Cold End Heat Exchanger Research Articles

Performance analysis and exergy assessment of an inertance pulse tube cryocooler

The world is facing the problems of the energy crisis. Thermal analysis and energy conservation of the engineering devices help to improve their performance. This paper conducted an experimental investigation for the performance analysis and exergy assessment of an Inertance Pulse Tube Cryocooler (IPTC) that uses working fluid -helium operated between 80 K cold end side temperature and room temperature.The variation of the different performance parameters like the effect of charge pressure, pulse tube volume, pulse tube length, etc., and its effect on the refrigerating effect isdescribed graphically. Exergy analysis involves the use and concepts of energy andexergy balances, enthalpy, entropy, and exergy calculations at various stages in thesystem. Exergy analysis identifies the zones of key exergy destruction that occurs insidethe system, which afterward can be subjected to its minimization to amend the systemperformance. The actual exergy efficiency value calculated for the overall system is 21.30 %. The decreasing order of exergy efficiency among the different components is acompressor (38.79 %), a hot end heat exchanger (6.19 %), regenerator, pulse tube andinertance tube (6 %), and cold end heat exchanger (2.70 %).

Design and experimental study of an outdoor portable thermoelectric air-conditioning system

This study aims to identify suitable microclimate cooling systems to reduce heat stress and improve human thermal comfort. A portable thermoelectric air conditioner was developed for local cooling of the human body. Effects of core components thermoelectric refrigerators (TECs), hot end heat dissipation, intake flow and cold end heat exchangers on TEAC performance. It is shown that, remarkably, this operating voltage can be distinguished from the optimal voltage for the maximum operational performance of TEAC. When the TECs operating voltage is 4V, the maximum COP is 2.2, and the best operating voltage is 10V, the maximum cooling capacity is 26.7 W (COP=0.92). Simulation data show that the area of the diffuser can effectively control the contact between the air and the cooling surface with an error of less than 10% compared to the experimental results. The fans and radiators attached to the hot side of the TEM play an important role in keeping the temperature difference on the hot side of the TECs as small as possible, by dissipating the heat generated on the hot side of the TEM to the external environment. In addition, the experimental refrigeration capacity is greater than 26.7 W and the new system has ultra-quiet operation at large refrigeration capacity, which has promising potential for advanced refrigeration, building air conditioning, ventilation systems and other applications. • Thermalelecrtic air conditioner (TEAC) can achieve a cooling capacity of 26.7W and a cooling coefficient of 0.92, enabling local cooling of the human body. • The maximum cooling capacity of thermoelectric refrigerator varies nonlinearly with the surface area and height of thermoelectric leg. • The increase of cooling capacity decreases with the increase of intake flow rate. • Increasing the strength of heat dissipation at the hot end of the thermoelectric cooler has a larger effect on the TEAC cooling capacity than on the cooling coefficient.

4 K GM-type pulse tube cryocooler with large cooling capacity

Owing to the advantages of large cooling capacity, low vibration and high reliability, GM-type pulse tube cryocoolers at liquid helium temperature have important applications in frontier fields of condensed matter physics research, quantum computing, etc. The phase shifter has an important influence on the cooling performance of pulse tube cryocooler. Previous researches on the phase shifter of GM-type pulse tube cryocooler mainly focused on the effect of a single phase shifter on the performance of the cryocooler at liquid helium temperature. In this paper, based on Sage software, a simulation model of a 4 K two-stage gas-coupled GM-type pulse tube cryocooler is first designed and constructed. The influence of the phase shifters of the two stages on the first-stage and the second-stage temperatures are calculated. The adjustment and optimization process of the cryocooler to obtain the liquid helium temperature is studied. Numerical simulations are given below. 1) The lowest temperature of the model is only about 100 K when the phase shifters of the two stages are closed. The lowest temperature of the model can be reduced to 2.7 K by optimizing the first-stage orifice valve, the second-stage orifice valve, the first-stage double-inlet valve and the second-stage double-inlet valve in sequence. 2) The first-stage orifice valve, the second-stage orifice valve, and the second-stage double-inlet valve have a significant effect on reducing the cooling temperature of the second stage, while the first-stage double-inlet valve has little effect on reducing the temperature of the second stage. 3) The first-stage orifice valve and the second-stage double-inlet valve have a significant effect on reducing the cooling temperature of the first stage, and the first-stage double-inlet valve has little effect on reducing the temperature of the first stage. The second-stage orifice valve will worsen the first stage performance. Finally, an experimental system is constructed. The lowest temperature of the experimental prototype can reach 3.1 K, and the cooling capacity of 0.8 W can be produced at 4.2 K, which is presently the best result obtained by the domestic two-stage gas-coupled valve-separated GM type pulse tube cryocooler. This research can not only promote the independent construction of domestic 4 K refrigeration platform, but also support the relevant frontier basic scientific research and the development of important scientific instruments and equipment. In the future, the structure of the first-stage cold-end heat exchanger and the impedance matching between the compressor and the cryocooler will be improved, and the gas coupling characteristics inside the cryocooler will be studied theoretically and experimentally in depth.

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.

Numerical simulation of a hybrid system using Peltier thermal switches in magnetic refrigeration

• A 2D transient model of a hybrid magnetic refrigeration system using Peltier modules as the heat switches was established. • The actual transient thermal response of the Peltier modules was considered in the model. • The comparison of the hybrid system with the AMR mode and the Peltier mode was done. • At 4.00 Hz and 0.20 A, the COP and cooling power density of the hybrid system exceeded that of the pure AMR mode. • The influence of operating parameters on the hybrid system performance was evaluated. To overcome the shortcoming of the low cooling power density in the ordinary magnetic refrigerator, a hybrid system using Peltier thermal switches in magnetic refrigeration has been proposed by researchers. In the system, the magnetic material is sandwiched between Peltier modules which are used as the thermal switches to transport the heat to and from the material undergoing the magnetic refrigeration cycle. To analyze the system, a two-dimensional transient model is established by considering the thermal characteristics of the Peltier module, which has not been done before. With the model, the performance of the hybrid system was firstly compared with that using the pure parallel plate active magnetic regenerator (AMR) mode and that using the pure Peltier mode. Compared with pure parallel plate AMR mode, the hybrid system using Peltier thermal switches in magnetic refrigeration can significantly increase the cooling power density at low frequencies (1.60 Hz – 4.00 Hz). In this frequency range, the coefficient of performance (COP) of pure parallel plate AMR mode decreased rapidly with the increase of frequency, while the COP of the hybrid system decreased slowly, and at 4.00 Hz and 0.20 A, the COP of the hybrid exceeded that of the pure parallel plate AMR mode. Compared with pure Peltier mode, the hybrid system can achieve the same cooling power with less power consumption and obtain a higher COP. Furthermore, the influence of operating parameters on the performance of the hybrid system, which included utilization factor, input current, the outlet temperature of the cold-end heat exchanger, frequency, and the number of refrigeration units, was investigated. The results show that, when using Peltier thermal switches, the actual transient thermal response of the Peltier module plays an important role in the hybrid system, which is ignored in previous literature. To achieve efficient operation at high frequency, when using Peltier thermal switches, the thermal response time of the Peltier modules as well as the Joule heating effect, etc, needs to be carefully evaluated.

Numerical investigation of temperature span of magnetic refrigerator using geometric configuration of gadolinium based parallel plate regenerator

In this manuscript, a numerical investigation on the temperature gradient of a magnetic refrigerator using different geometric configurations of a parallel plate regenerator is presented. The parallel plate regenerator is made up of gadolinium (Gd) as a magnetocaloric material with rectangular channels. The parallel plate regenerator is modeled and numerically investigated for 3D conjugated fluid convection and conduction heat transfer using Ansys Fluent. Two piston-cylinder displacers drive water as the working fluid through the regenerator loop. The hot and cold end heat exchangers are treated with the e-NTU method. The effect of changing the parallel plate regenerator’s dimensional parameters on temperature span is examined against the utilization factor of 0.1, keeping the regenerator’s porosity constant. The maximum temperature span is predicted by comparing simulated parallel plate magnetic regenerators for two diverse sets of dimensional parameters and surface areas is 36.5 K for magnetic field intensity of 0.8 T.

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.

Impact of Varying Load Conditions and Cooling Energy Comparison of a Double-Inlet Pulse Tube Refrigerator

Modeling and optimization of a double-inlet pulse tube refrigerator (DIPTR) is very difficult due to its geometry and nature. The objective of this paper was to optimize-DIPTR through experiments with the cold heat exchanger (CHX) along the comparison of cooling load with experimental data using different boundary conditions. To predict its performance, a detailed two-dimensional DIPTR model was developed. A double-drop pulse pipe cooler was used for solving continuity, dynamic and power calculations. External conditions for applicable boundaries include sinusoidal pressure from an end of the tube from a user-defined function and constant temperature or limitations of thermal flux within the outer walls of exchanger walls under colder conditions. The results of the system’s cooling behavior were reported, along with the connection between the mass flow rates, heat distribution along pulse tube and cold-end pressure, the cooler load’s wall temp profile and cooler loads with varied boundary conditions i.e. opening of 20% double-inlet and 40-60% orifice valves, respectively. Different loading conditions of 1 and 5 W were applied on the CHX. At 150 K temperature of the cold-end heat exchanger, a maximum load of 3.7 W was achieved. The results also reveal a strong correlation between computational fluid dynamics modeling results and experimental results of the DIPTR.

An experimental investigation on parallel-plate finned heat exchanger working with cryogenic oscillating helium flow

The space-cycle averaged Nusselt number is used to characterize the heat transfer characteristics of cold end heat exchanger in cryocoolers working with cryogenic oscillating helium flow. An experimental setup for cryogenic oscillating flow heat transfer measurement was designed and established. According to the experimental data obtained, it is evident that low temperature is significantly disadvantageous for heat transfer in oscillating flow. Similar to the experimental results at room temperature, under different mass flow rates, the heat exchanger has its own corresponding optimal Reynolds number at certain temperature for maximized heat transfer capacity.

A two-stage Stirling cryocooler capable of providing more than 100 W cooling power at 30 K

Regenerative cryocoolers with large cooling capacity at 30 K have a promising prospect in the fields of superconducting technology and gas liquefaction. Compared with other types of cryocoolers, Stirling cryocoolers have the advantages of high cooling capacity, high efficiency, fast cool-down process and compact configuration. A two-stage Stirling cryocooler with large cooling capacity driven by the crank-rod mechanism is developed based on the Sage simulation results, and the preliminary experimental results are presented. Firstly, the pressure characteristics under different working conditions are investigated. The amplitude of the pressure and the pressure ratio at the compression chamber increases as the charging pressure increases. Increasing the refrigeration temperature of the second stage results in the decrease of the pressure amplitude, and the decreasing rate increases as the heat load on the first stage increases. Then, the performance of the ambient heat exchanger is studied. As the charging pressure increases from 2.2 to 2.6 MPa, the heat rejected from the ambient heat exchanger increases from 7.57 to 9.19 kW when there are no heat loads at the two stages of the cryocooler. The heat rejected from the ambient heat exchanger increases by 400 W with every increase of 0.1 MPa of charging pressure. With the increase of the refrigeration temperature of the second stage, the heat rejected from the ambient heat exchanger decreases, and the decreasing rate increases as the heat load on the first stage increases. Furthermore, the influence of the variation of the charging pressure and heat loads at the two stages on the cooling performance is introduced. The temperature of the second-stage cold end heat exchanger drops to 30 K at a nearly constant cooling rate after the startup of the cryocooler. As the charging pressure increases from 2.2 to 2.6 MPa, the cooling rate increases from 16.59 to 19.46 K/min, and the cooling rate increases by about 0.72 K/min for every increase in pressure of 0.1 MPa. Under the charging pressure of 2.6 MPa, the second stage of the cryocooler reaches a no-load refrigeration temperature of 19.83 K, while the temperature of the first stage is 71.2 K. The no-load refrigeration temperature has a weak relationship with the charging pressure. As the charging pressure increases, the increasing rate of cooling capacity and COP with the refrigeration temperature increases. The cryocooler is capable of providing 110 W cooling power at 30 K with a relative Carnot efficiency of 10.96%. This is the best result ever reported in China. What is more, it is found that the cooling power at the two stages has little influence on the cooling performance of each other, which means the cooling power from the first stage can be applied in the pre-cooling process with little influence on the second stage. These results lay a solid foundation for future applications and performance improvement of the cryocooler.

Refrigeration mechanism of the gas parcels in pulse tube cryocoolers under different phase angles

The thermodynamic behavior of gas parcels in the key parts of the pulse tube cryocooler (PTC) is studied. The refrigeration mechanism of PTCs under different cold end phase angles is revealed by analyzing and comparing the heat transfer characteristics of the gas parcels at both sides of the cold end heat exchanger. Results show that the cold end phase angle, an important parameter of the PTC, determines the cooling performance of the PTC by affecting the heat transfer characteristics of the gas parcels in a cycle. In PTCs with a cold end phase angle normally between −30° and 60°, the gases pump heat from the cold end heat exchanger to the aftercooler all the way through the regenerator. In contrast, for the basic PTC with a cold end phase angle close to 90°, the heat transfer direction is reversed, the gases pump heat from the cold end heat exchanger to the hot end heat exchanger all the way through the pulse tube. This study unifies the various perspectives on the PTC’s refrigeration mechanism by revealing the inherent effect of the cold end phase angle, indicating that enhancing the heat pumping function of the gas in the regenerator is an essential way to improve the cooling performance.

Numerical investigation of room temperature magnetic refrigerator using microchannel regenerators

The paper reports numerical investigation of room temperature, active magnetocaloric regeneration (AMR) refrigerators/heat pumps using microchannel regenerator. The microchannel regenerators are made of a magnetocaloric material (MCM), Gd, with diameter of the circular channels ranging from 0.7 mm to 2.0 mm. Water, the working fluid, oscillates in the regenerator loop driven by two piston-cylinder displacers operating in a range of mass flow rates. Three dimensional conjugated fluid convection and conduction heat transfer in the microchannel regenerator was modeled and numerically simulated using ANSYS Fluent. The magnetocaloric effect (MCE) was incorporated into conservation of energy using a discrete method to simulate the magnetization and demagnetization of the MCM. The hot and cold end heat exchangers were treated with the ε–NTU method. Effects of utilization and porosity of the microchannel regenerator and cycle frequency on the cooling capacity and temperature span were examined. When the utilization, porosity and cycle frequency are 0.2, 0.5 and 5.0 Hz, respectively, the predicted maximum cooling capacity was about 22 W for a 0.8 T variation in intensity of magnetic field. The effects of magnetic field intensity, reservoir temperature span and flow rate profile on the refrigeration performance were also investigated. The performance of the microchannel regenerator is compared with that of the parallel plate regenerator for the no-load temperature span, cooling capacity and pumping power. Under specific geometric and operating conditions, the microchannel regenerator shows better performance than the parallel-plate one.

Design criteria of different heat exchangers for the optimal thermodynamic performance of regenerative refrigeration systems

Heat exchanger effectiveness significantly influences the corresponding regenerative refrigeration system performance, a larger heat exchanger effectiveness, however, does not always lead to a better system performance. This study analyzes the optimal thermal conductances1 of each heat exchanger to explore their different effects and inherent relations on the optimal system performance. We first derive the theoretical relation between system requirements and design parameters, and then optimize the system by the Lagrange multiplier method, which directly gives the optimal solutions. By analyzing different variations of the optimal thermal conductances versus various system requirements and boundary conditions, the contributions of each heat exchanger to the whole system are explored. It is found that the hot-end heat exchanger is to transfer heat from refrigerant to external fluid, thus its thermal conductance should match the mass flow rate of external fluid. The cold-end heat exchanger is essential to accomplish heat transfer from environment to refrigerant, so it is dominated by the cooling requirements. In addition, the regenerator is to reduce the system pressure ratio and it always induces most irreversibility of the system, thus it depends on both the pressure ratio and other operating conditions significantly. The results above provide useful design criteria of heat transfer processes for regenerative refrigeration system optimization.

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.

CFD investigation on characteristics of oscillating flow and heat transfer in 3D pulse tube

A CFD method is used to investigate the three dimensional oscillating flow and heat transfer in the pulse tube (PT) and heat exchangers (HEs) of a pulse tube refrigerator (PTR). Some interesting phenomena and characteristics have been found in the present work, and quantitative analyses in detail have been made. The transient temperature variation resembles sinusoidal in the central part of the pulse tube, while exhibits non-sinusoidal within 10mm away from the two end HEs, respectively. The lowest periodically averaged temperature appears not in the cold end HE but on the cross-section about 1mm away from the cold end HE, while the highest averaged temperature appears at about 3mm away from the hot end HE. This would increase the conduction loss, but benefits the coaxial space arrangement for a PTR. The heat transfer efficiency of the two HEs has significant influence on the PV power loss. Poor heat transfer can lead to a higher loss, even reaching to 10% of the total PV power when the heat transfer coefficient decreases to 102W/m2K. The efficiency of a pulse tube has been newly proposed, which can be used to describe the loss of pulse tube quantitatively. In summary, the effects of a series of factors on the loss of the pulse tube have been discussed, including the phase angle, the heat transfer coefficient of the HEs, the mass flow rate, and the gravity. The present study would give a better understanding on the mechanism of losses in a PT.

A global optimization method for regenerative air refrigeration systems

The air refrigeration systems always involve such physical processes as heat transfer processes in heat exchangers, compression processes in compressors and expansion processes in expanders. This contribution proposes a theoretical global optimization method for regenerative air refrigeration systems and introduces the entransy theory to analyze the heat transfer processes in the hot-end heat exchanger, the cold-end heat exchanger and the regenerator. Integration of the heat transfer analyses and the thermodynamic analyses for the compression and expansion processes yields a mathematical model to describe the physical relation between the design requirements and the unknown design parameters, i.e. the heat transfer area of each heat exchanger and the heat capacity rate and the intermediate temperature of the air. Based on this model, the optimization can be converted into a conditional extremum problem. That is, solving the problem via the Lagrange multiplier method offers an optimization equation group, which directly leads to the optimal values of all the unknown parameters. Finally, this optimization method is validated through an optimization case to minimize the total thermal conductance of all the heat exchangers in a typical regenerative air refrigeration system.

Optimal design of the pulse tube refrigerator with slit-type heat exchangers

A single-stage inline pulse tube refrigerator (PTR) with tapered slit-type heat exchangers utilized as the aftercooler and the cold end heat exchanger has been designed, fabricated and investigated. Simple energy conservation equation is applied for the design of the tapered slit-type heat exchangers with which the PTR is optimized. The air-cooled aftercoolers with different slit configurations have been compared in this paper with regard to its cooling capacity. The optimized PTRs driven by a single-piston linear compressor achieve the lowest temperature of 53.1 K and 53.5 K, and the cooling capacity of 3.0 W at 60 K and 3.5 W at 60 K, respectively. The result shows that the tapered slit-type heat exchangers can replace the mesh-type heat exchanger, but the geometric configuration of slits and the compressible volume should be carefully considered for optimum performance of the cooler.

CFD simulation and experimental validation of a GM type double inlet pulse tube refrigerator

Pulse tube refrigerator has the advantages of long life and low vibration over the conventional cryocoolers, such as GM and stirling coolers because of the absence of moving parts in low temperature. This paper performs a three-dimensional computational fluid dynamic (CFD) simulation of a GM type double inlet pulse tube refrigerator (DIPTR) vertically aligned, operating under a variety of thermal boundary conditions. A commercial computational fluid dynamics (CFD) software package, Fluent 6.1 is used to model the oscillating flow inside a pulse tube refrigerator. The simulation represents fully coupled systems operating in steady-periodic mode. The externally imposed boundary conditions are sinusoidal pressure inlet by user defined function at one end of the tube and constant temperature or heat flux boundaries at the external walls of the cold-end heat exchangers. The experimental method to evaluate the optimum parameters of DIPTR is difficult. On the other hand, developing a computer code for CFD analysis is equally complex. The objectives of the present investigations are to ascertain the suitability of CFD based commercial package, Fluent for study of energy and fluid flow in DIPTR and to validate the CFD simulation results with available experimental data. The general results, such as the cool down behaviours of the system, phase relation between mass flow rate and pressure at cold end, the temperature profile along the wall of the cooler and refrigeration load are presented for different boundary conditions of the system. The results confirm that CFD based Fluent simulations are capable of elucidating complex periodic processes in DIPTR. The results also show that there is an excellent agreement between CFD simulation results and experimental results.

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.

CFD simulation of a Gifford–McMahon type pulse tube refrigerator

Pulse tube refrigerator has the advantages of long life and low vibration over the conventional cryocoolers, such as Gifford–McMahon (GM) and Stirling coolers because of the absence of moving parts in low temperature. This paper performs a two-dimensional computational fluid dynamic (CFD) simulation of a Gifford–McMahon type double inlet pulse tube refrigerator (DIPTR), operating under a variety of thermal boundary conditions. A commercial Computational Fluid Dynamics (CFD) software package Fluent 6.1 is used to model the oscillating flow inside a pulse tube refrigerator. Helium is used as working fluid for the entire simulation. The simulated DIPTR consists of a transfer line, an after cooler, a regenerator, a pulse tube, a pair of heat exchangers for cold and hot end, an orifice valve with connecting pipe, a double inlet valve with connecting pipe and a reservoir. The simulation represents fully coupled systems operating in steady-periodic mode. The externally imposed boundary condition is sinusoidal pressure inlet by user defined function at one end of the tube and constant temperature or heat flux boundaries at the external walls of the hot end and cold-end heat exchangers. The general results, such as the cool down behaviors of the system, phase relation between mass flow rate and pressure at pulse tube section and the temperature profile along the wall of the cooler are presented. The simulation shows the minimum decrease in temperature at cold-end heat exchanger for a particular combination of cryocooler assembly. The CFD simulation results are compared with available experimental data. Comparisons show that there is a reasonable agreement between CFD simulation and experimental results.