Wednesday, October 22, 2008

TE 303 - HW #5, P3 - Effluent Pressure in a Non-Adiabatic Steam Diffuser - 10 pts

Steam enters a diffuser at a pressure of 14.7 psia, a temperature of 300oF and a velocity of 500 ft/s. Steam exits the diffuser as a saturated vapor with negligible kinetic energy. Heat transfer occurs from the steam to the surroundings at a rate of 19.59 Btu/lbm of flowing steam. Neglecting potential energy effects, determine the exit pressure in psia. Assume the diffuser operates at steady-state.

10 Old comments

5 comments:

Anonymous said...

How do you get pressure out of this once solved for H2?

Dr. B said...

Anonymous 9:06 AM:
If you are using the Thermal-fluids Toolbox (TFT), this is easy. Remember that given any 2 intensive variables, you can use the TFT or steam tables to determine the values of any other intensive variables. In this case, you know H2 and x2. So, you can use the TFProp function in the TFT to determine P.
If you are using the steam tables, then you need to interpolate on the saturated steam table because x2 = 1 (saturated vapor). Interpolate using H2 as the independent (X) variable and P as the dependent (Y) variable.

Best of luck !

Anonymous said...

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HINTS:
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* Be sure to check out the comments from Dr. B's course!

* Solve for H2 using the first law energy balance, and then use that value to find P2 (look at the phase!).

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ANSWERS:
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KE1 = 4.993 Btu/lbm

P2 = 60.9 psia

Anonymous said...

i'm stuck on calculating the KE1. If I plug in the given value for KE1, I get the right value for for H2 and P2. I am using KE1 = (500 ft/s)^2 divided by 2* gc. I am getting KE1 = 5097 btu/lbm. This is a little ways off from the 4.993 btu/lbm posted. Please advise

Dr. B said...

Are you single...
LOL, nice name !
Hmmm. What did you use for gc ? I used gc = 32.174 ft*lbm/(lbf*s^2).
Ekin1 = 500 ft/s)^2/{2*32.174 ft*lbm/(lbf*s^2)}.
I alos used 778.17 ft*lbf/Btu.
Maybe you used slightly different values for these. That is all I can think of. Try doing the calculations again.
Best of luck !