Effective Refrigeration Capacity Research Articles

Reduction of hysteresis losses in the magnetic refrigerant La0.8Ce0.2Fe11.4Si1.6 by the addition of boron

In an effort to improve the magnetocaloric effects of the NaZn13-type La0.8Ce0.2Fe11.4Si1.6 compound, the effect of boron doping on the magnetic properties and magnetocaloric properties has been investigated. The magnetic entropy change (ΔSM) for the La0.8Ce0.2Fe11.4Si1.6 compound, obtained for a field change of 0–5 T using the Maxwell relation exhibits a spike and appears to be overestimated and is thus corrected by using the Clausius-Clapeyron equation (CC). The ΔSM determined from the CC equation is estimated to be 19.6 J kg−1K−1. However, large hysteretic losses which are detrimental to the magnetic refrigeration efficiency occur in the same temperature range. In this work, we report a significant reduction in hysteretic losses by doping the La0.8Ce0.2Fe11.4Si1.6 compound with a small amount of boron to obtain La0.8Ce0.2Fe11.4Si1.6Bx compounds. The hysteresis loss decreases from 131.5 to 8.1 J kg −1 when x increases from 0 to 0.3, while ΔSM, obtained for a field change of 0–5 T, varies from 19.6 to 15.9 J kg−1K−1. This also simultaneously shifts the TC from 174 to 184 K and significantly improves the effective refrigerant capacity (RCeff) of the material from 164 to 305 J kg−1.

Effect of partial substitution of Ni by Co on the magnetic and magnetocaloric properties of Ni50Mn35In15 Heusler alloy

The magnetic and magnetocaloric properties of Ni48Co2Mn35In15 were studied using magnetization and heat capacity measurements. The magnetic entropy change (ΔSM) was evaluated from both magnetizing and demagnetizing fields. An inverse ΔSM for the magnetizing and demagnetizing processes were found to be 20.5 and 18.5 J kg−1 K−1, respectively, for ΔH = 5 T at the martensitic transition (T = TM). The normal ΔSM was found to be −5.4 J kg−1 K−1 for both fields at the paramagnetic/ferromagnetic transition (T = TC). The effective refrigeration capacity at TM and TC for magnetizing field was found to be 268 and 243 J/kg (285 and 243 J/kg for the demagnetizing field), respectively. We have also estimated the density of states, the Debye temperature, and the inverse adiabatic temperature change to be 4.93 states/eV f.u., 314 K, and −3.7 K, respectively, from the measured heat capacity data.

Large magnetocaloric effect in Ni50Mn33.66Cr0.34In16 alloy

A large isothermal magnetic entropy change with a peak value of 17.7 J kg−1 K−1 has been observed across the austenite–martensite phase transition in Ni50Mn33.66Cr0.34In16 alloy near 270 K. In comparison with the parent Ni50Mn34In16 alloy this temperature regime of the peak in isothermal entropy change is closer to the ambient temperature by nearly 30 K. The effective refrigerant capacity is calculated to be 254 J kg−1, which is 15% higher than that of the parent alloy.

Magneto-thermal and magneto-transport behavior around the martensitic transition in Ni 50− xCo xMn 40Sb 10 ( x = 9, 9.5) Heusler alloys

The structural, magnetic, magnetocaloric and magnetoresistance behavior in Ni 50− x Co x Mn 40Sb 10 ( x = 9 and 9.5) has been studied around the magnetostructural transition. The X-ray diffraction results at room temperature show that the compound with x = 9 is predominantly martensitic whereas the one with x = 9.5 is austenite in nature. The maximum magnetic entropy change of 9.2 J kg −1 K −1 was achieved in x = 9.5 at 246 K in a field of 50 kOe and a value of 8.2 J kg −1 K −1 was found near room temperature for x = 9. The effective refrigeration capacity of 106 J/kg has been calculated for x = 9, which is larger than the same observed in other Ni–Mn based Heusler alloy systems. A large magnetoresistance of 25% was obtained around room temperature for x = 9. The large difference in the magnetization between the martensitic and austenite phases is responsible for the large magnetocaloric effect and magnetoresistance in these compounds.

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.

Effect of R substitution on magnetic properties and magnetocaloric effects of La1−xRxFe11.5Si1.5 compounds with R = Ce, Pr and Nd

Magnetic properties and magnetocaloric effects of La1−xRxFe11.5Si1.5 (R = Pr, (0 ≤ x ≤ 0.5); R = Ce and Nd, (0 ≤ x ≤ 0.3)) compounds are investigated. Partially replacing La with R = Ce, Pr and Nd in La1−xRxFe11.5Si1.5 leads to a reduction in Curie temperature due to the lattice contraction. The substitution of R for La causes an enhancement in field-induced itinerant electron metamagnetic transition, which leads to a remarkable increase in magnetic entropy change ΔSm and also in hysteresis loss. However, a high effective refrigerant capacity RCeff is still maintained in La1−xRxFe11.5Si1.5. In the present samples, a large ΔSm and a high RCeff have been achieved simultaneously.

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.

Magnetocaloric properties of the La 0.7Pr 0.3Fe 13−xSi x compounds

Magnetic entropy change Δ S m , hysteresis loss and refrigerant capacity of NaZn 13-type La 0.7Pr 0.3Fe 13− x Si x (1.5⩽ x⩽2.0) compounds have been investigated. The Curie temperature T C increases linearly with the increase of silicon concentration. Although the maximum value of Δ S m under a field change of 0−5 T decreases from 30.5 to 11.4 J/kg K as x increases from 1.5 to 2.0, the hysteresis loss at T C reduces remarkably from 89.2 J/kg for x=1.5 to zero for x=2.0 because the increase of Si content can weaken the itinerant electron metamagnetic transition. The effective refrigerant capacity RC eff is maintained at high values of 362−439 J/kg for a field change of 0−5 T. This implies that a large Δ S m and a high RC eff can be achieved simultaneously in the La 0.7Pr 0.3Fe 13− x Si x compounds.

Effect of substitution of Co for Fe on the magnetic hysteresis loss and the refrigerant capacity in the La0.5Pr0.5Fe11.5Si1.5 compounds

Magnetic hysteresis loss and refrigerant capacity of the NaZn13-type La0.5Pr0.5Fe11.5−xCoxSi1.5 (0⩽x⩽1.0) compounds have been investigated. The substitution of Co in the La0.5Pr0.5Fe11.5Si1.5 causes the order of phase transition at TC to change from first order to second order at x=0.6. Although the magnetic entropy change decreases with increasing Co concentration, the hysteresis loss at TC also reduces remarkably from 94.8J∕kg for x=0to1.8J∕kg for x=0.4 because an increase in Co content can weaken the itinerant electron metamagnetic transition. The effective refrigerant capacity remains at a high value ranging from 355to433J∕kg for a field change of 0–5T as x varies from 0 to 1.0.

Thermomagnetic history dependence of magnetocaloric effect in Ni50Mn34In16

A large inverse magnetocaloric effect has been reported to be associated with the austenite to martensite phase transition in Ni50Mn34In16. It is shown here that the magnitude of the observed magnetocaloric effect as well as effective refrigerant capacity depend significantly on the thermo-magnetic history of the sample.

Large inverse magnetocaloric effect in Ni50Mn34In16

We report a study of the magnetocaloric effect in the ternary alloy system Ni50Mn34In16. This system undergoes an austenite–martensite phase transition, and the change in magnetic entropy is found to be quite large across this martensitic transition. This entropy change is due to an increase in entropy induced by the application of an external magnetic field and can lead to a large inverse magnetocaloric effect. Isothermal magnetic field variation of magnetization exhibits field hysteresis in Ni50Mn34In16 across the martensitic transition. But in spite of the hysteresis losses, a large effective refrigerant capacity can be obtained in this material over a wide temperature interval.

Comparison and analysis of the expansion process in a CO<SUB align=right>2 transcritical cycle

The isentropic and isenthalpic expansion processes in a CO 2 transcritical cycle were analysed thermodynamically. It was found that the effective refrigeration capacity of the cycle with the isentropic expansion process is higher than the cycle with the isenthalpic expansion process. The increment is slightly larger than the expansion work recovered because of the transcritical nature of the cycle. Further analysis and comparison were made for two decreasing throttling loss methods: using internal heat exchangers and using expanders instead of throttling valves. The results indicate that using high efficiency expanders in the transcritical cycle is the better method, and the work recovered by the expander is mainly from the flow work in the supercritical area, and from the internal energy change in the liquid-gas two-phase region. It is recommended that the flashing crash model can be used to simplify the characteristic equations of the liquid-gas two-phase adiabatic expansion process.