Large Refrigeration Research Articles

Magnetic properties and magnetocaloric effects in R3Ni2 (R = Ho and Er) compounds

Magnetic and magnetocaloric properties of R3Ni2 (R = Ho and Er) compounds have been investigated. Both Ho3Ni2 and Er3Ni2 compounds undergo two successive phase transitions: spin reorientation transition and second-order ferromagnetic-paramagnetic transition. The maximal values of magnetic entropy change are achieved to be 21.7 J kg−1 K−1 for Ho3Ni2 and 19.5 J kg−1 K−1 for Er3Ni2 for a field change of 0-5 T. A large refrigerant capacity (RC) of 496 J kg−1 in the composite material is also obtained. Large reversible magnetocaloric effect and RC indicate the potentiality of R3Ni2 (R = Ho and Er) compounds as candidates for low-temperature magnetic refrigerant.

Structure, magnetic, and magnetocaloric properties of amorphous and crystalline La0.4Ca0.6MnO3+δ nanoparticles

We report a systematic study of the effects of size reduction on the magnetic and magnetocaloric properties of amorphous and crystalline La0.4Ca0.6MnO3+δ nanoparticles. The materials were synthesized using a modified wet chemical Pechini route, starting with nitrate precursors to produce the perovskite structure. Phase purity, structure, size, and crystallinity were investigated using XRD and TEM. Thermal treatments resulted in nanocrystals with average diameters of 25nm, 50nm, and 130nm, as well as amorphous particles ∼10nm in diameter. Magnetic measurements revealed broad, second order ferromagnetic transitions in the nanocrystals. As particle size increased from 10nm to 130nm, the Curie temperature shifted from 40K to 255K. Magnetization, magnetic entropy change (ΔSM), and refrigerant capacity (RC) also increased with size in the nanocrystalline samples. For a field change of 5T, the 130nm particles exhibit a magnetic entropy change of 2.8J/kgK and a large refrigerant capacity of ∼240J/kg at 250K. Interestingly, the 10nm amorphous particles undergo the sharpest magnetic transition, leading to a larger value of ΔSM than in the 25nm or 50nm crystalline particles. These results reveal that size reduction has a significant impact on the magnetic and magnetocaloric properties of La0.4Ca0.6MnO3+δ.

The magnetic phase transitions and magnetocaloric effect in MnNi 1− xCo xGe alloys

The magnetic phase transitions and the magnetocaloric effects in MnNi 1− x Co x Ge ( x = 0.38 and 0.40) alloys were investigated. The substitution of Co for Ni in the MnNiGe antiferromagnet results in the metamagnetic transitions from antiferromagnetic to ferromagnetic state, which associates with very small thermal and magnetic hystereses. Positive and negative values of magnetic entropy changes are exhibited around the metamagnetic transition temperature and Curie temperature, respectively. The relatively large refrigerant capacity in low magnetic field along with the good reversibility suggest that MnNi 1− x Co x Ge ( x = 0.38 and 0.40) alloys are potential candidates for magnetic refrigeration.

Spin Physics at SPring-8 – Recent Results

We have been carrying out hadron photoproduction experiments at SPring-8 since the completion of the LEPS beam-line in 2000. The photoproduction of the ϕ, K, η and π0 mesons is studied by using linearly polarized photon beams with energies of Eγ = 1.5–2.9 GeV. Introducing a polarized nucleon target is expected to upgrade the LEPS experiments to a new level. The measurement of double spin polarization asymmetries provides important information to investigate the hidden nucleon structure, hadron photoproduction dynamics, and exotic hadron properties. We started developing a polarized HD target in 2005. Five large refrigerators necessary for the polarized target have been already obtained. We plan to carry out an experiment using polarized photon beams and the polarized HD target in 2011–2012. We also started constructing a new beam-line (LEPS2) at SPring-8 in 2010. The large acceptance E949 spectrometer, which has been used at BNL, will be transported to the LEPS2 beam-line in 2011. With these new developments, advanced studies of spin physics are expected in future experiments.

PST thin films for electrocaloric coolers

Relaxor behaviour in a thin film of partially ordered PbSc0.5Ta0.5O3 (PST) was confirmed via slim P–E loops and the frequency dependence of the temperature at which the dielectric constant is maximum. Indirect measurements of the electrocaloric effect suggest that removing a field of 774 kV cm−1 yields a temperature change of −3.5 °C to −6.9 °C over a broad range of operating temperatures near room temperature (1–127 °C), with a correspondingly large refrigerant capacity of 662 J kg−1. In addition to low electrical hysteresis, there is negligible thermal hysteresis. PST thin films are therefore promising for EC cooling near room temperature.

Magnetic entropy change and large refrigerant capacity of Ce6Ni2Si3-type GdCoSiGe compound

Magnetic entropy change (ΔSM) and refrigerant capacity (RC) of Ce6Ni2Si3-type Gd6Co1.67Si2.5Ge0.5 compounds have been investigated. The Gd6Co1.67Si2.5Ge0.5 undergoes a reversible second-order phase transition at the Curie temperature TC = 296 K. The high saturation magnetization leads to a large ΔSM and the maximal value of ΔSM is found to be 5.9 J/kg · K around TC for a field change of 0–5 T. A broad distribution of the ΔSM peak is observed and the full width at half maximum of the ΔSM peak is about 101 K under a magnetic field of 5 T. The large RC is found around TC and its value is 424 J/kg.

Exergoeconomic analysis of industrial brine chilling unit using aqua-ammonia vapour absorption refrigeration system

Exergoeconomic analysis of an industrial brine chilling unit using a large capacity aqua ammonia Vapour Absorption Refrigeration (VAR) system is carried out. The analysis is based on Tsatsaronis's Thermoeconomic Evaluation and Optimisation (TEO) Method which is one of the many methods that was developed since the pioneering work of Tribus and Evans. The economic cost of all the flows and product of the system are calculated. The objective function to be minimised is determined. As decision variables, generator, condenser and evaporator temperatures, pump efficiency and heat exchangers effectiveness are selected. The optimum configuration is obtained through the iterative procedure of Bejan, aiming the design improvement for minimum product cost and makes the overall system cost effective. The result shows considerable improvement in the system performance compared to that of the existing unit.

Indian frozen peas market: a case study on FPIL

Urban consumers in India have been increasing consumption of frozen processed food. With more supermarkets opening, especially in cities, women are increasingly shopping in these outlets as they are more convenient, comfortable and have the space to keep large refrigerators to store frozen processed food. The infrastructure in the cities is much more developed therefore retailers are able to store frozen processed food without worrying about consistent and long power cuts. The convenience of frozen processed vegetables, meats and ready meal has encouraged many women to increase the usage of these products as they reduce the preparation time. Peas are used in many vegetables and are demanded round the year by all the families and are also required in catering industry. The fresh peas are available only during winter season but are generally required in all the seasons. Also their harvest is limited to certain states. This gap between demand and supply is being managed by frozen peas available in the Indian market. This paper presents a case on Frozen Products Indian Ltd. and it evolves around frozen peas storage, individual quick freezing technique. It requires proper cold chain management right from sourcing, manufacturing, processing, dispatching for retailing and at consumers end. The complete temperature controlled supply chain is maintained using refrigerated vans and storage equipment.

Effects of pre-deformation on the martensitic transformation and magnetocaloric property in Ni-Mn-Co-Sn ribbons

This paper investigates the martensitic transformation and magnetocaloric effect in pre-deformed Ni-Mn-Co-Sn ribbons. The experimental results show that the reverse martensitic transformation temperature TM increases with the increasing pre-pressure, suggesting that pre-deformation is another effective way to adjust TM in ferromagnetic shape memory alloys. Large magnetic entropy changes and refrigerant capacities are obtained in these ribbons as well. It also discusses the origin of the enhanced martensitic transformation temperature and magnetocaloric property in pre-deformed Ni-Mn-Co-Sn ribbons.

De-Synchronization of the Distributed Refrigeration System

The supermarket refrigeration system typically has a distributed control structure, which simple and flexible, however, neglects interactions between its subsystems. Practice shows that these interactions lead to a synchronous operation of the display cases. It causes excessive wear on the compressors and increased energy consumption. The paper focuses on the synchronization analysis and de-synchronization control. The supermarket refrigeration system is modeled as a piecewise-affine switched system. The system behavior is decomposed such that synchronization analysis can be completed by using the Poincare map. A new de-synchronization scheme is proposed, which includes two steps: the synchronization monitoring and the de-synchronization control. Thus, the early warning of the synchronization can be given and then the de-synchronization controller can be activated. The scheme achieves better control performance and can deal with the large scale refrigeration system with different system parameters in the display cases.

The role of boron on the magneto-caloric effect of FeZrB metallic glasses

Fe-rich FeZrB metallic glasses exhibit magneto-caloric effect (MCE) around room temperature. Amorphous ribbons of two different compositions, Fe 91Zr 7B 2 and Fe 88Zr 8B 4, with respective Curie temperature values of 230 and 285 K have been studied. Although the maximum magnetic entropy change is relatively moderate ( | Δ S M | max ∼ 3 J K −1 kg −1 under an applied magnetic field change from 0 to 50 kOe), the MCE spreads over a broad temperature interval ( ∆T ∼ 200 K), giving rise to a large refrigerant capacity loss (RC ∼ 435 J kg −1) without any hysteresis. The Curie temperature can be easily tuned between 200 and 350 K by changing the boron content. Therefore, the MCE can be controlled over a wide temperature interval, thus making these amorphous alloys promising candidates for magnetic refrigeration near room temperature.

Large inverse magnetic entropy changes and magnetoresistance in the vicinity of a field-induced martensitic transformation in Ni50−xCoxMn32−yFeyGa18

Significantly large inverse magnetic entropy changes (ΔSM) and magnetoresistance (MR) were observed at the inverse martensitic phase transitions of the Ga-based magnetic shape memory Heusler alloys: Ni50−xCoxMn32−yFeyGa18. The crystal structures of alloys were tetragonal at 300 K and the phase transition temperatures and magnetic properties were found to be correlated with the degree of tetragonal distortion. The maximum peak values of the ΔSM and MR at H=5 T were determined as ≈(+)31 J Kg−1 K−1 and ≈−21%, respectively, for x=8 and y=2. The relatively small hysteretic loss and large refrigeration capacity observed in this system make these compounds promising materials for applications.

The heat transfer performance of horizontal tube bundles in large falling film evaporators

The performance of the horizontal heat transfer tube bundles in falling film evaporators in large compression refrigeration systems was investigated with numerical simulation in this paper. Four types of tubes, including plain tubes, and enhanced surface tubes of Turbo-B, Turbo-BII and Turbo-EHP, were employed in the simulation. Some factors, such as tube kind, tube pass arrangement, dry patch area on tube surface, liquid refrigerant flow rate, and number of flooded tubes, were analyzed based on simulated results. In the study, the maldistribution of liquid refrigerant flow caused by the distributor apparatus was discussed, which severely affects the performance of falling film evaporators according to the simulation. Some calculated results were verified by the experiment. These discussions and results can be used to guide the design of falling film evaporators under realistic flow conditions.

Gd–Dy–Al–Co bulk metallic glasses with large magnetic entropy change and refrigeration capacity

Novel Gd 56− x Dy x Al 24Co 20 ( x = 0, 14, 17) bulk metallic glasses (BMGs) were prepared by copper mold casting. They exhibit magnetic entropy changes (Δ S M ) comparable to that of Gd 53Al 24Co 20Zr 3 BMG and crystalline Gd. Moreover, these glassy alloys have broad entropy change peaks, resulting in the refrigeration capacities of 751.4 J kg −1, 702.8 J kg −1, and 682.3 J kg −1 for Gd 56Al 24Co 20, Gd 42Dy 14Al 24Co 20, and Gd 39Dy 17Al 24Co 20 at 5 Tesla. The large magnetocaloric effect makes these BMGs attractive candidates as magnetic refrigerant in temperature range of 50–140 K. It is also found that the Curie temperature of this kind of metallic glass linearly declines with the increase of Dy. The Δ S M of metallic glasses reaches maximum at certain content of Dy. These findings are expected to provide a meaningful guidance for the composition design of rare earth based glassy alloys for refrigeration application.

Reducing power consumption in multi-compressor refrigeration systems

An experimental analysis of compressor operation in a large refrigeration system was undertaken and a model for optimal compressor operation for energy efficiency was developed. The system used 5 screw compressors and ammonia as the refrigerant, with slide valves to regulate the compressors and match their refrigeration capacity with product freezing loads. Compressors in the existing system can operate simultaneously with reduced capacities, which results in reduced energy efficiency. Optimized operation was made both with and without a variable frequency drive. The results showed that the most electrical energy can be saved during days when not all of the tunnels were loaded. It is assumed that € 30 000–50 000 can be saved per year by optimizing the operation of the refrigeration system.

Magnetocaloric effect in DyCu 2

The magnetocaloric effect of the rare-earth intermetallic compound DyCu 2 is explored through magnetization measurements. DyCu 2 is paramagnetic at the room temperature but becomes antiferromagnetic below 27 K (Neel temperature). Strong temperature and field dependence of magnetization in DyCu 2 at and around the Neel temperature lead to a large magnetocaloric effect. An appreciable magnetocaloric effect persists well above the Neel temperature probably because of the presence of short-range ferromagnetic correlations in the paramagnetic state of DyCu 2. This along with the absence of magnetic hysteresis lead to a large effective refrigerant capacity of 194 J/kg below 44 K, which makes the material important as a potential magnetic refrigerant for the cryogenic liquefier cycles.

Safety Analysis of the 70 kA ITER HTS Current Lead Demonstrator

For the superconducting magnet system of the International Thermonuclear Experimental Reactor, ITER, 60 current leads for a total current of more than 2500 kA are needed. The use of High Temperature Superconductor current leads (HTS-CL) will reduce the resultant large refrigerator load considerably. Within the EU Fusion Technology Programme, the Forschungszentrum Karlsruhe and CRPP have developed and built a 70 kA HTS-CL demonstrator optimized for 50 K Helium operation. In 2004-2005, the CL was successfully tested with 50 K as well as 80 K Helium, and finally with LN2. In the meantime, ITER has decided to use HTS-CLs for the magnet system and China has taken the responsibility to provide the sc feeders for ITER including the current leads. In this paper, the performance of a 70 kA HTS-CL in fault conditions will be analysed using the FZK-CRPP demonstrator as a model. In particular, the quench performance and the safety behavior in case of a loss-of-flow accident (LOFA) will be described and an extrapolation of the leads performance in real ITER conditions will be given. Finally the effect of different shunt materials is discussed.

Three-Dimensional Modeling of HCFC-123 in the Atmosphere: Assessing Its Potential Environmental Impacts and Rationale for Continued Use

HCFC-123 (C2HCl2F3) is used in large refrigeration systems and as a fire suppression agent blend. Like other hydrochlorofluorocarbons, production and consumption of HCFC-123 is limited under the Montreal Protocol on Substances that Deplete the Ozone Layer. The purpose of this study is to update the understanding of the current and projected impacts of HCFC-123 on stratospheric ozone and on climate and to discuss the potential environmental effects from continued use of this chemical for specific applications. For the first time, the Ozone Depletion Potential (ODP) of a HCFC is determined using a three-dimensional model (MOZART-3) of atmospheric physics and chemistry. All previous studies have relied on results from two-dimensional models. The derived HCFC-123 ODP of 0.0098 is smaller than previous values. Analysis of the projected uses and emissions of HCFC-123, assuming reasonable levels of projected growth and use in centrifugal chiller and fire suppressant applications, suggests an extremely small impact on the environment due to its short atmospheric lifetime, low ODP, low Global Warming Potential (GWP), and the small production and emission of its limited applications. The current contribution of HCFC-123 to stratospheric reactive chlorine is too small to be measurable.

Weak exchange effect and large refrigerant capacity in a bulk metallic glass Gd0.32Tb0.26Co0.20Al0.22

The magnetic behavior and refrigeration capacity of Gd0.32Tb0.26Co0.20Al0.22, a bulk metallic glass (BMG) fabricated by a copper-mold suck-casting method, are investigated. The Curie temperature increases from 79 K at 200 Oe to 95 K at 50 000 Oe. A weak exchange field of 25 T in the BMG system, caused by the strong disorder, is derived by the mean-field approximation. The maximum magnetic entropy change (8.02 J kg−1 K−1) and the refrigerant capacity (642 J kg−1) for 5 T indicate the BMG has the better refrigerant efficiency compared to known magnetic refrigerants.

Large magnetic refrigerant capacity in Gd71Fe3Al26 and Gd65Fe20Al15 amorphous alloys

Magnetic entropy change and refrigerant capacity of Gd-based amorphous Gd71Fe3Al26 and Gd65Fe20Al15 alloys are investigated. The refrigerant capacities reach 750 and 726 J kg−1 for Gd71Fe3Al26 and Gd65Fe20Al15, respectively, which are much larger than those of all magnetocaloric materials ever reported. The peak values of magnetic entropy change under a field change of 0–5 T are 7.4 J kg−1 K−1 at 117.5 K and 5.8 J kg−1 K−1 at 182.5 K for Gd71Fe3Al26 and Gd65Fe20Al15, respectively. A very large refrigerant capacity and a considerable magnetic entropy change jointly make them attractive candidates for magnetic refrigerant.