Inertance Tube Research Articles

Theoretical and experimental investigations on the dynamic and thermodynamic characteristics of the linear compressor for the pulse tube cryocooler

Theoretical and experimental investigations on the dynamic and thermodynamic characteristics of a linear compressor incorporating the thermodynamic characteristics of the inertance tube pulse tube cold finger have been made. Both the compressor and cold finger are assumed as a one-dimensional thermodynamic model. The governing equations of the thermodynamic characteristics of the working gas are summarized, and the effects of the cooling performance on the working gas in the compression space are discussed. Based on the analysis of the working gas, the governing equations of the dynamic and thermodynamic characteristics of the compressor are deduced, and then the principles of achieving the optimal performance of the compressor are discussed in detail. Systematic experimental investigations are conducted on a developed moving-coil linear compressor which drives a pulse tube cold finger, which indicate the general agreement with the simulated results, and thus verify the rationality of the theoretical model and analyses.

Experimental Investigation of a Switched Inertance Hydraulic System With a High-Speed Rotary Valve

This paper reports on experimental investigations of a switched inertance hydraulic system (SIHS), which is designed to control the flow and pressure of a hydraulic supply. The switched system basically consists of a switching element, an inductance (inertance), and a capacitance. Two basic modes, a flow booster and a pressure booster, can be configured in a three-port SIHS. It is capable of boosting the pressure or flow with a corresponding drop in flow or pressure, respectively. This technique makes use of the inherent reactive behavior of hydraulic components. A high-speed rotary valve is used to provide sufficiently high switching frequency and to minimize the pressure and flow loss at the valve orifice, and a small diameter tube is used to provide an inductive effect. In this paper, a flow booster is introduced as the switched system for investigation. The measured steady-state and dynamic characteristics of the rotary valve are presented, and the dynamics characteristics of the flow booster are investigated in terms of pressure loss, flow loss, and system efficiency. The speed of sound is measured by analysis of the measured dynamic pressures in the inertance tube. A detailed analytical model of an SIHS is applied to analyze the experimental results. Experimental results on a flow booster rig show a very promising performance for the SIHS.

Tandem-type pulse tube refrigerator without reservoir

In this paper, a tandem-type pulse tube refrigerator without a reservoir is discussed and investigated. For its practical application a tandem-type compressor is designed to generate two pulsating pressure waves with opposite phases, simultaneously. A tandem-type pulse tube refrigerator consists of a tandem-type compressor and two identical pulse tube refrigerators. The two identical pulse tube refrigerators share the same heat exchangers and one can be connected with the other by an inertance tube without a reservoir. In this proposed configuration, the mechanical vibration and temperature oscillations in the cold-end heat exchanger can be internally suppressed due to its intrinsic opposite-characteristic operation. To examine the quantitative evaluation of the tandem feature which does not require a reservoir in the pulse tube, an evolutionary approach has been attempted. A general structure of a pulse tube refrigerator is modified into tandem Stirling-type and GM-type machines and the transformed configuration has been simulated for tandem operation. The simulation results clearly demonstrate that a properly designed tandem-type pulse tube refrigerator without a reservoir can function favorably.

An electrical circuit analogy model for analyses and optimizations of the Stirling-type pulse tube cryocooler

The existing electrical circuit analogy (ECA) models are mainly used to optimize the inertance tube and to analyze the crude phase of the dynamic pressure and the volume flow rate. The specific analyses and optimizations of other components or the whole Stirling-type pulse tube cryocooler (SPTC) with the ECA model have not been carried out. In this paper, a new ECA model including the main components of the SPTC such as regenerator, pulse tube, phase shifter and reservoir has been developed. To improve the practicability of the ECA model, based on the basic governing equations, calculation expressions of the above components are worked out, and their equivalent analogical electrical elements are defined according to the analogy theory. Through the developed ECA model, the specific pressure and volume flow rate at any position can be acquired. Further optimizations on the SPTC based on the ECA model show that, with the same pressure and PV power at the warm end of the regenerator, there exists an optimal phase angle between the pressure and the volume flow rate for the SPTC to achieve the highest gross cooling capacity. In addition, with the same ratio of the pressure to the volume flow rate and the same phase angle between them at the warm end of the regenerator, when the regenerator ineffectiveness loss is neglected, the SPTC efficiency keeps constant with variations of the PV power, however, the efficiency will increase with the increase of the PV power if the loss is considered.

Step By Step: Microsurgical training method combining two nonliving animal models

The learning of microsurgical techniques and the maintenance of microsurgical skills have been traditionally based on the use of living animals, mainly laboratory rats. This method although extremely valuable can be economically demanding both for the surgeon and the sponsoring institution; it also requires special training facilities that may not always be available or accessible. Furthermore ethical concerns can limit the use of living animals for training purposes. Alternative training methods, such as inert tubes and gloves have not gained popularity among surgeons since they do not offer an experience similar to that of a clinical situation. Non-living animal models include the use of chicken thighs and wings; they offer a practice experience that resembles a clinical situation to a considerable extent. This type of training is relatively cheap and easily available. The microscope and instruments required can be acquired over the internet, and the chicken pieces can be bought at the local supermarket. This approach allows a motivated trainee to rehearse different types of surgical techniques several times at a reasonable expense, helping to develop or maintain his surgical expertise if more complex facilities are not available. On the current manuscript we describe how to setup a small practice station, how to dissect the specimens, and how to practice both with the chicken thighs and with the chicken wings in a progressive fashion. This approach takes advantage on the versatility of the chicken thigh model and the small size of the chicken wing Brachial artery.

Modelling and analysis of hydraulic step-down switching converters

In this study, a steady state analysis of step-down converter systems, considering the load losses in the inertance tube and switched valve, is presented. The model describes the behaviour of the average load pressure as a function of the pulse-width modulated duty cycle. The steady state expressions for the load flow rate, high and low supply flow rates, and system efficiency are also discussed. A system prototype was developed and tested to evaluate the model accuracy. The system parameters (e.g. tube diameter and length and switching frequency) were analysed to predict the best system configuration. The study describes how the system efficiency is influenced by these parameters. The model presented allows the ideal parameter combination for maximum efficiency to be determined. It can be used for the preliminary design of switching converters, and a further time or frequency analysis can be performed for system optimization.

Influence of regenerator void volume on performance of a precooled 4 K Stirling type pulse tube cryocooler

Stirling type pulse tube cryocoolers (SPTC), typically operating at 30–60Hz, have the advantage of compact structure, light weight, and long life compared with Gifford–McMahon type (1–2Hz) PTC (GMPTC). The behavior of flow and heat transfer in the regenerator of a 4K SPTC deviates from that at warmer temperatures and low frequencies. In this paper the behavior of 4K regenerator at high frequencies is investigated based on a single-stage 4K SPTC precooled by a two-stage GMPTC. The 4K SPTC and the GMPTC is thermally coupled with two thermal bridges. The 4K SPTC uses a 10K cold inertance tube as phase shifter to improve phase relationship between mass flow and pressure. The regenerator void volume is an important factor that significantly influences the heat transfer between regenerator matrix and working fluid helium, pressure drop along the regenerator, and phase shift between mass flow and pressure. In this paper, influence of regenerator void volume on the performance of the 4K SPTC with different operating parameters including operating frequencies and average pressure is studied theoretically and experimentally. The first and second precooling powers provided by the GMPTC are obtained which are important parameters to evaluate the efficiency of the whole 4K system with precooling. The results of the regenerator void volume are given and discussed in normalized form for general use.

Cold Inertance Tube for 4 K Stirling Type Pulse Tube Cryocoolers

The losses in the regenerator are minimized when the amplitude of the mass flow is minimized for a given acoustic power which requires that the mass flow lags the pressure by about 30° at the cold end of regenerator. The phase shift provided by an inertance tube is strongly influenced by the temperature of the inertance tube and the acoustic power at the cold end of the regenerator. For a 4K Stirling type pulse tube cryocooler, the acoustic power at the cold end of the regenerator decreases significantly with the temperature thereby it's difficult to achieve ideal phase relationship with ambient inertance tube. While cold inertance tube provide a larger phase shift in that the viscosity of the working fluid decreases and the density increases as the temperature decreases. However, use of cold inertance tube increases additional heat load to the regenerator. Therefore it's of great significance to determine when a cold inertance tube should be used. In this paper effect of temperature of inertance tube is calculated for a 4K Stirling type pulse tube cryocooler with different acoustic powers at the cold end. A comparison of ambient temperature inertance tube and cold inertance tube is made.

Influence of the Gas Volume in the Void Tube Connecting Compressor and Inertance Tube on the Oscillating Flow in an Inertance Tube Phase Shifting System

Influencesof thegas volumein the void tube (connecting tube), connecting compressor and inertance tube, on the oscillating flowcharacteristics are experimentally investigated. Four void tubes, whose volumes are different from each other, are chosen to connect the compressor and the inertance tube respectively. Piston displacement of the compressor and dynamic pressure at the outlet of the compressor are measured by a laserdisplacement sensor and a quartz pressure sensor respectively. This investigation focuses on the piston displacement and mass flows at three special positions of the experimental system.The change of the amplitudes and phase angles of the piston displacement and the three mass flows caused by varying the void tubes with different dynamic pressures and frequencies are studied. This investigation is helpful to study the influence ofthe gas volumein the connecting parts of an inertance tube pulse tube cryocooler, such as transfer tube, cold finger and pulse tube, on oscillating characteristics of the cooler.

An Inter-phasing Stirling Pulse-tube Cryocooler without Reservoirs

Asubstantial fraction of the volume of a traditional pulse-tube cryocooler is occupied by a reservoir, which greatly reduces the specificpower of the cryocooler. This is undesirable for applications that require a small size and light weight.This paper presents aninter-phasing pulse-tube cryocooler conjoining two or more cold fingers via their inertance tubes. Because the volume flow in the cold fingers are elaborately adjusted to make the total volume flow into the junction of the inertance tubes zero, the reservoirs are allowed to be removed. Experimentsdemonstrated that, with an electric input power of 1kW, the cooling power at 77K reached 59.8W, corresponding to a relative Carnot efficiency of 16.8%. Compared with a traditional pulse-tube cryocooler, this cryocooler canachieve the same cooling performance.

Design and analysis of a high capacity stirling type pulse tube cryocooler for a helium recondensation system

This paper reports the system design and analysis of high capacity Stirling type pulse tube cryocoolers (PTC) intended to provide a cooling power of 10 W at 80 K for a small helium recondensation system. In the initial phase of the work, the regenerator and pulse tube were optimized using Sage software. The effect of the transfer line whose length is comparable to the wave length of the helium pressure wave is investigated. It is found that there is a magnification in the pressure amplitude at the expense of the PV power. Also a no load temperature of 74 K was achieved. A detailed inertance tube optimization and analysis is done and the cooler is tested with the optimized inertance. The performance improved with a no load temperature of 72 K.

Step piston pulse tube refrigerator

In this paper, a numerical simulation is done for a step piston pulse tube refrigerator. The step piston pulse tube refrigerator is a modification of an inertance tube pulse tube refrigerator, which has a step piston compressor. The step piston in a step cylinder forms a compression space which is connected to the after cooler and an expansion space which is connected to the buffer. Numerical simulation shows that it is more effective at higher refrigeration temperature. It also shows there is an optimum swept volume ratio of the expansion space over the compression space, and an optimum diameter and length of the inertance tube for a given refrigerator.

Theoretical and experimental investigations on Stirling-type pulse tube cryocoolers with U-type configuration to achieve temperature below 20 K

To achieve lower temperatures is a subject of recent research and development activities in the field of pulse tube cryocoolers. To reach a temperature of 20 K, multi-staging is necessary in Stirling-type pulse tube cryocoolers. In the present work, Sage software is used to design a three-stage gas-coupled as well as thermal-coupled pulse tube cryocooler. A single-stage and a two-stage pulse tube cryocoolers are developed, tested and are coupled by a thermal link to build up a three-stage thermal-coupled pulse tube cryocooler. The lowest temperature of 19.61 K is obtained with a cooling capacity of 220 mW at 30 K at the third stage operating at 17 bar charge pressure and 68 Hz frequency. The phase-shifting mechanism used is a double inlet valve at the third stage while the inertance tube is used for the other stages.

Performance of a precooled 4 K Stirling type high frequency pulse tube cryocooler with Gd2O2S

The efficiency of 4 K Stirling type pulse tube cryocoolers (SPTCs) is rather low due to significant regenerator losses associated with the unique properties of helium around 4 K and the high operating frequencies. In this paper, regenerator performance at liquid helium temperature regions under high frequencies is investigated based on a single-stage SPTC precooled by a two-stage Gifford-McMahon type pulse tube cryocooler (GMPTC). The 4 K SPTC used a 10 K cold inertance tube as phase shifters for better phase relationship between pressure and mass flow. The effect of the operating parameters, including frequency and average pressure on the performance of the 4 K SPTC, was investigated and the first and second precooling powers provided by the GMPTC were obtained. To reduce the regenerator heat transfer losses, a multi-layer regenerator matrix, including Gd2O2S (GOS) and HoCu2, was used instead of a single-layer HoCu2 around 4 K. A theoretical and experimental comparison between the two types of regenerator materials was made and the precooling requirements for a regenerator operating at high frequencies to reach liquid helium temperatures were given, which provided guidance for the design of a three-stage SPTC.

Parametric Study on Performance of Inertance Pulse Tube Cryocooler

The design parameters to affect the cooling capacity of a cryocooler were examined with the application of numerical modeling to optimize an inertance pulse tube cryocooler. This modeling includes the regenerator, pulse tube, inertance tube, gas reservoir, and heat exchangers. One-dimensional modeling on strings of acoustic and thermoacoustic elements was applied to compare the design parameters. The diameter and length of the pulse tube can significantly affect the cooling capacity and efficiency. The aftercooler was optimized by maintaining a certain size. The efficiency also improved as the length of inertance tube and volume of gas reservoir are increased. It was confirmed that effective design parameters are critical to the performance of an inertance pulse tube cryocooler considering the comparison of the dimensions of each part to optimize its cooling power and efficiency.

Measurement Method of Phase Characteristics for High Frequency Pulse Tube Cryocooler

The phase characteristics of the high frequency pulse tube cryocooler which include the mass flows, the pressure amplitudes, and the phase angles between them significantly affect the cooler performance. A measurement method by using pressure sensors, temperature sensors and linear variable differential transformer rods is presented to evaluate and estimate the phase characteristics for the key components within the cooler such as the compressor, the regenerator, the inertance tube. etc, also the construction method of the phasor diagram based on the measurement is given. The constructed phasor diagram can be used to compare with the design values and provide the optimization direction of the prototype.

Influence of the connecting tube at the cold end in a U-shaped pulse tube cryocooler

In some special applications, the pulse tube cryocooler must be designed as U-shape; however, the connecting tube at the cold end will influence the cooling performance. Although lots of U-shape pulse tubes have been developed, the mechanism of the influence of the connecting tube on the performance has not been well demonstrated. Based on thermoacoustic theory, this paper discusses the influence of the length and diameter of the connecting tube, transition structure, flow straightener, impedance of the inertance tube, etc. on the cooling performance. Primary experiments were carried out in two in-line shape pulse tube cryocoolers to verify the analysis. The two cryocoolers shared the same regenerator, heat exchangers, inertance tube and straightener, and the pulse tube, so the influence of these components could be eliminated. With the same electric power, the pulse tube cryocooler without connecting parts obtained 31W cooling power at 77K; meanwhile, the other pulse tube cryocooler with the connecting parts only obtained 27W, so the connecting tube induced more than a 12.9% decrease on the cooling performance, which agrees with the calculation quite well.

Investigation of a high frequency pulse tube cryocooler driven by a standing wave thermoacoustic engine

In this work, a typical thermoacoustically driven pulse tube cooler as a no-moving part device has been investigated by a numerical method. A standing wave thermoacoustic engine as a prime mover in coupled with an inertance tube pulse tube cryocooler has been modeled. Nonlinear equations of unsteady one-dimensional compressible flow have been solved by the finite volume method. The model presents an important step towards the development of nonlinear simulation tools for the high amplitude thermoacoustic systems that are needed for practical use. The results of the computations show that the self-excited oscillations are well accompanied by the increasing of the pressure amplitude. The necessity of implementation of a nonlinear model to investigate such devices has been proven. The effect of APAT length as an amplifier coupler on the performance of the cooler has been investigated. Furthermore, by using Lagrangian approach, thermodynamic cycle of gas parcels has been attained.

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.

Behavioural prediction of hydraulic step-up switching converters

In this paper the fundamental principles of energy-conservative hydraulic control based on the fluid inertance principle are discussed and a detailed analysis of step-up switched-inertance control is presented. A non-loss system comprising an inertance tube and switching valve is modelled and its operational curves are presented as a reference for an ideal behaviour. Considering the load loss at both the tube and the PWM switched valve, a linear mathematical model for the step-up switched-inertance hydraulic system is presented which describes the pressure response as a function of the PWM duty cycle. Mathematical expressions of the flow rates through the tube and the supply and return ports as well as the system efficiency are also presented. A system prototype is evaluated on a test rig and the experimental data compared with the theoretical results, demonstrating the model accuracy. The proposed model simplifies the analysis process for step-up switching converters and thus their restrictions and potential can be investigated more quickly.