AME 517, Fall 2009
Problem set #2
Assigned: 9/18/2009
Due: 9/29/2009, 4:30 pm
Homework may be submitted by email (ronney@usc.edu), by fax (213-740-8071) or put in my mailbox
(down the hall from my office in the OHE 430J suites, in the small room with
the copy machine). DEN students
should submit through the usual channels.
NOTE: You can use the Excel spreadsheets to
check your answers, but you need to show your work using the relevant
equations.
5.1 – answers: front 112 kW, rear 150 W, free
convection 266 W.
5.7 – answer:
5.18
5.19 –
answers: T1 = 362K, T2
= 275K (note: F1-2
isnÕt particularly easy to find, but it turns out to be 1/3; use the inside
sphere method)
5.20 – partial
answers: T1 = 364K for q = 0û; T1 = 306K for q = 60û
5.22 – answer: -137.4 W/m of collector length
Problem not in text
(from the midterm in a previous year):
We have discussed the Ògreenhouse effectÓ in
class, which causes the interior of an enclosure to reach a temperature higher
than that of the surrounding air when sunlight passes though a window of the
enclosure. Answer and explain
briefly the following questions
about this effect:
- Would running a fan inside the enclosure to
increase the convective heat transfer coefficient between the interior air
and the wall of the enclosure increase or decrease the temperature inside
the enclosure?
- If the window glass absorbed more at short
wavelengths than long wavelengths, would the interior of the enclosure be
warmer, cooler or the same temperature as the outside air?
- To maximize the greenhouse effect, would you
coat the interior of the enclosure with a low emissivity or high
emissivity material, or does the emissivity not matter? (Assume whatever coating you use,
the emissivity is independent of wavelength.)
- At night, will interior of the enclosure be
warmer, cooler or the same temperature as the outside air?
- If the window glass absorbed equally at all
wavelengths, would the interior of the enclosure be warmer, cooler or the
same temperature as the outside air?