Inertance Tube Research Articles

Study on the refrigeration performance of a miniature pulse tube cryocooler driven by a gas bearing compressor

Recent advancements in long-term space exploration, maintenance-free miniature-satellites and drone infrared detections have created a large demand for highly reliable and miniaturized cryocoolers working at 77–150 K. The pulse tube cryocooler (PTC) has no moving part at the cold end, and if driven by a gas bearing linear compressor which has no mechanical fatigue risk, a refrigeration system with high reliability and compactness will be generated. However, very few researches on the cooling performance of PTC driven by gas bearing linear compressor have been reported. In this study, a miniature PTC and gas bearing compressor are developed, with a weight of the whole refrigeration system about 0.97 kg. The maximum cooling capacity reaches 1.73 W at 77 K with input electric power of 66 W. The cooling capacity per unit weight for this cryocooler is 1.78 W/kg at 77 K, which is the highest compared to those of the existing typical miniature cryocoolers, showing its remarkable lower mass for refrigeration. In addition, the influence of the hot end heat dissipation temperature on the cooling performance is studied. It is found that the heat dissipation temperature of the hot end has a significant effect on the cooling performance. For every 10 K decrease in the hot end temperature, the maximum cooling capacity at 77 K increases by 3.45 % to 13.28 %, the relative Carnot efficiency rises by 4.38 % to 12.59 %. Besides, in the miniature PTC, the cooling performance is very sensitive to the length of the inertance tube, even a small change of 10–20 mm on the length of the inertance tube will lead to obvious effect on the optimum frequency and cooling performance of the system. These results will be helpful for the further research and development of the miniature pulse tube cryocoolers.

A design method based on neural network to predict thermoacoustic Stirling engine parameters: Experimental and theoretical assessment

A neural network-based design method for thermoacoustic Stirling engines (TASE) is presented in this work. The main goal of the article is to predict the design parameters (Length of resonator (stub) (LR), Length of inertance tube (Lin), Mean pressure (Pm)) of the thermoacoustic Stirling engine in such a way that the dynamic instability is guaranteed. In this regard, the governing equations of the engine are presented first. Next, with the help of the data extracted from the simulation of the governing equations of the engine, a neural network with the structure of 9–35-3 is trained. The effectiveness of the artificial neural network (ANN) structure is explored via regression and MSE (mean square error) analyses. Next, in order to evaluate and validate the neural network, the experimental data of the constructed thermoacoustic Stirling engine (SUTech-SR-4) is considered. It is important to note that the SUTech-SR-4 is introduced for the first time in this work. Investigations have shown that the neural network could estimate the engine design parameters well and with an acceptable approximation in such a way that the dynamic instability of the engine is also established. Besides, the value of the estimated design parameters for the engine made by the neural network was close to the experimental values. Following, the developed engine is introduced and its performance is discussed. The developed engine has been able to produce a power equivalent to 0.346 W at a pressure of 1 bar (with air working fluid) and a working frequency of 15.9 Hz. It should be noted that the method presented in this article can be used for other types of thermoacoustic Stirling engines. Moreover, the selection of design parameters for the presented method will depend on the physics of the engine and the available facilities.

Experimental investigation of displacer type pulse tube refrigerator with inertance tube or orifice

Displacer type pulse tube refrigerator (DPTR) can get high efficiency with strong phase shifting and acoustic work recovery to advantages. However, the optimal match of gas driving displacer can only be reached at one point, while the linear motor driving displacer has a complex structure. And for two-stage DPTR, more parameters need to be optimized such as step ratio. A well-matched displacer costs a lot and asks high quality manufacturing. In this work, an orifice and an inertance tube were added to the single-stage DPTR and two-stage DPTR as an additional adjustment parameter. For single stage DPTR, the experimental results indicate that the lowest temperature decreases from 44.7 K to 42.1 K after a suitable inertance tube was added. The cooling power can be increased with almost same efficiency by adding an orifice with appropriate opening turn. After adding an additional inertance tube of the two-stage DPTR, the lowest temperature of 15.6 K was achieved, while the lowest temperature of 15.7 K was achieved by installing an orifice to the two-stage DPTR.

Design and Optimization of a High Frequency Miniature Pulse Tube Cryocooler

A micro coaxial pulse tube cryocooler has been developed for infrared detection. This paper presents the experimental data of performance and describes the optimization process of a pulse tube cryocooler in detail. With a tiny size and high frequency, this cryocooler is driven by the linear compressor. The combination of inertance tube and buffer is adopted as phase shifter. The effect of the structure and operating parameters on cooling performance are investigated through experiments. As a result, the regenerator has a dimension of 40 mm length, and the optimal frequency is 175 Hz. It can provide a cooling power of 0.5 W at 80 K with a 30 W input electric power and 0.8 W at 150 K with a 10 W input electric power.

Advances in Pulse Tube Cooler with Dual-opposed Ambient Temperature Displacers

The pulse tube cooler offers several advantages, such as low vibration, high reliability, and no moving parts at the cold end. However, its efficiency is hindered by the limited phase modulation capability and acoustic power dissipation in the phase shifter. In response to this, Lihan Cryogenics has developed a Stirling pulse tube cooler employing ambient displacers. This innovative cooler comprises a moving magnet compressor with dual-opposed pistons and a co-axial cold finger. By utilizing ambient displacers, the cooler can recover expansion work and enhance cooling efficiency. This article highlights recent advancements in this type of cooler. To simplify manufacturing and increase reliability, the displacers now adopt a rod structure, reducing the requirement for supporting spring stiffness. Additionally, the cooler incorporates dual-opposed room temperature displacers, positioned orthogonally to the compressor piston axis (referred to as “OrthoCoolTM”). This arrangement results in low vibration, reduced flow resistance, and eased assembly and production challenges. Experimental tests demonstrate that compared to the cooler employing inertance tube phase modulation, the new ambient displacer structure effectively enhance system efficiency, achieving a cooling capacity of 100W at 77K with 1455W input electric power. The corresponding relative Carnot efficiency is 20%.

Study on Phase-Shift Mechanism and Kriging-Based Global Optimization of the Active Displacer Pulse Tube Refrigerators

Pulse tube refrigerators are widely used in certain special fields, such as aerospace, due to their unique advantages. Compared to a conventional phase shifter, the active displacer helps to achieve a higher cooling efficiency for pulse tube refrigerators. At present, the displacer is mainly studied by one-dimensional simulation, and the optimization method is not perfect due to its poor accuracy, which is not conducive to obtaining a better performance. Based on the current status of displacer research, phase-shift mechanisms of inertance tube pulse tube refrigerators and active displacer pulse tube refrigerators were firstly studied comparatively by multidimensional simulation, and then we determined the crucial effect properties that lead to a better cooling performance for the active displacer pulse tube refrigerator at different cooling temperatures. Finally, an efficient optimization method combining the Kriging model and genetic algorithm is proposed to further improve the cooling performance of the active displacer pulse tube refrigerator. The results show that the active displacer substantially improves the cooling performance compared to the inertance tube mainly by increasing the PV power and enthalpy flow in the pulse tube. The Kriging agent models of active displacer pulse tube refrigerator achieve 98.2%, 98.31%, 97.86%, and 97.32% prediction accuracy for no-load temperature, cooling capacity, coefficient of performance, and total input PV power, respectively. After optimization, the no-load temperature is minimally optimized for a 23.68% reduction compared to the initial one with a relatively high efficiency, and the founded optimization methods can also be weighted for multiple objectives, according to actual needs.

Comparative study of four displacer phase-shifters in a split pulse tube refrigerator working at 170 K

A pulse tube refrigerator (PTR) with a displacer phase-shifter has great potential for realizing high-efficiency PTRs. There are four types of displacer phase-shifters: passive rod displacer, passive rodless displacer, active rod displacer, and active rodless displacer. However, determining the displacer-type PTR with the greatest potential in engineering applications remains a challenge. Combined with response surface methodology, one-dimensional numerical simulations were conducted to address this problem. Energy efficiencies were compared at a cooling capacity of 50 W at 170 K. The piston-displacer phasor diagram, displacer force analysis, and key parameter distribution were used to explain the differences in performance. The phase-shifters were ranked from superior to inferior in terms of the relative Carnot efficiency based on the shaft power as follows: 24.2 % for the passive rod displacer, 23.8 % for the active rod displacer, 21.5 % for the active rodless displacer, 19.9 % for the inertance tube, and 13.3 % for the passive rodless displacer. The passive rodless displacer was unsuitable in the split structure with long connecting tubes because it failed to provide the ideal phase relation. The merit analysis of different displacer-type PTRs showed that the PTR with the passive rod displacer had the greatest potential for engineering applications. The relative Carnot efficiency was enhanced to 25.3 % by removing the hot heat exchanger, shortening the connecting tube, and changing the locations of the T-junction and phase-shifter. This study compared the four types of displacer phase-shifters simultaneously, which is scarce in the literature on PTRs. Moreover, it presents an effective approach to achieve a high-efficiency displacer-type PTR based on an existing inertance-tube-type PTR.

Effect of thermal dispersion and turbulent conduction on the heat transfer behavior of coaxial pulse tube cryocooler

In this article, a numerical analysis is conducted for a miniature coaxial pulse tube cryocooler including the effect of an axial conduction enhanced term. This term is a representative of supplementary energy loss, which happens because of turbulent conduction, mixing, and thermal dispersion. The complex physical domain of cryocooler is modeled intelligently in one-dimensional model by splitting the total computational domain into two subsections. The individual subsections of the cryocooler have been discretized into a number of small control volumes. Both subsections are merged together to make a complete computational domain for the cryocooler. The conservative form of the nonlinear, coupled partial differential equations demonstrating its heat and fluid flow aspects have been discretized into algebraic equations by utilizing the finite volume technique. Final discretized algebraic equations have been solved iteratively to predict its heat and fluid flow behaviors. Suitable relaxation factors have been incorporated to accelerate the convergence of the simulation. Moreover, the variation of mean cyclic energy, enthalpy, and exergy flow have been visualized along its physical domain with and without fluid axial conduction enhancement loss processes. Influences of different length of inertance tube, outer to inner radius ratio of annular passage, and length to radius ratio of pulse tube on no-load temperature is studied for with and without fluid axial conduction heat loss.

Effects of Compressor Frequency on Performance of Inertance Tube Pulse Tube Refrigerator: A Numerical Study

Pulse-tube refrigerators are considered as the mainstream elements in cryogenic plants. Normally, the efficacy of the inertance tube pulse tube refrigerator (ITPTR) is considered to be the highest among other pulse-tube refrigerators. In the current study, the mechanical performance of ITPTR system is numerically investigated to identify the impact of compressor frequency. The finite volume approach (FVM) is utilized to model the whole ITPTR with the specified boundary conditions using a commercial program ANSYS. The modelled ITPTR includes an inertance tube, reservoir, pulse-tube, cold heat exchangers, after cooler, regenerator, compressor and hot heat exchangers. These coupled systems that are simulated in a steady-state to reveal the performance and cooling rate. It has been discovered that the compressor’s frequency has a significant impact on the ITPTR’s performance and cooling rate. In four distinct ways, the compressor’s frequency has been changed from 10 Hz to 100 Hz. When the compressor runs at 20 Hz, the rate of cooling is determined to be at its highest.

Energy conversion efficiency improvement of a Stirling type PTR for dual temperature cooling by adopting two active work-recovery phase shifters

Deep space exploration is required to solve the problem of energy acquisition and efficient utilization. Improving energy conversion efficiency is vital to this issue. The Stirling type pulse tube refrigerators (PTR) that work in dual temperature zones play a pivotal role in the field of space detection, and the phase shifter of PTR profoundly affects the conversion efficiency of the exergy to cooling capacity. However, the typical phase shifter causes the acoustic power at the hot end of the cold finger to be dissipated into the form of heat, limiting energy efficiency. With the intention of improving the energy conversion efficiency in the PTR, a novel type of active phase shifter with work recovery on a dual temperature zone PTR is proposed and investigated in this article. Based on the pulse tube refrigerator with two separated cold fingers, inertance tubes with reservoirs, active piston phase shifters, and active work-recovery piston phase shifters have been comparatively investigated. While the refrigerator adopts active work-recovery piston phase shifters, a relative Carnot efficiency of 15.5% is obtained in the 35 K and 85 K temperature zones, which is the highest efficiency ever achieved in these temperature areas.

Sonication-Free Dispersion of Single-Walled Carbon Nanotubes for High-Sorption-Capacity Aerogel Fabrication.

Homogenously dispersing single-walled carbon nanotubes (SWNTs) in solvents has been one critical step towards exploiting their exceptional properties in high-performance components. However, the solubility of SWNTs is severely limited by the inert tube surfaces and strong tube-tube van der Waals attractions. Starting with carbon nanotubides, i.e., negatively charged SWNTs reduced by alkali metals, we herein propose a sonication-free approach to prepare an aqueous dispersion of SWNTs. The approach combines the spontaneous dissolution of nanotubides in polar aprotic solvents with polyvinylpyrrolidone wrapping and dialysis in deionized H2O, which results in well-dispersed, neutralized SWNTs. The gelation of concentrated SWNT dispersion leads to the formation of hydrogels, which is subsequently transformed into SWNT aerogels through lyophilization. The prepared SWNT aerogels exhibit high-mass-sorption capacities for organic solvent absorption, paving the way towards harvesting the extraordinary properties of SWNTs.

Frequency response characteristics of a thermally coupled three-stage Stirling-type pulse tube cryocooler capable of achieving 110 mW@7 K

Long-life cryocoolers operating below 7 K are crucial for infrared astronomy projects, such as the hybrid cryocooler employed as the MIRI cryogenic system in the James Webb Space Telescope, which provides a cooling temperature of 6.2 K. A totally thermally-coupled three-stage Stirling-type pulse tube cryocooler was developed in SITP to obtain a relatively high cooling capacity at 6∼7 K. With the cold inertance tube as the phase shifter of the third stage pulse tube cryocooler, a no-load temperature of 3.96 K was reached with He-4. The operating frequency was 26.5 Hz, and the average pressure was 1.68 MPa at room temperature. Simulation results show that the frequency of the third stage SPTC has significant effects on the impedance characteristics of the cold inertance tube and the efficiency of the low-temperature regenerator. The effect of frequency on the cooling capacity has been verified experimentally, and the optimal frequency changes with cooling temperatures and precooling temperatures. When the precooling temperatures of the first stage and the second stage were 90 K and 24 K, the cooling capacity of 58.5 mW@6 K and 113.4 mW@7 K under 100 W input electric power of the third stage SPTC were obtained with the optimized operating frequencies of 24.5 and 23 Hz, respectively. The total input electric power was 510 W when achiveing 113.4 mW@7 K.

Investigation of regenerator mesh characteristics for a pulse tube cryocooler

An investigation of regenerator mesh characteristics on a Pulse tube cryocooler’s performance is conducted using Sage V11 software. The cryocooler operates between temperatures of 300 K and 80 K. The components of the cryocooler are free piston linear compressor, aftercooler, regenerator, pulse tube, warm heat exchanger, and inertance tube- bounce space as the phase shifter. The performance of the regenerative cryocoolers depends on the regenerator. The regenerator of this cryocooler consists of a stack of stainless steel meshes. In this paper, a comparison of regenerator stainless steel meshes with mesh number #200, #300, #400, #500 and its combinations were analysed. To choose the best multi mesh combination, the length of the individual meshes is varied so that the total length of the regenerator is unchanged. The performance was analysed based on the Coeffcient of Performance of cryocooler for single mesh type and mesh combinations (combination two) at acceptor temperature of 80 K. The maximum performance with single mesh was with #400 mesh with COP of 6.12%. The cryocooler’s maximum Coeffcient of Performance was with the combination of #400 and #500 meshes in the regenerator. The best multi mesh combination gave 4.071 W cooling power with an input power of 61.92 W with a COP of 6.57%. There was an improvement of 7.26% with the use of multiple mesh regenerator.

Numerical analysis and experimental research of a 2W/35 K Stirling-type pulse tube cryocooler

Cooling to the temperature of liquid nitrogen to liquid hydrogen is a necessary working prerequisite for some infrared detectors. The development of compact and efficient miniature cryocoolers is of great significance for the space application of the detectors. The pulse tube cryocooler driven by a dual-opposed linear compressor is prospective in space applications due to the advantages of no low-temperature moving parts, compact structure, and high reliability. In this paper, a 2W/35K Stirling-type pulse tube cryocooler with a single-stage structure has been designed and tested. The influences of structural parameters of the phase shifters such as inertance tube, as well as the operating parameters such as operating frequency and charging pressure, on the cooling performance were investigated through numerical calculations and experiments.

A research of micro-pulse tube cryocooler with displacer phase shifter

• The phase relationships in the whole displacer PTC system were analyzed. • Three different sizes of a displacer type micro PTCs have been designed. • A 2D CFD model was constructed and used to characterize the displacer micro PTC. • A displacer provides a good phase shifting for a small-cooling-power micro PTC. • A cooling power of 1.5 W@80 K and a COP of 20.96% is obtained by the second micro PTC. Investigations of phase shifters and power recovery mechanisms are of sustainable interest for developing Stirling pulse tube cryocoolers (SPTC) with more compact design and higher efficiency. The warm displacer type SPTC has been demonstrated with a very promising theoretical efficiency benefiting from its strong phase shifting and work recovery functions. Extending this same phase shifting approach to miniature pulse tube refrigerators may provide advantages over the other alternatives, since inertance tubes are severely limited in their phase shifting capability when the associated acoustic power decreases below 20 W. A comprehensive investigation regarding the micro-pulse tube cryocooler with a displacer phase shifter is carried out in this work, including the design of the major components of the cryocooler, theoretical analysis regarding the phase relationship in the whole displacer type cryocooler system, and 2D simulation work addressing the performance of the cryocooler systems. In the optimum phase angle conditions of the 3 mm pulse tube size cryocooler, the mass flow rate leads the pressure wave by 28.8° at the regenerator warm end, and lags the pressure wave by 27.7° at the regenerator cold end. A cooling power of 1.5 W at 80 K and a COP (Coefficient of Performance) of 20.96% is obtained with an input power of 7.4 W.

Series inertance tube pulse tube refrigerator

A new type series inertance tube pulse tube refrigerator is introduced. It includes series cold heads. Each cold head's pulse tube connects an inertance tube as phase shifter. The acoustic power of the first pulse tube is partially used by the first inertance tube for phase shifting, while the remaining is used for generating additional cooling power. It is high efficiency with multi refrigeration temperature. A two-dimensional axisymmetric model was introduced for simulation by the commercial CFD software ANSYS Fluent. The numerical results show that it has high potential for getting higher efficiency. A protype series inertance tube pulse tube refrigerator was made and tested. Its efficiency is higher than the ordinary inertance tube pulse tube refrigerator at higher temperature range. At 232K, the efficiency is increased by 10%. The results show that it is valuable for further development.

A two-stage thermally-coupled pulse tube cryocooler working at 35 K for space application

The attainment and maintenance of a low temperature environment is essential for aerospace cryogenic detectors to achieve their required performance. Developing cryocoolers with features of high efficiency, compact structure, and long lifetime is the main challenge for cryogenic detector cooling. In this paper, a high efficiency thermally-coupled two-stage Stirling type pulse tube cryocooler working at 35 K for HgCdTe long wave infrared detector cooling is designed and tested. The thermally-coupled type avoids gas distribution at cold side which minimizes the inter-stage influence. The whole cryocooler is driven by one linear compressor which enables compact structure. The influence of operation frequency and mean pressure is studied by numerical calculation and experiments to determine the optimum operation condition. Acoustic impedance characteristics of both stages and the whole cold finger are also analyzed by comparing performance of cryocooler with different frequency, mean pressure and structure dimensions. The distributions of acoustic power and phase angle are presented to study the relation between impedance characteristic and the cooling performance. Impedance match between compressor and cold finger is also discussed by analyzing the efficiency of the linear compressor and the performance of cryocooler with different pulse tubes. Under optimum impedance match and operation condition of a working frequency of 39.2 Hz and a mean pressure of 2.45 MPa, the cryocooler provides a cooling power of 1 W at 35.1 K with an input electrical power of 150 W, which indicates a relative Carnot efficiency of 5%. This is a rather high efficiency for developed Stirling type multi-stage pulse tube cryocooler working at 35 K with only inertance tubes as phase shifter. The development of this cryocooler lays a solid base for the further optimization to realize a competitive candidate for aerospace cooling requirements.

Personality characteristics and medical impact of stimulant laxative abuse in eating disorder patients\u2014a pilot study

BackgroundStimulant laxative abuse as a purging behavior can be profound in those with eating disorders. However, the psychopathology leading to stimulant laxative abuse is poorly understood. Furthermore, the medical impact of stimulant laxative abuse has not been studied in this population.MethodsSix individuals abusing stimulant laxatives underwent a barium enema to assess for evidence of the cathartic colon syndrome and 29 individuals engaging in any purging behaviors completed the Tri-dimensional Personality Questionnaire-Short Form, Sensitivity to Punishment/Sensitivity to Reward Questionnaire-Short Form, Beck Depression Inventory, and the State Trait Anxiety Inventory questionnaires.ResultsThree of the six patients completing the barium enema had the radiographic findings consistent with cathartic colon. Individuals engaging in laxative abuse showed higher Novelty Seeking compared to those engaging in other forms of purging, and those engaging in any form of purging behavior showed greater Sensitivity to Punishment compared to Sensitivity to Reward. There was also the presence of greater Harm Avoidance than Reward Dependence in this population.ConclusionThere may be different psychopathology that contributes to the abuse of stimulant laxatives than that associated with other forms of purging. Regardless of the driving factor, further research is warranted to discover best therapeutic interventions given the potential to develop the cathartic colon syndrome with ongoing use of stimulant laxatives.Plain English SummaryCathartic colon is a condition whereby the colon, or lower intestine, is converted into an inert tube incapable of propagating fecal matter. It is thought to develop due to over-use of stimulant laxatives. However, it is unclear if this condition truly exists and whether it contributes to the constipation experienced by individuals with eating disorders who have extensive past histories of abusing laxatives. It is also unclear if laxative abuse presents with different medical complications than other forms of purging. The purpose of this study is to determine whether radiographic evidence of cathartic colon can be found in eating disorder patients abusing stimulant laxatives, whether there are different medical complications with laxative abuse versus other forms of purging, and to examine the psychological composition of individuals who engage in severe laxative abuse. Specifically, the authors investigated the interrelationship between Harm Avoidance and Reward Dependence, with emphasis on gaining a better understanding of Reward Dependence by examining both Sensitivity to Reward and Sensitivity to Punishment in patients who engage in severe laxative abuse. Our findings suggest that stimulant laxative abuse may cause the development of cathartic colon changes and that there may be unique psychopathology that contributes to the abuse of stimulant laxatives. Given the higher Novelty Seeking personality-dimension in those abusing laxatives, it is possible that this purging behavior may be considered addiction-like in nature, which would have distinct treatment implications.

Investigation on the cool-down speed of Stirling type pulse tube cryocooler with inertance tube

In some applications, the cool-down speed obtainable with a cryocooler is important besides the high efficiency at the working temperature. Because of the difference in configurations, the design and the control strategies for various cryocoolers may be different. This work numerically studies the cool-down characteristics of a Stirling-type pulse tube cryocooler (PTC), which uses inertance tube and reservoir as the phase shifter and work at the temperature region of liquid nitrogen. The cryocooler is predicted to provide a nominal cooling power of 18.7 W at 77 K. Three cool-down strategies, namely, cool-down with constant voltage at 66 Hz, cool-down with constant piston displacement by tuning the voltage at 66 Hz, and cool-down with constant piston displacement by tuning voltage and frequency simultaneously during the cool-down process, are investigated. The corresponding calculated cool-down time from the ambient temperature to 77 K of these strategies are 340, 275, and 260 s, respectively. Using the third strategy, the cool-down time can be reduced by 23%.

The Effect of Boron Addition on the corrosion behavior of Ni Cr Modental alloy prepared by powder metallurgy.

The powder metallurgy (PM) method was used to create the alloy. The sintering process was carried out in an inert high-temperature tube furnace in the presence of inert gas at a temperature of 1000 ° C for 8 hours (Argon). In this article, the effect of (B) at three wt.% (0.4,0.8,1.2) on the corrosion rate, hardness, and microstructure of alloys was examined. X-ray diffraction (XRD), open circuit potential, electrochemical tests (Tafel extrapolation method), and Macro hardness Brinell were used to study the effect of adding (B) in various amounts to alloys. Saliva was utilized as the corrosion solution for the testing. The inclusion of the alloy element (B) increased hardness and a decrease in particle size, as seen by the microstructures. Furthermore, the corrosion resistance of the master alloy improved next the addition, as shown by Corrosion potential has increased while corrosion current densities have decreased. The corrosion rate for A, A1, A2 and A3 was 14.50, 7.42, 2.03and 2.77 (mpy) respectively.