T.- 100 °C Vacuum T. = 20 °C Figure 1.17 Problem 1.12 Two walls facing each other are thin, very large in extent, highly conducting, and radiatively black on the facing surfaces (Fig. 1.17). They are separated by a vacuum. The outsides of the plates experi- ence convection (without radiation) as shown. Set up an equation for the temperature of the left-hand plate and solve it by iteration. Then find the temperature of the right-hand plate. [Tright = 42.5°C] 6-50 W/m²K h= 20 W/m²K

T.- 100 °C Vacuum T. = 20 °C Figure 1.17 Problem 1.12 Two walls facing each other are thin, very large in extent, highly conducting, and radiatively black on the facing surfaces (Fig. 1.17). They are separated by a vacuum. The outsides of the plates experi- ence convection (without radiation) as shown. Set up an equation for the temperature of the left-hand plate and solve it by iteration. Then find the temperature of the right-hand plate. [Tright = 42.5°C] 6-50 W/m²K h= 20 W/m²K

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 8.30P

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A long wire 0.7 mm in diameter with an emissivity of 0.9 is placed in a large quiescent air space at 270 K. If the wire is at 800 K, calculate the net rate of heat loss. Discuss your assumptions.
1.25 A spherical vessel, 0.3 m in diameter, is located in a large room whose walls are at 27°C (see sketch). If the vessel is used to store liquid oxygen at –183°C and both the surface of the storage vessel and the walls of the room are black, calculate the rate of heat transfer by radiation to the liquid oxygen in watts and in Btu/h.
1.26 Repeat Problem 1.25 but assume that the surface of the storage vessel has an absorbance (equal to the emittance) of 0.1. Then determine the rate of evaporation of the liquid oxygen in kilograms per second and pounds per hour, assuming that convection can be neglected. The heat of vaporization of oxygen at –183°C is .
1.11 Calculate the heat loss through a glass window 7-mm thick if the inner surface temperature is 20°C and the outer surface temperature is 17°C. Comment on the possible effect of radiation on your answer.
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.
An infrared camera is used to measure a temperature at a tissue location. The infrared camera uses the same equation as that in the lecture notes. When the total hemispherical emissivity is selected as &=1.0, the temperature reading on the camera is 45°C. (a) Based on the equation given in the notes, please calculate the radiation heat flux received by the camera qck. The Stefan-Boltzmann's constant ois 5.67*108 W/(m²K¹). (b) However, you notice that the actual emissivity of the tissue surface should be 0.95. The room temperature is 20°C. Use the equation again to calculate the temperature of the tissue location, note that qck should be the same as in (a). What is the absolute error of the measurement if both the room temperature and deviation from a perfect blackbody surface are not considered?
A small sphere (emissivity =0.503 radius=r1) is located at the center of a spherical abestos shell ( thickness =1.74 cm, outer radius= r2; thermal conductivity of abestos is 0.090 J/ (sm c degrees) The thickness of the shell is small compared to the inner and outer radii of the shell. The temperature of the small sphere is 695 degrees Celsius while the temperature of the inner surface of the shell is 352 degrees Celsius, both temperatures remaining constant. Assuming that r2/r1 =8.75 and ignoring any air inside the shell, find the temperature in degrees Celsius of the outer surface of the shell.
SUPPOSE THE AMBIENT TEMPERATURE IS 20degrees CELSIUS, AND THE HOT RESERVOIR CONSISTS OF A SPHERICAL TANK WITH A RADIUS OF 4.00 m, THAT ACTS AS AN IDEAL EMITTER OF RADIATION. IF ALL THE RADIANT ENERGY EMITTED BY THE TANK COULD BE CAPTURED, WHAT IS THE AVERAGE AMOUNT OF WORK THAT COULD BE DONE EACH SECOND? ( please only answer if your 100% correct) (show work)
The basal metabolic rate isthe rate at which energy is produced in the body when a person is at rest.A 75 kg (165 lb) person of height 1.83 m (6 ft) has a body surface areaof approximately 2.0 m2. (a) What is the net amount of heat this personcould radiate per second into a room at 18°C (about 65°F) if his skin’ssurface temperature is 30°C? (At such temperatures, nearly all the heatis infrared radiation, for which the body’s emissivity is 1.0, regardless ofthe amount of pigment.) (b) Normally, 80% of the energy produced bymetabolism goes into heat, while the rest goes into things like pumpingblood and repairing cells. Also normally, a person at rest can get rid ofthis excess heat just through radiation. Use your answer to part (a) to findthis person’s basal metabolic rate.
Liquefied natural gas (LNG) is transported around the globe using ships similar to thatshown in Figure QA3. This ship has four pressurised cylindrical steel tanks each ofradius of 20 m. The tanks are internally insulated with 30 cm of polyurethane foamwhich keeps the LNG at a constant -162 ºC. Take the effective sky temperature is 265K and the net radiative thermal energy exchange with the sky as 1x106 W. Calculate the surface temperature of the end (facing the sun) of a tank. Calculate the conductive heat transfer through the end (facing the sun)of a tank.
Liquefied natural gas (LNG) is transported around the globe using ships similar to thatshown in Figure QA3. This ship has four pressurised cylindrical steel tanks each ofradius of 20 m. The tanks are internally insulated with 30 cm of polyurethane foamwhich keeps the LNG at a constant -162 ºC. Take the effective sky temperature is 265K and the net radiative thermal energy exchange with the sky as 1x10^6 W. (a) Calculate the surface temperature of the end (facing the sun) of a tank.(b) Calculate the conductive heat transfer through the end (facing the sun)of a tank. answers: a) 375K b) 22.1kW
Liquefied natural gas (LNG) is transported around the globe using ships similar to thatshown in Figure QA3. This ship has four pressurised cylindrical steel tanks each ofradius of 20 m. The tanks are internally insulated with 30 cm of polyurethane foamwhich keeps the LNG at a constant -162 ºC. Take the effective sky temperature is 265K and the net radiative thermal energy exchange with the sky as 1x10^6 W. (a) Calculate the surface temperature of the end (facing the sun) of a tank.(b) Calculate the conductive heat transfer through the end (facing the sun)of a tank. DATA FOR QUESTION: Thermal conductivity, polyurethane foam = 0.02 W/mKStefan’s Constant = 5.67x10^-8 W/m^2K^4Emissivity, steel = 0.95 answers: a) 375K b) 22.1kW