Determine the equilibrium temperature of the absorber surface in Pro

Determine the equilibrium temperature of the absorber surface in Prob. 1298 if the back side of the absorber is insulated. Problem. 1298 The absorber surface of a solar collector is made of aluminum coated with black chrome (as = 0.87 and = 0.09). Solar radiation is incident on the surface at a rate of 600 W/m2 . The air and the effective sky temperatures are 25C and 15C respectively and the convection heat transfer coefficient is 10 W/m2K. For an absorber surface temperature of 70C determine the net rate of solar energy delivered by the absorber plate to the water circulating behind it. The absorber surface of a solar collector is made of aluminum coated with black chrome (as = 0.87 and = 0.09). Solar radiation is incident on the surface at a rate of 600 W/m2 . The air and the effective sky temperatures are 25C and 15C respectively and the convection heat transfer coefficient is 10 W/m2K. For an absorber surface temperature of 70C determine the net rate of solar energy delivered by the absorber plate to the water circulating behind it.

Reconsider Prob. 1298. Using EES (or other) software plot the net r

Reconsider Prob. 1298. Using EES (or other) software plot the net rate of solar energy transferred to water as a function of the absorptivity of the absorber plate. Let the absorptivity vary from 0.5 to 1.0 and discuss the results. Problem. 1298 The absorber surface of a solar collector is made of aluminum coated with black chrome (as = 0.87 and = 0.09). Solar radiation is incident on the surface at a rate of 600 W/m2 . The air and the effective sky temperatures are 25C and 15C respectively and the convection heat transfer coefficient is 10 W/m2K. For an absorber surface temperature of 70C determine the net rate of solar energy delivered by the absorber plate to the water circulating behind it.

A typical winter day in Reno Nevada (39 N latitude) is cold but su

A typical winter day in Reno Nevada (39 N latitude) is cold but sunny and thus the solar heat gain through the windows can be more than the heat loss through them during daytime. Consider a house with double-door-type windows that are double paned with 3-mm-thick glasses and 6.4 mm of air space and have aluminum frames and spacers. The house is maintained at 22C at all times. Determine if the house is losing more or less heat than it is gaining from the sun through an east window on a typical day in January for a 24-h period if the average outdoor temperature is 10C.

Repeat Prob. 12108 for a south window. Problem 12108 A typical winte

Repeat Prob. 12108 for a south window. Problem 12108 A typical winter day in Reno Nevada (39 N latitude) is cold but sunny and thus the solar heat gain through the windows can be more than the heat loss through them during daytime. Consider a house with double-door-type windows that are double paned with 3-mm-thick glasses and 6.4 mm of air space and have aluminum frames and spacers. The house is maintained at 22C at all times. Determine if the house is losing more or less heat than it is gaining from the sun through an east window on a typical day in January for a 24-h period if the average outdoor temperature is 10C.

A manufacturing facility located at 32 N latitude has a glazing area

A manufacturing facility located at 32 N latitude has a glazing area of 60 m2 facing west that consists of double-pane windows made of clear glass (SHGC = 0.766). To reduce the solar heat gain in summer a reflective film that will reduce the SHGC to 0.35 is considered. The cooling season consists of June July August and September and the heating season October through April. The average daily solar heat fluxes incident on the west side at this latitude are 2.35 3.03 3.62 4.00 4.20 4.24 4.16 3.93 3.48 2.94 2.33 and 2.07 kWh/daym2 for January through December respectively. Also the unit costs of electricity and natural gas are $0.09/kWh and $0.45/therm respectively. If the coefficient of performance of the cooling system is 3.2 and the efficiency of the furnace is 0.90 determine the net annual cost savings due to installing reflective coating on the windows. Also determine the simple payback period if the installation cost of reflective film is $20/m2 .

Solar radiation is incident on the front surface of a thin plate wit

Solar radiation is incident on the front surface of a thin plate with direct and diffuse components of 300 and 250 W/m2 respectively. The direct radiation makes a 30 angle with the normal of the surface. The plate surfaces have a solar absorptivity of 0.63 and an emissivity of 0.93. The air temperature is 5C and the convection heat transfer coefficient is 20 W/m2 K. The effective sky temperature for the front surface is -33C while the surrounding surfaces are at 5C for the back surface. Determine the equilibrium temperature of the plate.

Reconsider Prob. 1334. Using the EES (or other) software evaluate t

Reconsider Prob. 1334. Using the EES (or other) software evaluate the effect of the distance L between the black coaxial parallel disks (D = 1 m) on the radiation heat transfer coefficient. By varying the distance L between the disks from 0.05 to 3 m plot the radiation heat transfer coefficient hrad as a function of the distance L between the disks. Problem. 1334 Consider two black coaxial parallel circular disks of equal diameter D that are spaced apart by a distance L. The top and bottom disks have uniform temperatures of 500C and 520C respectively. Determine the radiation heat transfer coefficient hrad between the disks if they are spaced apart by L = D.

Consider two rectangular surfaces perpendicular to each other with a

Consider two rectangular surfaces perpendicular to each other with a common edge which is 1.6 m long. The horizontal surface is 0.8 m wide and the vertical surface is 1.2 m high. The horizontal surface has an emissivity of 0.75 and is maintained at 400 K. The vertical surface is black and is maintained at 550 K. The back sides of the surfaces are insulated. The surrounding surfaces are at 290 K and can be considered to have an emissivity of 0.85. Determine the net rate of radiation heat transfers between the two surfaces and between the horizontal surface and the surroundings.

Reconsider Prob. 1353. Using EES (or other) software investigate th

Reconsider Prob. 1353. Using EES (or other) software investigate the effects of the rate of the heat transfer at the base surface and the temperature of the side surfaces on the temperature of the base surface. Let the rate of heat transfer vary from 500 W/m2 to 1000 W/m2 and the temperature from 300 K to 700 K. Plot the temperature of the base surface as functions of the rate of heat transfer and the temperature of the side surfaces and discuss the results. Problem. 1353 A furnace is shaped like a long equilateral-triangular duct where the width of each side is 2 m. Heat is supplied from the base surface whose emissivity is 1 = 0.8 at a rate of 800 W/m2 while the side surfaces whose emissivities are 0.5 are maintained at 500 K. Neglecting the end effects determine the temperature of the base surface. Can you treat this geometry as a two-surface enclosure?

This question deals with steadystate radiation heat transfer between

This question deals with steadystate radiation heat transfer between a sphere (r1 = 30 cm) and a circular disk (r2 = 120 cm) which are separated by a center-to-center distance h 5 60 cm. When the normal to the center of disk passes through the center of the sphere the radiation view factor is given by Surface temperatures of the sphere and the disk are 600C and 200C respectively; and their emissivities are 0.9 and 0.5 respectively. (a) Calculate the view factors F12 and F21. (b) Calculate the net rate of radiation heat exchange between the sphere and the disk. (c) For the given radii and temperatures of the sphere and the disk the following four possible modifications could increase the net rate of radiation heat exchange: paint each of the two surfaces to alter their emissivities adjust the distance between them and provide an (refractory) enclosure. Calculate the net rate of radiation heat exchange between the two bodies if the best values are selected for each of the above modifications.