Study On The Heat Transfer And Pressure Drop Characteristics During Flow Boiling Of Liquefied Natural Gas In A Vertical Helix Micro-fin Tube

In recent decades, with the advantage of efficient, clean and economy, thedevelopment of the natural gas (NG) is very rapid.And the gasification of theliquefied natural gas (LNG) is a very significant process when making use ofthe natural gas. Research on the heat transfer and pressure dropcharacteristics during flow boiling of liquefied natural gas in a helixmicro-fin tube is extremely important for the design of the vaporizer, theenhancement of heat transfer and the calculation of the pressure drop. Mostgasification of the LNG happened in the tube heat exchanger is considered asa two-phase flow boiling process.Although the research on the two-phaseflow boiling proceed for a long time, it is difficult to find the research on theflow boiling of LNG or methane in tubes, especially in the helix micro-fintube. In this paper, the main purpose is based on experimental research on theflow boiling of LNG in a vertical helix micro-fin tube as well as theoretically analyzing the pressure drop and heat transfer characteristics. The main workis as following:1. The experimental system for the flow boiling of cryogenic fluid intubes was designed, machined and established.And we repeated andmodified the test rig for several times to meet the experimental requirements.The experimental conditions of the flow boiling of LNG in the vertical helixmicro-fin tube had been determined after theoretical calculation. Detailedexperimental procedure was done safe considering the explosivecharacteristics of LNG.2. Experiment on the flow boiling of LNG in a vertical helix micro-fintube measured the temperature and pressure drop under differentexperimental conditions is investigated. The LNG’s properties were alsocalculated. The frictional pressure drop and heat transfer coefficient wereobtained and the error of the experimental result was analyzed.3. The pressure drop characteristics of LNG during flow boiling in thevertical helix micro-fin tube were systematically studied which included thetotal pressure drop and the frictional pressure drop. The proportion of thethree different parts of the total pressure drop was studied. The influence ofthe heat flux, mass flow rate and inlet pressure on the frictional pressure dropand the total pressure drop were analyzed respectively. Result showed that the acceleration pressure drop was very low in the total pressure drop andboth the frictional pressure drop and the total pressure drop increased withthe increment of the heat flux and mass flow rate but decreased with theincrement of inlet pressure. Moreover, we compared the experimental datawith the predicted result calculated by different correlations and found thatthe prediction by Hu’s correlation was relatively suitable within ourexperimental range still leaving a large deviation. Finally, we developed anew correlation by modifying the ccoefficient on the basis of Hu’scorrelation and calculated the accuracy of the new correlation under ourexperimental conditions.4. The heat transfer characteristics of LNG during flow boiling in avertical helix micro-fin tube were systematically studied. The influence of theheat flux, the mass flow rate and the inlet pressure were obtained on the localand average heat transfer coefficient, respectively. In the region with lowquality the local heat transfer coefficient increased obviously with theincreasing of heat flux. The average heat transfer coefficient increased withthe increasing of heat flux. The local heat transfer coefficient increasedobviously with increment of the mass flow rate and decreased the incrementof inlet pressure. Finally, the experimental data with the predicted resultcalculated were compared by different correlations finding the Koyama’s correlation was most accurate.