Numerical Modeling of the Performance of R22 and R290 in Adiabatic Capillary Tubes Considering Metastable Two-Phase Region——Flow Characteristics and Parametric Analysis of R22 and R290

Characteristics of R22 and its new alternative refrigerant R200 flowing through adiabatic capillary tubes are investigated based on the homogeneous model. Extensive flow variables along tube length such as pressure, temperature, viscosity, velocity. Reynolds number, friction factor and vapor quality etc are compared between the two fluids under the same operating condition. Two cases are considered, namely, either the same tube length or the same mass flow rate as inlet condition. The results show that the mass flow rate in the capillary tube of R290 is 40% lower than that of R22 due to the differences of physical properties between the two fluids. Further. a parametric analysis is performed and it appears that effects of geometric and thermodynamic parameters on mass flow rate of R290 are weaker than that of R22. When the condensing temperature is increased from 40℃ to 50℃ C. the mass flow rate for R22 is increased by 16%. while the increasing rate for R290 is 13%.

Experimental Investigation of a Single-Stage Four-Valve Pulse Tube Refrigerator

In order to simplify the structure of the cold end of the pulse tube refrigerator (PTR) and have a better utilization of the cold energy of the system, a one-stage four-valve pulse tube refrigerator (FVPTR) with an "L" type pulse tube structure and two orifice valves at the hot end of pulse tube has been constructed. Verification experiments show that the two orifice valve structure performs better than one orifice valve structure. A lowest temperature of 67.5 K was obtained at a frequency of 2.5 Hz under a system average pressure of 1.5 MPa with 200 mesh bronze screens as regenerator material, 80 mesh copper screens as stuffing material of heat exchanger. Due to the difficulty in manufacturing the thin "L" type pulse tube, the wall thickness of the pulse tube in the experiment was relatively difficult for us to reach 0.5 mm as that of the ordinary pulse tube, which resulted in relatively big system loss and affected the minimum temperature of the system to some degree.

Energy distribution between liquid hydrogen and liquid oxygen temperatures in a Stirling/pulse tube refrigerator

A two-stage gas-coupled Stirling/pulse tube refrigerator(SPR),whose first and second stages respectively involve Stirling and pulse tube refrigeration cycles,is a very promising spaceborne refrigerator.The SPR has many advantages,such as a compact structure,high reliability,and high performance,and is expected to become an essential refrigerator for space applications.In research regarding gas-coupled regenerative refrigerator,the energy flow distribution between the two stages,and optimal phase difference between the pressure wave and volume flow,are two critical parameters that could widely influence refrigerator performance.The effects of displacer displacement on the pressure wave,phase difference,acoustic power distribution,and inter-stage cooling capacity shift of the SPR have been investigated experimentally.Notably,to obtain the maximum first-stage cooling capacity,an inflection point in displacement exists.When the displacer displacement is larger than the inflection point,the cooling capacity could be distributed between the first and second stages.In the present study,an SPR was designed and manufactured to work between the liquid hydrogen and liquid oxygen temperatures,which can be used to cool small-scale zero boil-off systems and space detectors.Under appropriate displacer displacement,the SPR can reach a no-load cooling temperature of 15.4 K and obtain 2.6 W cooling capacity at 70 K plus 0.1 W cooling capacity at 20 K with 160 W compressor input electric power.

Dynamic Experimental Study of a Multi-bypass PulseTube Refrigerator with Two-bypass Tubes

A dynamic experimental apparatus to measure the instantaneous velocity and pressure in the multi-bypass pulse tube refrigerator (MPTR) was designed and constructed. Some theortant experimental results of the instantaneous measurements of the velocity and the pressure in the MPTR with two-bypass tubes during actual operation are presented. The effects of the middle-bypass version on the dynamic pressure and mass flow rate at the cold end of the pulse tube are evaluated from experimental measurements.DC-flow phenomena are observed in this MPTR. The reasons of the multi-bypass version improved the performance of pulse tube refrigerator are given.

Advance in research of several types of streaming of pulse tube refrigerators

The pulse tube refrigerator （PTR） is a promising small-scale cryocooler. This paper first briefly introduces the history of the pulse tube refrigerator. It has pointed out that technology improvements and theoretical developments of the pulse tube refrig- erator closely relate with the internal streaming effects. Then the discovering history and classification of the streaming or DC （direct current） flow effect are summarized. It proposes for the first time that the physical significance of the streaming con- tains the driving mechanisms and the transport mechanisms. It demonstrates that the driving mechanisms are the asymmetry of fluid flow and temperature while the transport mechanisms are a loop or vorticity, which transmits nonlinear dissipations. The important advancements have been made over the past two decades all over the world in research of streaming of the pulse tube refrigerator including Gedeon DC flow, Rayleigb streaming, the third type of DC flow and the regenerator circulation. With regard to Gedeon DC flow, theoretical and experimental analyses have been made and different suppression methods are summarized. In the aspect of Rayleigh streaming, it mainly focuses on the analytical solution of the second-order mass flow and the research of tapered pulse tubes. In particular, limited research on the third type of DC flow and regenerator circulation is presented. The experimental measurement techniques of streaming also are summarized. Finally, this paper briefly discusses the key scientific and technical issues of the current research, and foretells the future development trends of streaming research in PTR.