Magneto-caloric effect in the pseudo-binary intermetallic YPrFe17 compound

We have synthesized the intermetallic YPrFe17 compound by arc-melting. X-ray and neutron powder diffraction show that the crystal structure is rhombohedral with View the MathML source space group (Th2Zn17-type). The investigated compound exhibits a broad isothermal magnetic entropy change {\Delta}SM(T) associated with the ferro-to-paramagnetic phase transition (TC \approx 290 K). The |{\Delta}SM| (\approx 2.3 J kg-1 K-1) and the relative cooling power (\approx 100 J kg-1) have been calculated for applied magnetic field changes up to 1.5 T. A single master curve for {\Delta}SM under different values of the magnetic field change can be obtained by a rescaling of the temperature axis. The results are compared and discussed in terms of the magneto-caloric effect in the isostructural R2Fe17 (R = Y, Pr and Nd) binary intermetallic alloys.Comment: Preprint, 5 pages (postprint), 4 figures, regular pape

Determining the minimum mass and cost of a magnetic refrigerator

An expression is determined for the mass of the magnet and magnetocaloric material needed for a magnetic refrigerator and these are determined using numerical modeling for both parallel plate and packed sphere bed regenerators as function of temperature span and cooling power. As magnetocaloric material Gd or a model material with a constant adiabatic temperature change, representing a infinitely linearly graded refrigeration device, is used. For the magnet a maximum figure of merit magnet or a Halbach cylinder is used. For a cost of \$40 and \$20 per kg for the magnet and magnetocaloric material, respectively, the cheapest 100 W parallel plate refrigerator with a temperature span of 20 K using Gd and a Halbach magnet has 0.8 kg of magnet, 0.3 kg of Gd and a cost of \$35. Using the constant material reduces this cost to \$25. A packed sphere bed refrigerator with the constant material costs \$7. It is also shown that increasing the operation frequency reduces the cost. Finally, the lowest cost is also found as a function of the cost of the magnet and magnetocaloric material.Comment: 12 pages, 10 figure

Passive force balancing of an active magnetic regenerative liquefier

Active magnetic regenerators (AMR) have the potential for high efficiency cryogen liquefaction. One active magnetic regenerative liquefier (AMRL) configuration consists of dual magnetocaloric regenerators that reciprocate in a persistent-mode superconducting solenoid. Issues with this configuration are the spatial and temporal magnetization gradients that induce large magnetic forces and winding currents. To solve the coupled problem, we present a force minimization approach using passive magnetic material to balance a dual-regenerator AMR. A magnetostatic model is developed and simulated force waveforms are compared with experimental measurements. A genetic algorithm identifies force-minimizing passive structures with virtually ideal balancing characteristics. Implementation details are investigated which affirm the potential of the proposed methodology

Magnetocaloric properties of LaFe13−x−yCoxSiy and commercial grade Gd

The magnetocaloric properties of three samples of LaFe13−x−yCoxSiy have been measured and compared to measurements of commercial grade Gd. The samples have (x=0.86, y=1.08), (x=0.94, y=1.01) and (x=0.97, y=1.07) yielding Curie temperatures in the range 276–288 K. The magnetization, specific heat capacity and adiabatic temperature change have been measured over a broad temperature interval. Importantly, all measurements were corrected for demagnetization, allowing the data to be directly compared. In an internal field of 1 T the maximum specific entropy changes were 6.2, 5.1 and 5.0 J/kg K, the specific heat capacities were 910, 840 and 835 J/kg K and the adiabatic temperature changes were 2.3, 2.1 and 2.1 K for the three LaFeCoSi samples respectively. For Gd in an internal field of 1 T the maximum specific entropy change was 3.1 J/kg K, the specific heat capacity was 340 J/kg K and the adiabatic temperature change was 3.3 K. The adiabatic temperature change was also calculated from the measured values of the specific heat capacity and specific magnetization and compared to the directly measured values. In general an excellent agreement was seen

Application of Peltier thermal diodes in a magnetocaloric heat pump

The major hurdle for commercialization of room temperature magnetic refrigeration is the inadequate power density of a device due to the low operating frequency. Limitation in the heat transfer rate imposed by solid-fluid convection is the primary cause. Applying Peltier thermal diodes in combination with microchannel heat exchangers has been investigated as a possible solution. This study improves in realism upon earlier work, mainly by extending the calculations with a modeled thermoelectric effect. After reverse engineering the Micropelt MPC-D701 Peltier module, behavior of a 2D single-stage device is examined, consisting of two Peltier modules with heat exchangers enveloping a thin layer of magnetocaloric material. The near optimal switching frequency is determined and performance characteristics are calculated for several configurations of varying load, field strength and fluid velocity. A better performance is observed without the magnetocaloric effect due to reduced heat leakage through the passive thermal diode. This behavior extends to multiple devices in series where active magnetic regeneration is induced. Two possible solutions were explored, but these did not show significant improvement in device performance when applying the magnetocaloric effect

Scaling of the entropy change at the magnetoelastic transition in Gd5(SixGe1-x)4

Differential scanning calorimetry under a magnetic field H has been used to measure the entropy change DS at the magnetoelastic transition in Gd5(SixGe12x)4 alloys, for x<0.5. We show that DS scales with the transition temperature, Tt , which is tuned by x and H, from 70 to 310 K. Such a scaling demonstrates that Tt is the relevant parameter in determining the giant magnetocaloric effect in these alloys, and proves that the magnetovolume effects due to H are of the same nature as the volume effects caused by substitutio