Homework 7

# Homework 7 - at 5 m/s OVer both surfaces of a l-rn long...

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Unformatted text preview: at 5 m/s OVer both surfaces of a l-rn long ﬂat maintained at 75°C. - , (a) Determine the velocity boundary layer tings f ness, the surface shear stress, and the heat ﬂ at the trailing edge. , (b) Determine the drag force on the plate and ' total heat transfer from the plate, each per width eitheplate. 'D : 00¢ng (W, Plot each of the parameters of part (a) as a func- : - tion of distance from the leading edge of the g Q “’ g W (W, plate. enameth g} 'rQGLWW (c) @ An elecnic air heater consists of a horizontal air of thin metal ships that are each 10 mm long in th 4 direction of an airstrearn that is in parallel ﬂo over the top of the strips. Each strip is 0.2 m wid and 25 strips are arranged side by side. forming continuous and smooth surface over which the tained at 500°C and the air is at 25°C. ’ _ What is the rate of convection heat causing; from the ﬁrst strip? The ﬁfth strip? mm the strips? .W=0_2 v I L=25AL=O.25m TS = 500 0c to a steady-state temperature TP, which is less tha -T_, and larger than Tm. Consider the product to be ' the form of a solid cylinder whose length is muc larger than its diameter. D = 50 mm. The surfac emissivity of the solid is a = 0.8. If the product IS placed in an oven Whose S faces are maintained at T; = 650 K and amIOBZ‘; pherio nitrogen is in cross flow over the prod- uct With T3, = 350 K and V = 3 m/s. what is the steady-state temperature of the product? One-hundred electrical components, each dissipat-i ing 25 W, are attached to one surface of a square? (0.2 In X 0.2 in) copper plate, and all the dissi-jgl pated energy is transferred to water in parallel over the opposite surface. A protuberance at thtea 97' ‘ leading edge of the plate acts to trip the boundarxg; plate itself may be assumed to b' layer, and" the isothermal. The water velocity and temperature a: 17°C. and the water’s ther mophysical properties may be approximated as ' v = 0.96 X 10“1 mzls, k = 0.620 W/m ' K, and Pr = 5.2. ' Copper plate. Contact area, A and a ‘ resistance. R; (a) What is the temperature of the copper plate? ' ~(b) If each component has a plate contact Surfs area of 1 cm2 and the corresponding contact I sis-tance is 2 X 10"“‘ In2 - K/W what is t per plate. To enhance heat transfer from a silicon chip of width W = 4 mm on a side. a copper pin fin is brazed to the surface of the chip. The pin length and diameter are L = 1?. mm and D = 2 mm, re- spectively, and atmospheric air at V = 10 m/s and T... = 300 K is in cross ﬂow over the pin. The sur- face of the chip, and hence the base of the pin, are maintained at a temperature of Tb = 350 K. (a) Assuming the chip to hem a negligible effect on ﬂow over the pin. what is the average con- vection coeﬁficient for the surface of the pin? (b) Neglecting radiation and assuming the convec- tion coefﬁcient at the pin tip to equal that cal- culated in part (a), determine the pin heat transfer rate. (c) Neglecting radiation and assuming the convec‘ tion coefﬁcient at the exposed chip surface to equal that calculated in part (a), determine the total rate of heat transfer ﬁom the chip. (A) [4 > ZBSLUZW? (a (7L use Chwrcmll cf Bernstein [aﬁeld/hey; (oi/Mars 0p we) CM? : [-0206 ...
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Homework 7 - at 5 m/s OVer both surfaces of a l-rn long...

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