12-41 Consider a circular grill whose diameter is 0.3 m. The bottom of the grill is covered with hot coal bricks at 1100 K, while the wire mesh on top of the grill is covered with steaks initially at 5°C. The distance between the coal bricks and the steaks is 0.20 m. Treating both the steaks and the coal bricks as blackbodies, determine the initial rate of radiation heat transfer from the coal bricks to the steaks. Also, determine the initial rate of radiation heat transfer to the steaks if the side opening of the grill is covered by aluminum foil, which can be approx-

12-41 Consider a circular grill whose diameter is 0.3 m. The bottom of the grill is covered with hot coal bricks at 1100 K, while the wire mesh on top of the grill is covered with steaks initially at 5°C. The distance between the coal bricks and the steaks is 0.20 m. Treating both the steaks and the coal bricks as blackbodies, determine the initial rate of radiation heat transfer from the coal bricks to the steaks. Also, determine the initial rate of radiation heat transfer to the steaks if the side opening of the grill is covered by aluminum foil, which can be approx-

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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A furnace is located next to a dense array of cryogenic fluid piping. The ice-covered piping approximates a plane surface with an average temperature of Tp = 0°C and a total, hemispherical emissivity of εp = 0.56. That is, the piping can be replaced by a flat surface with the given properties. The furnace wall has a temperature of Tf = 247°C and a total, hemispherical emissivity of εf = 0.86. To minimize the heat loading on the regirgeration equipment and piping, a reflective aluminum radiation shield with a total, hemispherical emissivity of εs = 0.13 on each of its sides is installed between the pipiing and the furnace wall as shown. Assume that all surfaces are diffuse and gray and treat the problem as one-dimensional (surfaces form infinite parallel plates). What is the heat load on on the refrigeration unit? That is, what is the net radiative power at the surface which approximates the dense array of ice-cold piping, qrad,p in Watts?
A surface gains 500 W/m2 heat at an equilibrium temperature of 30 °C and it is subjected to a simultaneous heat loss to environment by convection and to surroundings by radiation. The convection conditions are 10 °C and 20 W/m2 K. If the surface assumed to be black what should be the surrounding temperature to sustain this physical condition?
2_5190874259647370... A cylindrical shape is with diameter of 1.2m and length of 1.2m. The top surface has an emissivity of 0.7 and temperature 500 K. The bottom surface has an emissivity of o.5 and temperature 650 K. The side surface has an emissivity of 0.4. Determine the shape factors for all surfaces. E 0.0 L=650 K II >
Could you give me some explanation, the correct answer is at the bottom of the question.
A furnace is located next to a dense array of cryogenic fluid piping. The ice-covered piping approximates a plane surface with an average temperature of Tp = 0°C and a total, hemispherical emissivity of εp = 0.56. That is, the piping can be replaced by a flat surface with the given properties. The furnace wall has a temperature of Tf = 247°C and a total, hemispherical emissivity of εf = 0.86. To minimize the heat loading on the regirgeration equipment and piping, a reflective aluminum radiation shield with a total, hemispherical emissivity of εs = 0.13 on each of its sides is installed between the pipiing and the furnace wall as shown. Assume that all surfaces are diffuse and gray and treat the problem as one-dimensional (surfaces form infinite parallel plates). What is the heat load on on the refrigeration unit? That is, what is the net radiative power at the surface which approximates the dense array of ice-cold piping, qrad,p in Watts?
13-37 A row of tubes, equally spaced at a distance that is twice the diameter of the tubes, is positioned between two large parallel plates. The surface temperature of the tubes is constant at 10°C and the top and bottom plates are at constant temperatures of 100°C and 350°C, respectively. If the surfaces behave as blackbodies, determine the net radiation heat flux leaving the bottom plate. FIGURE P13–37 T3= 100°C T2 = 10°C T = 350°C
A 30 x 30 cm door in a brick kiln is at a distance of 3.5 m from a wall 12 m wide and 5 m high. The door is so located that a normal from the center of the door strikes the wall midway from the ends and 1.5 m above the floor. The opening into the kiln may be considered a black body; the wall is painted flat paint (Ɛ = 0.46). The temperature inside the kiln is 1 400 C and the wall temperature is 60 C. Determine (a) the configuration factor F12 and (b) the net radiant heat exchange between the opening and the wall when the fire door is open?
A furnace is located next to a dense array of cryogenic fluid piping. The ice-covered piping approximates a plane surface with an average temperature of Tp = 0°C and a total, hemispherical emissivity of εp = 0.53. That is, the piping can be replaced by a flat surface with the given properties. The furnace wall has a temperature of Tf = 206°C and a total, hemispherical emissivity of εf = 0.83. To minimize the heat loading on the regirgeration equipment and piping, a reflective aluminum radiation shield with a total, hemispherical emissivity of εs = 0.14 on each of its sides is installed between the pipiing and the furnace wall as shown. Assume that all surfaces are diffuse and gray and treat the problem as one-dimensional (surfaces form infinite parallel plates). What is the heat load on on the refrigeration unit? That is, what is the net radiative power at the surface which approximates the dense array of ice-cold piping, qrad,p in Watts?
Consider a 20-cm-diameter spherical ball at 800 K suspended in air as shown in Fig. 12-12. Assuming the ball closely approximates a blackbody, determine (a) the total blackbody emissive power, (b) the total amount of radiation emit- ted by the ball in 5 min, and (c) the spectral blackbody emissive power at a wavelength of 3 µ.m.
A concentric cylinder with outer and inner radii of 8 cm and 6 cm, respectively, has length of 1 mwith emissivities of the inner and outer radii at 0.4 and 0.6, respectively. Determine the heattransfer from the outer cylinder to the inner cylinder if the inner and outer temperatures are400K and 600K, respectively.
On a clear night, when the effective blackbody temperature of the space is - 30°C, the air contains water vapor at a partial pressure equal to that of ice or liquid water at 0°C. A very thin film of water, initially at 20°C, is placed in a very shallow well-insulated pan, placed in a spot sheltered from the wind with a full view of the sky. If hc = 2.6 W/m². °C, state whether ice will form, supporting the conclusion with suitable calculations.
A furnace has the shape of a cylinder and has R = H = 2m as its dimensions. The temperatures on the base, top, and side surfaces of the furnace are kept constant at 500, 700, and 1200 K accordingly. All three surfaces are black. Determine the net rate of radiation heat transfer from or to the top surface when the system is operating at a steady state.