Studies on Boiling Point Elevation of Water and it’s Correlation with Salt Concentrations for Application in Evaporator Design

Abstract

The boiling point of a solution increases with the increase of non-volatile solute concentration as the vapor pressure of solvent reduces due to addition of solute in it. Thus the solution need to be heated to a higher temperature in order to get the vapor pressure to become equal to the external pressure at the boiling point. Experiment shows that the change in boiling point of the solvent above a solution from that of the pure solvent is directly proportional to the molal concentration of the solute. Since evaporators dealing with boiling solutions, and in particular with solutions with non-volatile solutes, any problems related with heat transfer on it must account for the effect of boiling point elevation in designing the evaporator.

In this experimental studies the boiling point elevations of water due to presence of individual sodium and potassium salts like NaCl, NaOH, KCl, KNO3 as well as mixtures consisting of both NaCl & NaOH and KCl& KNO3 have been correlated to salt concentrations and solubility of the salts. The correlations are based on combination of Clasius-Clapeyran relation with Raoult’s law considering wide range of salt concentrations from 1.4 to 16 wt. %. The correlation takes care of two factors namely interaction between the salts and water common ion effect of the cations together.

Keywords: Boiling Point Elevation, Evaporator Design, Activity Co-efficient, Thermodynamics