Two new papers have been published by project partner DTU on their work on the magnetocaloric heat pump, which forms part of the RES4BUILD integrated energy system.
M. Masche, J. Liang, K. Engelbrecht, C.R.H. Bahl (2022) Improving magnetic cooling efficiency and pulldown by varying flow profiles, Applied Thermal Engineering, Volume 215, 118945 https://doi.org/10.1016/j.applthermaleng.2022.118945.
Abstract: 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 trapezoid-shaped 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 41.6to 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.
C.R.H. Bahl, J. Liang, M. Masche, K.K. Nielsen, K. Engelbrecht, (2022) Virgin effect in spheres of LaFeSi-based alloys, AIP Advances 12, 065216 https://doi.org/10.1063/5.0093772
Abstract: A virgin phase transition is observed in spherical particles of the industrially relevant magnetocaloric material La(Fe,Mn,Si)13Hy. Upon initial cooling, the phase transition is observed 2–3 K below the heating transition on all subsequent cooling and heating transitions. This virgin transition has been studied using differential scanning calorimetry and vibrating sample magnetometry. Incremental measurements show not only how the phase transition can be carefully approached but also that the initial full transformation requires cooling of about 6 K below the observed phase transformation. No signs of structural damage due to the thermal cycling were observed, neither macroscopically or by scanning electron microscopy.