Mechanical Engineering Answers

A horizontal metal plate which is completely insulated except for one exposed surface of 100 sq. ft. is heated electrically to maintain a temperature of 200 °F on the exposed surface. Heat is transferred from this surface by both radiation and conduction through air (assumed to be without motion) to a second plate of similar size maintained at a surface temperature of 100 °F. The distance between the parallel plates is 0.25-in., and each plate has an imissivity of 0.20. What is the watts input to the warmer plate?

Determine net radiant-heat exchange between the closed ends of a hollow cylinder 12-in. in diameter and 4-in. long. The ends are of Cr-Ni alloy with one end heated electrically to a temperature of 1900 °F and the other end maintained at 125 °F. The side wall of the cylinder is substantially nonconducting and reradiating.

A 6-in bare oxidized steel pipe (6.625 in O.D) carries steam at a temperature of 540°F and is loacted in a large room having wall temperatures of 80 °F. Determine the net radiant-heat exchange in BTU/(hr)(ft) between the pipe and the room, (a) if the surface temperature of the pipe is assumed to be the same as the steam temperature; (b) if the pipe is covered with a single layer of asbestos paper and the temperature of the outer surface of the paper is 530 °F; (c) if the asbestos paper painted with aluminum paint containing 26 percent aluminum and the surface temperature is 530 °F.

A steam radiator with enveloping radiating surface 60-in long by 26-in high by 12-in deep is supported above the floor of a large room. If the radiator surface, painted with lacquer containing 10 percent aluminum, is at a temperature of 200 °F and the room surfaces are at 70 °F, what is the rate of radiant-heat exchange between the radiator and the surfaces of the room?

Determine the net radiant-heat exchange between two parallel oxidized iron plates when the distance between them is 2 ft. and each plate measures 10 by 10 ft. The surface of one is at 200 °F and the other is at `100°F.

A 12-by-12 inches ingot iron casting 60-in high is stripped from its mold while its temperature is 1740 °F. If it stands on end on the floor of a large foundry having wall, floor, and roof temperatures of 80°F, what is the rate of radiant-heat exchange between the casting and the roof wall, and floor surfaces?

Heat radiates from a small sphere suspended in a large room. The surface of the sphere of 1.5 sq. Ft. is at a temperature of 580 °F, and the inside surfaces of the room are at a temperature of 80 °F. Assuming the emissivity of the sphere surface to be 0.30, calculate the radian-heat transfer in BTU/hr.

Two parallel rectangular surfaces 1m x 2m are opposite to each other at a distance of 4 m. The surfaces are black and at 100 °C and 200 °C, respectively. Calculate the heat exchange by radiation between the two surfaces.