Question

Consider steady flow of steam through a horizontal pipe at a rate of 0.5 kg/s: Steam enters the pipe as a saturated vapor at 0.5 MPa with a velocity of 12 m/s and exits at 0.45 MPa with a quality of 95% and a velocity of 10.5 m/s. Heat transfer from the pipe to the surroundings, which is at 300 K. takes place at an average outer surface temperature of the pipe) of 400 K. Saturated vapor 0.5 MPa 12 m/s Quality = 95% 0.45 MPa 10.5 m/s (a) State ALL assumptions and write and simplify ENERGY and ENTROPY balance equations to the exact form that you will use to solve this problem. (15 points)

Answer 1

Given Data & ma88 flow rate m = 0.5 kal Inlet Р. o • 5 MPа Cis 12 mis Saturated vapor Exit P=0.45 mpa 95% Quality x=0.95 C2 = 1o.smis. surface temperature Ts= 4ook

@ Assumptions ; 0 Steady flow procesa in pipe. © mis ma c constant mass flow rate), 7 No change in potential energy (2=22) No change in height or datum head c Horigontal). 7 No work output

Energy equation som - Apply steady flow energy equation 3* (but + 92.) +8= mil he + com flow e fg 22) tw for Chit qo') +0= " (he + " ) Q = Heat transfer h, ha= Specific enthalpy at niet and Exit C, C2 = velocity at inlet Exit and

3 entoopy balance (ds) : let Sie Specific entropy at innet - Sa= specific entropy at Exit ds(52-54) -

- ® Rate of heat transfer (8) t mi Chit ) +0= wiſho+z) - from steam table [ Pressure table] at wo P=015 mpa 1 (saturated vapor) - hec hg at 0.5mpa = 2748.1 kJ lkg g Siz Sg at 0.5 mPa = 6,8207 kilkge at on 0:45 mpa ,x=0.95 (dryness fraction * bf = 623.11 kilkg A hega 2119.95 Kolkg & Sf = 1089035 kJ lkg-K & Spg= 5.037 kJ I KgK » ha= hefx ( hog) = hf +(o.asxhing, 1 5 The = 9637.662 kg/kg

т т SqSf + se c Spg) sa = 1, go 304 г (5.365а) Sa= , возг +[o 9x x(6-3osə) ] 52 = 6, 86 674 т т «Я К

* (by + 2) +8 = *i ( 62 = c") - B3 ™ (ha teen-bi- ep)

• RE 05 [(2659.1069) 4 (1912 - 2 more w - (1922 000 J * = -55.52 kW] (-) figo . Hest 1088 • Heat Reject surrounding to the from pipe

© entropy generation 08. 6 (S) - 9 = 0.5C 6, 860755 - 6.89093 - [-55:52] = 0,1588395 kW - Yoo 8