Orifice Pulse Tube Refrigerator Research Articles

Investigations on nonlinear processes of a Gifford-McMahon type orifice pulse tube refrigerator

The target of this investigation is to illustrate the nonlinear fluid flow, heat transfer, and vortex formation phenomena in an orifice pulse tube refrigerator by numerical simulation. Numerical results confirm that jet streaming is generated at the low-temperature end of the pulse tube in between the junction of U-shaped tube and pulse tube. The primary vortex, which is generated due to the minor loss, continuously grows because of velocity change and eventually leads to the formation of secondary eddy. Consequently, flow straighteners have been adopted at the hot side of the regenerator, hot heat exchanger, and both sides of U-shaped tube. It is noticed that, jet streaming has been suppressed at the cold end of the pulse tube. Nevertheless, the streaming effect generated due to the oscillating flow of the gas parcels within the pulse tube, and third type of streaming have not been suppressed with the flow-straightener. Additionally, the numerical simulation shows different gas flow behaviors within the pulse tube that occurs due to the oscillating pressure pulse. An experimental investigation is conducted to compare experimental results with the numerical results and a valid agreement is observed between them.

Thermoeconomic performance optimization of an orifice pulse tube refrigerator

The thermodynamic process parameters such as cooling capacity and percentage Carnot efficiency of an orifice pulse tube refrigerator are maximized using a novel hybrid statistical simulation approach. With the help of a one-dimensional numerical model, the inside gas flow and thermal processes responsible for the production of cooling effect inside the tube have been solved. Subsequently, the thermodynamic process parameters are calculated as a function of input geometrical parameters of the regenerator, pulse tube, and orifice valve. Response surface methodology is thereupon applied to investigate the influence of input factors on outputs. Desirability method is finally adopted to maximize both cooling capacity and percentage Carnot efficiency. A sensitivity investigation has been undertaken to find out the degree of influence of each input on the output. An experimental investigation has been conducted at the optimal set of parameters so as to validate the proposed methodology. The investigation shows that, there exists an almost linear relationship among the geometrical parameters of the pulse tube on outputs, and a nonlinear quadratic relationship among the geometrical parameters of regenerator on outputs. Finally, possible combination of input parameters have been generated by the model at which both the outputs are maximum.

Optimal design of thermal performance of an orifice pulse tube refrigerator

In this paper, simultaneous influence of low and high pressure of helium compressor, frequency, opening coefficient of orifice valve and waiting time of rotary valve on the cooling capacity and “coefficient of performance” (COP) of a single-stage orifice pulse tube refrigerator is studied. “Box–Behnken design” model is opted here to create a design data matrix by utilizing the above design variables and responses (i.e., cooling capacity and COP). A numerical model is used to estimate the responses from the design variables, and effects of each design variable on the responses are studied through “analysis of variance.” Finally, input variables are ranked according to their ability to change the outputs by using the sensitivity analysis. A regression equation, which establishes a functional relationship between the design variables and response, is maximized by using “particle swarm optimization” method. ANN model is also applied to find the relationship between design variables and responses. Furthermore, by using the optimal range of inputs, an experimental investigation is carried out. Novelty of this article includes the study of simultaneous influences of aforementioned input variables on COP and cooling capacity, and also the sensitivity analysis. It has been observed that the cooling power and COP are increased by 10.8% and 0.76%, respectively, after optimization within the range of selected input parameters.

Comparative Analysis of Calculation Models of Pulse Tube Thermoacoustic Refrigerator

A comparative analysis of different computational methods was implemented to evaluate their usage in engineering design methodology of orifice pulse tube refrigerator (OPTR). A thermodynamic model to estimate the lowest temperature level in cold heat exchangerfor a given ratio of the pulse tube and compliance was developed. Two detailed time-dependent axisymmetric computational fluid dynamic (CFD) models of the OPTR to predict its performance was considered. The computational results were compared with experimental results to validate the choice of model for numerical design methodology.

Optimal Design of Orifice Pulse Tube Refrigerator Based on Response Surface and Genetic Algorithm

The modeling and optimization of a pulse tube refrigerator is a complicated task, due to its complexity of geometry and nature. The present work aims to optimize the orifice type pulse tube refrigerator (OPTR) using the response surface methodology (RSM). The influence of operating condition like frequency, charging pressure, orifice opening, and geometrical dimensions of pulse tube and regenerator on cold end temperature and input compressor power in the OPTR is investigated. For a fixed reservoir volume and regenerator size and porosity, the optimized value of the above parameters suggested by the response surface methodology has been solved using available one-dimensional code. It is reported that the cold head temperature varies due to variation in dimension of the pulse tube and regenerator in between 44 and 160 K, and compressor work varies from 265 to 1288 W. Using the results from the simulation, RSM is conducted to analyze the effect of the independent variables on the responses. To check the accuracy of the model, the analysis of variance method has been conducted. A quadratic model for cold end temperature and compressor input power has been developed. Based on the proposed mathematical RSM models, a novel multi-objective optimization study, using the non-dominated sorting genetic algorithm, has been performed to optimize the responses by generating the pareto frontiers. To avoid subjectiveness and imprecision, maximum deviation theory is used to rank the pareto frontiers based on composite scores.

Numerical simulations of transport processes in a pulse tube cryocooler: Effects of taper angle

A numerical model is developed for the prediction of the performance and transport characteristics in an orifice pulse tube refrigerator (OPTR). The OPTR is studied for a two specific geometries. In the first geometry (A), only the taper angle of the pulse tube is changed. In the second geometry (B), the taper angle of the pulse tube is varied along with the diameter of the hot heat-exchanger. The taper angle of the pulse tube is shown to have significant effects on the secondary streaming patterns observed in the pulse tube. Tapering the pulse tube improved the performance of the OPTR only for Geometry-B. In this case, suppression of velocity streaming is achieved in the warm end of the pulse tube.

Optimal performance of regenerative cryocoolers

The key component of a regenerative cryocooler is its regenerative heat exchanger. This device is subject to losses due to imperfect heat transfer between the regenerator material and the gas, as well as due to viscous dissipation. The relative magnitudes of these losses can be characterized by the ratio of the Stanton number St to the Fanning friction factor f. Using available data for the ratio St/ f, results are developed for the optimal cooling rate and Carnot efficiency. The variations of pressure and temperature are taken to be sinusoidal in time, and to have small amplitudes. The results are applied to the case of the Stirling cryocooler, with flow being generated by pistons at both sides of the regenerator. The performance is found to be close to optimal at large ratio of the warm space volume to the regenerator void volume. The results are also applied to the Orifice Pulse Tube Refrigerator. In this case, optimal performance additionally requires a large ratio of the regenerator void volume to the cold space volume.

An internal streaming instability in regenerators

Various oscillating-wave thermodynamic devices, including orifice and feedback pulse tube refrigerators, thermoacoustic-Stirling hybrid engines, cascaded thermoacoustic engines, and traditional Stirling engines and refrigerators, utilize regenerators to amplify acoustic power (engines) or to pump heat acoustically up a temperature gradient (refrigerators). As such a regenerator is scaled to higher power or operated at lower temperatures, the thermal and hydrodynamic communication transverse to the acoustic axis decreases, allowing for the possibility of an internal acoustic streaming instability with regions of counterflowing streaming that carry significant heat leak down the temperature gradient. The instability is driven by the nonlinear flow resistance of the regenerator, which results in different hydrodynamic flow resistances encountered by the oscillating flow and the streaming flow. The instability is inhibited by several other mechanisms, including acoustically transported enthalpy flux and axial and transverse thermal conduction in the regenerator solid matrix. A calculation of the stability limit caused by these effects reveals that engines are immune to a streaming instability while, under some conditions, refrigerators can exhibit an instability. The calculation is compared to experimental data obtained with a specially built orifice pulse tube refrigerator whose regenerator contains many thermocouples to detect a departure from transverse temperature uniformity.

パルス管冷凍機と熱駆動熱音響冷凍機の効率

We discuss the heat flow and work flow of an orifice pulse-tube refrigerator and a heat-driven thermoacoustic cooler consisting of a single looped tube. It is shown that, while the orifice of the orifice pulse-tube refrigerator is essential for increasing the cooling power, it decreases the efficiency because of the dissipation introduced by itself. It is also shown from the energy flow diagram that dissipation of the work flow inherently occurs in the heat-driven thermoacoustic cooler, resulting in a reduction in efficiency. We present that these unwanted dissipations would be avoided by the addition of a feedback path for the work flow. The modified refrigerator and the cooler would achieve efficiencies much higher than those of the original ones, especially at noncryogenic temperatures.

Numerical simulations comparing nonlinear acoustic effects in straight and tapered tubes

In their efforts to improve the efficiency of an orifice pulse tube refrigerator, Olson and Swift [Cryogenics 37, (769–776 (1997)] reported on the benefit of using an optimal taper angle in the construction of the conical pulse tube. They concluded that this geometry effectively suppressed nonlinear acoustic streaming which was interfering with the desired heat transfer within the device. To investigate further the effects of tube geometry on streaming, a numerical simulation is developed for a tube with varying degrees of taper angle. This 2-D finite-difference model, based on the work of Sparrow and Raspet [J. Acoust. Soc. Am. 90, 2683–2691 (1991)], compares nonlinear acoustic propagation in a straight cylindrical tube with that in a tapered conical tube. Development of the model equations in cylindrical and spherical coordinates as well as refinement of the computational grid near the boundaries are considered. [Work supported in part by ONR.]

C09 オリフィス型パルス管冷凍機における熱流動数値解析(パルス管冷凍機,熱音響機器及び関連要素と応用システム(3))

Numerical analysis of viscous compressible flow in an orifice pulse-tube refrigerator was performed to investigate the effect of the thickness of a pulse tube wall on refrigeration in a orifice pulse-tube refrigerator. Transient axisymmetric two-dimensional equations of continuity, momentum and energy were solved utilizing the TVD scheme. A physical model combining a pulse tube with a wall and a regenerator is used for numerical simulation. In this paper, we analyzed the change in wall temperature, wall temperature profiles and heat flowing in the wall for various thickness of the wall.

Dependence of convective secondary flow on inclination angle in an inclined pulse tube refrigerator revealed by visualization

Secondary flow in an inclined orifice pulse tube refrigerator at typical inclination angles of 0–180° was studied by using a smoke-wire flow visualization technique. It was revealed that the secondary flow formed a unicellular convective flow in the pulse tube and had two flow patterns depending on the angle. This dependence of flow pattern on the inclination angle is well explained by the superposition of gravity-driven convective flow on acoustic streaming. Even if the cold end was lower than the hot end, the gravity-driven convective flow occurred and the secondary flow was affected by gravity.

Characteristics of the double inlet pulse tube

The performance of the double inlet pulse tube (DIPT) is analyzed using a linearized model that takes account of the void volume of the regenerator. The maximum rate of refrigeration obtainable with the regenerator is determined as a function of frequency and void volume. This rate can be achieved by a DIPT with infinitely large reservoir volume. Corrections resulting from a finite reservoir volume are important only at low frequency. The coefficient of performance of a DIPT with optimized rate of refrigeration is less than half of the thermodynamic maximum. The results obtained for the DIPT are compared with corresponding results for the optimized orifice pulse tube refrigerator (OPTR). The large improvements in performance obtained with the DIPT over the OPTR are due primarily to an increase in the pulse tube pressure. The maximum rate of refrigeration decreases as the temperature at the cold side decreases. This is caused primarily from the resulting decrease in cold side flow rate. At given temperature ratio, addition of the second inlet reduces the flow rate through the regenerator over a range of intermediate frequencies.

A pulse-tube refrigerator using variable-resistance orifice

In the present study, we propose a new design of orifice pulse-tube refrigerator (VROPT) using a variable-resistance valve to replace the conventional orifice. The variable-resistance orifice (VRO) is basically a high-speed solenoidal valve similar to the fuel jet device widely used in automobile engines. By changing the frequency and periods of ON and OFF of the valve through an electronic device, we can change the flow resistance of the VRO. This thus provides a possibility for an OPT to be controlled on-line during operation. From the results obtained in the present study, we have shown that VROPT is able to achieve on-line control by regulating the duty cycle d or frequency f v of the VRO. We also show that VROPT will not loss its thermal performance as compared to conventional OPT.

Performance of the inertance pulse tube

The rate of refrigeration of the inertance pulse tube (IPTR) is found as a function of the relevant parameters. In the simplified case of infinite volume of the reservoir and zero dead volume of the regenerator, these parameters are the dimensions of the inertance tube, the volume of the pulse tube, the conductance of the regenerator, the driving pressure, and the frequency. The effective conductance of the inertance tube is determined using a simple turbulent flow model. It is found that the performance of the IPTR is superior to that of the orifice pulse tube refrigerator (OPTR) over a limited range of frequencies. The improvement is explained in terms of the pressure amplitude in the pulse tube, the flow rate between the regenerator and the pulse tube, and the phase angle between these parameters. The analysis is extended to the case of finite reservoir and regenerator volumes. It is indicated how the results obtained can be useful in experimental work.

Experimental study on the design of orifice pulse tube refrigerator

An experimental study on the design of a single-stage orifice pulse tube refrigerator (OPTR) was carried out. It was shown experimentally that there exists an optimum operating frequency which increases with decreasing pulse tube volume. For a fixed pulse tube volume, increasing the pulse tube diameter will improve the performance. The experimental results are used to derive a correlation for the performance of OPTR which correlates the net cooling capacity with the operating conditions and the dimensions of the OPTR.

Flow characteristics of a metering valve in a pulse tube refrigerator

Flow characteristics through a metering valve, a component in orifice pulse tube refrigerators and double-inlet pulse tube refrigerators, are discussed in this paper. Under the assumption that the inertial and convective terms in the momentum equation for a compressible flow can be neglected compared to the pressure gradient term, an expression is obtained for the transient mass flow rate in terms of the local temperature and pressure as well as pressures across the valve. Depending on where the local pressure and temperature are evaluated, two algebraic expressions for the mass flow rates in terms of the effective area are obtained. The values of the effective areas in these two expressions for different openings of the valve at an oscillating frequency of 1 Hz were evaluated based on pressure and temperature measurements. The results are useful for the numerical simulation of the performance of an orifice pulse tube refrigerator or a double-inlet pulse tube refrigerator.

Analysis of an orifice pulse tube refrigerator using the method of characteristics

The behaviour of the various gas elements which enter the tube of a pulse tube refrigerator from its cold end has been analysed using the method of characteristics. It is found that, in an orifice pulse tube refrigerator, the gas elements can be divided into three parts. The specific cooling capacity produced by the second part of the gas elements is the largest. If the total mass is fixed, in order to improve the overall cooling capacity of an orifice pulse tube refrigerator, the ratio of the gas elements in the second part should be increased, while those in the first part and the third part should be decreased.

Parametrical study for performances comparison between classic orifice pulse tube and hybrid Stirling pulse tube refrigerators

Parametrical study for performances comparison between classic orifice pulse tube and hybrid Stirling pulse tube refrigerators

Acoustic recovery of lost power in pulse tube refrigerators

In an efficient Stirling-cycle cryocooler, the cold piston or displacer recovers power from the gas. This power is dissipated into heat in the orifice of an orifice pulse tube refrigerator, decreasing system efficiency. Recovery of some of this power in a pulse tube refrigerator, without sacrificing the simplicity and reliability inherent in a system with no cold moving parts, is described in this paper. In one method of such power recovery, the hot ends of both the regenerator and the pulse tube are connected to the front of the piston driving the refrigerator. Experimental data is presented demonstrating this method using a thermoacoustic driver instead of a piston driver. Control of time-averaged mass flux through the refrigerator is crucial to this power recovery, lest the refrigerator’s cooling power be overwhelmed by a room-temperature mass flux. Two methods are demonstrated for control of mass flux: a barrier method, and a hydrodynamic method based on turbulent irreversible flow. At −55 °C, the refrigerator provided cooling with 9% of the Carnot coefficient of performance. With straightforward improvements, similar refrigerators should achieve efficiencies greater than those of prior pulse tube refrigerators and prior standing-wave thermoacoustic refrigerators, while maintaining the advantages of no moving parts.