Question

Test Yourself A Shell-and-tube heat exchanger, consisting of a single shell and 30.000 tubes, each executing two passes, is used in a large steam power plant to condense steam to liquid water. The steam condensed in the shell side of the heat exchanger with an associated convection coefficient (h) of 11.000 W/m2.°C. The heat transfer rate through the heat exchanger (O is 2x10' W. Cooling water is passing through a thin tubes with D = 2.5 cm, at a rate of 3x10' kg/s (the flow rate per tube is therefore I kg/s). If the cooling water enters at 20°C and the steam condenses at 50°C, Calculate: 1- The temperature of the cooling water emerging from the condenser 2- The required tube length L per pass. Answer: (1) T... = 36.0°C (2) L = 4.51 m

heat transfer

Answer 1

* Steam -Tei TAL Wor 100 Steem out (mn) given No 30.000 D: 0.025 m hos J1000 W/mK Itho m J Kalree. Q = 2x109 w | This 500 min L fno 50 Apply SFEE heet 22 heo Teit 2 To Melpe Teo = 200+ 2x , Teo = 36.0°C) Am. 3 x 109 x4197 O now Now determine the NTV - UA Cmin properties of water at 300k thi) + (me] f 810ou, ep=417 2.1, 4+855x10 K: 0:613 we pro 5.831 L. Find Renolds number Rens , 9m 4 m 48/ ĀDety (0-02) U 0.025 x&scuoc - 59567 the flow is turbulent. then nussuit Number for this 0.023x . Nup = 0.023 Repuis proy =0.023 x (59567)x 1583)054 NDO = 308 hip sneb, his 3088 0:613 - 7543 hora Hence rit

now overall head transfer cofficient 3 0 : 1 : [ltrus) + (%1000)) mobile 10: 4474 W/m2] now G: Cmex = 0 Emin = mcepe 2 3410" X4197 = 1.25x108 WIK and . Cmin ao (max and morn possible heat transfer is Emox a Cmin (Thirtei) Emox = 1.25x108 (50-20) $ 3.76x109 w and Effectiveness = L = 2x109,- 0.532 79% 7.76x109 Now see Chort of Heat exchanger in between effectivness inymoris and NTV in x- axis, and . gotio of specific heat in bent. then at Cmin co and E= 0.532. The value (max of NTU = 0.76 approx. then length of tube MTU = ULA) MTU2 U (21PLN) LE N70. (min 210N) (U L- 076 x 1025 x108 L 4474 x 30000X2XNX VOLS = 4.51 m appoor Ang Tmin Emin