Stirling-type Pulse Tube Coolers Research Articles

Performance improvement of a Stirling-type two-stage pulse tube cooler by using stepped displacer plus bypasses phase shifter

Stirling-type pulse tube cooler (SPTC) is the most prospective thermoacoustic refrigerator due to its long lifetime, high reliability and low vibration, and the phase shifter significantly affects the energy conversion efficiency of SPTC. A novel phase shifter of the stepped displacer plus bypasses (SD-B) is proposed in this paper. Thermoacoustic impedance characteristics of the stepped displacer (SD) and the stepped displacer plus bypasses (SD-B) are analyzed. Based on the two-stage SPTC, the effect of additional combined DC flows in the system is first investigated. Results indicate that the cooling capacity could be improved through introducing additional DC flows in the positive direction from the hot end of regenerator to pulse tube. While for SD, negative DC flows are induced due to the clearance seal gaps between the displacer piston and cylinder shell. Thus, SD-B is explored to improve energy conversion efficiency through naturally introducing DC flows by bypasses. The influence of the opening diameter of two bypasses is investigated, and comparisons between the SD and SD-B are performed. Results indicate that with SD-B, the cooling capacity at 20 K achieves a maximum of 2.04 W with a relative Carnot efficiency of 13.0%, 56.9% higher than that of SD.

Innovative phase shifter for pulse tube operating below 10 K

Stirling type pulse tubes are classically based on the use of an inertance phase shifter to optimize their cooling power. The limitations of the phase shifting capabilities of these inertances have been pointed out in various studies. These limitations are particularly critical for low temperature operation, typically below about 50K. An innovative phase shifter using an inertance tube filled with liquid, or fluid with high density or low viscosity, and separated by a sealed metallic diaphragm has been conceived and tested. This device has been characterized and validated on a dedicated test bench. Operation on a 50–80K pulse tube cooler and on a low temperature (below 8K) pulse tube cooler have been demonstrated and have validated the device in operation. These developments open the door for efficient and compact low temperature Stirling type pulse tube coolers. The possibility of long life operation has been experimentally verified and a design for space applications is proposed.

Improved Performance of an Indigenous Stirling Type Pulse Tube Cooler and Pressure Wave Generator

Sustained efforts have been made in our laboratory to improve the performance of an indigenously developed pressure wave gen- erator by reducing the mechanical losses and the required input power. An acoustically matching pulse tube cooler, with a design target of 0.5W at 80K, was designed using Sage and experience gained from previous studies. The pulse tube cooler was fabri- cated and tested. The effect of regenerator stacking pattern on the cooler performance was studied by filling the regenerator with mesh of the same size #400 and with multi meshes #250, 325, 400. In present experiments, regenerator with #400 mesh at 30bar filling pressure performed better with more energy efficiency. A no load temperature of 74K was achieved with input power of 59W corresponding to a cooling power of 0.22W at 80K. Parasitic heat load to the cooler was measured be 0.68W. This heat load is primarily by heat conduction through the regenerator and pulse tube wall. By reducing the wall thickness from 0.30mm to 0.15mm, the parasitic loads can be reduced by 50%.

Investigation on High-Power Stirling-Type Pulse Tube Coolers for Cooling HTS Motors

High-power Stirling-type pulse tube coolers (HSPTCs) driven by oil-free linear compressors are promising candidates for cooling HTS devices for the advantages of simple configuration, low noise and stable operation. Three U-shaped two-stage pulse tube coolers driven by a 10 kW linear compressor were built and studied. The effects of flow inhomogeneity on the temperature profiles along the regenerator and on the cooling capacity were investigated experimentally. By optimizing the impedance matching and operating conditions, the first cooler can reach a base temperature of 44.2 K; the second cooler reaches a base temperature of 27.1 K and provides a cooling power of 50 W at 45.6 K with 4.8 kW of power; the last cold head reaches a base temperature of 13.27 K and provides a cooling power of 18.3 W at 30 K. The present results form a foundation for building a HSPTC system capable of providing a cooling power of 80 W at 30 K.

Advances in High Power Stirling-Type Pulse Tube Cooler

High power Stirling-type pulse tube coolers (HSPTCs) with oil-free linear compressors are promising solutions for cooling superconducting magnets. The cooling capacity of HSPTC ranges from 50 W to a few kilowatts below 100 K. At present the lowest refrigeration temperature of HSPTC has reached below 30 K. After a brief introduction of Stirling-type PTC, this paper reviews the newest developments in HSPTC. At the same time, the potential of HSPTC to be applied in cooling superconducting magnets is analysed. Possible future advances and prospective research emphases are also presented.

High-power Stirling-type pulse tube cooler working below 30 K

High-power Stirling-type pulse tube coolers (PTCs) are promising candidates for cooling HTS devices and gas liquefaction or separation applications. Nevertheless, till now most high-power Stirling-type PTCs are not able to reach a refrigeration temperature below 35 K. Here, a high-power two-stage Stirling-type PTC was designed, manufactured and experimentally investigated. In order to realize a convenient coupling with a thermal load, U-shape configuration is adopted in both stages, which makes it more challenging to distribute the gas flow and reduce dead volume in the cold end heat exchanger. By optimizing operating conditions, flow straightener, and double-inlet opening, the cooler has reached no-load refrigeration temperatures of 29.6 K and 27.1 K at 55 Hz and 40 Hz, respectively. Furthermore, the cooler is able to provide cooling powers of 50 W at 45.6 K and 100 W at 59.3 K when input pV powers are 4.77 kW and 4.59 kW, respectively.

Investigation on regenerator temperature inhomogeneity in Stirling-type pulse tube cooler

Regenerator is one of the most crucial components to pulse tube cooler (PTC) and thermoacoustic engine. As such regenerator is scaled up to high-power, the thermal and hydrodynamic communication transverse to the acoustic axis gets weaker and weaker. Under this condition, any unsymmetric factor could cause serious instability to the cooler or engine, which degrades their performance. Investigation has been carried out on a high-power two-stage thermal-coupled U-shape Stirling-type PTC. By detailed circumferential temperature measurements along the middle heat exchanger and second stage regenerator, a kind of temperature inhomogeneity caused by unsymmetric pre-cooling effect of inter-stage thermal bridge was found in the lower part of the regenerator of the PTC. The temperature inhomogeneity originating from the middle heat exchanger of the second stage regenerator amplified itself in the lower part of the regenerator and then internal streaming formed. The maximal radial temperature difference could reach 30–40 K. Experimental results show that the temperature inhomogeneity intensifies with increased pre-cooling power and its direction can be reversed by changing the pre-cooling effect of the first stage PTC to heating effect by using external thermal load. This research shows that it is important to maintain the heating or cooling effects of heat exchangers uniform in high-power regenerative coolers and engines.

Numerical study on transverse asymmetry in the temperature profile of a regenerator in a pulse tube cooler

Transverse asymmetry in the temperature profile of the regenerator in a Stirling-type pulse tube cooler as observed in experiments was analysed in a numerical study. The asymmetry was reproduced using a one-dimensional model of the cooler where the regenerator was modelled using two identical parallel regenerator channels. The asymmetry was caused by a circulating flow that was superimposed on the oscillating flow. The primary mechanism driving the circulating flow was due to the wave form of the pressure difference between the ends of the regenerator and the dependence of the instantaneous mass flow rate on the pressure difference and temperature.

300 Hz thermoacoustically driven pulse tube cooler for temperature below 100K

This letter introduces a thermoacoustically driven pulse tube cooler system working at around 300Hz. In the system, a thermoacoustic standing-wave engine is used to drive a Stirling-type pulse tube cooler. Besides the design considerations for key components in each subsystem, the benefits of using the acoustic amplifier tube to couple the engine and the cooler have been analyzed through both calculations and experiments. So far, a lowest no-load temperature of 95K has been obtained on the system with the acoustic amplifier tube being used. Since high frequency operation of the system could lead to a much reduced system size, the result shows the potential of using the system in small-scale cryogenic applications.

Thermodynamic analysis of GM-type pulse tube coolers

The thermodynamic loss of rotary valve and the coefficient of performance (COP) of GM-type pulse tube coolers (PTCs) are discussed and explained by using the first and second laws of thermodynamics in this paper. The COP of GM-type PTC, based on two types of pressure profiles, the sinusoidal wave inside the pulse tube and the step wave at the compressor side, has been derived and compared with that of Stirling-type PTC. Result shows that additional compressor work is needed due to the irreversible entropy productions in the rotary valve thereby decreasing the COP of GM-type PTC. The effect of double-inlet mode on the COP of PTC has distinct improvement at lower temperature region (larger T H/ T L). It is also shown that the COP of GM-type PTC is independent of the shape of the pressure profiles in the ideal case of no flow resistance in the regenerator.