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A spherical satellite in near-earth orbit is exposed to solar irradiation of
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Fundamentals of Heat and Mass Transfer
- Consider an ideal gas enclosed in a spectral tube. When a high voltage is placed across the tube, many atoms are excited, and all excited atoms emit electromagnetic radiation at characteristic frequencies. According to the Doppler effect, the frequencies observed in the laboratory depend on the velocity of the emitting atom. The nonrelativistic Doppler shift of radiation emitted in the x direction is f = f0(1 + vx / c). The resulting wavelengths observed in the spectroscope are spread to higher and lower values because of the (respectively) lower and higher frequencies, corresponding to negative and positive values of vx. We say that the spectral line has been Doppler broadened. This is what allows us to see the lines easily in the spectroscope, because the Heisenberg uncertainty principle does not cause signifi cant line broadening in atomic transitions. (a) What is the mean frequency of the radiation observed in the spectroscope? (b) To get an idea of how much the spectral line is…arrow_forwardA 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.arrow_forwardDetermine the net heat transfer by radiation between two gray surfaces, A (εA= 0.90) andB (εB= 0.25) at temperatures 500°C and 200°C, respectively if a. surfaces are infinite parallel planes b. surface A is a spherical shell 3 m in diameter and surface B is a similar shell concentric with A and 0.3 m in diameter c. surfaces A and B concentric cylindrical tubes with diameters of 300 mm and 275 mm, respectively d. both surfaces are squares 2 m × 2arrow_forward
- QUESTION 9 A manufacturing factory located at 30° N latitude has a window area 35 m² that consists of double- pane windows made of clear glass (SHGC = 0.766) as given in the Figure Q2. To reduce the solar heat gain on a hot day, a reflective film that reduce the SGHC to 0.261 is considered. The building need cooling during the months of June, July, August and September and need heating during the months of October through April. The average daily solar heat fluxes incident on the west side of this latitude is given in the Table Q2 below. The unit cost of electricity and the natural gas are RM 0.30/kWh and RM1.75/therm, respectively. If the coefficient of performance of the cooling system is 3.0 and the efficiency of the furnace is 0.80. Determine: i. the net annual cost savings due to installing reflective coating on the windows ii. the simple payback period if the installation cost of the reflective film is RM 70/m² Glass Solar Radiation Reflective film KAir space Reflected…arrow_forwardYou can neglect radiation at the bottom of the plate; the bottom side of the plate has water flowing underneath it. Often, when dealing with liquids (rather than gases), one can neglect radiation because heat transfer due to convection is so much larger (liquids tend to have higher convection coefficient values than gases).arrow_forwardA 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/day · m² 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. Answers:…arrow_forward
- A typical car's exterior consists of a thin layer of silica (SiO2) over an opaque painted metal panel. Silica is transparent in the visible wavelengths but offers high reflectance in the near- to mid- infrared wavelengths. The plot on the next page depicts the diffuse spectral reflectivity (pa) of the car's surface: Spectral reflectivity, P₂ 0.8 0.6 0.4 ལ 0.2 0 0.1 1 1 10 Wavelength, λ(μm) 100 If the car's exterior temperature is T₁ = 77°C, determine both the total absorptivity (a) and the total emissivity (a) of the silica-covered panel. Assume that the Sun's temperature is Tsun = 5800 K.arrow_forwardA thermocouple whose surface is diffuse and gray with an emissivity of 0.60 indicates a temperature of 165.0°C when used to measure the temperature of a gas flowing at low speed through a large duct. The walls of the duct have an emissivity of 0.85 and are at a uniform temperature of 450.0°C. If the convection coefficient for the gas flowing over the thermocouple is 75.0 W/(m2-K) and there are negligible conduction losses from the thermocouple, calculate the actual temperature of the gas.arrow_forwardA proposed method for generating electricity from solar irradiation is to concentrate the irradiation into a cavity that is placed within a large container of a salt with a high melting temperature. If all heat losses are neglected, part of the solar irradiation entering the cavity is used to melt the salt while the remainder is used to power a Rankine cycle. (The salt is melted during the day and is resolidified at night in order to generate electricity around the clock.) 9R = Est-3.45 MW i Salt Tsalt = 1000°C Mirror MW qR Consider conditions for which the solar power entering the cavity is asol = 7.10 MW and the time rate of change of energy stored in the salt is Est = 3.45 MW. For a cavity opening of diameter D, = 1 m, determine the rate of heat transfer to the Rankine cycle, qr, in MW. The temperature of the salt is maintained at its melting point, Tsalt = Tm= 1000°C. Neglect heat loss by convection and irradiation from the surroundings. Sun Heliostatsarrow_forward
- Determine the following: a. Average emissivity of both surfaces b. Absorptivity of both surfaces c. reflectivity of both surfaces d. which surface is more suitable to serve as a solar absorber?arrow_forward4. The filament of a 75 W light bulb may be considered as a black body radiating into a black enclosure at 70° C. the filament diameter is 0.10 mm and length is 5 em. considering the radiation, determine the filament temperature .arrow_forwardIrradiation on a semi-transparent medium is at a rate of 640 W/m². If 160 W/m² of the irradiation is reflected from the medium and 130 W/m² is transmitted through the medium, 1) Determine the absorptivity of the medium. 2) Determine the reflectivity of the medium. 3) Determine the transmissivity of the medium.arrow_forward
- Principles of Heat Transfer (Activate Learning wi...Mechanical EngineeringISBN:9781305387102Author:Kreith, Frank; Manglik, Raj M.Publisher:Cengage Learning