Talk:Vapor quality

Vapor fraction

Is this the same as vapor phase fraction? If so, should it be included? --128.250.5.246 (talk) 06:40, 16 October 2010 (UTC)

Moved content

Quality (physics) had a lot of duplicate/overlap material so I have merged it here. David Hollman (Talk) 09:27, 14 September 2010 (UTC)

Error in equation for superheated or subcooled fluids

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An alternative definition is the 'equilibrium thermodynamic quality'. It can be used only for single-component mixtures (e.g. water with steam), and can take values < 0 (for sub-cooled fluids) and > 1 (for super-heated vapors):

$\chi _{eq}={\frac {h-h_{f}}{h_{fg}}}$

where h is the mixture specific enthalpy, defined as:

$h={\frac {m_{f}\cdot h_{f}+m_{g}\cdot h_{g}}{m_{f}+m_{g}}}.$

Subscripts f and g refer to saturated liquid and saturated gas respectively, and fg refers to vaporization.

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The formula for $\chi _{eq}={\frac {h-h_{f}}{h_{fg}}}$ is fine, but the formula for $h={\frac {m_{f}\cdot h_{f}+m_{g}\cdot h_{g}}{m_{f}+m_{g}}}.$ is incorrect for subcooled or superheated vapours. The formula for $\chi _{eq}$ can never exceed 1 using the definition of h here as it is based on saturation condition only. Consider a superheated fluid: mf is zero, therefore h must be equal to hg, which means xeq = 1. hg at superheat (or hf for subcooled) needs to reflect the actual enthalpy, not at saturation condition. The formula as given is only valid within the two phase region or at saturation. 86.20.225.229 (talk) 12:59, 15 January 2024 (UTC)