Study On Heat Transfer Performance Of Slit-type Heat Exchangers In Oscillating Flow At Cryogenic Temperatures

More attention is paid to the regenerative refrigerators from the fields of space technology,military and superconductivity industry,thanks to their high reliability and long life at cryogenic temperatures.However,these application occasions have many stringent requirements so that the refinement design of the regenerative refrigerators must be considered,bringing out great challenges in the design of refrigerator systems as well as the components for achieving high efficiency.This work is devoted to explore the heat transfer characteristics of the oscillating flow of compressible fluid in the flow path of the cold-end heat exchanger of a regenerative refrigerator.Considering that the traditional experimental correlations are generally based on the constant flow in a single direction or the ambient temperature environment,this work will mainly focus on the following research:1.Experimental study on the heat transfer characteristics of oscillating flow in heat exchangers at the temperature of liquid nitrogen.Based on previous experiment devices,the liquid nitrogen preheating heat exchangers are added to investigate heat transfer performance of slit type heat exchangers working above the liquid nitrogen temperature zone.The difference in the heat transfer performances between parallel plate and radiant plate slit-type heat exchangers was investigated,and then are compared with the previous normal temperature experimental results,the necessity of the experiment at the cryogenic temperatures and the optimized heat exchanger selections are therefore demonstrated.2.Numerical simulation on geometry discontinuity effect of parallel-plate heat exchanger performance in cryogenic oscillating flow.A 2-D computational fluid dynamics model was built to study the flow and heat transfer characteristics of parallel-plate heat exchangers working in oscillating flow with different entrance angles.With a working condition decided.the influences of entrance angle and initial temperature are numerically analyzed.The variation of heat transfer performance with cross-sectional parameter is emphasized.Results show that decreasing the flow entrance flange angle can balance the flow distribution,so that heat transfer is enhanced.This research helps to understand the variable cross-sectional area effect of heat exchanger performance in oscillating flow.3.Experimental platform construction and preliminary experiments of the oscillating flow and heat transfer characteristics at cryogenic temperatures.Based on the literature research and previous results,a research and test device for alternating heat transfer characteristics above 30K was designed and constructed.The influencing factors of cooling characteristics of this test device are studied by means of conduction only and conduction-convective,respectively.With the optimization in the operation of test facility,the feasibility of future experimental work can be ensured.