Power density

About: Power density is a research topic. Over the lifetime, 9534 publications have been published within this topic receiving 197264 citations. The topic is also known as: volumic power & volume power density.

Fe(CN)63− ion-modified MnO2/graphene nanoribbons enabling high energy density asymmetric supercapacitors

Abstract: Due to its high theoretical specific capacitance and high oxygen evolution potential, MnO2 has been considered as a promising positive electrode material for high-energy asymmetric supercapacitors (ASCs). However, the search for MnO2 positive electrodes with high specific capacitance and excellent rate performance for ASCs remains challenging. Herein, for the first time we report a novel strategy for the synthesis of Fe(CN)63− ion-modified MnO2/graphene ribbons (m-MnO2/GRs) as the positive electrode for high energy density ASCs. Benefiting from vertically aligned MnO2 grown on the interconnected graphene ribbon and Fe(CN)63− ion modification, the m-MnO2/GR exhibits a high specific capacitance of 435 F g−1, excellent rate capability and cycling stability. More importantly, the assembled m-MnO2/GR//GR ASC exhibits a high energy density of 57.8 W h kg−1 at a power density of 1.2 kW kg−1, as well as outstanding cycling stability with 100% capacitance retention after 10 000 cycles. More importantly, such a device can be charged/discharged within 0.79 s in an ultrafast manner to deliver a high specific energy of 10.5 W h kg−1 at an ultrahigh specific power of 48 kW kg−1. Thus, our strategy could be possibly used for the design and fabrication of new energy storage devices with high energy and power densities for future applications.

Using Flow Electrodes in Multiple Reactors in Series for Continuous Energy Generation from Capacitive Mixing

Abstract: Efficient conversion of “mixing energy” to electricity through capacitive mixing (CapMix) has been limited by low energy recoveries, low power densities, and noncontinuous energy production resulting from intermittent charging and discharging cycles. We show here that a CapMix system based on a four-reactor process with flow electrodes can generate constant and continuous energy, providing a more flexible platform for harvesting mixing energy. The power densities were dependent on the flow-electrode carbon loading, with 5.8 ± 0.2 mW m–2 continuously produced in the charging reactor and 3.3 ± 0.4 mW m–2 produced in the discharging reactor (9.2 ± 0.6 mW m–2 for the whole system) when the flow-electrode carbon loading was 15%. Additionally, when the flow-electrode electrolyte ion concentration increased from 10 to 20 g L–1, the total power density of the whole system (charging and discharging) increased to 50.9 ± 2.5 mW m–2.

Achieving ultrahigh energy storage density and energy efficiency simultaneously in sodium niobate-based lead-free dielectric capacitors via microstructure modulation

Abstract: Recently, dielectric capacitors have drawn much attention from researchers and engineers due to their ultrahigh power density, ultrafast charge–discharge rate, and good temperature and fatigue stability. However, most related research mainly focuses on the improvement in dielectric breakdown strength and energy storage density rather than that in energy efficiency. In this study, we adopted the spark plasma sintering method to modify the microstructure and electric conductivity of Na0.7Bi0.1NbO3 lead-free ceramics, and subsequently enhanced their energy storage properties. As a result, the Na0.7Bi0.1NbO3 ceramics prepared by the spark plasma sintering method display a considerably large energy storage density of 3.41 J cm−3 with an ultrahigh energy storage efficiency of 90.8% at 28 kV mm−1. The improvement of energy storage performance is ascribed to the reduction of electric conductivity, which can be analyzed by the X-ray photoelectron spectroscopy and high-temperature complex impedance spectra. This study not only paves the way for environment-friendly Na0.7Bi0.1NbO3 lead-free ceramics to be developed for energy storage applications, but also interprets the internal mechanism of microstructure modulation which enhances energy storage properties.

Numerical analysis of thermomagnetic generators

Abstract: Thermomagnetic generators allow direct conversion of heat energy to electrical energy. Temperature cycling about or near the Curie temperature causes changes in magnetization, resulting in time variant magnetic flux and induced voltage in a surrounding conductor. Numerical analyses of regenerative thermomagnetic generators with perfect regeneration have been performed for three working materials: iron, gadolinium, and Ho69Fe31. Power density above 20 W/kg of shunt material and efficiency approaching Carnot limits are possible over temperature differences of 50 K. Analytical studies performed during the 1950s predicted maximum power density less than 7 W/kg and efficiency less than 1% for nonregenerative cycles.

Analysis of Theoretical Limits of Forced-Air Cooling Using Advanced Composite Materials With High Thermal Conductivities

Abstract: Cooling systems take a significant portion of the total mass and/or volume of power electronic systems. In order to design a converter with high power density, it is necessary to minimize the converter's cooling system volume for a given maximum tolerable thermal resistance. This paper theoretically investigates whether the cooling system volume can be significantly reduced by employing new advanced composite materials like isotropic aluminum/diamond composites or anisotropic highly orientated pyrolytic graphite. Another strategy to improve the power density of the cooling system is to increase the rotating speed and/or the diameter of the fan, which is limited by increasing power consumption of the fan. Fan scaling laws are employed in order to describe volume and thermal resistance of an optimized cooling system (fan plus heat sink), resulting in a single compact equation dependent on just two design parameters. Based on this equation, a deep insight into different design strategies and their general potentials is possible. The theory of the design process is verified experimentally for cooling a 10 kW converter. Further experimental results showing the result of the operation of the optimized heat sink are also presented.