# Steam tables and enthalpy

1. May 17, 2007

Hello again...i was wondering if you can help?

I am using enthalpy equations to try and find h1 and h2 to work out 'work and heat transfers' for water, for a piston type question.

I have calculated work done using: [w = -PDV]

To find the heat transfer i need to use: [Q=m.(h2-h1)]

i have obtained h1 using: h1 = hf + x(hg-hf) (using steam tables)

This has been calculated at 1826 kg/m3, from a revision guide all it states to calculate h2 is:

''From the steam table using h1 find h2?''

This is the only piece of information i need to complete the heat transfer calculation (to find h2) can you help at all? I dont now how to find h2.

I know m = 0.15, and h1 is 1826kg/m3 and Q is 223 kj

But h2?!?!?!

Guidance on how to look this up would be appreciated.

2. May 18, 2007

### teknodude

It would help if you could post the complete problem statement. For these types of problems, it usually helps to draw out the P-V and T-S diagrams. I suspect the equation relating enthalpy and work will help here, it should be somewhere in your text

3. May 19, 2010

### nyasha.shumba

Posting the whole question would have got the job done but anyway have you tried these formulas

h2=hf2+(x2hfg)
since hf2 can be found on the tables and hfg

or w=h1-h2