Performance Of Pulse Tube Refrigerator Research Articles

Multi-dimensional flow simulation analysis and kriging-based optimization study on thermodynamic process mechanism of pulse tube refrigerator with displacer

Pulse tube refrigerators with active displacers have become increasingly popular due to superior phase shift capability and avoidance of dissipation losses. However, mechanisms of thermodynamic processes within refrigerators due to variations in parameters related to critical structures and operations are not yet clear, making it difficult to optimize the comprehensive performance. In this paper, multi-dimensional flow simulation method instead of one-dimensional simulation method with poor computational accuracy is used to analyze the influence of five key parameters on performance of pulse tube refrigerators with active displacers. An intelligent optimization algorithm combined with efficient Kriging surrogate models is developed for single-objective and multi-objective optimization. Results demonstrate that the mean errors of the Kriging models for cooling capacity, total input power and performance coefficient are 1.81%, 3.94% and 3.37%. The single-objective optimization produces a maximum cooling capacity of 7.29 W and performance coefficient of 7.38%. The combined optimal solution delivers 6.65W in cooling capacity and 7.02% in performance coefficient, obtaining improvements of 150.94% and 75.94%. This study reveals the influence mechanism of key parameters on cooling performance of pulse tube refrigerators with displacers and establishes an efficient global optimization method, which is of great significance for the development of advanced refrigeration technology.

Multi-Objective Parameter Optimization of Pulse Tube Refrigerator Based on Kriging Metamodel and Non-Dominated Ranking Genetic Algorithms

Structure parameters have an important influence on the refrigeration performance of pulse tube refrigerators. In this paper, a method combining the Kriging metamodel and Non-Dominated Sorting Genetic Algorithm II (NSGA II) is proposed to optimize the structure of regenerators and pulse tubes to obtain better cooling capacity. Firstly, the Kriging metamodel of the original pulse tube refrigerator CFD model is established to improve the iterative solution efficiency. On this basis, NSGA II was applied to the optimization iteration process to obtain the optimal and worst Pareto front solutions for cooling performance, the heat and mass transfer characteristics of which were further analyzed comparatively to reveal the influence mechanism of the structural parameters. The results show that the Kriging metamodel presents a prediction error of about 2.5%. A 31.24% drop in the minimum cooling temperature and a 31.7% increase in cooling capacity at 120 K are achieved after optimization, and the pressure drop loss at the regenerator and the vortex in the pulse tube caused by the structure parameter changes are the main factors influencing the whole cooling performance of the pulse tube refrigerators. The current study provides a scientific and efficient design method for miniature cryogenic refrigerators.

Numerical simulation of a two‐stage pulse tube refrigerator based on adiabatic model

AbstractCryocoolers are devices that are capable of achieving and maintaining cryogenic temperatures for a number of applications such as high‐energy physics, cooling of superconducting magnets, sensors, high‐vacuum production, cryotronics, cryonics, and so on. All the above applications need coolers with high reliability, efficiency, low maintenance, and low cost. The absence of moving parts at the cryogenic temperatures makes the pulse tube (PT) coolers quite suitable for the above applications. In spite of considerable developments in the area of PT cryocoolers, many of the fundamental processes responsible for the cold production are not fully understood. In this work, we present the results of numerical simulations of two‐stage pulse tube refrigerators (PTR) using adiabatic flow of gas through the pulse tube system. A two‐stage PTR is the improved version of single‐stage system to achieve temperature close to 4 K. Assuming adiabatic gas flow through PTs, the algebraic equations for pressure, mass flow, and volumes at different locations have been derived and solved by a MATLAB based program. Using the above, the performance of PTR has been optimized for different operational parameters. The cooling powers predicted by the model have been compared with the experimental data, and they are in good agreement with each other.

Impact of coiled type inertance tube on performance of pulse tube refrigerator

An inertance tube is widely used to provide a phase shift between mass flow and pressure wave in pulse tube refrigerator (PTR). The inertance tube is usually coiled around the outer surface of a liner compressor or in a reservoir to reduce installation space. The performance of PTR is strongly influenced by different coiled types of inertance tube. Based on 1-D model (DeltaEC) and 3-D model (CFD), a coupling model is proposed to simulate the cooling performance of a PTR. The characteristics of phase shift and energy flow in the PTR are also analyzed in detail. The simulation results show that the phase shift ability of inertance tube would decrease while increasing the number of coiling turns, which would cause the increase of average mass flow rate within the regenerator. Therefore, more PV power would be consumed for the same cooling capacity. In order to improve the cooling performance of the PTR, it is necessary to adjust the length of the inertance tube when it is coiled. At last, the simulation results are verified by the test results.

Numerical and experimental characterization of the inertance effect on pulse tube refrigerator performance

A synergistic investigation of numerical and experimental studies is reported to elucidate the effects of the inertance tube length and diameter on the flow physics and the performance of a single stage inertance pulse tube refrigerator (IPTR). A time-dependent axisymmetric compressible computational fluid dynamic (CFD) model of the IPTR is used to predict its performance. The phase relationships between the pressure and the mass flow in the regenerator, pulse tube and inertance tube regions and the performance of the system are determined from the numerical simulations. The predictions from the computational model show that the phase angle difference between the pressure and the velocity at the center of the regenerator is the minimum and the pressure amplitude is the maximum at the optimum inertance value that leads to the largest acoustic power. In the experimental studies, the effect of inertance is studied for tubes of two different diameters and various lengths. The effect of input power supplied to the PTR on its performance was also studied. The experimental results complement the observations from the numerical simulations.

Study on Flow Properties of Straightener in Pulse Tube Refrigerator with Numerical Simulation

The straightener of pulse tube refrigerator (PTR) can change gas flow distribution in the tube and improve performance of PTR .In this paper numerical simulation is used to study and optimize the property parameters of straightener with helium as work fluid. The straightener is treated as porous media. The key parameter fk. is defined as the ratio of streamwise and transverse permeabilities. The smallest length of straightener is optimized by changing the value of fk. The result shows that straightener can change gas flow distribution in tube and improve performance of PTR. fk. is bigger, the length of straightener is shorter and streamwise pressure drop is smaller.

Design of compact phase controller for pulse tube refrigerator

A compact phase controller of pulse tube refrigerator is proposed in this paper. Most pulse tube refrigerators available now consist of a long inertance tube and reservoir as the phase controller. The long inertance tube and reservoir present a challenge for compact packaging in some applications. To overcome this disadvantage, the long inertance tube and reservoir are replaced with the compact phase controller consisted of mass, spring and damper in pulse tube refrigerator. This process is achieved using similarity of mechanical, electrical, and acoustic system and the specific configuration of the compact phase controller is designed. From the simulation code in this paper, the performance of pulse tube refrigerator with the designed compact phase controller is confirmed to be comparable to pulse tube refrigerator with the long inertance tube and reservoir.

Effect of pulse tube volume on dynamics of linear compressor and cooling performance in Stirling-type pulse tube refrigerator

In a Stirling-type pulse tube refrigerator (PTR), the pulse tube volume affects the dynamic behavior of a linear compressor as well as the cooling performance of PTR. In this study, PTRs which have different pulse tube volume are tested and simulated. The simulation code is verified with the experimental measurement of piston displacement, pressure wave, input power and cooling capacity. And then, the power transfer from the electric power input to the cooling capacity is explained with the simulation results. The smaller pulse tube increases the resonant frequency of a linear compressor and suppresses the piston motion because it imposes larger gas spring effect and also larger gas damping effect to the piston. The smaller one allows larger power transfer from electric power to expansion PV work despite the smaller piston displacement, but shows less cooling capacity due to larger thermal losses.

CFD analysis of high frequency miniature pulse tube refrigerators for space applications with thermal non-equilibrium model

High frequency, miniature, pulse tube cryocoolers are extensively used in space applications because of their simplicity. Parametric studies of inertance type pulse tube cooler are performed with different length-to-diameter ratios of the pulse tube with the help of the FLUENT (R) package. The local thermal non-equilibrium of the gas and the matrix is taken into account for the modeling of porous zones, in addition to the wall thickness of the components. Dynamic characteristics and the actual mechanism of energy transfer in pulse are examined with the help of the pulse tube wall time constant. The heat interaction between pulse tube wall and the oscillating gas, leading to surface heat pumping, is quantified. The axial heat conduction is found to reduce the performance of the pulse tube refrigerator. The thermal non-equilibrium predicts a higher cold heat exchanger temperature compared to thermal equilibrium. The pressure drop through the porous medium has a strong non-linear effect due to the dominating influence of Forchheimer term over that of the linear Darcy term at high operating frequencies. The phase angle relationships among the pressure, temperature and the mass flow rate in the porous zones are also important in determining the performance of pulse tuberefrigerator.

A new computational model for entire pulse tube refrigerators: Model description and numerical validation

In present paper, a new modeling approach for the performance of pulse tube refrigerator is proposed. The new approach combines one-dimensional and two-dimensional models (1-D and 2-DCC model) together, and can be used to simulate the fluid flow and heat transfer processes of the basic type, orifice type and double-inlet type pulse tube refrigerators (PTRs). With the present model, the complicated fluid flow and heat transfer characteristics in the PTR system can be efficiently depicted and the computational time can be greatly reduced. Then based on the approach, the distribution characteristics of the flow and temperature fields of the three types of PTR are numerically analyzed. The complicated fluid flow and heat transfer phenomena in PTR, such as DC flow, velocity and temperature annular effects are presented vividly. The numerical results show that the 1-D and 2-DCC model is reliable and practical, which can be used to explore the physical mechanism of the thermodynamic processes of the PTR system and optimize the design of the PTR system and its components.

Two-dimensional numerical simulation and performance analysis of tapered pulse tube refrigerator

Numerical simulation of two-dimensional viscous compressible oscillating flow was carried out for the uniform cross-section and tapered pulse tubes. Based on the numerical results, it was found that for the taper pulse tube refrigerator, there was an optimum taper angle, with which the performance of a cryogenic refrigerator can be greatly improved. However, on the other hand, the results also demonstrated that when the taper angle becomes much larger than this optimum value, the cooling performance becomes weaker than that of the circular tube. We discussed the effect of the tapered pulse tube on the performance of pulse tube refrigerator based on an evaluation of the secondary flow in the pulse tube. It was found that in comparison with the uniform cross-section pulse tube, the magnitude of the secondary flow in the tapered pulse tube decreases while its distribution becomes less uniform, which explains why the performance of the tapered pulse tube can be improved compared with the uniform cross-section pulse tube.

Experimental research of Stirling type pulse tube refrigerator with an active phase control

A Stirling type pulse tube refrigerator with an active phase control has been experimentally investigated. A phase shifter, which controls the phase angle between the mass flow and the pressure inside a pulse tube, plays a key roll in the performance of pulse tube refrigerators. In this study, an electrically driven and mechanically damped linear compressor, which is directly connected at the warm end of the pulse tube using a connecting tube, is used as the active phase controller (APC). Therefore, this active phase control pulse tube refrigerator (APCPTR) has no reservoir. Amplified electric signals of a function generator are supplied to both the main linear compressor, which is used as the pressure wave generator (PWG), and the APC. The type of these two linear compressors is a dual-opposed piston. The advantage of this phase sifter is easy to control the electric input power and the phase angle between the PWG and the APC. In order to clarify the characteristics of the APCPTR, the cold end temperature and the gas pressure have been measured.

Refrigeration performance enhancement of pulse tube refrigerators with He–H 2 mixtures and Er 3NiH x regenerative material

The computation with heat transfer, fluid flow and thermodynamics indicates that higher pulse tube refrigeration performance can be achieved with He–H 2 mixtures as working fluids than that with pure He in the cooling temperature region of 30 K. In addition, it is found that Er 3Ni, a regenerative material, is able to absorb H 2 and forms Er 3NiH x . The hydrogen absorption capacity of Er 3Ni is about 3.5 H/Er 3Ni in the H 2 pressure region of 0.1–2.0 MPa at 30 °C. The calculation shows that the regenerative performance of Er 3NiH 3.5 is better than that of Er 3Ni due to its higher volume specific heat. Experimental results show that the pulse tube refrigeration performance in 30 K cooling temperature region is obviously enhanced with He–H 2 mixtures and Er 3NiH x regenerative material.

He-H2 mixture and Er3NiHx packing for the refrigeration enhancement of pulse tube refrigerator

The computation with the theory of modified Brayton Cycle indicates that higher cooling power and coefficient of performance for a pulse tube refrigerator can be achieved with He-H2 mixture as working gas than those with pure He in the temperature region of 30 K. In addition, it is found that Er3Ni, a regenerative material, is able to absorb H2 and produces Er3NiHx. The computation presents that the regenerative performance of Er3NiHx is better than that of Er3Ni due to its higher volume specific heat. Experimental results show that the pulse tube refrigeration performance in 30 K temperature region is enhanced greatly with He-H2 mixture and Er3NiHx packing.

Improvement of the thermal performance of pulse tube refrigerator by using a general principle for enhancing energy transport and conversion processes

In engineering fields there are such energy transport and/or conversion processes in which the resulting quantity is expressed by the dot production of two vectors. For such processes, the reduction of the intersection angle (or phase angle shift) between the two vectors is the most fundamental way for enhancing the processes (field synergy principle). For a pulse tube refrigerator (PTR) its cooling capacity at the hot end is shown to be proportional to the dot production of velocity vector and pressure vector. Detailed numerical analyses are conducted for the PTR to reveal the variation of its cooling capacity with the phase angle shift between the velocity wave and pressure wave. Numerical results clearly reveal the size effect of the orifice and double inlet valve of the PTR on the phase angle shift, and hence, on the PTR cooling capacity. The field synergy principle is further used to determine the optimum length to diameter ratio of the pulse tube and the optimal molar percentage of helium for a PTR using hydrogen/helium mixture as a working medium. Simulation results definitely show that the field synergy principle is a powerful guide to enhance energy conversion and transport processes.

Pressure Gradients in the Regenerator and Overall Pulse-Tube Refrigerator Performance

Significant pressure drops in the regenerator are typical in pulse-tube cryocoolers, with significant impact on performance. Irreversibilities due to viscous friction obviously lower efficiency, but in the pulse tube, this is not necessarily the most crucial issue. Indeed, by virtue of having only one driven element (the compressor), the pulse tube is a rather inflexible device from a design standpoint. Pressure and velocity amplitudes and phases determine energy fluxes. Impedances ultimately determine how large these fluxes are, hence how good a refrigerator a given design will produce. Impedance values are determined by the volume distribution, the orifice resistance, and the effect of viscous friction in the regenerator. The focus is on friction, which is difficult to deal with, especially if the device includes a bypass. An asymptotically consistent analysis has been developed, in which the regenerator is represented as an arbitrary porous medium. In contrast with most models, the analysis initially assumes arbitrary large pressure gradients and, of course, arbitrarily large temporal pressure fluctuations. The model thus obtained shows that when pressure differences due to viscous friction are comparable with the amplitude of temporal variations, viscous irreversibilities are much larger than the thermal ones. The regenerator formulation is then incorporated within a small-amplitude, harmonic model of the overall device, including the bypass, if any. For simple assumptions with respect to the temperature profile along the regenerator, such as linear and exponential profiles, closed-form solutions are obtained. Finally, the results are analyzed and their relevance is discussed.

Maximum attainable performance of pulse tube refrigerators

The nondimensional rate of refrigeration 〈 H ̇ 〉 of pulse tubes is shown to have a maximum attainable value of 1/4. The analysis is based on a linearized model in which the regenerator is thermally perfect and has negligible dead volume. The temporal variations are taken to be sinusoidal. At maximum 〈 H ̇ 〉 , the coefficient of performance (COP) equals one-half the temperature ratio T c / T h across the regenerator. In general, COP is a fraction between 0 and 1 of T c / T h . The difference between the actual power provided at the driver side and the ideal power corresponding to COP= T c / T h is dissipated in the regenerator. The resulting heat is transported to the warm end of the regenerator, where it is removed as part of the total heat flow rate.

Pressure gradients in the regenerator and overall pulse-tube refrigerator performance

Pressure gradients in the regenerator and overall pulse-tube refrigerator performance

Analytical study of the performance of pulse tube refrigerator with symmetry-nozzle

This paper analyzes the mechanism of the symmetry-nozzle instead of needle valve or orifice to improve the performance of pulse tube refrigerator in experiments. Their identifications are to result in a similar reciprocal movement in the hot end of the pulse tube; their differences are that their flow coefficients have different characteristics. The flow coefficient of the symmetry-nozzle has a positive feedback to flow rate while the orifice has little relation to flow rate generally. Further analysis shows that this feature results in large refrigeration when the pressure ratio and mass flow amount are same, which explains the reason for even lower temperature and a larger refrigeration amount when using the symmetry-nozzle.

Dynamic experimental study of a multi-bypass pulse tube 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 important 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.