Question

Liquid water flows in an ASTM B75 copper tube at a mass flow rate of 3.6 g/s. The water enters the tube at 40°C, and the tube surface is subjected to a constant heat flux at a rate of 1.8 kW. The tube is circular with an inner diameter of 25 mm and a length of 3 m. The maximum use temperature for ASTM B75 copper tube is 204°C. Would the surface temperature of the tube exceed the maximum use temperature for the copper tube? If so, determine the axial location along the tube where the tube's surface temperature reaches 204°C. Evaluate the fluid properties at 100° C. The fluid properties at 100°C are cp = 4217 J/kg.K, k= 0.679 W/m.K, u = 0.282 x 103 kg/m.s, and Pr = 1.75. Is this an appropriate temperature at which to evaluate the fluid properties? The surface temperature of the tube at the exit is 'C. The surface temperature of the tube is greater than 204°C. The axial location along the tube where its surface temperature reaches 204°C is m. 100°C is an appropriate temperature to evaluate the specific heat of water.

Answer 1

Given that :
Answer: Here mw = 3,6 gm ls. mw-3-6x10 ? kals. Ti=40°C.. å = 18 kw d.25 mm. d=2m. (To max = 204°c. at " T 100 100c. fluid P = 958.40 kg / m3 * M = .8.282 x 103. N5 / m² Pas 1.75 cp = 4.217 kJ lk gk K = 0.679 w/mk mass flow rate of water on a clav) 3.6x1099 (958-c00)-(714).60.02592( Voc velocity of water

.. w = 0.00761 mls. Reynold's number Relevo ). Res 1958.40) 20-00761] (0.025) 0.282x103. Re 365016. .. Rec2000 The flow is laminar flow. => for fully developed lampnar flow, under constant heat flux conditions No = 48 1 = 4.3636 = (ho L'hs (4.3636) (0.679) -0.025 2.96 0-025 he: 118.51 W/mk? out let temperature of water ...as mc :(76-T;) 1,8 x 103 € 3.6 x 103 x 4.217X109 x (7-40) To = 15856€.

a = hALTS-Tm) fally dero flow. at the ! = length of pipe. exit surface temp of copper tube is. gcha (T5-Ton). at exit Tm - 118X103 = (118.51) (1) 60-025) (2) (75 - 158.56 ). [ (To Bexit = 255.25e The surface temperature of tule out the exit ist sex 285-28 .: Maximum allowable surface temp of tube is 2.04 ... The tube surface temperature at the exit exceeds. the maximum allowable demp. . . ..(Tolexit > (Tmar) use. temp Q = (h) { 142).(T5-T) length of the tuke at which Is=204c.

surface temp of length 9. The of relationship to the the tube is linear. when. Hak Is, = 2050 lg - 2m - T - 255.252 15 - 0 1 -о Ts, -0 1-0 255.25- 0 2ou-o Fix 598 m 3 = 204c. thx = 1.598 m Mean temperature of water (Tm ) weita / Tit To 1. 158.56+40 (Tom Duration - 99.28°c. .. (I mean weiter = 100% is an appropricite temperature to consider the water properties :