| When a liquid wets a heat solid wall, the evaporating extended meniscus formed on a solid surface is often divided into three distinct regions:the equilibrium thin film, the evaporating thin film, and the intrinsic meniscus. The intrinsic meniscus is dominated by capillary forces, while the evaporating thin film region is controlled by both capillary forces and disjoining pressure.The evaporating thin film region is characterized by high heat transfer rates because its small thickness results in a very low conduction resistance, and the important method to obtain high heat transfer coefficient and high heat flux.Flat heat pipes with microgrooves can achieve very high heat fluxes due to evaporation at thin liquid films. The evaporating thin film region near the triple interline can significantly affect the heat and mass transport characteristics of flat heat pipes with microgrooves.The main work and conclusions of this paper as follows:1. Three-dimensional nonequilibrium molecular dynamics simulations are performed for coupling between momentum and energy transfer at a solid-liquid interface of the evaporating thin film. The solid-solid interactions are modeled by the embedded atom method which includes multi-body interactions in metals. The heat flux through the nanochannel and thermal conductivity is calculated directly by Green-Kubo method. The wall model has great effect on the interfacial thermal resistance length, while it has little effect on the slip length at the slid-liquid interface.2. The velocity slip and temperature jump at the solid-liquid interface obtained by molecular dynamics simulations are applied to the boundary conditions at the solid-liquid interface of the evaporating thin film. It is found that when the liquid can not wet the solid surface, the temperature jump at the solid-liquid interface can significantly reduces the effective superheat degree of the evaporating thin film region. Although the velocity slip at the solid-liquid interface can enhance the heat and mass transport characteristics of the evaporating thin film, coupling of the velocity slip and temperature jump at the solid-liquid interface result in a sharp decrease of the heat and mass transport characteristics of the evaporating thin film.3. A detailed mathematical model predicting the heat and mass transport characteristics of the evaporating thin film is developed. The model considers the effects of inertial force and evaporation coefficient. The heat and mass transport characteristics decreases sharply as the evaporation coefficient decreases. The effect of the inertial force on the heat and mass transport characteristics of the evaporating thin film can be neglected.4. The heat transfer characteristics under the conditions of different heat loads and incline angles, including the start-up performance, temperature uniformity and thermal resistance of a novel flat heat pipe with microgrooves, have been investigated experimentally. It is found that the novel flat heat pipe with microgrooves has uniform temperature distribution. The novel flat heat pipe with microgrooves can sharply enhance heat transfer compared with the material of the flat heat pipe.5. A detailed mathematical model predicting the flow and heat transfer in flat heat pipes with microgrooves is developed. The model of heat and mass transport characteristics of the evaporating thin film is applied to simulate the heat transfer for the evaporator of the flat heat pipes with microgrooves. Compared with the previous model for the flow and heat transfer of the flat heat pipes with microgrooves, the wall temperature of the flat heat pipe with microgrooves calculated by the present model is in better agreement with the experimental results. |
