Experimental Study On Bubble Behavior In Three-sided Heated Narrow Rectangular Channel

Narrow rectangular channels are widely used in nuclear power system,microelectronic cooling system and spacecraft cooling system because of their compact structure and high heat transfer efficiency.The bubble behavior in narrow rectangular channel has become a research hotspot in recent years because of its different geometric size limitation from that in conventional channel.At present,a lot of research has been done on the bubble behavior in single-sided heating channel.However,the heat flux density in narrow corner of narrow rectangular channel heated in practice is large and the mutual disturbance of thermal boundary layer occurs complex.The behavior of miscellaneous bubbles is different from that of one-sided heating channel.Therefore,the behavior of bubbles in one-sided heating channel can not be simply used to simulate the behavior of bubbles at the corner of a narrow rectangular channel.Based on this,the experiment section of three-sided heating narrow rectangular channel is selected to conduct in-depth research on the behavior of bubbles at the corner of narrow rectangular channel by image processing analysis method.By observing the experimental phenomena of bubble behavior,the basic characteristics of single bubble growth process in narrow rectangular channel heated on three sides are classified and summarized.The results show that four types of typical bubble behavior are found: bubbles at narrow edges in narrow rectangular channel can be divided into three categories: buoyancy,aggregation and continuous growth,and only one type of single bubble growth can be observed on the middle heating surface.Compared with the traditional one-sided heating surface,the bubble detachment diameter at the narrow edge is larger and the deformation of the bubble is more obvious.At high supercooling,the bottom of the bubble begins to deform,and at medium supercooling,the bottom and top of the bubble deform in varying degrees,while at low supercooling,the growth of the bubble keeps the same shape.A quantitative analysis of the behavior characteristics of bubbles at narrow corner is carried out.The results show that the density of vaporization core is U-shaped in the whole narrow rectangular channel.Under different working conditions,the density of vaporization core is mainly affected by wall superheat and horizontal position.The diameter of bubble detachment is mainly affected by wall superheat,mainstream supercooling and mass flow velocity.The detachment frequency is mainly related to the wall superheat.The experimental results are compared with the conventional size channel model and the narrow rectangular channel model with one side heating.It is found that the experimental results are not applicable to the existing models.Based on the factors affecting the dynamic parameters of the bubble,the prediction formula of the bubble behavior at the narrow corner is proposed.Compared with the experimental results,the errors are within 30%.