# The relationship between temperature and pressure for water?

1. Nov 26, 2014

I have been looking everywhere for some equation that relates temperature and pressure at a constant volume for water. I am doing a project where I am designing a solar collector and it's thermodynamic processes and I want to ensure my values are accurate in a controlled volume. Attached is the diagram of my project thus far. Any help with regards to a confirmation of the accuracy of these values or an equation to find more accurate ones would be appreciated. Thanks!

NOTE: These values are ones I made up, my goal is to find better more reasonable values.

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• ###### Justin Hall - Honors Report Diagram.jpg
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Last edited: Nov 26, 2014
2. Nov 26, 2014

### Khashishi

what are the fluids involved?
Is the pressure really 100 bar before the turbine and 1.5 bar after?

3. Nov 26, 2014

The top loop is water and bottom loop is your average molten salt. These values are ones I made up in a system. The 100 bar to 1 bar seems unrealistic and that's why I am trying how to find more realistic values for this project.

4. Nov 26, 2014

### Khashishi

510C is above the critical temperature for water, so water will be similar to an ideal gas at that point. Liquid water is essentially incompressible. If the temperature drops to the boiling point, some steam will condense into water, bringing the pressure down, dropping the boiling point. So the boiling point will follow the temperature for a while, and you will have some combination of liquid and gas water. So look at a phase diagram for water, and take a look at w

I modified http://commons.wikimedia.org/w/index.php?title=User:Matthieumarechal&action=edit&redlink=1 [Broken]'s CC diagram off of wikipedia. The yellow-orange roughly shaded region is the range of densities and temperatures you might expect. The details will depend on all sorts of details of the setup. If you have a combination of liquid and gaseous water after the cooler, then you will lie somewhere on the liquid/vapor phase boundary line.

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• ###### Untitled.png
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5. Nov 26, 2014

Hmm, I'm still a bit confused. I still am having trouble finding values for each segment of the system. Going off the assumption that “…steam inlet conditions of 510°C, 10 MPa, and a flow rate of 50,000 kg/hr” how can I effectively find the mass flow rate, temperature, and pressure of each segment? Also what is the best way to find the work of the pump [new in diagram 2] and the turbine as well as the heat transfer of the heat exchanger. I have attached a new hopefully more clear diagram.

Last edited by a moderator: May 7, 2017
6. Nov 26, 2014

### Khashishi

Mass flow rate is equal everywhere if it's not bunching up. There's not enough information for pressure and temperature, but you can get a rough range of values based on the phase diagram.

7. Nov 26, 2014

Hmm, with only the values given in this diagram, what would you choose for the remaining segments in order to find W and Q?

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• ###### Diagram 2 V.png
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8. Nov 26, 2014

### Khashishi

Read up on a Carnot engine. Your real engine won't be as efficient, but it does put some limits on what is possible.

9. Nov 26, 2014