Figure 2 shows a desuperheater, a steady-flow device in which 100 kg/s of superh
ID: 2991779 • Letter: F
Question
Figure 2 shows a desuperheater, a steady-flow device in which 100 kg/s of superheated steam [1] are combined with cooler liquid water [2] to produce a stream of saturated steam [3]. Heat losses to the surroundings is 2000 kJ/s
a. Determine the required mass flow rate m2 of liquid water, in kg/s. State clearly all assumptions you make in your analysis.
b. The superheated steam is delivered to the desuperheater in five (5) large pipes, each .5m in diameter. If the mass flow m1 is divided equally among the pipes, determine the velocity of the superheated steam (m/s) in a pipe.
1) = steam, at 5 bar,200 Degree c 2) = liq. H2O @ bar , 25 degree C 3) = steam, sat. @ 5 bar m = 100 kg/sExplanation / Answer
writing energy balance eqn MFR=mass flow rate
MFR*(h super steam) + MFS*(h cold water) + 2000 kW = (MFR of super steam + cold water)*(H saturated steam)
(h super steam) = 2849.65 kJ/kg from steam table ; specific volume = 0.351165 m3/kg
(h cold water) = 671.11 kJ/kg ; ( H saturated steam) =2756.82 kJ/kg
=>(100)*(2849.65) + (MFR)(671.11) + 2000 = (100 + MFR )*(2756.82)
=>286965 + MFR*671.11 = 275682 + 2756.82*MFR
=>11283 = 2085.71*MFR
=>m2 the MFR of liquid water is 5.41 kg/s (ans)
B) velocity of pipe flow
= 100 kg/s * specific volume / [ 5 * Area of 1 pipe ]
=100 * (0.351165) / [0.98175] = 35.77 m/s (ans)
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