Finding the enthelpy for a sub-cooled working fluid using steam tables

[CuriousQuazim]

Hi guys, kind of stuck here because I either don't remember or wasn't taught this but...

I'm working with refrigeration and I've come across a problem that involves a state where the fluild has been sub-cooled by 10K - Its easy enough dealing with super heated fluids but when it comes to sub cooled, how can I go about calculating the values using the steam tables? It's easy enough using a P-h diagram but that is neither as accurate as I'd like it to be nor is it a method I'd like to rely on.

So yes, for a given working fluid and its respective steam table (Rogers & Mayhew) how would one go about finding the subcooled enthalpy/Entropy?

Thanks for the help in advance guys ^^, really appreciate what you guys do.

 

[Achy47]

Hi there,

Calculating the properties of a subcooled fluid using steam tables can be a bit tricky, but it is definitely possible. First, let's define what subcooling means. Subcooling refers to a state where a fluid is at a temperature below its saturation temperature at a given pressure. In other words, the fluid is still in liquid form but is at a lower temperature than it would be at that pressure in a saturated state.

To calculate the enthalpy and entropy of a subcooled fluid, you will need to use the specific volume and specific heat data from the steam table. Here are the steps you can follow:

1. Determine the pressure and temperature of the subcooled fluid. This information will be given in the problem or you can measure it using a pressure and temperature sensor.

2. Look up the specific volume (v) and specific heat (Cp) of the fluid at the given pressure and temperature in the steam table.

3. Use the following equation to calculate the enthalpy (h) of the subcooled fluid:
h = v * Cp * (T - Tsat)

Where:
h = enthalpy (kJ/kg)
v = specific volume (m^3/kg)
Cp = specific heat (kJ/kgK)
T = temperature of the subcooled fluid (K)
Tsat = saturation temperature at the given pressure (K)

4. To calculate the entropy (s) of the subcooled fluid, use the following equation:
s = Cp * ln(T/Tsat) - R * ln(v/vsat)

Where:
s = entropy (kJ/kgK)
Cp = specific heat (kJ/kgK)
T = temperature of the subcooled fluid (K)
Tsat = saturation temperature at the given pressure (K)
R = specific gas constant (8.314 kJ/kgK)
v = specific volume (m^3/kg)
vsat = specific volume at saturation at the given pressure (m^3/kg)

5. Now, you have the enthalpy and entropy values for the subcooled fluid. You can use these values to solve any other problems or calculations related to the fluid.

I hope this helps! Let me know if you have any further questions or need clarification on any of the steps. Good luck with your research!