Vapor Pressure of Aqueous Solutions of Ethylene Glycol, Glycerol, and Triethylene Glycol as Working Fluids of Frost-Free Air-Source Heat Pumps at 253 to 323 K

Abstract

Organic solutions are commonly used in frost-free air-source heat pumps (FFASHPs) due to their lower corrosiveness and cost-effectiveness. However, there is a shortage of vapor pressure data for organic solutions, which is crucial for their application in FFASHPs, particularly at subzero temperatures. This paper developed an apparatus with low leakage and good insulation for measuring vapor pressure using the static method and proposed experimental procedures that included zero setting, cleaning, drying, leak hunting, rinsing, multiple degassing, recording, and remeasuring of discharged solutions. The reliability and accuracy of the apparatus and procedures were verified by comparing experimental data with standard data of distilled water from 278 to 323 K and pure n-heptane from 253 to 303 K. The equilibrium vapor pressures of three organic solutions, namely, aqueous solutions of ethylene glycol, glycerol, and triethylene glycol, commonly utilized in FFASHPs, were measured in a temperature range of 253 to 323 K and a concentration range of 0 to 54.5 wt %. A total of 199 data points were obtained, ranging from 0.0858 to 12.3990 kPa, and fitted using modified Antoine equations, with temperature and concentration serving as independent factors. The mean absolute relative deviations between the experimental and calculated data were determined to be 1.48, 2.35, and 2.13% for aqueous solutions of ethylene glycol, glycerol, and triethylene glycol, respectively. The study’s findings provide crucial data and equations for the three organic solutions employed in FFASHPs.