• Energy Research

Abstract A thermodynamic performance analysis is developed for a Steyert-like rotary magnetic refrigeration (RMR) system operating in the near-room temperature range with two possible, alternative, gadolinium compounds. The first magnetocaloric material (MCM) is an alloy (Gd 7 Pd 3 ) with a well defined Curie temperature (around 318 K), while the second MCM (Gd 76 Pd 24 ) is an eutectic compound with a smoothed double Curie transition (at 298 and 318 K, respectively). The main issues linked to the thermodynamic properties of the magnetic material are outlined and the influence of the magnetocaloric properties on the global performance (useful effect, coefficient of performance, and so on) of the refrigeration system is discussed.

Abstract A linear reciprocating magnetic refrigerator prototype was designed and built with the aid of an industrial partner. The refrigerator is based on the Active Magnetic Regenerative cycle, and exploits two regenerators working in parallel. The active material is Gadolinium in plates, 0.8 mm thick, for a total mass of 0.36 kg. The device is described and results about magnetic field and temperature span measurements are presented. The designed permanent magnet structure, based on an improved cross-type arrangement, generates a maximum magnetic field intensity of 1.55 T in air, over a gap of (13 × 50 × 100) mm 3 . The maximum temperature span achieved is 5.0 K, in a free run condition.

Active Magnetic Regeneration (AMR) is a configuration that allows magnetic refrigeration to be suitable also for room temperature applications. This work is intended to detect, by means of a 1-D numerical model, the influence on the regenerator performances of the working condition ambient temperature (T(CURIE) +/- 20 K) and of the operating parameters fluid mass flow rate (utilization factor 0.5 divided by 3.5) and cycle frequency (0.1 divided by 0.6 Hz). Simulations show that, tuning the fluid mass flow rate, a gadolinium AMR (395 g, f = 0.25 Hz, Delta B = 1.7 T) can reach a maximum cooling capacity of 130 W and a 40 W cooling power over a temperature span of 30 K. A COP of 5 can also be achieved with a temperature span of 30 K and a cooling power of 35 W. Frequency has a weak influence on the AMR's COP, while the ambient temperature is crucial. The system loses the 60% of cooling capacity if the ambient temperature is 20 K away from the material Curie temperature.

From heat capacity measurements performed in the 5-350 K temperature range at 0- and 5-Tesla applied magnetic field on the intermetallic compounds Gd/sub 7/Pd/sub 3/ and Gd/sub 7/Pd/sub 2/Ni, and on the eutectic between Gd and Gd/sub 7/Pd/sub 3/ with composition Gd/sub 76/Pd/sub 24/, the main magnetocaloric properties of the alloys were obtained, namely the isothermal entropy change /spl Delta/S/sub M/, the adiabatic temperature rise /spl Delta/T/sub ad/ and the refrigerant capacity Q.