Last updated: 5/8/2012

Sample Heat Transfer Concepts Quiz

1. At a particular instant in a cool-down transient, the temperature distribution in an infinite plane wall looks as seen in the graphic. Recall that the left side is adiabatic, while the right side is exposed to a fluid (at a non-dimensional temperature = 0.0). The transient started from a uniform, non-dimensional temperature of 1.0.

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The Biot number is closest to: a. 0.1 b. 1.0 c. 10.0 d. 100.0

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2. The heat flux as a function of position for a plane wall in steady-state and with uniform thermal conductivity is shown in the left hand graph.



The corresponding temperature profile in the plot on the right is: a. T1 (blue) b. T2 (red) c. T3 (yellow) d. T4 (green)

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3. The computed normalized temperature profiles along the length of two cylindrical pin fins are shown in the figure below (the base is to the left). The usual assumptions for extended surface heat transfer (uniform thermal conductivity, uniform convective heat transfer coefficient, etc. apply).



The efficiency of the fin corresponding to the red (lower) curve in the plot is closest to: a. 90% b. 80% c. 70% d. 60%

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4. Consider the two fins whose normalized temperature profiles are seen in Question 3. Assume the materials and dimensions are identical. One is cooled by natural convection only, while the other has a fan blowing over it.

Which of the following statements is true? a. The blue (upper) one has the fan and lower overall thermal resistance. b. The blue (upper) one has no fan and lower overall thermal resistance. c. The blue (upper) one has the fan and higher overall thermal resistance. d. The blue (upper) one has no fan and higher overall thermal resistance.

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5. The normalized temperature profiles for the two fluids in a concentric tube counterflow heat exchanger are shown in the figure. The ratio of the heat capacity rate (mass flow times specific heat) of the hot (red) fluid to that of the cold (blue) fluid is:



C_hot/C_cold = a. .33 b. .50 c. 2.0 d. 3.0

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6. The normalized temperature profiles for the two fluids in a concentric tube counterflow heat exchanger are shown in the figure accompanying Question #5.

The effectiveness of this exchanger is close to = a. 0.18 b. 2.0 c. 0.5 d. 0.92

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7. The internal flow (pipe) module allows two different wall thermal boundary conditions: constant temperature and constant heat flux.



If you were to plot the mixed mean temperature of the fluid for the parameters for which the isotherms are plotted above, you would find it to be:

a. decreasing along the pipe. b. non-linear function of position along pipe, increasing fastest at the beginning c. increasing exponentially along the pipe. d. linear, increasing function of position along pipe.

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