Study On Inter-layer Convection Theory—A Way Of Convective Heat Transfer Enhancement

With the operation of the equipment,temperature increase and heat accumulation have become an inevitable problem in refrigeration,aerospace,electronics and other fields.If the accumulated heat cannot be removed in time,the service life of the equipment will be shortened,and the efficiency of the equipment will be affected.Thus,heat transfer enhancement has become a key factor in recent research.Now,the research on convective heat transfer enhancement has developed a lot.The convection phenomenon ranges from natural convection to forced convection,from gas convection to fluid convection.Boiling and condensation are also common convection phenomena.When it comes to condensation heat transfer,there are two types of condensation:film condensation and dropwise condensation.With the continuous improvement of convective heat transfer,film cooling and spray cooling are put into use,which have effectively improved the efficiency and increased the service life of the equipment.Among these convection phenomena,greater heat transfer coefficient can be obtained in film convection and dropwise convection.It is an undisputed experimental conclusion,but few theoretical explanations are given.In this paper,differential methods are used to research on the means of heat transfer enhancement.The inter-layer convective heat transfer theory is established to enrich the theory system of convective heat transfer.The theory also provides a theoretical basis for elucidation of film heat transfer and dropwise heat transfer.First,the total differential of the average convective heat transfer coefficient is analyzed.The means of convective heat transfer enhancement are analyzed with the partial differential.The concept of inter-layer convection is put forward.The inter-layer convective heat transfer theory is established based on the traditional convective heat transfer theory.The significance of inter-layer convection theory is also presented in this paper by matching inter-layer convective heat transfer and the convection phenomena.This theory is used to explain the ways to strengthen convective heat transfer.Second,film inter-layer convective heat transfer is focused on.The reason of heat transfer enhancement of film inter-layer convective heat transfer is given with the inter-layer convection theory.It is found that the heat transfer effect of liquid film is better than that of gas film.The thermal resistance of film inter-layer convective heat transfer is also analyzed theoretically.The conclusion is obtained that the temperature of film inter-layer affects the thermal resistance and that with the development of inter-layer fluid,the thermal resistance will be larger and larger.In addition,the mechanism of the transition from film heat transfer to dropwise heat transfer is introduced.Third,dropwise inter-layer convective heat transfer is focused on.Based on the inter-layer convection theory,the mathematical model about the transition from film inter-layer convective heat transfer to dropwise inter-layer convective heat transfer is established.It is confirmed in theory that heat transfer coefficients for dropwise inter-layer convective heat transfer are larger than those for film inter-layer convective heat transfer and that the ratio can even be more than an order of magnitude.What's more,it can be concluded from theoretical analysis that relative to turbulent flow,laminar flow is the better situation to achieve the superiority of dropwise inter-layer convective heat transfer.Combined with the condensation of steam,the effects of the change of drop quantity on the advantage of dropwise convective heat transfer are shown by drawing an instance curve.Conclusions are obtained that when the drop quantity increases and the radius.decreases,the heat flux of dropwise inter-layer convection will be larger.