cm radius. The heater is designed to produce 1300 watts of radiant power. What would be the temperature of the tubes if the emissivity of the tubes is 0.60. a. 570 K b. 934 K c. 980 K d. 1068 K
1. A glass window allows 95% of radiant energy between 0.32 < 1 < 2.6 microns to pass. Any wavelength outside of this range will not pass through the glass. Compute the energy rate passed through the glass window if the incident energy rate on the glass is 1200 W/m^2. 0.9 0.4 E0-a ot 0.4 0.2 0.1 15,000 AT(Micron-Rankine) S000 10,000 20.000 25,000 30,000 33,000 00 1.0 2.0 3.0 4.0 5.0 6.0 7.0 Amax Ans. 1026 W/m^2
Molten metal at 2000 C is poured using crucible. The liquid metal jet has a diameter of 3 mm with an insulation shield of 5 cm diameter. There is a slit of 30 degrees around the insulation shield. The temperature inside the room is 30 C and the shield is 700 C. Assuming black bodies, find the net heat transfer between jet and shield, jet and room, shield and the room. One of the steps is wrong A) Resistance network is required to be built B) To find the view factor between metal and shield , ratio of the angles is used C) View factors are one of the most important steps to solve the problem D) None of the above E) Slit doesnot participate in radiation
a. What does it mean when we say that a surface 'sees itself' in the context of radiative heat transfer? b. If heat transfer by conduction through a medium occurs under steady- state, will the temperature at a particular location vary with time? Will the temperature vary with location in the medium?
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:…
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A long, horizontal, cylindrical steel reactor, 1 m in diameter, has a surface temperature of 300ºC. The emissivity of the steel is 0.6, and the heat transfer coefficient for natural convection is 5 W m−2 K−1 . Heat is lost by convection to the air at 15ºC, and also by radiation to the surroundings, which can be considered to be a black body at 15ºC. a) Calculate the total heat loss per metre length of the reactor, and the proportions lost by convection and radiation b) The reactor is then insulated with a thin layer of insulation material to reduce the total heat loss to one-tenth of its original value. This causes the surface temperature of the steel to rise to 400ºC. The thermal conductivity of the insulation is 0.01 W m−1 K−1 , and its surface emissivity is 0.2. Show that the resulting surface temperature of the insulation is about 89ºC, and calculate the thickness of insulation required, stating any assumptions made. Specifically need help with part b
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4. The surface temperature of a planet is T, and the measured temperature is Tm (i.e. the temper- ature measured at the top-of-atmosphere based on the upwards flux Ft there). Assume radiative equilibrium. (a) Show that the infrared optical depth of the planet's surface 7 is related to the surface temperature T, and the measured temperature Tm by Calculate the infrared optical depth at the surfaces of (a) Earth, where T, = 300 K and Tm = 250 K. (b) Venus, where T, = 750 K and Tm = 230 K. (c) Mars, where T, = 240 K and T, = 220 K.
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.)
A pipe still uses 7110 lb per hour of a cracked gas (Net Heating Value (NHV) 20560 Btu per lb). The radiant section contains 1500 sq ft of projected area, and the tube (5 in. outside diameter) are spaced at a center-to-center distance of 10 in. there is only one row of radiant tubes, and they are 40 ft long. The ratio of air to fuel is (21 (30 percent excess air). a) What percentage of the heat liberation is absorbed in the radiant section? b) How many Btu are absorbed per hour through each square foot of projected area?

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