A Theoretical And Experimental Study Of Heat And Mass Transfer Characteristics Of Multi-Component Condensing Gas Supersonic Flows

Natural gas supersonic dehydration and purification technology is of a series of advantages over conventional natural gas treatment methods, such as very simple equipment structure, small in size, light in weight, no moving parts and needing no extra energy but the excess pressure of wells. However, in order to ensure the designed separation performance, it is of vital importance to understand the flow and condensation characteristics of natural gases in Laval nozzle which is the key part of the supersonic dehydration and purification system. The present work is aimed at understanding the flow and condensation characteristics of natural gases flowing through Laval nozzles. The main work is summarized as follows.A spontaneous condensation mathematical model for supersonic flow with condensation of water vapor in Laval nozzles is developed. The numerical results of the model are compared with and the good agreement is obtained with the experimental data from literatures. The model was then extended to study the influences of friction drag and expansion rate on spontaneous condensation parameters of condensable water vapor flow through Laval nozzles. The results show that both the friction drag and the expansion rate have obvious and important influences on the flow and condensation characteristics. A numerical simulation was also performed for the water vapor supersonic flow in Laval nozzles with the existence of exoteric nuclei. It was found that the exoteric nuclei may significantly promote the water vapor condensation process.A spontaneous condensation physical mathematical model for supersonic condensing flow of two-component gas mixtures (one non-condensable inert gas and condensable vapor) in Laval nozzles is established to study the supersonic flow and spontaneous condensation process of nitrogen-water, methane-water and methane-nonane mixtures. The obvious influences of inlet pressure, temperature and supersaturation were found from the simulation results of the nitrogen-water vapor flow process on extreme supercooling, nucleation rate, droplet number, droplet size and liquid phase fraction. For the methane-water vapor flow, the supercooling increases to 40K right after the throat of the nozzle (x=10.0mm), and the vapor begin to condense companying with a condensation shock and a heating effect to the flow from latent heat release, the nucleation rate quickly increases to 1024kg-1s-1. Nonane in the methane-nonane vapor mixture begins to condense as the supercooling increases to 72K. No obvious condensation shock can be observed of the methane-nonane vapor mixture flow, which may be well attributed to the fact that the latent heat and the quantity of the nonane condensed are much smaller than water vapor.A mechanism and mathematical model is developed for the supersonic flow and spontaneous condensation process of three-component mixtures (one non-condensable insert gas plus two different condensable gases). And then the model is used to simulate the supersonic flow and condensation characteristics of methane-water vapor-nonane mixtures. It is found that the existence of water vapor is enhanced the condensation process of nonane vapor to some extent. The mechanism model and the simulation results are helpful for understanding the flow and condensation characteristics of natural gas, controlling the nucleation rate and/or droplet growth rate, and improving the separation efficiency of supersonic separators.An experimental rig for testing the flow and condensation characteristics of wet air is set up, a series of experimental results are obtained. The simulation results from the previous physical and theoretical model are compared against the experimental results. It is found that the heterogeneous model can predict the experimental data of both pressure and droplet sizes.