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Heat exchanger problem in Thermodynamics.

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HollowScar
#1
Nov25-10, 04:30 PM
P: 7
Hi!

I get the basics now, but this problem has got me stumped. I am trying to figure out where to start.

1. The problem statement, all variables and given/known data

In a heat exchanger, cold water flows through the tubes of the exchanger. It enters at 5.5C, and leaves at 65C. In the shell of the exchanger steam is being condensed. The steam enters at atmospheric pressure and 100C, and the condensate that is formed leaves the exchanger before it can be cooled. The flow rate of the steam is 15.0 kg/s. What is the cooling flow rate?

2. Relevant equations

Oil flows through a heat exchanger at a flow rate of 125 L/min. It enters at 20C and leaves at 75C. The oil has a specific heat of 2.84 kJ/kgK and a relative density of 0.8. The oil is being heated by steam. The steam enters the heat exchanger at 100C and the condensate formed leaves the heat exchanger at 85C. Calculate the mass flow rate of the steam.

3. The attempt at a solution

First thing we know is that cool water flows through the tube, and exits as warm water. In the shell, steam is being condensed. So basically water turns into steam.

Q (cool water absorbing heat) becomes hot water.
Q = mcΔt + mLv + mcΔt (water becomes steam)

The idea is solid, but I am not sure how I take the above, and find the flow rate. For all I know, those two are different categories.

Thank you for your help. I am this close to finishing up the course, so stumbling at this point does hurt, but the help which I receive will mean a lot to me.
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