Thermal Expansion: A solid object has a volume density ?0 at a temperature of 315 K. The coefficient of volume expansion for the material of which it is made is 7.00 × 10-5 K-1. What will be its density (in terms of ?0 at a temperature of 425 K, assuming that it does not melt and that its thermal properties do not change with temperature?
Fill in the blank(s) with the appropriate word(s).
0.992 ?0
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The conversion of solar energy into electric power by means of photovoltaic panels will be an important part of the transition from fossil fuels to sustainable energy resources. As described in detail in Principles of Sustainable Energy, a typical PV panel consists of a top layer of glass attached with a thin optically clear adhesive to a very thin layer of photoelectric material such as doped-silicon in which the incident solar irradiation is converted into electric energy. Experiments have shown that the solar to electric efficiency ?=0.55-0.001Tsilicon, where Tsilicon is the silicon temperature in K. In a typical installation where solar irradiation is G=700 W/m2, 7% is reflected from the top surface of the glass, 10% is absorbed by the glass, and 83% is transmitted to the
photovoltaic active layer. A part of irradiation absorbed by photovoltaic material is converted into heat and the remainder is converted into electric energy. The silicon layer is attached by a 0.01-mm thick layer of solder to a 3-mm thick aluminum nitride substrate as shown in the schemetic. Determine the electric power produced by this PV panel, assuming the following properties for the pertinent materials: conductivity of the glass kg=1.4 W/(m K), conductivity of the adhesive ka=145 W/(m K), the emmisivity of the glass is 0.90, heat transfer coefficient from the top of the panel to the surrounding is 35 W/(m2 K), and the surrounding air temperature is Tair=200C. The solar PV panel is 5 m long and 1 m wide and is situated on the roof where the bottom is considered insulated. (Hint: Start by applying first law of thermodynamics to the photovoltaic-active layer and note that some of the irradiation will be converted to electricity and some of it transmitted thermally)
GIVEN
• Electric efficiency ?=0.55-0.001Tsilicon
• Solar irradiation is G=700 W/m2
• Thickness of solder(ts=0.01 mm
• Al substrate thickness (tAl)=3 mm=0.003 m
• Conductivity of the glass kg=1.4 W/(m K)
• Conductivity of the adhesive ka=145 W/(m K)
• Emissivity of the glass is 0.90
• Heat transfer coefficient from the top of the panel to the surrounding(hc)= 35 W/(m2 K),
• Surrounding air temperature is Tair=200C.
• Solar PV panel area= 5 m*1m
FIND
Electric power produced by the PV panel.
ASSUMPTIONS
• 1 Dimensional steady state heat transfer
• Thermal conductivity remains constant.
SKETCH
The lunar highlands appear brighter than the mare, because these highlands are due to meteor impact that completely avoided the mare
Indicate whether the statement is true or false
Hydrogen lines are weak in M class stars because they have much less of it than do A class stars
Indicate whether the statement is true or false
Opposing shearing forces of 3000 N are applied to the 4.00-cm × 5.00-cm faces of a metal block measuring 3.00 cm × 4.00 cm × 5.00 cm. By what amount does the block become slanted? The shear modulus for this metal is 8.10 × 1010 N/m2
A) 5.56 × 10-7 m B) 9.88 × 10-7 m C) 6.98 × 10-6 m D) 1.54 × 10-6 m E) 3.08 × 10-6 m