13.74 Most architects know that the ceiling of an ice-skating rink must have a high reflectivity. Otherwise, condensationmay occur on the ceiling, and water may drip onto the ice, causing bumps on the skating surface. Condensation will occuron the ceiling when its surface temperature drops below the dew point of the rink air. Your assignment is to perform ananalysis to determine the effect of the ceiling emissivity on the ceiling temperature, and hence the propensity forcondensation.Outdoor airInsulation, k = 0.035 W/m K, thickness t= 0.3 mTopCeiling, T,E = 0.05 or 0.94Walls,Rink airT, = 15°CIce,Tice = -5°CThe rink has a diameter of D = 50 m and a height of L = 10 m, and the temperatures of the ice and walls are -5°C and 15°C,respectively. The rink air temperature is 15°C, and a convection coefficient of 5 W/m² . K characterizes conditions on theceiling surface. The thickness and thermal conductivity of the ceiling insulation are o.3 m and o.035 W/m · K, respectively,and the temperature of the outdoor air is -5°C. Assume that the ceiling is a diffuse-gray surface and that the walls and icemay be approximated as blackbodies.(a) Consider a flat ceiling having an emissivity of o.05 (highly reflective panels) or o.94 (painted panels). Perform anenergy balance on the ceiling to calculate the corresponding values of the ceiling temperature. If the relative humidity ofthe rink air is 70%, will condensation occur for either or both of the emissivities?(b) For each of the emissivities, calculate and plot the ceiling temperature as a function of the insulation thickness for 0.1stsim. Identify conditions for which condensation will occur on the ceiling.

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Answered: 13.74 Most architects know that the…

Elements Of Electromagnetics

7th Edition

ISBN:9780190698614

Author:Sadiku, Matthew N. O.

Publisher:Sadiku, Matthew N. O.

ChapterMA: Math Assessment

Section: Chapter Questions

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2 parts ( C&D) Read and solve carefully please write clearly and box the final answer(s) label them Hint: Pay attention to numbers bolded
1) The spectral, hemispherical absorptivity of an opaque surface and the spectral irradiation at the surface are as shown. d' 1.0 G₂ (W/m².um) 500 0.2 0 0 0 2 4 6 8 10 12 14 16 0 2 4 6 8 10 12 14 16 λ(μm) λ(μm) a) How does the spectral, hemispherical reflectivity vary with wavelength? b) What is the total, hemispherical absorptivity of the surface? c) If the surface is initially at 500 K and has a total, hemispherical emissivity of 0.8, how will its temperature change upon exposure to the irradiation?
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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/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:…
QUESTION 2 The Air Mass is.. A. the mass of air through which blockes solar irradiance. B. the mass of air through which the solar radiance passes. C. the mass of air through which the solar irradiance passes. O D. the mass of solar irradiance.
A glass window pane and a pyrex window pane are held together as shown below. Heat is flowing through the combination from the hot side to the cold side. The temperatures of the hot surface and the cold surface are shown, with the temperature of the surface between them. The glass pane has a thickness of 3.00 mm. Find the thickness of the pyrex pane. (The cross-sectional areas are not needed.) Thermal conductivity of glass kglass = 0.800 J/s-m-C° Thermal conductivity of pyrex: kpyrex = 1.15 J/s-m-C° pyrex glass heat heat 3.00 mm T, = 38 °c T3 = 20° c %3D T2 = 23.4°C
A solar dish with a concentration ratio of 80 means O a. solar irradiance is multipled 80 times O b. solar power is multiplied 80 times O C. temperature is multiplied 80 times O d. reflector diameter is multiplied 80 times
The tungsten filament of an incandescent light bulb has a temperature of approximately 3000 K. The emissivity of tungsten is approximately 1/3, and you may assume that it is independent of wavelength. To increase the efficiency of an incandescent bulb, would you want to raise or lower the temperature? (Some incandescent bulbs do attain slightly higher efficiency by using a different temperature.)
6.4 Two large diffuse parallel plates are maintained at temperatures T₁ = 1400 K and T₂ = 700 K. The plates are made from the same metal, and their spectral emissivities as a function of wavelength, &, are approximated as shown by two constant values joined by a linear decrease with wavelength. Compute the net radiant energy flux being transferred from plate 1 to plate 2. What is the energy flux if both plates are assumed gray with an approximate average emissiv- ity of 0.5 applied over the entire spectral range? 91 T₁ = 1400 K, Ex T₂ = 700 K, EX 92-91 0.85 Ex 0.15 0 Answer: q₁106,850 W/m²; 91.gray = 68,070 W/m². 2 λ (μm) 7
You have stated that the convective area is πr^2. Please explain this. πr^2 is the area for a circle, not a sphere. It should be 4πr^2 as this is equal to the surface area of the sphere as you have done correctly in the radiative area. A conv= 4πr^2*3*293-292 = 0.377 A rad = 4πr^2*0.2*5.67x10^-8*(292^4-291^4) = 0.144 I have tried to multiply the convective area by 4πr^2 instead of πr^2 but it is giving me an incorrect total heat transfer rate of 0.377+0.144 = 0.521 the correct answer is supposed to be 0.236
To correct the vision of a hyperopic eye, a corrective lens should enable the wearer to focus on objects that are as close as the ideal near point. One way to think of this is that the corrective lens should take an object located at the ideal near point and create an image of it at the wearer's near point. (Remember that the wearer's eye is a short distance behind the corrective lens.) Draw a ray diagram showing this situation and find the necessary focal length of the lens in terms of the wearer's near point, the ideal near point, and the distance between the corrective lens and the eye.

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