Question

Cold water with properties as shown in Table 4 flows at rate of 4 kg/s is heated from 28 oC to 54 oC in a shell-and-tube heat exchanger as shown in Figure 4.The cold water inters the tubes through thin-walled tubes, each tube has diameter of 19 mm, and the average velocity inside each tube is 0.355 m /s. The shell side, one pass is used with hot water as the heating fluid 1.8 kg/s entering the exchanger at 93 oC. The convection heat transfer coefficient between the hot water in the shell and the tubes surface is 1450 W/m2 oC.

Determine: a) The heat transfer rate b) The overall heat transfer coefficient c) The approximate number of tubes d) The length of the tubes required

Table 4 water properties Kinematic viscosity 0.65 x 106 (m2/s) 992 (kg/m2 Density Thermal conductivity 0.631 (W/m C) 4179 (J/kg °C) Specific heat Prandtle number 4.32 Hot water 1.8 kg/s Tube outlet Shell inlet Baffle Shell outlet Tube inlet Cold water 4 kg/s Figure 4

Answer 1

Cofd watr Hot wate in we =4 Kls Tui 98 h-1450 Wn Twi -28 c Two = S4C Dtalse -19 mm Anceamng The By t'c Tni =Tne = 9ic V0.355 Ms Cw= 41798 - (6716 Ch 0 Cun Cuin Thi-Tei) Pmon 16 H6(93-28) Qman Cman Ch=O E1086-54 K w Tw0-Tw;) absasbed y-28) 16916 0 absorbed =4 340616 Kw UAS Truin NTU Smax hi MTO O.4 51 NTO NTO Rn Co-6) NTU NTUS OOSI

(Re) 4 mw TT DA Maes plous Aate eAV) loel tube uRugh 991 C.0997 fofal No 40.081 O.0997 41 tabes Re = 4Eev) A4x0.0997 3.14x 19 O-6510 992 Re t0866.85 tuhulaut) O.8 .:Nu - O.023 Re Ps O-023 Ct0366-85) Nu = 67.36 Nu 1000 0-63 7-36 (5) 4i-) 2237.2 4i= 879.79 M 2 2239-2 1450

CAs NTU Cucin CAs) TDL)N C.SI X 4 449 839.76 O.SIXGX4179 7TDN O.SIKGY7 879.76 2-14 819 A4 (000 3.96 m