Experimentation And Robust Modeling On Natural Convection Heat Transfer Characteristics On Horizontal Cylinder At Low Temperatures And Pressures

Natural convection is one of the most important aircraft heat transfer forms.High-power electronic equipment has been widely used in aircraft,whose heat dissipation form is usually natural convection,with the continuous development of airborne electronic equipment system.Therefore,accurate natural convection heat transfer coefficient is of great importance for airborne electronic equipment’s thermal design.At present experimental correlations are generally used in large aircraft thermal analysis to determine the natural convection heat transfer coefficient and solve the convection heat transfer problem.Literature survey shows that less research is conducted at low temperature and pressure worldwide on natural convection heat transfer coefficient,so research on coupling conditions is needed to obtain more accurate natural heat transfer coefficient and correlations.The natural convection heat transfer from the experimental and simulation aspects is investigated in this paper.In this paper,the specific research content and conclusions are as follows:1.Firstly,this study designs and builds experimental devices to measure natural heat transfer coefficient at high temperatures and vacuum.Natural convection occurs in a sealed copper cavity that provides controlled absolute pressure from 10-5 Pa to 10-1 Pa to simultaneously realize low temperature and low pressure.The natural convection process was studied in this paper using a horizontal pipe as the research object and air as the working medium.Experimental correlation formula is obtained through the dimensionless method.The correlation agrees with experimental data.Compared to the corresponding reference data,the formula deviation is ±22%.2.Secondly,for sub-atmospheric and low-temperature atmospheres this apparatus adopts a cryocooler to provide controlled temperature during233/213/193/173 K.While the pressure domain inside the inner copper cavity ranges from 1/10/30/50/8/100 k Pa respectively.The stable temperature of the pipe is obtained through experiments and the heat exchange amounts of radiation and natural convection are calculated and the heat transfer coefficient of natural convection is given.Experimental correlation formula is obtained through the dimensionless method.The correlation agrees with experimental data.Compared to the corresponding reference data,the formula deviation is ±18%.3.Also,the analytical technique helps to identify the relationship between factors influencing the phenomena of natural convection heat transfer and its output.Inputs are prioritized by the cause-and-effect process,based on interactions,and this information is used to manage inputs for output optimization and predictive modeling.For the design of components/heat exchangers operating under vacuum conditions,the correlation and the analytical model could be useful.The results of the study provide useful support for the thermal design of aircraft operating in the stratosphere and airborne facilities in such an environment.Through these three research aspects,this paper obtains a high-precision system for measuring natural convection heat transfer coefficient and a robust modeling based statistical predictive model,providing accurate experimental data and correlation for natural convection heat transfer coefficient on a horizontal tube under low-temperature low-pressure conditions,providing guidance and assistance.