# Lockhart–Martinelli parameter

The Lockhart–Martinelli parameter (${\displaystyle \chi }$) is a dimensionless number used in internal two-phase flow calculations.[1] It expresses the liquid fraction of a flowing fluid. Its main application is in two-phase pressure drop and boiling/condensing heat transfer calculations.

It is defined as:

${\displaystyle \chi ={\frac {m_{\ell }}{m_{g}}}{\sqrt {\frac {\rho _{g}}{\rho _{\ell }}}},}$

where

• ${\displaystyle m_{\ell }}$ is the liquid phase mass flowrate;
• ${\displaystyle m_{g}}$ is the gas phase mass flowrate;
• ${\displaystyle \rho _{g}}$ is the gas density;
• ${\displaystyle \rho _{\ell }}$ is the liquid density.