Precise Method for Determining the Enthalpy of Vaporization of Concentrated Salt Solutions Using a Bubble Column Evaporator

An improved bubble column evaporator (BCE) system was used to determine accurate and precise enthalpy of vaporization (Delta H (vap)) values for concentrated salt solutions. The method is based on the steady state volumetric energy balance developed in a BCE. The BCE system offers a novel and simple approach for Delta H (vap) measurements because it only requires measurement of the hydrostatic differential pressure across the column and the temperatures of the steady state column and the inlet gas. In this work an automatic acquisition system was developed in order to study the frequency distribution of Delta H (vap) values. It was established that vacuum insulation of the bubble column and a data acquisition system enhanced both the accuracy and precision of Delta H (vap) measurements. In addition, a hygrometer was used to measure vapor pressures of concentrated Li2SO4 and ZnSO4 solutions to determine new Delta H (vap) values. The results obtained are in better agreement with expected values and indicate the conditions required to enhance evaporative cooling systems and improve thermal desalination. An analysis was also carried out on the effect of salt concentration on Delta H (vap) and on calculated values of the partial molar enthalpy of dilution (Delta H (dil)).