The Operation Of The Pulsating Heat Pipe And Heat Transfer

Running mechanism and heat transfer characteristics of pulsating heat pipe is studied in this paper .Effects of some factors are also investigated.And the heat transfer regularity is analysed preliminarily.First ,Flow of looped pulsating heat pipe was studied by a visualized experimental method in this work. When running stably, flow character of working fluid and typical phenomena in PHP was observed. And the relations between heat transfer rate and charging ratio, cooling, method, relative position of heating end and cooling end etc was investigated; On the basis of experimental result, some elemental problem about running of PHP was discussed and analyzed.In the experiment,nuclear boiling was not seen under most charging ratio.the power of working fluid circulation comes from the tempestuous expansion of vapor slugs flowing over heating end.In bottom heat mode ,most of the movement of working fluid is pulsating and one-direction circulating flow,not random reciprocal oscillating in certain straight pipe or U-shaped pipe.Under both air cooling and water cooling method,heat transfer rate achieves optimum at filling rate 35%. Compared with in bottom heating mode ,heat transfer performence is ratherly bad in side and top heat mode ,even fails to run.Temperature difference ,filling rate ,convection condition,ratio of heating and cooling part length,condition of inner surface of heat pipe ,etc have influence on stablity of running of PHP.To approaching actual application,after visualized experiment,runnmg and heat transfer of copper-water looped PHP under air cooling condotion is investigeted.Effect of filling rate,diameter, ratio of heating and cooling part length on heat transfer performence is studied.The optimum filling rate is the same with visualized experiment ,i.e.,about 35% .And PHP with smaller inner diameter has better performence. Effect of ratio of heating and cooling part length on heat transfer performenc is conspicuous,this indicates thermal resistence of PHP self is strongly relevant to outer conditions.Fluctuation of temperature of heat pipe wall at heating and cooling end is also recorded .Many anti-phase half waves and a few in-phase half waves are discoveredon the two curves,and also the regular phase relation of anti-phase half waves is obtained.Therefore three reasons of temperature fluctuation of heat pipe wall is analysed, anti-phase half waves are caused by oscillating and standstill in running of PHP. in-phase half waves are caused by rather big perturbation of outer condition.The unregular wave exists mainly because running of PHP is not uniform and constant, Otherwise heat transfer is different when vapor slug flowing over sampling points from liquid plug,minute perturbation is also contributed to it.At the end of this paper,the regularity of heat transfer is analysed preliminarily.Relationship of heat transfer rate and filling rate is obtained,as well as the relationship of velocity and inner diameter,filling rate.