Two phase friction factor for para‐hydrogen between one atmosphere and the critical pressure

The Martinelli model for pressure drop in flowing two‐phase systems has been examined in detail for para‐hydrogen from 1 atm. to its critical pressure. Amethod for obtaining the Martinelli Φ term, two phase friction factor, at intermediate pressures is presented. Φ 2 can be expressed as a function of pressure and quality. The Martinelli β term, ratio of actualvapor or gas area to an idealized cylindrical area, is found to vary greatly and to indicate first an increase in gas‐liquid interface to gas volume ratio and then a decrease with increasing pressure. Some experimental data are examined in light of this development.