Algorithm for a modified Martin-Stanford equation of state

Abstract

An algorithm is described which calculates pressures as a function of temperatures and volumes down to and below the critical volume. It will operate with only critical pressure, temperature, volume, and normal boiling point or sublimation temperatures as input parameters. It also provides the option of using vapor-pressure, isochoric and/or liquid density data to improve its predictive ability. Two equations of state are available options. the algorithm calculates the vapor pressure, coexistence line, and relative amounts of liquid and vapor. Its utility is demonstrated by application to hydrogen, helium, neon, carbon dioxide, water, ammonia, argon, and methane, which cover the range of normal values for critical compressibility. Coefficients are given to accurately calculate PVT data for hydrogen, neon, helium, argon, methane, carbon dioxide, ammonia, and water.