Experimental And Simulation Study On Natural Convection On Horizontal Pipe At Low Temperature And Pressure

Natural convection is one of the most important heat transfer forms in large aircraft.With the continuous development of airborne electronic equipment system,high-power electronic equipment has been widely used in aircraft,whose heat dissipation form is usually natural convection.Therefore,accurate natural convection heat transfer coefficient is of great importance to the thermal design of airborne electronic equipment.At present,experimental correlations are generally used in the thermal analysis of large aircraft to determine the natural convection heat transfer coefficient and solve the convection heat transfer problem.Literature survey shows that less research is executed at home and abroad on natural convection heat transfer coefficient at low temperature and pressure,so it is necessary to carry out research in coupling conditions to obtain more accurate natural convection heat transfer coefficient and correlations.This paper investigates the natural convection heat transfer from the experimental and simulation aspects.The specific research contents and conclusions in this paper are as follows:(1)this paper design and build experimental apparatus to measure the natural convection heat transfer coefficient at low temperature and pressure.This apparatus adopts a cryocooler to provide controlled temperature during-40? to-100?.Natural convection happens in a sealed copper cavity which provides controlled absolute pressure condition during 1 kPa to 100 kPa,so as to realize the low temperature and low pressure simultaneously.In this paper,the natural convection process was studied by using a horizontal pipe as the research object and air as the working medium.(2)in this paper,the stable temperature of the pipe in various working conditions is obtained through experiments,and the heat exchange amounts of radiation and natural convection are calculated,and then the heat transfer coefficient of natural convection is given.Through the dimensionless method,the experimental correlation formula is obtained.The correlation is in good agreement with the experimental data.Compared with the corresponding reference data,the formula deviation is within ±20%.(3)in this paper,a natural convection simulation model of horizontal pipe is established.Numerical simulation is carried out under different conditions to obtain the stable temperature of horizontal pipe,and the flow field of natural convection is analyzed.On this basis,the relationship between Nussel and Rayleigh number is studied and compared with the experimental data.The results show that the simulation calculation is in good agreement with the experimental data,which proves that the simulation model has strong reliability and generalizability.Through these three aspects of research above,this paper obtain a system of high accuracy to measure natural convection heat transfer coefficient and a computational fluid dynamics simulation model,provide accurate experimental data and correlation for natural convection heat transfer coefficient on horizontal tube under low temperature low pressure conditions,which provide guidance and assistance for thermal engineering design of the aircraft and its electronic equipment and for other surveys on low temperature and low pressure fields.