Report discussing progress in research and development by the Health Instrument Divisions, Hanford Works, for the term from January through March, 1951.

The majority of two-phase flow problems involving equations of state are solved by use of point-wise utilization steam table values. In this manner, problems involving the use of the various flow equations of continuity, momentum and energy are generally forced into iterative solutions. Considerable effort towards the development of an analytical expression for the state equation seems indicated so as to simplify the analysis of two-phase problems, particularly the transient cases. The question of instability of state and mixture condition is particularly apparent in the analysis of systems undergoing phase transformation as demonstrated by the significant difference between simple theory and experimental critical flow determinations. The assumption of homogeneous, equilibrium mixtures is indicated as a first attack upon the problem.