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Compute the ratio of the rate of heat loss through a single-pane window with area 0.15 m2 to that for a double-pane window with the same area. The glass of a single pane is 4.2 mm thick, and the air space between the two panes of the double-pane window is 7.0 mm thick. The glass has thermal
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- (a) The inside of a hollow cylinder is maintained at a temperature Ta, and the outside is at a lower temperature, Tb (Fig. P19.45). The wall of the cylinder has a thermal conductivity k. Ignoring end effects, show that the rate of energy conduction from the inner surface to the outer surface in the radial direction is dQdt=2Lk[TaTbln(b/a)] Suggestions: The temperature gradient is dT/dr. A radial energy current passes through a concentric cylinder of area 2rL. (b) The passenger section of a jet airliner is in the shape of a cylindrical tube with a length of 35.0 m and an inner radius of 2.50 m. Its walls are lined with an insulating material 6.00 cm in thickness and having a thermal conductivity of 4.00 105 cal/s cm C. A heater must maintain the interior temperature at 25.0C while the outside temperature is 35.0C. What power must be supplied to the heater? Figure P19.45arrow_forwardHot water at 85 Degrees Celsius is transferred inside a metal pipe with outer diameter 30mm. A circumferential fin with a rectangular profile is placed on the outer surface of the pipe for cooling. The fin is 80 mm in diameter and 8mm thick. If the heat convection coefficient of the environment outside the pipe = 20 W/m2.°C and the ambient temperature 22 Degree Celsius. Assume that the temperature of the outer surface of the pipe equals the hot water temperature. A. Determine the heat loss by the fin. B. Determine the fin effectiveness. (Thermal conductivity of the fin material 125 W/m.°C)arrow_forwardThe thermal conductivities of human tissues vary greatly. Fat and skin have conductivities of about 0.20 W/m · K and 0.020 W/m · K respectively, while other tissues inside the body have conductivities of about 0.50 W/m · K. Assume that between the core region of the body and the skin surface lies a skin layer of 1.0 mm, fat layer of 0.50 cm, and 3.2 cm of other tissues. (a) Find the R-factor for each of these layers, and the equivalent R-factor for all layers taken together, retaining two digits. Rskin m2 · K/W Rfat m2 · K/W Rtissue m2 · K/W R m2 · K/W (b) Find the rate of energy loss when the core temperature is 37°C and the exterior temperature is 0°C. Assume that both a protective layer of clothing and an insulating layer of unmoving air are absent, and a body area of 2.0 m2. Warrow_forward
- The thermal conductivities of human tissues vary greatly. Fat and skin have conductivities of about 0.20 W/m · K and 0.020 w/m · K respectively, while other tissues inside the body have conductivities of about 0.50 W/m · K. Assume that between the core region of the body and the skin surface lies a skin layer of 1.0 mm, fat layer of 0.50 cm, and 3.2 cm of other tissues. (a) Find the R-factor for each of these layers, and the equivalent R-factor for all layers taken together, retaining two digits. m² - K/W Rskin m² . K/W Rfat m² - K/W Rtissue |m² - K/W R (b) Find the rate of energy loss when the core temperature is 37°C and the exterior temperature is 0°C. Assume that both a protective layer of clothing and an insulating layer of unmoving air are absent, and a body area of 2.0 m2.arrow_forwardHot oil is to be cooled by water in a one-shell-pass and eight-tube-passes heat exchanger. The tubes are thin-walled and are made of copper with an internal diameter of 1.4 cm. The length of each tube pass in the heat exchanger is 5 m, and the overall heat transfer coefficient is 310 W/m2?K. Water flows through the tubes at a rate of 0.2 kg/s, and the oil through the shell at a rate of 0.3 kg/s. The water and the oil enter at temperatures of 20°C and 150°C, respectively. Determine the rate of heat transfer in the heat exchanger and the outlet temperatures of the water and the oil.arrow_forwardA copper sheet of area A is bonded to an unknown metal sheet of area A. The thickness of the unknown metal is half that of the copper. The outside surface of the copper sheet is held at a temperature of 80°C and the unknown metal sheet at 40°C. If the temperature of the copper-unknown metal interface is 60°C, what is the thermal conductivity of the unknown metal in (W/mK)? (Kcu = 386 W/m.K). Select one: O a. 193 b. 772 c. 258 O d. 386 O e. 220 Oarrow_forward
- An electric stove burner has surface area 325 cm² and emissivity e = 1. The burner consumes 1500 W and is at 900 K. If room temperature is 300 K, what fraction of the burner's heat loss is from radiation?arrow_forwardThe amount of heat per second conducted from the blood capillaries beneath the skin to the surface is 230 J/s. The energy is transferred a distance of 1.8 × 10-3 m through a body whose surface area is 1.7 m2. Assuming that the thermal conductivity is that of body fat, determine the temperature difference between the capillaries and the surface of the skin.arrow_forwardA flat-plate solar collector is used to heat water by having water flow through tubes attached at the back of the thin solar absorber plate. The absorber plate has a surface area of 2 m2 with emissivity and absorptivity of 0.9. The surface temperature of the absorber is 35°C, and solar radiation is incident on the absorber at 500 W/m2 with a surrounding temperature of 0°C. Convection heat transfer coefficient at the absorber surface is 5 W/m2∙K, while the ambient temperature is 25°C. Net heat rate absorbed by the solar collector heats the water from an inlet temperature (Tin) to an outlet temperature (Tout). If the water flow rate is 5 g/s with a specific heat of 4.2 kJ/kg∙K, determine the temperature rise of the water.arrow_forward
- The outer surface of a spacecraft in space has an emissivity of 0.8 and a solar absorptivity of 0.3. If solar radiation is incident on the spacecraft at a rate of 950 W/m2, determine the surface temperature of the spacecraft when the radiation emitted equals the solar energy absorbed.arrow_forwardThe tungsten filament of a light bulb has an operating temperature of about 2100 K.If the emitting area of the filament is 1 cm2, and its emissivity (ε) is 0.68, what is the power output of the light bulb?arrow_forwardA thin metal plate is insulated on the back and exposed to solar radiation on the front surface. The exposed surface of the plate has an absorptivity of 0.7 for solar radiation. If solar radiation is incident on the plate at a rate of 550 W/m2 and the surrounding air temperature is 10°C, determine the surface temperature of the plate when the heat loss by convection equals the solar energy absorbed by the plate. Take the convection heat transfer coefficient to be 25 W/m2·K, and disregard any heat loss by radiation.arrow_forward
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