Numerical And Experimental Study On A Slug Flow Model Of Pulsating Heat Pipes With Hydrogen

Pulsating heat pipe(PHP)is a high efficiency heat transfer element.Owing to the pressure fluctuation caused by the phase change of internal working fluid,liquid slugs and vapor plugs in PHP move and transfer heat effectively.Cryocoolers have been widely used with the development of industries related to cryogenics.How to distribute the cooling power of the cold heads to a large surface(or a bulk space)?Cryogenic PHP provides an option to this issue.Considering the difficulties of visualization at cryogenic temperatures,it is useful to build a model to investigate the flow pattern and heat transfer characteristics of cryogenic PHPs.In this thesis,the following works on PHP with hydrogen has been carried out:1.In terms of the typical flow pattern,slug flow,in the closed loop PHP,a model is established by solving the equations of mass,momentum and energy conservation of liquid slugs and vapor plugs.Ethanol is used to verify the model.The heat flux calculated by the model is close to the experimental results.The following phenomenon is also obtained by the model,which indicates the effectiveness of the model:(1)seperation and merge of liquid slugs,(2)formation of new bubbles,(3)unidirectional flow and the change of the flow direction,and(4)oscillation of liquid slugs.2.The model is applied to the PHP with hydrogen(the lengths of adiabatic section La are 100 mm and 500 mm).The following results are obtained:(1)After the start-up process,working fluid in the PHP with hydrogen flow in a fixed direction.(2)Newly generated bubbles are unstable.3.Experimental investigation on the PHP with hydrogen(La=100 mm and 500 mm)is carried out.The results are as below:(1)The effective thermal conductivities from experiments are consistent with theoretical results when heat load Q is between 0.8 W and 2.8 W.It indicates the flow pattern is slug flow in this region.(2)When Q is the same,the temperature difference of the PHP with La=100 mm is similar to that of the PHP with La=500 mm.(3)The temperature difference will drop if condenser temperature Tc increases,which is consistent with the results calculated by the model.