sider a shed with an 8-ftx12-ft base and 4-ft height. The temperature of the outer surface of th and the walls of the shed is to be maintained at least 20°C on a quiescent night when outsi perature is 0°C and sky temperature is -15°C. What is the rate of total heat loss from the building? Ignore the heat transfer through the ground. Assume the emissivity

sider a shed with an 8-ftx12-ft base and 4-ft height. The temperature of the outer surface of th and the walls of the shed is to be maintained at least 20°C on a quiescent night when outsi perature is 0°C and sky temperature is -15°C. What is the rate of total heat loss from the building? Ignore the heat transfer through the ground. Assume the emissivity

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.

Chapter8: Natural Convection

Section: Chapter Questions

Problem 8.7P

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Three thin sheets of polished aluminum are placed parallel to each other so that the distance between them is very small compared to the size of the sheets. If one of the outer sheets is at 280C and the other outer sheet is at 60C, calculate the temperature of the intermediate sheet and the net rate of heat flow by radiation. Convection can be ignored.
A 1.2 m wide and 5.1 m long solar collector is mounted to a roof. Now the average surface temperature of the solar collector is measured to be 50 oC. The effective surrounding sky temperature is 8 oC. If the emissivity of the collector is 0.88, determine the rate of heat transfer from the collector to the surroundings due to radiation.
An astronaut performing an extra-vehicular activity(space walk) shaded from the Sun is wearing a spacesuitthat can be approximated as perfectly white (e = 0) exceptfor a 5 cm × 8 cm patch in the form of the astronaut’snational flag. The patch has emissivity 0.300. The spacesuitunder the patch is 0.500 cm thick, with a thermalconductivity k = 0.0600 W/m °C , and its inner surface isat a temperature of 20.0 °C . What is the temperature of thepatch, and what is the rate of heat loss through it? Assumethe patch is so thin that its outer surface is at the sametemperature as the outer surface of the spacesuit under it.Also assume the temperature of outer space is 0 K. You willget an equation that is very hard to solve in closed form,so you can solve it numerically with a graphing calculator,with software, or even by trial and error with a calculator.
A 2-m-internal-diameter double-walled spherical tank is used to store iced water at 0°C. Each wall is 0.5 cm thick, and the 1.5-cm-thick air space between the two walls of the tank is evacuated in order to minimize heat transfer. The surfaces surrounding the evacuated space are polished so that each surface has an emissivity of 0.15. The temperature of the outer wall of the tank is measured to be 20°C. Assuming the inner wall of the steel tank to be at 0°C, determine (a) the rate of heat transfer to the iced water in the tank and (b) the amount of ice at 0°C that melts during a 24-h period.
Determine the heat flow between the roof and floor of 4 × 3 m size of a furnace of 4 m × 4 m × 3m size when the roof is at 1200 K and the floor is maintained at 600 K, with the other surfaces non-absorbing and reradiating. The surface emissivity of the hotter surface is 0.8 and that of the cooler surface 0.6.
Air is flowing between two infinitely large parallel plates. The upper plate is at 500 K and has an emissivity of 0.7, while the lower plate is a black surface with temperature at 330 K. If the air temperature is 290 K, determine the convection heat transfer coefficient associated with the air.
A hot liquid is filled in a spherical tank with an inner diameter of 3 m and a wall thickness of 3 cm. The tank wall is made of a material with a thermal conductivity of 0.15 W/m∙K.The hot liquid in the tank causes the inner surface temperature to be 100°C, while the tank outer surface is exposed to air at 20°C and has an emissivity of 0.35. Determine the outer surface temperature of the tank. Assume that the properties of air can be evaluated at 40°C and 1 atm pressure. Is this a good assumption?
A group of 25 power transistors, dissipating 1.5 W each, are to be cooled by attaching them to a black-anodized square aluminum plate and mounting the plate on the wall of a room at 30°C. The emissivity of the transistor and the plate surfaces is 0.9. Assuming the heat transfer from the back side of the plate to be negligible and the temperature of the surrounding surfaces to be the same as the air temperature of the room, determine the size of the plate if the average surface temperature of the plate is not to exceed 50°C.
Two concentric spheres of diameters D1 = 15 cm and D2 = 25 cm are separated by air at 1 atm pressure. The surface temperatures of the two spheres enclosing the air are T1 = 350 K and T2 = 275 K, respectively, and their emissivities are 0.75. Determine the rate of heat transfer from the inner sphere to the outer sphere by (a) natural convection and (b) radiation.
A 2-m-diameter thin-walled stainless steel spherical tank is filled with chemicals undergoing a reaction. The reaction releases heat through the tank, where the tank outer surface temperature is 50°C and is exposed to air at 20°C. The stainless steel surface of the tank has an emissivity of 0.35. Determine the rate of heat release from the chemical reaction inside the tank. Is the given emissivity value reasonable for a stainless steel surface? What is the contribution of natural convection to the overall rate of heat loss at the tank surface?
A sphere has a radius of 0.100 m. Its surface can be treated as a greysurface with emissivity 0.20 and a uniform temperature of 19 degrees C. It isplaced in a room where the room surfaces are at an averagetemperature of 18 degrees C. The air in the room is at 20 degrees C. Determine the totalheat transfer rate to/from the sphere if its convective heat transfercoefficient is 3.0 W/m^2K. (The surface area of a sphere is 4πr^2.) The answer is 0.236W Equations to help: Heat Transfer by convection: Q = Ahc(Tf-Ts) Heat Transfer by radiation: Q = Aεσ(T^4(1)-T^4(2))
According to an Atomic Energy Commissionreport, a hydrogen bomb can be approximated as a large fireball at a temperature of 7200 K. You are to assess theimpact if such a bomb exploded 5 km above a city. Assumethe diameter of the fireball to be 1 km, and the blast to last15 s. Investigate the level of radiation energy people, plants,and houses will be exposed to and how adversely they will beaffected by the blast.