Che 342 Practice Prob Vi

The Cooper Union Department of Chemical Engineering ChE342

Heat and Mass Transfer

Practice Problem Set V

!" Consider a hot a#tomoti$e engine% &hich can be appro'imated appro'imated as a (")*m* high% ("4(*m*&ide% and ("+*m*long rectang#lar bloc," The bottom s#rface of the bloc, is at a temperat#re of !((oC and has an emissi$it- of (".)" The ambient air is at 2(oC% and the road s#rface is at 2)oC" /hat is the rate of heat transfer from the bottom s#rface of the engine bloc, b- con$ection and radiation as the car tra$els at a $elocit- of +( ,m0h" 1ss#me the o& to be t#rb#lent o$er the entire s#rface beca#se of the constant agitation of the engine bloc," !+5 /% !.+ /% !.+4 /6 2"

1ir at ! atm is o&ing in parallel o$er a 3*mlong at plate &ith a $elocit- of  m0s" The air has a free stream temperat#re temperat#re of !2( oC and the s#rface temperat#re temperat#re of the plate is maintained at 2( oC" Calc#late the distance  x from the leading edge of the plate &here the critical 7e-nolds n#mber 7ecr8 ) ' !()6 is reached" Then% #sing an- soft&are% e$al#ate the local con$ection heat transfer coe9cient along the plate" :- $ar-ing the location along the plate for ("2 ≤ x ≤  3 m% plot the local con$ection heat transfer coe9cient as a f#nction of x % and disc#ss the res#lts" 3"

1 )*m*long strip of sheet metal is being transported on a con$e-or at a $elocit- of ) m0s% &hile the coating on the #pper s#rface is being c#red binfrared lamps" The coating on the #pper s#rface of the metal strip has an absorpti$it- of ("5 and an emissi$it- of ("% &hile the s#rro#nding s#rro#nding ambient air temperat#re temperat#re is 2) oC" 7adiation heat transfer occ#rs onl- on the #pper s#rface% &hile con$ection heat transfer occ#rs on both #pper and lo&er s#rfaces of the sheet metal" f the infrared lamps s#ppl- a constant heat #' of )((( /0m2% determine the s#rface temperat#re temperat#re of the sheet metal" E$al#ate the properties of air at o +( C" !3+oC6 4"

 The o#ter s#rface of an engine is sit#ated sit#ated in a place &here oil oil lea,age can occ#r" occ#r" /hen lea,ed oil comes in contact &ith a hot s#rface that has a temperat#re temperat#re abo$e its a#toignition temperat#re% the oil can ignite spontaneo#sl-" spontaneo#sl-" Consider an engine co$er that is made of a stainless steel plate &ith a thic,ness of ! cm and a thermal cond#cti$itcond#cti$it- of !4 /0m;