Influences Of Normalizing Pretreatment On The Pulsating Heat Pipe

Pulsating heat pipe(PHP)is a kind of wide application prospect of the new cooling element.Start-up time is one of the most important indexes for evaluating heat transfer performance of pulsating heat pipe and is also a hot spot in the field in the direction of the PHP content,which is closely related to the surface structure and working medium wettability of tube inner wall.It is an technological innovation to improve the PHP start performance that treat tube by heat treatment to improve the surface structure.Researching the influence on the PHP start properties by the normalizing and annealing pretreatment process is of great significance.In this article,through the experiment to contrast and research the influence rule of the normalizing and annealing heat treatment process for PHP start and heat transfer performance.The main research contents and results are as follows:1.The experimental study of the heat treatment process influence on PHP tube wall surface properties.Main work includes: 1)Respectively used oxyacetylene normalizing,brazing furnace normalizing,500? muffle furnace annealing keeping 5 hours and 480? muffle furnace annealing keeping 9 hours these four kinds of heat treatment process for PHP to treat the PHP.2)The structures of the inner wall of copper tube prepared by these four processes were observed by the 3D laser confocal microscope and their structure and working medium wettability of inner wall were investigated comparing with the PHP without treatment.3)Improved the semi-quantitative test method about using contact Angle measurement instrument test concave surface wettability,then studied the law of normalizing and annealing these four heat treatment processes' function for the wettability of anhydrous ethanol on the copper tube surface.Found : 1)By observing the change of the structure and working medium wettability of inner wall treated by using oxyacetylene normalizing,brazing furnace normalizing,500?muffle furnace annealing keeping 5 hours and 480 ? muffle furnace annealing keeping 9hours these four ways with that of without treatment PHP,the structures of treated inner wall changed obviously which was significantly related to the pretreatment processes and conditions,that obviously copper pipe inner surface become rough and the wall surface structure become black crystal covered by ravines and wall color obviously deepened.2)The wettability of anhydrous ethanol on the tube wall has been improved significantly after treated by oxyacetylene normalizing,brazing furnace normalizing,500? muffle furnace annealing keeping 5 hours and 480? muffle furnace annealing keeping 9 hours these four ways.2.The experimental study on the PHP start and heat transfer performance.The performance comparison test bench set up that the same geometric parameters pulsating heat pipe as the object and the oxyacetylene normalizing treatment with untreated pipes as pulsating heat pipe tube bodies with the anhydrous ethanol as working medium at50% liquid rate at the bottom of the vertical heating.Under the conditions of the differentheating power 30 w,40 w,50 w,60 w,70 w,80 w,90 w,observes the change of the start-up performance and heat transfer resistance of pulsed heat pipe with the oxyacetylene normalizing treatment and without treated.The following conclusions can be drawn from the analysis of the experimental data.1)The results reveal that oxyacetylene normalizing treatment of pulsating heat pipe start-up time is less than the untreated.In addition,the start-up time could be reduced especially at the lower heating power.When the heating power is 30 W,the start-up time is reduced by the 74 s in comparison to the PHP without treatment.2)The comparison results of the minimum starting power reveal that the minimum starting power of the oxyacetylene normalizing treatment of pulsating heat pipe is 17 W that is 13 W less than 30 W that of untreated pulsating heat pipe,fell by 43%.3)The results reveal that oxyacetylene normalizing treatment of pulsating heat pipe start-up temperature is lower than that of untreated,basically a difference of around 10 ? which the maximum reduction can achieve 19.5 ?.4)The comparison results of the heat transfer resistance reveal that oxyacetylene normalizing treatment of pulsating heat pipe heat transfer resistance is significantly lower compared with the untreated,basically fell by about 30% that the highest fell by 35.5%.3.The influence of inner surface properties on the start-up procedure of PHP was analyzed theoretically.The structure of treated inner wall and the wettability of anhydrous ethanol on the tube wall has been improved treated by oxyacetylene normalizing,brazing furnace normalizing,500? muffle furnace annealing keeping 5 hours and 480? muffle furnace annealing keeping 9 hours these four ways which results in that the adhesion between the bubble and the inner wall and the difficulty of bubble generation and detachment in startup stage is reduced so that can shortens the pulsating heat pipe start-up time and improves pulsating heat pipe startup performance.