A Novel Method For Enhancement Of Critical Heat Flux In The Process Of Boiling Heat Transfer

Nucleate boiling is an efficient heat transfer mechanism.It can achieve large heat flux transmission under a small heat transfer temperature difference.It is widely used in many industrial fields,such as various energy and power equipment,heat pump,refrigerator,boiler,etc.However,there is a critical value reached during nucleate boiling heat transfer called the critical heat flux(CHF).When the heat flux exceeds the critical heat flux,the heat transfer mechanism changes from the efficient nucleate boiling to the inefficient membrane state.At this time,the heat transfer surface is covered by the gas film,and the heat transfer deteriorates.Therefore,enhancing the critical heat flow density of the nucleate boiling can not only ensure the safe operation of the equipment,but also effectively reduce the size of the equipment.In order to improve the critical heat flux in boiling heat transfer,the researchers put forward different strengthening methods.In this paper,a new type of boiling heat transfer surface is proposed.The alternate temperature distribution of the heat transfer surface is made by using different thermal conductive materials.In the process of boiling heat transfer,the surfaces of different thermal conductivity are in different boiling regions.In this paper,a numerical simulation method is used to design the heat transfer surface of the bi-conductive surface.The experimental results show that the critical heat flux of the nucleate boiling on the new heat transfer surface is higher than the critical heat flux on the plain heat transfer surface.At the same time,the influence of different low thermal conductivity materials,the limited space of different sizes and the different ways of inlet liquid on the boiling heat transfer characteristics are also studied.It is shown that different sizes of the limited space gap,when the bubble separate from the boiling heat transfer surface,with the increase of the micro-channel gap,the drag force of boiling liquid on the heat transfer surface reflux decreases.The liquid can then be promptly added to the boiling heat transfer surface so the boiling heat transfer surface can maintain wet state,thereby improving the critical heat flux.In different heat transfer surface and different micro-channel gaps(compared to the liquid supplying from two directions),when bubbles separate from the liquid the surface,the liquid supplying from four directions is more likely to flow back to the boiling heat transfer surface,thus maintaining the wet state of the heat transfer surface.Therefore,the critical heat flux is higher than the critical heat flux of the two directions.When the low thermal conductivity material is PTFE,for different low thermal conductivity materials,it has larger temperature gradient on the heat transfer surface and different boiling regions are formed during the boiling process,so that the whole heat transfer surface can maintain the wetting state and the critical heat flux increases.