HeatTransfer-I-Section-7

17 example 4 it is proposed to measure air velocity

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Unformatted text preview: rst case scenarios for system temperature, since your buddy can neither pay you (or buy you a beer) nor does he have the 'me to wait for you to do a detailed analysis, as his project is due the next day. Evaluate system temperatures under the following condi'ons assuming that the chips have a low profile (i.e. they do not seriously protrude into the air stream): –  First, find the average surface temperature of the circuit board by assuming that all the heat dissipated by the chips is conducted into the board and is evenly distributed over the en9re surface and then removed by convec'on from both sides of the board. –  Next, find the average surface temperature of the chip you expect to have the worst cooling scenario, assuming that no heat is conducted into the board, but rather, is all convected from the chip surface. Why is this temperature so large? Is it a realis'c cooling scenario? –  Finally, it is now gerng late and you stumble upon the thermal “specs” for his chips (which he was using as a drink coaster) and you find that a typical chip to board thermal resistance is Rcb = 7.5 K/W. Use this informa'on to examine a more realis9c scenario that has some heat produced by the chip conduc'ng into the board and then convected away from both board surfaces, and some heat convected from the chip surface. 17 Example 4 •  It is proposed to measure air velocity using a thin copper strip [ks = 400 W/mK] of length 2 [cm] and width 4 [cm]. The blade is heated using an electric current which provides 0.03 [W/ cm2]. The blade is thin enough that longitudinal conduc'on is negligible. A temperature sensor placed at the trailing edge reads a temperature of 30 C in...
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