Refrigerant Capacity Values Research Articles

Large reversible magnetocaloric effect in DyCuAl compound

Large reversible magnetocaloric effect, which is associated with a second-order magnetic transition at 28 K, has been observed in DyCuAl compound. The maximum values of magnetic entropy change −ΔSM and adiabatic temperature change ΔTad are 20.4 J kg−1 K−1 and 7.7 K for a field change of 0–5 T, respectively. Especially, the large values of −ΔSM (10.9 J kg−1 K−1) and ΔTad (3.6 K) with a considerable refrigerant capacity value of 150 J kg−1 are also obtained for a relatively low field change of 0–2 T, suggesting that DyCuAl compound could be considered as a good candidate for low-temperature magnetic refrigerant.

Magnetocaloric effect in La1−xPrxFe10.7Co0.8Si1.5 compounds near room temperature

The magnetic properties and magnetocaloric effects in NaZn13-type La1−xPrxFe10.7Co0.8Si1.5 compounds have been investigated. Partially replacing La with Pr leads to a small reduction in the Curie temperature TC due to the lattice contraction, but the values of TC for La1−xPrxFe10.7Co0.8Si1.5 are close to room temperature. The maximum values of magnetic entropy change ΔSm in La1−xPrxFe10.7Co0.8Si1.5 with x ⩽ 0.5 are in the range 13.5–14.6 J kg−1 K−1 for a field change of 0–5 T, and correspondingly the values of the refrigerant capacity (RC) are 373–353 J kg−1. In particular, the values of ΔSm and RC for a low field change from 0 to 2 T are also obtained to be as high as 7.0–8.1 J kg−1 K−1 and 128–139 J kg−1, respectively. No magnetic hysteresis is observed in the magnetization as a function of both the temperature and the magnetic field in the La1−xPrxFe10.7Co0.8Si1.5 compounds. The large reversible ΔSm and the high reversible RC for a low field change indicate that La1−xPrxFe10.7Co0.8Si1.5 may be a promising candidate for magnetic refrigeration near room temperature.

A semi-empirical model for steady-state simulation of household refrigerators

A semi-empirical modeling approach for simulating the steady-state behavior of vapor-compression refrigeration systems is presented in this study. The model consists of first-principles algebraic equations adjusted with experimental data obtained from the refrigeration system under analysis. Measurements of the relevant variables were taken at several positions along the refrigeration loop, supplying data for the calibration of the computer model. The predicted values of refrigeration capacity and power consumption when compared with experimental data were within ±10% error bands. The model was also employed to assess the effect of various system parameters on the refrigerator performance. Although a top-mount frost-free refrigerator was chosen for this study, the modeling methodology can be easily extended to other types of refrigeration systems, from domestic refrigerators to heat pumps.

Large magnetocaloric effect and enhanced magnetic refrigeration in ternary Gd-based bulk metallic glasses

The magnetocaloric effect and refrigeration capacity (RC) of Gd55Co20Al25 and Gd55Ni25Al20 bulk metallic glasses (BMGs) have been investigated. Large magnetic entropy changes ΔSM of 11.2 and 10.8 J kg−1 K−1 and large RC values of 846 and 920 J kg−1 are obtained for Gd55Co20Al25 and Gd55Ni25Al20, respectively, at a field change of 7 T. The RC value (640 J kg−1 at 5 T or 920 J kg−1 at 7 T) of Gd55Ni25Al20 BMG is larger than that reported for all magnetocaloric materials, including crystalline and amorphous materials measured under the same conditions. The large RC value is due to the broad ΔSM peak (more than 100 K), which is caused by the disordered structure of an amorphous material. The large ΔSM and RC values make these Gd-based ternary BMGs attractive candidates for magnetic refrigeration applications.

Magnetic properties and magnetocaloric effects in Tb 6 Co 1.67 Si 3 compound

Magnetic properties and magnetocaloric effects of Tb6Co1.67Si3 have been investigated by magnetization measurement. This compound is of a hexagonal Ce6Ni2Si3-type structure with a saturation magnetization of 187 emu/g at 5K and a reversible second-order magnetic transition at Curie temperature TC = 186K. A magnetic entropy change ΔS = 7Jkg−1K−1 is observed for a magnetic field change from 0 to 5T. A large value of refrigerant capacity (RC) is found to be 330J/kg for fields ranging from 0 to 5T. The large RC, the reversible magnetization around TC and the easy fabrication make the Tb6Co1.67Si3 compound a suitable candidate for magnetic refrigerants in a corresponding temperature range.

The magnetocaloric effect and hysteresis properties of melt-spun Gd5Si1.8Ge1.8Sn0.4 alloy

The master Gd5Si1.8Ge1.8Sn0.4 MCE alloy was prepared by the arc-melt method. The alloy was re-melted and melt-spun by single-roller melt spinning at different copper wheel speeds. Temperature-dependent x-ray diffraction (XRD) and magnetic measurement confirm the first-order magnetic–crystallographic transition of as-cast Gd5 Si1.8Ge1.8Sn0.4. From powder XRD results, the melt-spun technique preserves the monoclinic phase of Gd5Si1.8Ge1.8Sn0.4 but broadens the corresponding Bragg reflection which implies the smaller crystalline size of the melt-spun ribbons. For the spun ribbons, the refrigerant capacity (RC) is comparable to that of the as-prepared Gd5Si1.8Ge1.8Sn0.4. The thermal (∼9.2 K) and magnetic hysteresis (∼62 J kg−1 at 270 K) near TC of the as-cast alloy have been significantly reduced (∼4 K and ∼5.7 J kg−1 to ∼7.5 J kg−1 for ribbons, respectively) with the help of the melt-spun technique. The low hysteresis and large RC values make the spun ribbons suitable for magnetic refrigeration application near room temperature.

Large magnetic entropy change in Ni50Mn50−xInx Heusler alloys

The magnetocaloric properties of polycrystalline Ni50Mn50−xInx (15⩽x⩽16) associated with the second order magnetic transition at the Curie temperature and the first order martensitic transition were studied using magnetization measurements. The refrigeration capacity and magnetic entropy change were found to depend on the In concentration and reach a maximum value of refrigeration capacity of 280J∕kg with a magnetic entropy change of −6.8J∕kgK at 318K for a magnetic field change of 5T. These values of the magnetocaloric parameters are comparable to that of the largest values reported near the second order transition of metallic magnets near room temperature.

Magnetic properties and enhanced magnetic refrigeration in (Mn1−xFex)5Ge3 compounds

Magnetic and magnetocaloric effects of (Mn1−xFex)5Ge3 compounds are studied systematically. The maximum of magnetic entropy changes of 8.01 J/kg K under an external field change of 5 T is obtained for (Mn0.9Fe0.1)5Ge3, which is the largest value in Mn5Ge3-based solid solutions. Moreover, the Fe substitution increases the refrigeration capacity (RC) value greatly. The largest RC value of 237 J/kg in (Mn0.8Fe0.2)5Ge3 even compares favorably to that of many well-known magnetic refrigeration materials. Thus the Fe-containing (Mn1−xFex)5Ge3 compounds are much-improved magnetic refrigerants for the application of room-temperature magnetic refrigeration. The increase of the RC value is probably resulted from the formation of magnetic nanostructure.

The influence of Co addition on the magnetocaloric effect of Nanoperm-type amorphous alloys

The effect of Co addition on the magnetocaloric effect of amorphous alloys with Nanoperm-type composition has been studied for temperatures above room temperature. Co addition produces an increase in the maximum magnetic entropy change and a shift of its associated temperature to higher temperatures. The maximum refrigerant capacity (RC) value obtained in this study is 82Jkg−1 for a maximum applied field H=15kOe. This value is ∼30% larger than that of a Mo-containing Finemet-type alloy measured under the same experimental conditions. However, the RC of the alloys, when calculated from temperatures corresponding to the half-maximum entropy change value, deteriorates with the presence of Co in the alloy. The field dependence of the magnetic entropy change has also been analyzed, showing a power dependence for all the magnetic regimes of the samples. This field dependence at the Curie temperature deviates from mean field predictions.

Amorphous-FeCoCrZrB ferromagnets for use as high-temperature magnetic refrigerants

Magnetic metallic glasses, having large magnetic moments and high Curie temperatures (TC), have not been widely studied as magnetic refrigerants. In this study, we report on the magnetocaloric effects of five FeCoCrZrB amorphous alloys [(FexCoyCrz)91Zr7B2, with Fe:Co:Cr ratios of 100:0:0, 90:15:5, 85:5:10, and 75:15:10] chosen for efficiently surveying the high TC metallic glass composition surface. Magnetic isotherms were measured at 25K intervals from 25to525K. The entropy change (ΔS) due to the magnetocaloric effect was computed by integrating the magnetic isotherms. The refrigeration capacity (RC) was computed by Wood-Potter method. At 3979kA∕m (50kOe) the FeCoCrZrB alloys have RC values of 240–320J∕kg; at 796kA∕m (10kOe) the alloys have values of 32–54J∕kg. The RC values favorably compare with values reported for other refrigerant materials. The peak ΔS temperature depends strongly on composition, varying from 200to450K. The wide flexibility in choosing amorphous alloy compositions allows them to be fine tuned for multistage high temperature refrigerators. The saturation magnetization at 25 and 300K and Curie temperatures are also reported for the five alloys.