Thermodynamic properties of compressed liquids

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Discussion Overview

The discussion revolves around the thermodynamic properties of compressed liquids, specifically focusing on how to obtain properties such as internal energy (u), enthalpy (h), entropy (s), and specific volume (v) for liquids like water at pressures below 5 MPa. Participants explore the availability of data and equations relevant to these properties.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant expresses difficulty in finding thermodynamic properties for compressed liquids at pressures lower than 5 MPa, specifically asking about 0.5 MPa.
  • Another participant provides a link to a table that starts at 2.5 MPa, suggesting it may be useful.
  • A different participant notes that the values for compressed liquids do not significantly differ from saturation values.
  • Equations related to the thermodynamic properties of compressed liquids are shared, detailing how to calculate changes in internal energy, enthalpy, and entropy with respect to pressure.
  • One participant indicates a lack of familiarity with the equations provided, expressing gratitude for the assistance despite the confusion.

Areas of Agreement / Disagreement

Participants do not reach a consensus on how to obtain the desired thermodynamic properties at pressures below 5 MPa. There are multiple viewpoints regarding the availability of data and the applicability of the provided equations.

Contextual Notes

The discussion highlights limitations in available data for compressed liquids at lower pressures and the potential need for further clarification on the equations presented. Some assumptions about the constancy of specific volume and the coefficients used in the equations may not be universally accepted.

guideonl
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TL;DR
required properties for compressed liquids
Hi All,
I have review my thermodynamic notes (~35 year ago..), and I could not able to restore how to get thermodynamic properties (u,h,s,v ..) for compressed liquids. I have found properties tables for compressed liquids ( for water..) but unfortunately the data starts at 5MPa. What if I look for properties of compressed liquids (let say water) at pressures smaller than 5MPa? let say 0.5MPa?
 
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Thank you,
It was helpfull
 
Equations that might be helpful to you are
$$\left(\frac{\partial u}{\partial P}\right)_T=(P\beta-T\alpha)v$$
$$\left(\frac{\partial h}{\partial P}\right)_T=(1-T\alpha)v$$
$$\left(\frac{\partial s}{\partial P}\right)_T=-\alpha v$$where v is the specific volume, ##\alpha## is the volumetric coefficient of thermal expansion, and ##\beta## is the bulk compliance:$$\alpha=\left(\frac{\partial \ln{v}}{\partial T}\right)_P$$and $$\beta=-\left(\frac{\partial \ln{v}}{\partial P}\right)_T$$In these equations, away from the critical point, you can treat the specific volume as constant, and values of the coefficient of thermal expansion and bulk compliance (or its reciprocal, the bulk modulus) are in tables.
 
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Likes   Reactions: Lnewqban
Sorry,
I'm not femiliar with latest formulas you noted above..
Thanks any way
 

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