Numerical Simulation And Experimental Study Of The Thermosyphon With Carbon Dioxide

Refrigerator at low temperature plays a more and more important role in biomedical materials and food preservation,but there are some shortcomings in the traditional way of transfering cold energy,such as low efficiency and operation instability.By contrast,there are some advantages of two-phase closed thermosyphon,including a simple structure,low cost and good heat transfer performance,which can be used as a transmission system of cold energy.However,the research of thermosyphon at low temperature mostly focused on the cryogenic temperature zone,and the studies of thermosyphon closely related to the temperature zone(213 ~ 253 K)of the cold chain are very scarce,which limits its application in the field of the cold chain.In this paper,the current research about theoretical models,numerical simulation and experimental studies on the thermosyphon was disscussed in detail,and then on this basis,the paper mainly carried out the following main aspects of the research work and prepare for the application of the thermosyphon in the temperature zone of the cold chain:(1)By improving the phase change model,the condensation frequency can changed automatically when the evaporation frequency is certain,thus ensuring the conservation of heat and mass transfer.Also,when the empirical value of evaporation frequency is too large that cause large condensation frequency with divergency,the gas-phase thermal conductivity kv can be adjusted to ensure the convergence of the model.Finally,the reliability of the improved phase change model was verified on the basis of experiments in the previous literature.(2)The thermosyphon using carbon dioxide as working medium was designed and manufactured,the shape of evaporation section is rectangular and the condensation section is made into a cold chamber connected with the cold head of the refrigerator.The thermosyphon was numerically simulated by the help of the phase change model at a specific heating power and the heat transfer performance was predicted meeting the basic requirements of the thermosyphon as an application in the cold chain.(3)A test bench of the thermosyphon with carbon dioxide was built to study the influence of inclination angle and heating power on heat transfer performance.Also,the influence of input power of refrigerator on overall heat transfer efficiency were studied experimentally.Firstly,the temperature of the surface of the whole thermosyphon is evenly distributed,which conforms to the basic requirements of the design for the thermosyphon.Secondly,the experimental thermosyphon has its optimal inclination angle of 20° ensuring the best heat transfer performance,but generally the inclination angle has a small influence on it.Thirdly,although the heating power has little effect on the uniformity of wall temperature distribution of the thermosyphon,it has some certain effects on the heat transfer capacity.When the heating power gradually increased,the heat transfer capacity gradually enhanced,but after reaching a certain value,the heat transfer capacity begined to decline.Finally,when the operating temperature is high,the increase of the input power for the refrigerator will reduce the overall heat transfer efficiency,and when the operating temperature is low,the increase of the input power for the refrigerator will improve the overall heat transfer efficiency.