Molecular Dynamics Simulation Of Micro-scale Liquid-Vapor Phase-Change Heat Transfer

Toward the development of high-speed, miniaturized and integrated electronic devices, cooling of these devices has been a widespread concern. Because much heat absorbs or releases during the phase change of micro-scale films, it is very attractive for applications in the cooling of electronic devices. As a heat transfer device based on the liquid phase change in micro-scale channel, micro heat pipe has advantage of high heat transfer efficiency. It is very important to study the heat transfer during the phase change of the working fluid in micro heat pipes. Because the thickness of liquid film playing an important role in phase-change heat transfer in micro heat pipe is nano-scale, and molecular dynamics (MD) method is suitable for studies on nano-scale due to the capability of analysis of atom structure, therefore, the molecular dynamics method is adopted for studies in this thesis, the calculation software we used is LAMMPS.First, the density and thermal conductivity of micro-scale water films were calculated using three common-used water models (SPC, SPC/E, TIP4P) in this thesis. And the simulated values are compared with experimental and simulated ones in literatures. TIP4P is picked out because the simulated values using this model are most consistent with the ones in literatures. Furthermore, other basic properties and phase change of water were simulated using this model, and the conclusions drawn from those simulation are also consistent with those in literatures, which further demonstrates the feasibility of the adopted model and the simulation method.Then, the influence of the system temperature and the thickness of liquid film on the evaporation rate of the liquid phase change were studied in micro-scale. Simulations of the influence of temperature (375 K-425 K) on the evaporation rate of the phase change at the film thickness of 2 nm are performed. In addition, at temperature of 400 K, the influence of the film thickness (2 nm,3 nm,4 nm) on the evaporation rate of the phase change was simulated. Three conclusions are drawn from these simulations. First, the evaporation rate exponentially decreases with time. Second, the evaporation rate increases with temperature under the same thickness. Third, the evaporation rate increases with the thickness of the liquid film at the same temperature.Finally, the characteristics of the phase-change heat transfer of argon films in the micro-scale channel were studied. The characteristics of the phase-change heat transfer in rectangular channels were simulated to study the influence of channel height (23 nm,32 nm, 42 nm,52 nm) and thickness of liquid film (3 nm,4 nm,5 nm). The results show that the heat transfer performance of the phase change of the liquid film in the micro-scale channels is better than that in macro-scale channels. In addition, the heat flux rate increases with the increase of channel height and the liquid film thickness. At the initial moment, the evaporation rate is inversely proportional to the channel height and the thickness of the liquid film.The above-mentioned research results could provide a guideline for designs of micro heat pipes and other heat transfer devices, the operation principle of those is based on the phase-change heat transfer of the internal liquid. In addition, the research results also provide a basis for the optimization of heat transfer devices.