Homework S et # 1 – Due September 25, 2 006 1. A single-pass, cross-fow heat exchanger uses hot exhaust gases (mixed) to heat water (unmixed) rom 30 to 80 °C at a rate o3 g!s" #he exhaust gases ha$ing thermoph%sical properties similar to air, enter and exit the exchanger at &&' and 00 °C, respecti$el%" the o$erall heat transer coe*cient is &00 +!m & ", estimate the reuired surace area" &" Consider the fui d condi ti ons and o$erall heat transer coe*cient o.r o/lem or a concentric tu/e heat exchanger operating in parallel fow" #he thin-walled separator tu/e has a diameter o00 mm" (a) ete rmine the reuired length or the exchang er " (/) As suming water fow ins ide the separator tu/e to /e ull% de$eloped, esti mate the con$ection heat transer coe*cient" (c) 1si ng the o$era ll coe *cie nt and the inlet tempera tur es r om .r o/l em , plot the heat tran s er rate and fuid ou tl et temperatures as a uncti on oth e tu /e length o r m L 400 60 ≤ ≤ and the parallel-fow con2guration" (d) the ex changer were operated in counter -fow wit h the same o$e rall coe*cient and inlet temperatures, what would /e the reduction in the reuired length relati$e to the $alue ound in part (a)(e) 4o r the counter -fow con2gurat ion, plot the eecti$e ness and fuid outlet tempera tures as a unction othe tu/e length or m L 400 60 ≤ ≤ " 3" 5aturated stea m at 0"6 /ar is condensed in a shell-and-tu/e heat exchanger with one shell pass and two tu/e passes consisting o30 /rass tu/es, each with a length per pass o& m" #he tu/es ha$e inner and outer diameters o3"6 and '"7 mm" respec- ti$el%" Cooling water enters the tu/es at &0°C with a mean $elocit% o"&' m!s" #he heat transer coe*cient or condensation on the outer suraces othe tu/es is 3,'00 +!m & "" (a) eter mine the o$erall heat trans er coe*cient, the cooling water outlet temperature, and the steam condensation rate" (/) +ith all other conditions remaining the same, /ut accounting or changes in the o$erall heat tra nser coe*ci ent, plo t the coo ling water out let temper ature and the steam condensation rate as a unction othe water fow rate or kg/s 30 10 ≤ ≤ m " 6" A eed-wa ter heater that supplies a /oiler cons ist s oa shell-a nd-t u/e heat exchanger with one shell pass and two tu/e passes" ne hundred thin-walled tu/es each ha$e a diameter o&0 mm and a length (per pass) o& meter " 1nder normal operating condi - ti ons water enters the tu/es at 0 g!s and &70 , and is heated /% condensing saturated steam at atmosphere on the outer surace othe tu/es" #he con$ection coe*cient othe saturated steam is 0,000 +!m & "" (a) eter mine the water outlet temperature" (/) +ith all other cond itions rema ining the same, /ut accounting or changes in the o$era ll heat transer coe*cient, plot the water outlet temperature as a unction othe water fow rateorkg/s 20 5 ≤ ≤ m " (c) n the plot opart (/), generat e two additional cur$es or the wate r outlet temper ature as a unction ofow rate or ouling actors ofR =0"000& and 0"000' m & "!+" '" 5atura ted water $ apor lea$es a steam tur/ine at a fow ra te o"' g!s and a pr essur e o0"'/ar" #he $apor is to /e completel% condensed to saturated liuid in a shell-and- tu/e heat exchanger that uses cit% water as the cold fuid" #he water enters the thin- walled tu/es at 9°C and is to lea$e al '9°C" Assuming an o$erall heat transer coe*cient o&,000 +!m & ", determine the reuiredheat exchanger surace area and the water fow rate" Ater extended operation, ouling causes the o$erall heat transer coe*cient to decrease to ,000 +!m & "and to completel% condense the $apor, there must /e an atten dan t redu ction in the $apor fow rate" 4or the same water inl et temper ature and fow rate, what is the new $apor fow rate reuir ed or compl ete condensationME_437-061: Home Wo rk Problems
