MEN 310 Exam 2 with Solution, Fall 1999

; TEST— MEN310 (Heat Tra nsfer) - December 17, 1999 1. A thermocouple junction may be approximated as a sphere of diameter d=2 mm, with 130 Wim°C, p=8600 ke/m? and o,-04 ki/kg°C. The heat transfer coefficient between the gas stream and the junction is h=280 W/m”C. How long. - . will it take for thé thermocouple to. record’ 98% of the applied -.temperature _ difference?” TR ee #2. Air at T.=40 °C flows with a velocity u.=8 m/s along a flat plate L=3 m long which is maintained at a uniform temperature of 100 °C. Determine the local heat - transfer coefficient at the end of the plate and the average heat transfer coefficient over the entire length of the plate. Assume Recig=2X10°. . A carbon-steel bar of 4 em by 4 cm cross section (o=1x10° mfs, k=35 W/m°C) is initially at uniform temperature T=425 °C. Suddenly all its surfaces are exposed to cooling by an air stream at T.=25°C With a héat transfer coefficient h=100 Wim, By using an explicit finite difference scheme and mesh size AxAy=1 em. Calculate the center temperature 10 s after the start of cooling. us Pa) Points: 1 (25%), 2 (25%) and 3 (50%). ene tees = @ To — Ty Te _ Pov Do ee AA ule ste) ‘a8 L- 0.092534 Suc. TEL.: 950415 - TELEX: 20049 AQUALI LE -8.P 80106 -BEYROUTH - UBAN Pee 0-698S4.. / ce 20.0802 ~o.% Sty, 774 = 0.0296 Re, 5 P%{— = te a 0-2 he 0.0296 Rey —> Sty- Sf = tele oh } ae ” Bo, Uso as 5! ‘ (tools gusset) Get > > he. 18.89 Where Chim “S > Seite (to get ha gees - : S85 wa kA Az +04 (extenpolete) - h- Zo eC . @) Se Gam mir00e, 3: eam Ee. le) Ton toc — TWpaloo®C a Te WC = S42K . Uso = Vaafe a Le am. Rees 2.10 _ ‘pe 2o-080rHtO* he Oe gag IHG le. BY3K— } gg orguaod Meer 6 ive = \.90%537 Ry Ba3 idk. wats 1. 1GHIT > Regae beet’. td eg TEL.: 950415 - TELEX: 20049 AQUALI LE - 8.2. 80106 - BEYROUTH - ISAN - [4-029 F936 YET © (more. claie fo Re ~Seactaod) Prrres ate see