This
page will describe PHYS 213 James Scholar Assignment 3.
1. Please read the article “ThermoelectricEnergyRecoveryScience”, which discusses several modern applications of thermodynamics to heating, cooling and power generation, using semiconductors, and write a 1-2 page essay on it.
2. Read the article “solar-poweredCardboardOven” on the Kyoto Box. Now tell me how it works.
And then *calculate* what temp you can expect from it. You should do everything symbolically first, then put numbers in at the end (you can get info on the sun from the slides in Lect. 8).
You may assume the top of the box (which has the acrylic cover) is 1m x 1m, and that the box has a height of 0.1 m. (we'll neglect the slight difference in the sizes of the inner (black) box and the outer (reflective) box. You should also assume that the sunlight hits only the top of the box, and at normal incidence. Also, for the purpose of the calculation, you may assume that the acrylic is 100% transparent to visible radiation, and 100% absorbing (and then re-emitting) of IR. Also, you can assume that the inner box has an emissivity and absorptivity =1; however, let the reflectivity of the foil on (inner surface of) the outer box have reflectivity R (where the emissivity is then 1-R). Finally, newspaper or straw is used to insulate the inner from the outer box (so that ideally the only thermal link is through radiation.
Calculate what the thermal conductivity of the 'insulation' should be (assuming a thickness of 2cm, as in the photo), so that the thermal link from convection/diffusion is less than 10% that of radiation.
After you complete your calculations, comment on what the optimal dimensions of the box should be.
(Note: although you can readily find the basic principles behind the solar oven on many websites, most of them get caught up with using some sort of parabolic collector to increase amount of sunlight collected. However, we ignore this complication here. To complete the above assignment, I would first recommend looking in detail at the class notes on calculating the earth temp.
Deposit your paper here by 5pm Wednesday, April 28, 2010.
View the articles here.