Nanofilm boiling and evaporation of working fluids R32/R1234ze(E) on metal walls: Insights from molecular dynamics simulations

Understanding energy transfer between working fluid and vapor is a critical issue in absorption refrigeration and thermophysics for the aim of intensifying heat conversion. However, it is difficult to achieve by experimental measurements due to the difficulty in catching the detailed and accurate modeling information, e.g., specific working fluid, and its underlying molecular mechanism. In order to study the evaporation and boiling behavior of refrigerant mixture from the microscopic point of view, the nanofilm consisting of different working fluids, with the evaporation model of R32/R1234ze (E) on metal wall, was established by utilizing molecular dynamics (MD) method. The effect of different mole ratios, i.e., pure R32, 3:1, 1:1, 1:3, pure R1234ze (E), on the evaporation and boiling behavior of mixtures was analyzed. The results show that the probability of explosive boiling decreases with the decrease of R32 molecular mole ratios. Thus, in turn, the performance of refrigerant mixture is observed to be better than that of pure refrigerant. Insights from this simulation research could provide an effective reference for the MD interactions and have potential benefit in developing efficient and sustainable processes for industries to minimize the chemical usage and environmental damage.

The Influence of Water on the Heat Loss of Hot Mix Asphalt

Compaction of hot mix asphalt (HMA) is a process of altering the internal structure of the material and, as a consequence, also its performance characteristics. The process should ensure the adequate viscosity of binder, a property depending on the temperature and the material-specific property (hardness) of the binder (in the case of HMA). One of the external factors that can affect the process of compaction is the presence of water quickly decreasing the HMA temperature. This paper presents a theoretical model for determining the HMA temperature variation under the effect of water. One of the model parameters is the heat transfer coefficient α for the outward flow of heat. Its value varies strongly in the interfacial zones of the HMA layer (i.e., near the top and bottom surfaces) due to the effect of external factors. The paper presents the attempt to estimate the average value for the whole paving process depending on the precipitation rate (amount of water involved in the process). The temperatures obtained from the model were verified experimentally on laboratory specimens cooled with water. The temperature was measured on the surface and across the specimen section. The drop of temperature of HMA was almost instantaneous on the surface—due to the thermal processes involving water (boiling and evaporation)—and much slower across the layer thickness.