Limin Qiu

Experimental study on a double-orifice two-stage pulse tube refrigerator

This paper describes the basic structure of a two-stage pulse tube refrigerator. A novel phase shifter termed a double-orifice is introduced. The machine was driven by a valved compressor and the on-off timing was controlled by a computer and solenoids. The lowest temperature of 3.1 K at the cold end of the second stage was achieved.

Performance improvement of a pulse tube cooler below 4 K by use of GdAlO3 regenerator material

Abstract The cooling power and coefficient of performance of a two-stage pulse tube cooler below 4 K have been increased greatly by using the newly developed ceramic magnetic regenerative material GdAlO 3 (GAP). Cooling powers of 200 mW at 2.8 K, 300 mW at 3.13 K, and 400 mW at 3.70 K have been achieved with a compressor input power of about 4.8 kW. The results show that the cooling power near 3.0 K increases by 150% compared to that of the same pulse tube cooler (PTC) employing only conventional HoCu 2 and ErNi regenerator materials.

Three-dimensional Computational Fluid Dynamics Modeling of Two-phase Flow in a Structured Packing Column

Abstract Characterizing the complex two-phase hydrodynamics in structured packed columns requires a powerful modeling tool. The traditional two-dimensional model exhibits limitations when one attempts to model the detailed two-phase flow inside the columns. The present paper presents a three-dimensional computational fluid dynamics (CFD) model to simulate the two-phase flow in a representative unit of the column. The unit consists of an entire corrugation channel and describes well the real liquid flow conditions. The detailed unsteady two-phase 3D CFD calculations on column packed with Flexipak 1Y were implemented within the volume of fluid (VOF) mathematical framework. The CFD model was validated by comparing the calculated thickness of liquid film with the available experimental data. Special attention was given to quantitative analysis of the effects of gravity on the hydrodynamics. Fluctuations in the liquid mass flow rate and the calculated pressure drop loss were found to be qualitatively in agreement with the experimental observations.

Two-stage pulse tube cooler for operation of a Josephson voltage standard near 4 K

Cryogen-free operation of Josephson voltage standards requires a low-noise cryocooler that provides a cooling power of 100 mW or less at 4.2 K, and about 1 W of precooling at an intermediate temperature near 70 K. Due to its intrinsic low level of mechanical vibrations a pulse tube cooler (PTC) appears to be a suitable candidate for such an application. In this work, a two-stage pulse tube cooler has been developed and optimized for cooling of a 1 V or 10 V Josephson voltage standard near 4 K. The performance of the PTC, which is driven by a compressor with a rated input power of 1.7 kW, is optimized under three different conditions. So far, a minimum temperature of 2.66 K and a maximum cooling power of 202 mW at 4.2 K with coefficient of performance (COP) of 1.15×10−4 have been achieved. The performance of the cryocooler is expected to fully satisfy the cooling requirement of the voltage standard. In addition, the experimental results are also compared with those obtained by driving the same cooler by us...

Valve timing effect on the cooling performance of a 4 K pulse tube cooler

Generally, a compressor together with a rotary valve system generates the pressure oscillation in GM-type cryocoolers. The timing of the rotary valve, which is one of the key operating parameters for cryocoolers, determines the relationship between intake and exhaust processes. A systematic investigation of valve timing effects on cooling performance of a two-stage 4 K pulse tube cooler (PTC) is reported. The experiments show that the optimization of valve timing can considerably improve the cooling performance for both stages. For the same PTC, a performance comparison for operation on different compressors with various input powers ranging from 0.5 to 6.0 kW is also presented.

Thermoacoustic compression based on alternating to direct gas flow conversion

We present a remarkable thermoacoustically driven compression effect based on the conversion of gas flow from an alternating state to a direct state. The alternating gas flow is generated by the thermoacousticeffect in thermoacoustic engines, whereas direct gas flow is achieved by means of the flow rectification effect of check valves. A demonstrative thermoacousticcompressor consisting of two standing-wave thermoacoustic engines, two reservoirs, and three check valves is constructed for experimental investigation. With nitrogen as a working gas and an initial pressure of 2.4 MPa in all components, a usable pressure difference of 0.4 MPa is achieved, with the average gas pumping rate reaching 2.85 Nm3/h during the first 3 s of the compression process. The simple mechanical structure and thermally driven nature of the compressor show potential in gas compression, power generation, and refrigeration applications.

STUDY ON A SINGLE‐STAGE 120 HZ PULSE TUBE CRYOCOOLER

Miniaturization of pulse tube cryocoolers is required for some particular applications where size and mass for devices are limited. In order to pack more cooling power in a small volume, higher operating frequencies are commonly used for Stirling‐type pulse tube cryocoolers. To maintain high efficiency of the regenerator with a higher frequency, a higher charging pressure, smaller hydraulic diameters of regenerator material and a shorter regenerator length should be applied. A rapid growth of research and development on pulse tube cryocoolers operating at a high frequency over 100 Hz in the last 3 years has occurred.In this study, a single stage pulse tube cryocooler with 120 Hz to provide 10 W of lift at 80 K has been developed by using the numerical model, known as REGEN 3.2. Experiments performed on this cryocooler driven by a CFIC linear compressor show that a no‐load temperature of 49.6 K was achieved and the net refrigeration power at 78.5 K was 8.0 W. The effect of pulse tube orientation was tested...

A Mathematical Model for Designing Optimal Shape for the Cone Used in Z-flow Type Radial Flow Adsorbers

Abstract Nonuniform flow distribution along the radial direction usually exists in a Z-flow type radial flow adsorber, which will decrease the utilization of adsorbent and the switching time and may result in operating safety problems in cryogenic air separation. In order to improve the uniformity of the flow distribution along the radial direction in the adsorber, a differential equation is derived through pressure drop analysis in the Z-flow type radial adsorber with a cone in the middle of the central pipe. The differential equation determines the ideal cross-sectional radii of the cone along the axis. The result shows that the cross-sectional radius of the cone should gradually decrease from 0.3 m to zero along the axis to ensure that the process air is distributed uniformly in the Z-flow type radial flow adsorber and the shape of the cone is a little convex. The flow distribution without the cone in the central pipe is compared under different bed porosities. It is demonstrated that the proposed differential equation can provide theoretical support for designing Z-flow type radial flow adsorbers.

Modification test of staged pulse tube refrigerator for temperatures below 4 K

Structure modification tests of a staged pulse tube refrigerator have been carried out for the purpose of increasing the performance and simplicity. The influence of operation parameters on cooling effect has been tested. To reach liquid helium temperatures by a two-stage pulse tube refrigerator, a double-orifice configuraton is utilized for enhancing the phase shift effect. Experimental results and a discussion are also presented.

Investigation on Gedeon Streaming in a Traveling Wave Thermoacoustic Engine

Introducing feedback path, traveling wave thermoacoustic engines realize relatively higher efficiency in thermoacoustic conversion. However, the toroidal topology allows acoustically induced streaming, which can seriously degrade performance of traveling wave thermoacoustic engines. With measurements of pressure and temperature distributions as effective approaches, four methods were applied to study the streaming in the thermoacoustic engine. The effects of Gedeon streaming on the temperature profile, the pressure ratio, and the thermoacoustic conversion efficiency of the engine were experimentally investigated. Experiments show that the performance of the engine can be remarkably improved with efficient streaming suppression. When Gedeon streaming is suppressed completely, maximal pressure ratio of 1.302 with nitrogen at 1.57 MPa as working gas and the maximal pressure difference of 0.63 MPa with working pressure at 2.54 MPa were obtained. This research is of importance for further understanding the mec...