Heat transfer from an electronic circuit board is to be determined by placing a model for the board in a wind tunnel. The model is a 15-cm-square plate with embedded electrical heaters. The wind from the tunnel air is delivered at 20°C. Determine the average temperature of the model as a function of power dissipation for an air velocity of 2.5 and 10 m/s. The model is pitched 30° and yawed 10° with respect to the flow direction. The surface of the model acts as a blackbody.
GIVEN
• A Model square electronic circuit board pitched 30° and yawed 10° in a wind tunnel
• Length of a side (L) = 15 cm = 0.15 m
• Air temperature (T?) = 20°C = 293 K
• Air velocity (U?) = 2.5 m/s or 10 m/s FIND
• The average surface temperature of the model (Ts) as a function of power dissipation (Q )
ASSUMPTIONS
Steady state
The surface of the model acts as a black body (? = 1.0)
The wind tunnel acts as a black body enclosure at the air temperature.
SKETCH
The Reynolds number is
The pitch and yaw angles as well as the Reynolds numbers fall within the range of
The rate of power dissipation is the sum of the convective and radiative losses
Checking the units, then eliminating for clarity
Similarly, for U? = 10 m/s
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