A MUTISCALE HYBRID SIMULATION STUDY ON CONDENSATION OF VAPOR FLOW IN A NANOCHANNEL

摘要

Phase-change process is commonly applied in thermal engineering for heat pipes and other phase-change heat exchangers, and shows great significance for theoretical and applied research. The typical condensation process in a nanochannel contains inherent multiscale characteristics from microscopic interfacial phenomena to macroscopic heat transfer and fluid dynamics. For the first step of intensive understanding, the unsteady condensation process of vapor flow in a nanochannel was studied using a hybrid simulation method. The computational domain includes the continuum region (C region) covering the main flow area and the particle region (P region) covering wall-neighboring area. The continuum-based finite volume method and the particle-based molecular dynamics simulation method were carried out simultaneously in corresponding regions and were coupled through the hybrid region (H region). The necessary information is transferred through H region and the coupling criteria is discussed based on conservation laws. The temporal profiles of density, temperature and velocity in P region were obtained statistically and show that the heat transfer is intensive at initial and then decreases gradually with time. The results in C region show that the flow and temperature fields are obviously influenced by the phase-change process occurring in P region. In addition, the temporal condensation flux in P region was expressed as an exponential decay function and it shows that the condensation process almost ceases when t>40 ns. The results have provided an overview on condensation phenomenon from molecular level to continuum level and proved that the particle-continuum multiscale hybrid method is very promising for the simulation of complicated mass and heat transfer process.