**AME 517, Fall 2009**

**Problem set #2**

**Assigned: 9/18/2009**

**Due: 9/29/2009, 4:30 pm**

** **

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: T_{1} = 362K, T_{2}
= 275K (note: F_{1-2}
isnÕt particularly easy to find, but it turns out to be 1/3; use the inside
sphere method)

5.20 – partial
answers: T_{1} = 364K for q = 0û; T_{1} = 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?