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Hi I am using the steam table to find the value of enthalpy and entropy at a given point. But I have a doubt I have seen two examples

Example 1

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Example 2

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You can see in one case they calculate h using temperature and other using pressure why is it so. In both the cases saturated water is entering the entering the boiler. P1,T1 defines the state of water before entering the boiler.

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Since there’s a unique saturation (boiling) temperature for a given saturation pressure, and vice versa, you can specify either to determine the specific enthalpy and other properties. Your two examples involve multitple saturation values.

Most of the steam tables I have seen start with a column for saturation temperature then the next column gives the associated saturation pressure.

In the first example where the saturation temperature is 75 C the associated saturation pressure in my tables is 38.58 kPa. But the saturation temperature associated with $P_1$ = 50 kPa is about 81.3 C using interpolation. It's not clear to me which $h$ and $v$ values they are interested. The ones for 75 C which are the ones they show? Or the ones for P1 and 81.3 C which would be different.

Maybe you can give us the context of their example 1?

Hope this helps

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