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- ItemPredicting the dominating factors during heat transfer in magnetocaloric composite wires(Amsterdam : Elsevier B.V., 2020) Krautz, M.; Beyer, L.; Funk, A.; Waske, A.; Weise, B.; Freudenberger, J.; Gottschall, T.Magnetocaloric composite wires have been studied by pulsed-field measurements up to μ0ΔH = 10 T with a typical rise time of 13 ms in order to evaluate the evolution of the adiabatic temperature change of the core, ΔTad, and to determine the effective temperature change at the surrounding steel jacket, ΔTeff, during the field pulse. An inverse thermal hysteresis is observed for ΔTad due to the delayed thermal transfer. By numerical simulations of application-relevant sinusoidal magnetic field profiles, it can be stated that for field-frequencies of up to two field cycles per second heat can be efficiently transferred from the core to the outside of the jacket. In addition, intense numerical simulations of the temperature change of the core and jacket were performed by varying different parameters, such as frequency, heat capacity, thermal conductivity and interface resistance in order to shed light on their impact on ΔTeff at the outside of the jacket in comparison to ΔTad provided by the core.
- ItemIn-situ and ex-situ measurements of thermal conductivity of supercapacitors(Amsterdam [u.a.] : Elsevier, 2014) Hauge, H.H.; Presser, V.; Burheim, O.Thermal signature of supercapacitors are investigated in-situ and ex-situ using commercial supercapacitors. Regarding the in-situ method, four supercapacitors were connected in series, with thermocouples embedded between the supercapacitors. As the applied current was increased, the temperature measured at the intrinsic positions also increased. When cycling at a current density of 0.11Acm-2 the centre temperature increased by 14K compared to the stack surface temperature. This is an important figure as literature states that an increase of 10K leads to a corresponding decrease in the lifetime by a factor of 2. Using the obtained temperature profiles, the effective thermal conductivity of the stack was found to vary between 0.5WK-1m-1 and 1.0WK-1m-1, depending on the compaction of the stack. For the ex-situ measurements, the thermal conductivity and the thicknesses of the supercapacitor material layers were measured individually in order to determine the corresponding thermal conductivity of the stack. When using this method an effective thermal conductivity of the stack of 0.53 ± 0.06WK-1m-1 was obtained. The analysis also demonstrated that the main contributor to the thermal resistivity and conductivity of the supercapacitor construction is the electrodes. This demonstrates that when managing heat from supercapacitors it is important to focus on the thermal conductivity of the components materials.