Name: ______________________
ME 126 Heat Transfer
Test 3
1. (10 points) A stainless steel spherical at 873K receives irradiation from another
adjacent body assumed to be a black body at 327°C. The ball has the following
properties: emissivity = 0.3, reflectivity = 0.5, transmissivity = 0.2 Determine the
following for the stainless-steel ball:
a. Emissive Power, E
b. Irradiation energy, G
c. Net Heat flux, q”
2. (10 points) Air at 27°C and a velocity of 5m/s passes over a small computer chip
(surface area is 20mm x 20mm) maintained at surface temperature of 127°C. To
increase the heat removal rate, a stainless steel (AISI 304) pin fin of diameter 5mm
is attached to the surface of the computer chip.
a. Determine the convection from the computer chip base.
b. Find the maximum heat transfer rate from the pin fin.
c. Determine the approximate length to the heat rate in part a.
d. If the pin fin was instead a rectangular fin of similar length (width = 5mm;
thickness = 5 mm), what is the max heat transfer rate?
3. (10 points) Air enters a tube at a temperature Tm,i = 293K. The tube has a diameter
of 25-mm diameter, 1.5 m with a mass flow rate of 6 × 10-4 kg/s. A constant heat
flux heats the air so that its bulk mean temperature at the exit is Tm,o = 50°C.
Assume fully developed flow.
a. Find the required heat flux (W/m2)
b. Find the convective heat transfer coefficient
c. Find the wall surface temperature at the outlet (K)