A long cylindrical power cable is shielded with polyethylene insulation. The power cable is placed in parallel with a long cylindrical metal rod that is maintained at a temperature of 150°C. Both the power cable and the metal rod have the same diameter of 1 cm, and they are inside a blackbody surrounding at 27°C. Their distance apart from each other, measured from their centers, is 20 cm. The emissivity values for the metal rod and the polyethylene insulation are 0.33 and 0.95, respectively. According to the ASTM D1351-14 standard specification, the polyethylene insulation is suitable for operation at temperatures up to 75°C. If the radiation heat transfer per unit area from the metal rod is 445 W/m², determine the surface temperature of the cable and check whether the polyethylene insulation for the power cable would comply with the ASTM D1351-14 standard specification. The surface temperature of the cable is 127.11 > °C. No →, the polyethylene insulation for the power cable will not comply with the ASTM D1351-14 standard specification.

A long cylindrical power cable is shielded with polyethylene insulation. The power cable is placed in parallel with a long cylindrical metal rod that is maintained at a temperature of 150°C. Both the power cable and the metal rod have the same diameter of 1 cm, and they are inside a blackbody surrounding at 27°C. Their distance apart from each other, measured from their centers, is 20 cm. The emissivity values for the metal rod and the polyethylene insulation are 0.33 and 0.95, respectively. According to the ASTM D1351-14 standard specification, the polyethylene insulation is suitable for operation at temperatures up to 75°C. If the radiation heat transfer per unit area from the metal rod is 445 W/m², determine the surface temperature of the cable and check whether the polyethylene insulation for the power cable would comply with the ASTM D1351-14 standard specification. The surface temperature of the cable is 127.11 > °C. No →, the polyethylene insulation for the power cable will not comply with the ASTM D1351-14 standard specification.

Principles of Heat Transfer (Activate Learning with these NEW titles from Engineering!)

8th Edition

ISBN:9781305387102

Author:Kreith, Frank; Manglik, Raj M.

Publisher:Kreith, Frank; Manglik, Raj M.

Chapter11: Heat Transfer By Radiation

Section: Chapter Questions

Problem 11.64P

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Similar questions

11.31 A large slab of steel 0.1 m thick contains a 0.1 -m-di- ameter circular hole whose axis is normal to the surface. Considering the sides of the hole to be black, specify the rate of radiative heat loss from the hole. The plate is at 811 K, and the surroundings are at 300 K.
Two large parallel plates with surface conditions approximating those of a blackbody are maintained at 816C and 260C, respectively. Determine the rate of heat transfer by radiation between the plates in W/m2 and the radiative heat transfer coefficient in W/m2K.
Determine the total average hemispherical emissivity and the emissive power of a surface that has a spectral hemispherical emissivity of 0.8 at wavelengths less than 1.5m, 0.6 at wavelengths from 1.5to2.5m, and 0.4 at wavelengths longer than 2.5m. The surface temperature is 1111 K.
1.28 The sun has a radius of and approximates a blackbody with a surface temperature of about 5800 K. Calculate the total rate of radiation from the sun and the emitted radiation flux per square meter of surface area.
11.68 Two infinitely large, black, plane surfaces are 0.3 m apart, and the space between them is filled by an isothermal gas mixture at 811 K and atmospheric pressure. The gas mixture consists of by volume. If one of the surfaces is maintained at 278 K and the other at 1390 K, calculate (a) the effective emissivity of the gas at its temperature, (b) the effective absorptivity of the gas to radiation from the 1390 K surface, (c) the effective absorptivity of the gas to radiation from the 278 K surface, and (d) the net rate of heat transfer to the gas per square meter of surface area.
Determine the rate of radiant heat emission in watts per square meter from a blackbody at (a) 15C, (b) 600C, and (c) 5700C.
11.41 Determine the steady-state temperatures of two radiation shields placed in the evacuated space between two infinite planes at temperatures of 555 K and 278 K. The emissivity of all surfaces is 0.8.
The human skin is “selective” when it comes to theabsorption of the solar radiation that strikes it perpendicularly.The skin absorbs only 50 percent of the incident radiationwith wavelengths between l1 = 0.517 mm and l2 =1.552 mm. The radiation with wavelengths shorter than l1and longer than l2 is fully absorbed. The solar surface maybe modeled as a blackbody with effective surface temperatureof 5800 K. Calculate the fraction of the incident solar radiationthat is absorbed by the human skin.
Consider a 20-cm-diameter spherical ball at 800 K suspended in air. Assuming the ball closely approximates a blackbody, determine (a) the total blackbody emissive power, (b) the total amount of radiation emitted by the ball in 5 min, and (c) the spectral blackbody emissive power at a wavelength of 3 mm.
Daylight may be approximated as a blackbody at the effective surface temperature of 5800 K. Determinethe fraction of radiation emitted that falls in the UV (0.1 – 0.4 μm) and visible (0.4 – 0.76 μm) region.(Ans: 0.1245, 0.4243)
Two long parallel 20-cm-diameter cylinders are located 30 cm apart from each other. Both cylinders are black, and are maintained at temperatures 425 K and 275 K. Determine the rate of radiation heat transfer per unit area (in watts/m2) between the cylinders.