• Energy Research
• 2021-2025close

Supporting data for publication 'Performance analysis of a high-efficiency multi-bed active magnetic regenerator device" submitted to the Applied Thermal Engineering (DOI 10.1016/j.applthermaleng.2021.117569)The Excel sheet summarizes the experimental output parameters for the performance data presented in the publication. All data were measured continuously after reaching steady-state conditions, and the data were averaged over a time span of 600 s.

Abstract We present the performance of an active magnetic regenerator prototype with a multi-bed concept and parallel flow circuit. The prototype applies a two-pole permanent magnet (maximum magnetic flux density of 1.44 T) that rotates over 13 tapered regenerator beds mounted on a laminated iron yoke ring. Each bed is filled with about 262 g of spherical particles, distributed in layers of ten alloys of La(Fe,Mn,Si)13Hy (CALORIVAC HS) with different Curie temperatures. Other important features are the solenoid valves, the monitoring of the temperatures exiting each bed at the cold side, and a torque meter used to measure the magnetic power required to drive the cycle. The opening behavior of the solenoid valves (i.e., the blow fraction) could be adjusted to correct flow imbalances in each bed. The device provided a maximum cooling power of about 815 W at a cycle frequency of 1.2 Hz, a utilization of 0.36, and a hot reservoir temperature of 295 K while maintaining a 5.6 K-temperature span with a coefficient of performance of 6.0. In this case, the second-law efficiency was 11.6%. The maximum second-law efficiency of 20.5%, which represents one of the largest for a magnetocaloric device, was obtained at a cycle frequency of 0.5 Hz, a utilization of 0.34, and a hot reservoir temperature of 295 K at a temperature span of 10.3 K. Under these conditions, the device absorbed a cooling load of 288 W with a coefficient of performance of 5.7. It was also shown that an unbalanced flow due to different hydraulic resistance through the beds can cause cold side outlet temperature variations, which reduce the system performance, demonstrating the importance of a well-functioning, balanced flow system.

Supporting data for publication 'Performance assessment of a rotary active magnetic regenerator prototype using gadolinium" submitted to the Applied Thermal Engineering (doi:10.1016/j.applthermaleng.2021.117947)The Excel sheet summarizes the experimental output parameters for the performance data presented in the publication. In addition, an efficiency calculation tool is provided in the spreadsheet to calculate real system efficiencies considering losses due to inefficiencies. All data were measured continuously after reaching steady-state conditions, and the data were averaged over a time span of 600 s.

This study investigates the influence of wood pellet properties on the grindability of pellets in a lab-scale disc mill. The pellet properties investigated included wood type, moisture content, internal pellet particle size distribution, particle density, and durability. Two pellet qualities for industrial use (designated I1 and I2 as per ISO 17225-2:2014) and two types of semi-industrial pellets (beech and pine) were used and grinding was performed on as-received and oven-dried pellets. The grinding performance was assessed by measuring the grinding energy and analyzing the changes in particle morphology (size and shape) with respect to the internal pellet particle morphology. Von Rittinger’s comminution law was used to characterize the pellet grindability. Drying pellets increased their brittleness and improved their grindability, resulting in both grinding energy savings and a higher milled product fineness, and the impact of drying was larger for industrial pellets. Beech pellets had a better grindability (kWh mm t-1 dry wood) than pine pellets (kWh mm t-1 dry wood). The moisture content of pellets did not influence the shape of the milled particles in terms of circularity and elongation ratio. The study also showed that the proposed disc mill has the potential to quickly determine the relative grindability characteristics of various pellet qualities.

We present the experimental results for a rotary magnetocaloric prototype that uses the concept of active magnetic regeneration, presenting an alternative to conventional vapor compression cooling systems. Thirteen packed-bed regenerators subjected to a rotating two-pole permanent magnet with a maximum magnetic field of 1.44 T are implemented. It is the first performance assessment of the prototype with gadolinium spheres as the magnetocaloric refrigerant and water mixed with commercial ethylene glycol as the heat transfer fluid. The importance of various operating parameters, such as fluid flow rate, cycle frequency, cold and hot reservoir temperatures, and blow fraction on the system performance is reported. The cycle frequency and utilization factor ranged from 0.5 to 1.7 Hz and 0.25 to 0.50, respectively. Operating near room temperature and employing 3.83 kg of gadolinium, the device produced cooling powers exceeding 800 W at a coefficient of performance of 4 or higher over a temperature span of above 10 K at 1.4 Hz. It was also shown that variations in the flow resistance between the beds could significantly limit the system performance, and a method to correct those is presented. The performance metrics presented here compare well with those of currently existing magnetocaloric devices. Such a prototype could achieve efficiencies as high as conventional vapor compression systems without the use of refrigerants that have high global warming potential.

Supporting data for publication 'Novel design of a high efficiency multi-bed active magnetic regenerator heat pump" submitted to the International Journal of Refrigeration (DOI 10.1016/j.ijrefrig.2021.09.007)The videos show the operation of the novel magnetocaloric heat pump called the MagQueen, which has been developed by DTU Energy.The Excel sheet summarizes the experimental output parameters for the performance data presented in the publication. All data were measured continuously after reaching steady-state conditions, and the data were averaged over a time span of 600 s.

Magnetic refrigeration systems are promising cooling solutions that employ the active magnetic regenerator refrigeration cycle to achieve practical temperature spans and environmental benefits. The hydraulic system that ensures a continuous flow of the heat transfer fluid through the system with a reciprocating flow in each regenerator bed is critical to the performance of the refrigeration cycle. Hence, we investigate the characteristics of the parallel flow circuit of a rotary active magnetic regenerator system, which consists of thirteen trapezoidshaped regenerators, each filled with 295 g of gadolinium spheres. Fluid flow is controlled via electrically actuated solenoid valves (both piloted and direct-acting) connected to the regenerator hot side. By varying the percentage of opening of the control valves, different blow fractions (or fluid flow waveforms) could be investigated. The objective of the study is twofold: (i) assess whether flow imbalances of the heat transfer fluid exist in the cold-to-hot blow (cold blow) and hot-to-cold blow (hot blow) directions, and (ii) determine whether there is an optimal value of the blow fraction both to maximize the cooling performance and realize a rapid temperature pulldown. Flow resistance measurements demonstrate a symmetric flow circuit design and resistances that are similar in the cold and hot blow directions. Moreover, for the studied temperature spans of 6 K and 16 K, the best blow fraction was found to be about 41.6 %. For instance, at a 16 K span, a utilization of 0.32, and at 1.4 Hz, increasing the fluid blow fraction from 25.0 to 41.6 % enhanced the cooling capacity and second-law efficiency from 70 to 330 W and from 2.6 to 17.4 %, respectively. In turn, lower blow fractions favored a more rapid temperature pulldown. The magnetocaloric system was about 30 % faster in establishing approximately 14 K temperature span when the blow fraction was reduced from 41.6 to 30.6 %. Hence, magnetic refrigeration systems can benefit greatly from solenoid valves, which allow the system to operate either in a time-saving mode or an energy-saving mode.

Abstract Caloric cooling relies on reversible temperature changes in solids driven by an externally applied field, such as a magnetic field, electric field, uniaxial stress or hydrostatic pressure. Materials exhibiting such a solid-state caloric effect may provide the basis for an alternative to conventional vapor compression technologies. First-order phase transition materials are promising caloric materials, as they yield large reported adiabatic temperature changes compared to second-order phase transition materials, but exhibit hysteresis behavior that leads to possible degradation in the cooling performance. This work quantifies numerically the impact of hysteresis on the performance of a cooling cycle using different modeled caloric materials and a regenerator with a fixed geometry. A previously developed 1D active regenerator model has been used with an additional hysteresis term to predict how modeled materials with a range of realistic hysteresis values affect the cooling performance. The performance is quantified in terms of cooling power, coefficient of performance (COP), and second-law efficiency for a range of operating conditions. The model shows that hysteresis reduces efficiency, with COP falling by up to 50% as the hysteresis entropy generation (qhys) increases from 0.5% to 1%. At higher working frequencies, the cooling performance decreases further due to increased internal heating of the material. Regenerator beds using materials with lower specific heat and higher isothermal entropy change are less affected by hysteresis. Low specific heat materials show positive COP and cooling power up to 2% of qhys whereas high specific heat materials cannot tolerate more than 0.04% of qhys.