Divergency and consistency between frictional pressure drops from momentum balance and energy balance for two-phase flow

Abstract

Frictional pressure drop is determined by either subtracting hydrostatic head from total pressure drop according to momentum balance, or subtracting potential energy term from total pressure drop according to energy balance. The divergency and consistency between momentum balance and energy balance are discussed for two-phase flow. In vertical bubbly and intermittent flows at high gas–liquid ratios, the experimental results indicate that the frictional pressure drops from energy balance are significantly greater than those from momentum balance. It is found that liquid holdup leads to the increase of hydrostatic head in the momentum equation of gas–liquid two-phase flow. However, the increment in hydrostatic head turns to be a part of irreversible pressure loss instead of potential energy. At high gas–liquid ratios from 500 to 10000, up to 99 percent of the hydrostatic head does not turn into the potential energy and is thus not recoverable in vertical bubbly and intermittent flows.