Helium Liquefaction Research Articles

Experimental investigation and optimization of small-scale helium liquefaction with multi-cryocoolers

Small-scale helium liquefiers using regenerative cryocoolers with cooling power up to 1.5W at 4.2K could be used to re-liquefy evaporated helium gas of small- and medium-sized cryogenic devices such as MEG and PPMS. A serial–parallel-path helium liquefier with a liquefaction rate of 83Litres per day (L/d) using five 4K G-M cryocoolers is developed, and has been applied to the Wuhan National High Magnetic Field Center (WHMFC) in China. Different from parallel-path helium liquefier, the helium gas is effectively, stepwise precooled by heat exchangers on multi-cold flanges, and thus the additional purifier and precooling coil heat exchangers on the thinner part of the cold head cylinder containing the 2nd stage displacer could be removed to simplify the construction. Through theoretical calculation and conclusive analysis, an optimum configuration is proposed and makes a reference to the design of serial–parallel-path helium liquefier with multi-cryocoolers.

Comparative design evaluation of plate fin heat exchanger and coiled finned tube heat exchanger for helium liquefier in the temperature range of 300-80 K

Present Indigenous Helium Liquefaction system at RRCAT uses the cross-counter flow coiled-finned tube heat exchangers developed completely from Indian resources. These coiled-finned tube heat exchangers are mainly suitable up to medium capacity helium liquefiers. For large capacity helium liquefier, plate fin heat exchangers are more suitable options. This paper presents the comparative evaluation of the design of both types of heat exchangers in the temperature range of 300-80 K for helium liquefier.

Recent trials with the experimental helium liquefier developed by BARC

An experimental helium liquefier has been designed and fabricated by Cryo-Technology Division and installed at Bhabha Atomic Research Centre, Mumbai. The helium liquefaction process is based on a modified Collin's cycle consisting of one pre-cooler turboexpander, a pair of by-pass turboexpanders (warm and cold) and a series of 7 compact brazed plate fin high effectiveness heat exchangers. Liquid nitrogen pre-cooling facility along with another heat exchanger to recover cold of gaseous nitrogenhas also been provided in the system. After the full installation of the process compressor and its integration with the helium liquefier cold box, trial runs were started. A lowest temperature of about 7.8 K was registered in a temperature sensor located downstream of the JT valve.

Evaluating performance of mixed mode multistage helium plants for design and off-design conditions by exergy analysis

Performance of mixed mode helium liquefaction and refrigeration systems based on a number of refrigeration stages has been studied taking compressor discharge pressure, heat exchanger effective UA and expander flow rate as independent parameters. Due to constraints of space and minimum flow rate through expanders (to attain operational reliability), helium plants often have to be designed with heat exchanger UA and number of stages less than the optimum values. It is useful for designers to evaluate the penalty in cold box exergy efficiency when the plant is designed or operated under such constraints. Performance of pure liquefier, pure refrigerator and mixed mode systems when operated at off-design conditions has been evaluated. Exergy efficiency has been used as the tool for the entire analysis of this paper.

Magnetic and Magnetocaloric Properties of Er2TiMnO7 Compound

Magnetic properties and magnetocaloric effects of the Er2TiMnO7 compound have been evaluated by magnetization and heat capacity measurements. The reversible magnetic-entropy change is found to be just above the boiling point of helium and hydrogen liquefaction temperature range of 2 to 50 K.

Role of heat exchangers in helium liquefaction cycles: Simulation studies using Collins cycle

Energy efficiency of large-scale helium liquefiers generally employed in fusion reactors and accelerators is determined by the performance of their constituting components. Simulation with Aspen HYSYS ® V7.0, a commercial process simulator, helps to understand the effects of heat exchanger parameters on the performance of a helium liquefier. Effective UA (product of overall heat transfer coefficient U, heat transfer surface area A and deterioration factor F) has been taken as an independent parameter, which takes into account all thermal irreversibilities and configuration effects. Nondimensionalization of parameters makes the results applicable to plants of any capacity. Rate of liquefaction is found to increase linearly with the effectiveness of heat exchangers. Performance of those heat exchangers that determine the inlet temperatures to expanders have more influence on the liquid production. Variation of sizes of heat exchangers does not affect the optimum rate of flow through expanders. Increasing UA improves the rate of liquid production; however, the improvement saturates at limiting UA. Maximum benefit in liquefaction is obtained when the available heat transfer surface area is distributed in such a way that the effectiveness remains equal for all heat exchangers. Conclusions from this study may be utilized in analyzing and designing large helium plants.

Role of expanders in helium liquefaction cycles: Parametric studies using Collins cycle

Large scale helium liquefaction/refrigeration plant is a key subsystem of fusion devices. Performance of these plants is dependent on a number of geometric and operating parameters of its constituting components such as compressors, heat exchangers, expanders, valves, etc. Expander has been chosen as the subject matter of analyses in the present study. As the sensible cold of helium vapor is lost in liquefiers, the expanders in liquefaction cycles have to provide more refrigeration than those in refrigeration cycles. The expander parameters such as rate of mass flow, operating pressure, inlet temperature, etc. are inter-dependent, and hence, it is difficult to predict the system behavior with variation of a particular parameter. This necessitates the use of process simulators. Parametric studies have been performed on Collins helium liquefaction cycle using Aspen HYSYS ®. Collins cycle has all the basic characteristics of a large-scale helium liquefier and the results of this study may be extrapolated to understand the behavior of large scale helium liquefiers. The study shows that the maximum liquid production is obtained when 80% of the compressor flow is diverted through the expanders and it is equally distributed between the two expanders. The relationships between the liquid production and the isentropic efficiency of expanders are almost linear and both the higher and lower temperature expanders exhibit similar trends.

Successive magnetic transitions and low temperature magnetocaloric effect in RE 2Ni 7 (RE=Dy, Ho)

Magnetic properties of rare-earth intermetallics RE 2Ni 7 (RE=Dy, Ho) are reported. Both the samples undergo two successive magnetic transitions at T h (paramagnetic to ferromagnetic) and T l (spin reorientation) below 100 K. The transitions are found to be second order in nature as evident from the Arrot plot analysis. Large reversible magnetocaloric effect (MCE) was observed at low temperature in the studied samples. The maximum value of the magnetic entropy change in Ho 2Ni 7 is found to be −12.5 J/kg K (for 0 to 50 kOe of field change) around 25 K with a high relative cooling power (RCP) of 534 J/kg. The Dy counterpart also shows moderately large values of MCE (−7.3 J/kg K) and RCP (475 J/kg) around the magnetic transition region for similar change in the magnetic field. RE 2Ni 7 compounds can be promising materials for magnetic refrigeration in the temperature range of helium and hydrogen liquefaction.

Exergy analysis of helium liquefaction systems based on modified Claude cycle with two-expanders

Large-scale helium liquefaction systems, being energy-intensive, demand judicious selection of process parameters. An effective tool for design and analysis of thermodynamic cycles for these systems is exergy analysis, which is used to study the behavior of a helium liquefaction system based on modified Claude cycle. Parametric evaluation using process simulator Aspen HYSYS® helps to identify the effects of cycle pressure ratio and expander flow fraction on the exergetic efficiency of the liquefaction cycle. The study computes the distribution of losses at different refrigeration stages of the cycle and helps in selecting optimum cycle pressures, operating temperature levels of expanders and mass flow rates through them. Results from the analysis may help evolving guidelines for designing appropriate thermodynamic cycles for practical helium liquefaction systems.

A self-circulation helium liquefaction system with five 4 K G-M cryocoolers

A self-circulation helium liquefaction system (SCHLS) with five 4 K G-M cryocoolers is developed to supply liquid helium (LHe) for SECRAL (a superconducting ECR ion source used in Lanzhou city, China). LHe is vaporized in SECRAL and warmed up to room temperature. SCHLS will re-liquefy the helium gas at a rate of 83.2 L/day under normal atmosphere pressure. With SCHLS, SECRAL system can run online without any interruption of refilling LHe.

Excellent Magnetocaloric Effect in Er60Al18Co22 Bulk Metallic Glass

Excellent magnetocaloric effect with a maximum entropy change and refrigeration capacity of 17.6 J·kg−1·K−1 and 546 J·kg−1, respectively, has been discovered in the Er60Al18Co22 bulk metallic glass under the field of 50 kOe in the temperature range of helium liquefaction. This MCE results from the second-order magnetic transition from the paramagnetic to the ferromagnetic state. Our analysis based on mean-field theory suggests that the excellent MCE is attributed to the strong exchange of magnetic moment in the glassy structure.

Small scale helium liquefaction systems

We have developed two small-scale helium liquefaction systems that provide solutions for liquid helium usage in laboratories. These helium liquefaction systems use two-stage pulse tube cryocoolers to provide cooling at 4 K. The cold head/liquefier resides inside of the neck of a dewar. The room temperature helium gas to be liquefied enters the neck of the dewar and is efficiently pre-cooled down to 5–6 K by means of the regenerators and pulse tubes of the cold head before being liquefied. Two models of liquefaction system, LHeP12 and LHeP18, produce liquid helium from room temperature gas with the rates of >12 L/day and 18 L/day.

Closed-Loop Cryogenic Cooling for a 21 T FT-ICR Magnet System

A closed-loop cooling concept for 21 T Fourier transform ion cyclotron resonance (FT-ICR) superconducting magnets is presented. In the magnet system, low temperature superconducting coils are immersed in a subcooled 1.8 K bath, which is connected to the saturated helium reservoir through the weight load relief valve. Saturated liquid helium is refrigerated by a Joule-Thomson (JT) heat exchanger and flows through the JT valve, isenthalpically dropping its pressure to approximately 1.6 kPa, corresponding to a saturation temperature of 1.8 K. Helium gas exhausted from JT pump is liquefied by a two-stage cryocooler located after the vapor purify system. In the present paper, the amount of heat budget is determined and the structural design of cryostat is carried out by the relevant analyses. The position of a cryocooler in the magnet system is investigated, taking into account the requirement of magnetic field for normal performance. Helium liquefaction system, a key component of the closed-loop cooling system, is fabricated and tested in order to demonstrate the feasibility of our new cryogenic cooling for high field magnets.

Magnetocaloric effect of Ho-, Dy-, and Er-based bulk metallic glasses in helium and hydrogen liquefaction temperature range

The authors study the magnetocaloric effect and refrigerant capacity of Ho30Y26Al24Co20, Dy50Gd7Al23Co20, and Er50Al24Co20Y6 bulk metallic glasses. Their magnetic entropy changes associated with spin glass to paramagnetic transition are larger than those of Gd, Gd5Si2Ge1.9Fe0.1, and many other intermetallic compounds reported in the same temperature range. The good refrigerant efficiency combined with their high electrical resistivity, high thermal stability, outstanding mechanical properties, and tunable nature makes these glassy materials be attractive candidates for magnetic refrigerants in helium and hydrogen liquefaction temperature range of 2–50K.

Tsukuba Magnet Laboratory: Present status and future vision

The Tsukuba Magnet Laboratory (TML) has been a user facility for external users since April 1998 and contracted 91 collaborative studies with external research groups in the 2005 fiscal year. Internal and external researchers use high magnetic fields for magnetic processing as well as extreme-environment measurements. In 2006, two major changes were made to expand the experimental possibilities. One was the replacement of the helium liquefaction system, and the other was the remodelling of the 15 MW DC power supply. TML has also built an NMR complex including a 930 MHz and a 920 MHz NMR spectrometer. We have also started a collaborative study on high-field magnet development with the High Field Laboratory for Superconducting Materials. The projects include the development of a 30 T class superconducting magnet and a 50 T class hybrid magnet.

Helium liquefaction with a commercial 4 K Gifford-McMahon cryocooler

This paper describes helium liquefaction using a commercial cryocooler with 1.5 W cooling power at 4.2 K (Sumitomo model RDK415D with compressor CSW-71D, consuming 6.5 kW electrical power), equipped with heat exchangers for precooling the incoming gas. No additional cooling power of cryoliquids or additional Joule–Thomson stages were utilized. Measurements of the pressure dependence of the liquefaction rate were performed. A maximum value of 83.9 g/h was obtained for 2.25 bar stabilized input pressure. Including the time needed to cool the liquefied helium to 4.2 K at 1 bar after filling the bottle connected to the cold head, and correcting for heat screen influences, this results in a net liquefaction rate of 67.7 g/h. Maintaining a pressure close to 1 bar above the bath during liquefaction, a rate of 55.7 g/h was obtained. The simple design enables many applications of the apparatus.

Helium liquefaction with a 4 K pulse tube cryocooler

Helium liquefaction with a two-stage 4 K pulse tube cryocooler is introduced in this paper. The helium liquefier has a feature of precooling helium gas to be liquefied by using inefficiency of the second stage regenerator in the pulse tube cryocooler. This process reduces enthalpy of the incoming helium gas when entering the condenser and significantly increases the condensation rate. Numerical analysis predicts the precooling heat load on the second stage regenerator, decreases the PTC second stage cooling capacity by only 11% of the heat actually absorbed into the regenerator. A prototype pulse tube helium liquefier was built, which has two precooling heat exchangers on the first stage cold head and the second stage regenerator. It continuously liquefies helium with a rate of 4.8 l/day under normal pressure while consumes 4.6 kW power input.

Optimization of a liquefaction plant using genetic algorithms

This paper presents an optimization methodology for liquefaction/refrigeration systems in the cryogenic field. The Figure of Merit has been chosen as the evaluation index, and genetic algorithms as evaluation criteria. This methodology has been applied to an existing helium liquefaction system that works according to a Collins cycle. The results show the possibility of adjusting some of the thermal-pressure variables for the system in order to improve the Figure of Merit.

Cryocooled refrigeration for sensitive measuring instrumentation

We describe recent advances in the development of a general-purpose cryocooled dewar designed to eliminate the liquid helium boil-off, as well as provide a low mechanical vibration environment suitable for sensitive measuring instrumentation. Because of the high degree of thermal integration, this system is more efficient in power consumption and cooling requirements than helium liquefaction facilities that recover the helium gas at room temperature. In this report, we outline important elements of the dewar cryogenic design, as well as its ability to operate without degrading the ultimate sensitivity of measuring instrumentation such as a superconductive quantum interference device (SQUID), magnetometer.

Transient testing of perforated plate matrix heat exchangers

Till recently, perforated plate matrix heat exchangers (MHEs) were used mainly in helium liquefaction systems and Brayton cycle refrigerators. Currently they are also being used in Kleemenko or J-T refrigerators operating with a mixture of gases. It is now well understood that the effectiveness of a MHE is strongly dependent on the number of plate–spacer pairs used. It has also been shown that the traditional methods used for reducing the transient single blow method to determine the heat transfer coefficients cannot be used for MHEs. In this paper we show that the traditional methods can indeed be used for determining the heat transfer coefficients using the transient testing methods, provided certain conditions are met.