Research On The Heat Transfer Characteristics Of Mixed Refrigerants With A Large Temperature Slip In Nucleate Pool Boiling On A Horizontal Tube

With the increasing demand for energy, technology of exploiting, transporting and uti-lizing of natural gas is developing very rapidly. In a large natural gas liquefaction process, coil-wound heat exchangers have been fairly widely used.In a coil-wound heat exchanger, the heat transfer tubes are arranged into a spiral which helix angle is very small, so they can be regarded as approximate horizontal tubes. The refrigerant flows outside the tubes and boiling so that the working fluid flows in the tubes can be cooled down.Optimizing design of coil-wound heat exchangers will help improve the natural gas liq-uefaction plant capacity, reduce energy consumption and costs, especially for large natural gas liquefaction process seem more significant. However, it is still lack of a series of correlations which can accurately predict heat transfer process in the coil-wound heat exchanger, espe-cially mixed refrigerants boiling process. the main reason is by far, the experiments of the large temperature glide refrigerant mixtures boling on horizontal tubes are still relatively scarce. Based on this, the author regarded ethane, propane, isobutane and their mixtures as experimental subjects which are commonly used during natural gas liquefaction process as refrigerant components, designing an experimental methods for research on the heat transfer characteristics of mixed refrigerants with a large temperature slip in nucleate pool boiling on a horizontal tube, After that, a set of automatic control system of pool boiling experiment is built.Through visualized analysis of comparing mixed refrigerants boiling on a horizontal tube, a significant impact on gasification cores and bubble departure diameter is founded which has a relative contact between components of mixed refrigerant and size of the pool boiling heat flux.The analysis of experimental results shows that the greater the temperature glide of mixed refrigerant tends to bring about a greater degree of weakening on pool boiling heat transfer. The pool boiling heat transfer is greatly worsen especially when the minimum heat transfer coefficient is only 40% of its ideal heat transfer coefficient for binary mixed refriger-ants of isobutane and ethane which has a large temperature glide. Analysis and conclusions of this paper can be used to explain the reasons of sharply decreases of efficiency in the natural gas liquefaction process during low-temperature section.