Friday, April 14, 2006
HW #5 - P #6 - An Ideal, Adiabatic Open Feedwater Heater - 6 pts
In steam power plants, open feedwater heaters are frequently utilized to heat the feedwater by mixing it with steam bled off the turbine at some intermediate stage. Consider an open feedwater heater that operates at a pressure of 1000 kPa. Feedwater at 50°C and 1000 kPa is to be heated with superheated steam at 200°C and 1000 kPa. In an ideal feedwater heater, the mixture leaves the heater as saturated liquid at the feedwater pressure. Determine the ratio of the mass flow rates of the feedwater and the superheated vapor for this case.
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5 comments:
I'm having trouble with KE again. In this problem, can or can't we assume that the deltEkinetic is neglible. There isn't anything about the cross-sectional area so I'm guessing that we DO need to worry about it. However, I don't know how to go about finding the velocity for each tube. Any hints?
I understand that one of the input is a superheated vapor and that the single output is a saturated liquid, but what is the other input (P=1,000kPa and 50 c)-I don't know how to find its enthalpy? For the other two that I know what state they're in, I just look up in the table for their enthalpy values right?
yoda 9:52 PM
On this one, you can assume that changes in Ekin are negligible. Changes in Epot are negligible as well.
graham 3:10 PM
Yep, your ratio is upside down ! It is hard for me to tell why.
The superheated steam gives up or shares ALOT of energy as it condenses. This much energy can heat up ALOT of water.
This feedwater heater is just like example 5C-4. Check it out !
yoda 7:18 PM
The other input is subcooled liquid water at 50 degC and 1 MPa. Look in the subcooled liquid water tables or use the NIST Webbook.
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