Low temperature simulation of ammonia refrigeration based on dissipative molecular dynamics

Abstract

To solve the problem of heat resistance of the oil film in the evaporator pipeline of the ammonia refrigeration system, it is extremely important to study the interaction mechanism of the oil/ammonia system. The method of dissipative molecular dynamics is used to simulate the oil/ammonia flow state at different temperatures and concentrations, and the mechanism of its interaction was analyzed. It was also found that various parameters are greatly affected by temperature in the research process, the linear relationship of temperature on various parameters was quantitatively calculated. The oil/ammonia system were divided into emulsion and layered liquid. The oil phase (or ammonia phase) with low percentage at low temperature all exists in the form of droplets. The oil-ammonia interfacial tension first increases and then decreases with the increase of oil content. At the same temperature, the interfacial tension reached its maximum when the oil content was 70%. The oil percentage of 30% concentration was the phase inversion point. When the oil percentage was 30-70%, the oil and ammonia two phases were stratified, and the oil adhered to the surface of the pipe wall. Therefore, the heat transfer performance of the system was the worst when the oil content was 30-70%. As the temperature increased, the interaction parameter aij decreased significantly. The linear relationship between ? and 1/T was very consistent with the Flory-Huggins mean field theory. This linear equation provided a basis for subsequent related research.