Coaxial Pulse Research Articles

Numerical and experimental investigation of 12 W/60 K high-efficiency coaxial pulse tube cryocooler

Maintaining a low-temperature environment is paramount in pursuing reliable operation for infrared detectors. To address the rising demand for long-wave infrared detectors functioning in low-temperature environments around 60 K, this study investigates the enhanced efficiency of a 60 K coaxial pulse tube cryocooler (PTC) through both simulation analysis and experimental methods. A PTC model was developed using Sage software to optimize parameters such as cold finger size. Analysis of the internal flow field highlighted that variations in cold head temperature, frequency, and input power significantly impact phase angle distribution within the regenerator. Experimental results yielded the same conclusion and confirmed how these critical factors affect the PTC’s performance. Through systematic optimization of simulations and experiments, a cooling performance of 12.7 W/60 K was achieved with an input power of 300 W. Furthermore, when the input power of the PTC was 200 W, a cooling capacity of 9.2 W/60 K was achieved, demonstrating a relative Carnot efficiency of 18.3 %.

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.

“Investigation Variable Parameters in Cryocooler Design: CFD simulation of Coaxial Pulse tube Cryocooler”

“Investigation Variable Parameters in Cryocooler Design: CFD simulation of Coaxial Pulse tube Cryocooler”

Numerical investigation on non-linear streaming effects in a two-stage coaxial pulse tube cryocooler

Stirling pulse tube cryocoolers (PTC) are widely used in aerospace applications for the cooling of infrared sensors and for filtering background thermal noise in the astro-imaging devices, etc. Present investigation aims to use numerical methods to demonstrate the nonlinear fluid flow, heat transfer, and vortex generation phenomena in a two-stage coaxial type inertance pulse tube cryocooler. The numerical simulation is conducted using commercially available Fluent® code for both single-stage and multi-stage configurations to show nonlinear processes with varying heat load conditions. It has been noticed that the width of the vortex produced inside the pulse tube grows with an increase in heat load capacity. This undesirable flow conditions yields an adverse effect in the cooling behavior and reduces overall performance of cryocooler with higher heat load. Additionally, streamlines, stream function, pressure and temperature variation plots are given for both stages with different heat load capacity to substantiate our results.

CFD investigation on the radial heat transfer in a two stage co-axial pulse tube cooler working at liquid hydrogen temperature

Co-axial pulse tube coolers are very popular in practical applications due to their compactness, while radial heat transfer between regenerator and pulse tube due to temperature mismatch at the same axial location affects the cooling performance. Two stage pulse tube coolers are commonly used at liquid hydrogen temperature, and multiple radial heat transfer occurs in gas-coupled co-axial pulse tube cooler system due to the first stage annular pulse tube. CFD simulation models with and without radial heat transfer based on an actual gas-coupled two stage co-axial pulse tube cooler have been conducted to analyze the mechanism and effect. The heat transfer processes between the gas and pulse tube wall are analyzed and compared. Simulation results indicate that after introducing radial heat transfer, expansion efficiency of the second stage pulse tube is improved from 74% to 90.9% with radial heat flow from it to the regenerator and the first stage pulse tube. The cooling power at the second stage is notably increased compared to the model without radial heat transfer, while minor performance reduction at the first stage. This study may provide a valuable reference for the design of multi-stage pulse tube coolers.

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.

Distortion Evaluation of EMP Sensors Using Associated-Hermite Functions

Electromagnetic pulse (EMP) is a kind of transient electromagnetic phenomenon with short rise time of the leading edge and wide spectrum, which usually disrupts communications and damages electronic equipment and system. It is challenging for an EMP sensor to measure a wideband electromagnetic pulse without distortion for the whole spectrum. Therefore, analyzing the distortion of EMP measurement is crucial to evaluating the sensor distortion characteristics and correcting the measurement results. Waveform fidelity is usually employed to evaluate the distortion of an antenna. However, this metric depends on specific signal waveforms, thus is unsuitable for evaluating and analyzing the distortion of EMP sensors. In this paper, an associated-hermite-function based distortion analysis method including system transfer matrices and distortion rates is proposed, which is general and independent from individual waveforms. The system transfer matrix and distortion rate can be straightforwardly calculated by the signal orthogonal transformation coefficients using associated-hermite functions. Distortion of a sensor vs. frequency is then visualized via the system transfer matrix, which is convenient in quantitative analysis of the distortion. Measurement of a current probe, a coaxial pulse voltage probe and a B-field sensor were performed, based on which the feasibility and effectiveness of the proposed distortion analysis method is successfully verified.

Design and optimization of heat exchanger in coaxial pulse tube cryocooler working above 100 K

The coaxial pulse tube cryocooler (PTC) has the advantages of without moving parts at the cold end, compactness and high-efficiency, it shows great application potential in many fields. The present work numerically and experimentally investigated a coaxial PTC working at temperature range from 90 K to 260 K. To improve its efficiency, the exergy analysis method was used to study the distribution of available energy loss in the coaxial PTC. To reduce one of the main available energy losses coming from the heat exchanger, three types of heat exchanger, slit, circular hole (CH) and copper mesh (CM), were analyzed and optimized based on the law of conservation of energy. Finally, two different cold end and hot end heat exchangers are designed respectively in the experiment. The results show the optimized pulse tube cooler can supply 50 W cooling power at 185.3 K with 200 W input power. To the best of our knowledge, its relative Carnot efficiency (16% at 165 K) lies one of the best results in the world. The experimental results also show that the refrigeration efficiency of the present PTC could be much improved by optimizing its operating parameter. In summary, the present PTC can work efficiently at a wide temperature range from 90 K to 260 K, which shows great potential candidate for small refrigerators such as vaccine preservation, organ freezing transportation and outdoor preservation of wildlife samples.

Investigation of intermediate cooling capacity from a single-stage coaxial pulse tube cryocooler

Pulse tube cryocoolers (PTCs) are suitable for cooling infrared detectors in space. With the development of multi-spectral detection, multi-temperature cooling of PTCs is essential. Multi-stage and two cold finger coolers are commonly used, which are not compact and difficult to control. To further compactness, we investigate the intermediate cooling capacity of a single-stage coaxial PTC in this paper. The single-stage PTC achieves dual temperature cooling by obtaining cooling power simultaneously from the cold end and the middle of its cold finger. Based on theoretical and simulation analysis, the effects of inter-cooling power on the temperature variation, loss, and phase angle, and the cooling performance at the dual-temperature zone with different input power are derived. Additionally, some experiments are carried out to demonstrate the accuracy of the theory and simulation, and the reasons for the difference between the simulation and the experiment are explained. The experiment shows that the cooling temperature of the cold end can increase from 70.7 K to 87.4 K when the inter-cooling capacity increase from 1 W to 4 W with an input power of 150 W and a cooling capacity of 4 W.

Numerical investigation on the influence of radial thermal conduction in a co-axial pulse tube cooler

A co-axial pulse tube cooler, whose regenerator normally surrounds the pulse tube, has the most compact structure. Internal radial thermal conduction may occur between the regenerator and pulse tube due to the temperature mismatch at the same axial location. Theoretical analysis indicates that radial transferred heat flow from pulse tube to regenerator can increase the cooling power, while the opposite radial heat flow which flows from regenerator to pulse tube would decrease the cooling power. Then CFD models with and without radial thermal conduction based on a practical single-stage pulse tube cooler have been conducted to further analyze the mechanism and effect. Simulation results show that after introducing radial thermal conduction, the maximum temperature difference between the gas in regenerator and pulse tube is reduced from 25 K to below 10 K, and cooling power is reduced by 5.8% as a result of the time-averaged radial heat flow from regenerator to pulse tube. The influence of thermal conductivity of the coupled wall between regenerator and pulse tube is also discussed. This study provides a better understanding on the radial heat thermal conduction in a single stage co-axial pulse tube cooler, which sets the basis for optimizing the geometrical arrangement of co-axial pulse tube coolers.

Absolute distance measurement to coaxial multi-targets based on optical balanced cross-correlation using a single femtosecond laser.

We describe a high-precision ranging method based on an optical balanced cross-correlation system with a scanning repetition rate using a single femtosecond laser. By scanning the repetition rate of a laser, measuring pulses can be overlapped with reference pulses. It is an effective method to make reference pulses overlap with coaxial multiple target pulses without additional mechanical devices. The overlapped pulses are launched to the optical balanced cross-correlation system, which improves the time resolution measurement to the attosecond level. Two nominal distances are measured, and an additional commercial laser interferometer is used as a comparison to evaluate the accuracy of our measurement system. Moreover, the thickness of three stacked glasses is measured by our measurement system to verify that this system can measure coaxial multiple targets more quickly than conventional optical balanced cross-correlation systems using a single optical frequency comb.

Acceleration Characteristics of Ions Exhausted from Short Pulse Coaxial Laser-Assisted Pulse Plasma Thruster

Acceleration Characteristics of Ions Exhausted from Short Pulse Coaxial Laser-Assisted Pulse Plasma Thruster

Investigation of Intermediate Cooling Capacity from Single-Stage Coaxial Pulse Tube Cryocooler

Investigation of Intermediate Cooling Capacity from Single-Stage Coaxial Pulse Tube Cryocooler

A High Efficiency Coaxial Pulse Tube Cryocooler for Cooling Medium-Wave Infrared Detectors

In order to meet the cooling demand of a medium-wave infrared detector, a coaxial pulse tube cryocooler (PTC) working at temperature around 90 K has been designed. The cooling capacity is requested to exceed 7 W at 90 K with an input electric power of 100 W. The compressor is made based on an engineering prototype which has been successfully applied in space. Experimental studies have been carried out to improve the performance of the cold finger from the aspects of inertance tube, cold-side heat exchange, hot-side flow straightener. By carrying out these optimizations the PTC can achieve a 7.64 W cooling capacity at 90 K when the input electric power is 100 W, and its relative Carnot efficiency is higher than 15% at temperature between 80 and 100 K.

A completely co-axial two-stage pulse tube cooler working at liquid hydrogen temperatures

<p indent=0mm>Pulse tube coolers, which work at liquid hydrogen temperature, are widely used in applications such as cooling infrared sensors and superconducting devices because of the advantage of no moving parts at low temperatures. Pulse tube coolers can be divided into three types according to their shape: In-line type, U-type, and co-axial type. In-line type and U-type pulse tube coolers separate the regenerator and the pulse tube, both of which are only connected through the cold end heat exchanger. For co-axial pulse tube coolers, the regenerator normally has an annular cross section surrounding the pulse tube. They are becoming increasingly popular in practice for their compactness, but the thermal contact between the regenerator and the pulse tube may affect the system performance. Few studies have been conducted on the influence of radial thermal contact, most of which are based on a single-stage pulse tube cooler and deviate from an actual co-axial type pulse tube model. For pulse tube coolers working at liquid hydrogen or a low temperature, two-stage cold heads are commonly used. In this study, theoretical analyses are conducted on the basis of a two-stage gas-coupled pulse tube cooler to investigate the influence of radial heat transfer. Based on the simulations, a completely co-axial two-stage pulse tube cooler is set up and experimental studies are carried out. Four models (corresponding to different shapes of cold heads) are constructed to theoretically analyze the mechanism based on the Sage software. Without radial thermal contact (corresponding to a two-stage U-type cold head), the temperature distributions along the pulse tubes are nonlinear, especially the 2nd stage pulse tube due to the large temperature span. Corresponding to the position of the 1st cold end, the temperature of the 2nd stage pulse tube is high to <sc>230 K;</sc> at the same axial location, the temperature difference between the 2nd stage regenerator and the pulse tube is approximately <sc>190 K.</sc> Radial heat transfer on the 2nd stage pulse tube (corresponding to 1st stage U-type and 2nd stage co-axial type cold head or the completely co-axial two-stage cold head) can cool down the 2nd stage pulse tube effectively; at the same axial location, the temperature difference between the 2nd stage regenerator and the pulse tube decreases to <sc>60 K</sc> with the 1st stage U-type and 2nd stage co-axial type cold head; such a difference also decreases to <sc>75 K</sc> with the completely co-axial two-stage cold head. Radial heat transfer increases the enthalpy flow in the 2nd pulse tube, and the expansion efficiency of the pulse tube increases from 69% to approximately 85%. The cooling performance is also improved. Meanwhile, the radial heat transfer between the 1st stage regenerator and the pulse tube (corresponding to 1st stage co-axial type and 2nd stage U-type) has a relatively minor effect on the system performance. Exergy losses are also investigated with different models. Therefore, a well-matched geometrical arrangement of the co-axial configuration is essential for achieving the optimal performance. The completely co-axial two-stage cold head not only improves the compactness but also the cooling performance. Experiments are then performed. As a result, a completely co-axial two-stage pulse tube cooler is built. A cooling power of <sc>1.2 W</sc> at <sc>20 K</sc> is obtained with <sc>223 W</sc> PV power input.

Analysis of coupling characteristics of coaxial line parallel to lightning current channel

Base on the analysis of the coaxial coupling theory, the experimental model of the coaxial cable short-range coupling lightning electromagnetic pulse is established to study the problem of coaxial cable short-range coupling lightning electromagnetic pulse on the ship mast and high tower. The combination wave generator is used to simulate the 8/20 μs lightning current waveform, and the metal bar with the length of 1 m and diameter of 0.016 m is used to simulate the lightning channel as the radiation source. The length of the coaxial cable and the distance from the radiation source are changed for the test. The conclusion is as follows: when the coaxial cable is coupled with lightning wave in a short distance, the voltage waveform of cable terminal is still double exponential wave, with strong damping oscillation at 0.1 ∼0.4 μs. When the cable terminal is open circuit or connected with matching resistance, the rising time is shorter, about 1 μs; when the cable terminal shielding layer is grounded, the rising time is longer, about 10 μs. The peak voltage and energy coupled to the coaxial cable at short distance are positively correlated with the cable length, and inversely correlated with the distance from the radiation source. The energy that the cable is coupled to mainly comes from the low-frequency part, and there are multiple energy peaks below 100 Hz. Using fitting curve and experimental data, when the coaxial cable terminal is open circuit, the lightning current reaches 30 kA, the cable length is 30 m, and the distance from the lightning channel is 0.15 m, the peak value of the voltage coupled to the cable terminal is 66 V. It has certain guiding significance and value in the practical application of electromagnetic pulse protection.

Coaxial Stirling pulse tube cryocooler with active displacer

Coaxial pulse tube cryocoolers are the configuration of choice as they allow better access to the cold head. Hence, a previously built and tested in-line pulse tube cryocooler which uses an active displacer for phase control has been modified into a coaxial configuration. The active displacer allows the mass flow and the pressure pulse at the cold end of the pulse tube to be easily adjusted for optimum performance. The displacer also allows the expansion power at the warm end of the pulse tube to be recovered in order to operate more efficiently. A numerical Sage model is used to demonstrate this by examining the work flows throughout the cryocooler and it is shown that more than 6% of the power required to drive the cryocooler comes from the warm end of the pulse tube via the displacer. When using an inertance tube or orifice, this expansion power is dissipated as heat which is why using a displacer can lead to a more efficient cryocooler. Moreover, the effect of changing the displacer phase and stroke on cryocooler performance and pressure characteristics is examined both experimentally and numerically.

Design of a two-stage gas-coupled high-frequency pulse tube cryocooler working around 4 K

High-frequency pulse tube cryocooler have unique advantages for aerospace and ground applications. However, it is difficult to obtain lower cooling temperature: to obtain the liquid helium temperature, three-stage or four-stage structure by thermal coupling are currently used. In order to further improve the compactness, a two-stage gas-coupled high-frequency multi-bypass coaxial pulse tube cryocooler has been designed. The simulation results indicate that the designed cryocooler can provide a cooling capacity of 25 mW@4.2 K with 416 W input electrical work. The interaction between structural parameters and operating conditions, as well as some preliminary test results will be presented in this paper.

Numerical modelling of a coaxial Stirling pulse tube cryocooler with an active displacer for space applications

A numerical model for a coaxial Stirling pulse tube cryocooler with an active displacer has been developed. An active displacer, in place of an inertance tube, has already demonstrated good efficiency in an in-line pulse tube, but incorporating this design into a coaxial configuration permits better access to the cold head. A model of the coaxial cold head was developed to include the radial flow and cooling in this region. The sub-assembly models were validated with flow testing of the physical sub-units of the cryocooler. The performance has been predicted for the cryocooler as a function of: fill pressure, operating frequency, and phase angle between the position of the linear compressor and displacer. The projected difference in performance and efficiency of the coaxial configuration was compared to the in-line design. The coaxial cryocooler numerically simulates 6 W of cooling at 80 K with an input power of 85 W, at a fill pressure of 28 bar, an operating frequency of 60 Hz, and a compressor-displacer phase angle of 41°. Overall, the coaxial cryocooler outperforms the in-line design in terms of cooling power, but not in terms of efficiency.

Temporal stitching in burst-mode filamentation

The creation of single optical filaments in air is bound by constraints on laser power, divergence, wavelength, pulse duration, and atmospheric parameters. The consequential characteristics of the filaments produced limit some potential applications, particularly those related to a filament’s spatial and temporal extent. Here, we demonstrate, for the first time, the temporal concatenation or stitching of up to 32 filaments, each separated by times typically ∼0.5ns, forming a single stream of coaxial filamenting laser pulses.