Pool boiling heat transfer coefficient of dimethyl ether and its azeotropic ternary mixtures

Abstract

Dimethyl ether (DME) is a popular medium widely used in industrial applications. Being highly flammable substance, only recently it has again found commercial use as a primary working fluid in cooling and heating systems. Known as refrigerant RE170, it is now considered to be one of the potential natural refrigerants of the future due to minimal Global Warming Potential and zero Ozone Depletion Potential.Two novel azeotropic ternary mixtures of RE170/R1234yf/R152a were developed in order to improve cooling capacity and performance of a dimethyl ether refrigeration cycle. The mass ratios were purposefully selected to offer high cycle efficiency COP, high specific cooling capacity qe, small specific volume of vapour, reduced compressor power requirements, and the smallest possible temperature glide.The mixtures were subjected to experimental analysis in order to establish to what degree the added fluids (R1234yf and R152a) influence boiling and heat transfer performance. Boiling curves and heat transfer coefficients were determined experimentally and compared with the values obtained for pure RE170. Finally, several known heat transfer coefficient correlations (suitable for both hydrocarbons and synthetic refrigerants) were applied to the resulting data and evaluated for accuracy by evaluation of MAPE. The Cooper correlation was the most accurate for for ternary mixtures of dimethyl ether in the broadest range of temperatures, heat fluxes, and compositions (MAPE between 3.5-19.8). In order to improve the accuracy even further, the original Cooper correlation was modified with the acentric factor and the molecular mass power factor was optimised for modern chloride-less refrigerants. Resulting equation, when applied to ternary mixtures, returns errors below 5% in the entire range of experimental data.