# Reading a pressure vs enthalpy graph

## Main Question or Discussion Point

ive got a pressure vs enthalpy graph which is based on the data for refrigerant 141b. If ive got a given pressure, and i want to find the enthalpy at that pressure how do i know where to stop when going along horizontally from a given pressure value?

## Answers and Replies

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Hi there:

If you know you pressure value, by knowing either temperature, entropy or some other physical value, you should be able to locate your state point on the chart.

With two given values, a state point is defined ...

Thanks,

Gordan

i see, ive got temperature values, but does the state point also depend on whether it is saturation liquid or saturation vapour?

Hi there:

If you are in the saturated are, in addition to pressure and temperature values, you need to know the degree of saturation. It goes from 0 to 1 (no vapor to all vapor) -- this should define your state point. Just read the other state physical values from your chart.

Thanks,

Gordan

anony mouse, you need 2 properties to get all the properties from any such property curve. if its outside the saturation region, P and T are independent. But inside, P and T are dependent, so required states change. But in any case, one needs at least 2 properties to define everything