METHOD AND SYSTEM FOR DETERMINING VAPOR PRESSURE OF LIQUID COMPOSITIONS

摘要

The vapor pressure of a mufti-component liquid composition is measured by providing an eductor through which the liquid composition is caused to flow at selected inlet pressures to provide incrementally changing pressure differentials across the eductor. The pressure differential is read for each incremental change across the eductor and the suction port pressure is read at each incremental pressure differential until the suction port pressure as a function of the pressure differential indicates a change in slope or point of inflection along the so-called dead fluid curve indicating the bubble point or true vapor pressure of the liquid composition. A motorized pressure regulator valve may be interposed in the liquid composition flow conduit upstream of the eductor for incrementally changing the pressure differential. The point of inflection may be obtained by determining the mathematical relationship using the cubic spline fit technique and calculating the second derivative of the function of the suction port pressure versus the pressure differential across the eductor until the second derivative equals zero.