New Concentration Correlations of NaOH Aqueous Solutions for a Thermodynamic Process

Abstract

Some processes such as air conditioning absorption systems have been developed as a feasible and economical alternative to help reduce the consumption of fossil fuels and prevent the impact of gas emission produced by electrical air conditioning. However, a main disadvantage of these systems is the absorbent’s crystallization phenomenon in the working mixture, which occurs when the absorbent concentration is higher than the saturation point. Among the aqueous working mixtures, NaOH solution shows several advantages for absorption system applications. The aim of this paper is to propose new mathematical correlations to predict or estimate the NaOH concentrations and refractive index in aqueous solutions (H2O–NaOH) for an air conditioning absorption system application. The experimental measurements of NaOH concentration and refractive index were made in situ from aqueous solutions with concentrations from 20 to 50% (weight/weight %, with increases of 5%) and temperatures between 10 and 60 °C (with increments of 1 °C). Two correlations for predicting the concentration of NaOH and refractive index based on cubic regression models with R 2 of 0.99704 and 0.99918, respectively, are presented for the first time. The normalized error for NaOH estimation using experimental data lies between −0.026 and 0.040, and for refractive index, the estimation lies between −0.002 and 0.001. Both correlations present a good fit to predict the NaOH concentration between 25 and 45% of concentration ratio.