Study On Heat Transfer Distortion Characteristics And Prediction Model Of Supercritical Pressure CO₂ In Spiral Pipeline

As a natural refrigerant,carbon dioxide has regained favor in the fields of automobile air conditioning,Marine air conditioning and heat pumps due to its zero ozone layer destruction potential(ODP)and low greenhouse effect potential(GWP).However,the critical temperature of CO2 is relatively low(31.05?),and the practical application requires a trans-critical refrigeration cycle,that is,the exothermic process of CO2 occurs under supercritical pressure.Due to the thermal physical parameters of the supercritical CO2 changes with temperature and pressure is very big,especially in the critical region,thermal physical property parameters of distortion of the laws of flow and heat transfer of supercritical CO2 is extremely complex,so the distortion characteristics and its prediction model for CO2 supercritical CO2 heat transfer across critical refrigeration cycle system design and simulation are particularly important.Based on the numerical simulation for the flow and heat transfer characteristics of supercritical CO2 in helical tube,this paper discusses the working condition of different parameters on the heat transfer of supercritical CO2 distortion behavior and the effect of supercritical CO2 are brought forward in the helical tube heat transfer correlations,and further reveals the extraordinary gravitational field conditions and add in-line vortex generator effect on the properties of supercritical CO2 heat transfer mechanism.The main work and research results of this paper are as follows:(1)Three-dimensional cartesian coordinates based on the conservation equations of the compressible fluid and the SST k-? turbulence model,using business mathematics software calls Property query software database for thermal physical parameters of the supercritical CO2,under the pressure of supercritical CO2 in helical tube heat transfer numerical calculation of cooling,to get the internal flow field temperature distribution,velocity distribution and turbulent structure in detail,analyzes the quality of pipe diameter,helical tube,inlet pressure,flow rate,heat flux and flow direction,the influence of factors on the heat transfer of supercritical CO2,The mechanism of the effect of buoyancy lift,centrifugal force and flow acceleration on the heat transfer distortion of supercritical CO2 was revealed.Based on the least square method,a new criterion correlation formula for supercritical CO2 cooling and heat transfer in a helical tube under conventional gravity field was proposed.(2)For the working conditions of unconventional gravity fields(such as vehicle-mounted,airborne and shipboard),the effect of the combined action of inertial force and gravity on supercritical CO2 heat transfer must be considered.In this paper,by changing the N-S equations in the size of the volume force and direction to simulate microgravity and gravity condition,based on the numerical method to obtain the unconventional gravitational field under supercritical CO2 flow field of the helical tube details and compared with conventional gravity field under the conclusion and found that the size of the volume force and the direction of heat transfer of supercritical CO2 effect obviously,further analyzes the unconventional under gravity field inlet pressure,mass velocity and heat flux on the heat transfer mechanism of the influence of supercritical CO2 puts forward a new suitable for unconventional gravitational field under rule of helical tube heat transfer of supercritical CO2 cooling correlations.(3)The longitudinal vortex generator in the tube can effectively cause the axial eddy current effect,improve the turbulence intensity in the tube,improve the overall heat transfer performance in the tube,and thus inhibit the heat transfer deterioration.In this article,through the simplification of the length of the helical tube model,based on the numerical method to obtain the tube set longitudinal vortex generator in the different shape structure,fin height,density and the helical tube under different forms of the pipeline between supercritical CO2 flow field information,strengthen heat transfer mechanism of vortex generator is analyzed,the results showed that the vertical helical tube with a vortex generator can generate strong turbulent kinetic energy and vortex disturbance,compared with other forms has better heat transfer performance.