Gifford-McMahon Cryorefrigerator Research Articles

Thermo-hydrodynamic analysis and optimal design of a GM cycle cryorefrigerator using response surface methodology and particle swarm optimization

In this investigation, the response surface methodology is implemented to analyze the influences of high and low pressure of the compressor, frequency and waiting time of the rotary valve on the cooling capacity and COP of Gifford-McMahon (GM) cryorefrigerator. A one-dimensional numerical model based on finite volume discretization method (FVM) of the governing equations is employed to calculate the cooling capacity and COP of the Gifford-McMahon cryorefrigerator. Analysis of variance (ANOVA) is performed to visualize the impact of the aforementioned input parameters on both cooling capacity and COP. Finally, the particle swarm optimization (PSO) method is opted to optimize the regression equations so obtained from the response surface analysis, to maximize the cooling capacity and COP of the Gifford-McMahon cryorefrigerator. Results reveal that both COP and cooling capacity are not able to produce maximum performance at a particular combination of those input parameters. At a lower pressure ratio, the COP is maximum, while at a higher pressure ratio the cooling capacity is maximum. Furthermore, at a nominal value of waiting time, the cooling capacity is maximum and a higher value of waiting time the COP is maximum. It is observed that, after optimizing the parameters by PSO, the cooling power increases by 11.3% and COP increases by 6.43%.

The characteristics of a 4 K Gifford-McMahon cryocooler with a second stage-regenerator packed with cenospheres

Designing efficient Gifford- McMahon (GM) cryocoolers that would allow cooling to temperatures below 4.2 K is considered an important step in the development of helium temperature technologies. Modern two-stage GM machines ensure cold production up to 4.2 K, but with relatively low efficiency, due mainly to the low heat capacity of the material used for the second-stage regenerator packing of GM machines. Two urgent problems are solved, in order to create 4 K GM cryocoolers: the non-stationary heat exchange processes in GM regenerators are described; the efficiency indicators of a GM second-stage regenerator based on cenospheres filled with helium are identified. A comparative analysis of the various types of regenerator packing, which make it possible to obtain temperatures below 4.2 K, is performed, and the advantages of helium-filled cenosphere packing are substantiated. The operation of a two-stage GM cryorefrigerator with a cooling capacity of 0.2 W at a temperature level of 4.2 K is analyzed using the wave approach to regenerator modeling. It is shown that the GM machine can be improved by using a regenerator filled with cenospheres in its second stage.

Compact Design of Cryogen-Free HTS Magnet for Laboratory Use

A compact high temperature superconductor magnet cooled by a single stage Gifford-McMahon cryorefrigerator was designed, manufactured and tested. The arrangement of the magnet was optimized to maximize cooling efficiency of the Bi2223/Ag winding and minimize the heat generation by eddy current losses during high-speed excitation. To achieve wide angular access and adequate magnetic field homogeneity in the magnet center a split-pair coil configuration was used. Maximum magnetic field in the magnet center is 1.8 T @ 14.5 K, inner diameter of the magnet winding is 50 mm, outer diameter is 98 mm and total width of the magnet winding including 14.2 mm air-gap is 72 mm. Performance of the magnet was tested also at liquid nitrogen, sub-cooled liquid nitrogen and liquid helium temperatures. New vacuum cryostat system with a free access to the magnet space was designed and manufactured. Calculations of the magnet behavior with iron poles were evaluated and compared with the magnet without iron. Experimental results agree well with the magnet parameters obtained by FEM simulation

Effects of drive rotation speed on cold production and startup period in a Gifford-McMahon cryorefrigerator with slide valve gas distribution

Studies have been done on a one-stage microcooler in a Gifford-McMahon cryorefrigerator with a gas distribution mechanism including a rotating slide valve.

Theoretical analysis of a dynamically balanced Gifford-McMahon cryorefrigerator

A non-linear model describing the dynamics, fluid dynamics and thermodynamics of a dynamically balanced Gifford-McMahon (G-M) cryorefrigerator has been developed. The cryorefrigerator consists of two horizontally opposed first- and second-stage displacers, a first- and a second-stage thermal regenerator, and a rotary valve that cycles the compressor supply gas pressure. The model accurately describes the motion of the displacers and the refrigeration produced at the two stages of the cold head. The analytical model consists of a set of twelve first order non-linear differential equations. The numerical solution of the system is presented in the form of pressure histories in each chamber, position and velocity histories of each displacer and P-V diagrams of the two stages of the cold head. The performance of the cryorefrigerator is calculated under various conditions. It is clearly shown that the device can achieve non-impacting displacer motion with sufficient cooling capacities of the two stages. This nonimpacting operation creates a very low vibration device, which is valuable in applications where low vibration is required, such as magnetic resonance imaging (MRI) systems. It was also shown that the cooling capacity of the device can be optimized over the operating frequency.

Experimental study of two-stage Gifford-McMahon Cryorefrigerator

ABSTRACT Experimental results of two-stage Gifford-McMahon cryorefrigerator are described. In prototype experiments, drive mechanism is Scotch Yoke type driven by stepping motor. Copper meshes and lead balls are used for regenerator's materials in the first stage and in the second stage, respectively. To find optimal conditions of the cryopump, no load temperature and refrigeration capacity according to the variation of cycle frequency and operating pressure are measured, and the cool down and load characteristics at partiular cycle frequencies are presented. In general, as the cycle frequency is lowered, no load temperature is dropped but refrigeration capacity is diminished. As the representative result, in a case that the cycle frequency is 70 rpm and steady state pressure is 14 atm, no load temperature of the second stage is lowered to 9.5 K in 55 minutes, and in this situation the refrigeration capacity of the first stage is 42 W at 80 K, that of the second stage is 11 W at 20 K.

Dynamic modelling of a Gifford-McMahon cryorefrigerator

The dynamic characteristics of a pneumatically driven Gifford-McMahon cryorefrigerator are modelled when the cryorefrigerator is operating in the steady state regime. The mathematical model, which includes dynamic, fluid dynamic and thermodynamic effects, consists of a set of six simultaneous differential equations. The model variables were determined to be the gas masses in the various chambers of the cryocooler's two stages, and the displacer's position and velocity. The non-linear time-varying system of differential equations is solved by numerical integration routines that use the Adams - Moulton method with an adaptive integration step size and a user specified tolerance. A direct comparison of the algorithm predicted results and actual experimental data indicates that the algorithm models the trends of the physical phenomena in an accurate fashion.

Parametric analysis and optimization of a Gifford - McMahon cryorefrigerator

A parametric analysis was carried out in order to examine the effect on the cooling capacities of the two stages of a commercial pneumatically driven cryorefrigerator, caused by a variation of several design parameters of the cryorefrigerator. The analysis was performed by using a previously developed algorithm that modelled the dynamic characteristics of a pneumatically driven Gifford-McMahon cryorefrigerator, in the form of first-order partial differential equations. In addition, a state of the art optimization design approach is presented, which maximizes the capacities of the two stages by calculating the optimal values of the critical design parameters that minimize an appropriate objective function.