Question

For H2O, determine the specific volume at the indicated state, in m3/kg. (a) T = 400°C, p = 20 MPa. (b) T = 120°C, p = 20 MPa. (c) T = 40°C, p = 2 MPa.

I have figured out how to do A, but can't get the correct answer for B or C. All the examples I am finding are with numbers that are listed already on the charts, and mine are not so I need to approach the problem from a different angle. I tried interpolating between two points on the Properties of Compressed Liquid Water and got v=1.05 but this is not the correct answer. I'm fairly confident that my interpolation is right and had a friend double check it for me, so I must be approaching the problem wrong in some other way.

Please do not post the solution using different numbers. I have had issues in the past with someone copy and pasting the solution from another, easier, number set and essentially wasting one of my questions. I always look at similar questions that have been posted before posting my own and know that they are not helping me with this particular problem. I only get 20 a month so I have to make them count! Thanks in advance :)

Answer 1

We need to find the specific volume of water at the given conditions and to draw the T-V diagram.

The temperature of water T = 400°C

The pressure of water p = 20 MPa

The specific volume from the Table A-4

Specific volume v = 0.00994 m3/kg

The saturated temperature (at 20 MPa) Tsat = 365.81°C

The critical temperature of water Tc = 374.15°C (Table A-1)

The state is superheated water vapor.

Part (b)

Step 2 of 3:

We need to find the specific volume of water at the given conditions and to draw the T-v diagram.

The temperature of water T = 40°C

The pressure of water p = 20 MPa

The specific volume from the Table A-5

Specific volume v = 0.992/103 m3/kg

The saturated temperature (at 20 MPa) Tsat = 365.81°C

The state of the water is compressed liquid water.