ميحرلا نحرلا ا مسب Q # 1
The temperature distributions in C inside layers: A, B and C within the composite wall shown below are
A AA
x 168 Mx
T
B BB
x 180 200 x
T
C 2CC
x 181 . 25 500 x
T
where xA, xB and xC are in meters and they start from surfaces 2, 3 and 4, respectively, as shown below.
Layers A and B has no heat generation while the volumetric heat generation in layer C is q. Calculate the following:
A) The q knowing that LC=0.05 m; kC=400 W/mK.
B) The thermal conductivity of layer B, kB, knowing that LB=0.06 m.
C) The constant M knowing that kA=2.0 W/mK.
Q # 2
The fin shown in the figure below has a base temperature of Tb 80C. Its thermal conductivity is mK
W 100
k
. It is subjected to convection with T 30Cand h 25 W m2K. The fin diameter is equal to D=0.01 m and L=0.03 m. The fin tip is insulated. Calculate the following:A) The fin heat transfer rate.
B) The fin effectiveness.
Q # 3
A tube bank consists of a square array of 100 tubes (NL = NT = 10) arranged in-line position. The tubes have a diameter of 0.01 m and length 1.5 m; the center-to-center tube spacings are SL 0.02mand
m 015 . 0
ST . If the surface temperature of the tubes is maintained at 350 K and air enters the tube bank at Ti = 300 K and V = 5 m/s. Compute the following:
A) The average convection heat transfer coefficient.
B) The average temperature of air as it leaves the bank of tubes.
C) The total heat transfer rate from the tubes.
Air properties m3
kg 1614 .
1
; cp 1007J kgK; k0.0263W mK; 15.89106 m2 s;Pr 0.707; 7Prs 0. . Q # 4
Consider the two concentric spheres with diffuse gray surfaces that are shown below. Knowing that the space between the two surfaces is evacuated, Draw the thermal radiation resistance diagram and calculate the following:
A) The view factors F21 and F22.
B) The net radiation heat transfer rate between the surfaces 1 and 2.
C) The radiosity for surfaces 1 and 2, J1 and J2.
Hint: The sphere surface area is D2; 5.67108 W m2K4