I have a problem when calculating the temperature drop after a pressure release in a water sample. I use the following expression for the adiabatic temperature change:(adsbygoogle = window.adsbygoogle || []).push({});

(delta T/delta P)= alpha*T*V/Cp

where alpha is the thermal expansion coefficient, T is the temperature in Kelvin, V is the specific volume and Cp is the specific heat. I have appropriate equations to calculate all these parameters (all dependent on both pressure and temperature).

I calculate the temperature drop numerically integrating this equation with 0.1 MPa pressure increments. Nevertheless, for expansions from 100 MPa and -10ºC, I obtain surprising results: a little temperature increase (sample temperature after expansion is about -9.8ºC). That is due to the negative sign of the thermal expansion coefficient at low pressures and temperatures. However, in practice, I record a temperature drop in the sample (about -10.3ºC). Is the equation employed valid for negative thermal expansion coefficients??? How can I explain this behaviour??? Thanks in advance.

**Physics Forums | Science Articles, Homework Help, Discussion**

Dismiss Notice

Join Physics Forums Today!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

# Calculation of temperature drop after a pressure release

**Physics Forums | Science Articles, Homework Help, Discussion**