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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
- 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.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_forwardQUESTION 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_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 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_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
- Irradiation 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_forwardAn electric heating system is installed in the ceiling of a room 5 m (length) × 5 m (width) ×2.5 m (height). The temperature of the ceiling is 315 K whereas under equilibrium conditions the walls are at 295 K. If the floor is non-sensitive to radiations and the emissivities of the ceiling and wall are 0.75 and 0.65, respectively. Calculate the radiant heat loss from the ceiling to the walls. The answer should be 1595 W. Please show steps in your solutionarrow_forwardQuestion 30 of 30 く - / 4.3 View Policies Current Attempt in Progress Two concentric spheres of diameter D = 0.8 m and D2 = 1.2 m are separated by an air space and have surface temperatures of T = 410 K and T2 = 300 K. (a) If the surfaces are black, what is the net rate of radiation exchange between the spheres, in W? 912 = W (b) What is the net rate of radiation exchange between the surfaces if they are diffuse and gray with &j = 0.5 and ɛ2 = 0.05, in W? 912 = i W (c) What is the net rate of radiation exchange if D2 is increased to 20 m, with ɛ2 = 0.05, ɛ = 0.5, and D = 0.8 m, in W? 912 = W (d) What is the net rate of radiation exchange if the larger sphere behaves as a black body (ɛ2 = 1.0) and with &j = 0.5, D2 = 20 m, and D = 0.8 m, in W? 912 = i W Physical Properties Mathematical Functions IIarrow_forward
- A spherical particle of diameter D1 length L = 0.5 m. = 10 mm is suspended by a thin wire within a cylindrical tube of inner diameter D2 = 30 mm and A4 A2 D2 L + A1 A3 Determine the view factors F1,F12, F13, and F14 for S = 80 mm. The view factor between the sphere and the bottom end of the (-1/2) tube (a disk of radius r3) is F13 = 0.5 1 – (1+ R;)|where R3 = r3 /S. F11 i F12 = i F13 i F14 = iarrow_forwardConsider a silicon wafer positioned in a furnace that is zone-heated on the top section and cooled on the lower section. The wafer is placed such that the top and bottom surfaces of the wafer exchange radiation with the hot and cold zones respectively of the furnace. The zone temperatures are Tsur.h = 900 K and Tsur.c = 330 K. The emissivity and thickness of the wafer are ɛ = 0.65 and d = 0.78 mm, respectively. With the ambient gas at T, = 700 K, convection heat transfer coefficients at the upper and lower surfaces of the wafer are 8 and 4 W/m2-K. Find the steady-state temperature of the wafer, in K. Tw i Karrow_forwardA small sphere (emissivity = 0.745, radius = r1) is located at the center of a spherical asbestos shell (thickness = 1.72 cm, outer radius = r2; thermal conductivity of asbestos is 0.090 J/(s m Co)). The thickness of the shell is small compared to the inner and outer radii of the shell. The temperature of the small sphere is 727 °C, while the temperature of the inner surface of the shell is 406 °C, both temperatures remaining constant. Assuming that r2/r1 = 6.54 and ignoring any air inside the shell, find the temperature in degrees Celsius of the outer surface of the shell.arrow_forward
- Principles of Heat Transfer (Activate Learning wi...Mechanical EngineeringISBN:9781305387102Author:Kreith, Frank; Manglik, Raj M.Publisher:Cengage Learning