Question

Question 3 A counter flow single pass double pipe heat exchanger is supplied with hot water at 120°C that is to be cooled by water entering at 20°C. The mass flow rate of the hot stream is 5 kg/s, and that of the cold stream is 6 kg/s. The specific heat capacity of both fluids may be taken as 4180 J/kg.K. The overall U value is 1500W/m2.K, and the surface area for heat transfer is 20 m2 a) Determine the maximum theoretical rate of heat transfer [4] b) Hence determine the actual rate of heat transfer based on the heat exchanger's effectiveness [5] c) Determine the respective stream outlet temperatures [3] d) Calculate the LMTD [3] e) The Zhukauskas regression method is one means of calculating the heat transfer rate from tube banks in heat exchangers. Explain the key steps involved. Also discuss the limitations of this method [5] [Total marks 20

Answer 1

T 120°c This mu 5 hylsee G 4180 81 lugh Tho Too me biglie Cp-hisuutluyu 20°c - Tei distance cu Man. Theoretical IT Oman : (MC) min (Tui - Teil Effectivenes -(1-CONTU E. 1-e 1-cē 15(1-CONTO -(1.-0.83)*1.631 1 - e E 1 -0.83 0 (1-0.83)x1435 5x4180 (120-20) Oman - 2090 kW 0 NTU Method E=0.614 NTU : VA (mcp) min 1560 x 20 15x4180) Gact € Onom -0.014 X 20 GO Cuct =1283.35kW NTO=1.435 Oact: mucp (Thi Tho) C = Capacity rate Ratio (2 33. 3 - 5 x 4.8 ( 20 - - ) C- The - 58.59°C (map) min Twi (p) mu ċ- 1 - / -0.83 20) Ourt - mccpl To-Tei) 1283.35 = 6*4.180 (Teo- To = 71.17°C

а) 0 : Tui To 0, - Тъ, Т. - | 20 11. 17 - 53.59 - 20 9. : 48, 8?“. С, - 33, 59 °a ) М10 - 9. - 9, luco 2 Р. Р3 - 38.5 3 Inchs 4 Р. Я? 39. 9 ) ЕМТІ - 47. Бо °C Ay