MEN 310 Exam 3, Fall 1999

Pl my | ~ - kK Mi . “a tf \ TEST —MEN31LO (eat Transfer} January 31, 2000 1, Water at T; = 24 °C is to be heated to T2= 74°C by passing it through a tube ..&/ bundle in staggered tube arrangement. Tubes havé an outside diameter D=2.5.cm 3. -vand“aré “maintained at a uniform surface temperature ‘T,,’ =.100 °C. The m ’-longitudinal and the transverse pitches for the stazgeied arrangement are 1.5D and 2D respectively. The velocity of water just before entering the tube bundle is u.= 0.3 ms. Determine the average heat transfer coefficient and the number of rows in the direction of flow needed to achievé the above temperature rise of water. . (2) thin vertical panel L=3 m high and w=1.5 ™m wide is thermally insulated on . one side and exposed fo a Sdlar radiation flux of 1250 W/m? on the other side. The exposed surface has the following absorption properties for solar radiation %=0.1 for 0.0<4<2.4 ym Oj. =0.2 for 24<A<5.0pm m=0.8 for 5.052<10.0um @,=0.1 for 10.0<A<oum Assuming that the energy absorbed by the plate is dissipated into the surroundings quiescent air at atraospheric pressure and.T = 300 K,;detenmine. the surface temperature of the panel. . ’ wo parailel plates are at temperature T, and T and have emissivities ¢) = 0.8 and €2 = 0.5. A radiation shield having the same emissivity ¢ on both sides is placed between the plates. Calculate the emissivity of the shield in order to reduce the radiation exchange between the two plates to one tenth of that without the shield. uy Points: 1 (55%), 2 (40%) and 3 (25%). L, Pz G45 .loS036 GE oe ase > Mage 0: [S| Cp = 4 APG lo? Hes 3.83339 G/atec xt! Re 0 CC6F24 W/o “Hh ( hous G. aL Ly. h- 4192. IAL isto.) Pow d Dv Nek (te); 2 “ores A Ahe tabrance Q4A4A.6382 7 | topo eicowd = 104. ST Use (08s E , af OTE 056? Ya & . 6.AY —» R. Re ane) S02 (Re) . Pros OGXS CEPA. i Ay » | ewe the ate a a, A oa ay TR spelade TALees somber oJ tee aa’ : winch Too, Teo,) tes dy the watrones ey a LEB ek t Tee Zee Cas 4 ols at