Question

Problem 4: Heat Exchangers Analysis (25 points) A counterflow plate-type heat exchanger as shown in the figure below is used to cool propane fuel W 50 mm H 25 mm Saturated Vapor propane Thickness t =5 mm H 25 mm Cooling water Length L The flow rate of the cooling water is 0.2 kg/s, while the flow of the propane is 0.1 kg/s. The water enters the heat exchanger at a temperature of 20°C while the propane enters at its saturation temperature of 85°C. The convection coefficient on the hot propane side is 10 000 W/m2.K. The two fluids are separated by a layer of copper with a thickness t = 5 mm. The dimensions of the heat exchanger are as follows: Height H 25 mm, Width W 50 mm, and Length L Assume constant properties: For copper: ke 400 w/m2.K, For water liquid: Cpc= 4178 J/kg.K; u 725x10 N.s/m2; k = 0.625 W/m.K; Pr 4.85, For propane: Cph=1700 J/kg.K; heat of vaporization of propane h165 kJ/kg. For what length of heat exchanger L the propane is condensed to a sub-cooled liquid with an outlet temperature of 60°C? Assume that the heat exchanger is well insulated and that the overall heat transfer cocfficient U is constant throughout the heat exchanger

Answer 1

Fic Teh6 Tin fropene 0340 water balance quaron wat Heal fo b gain by Cooingfloid h TTne)-m Te-Te) Hot Heat Pluid 0.2xp178 (Te- 0) OX 7008S- 60) 4250 Tee 20 835.6 5086 Tep-20

25. oB C Tee LMTD For onter low LMTD 40 MTD 60-40 2o MTD (am) 20 49,32 Om 49. 826 c UAOM hw l0G.82 hp 1esk 6G.103 m2 K2 20.0/559

'small Oomee= ) Co10) man COmon 6S X0.1XI70 OSol C0UAOM /1osO A 64.103x 49326 3.494Cm2 A Reetamguter duet tpe Areg of Heat ex c e honger 2X wicth+ Heg ht) X length. A 0o5+ 0.025) X length 34996

3.4946 o.IS lonyth lemgth 3. 2973 m ength of heat Cc hanger yegi red to condensed propame Cxc 93.2973 m