Investigation On Flow And Heat Transfer Characteristics Of Condensation In Tubes For Nitrogen And Neon

Flow condensation of cryogenic fluids is widely occured in air separation industry,natural gas liquefaction industry,and cryogenic two-phase thermal control system for electronics cooling,biological and medical instrument and space application and so on.The flow and heat transfer characteristics of cryogenic flow condensation have a great impact on the performance of the devices.In this dissertation,the flow condensation of cryogenic fluids,including nitrogen and neon,is theoretically and experimentally investigated.The main contents of this dissertation are as follows:Experimental investigation and simulation on the flow pattern of cryogenic flow condensation.The visualization experiment of nitrogen flow condensation is conducted in horizontal tubes with the tube diameter of 4mm,2mm and 1mm.Based on the experimental results and the thermal properties of cryogenic fluids,a revised flow pattern map based on the flow pattern map of Breber is proposed.In order to study the flow pattern of neon flow condensation,the simulation of nitrogen and neon flow condensation in a horizontal tube is conducted.The simulation is validated by the comparison of the simulated results of flow pattern and the experimental data of nitrogen.For neon,the simulation shows that annular flow is the main flow pattern for high mass flux condition,and stratified flow is the main flow pattern for low mass flux condition.The simulated flow pattern of neon agrees well with the prediction by the revised flow pattern map.Experimental investigation on nitrogen flow condensation heat transfer coefficient and pressure drop is conducted.The heat transfer coefficient and pressure drop are measured for the nitrogen flow condensation in horizontal tubes with the diameter of 4mm,2mm and 1mm at the saturation temperature of 104 K.The heat transfer coefficient and pressure drop increase with the mass flux and the vapor quality,and decrease with the tube diameter and the saturation temperature.The measured heat transfer coefficient and pressure drop are compared with previous correlations for heat transfer and pressure drop,and it is found the Shah correlation for heat transfer coefficient and the Friedel correlation for the pressure drop show the best agreement with the experimental results.With the consideration of the thermal properties of cryogenic fluids,revised Shah correlation and revised Friedel correlation are proposed.Experimental investigation on neon flow condensation heat transfer coefficient and pressure drop is conducted.The heat transfer coefficient and pressure drop are measured for the neon flow condensation in horizontal tubes with the diameter of 4mm,2mm and 1mm at the saturation temperature of 37.5K.The effects of inlet parameters and boundary conditions on the heat transfer coefficient and pressure are analyzed.The previous correlations and the revised correlations developed with the experimental results of nitrogen for heat transfer coefficient and pressure drop are evaluated by the comparison with the experimental results of neonBased on the experimental investigation and simulation on the flow pattern of cryogenic flow condensation,the annular flow and stratified flow are the main flow pattern for the experimental conditions in this dissertation.Annular flow condensation model and stratified flow condensation model are established.The interfacial stress is considered in the annular condensation model,and the model is validated by previous experimental results and the experimental results in this paper.The effects of fluid,tube diameter,mass flux and saturation temperature on the thickness of the liquid film,the velocities of vapor and liquid film,the heat transfer coefficient and the pressure drop are discussed through the model.The stratified flow condensation model is established.The liquid-vapor interface is assumed to be an arc,and it can be solved by the minimum energy principle of the cross-section.The total energy of the cross-section is composed of the gravitational potential energy and the interface energy.Based on the calculation of the interface,the heat transfer models of the falling film region and the liquid pool region are established.The model is validated by previous experimental results and the measured values in this paper.Based on the model,the effects of fluid,tube diameter,mass flux and saturation temperature on the liquid-vapor interface and the heat transfer coefficients of the falling film region,condensate pool region and the cross-section are discussed.