Numerical Simulation And Visualization Investigation On The Condensation Of Nitrogen With Noncondensable Gas

The increasing demand for industrial gas is driving the continuous developments of air separation units in the direction of large-scale and low energy consumption.The structure design and heat transfer performance of main condenser-evaporator which is one of the key components directly affects the energy consumption of the air separation units.Due to the limited understanding of the condensation mechanisms in the main condensing-evaporator,there is still much room for improvement in the heat transfer efficiency.The volume fraction of He and Ne as noncondensable gas can be as high as 30%in the main condenser-evaporator,which severely affects the heat transfer efficiency of the main condenser-evaporator.Due to the crucial distinction between the properties of cryogenic fluid and non-cryogenic fluid,the experimental results of non-cryogenic fluids are not suitable for cryogenic fluids.In order to obtain the accurate heat transfer correlation,the flow pattern information of two-phase flow must be observed.Presently,the visualization research of cryogenic condensation with noncondensable gas is in the blank stage.The difficulties lie in the accurate measurement of temperature,pressure and noncondensable gas concentration at low temperature.And heat insulation and sealing is more challenging in the visualization research of cryogenic fluid.A two-dimensional steady-state model of vapor condensation of nitrogen with noncondensable gas is established based on FLUENT.The VOF method and UDF are applied to define the condensation model.The influence of the mass fraction of noncondensable gas and system pressure on condensation heat transfer coefficient and liquid film thickness were analyzed and discussed.A visualized experiment setup for cryogenic condensation is designed to study the condensation mechanisms of nitrogen vapor with and without noncondensable gas on the vertical plate.The influence of the mass fraction of noncondensable gas on the heat transfer coefficient of condensation is analyzed.A heat transfer correlation of the condensation of nitrogen vapor with noncondensable gas is obtained based on the experimental data.The original experimental images obtained by the high speed camera were postprocessed.The topological structure of the experimental images and the velocity of the interfacial waves were extracted.The effects of system pressure and mass fraction of noncondensable gas on the fluctuation of film and the ripple velocity were analyzed.