Mass-specific Power Research Articles

Induced Power Scaling Alone Cannot Explain Griffenfly Gigantism.

Paleozoic skies were ruled by extinct odonatopteran insects called "griffenflies," some with wingspans 3 times that of the largest extant dragonflies and 10 times that of common extant dragonflies. Previous studies suggested that flight was possible for larger fliers because of higher atmospheric oxygen levels, which would have increased air density. We use actuator disk theory to evaluate this hypothesis. Actuator disk theory gives similar estimates of induced power as have been estimated for micro-air vehicles based on insect flight. We calculate that for a given mass of griffenfly, and assuming isometry, a higher density atmosphere would only have reduced the induced power required to hover by 11%, which would have supported a flyer 3% larger in linear dimensions. Steady-level forward flight would have further reduced induced power but could only account for a flier 5% larger in linear dimensions. Further accounting for the higher power available due to high-oxygen air and assuming isometry, we calculate that the largest flyer hovering would have been only 1.19times longer than extant dragonflies. We also consider known allometry in dragonflies and estimated allometry in extinct griffenflies. But such allometry only increases flyer size to 1.22times longer while hovering. We also consider profile and parasite power, but both would have been higher in denser air and thus would not have enhanced the flyability of larger griffenflies. The largest meganeurid griffenflies might have adjusted flight behaviors to reduce power required. Alternatively, the scaling of flight muscle power may have been sufficient to support the power demands of large griffenflies. In literature estimates, mass-specific power output scales as mass0.24 in extant dragonflies. We need only more conservatively assume that mass-specific muscle power scales with mass0, when combined with higher oxygen concentrations and induced power reductions in higher-density air to explain griffenflies 3.4times larger than extant odonates. Experimental measurement of flight muscle power scaling in odonates is necessary to test this hypothesis.

A Review on Thermophotovoltaic Energy Conversions and its Space Power Applications

Thermophotovoltaic (TPV) system coverts heat radiations from various sources like Thermophotovoltaic (TPV) system coverts heat radiations from various sources like combustion of fuels, industrial waste heat and nuclear energy into electricity. To fulfil the demand of energy TPV is an alternate, can enable approaches to energy storage and conversion. The TPV model consists of multiple arrays of TPV cells, an emitter, a radiator and a filter. one of the important advantages of TPVs are the high efficiencies and direct conversion of DC power. This paper presents the research being conducted till date in the field of Thermophotovoltaic cell and space applications of TPV cells. We have Thermophotovoltaic has been regarded as an energy substitute in radioisotope deep space power system for thermoelectric. TPV provides outstanding potential improvement in mass specific power as well as in efficiency. TPV system also proposed for inner planetary solar system. This idea leads TPV capability to store energy in the form of heat energy rather than electrical energies which is common in photovoltaic system. The current effort to derive the demonstration of efficiency conversion up to 19% and it enhances the specific power W/kg at the system level. Next generation TPV concepts are also reviewed in order to explore the future space power application. The application of TPV that includes radioisotope Thermophotovoltaic (RTPV) and solar Thermophotovoltaic (STPV) plays a vital role in deep space powered systems.

Two-stage confinement derived small-sized highly ordered L10-PtCoZn for effective oxygen reduction catalysis in PEM fuel cells

Intermetallic ordered PtCo is effective for high oxygen reduction reaction (ORR) activity and stability. However, preparing small-sized, highly ordered PtM alloys is still challenging. Herein, we report a controlled two-stage confinement strategy, in which highly ordered PtCoZn/NC nanoparticles of 5.3 nm size were prepared in a scalable process. The contradiction between the high ordering degree with the small particle size as well as the atomic migration with the space confinement was well resolved. An outstanding PEMFC performance was achieved for L10-PtCoZn/NC with a high mass activity (MA) of 1.21 A/mgPt at 0.9 ViR-free, 80.1 % MA retention after 30 k cycles in H2-O2 operation, and a high mass-specific power density of 8.24 W mg-1Pt in H2-Air operation with a slight loss of cell voltage@0.8 A cm−2 of 28 mV after 30 k cycles. The high performance can be ascribed to the high Pt area exposure, the enhanced Pt-Co coupling, and the prevented agglomeration in the mesoporous carbon wall. Overall, this strategy may contribute to the commercialization of fuel cells.

A new variety of axial piston hydraulic machines with multi-row units and a dual oscillating unit

The possibility of increasing the working volume, power, specific energy capacity (energy efficiency), and acceleration response of hydraulic machines under reduced supply and torque pulsation is investigated. The research methodology included the geometric, kinematic, power, and energy analysis of a four-row axial piston hydraulic machine with a dual oscillating unit and without an end distribution system. As a result, a new type of compact rotary hydraulic machines with volumetric action was created. In the proposed model, each subsequent row of cylinders is located in the inter-cylinder space of the previous cylinders with smaller radii. Such a design provides for a 24.5-fold increase in the working capacity and power of a hydraulic machine compared to a single-row design, as well as an increase in the acceleration response in the hydraulic motor mode. The elimination of end distribution systems excludes the possibility of violation of joint tightness between blocks and distribution disks due to block overturning by piston centrifugal forces at high rotation speeds and a multiple reduction of supply and torque pulsation. It was established that the increase in the specific power capacity of a hydraulic machine depends on its particular implementation, potentially reaching 18–25 kW/kg. The abovementioned features of the proposed axial piston hydraulic machine with a dual oscillating unit ensure the compactness of oscillating units, minimum dimensions of the cylinder blocks, and the hydraulic machine as a whole, resulting in its minimum mass and maximum specific power capacity.

Ultrathin Ultralow‐Platinum Catalyst Coated Membrane for Proton Exchange Membrane Fuel Cells (Small 21/2023)

Proton Exchange Membrane Fuel Cells In article number 2207155, Huiyuan Liu, Yujiang Song, and co-workers construct ultrathin ultralow-Pt integrated catalyst coated membrane by proton-initiated regioselective nucleation and growth of Pt/Pd catalyst layer on membrane. The highly active ultrathin catalyst layer greatly facilitates mass transfer and enhances the peak mass specific power density up to 59.9 W mgPt, Cathode−1 for proton exchange membrane fuel cell.

A power amplification dyad in seahorses.

Throughout evolution, organisms repeatedly developed elastic elements to power explosive body motions, overcoming ubiquitous limits on the power capacity of fast-contracting muscles. Seahorses evolved such a latch-mediated spring-actuated (LaMSA) mechanism; however, it is unclear how this mechanism powers the two complementary functions necessary for feeding: rapidly swinging the head towards the prey, and sucking water into the mouth to entrain it. Here, we combine flow visualization and hydrodynamic modelling to estimate the net power required for accelerating the suction feeding flows in 13 fish species. We show that the mass-specific power of suction feeding in seahorses is approximately three times higher than the maximum recorded from any vertebrate muscle, resulting in suction flows that are approximately eight times faster than similar-sized fishes. Using material testing, we reveal that the rapid contraction of the sternohyoideus tendons can release approximately 72% of the power needed to accelerate the water into the mouth. We conclude that the LaMSA system in seahorses is powered by two elastic elements, the sternohyoideus and epaxial tendons. These elements jointly actuate the coordinated acceleration of the head and the fluid in front of the mouth. These findings extend the known function, capacity and design of LaMSA systems.

From PET Bottles Waste to N-Doped Graphene as Sustainable Electrocatalyst Support for Direct Liquid Fuel Cells

Direct liquid fuel cells represent one of the most rapidly emerging energy conversion devices. The main challenge in developing fuel cell devices is finding low-cost and highly active catalysts. In this work, PET bottle waste was transformed into nitrogen-doped graphene (NG) as valuable catalyst support. NG was prepared by a one-pot thermal decomposition process of mineral water waste bottles with urea at 800 °C. Then, NG/Pt electrocatalysts with Pt loadings as low as 0.9 wt.% and 1.8 wt.% were prepared via a simple reduction method in aqueous solution at room temperature. The physical and electrochemical properties of the NG/Pt electrocatalysts are characterized and evaluated for application in direct borohydride peroxide fuel cells (DBPFCs). The results show that NG/Pt catalysts display catalytic activity for borohydride oxidation reaction, particularly the NG/Pt_1, with a number of exchanged electrons of 2.7. Using NG/Pt composite in fuel cells is anticipated to lower prices and boost the usage of electrochemical energy devices. A DBPFC fuel cell using NG/Pt_1 catalyst (1.8 wt.% Pt) in the anode achieved a power density of 75 mW cm−2 at 45 °C. The exceptional performance and economic viability become even more evident when expressed as mass-specific power density, reaching a value as high as 15.8 W mgPt−1.

Wing kinematics measurement and aerodynamics of hovering droneflies with wing damage

In this study, we performed successive unilateral and bilateral wing shearing to simulate wing damage in droneflies (Eristalis tenax) and measured the wing kinematics using high-speed photography technology. Two different shearing types were considered in the artificial wing damage. The aerodynamic force and power consumption were obtained by numerical method. Our major findings are the following. Different shearing methods have little influence on the kinematics, forces and energy consumption of insects. Following wing damage, among the potential strategies to adjust the three Euler angles of the wing, adjusting stroke angle (φ) in isolation, or combing the adjustment of stroke angle (φ) with pitch angle (ψ), contributed most to the change in vertical force. The balance of horizontal thrust can be restored by the adjustment of deviation angle (θ) under the condition of unilateral wing damage. Considering zero elastic energy storage, the mass-specific power (P 1) increases significantly following wing damage. However, the increase in mass-specific power with 100% elastic energy storage (P 2) is very small. The extra cost of the unilateral wing damage is that the energy consumption of the damaged wing and intact wing is highly asymmetrical when zero elastic energy storage is considered. The insects may alleviate the problems of increasing power consumption and asymmetric power distribution by storage and reuse of the negative inertial work of the wing.

Integrated Gas Diffusion Electrode with High Conductivity Obtained by Skin Electroplating for High Specific Power Density Fuel Cell.

Smaller volume/weight and higher output power/energy density are always the goals of electrochemistry energy devices. Here, a simple strategy is proposed to prepare an integrated gas diffusion electrode (GDE) with high conductivity through skin electroplating. The skin electroplating is the combination of magnetron sputtering and spatial confinement electroplating. The electroplated metal obtained by skin electroplating is uniformly, continuously, and tightly attached to the surface of carbon paper like a layer of skin. Uniform and continuous electroplating metal layer endows the integrated electrode excellent conductivity with the square resistance as low as 27mΩsq-1 . In application, the self-breathing fuel cell with 1cm2 active area can harvest ultrahigh volume specific power density (20.9kWL-1 ). Additionally, the weight of the fuel cell stack (23W) with the integrated electrode is only 20g, which is only 7% of the commercial stack with the same power. The mass specific power density reaches 1150Wkg-1 , which is 15 times of the commercial stack. Outstandingly, the stack can charge 4 mobile phones at the same time. More importantly, the skin electroplating provides an effective strategy to improve the specific power density of other energy devices including Zn-air batteries, Li-air batteries, and so on.

Control of self-organization of drop-casted Nafion film for improving proton conduction in a polymer-electrolyte-membrane fuel cell to raise its output power density

A simple drop-cast method to directly deposit Nafion polymer electrolyte membrane (PEM) on nanostructured thin-film catalyst layer composed of stacked Pt nanoparticles prepared by pulsed laser deposition (PLD) was demonstrated. Through optimization of solvent composition and drying temperature of Nafion solution to control self-organization of Nafion, a uniform PEM with better bulk and interface microstructures could be produced, leading to a significant improvement in the output current density of a PEM fuel cell over that using reference commercial PEMs. The formation of facile proton conduction pathways in the bulk Nafion membrane resulted in a 35% reduction in ohmic resistance compared to that with the commercial membrane. Moreover, the infiltration of Nafion in the catalyst layer formed suitable proton transport network to render more catalyst nanoparticles effective and thus lower charge-transfer resistance. With the optimized PLD, drop-cast, and hot-pressing conditions, the current density of PEMFCs using drop-casted PEM reached 1902 mA cm−2 at 0.6 V at 2 atm H2 and O2 pressures with a cathode Pt loading of 100 μg cm−2, corresponding to a power density of 1.14 W cm−2 and a cathode mass-specific power density of 11.4 kW g−1.

Muscle preactivation and the limits of muscle power output during jumping in the Cuban tree frog Osteopilus septentrionalis.

Previous studies of jumping in frogs have found power outputs in excess of what is possible from direct application of muscle power and concluded that jumping requires the storage and release of elastic strain energy. Of course, the muscles must produce the work required and their power output should be consistent with known muscle properties if the total duration of muscle activity is known. Using the Cuban tree frog, Osteopilus septentrionalis, I measured jumping performance from kinematics and used EMG measurements of three major jumping muscles to determine the duration of muscle activity. Using the total mass of all the hindlimb muscles, muscle mass-specific work output up to 60 J kg-1 was recorded. Distributed over the duration of the jump, both average and peak muscle mass-specific power output increased approximately linearly with the work done, reaching values of over 750 and 2000 W kg-1, respectively. However, the muscles were activated before the jump started. Both preactivation duration and EMG amplitude increased with increasing amounts of work performed. Assuming the muscles could produce work from EMG onset until toe-off, the average muscle mass-specific power over this longer interval also increased with work done, but only up to a work output of 36 J kg-1. The mean power above this value of work was 281 W kg-1, which is approximately 65% of the estimated maximum isotonic power. Several reasons are put forward for suggesting this power output, although within the known properties of the muscles, is nevertheless an impressive achievement.

Effect of pre-annealing of Mo foil substrate on CZTSSe thin films and Mo(S,Se)2 interface layer

Cu2ZnSn(S,Se)4 (CZTSSe) thin film deposited on flexible Mo foil substrate has advantage of high mass specific power and good ductility. However, a thick Mo(S,Se)2 interface layer is easily to be formed between CZTSSe and Mo foil substrate. The ohmic contact property of CZTSSe/Mo is deteriorated by the formation of Mo(S,Se)2. In this work, the Mo foil substrate was pre-annealed to inhibit the growth of Mo(S,Se)2 interface layer. CZTSSe thin films were prepared on the pre-annealed Mo foil substrate by sol-gel and selenization methods. The pre-annealing treatment of Mo foil substrate leads to the oxidation of Mo. During the high temperature selenization process, the MoOx acts as a buffer layer to suppress the formation of the Mo(S,Se)2 interface layer. With the increase of the pre-annealing temperature of the Mo foil substrate, the thickness of the Mo(S,Se)2 interface layer decreases, and the resistance of CZTSSe/Mo(S,Se)2/Mo structure decreases. The ohmic contact properties of CZTSSe/Mo can be improved by the pre-annealing treatment of metal Mo foil substrates.

Thermoelectric generator based on anisotropic wood aerogel for low-grade heat energy harvesting

• A CNT/PEDOT-decorated thermoelectric network is constructed from wood-based framework. • The anisotropic structure is advantageous to convert low-grade heat energy. • Ordered porous structure and energy filtering effect enhance the TE performance. • Successful application as a device for waste heat energy harvesting and conversion. Thermoelectric generators (TEGs) have received increasing attention due to their potential to harvest low-grade heat energy (<100 °C) and provide power for the Internet of Things (IoT) and wearable electronic devices. Herein, a wood-based ordered framework is used to fabricate carbon nanotube/poly(3, 4-ethylenedioxythiophene) (CNT/PEDOT) wood aerogel for TEG. The prepared CNT/PEDOT wood aerogel with an anisotropic structure exhibits a low thermal conductivity of 0.17 W m −1 K −1 and is advantageous to develop a sufficient temperature gradient. Meanwhile, CNT/PEDOT composites effectively decouple the relationship between the Seebeck coefficient and electrical conductivity by energy filtering effect to enhance thermoelectric (TE) output properties. The vertical TEG assembled by the CNT/PEDOT wood aerogels reveals an output power of 1.5 μW and a mass-specific power of 15.48 μW g −1 at a temperature difference of 39.4 K. Moreover, the layered structure renders high compressibility and fatigue resistance. The anisotropic structure, high mechanical performance, and rapid thermoelectric response, enabling the TEG based on CNT/PEDOT wood aerogel offer opportunities for continuous power supply to low-power electronic devices.

Royal knifefish generate powerful suction feeding through large neurocranial elevation and high epaxial muscle power.

Suction feeding in ray-finned fishes involves powerful buccal cavity expansion to accelerate water and food into the mouth. Previous XROMM studies in largemouth bass (Micropterus salmoides), bluegill sunfish (Lepomis macrochirus) and channel catfish (Ictalurus punctatus) have shown that more than 90% of suction power in high performance strikes comes from the axial musculature. Thus, the shape of the axial muscles and skeleton may affect suction feeding mechanics. Royal knifefish (Chitala blanci) have an unusual postcranial morphology, with a ventrally flexed vertebral column and relatively large mass of epaxial muscle. Based on their body shape, we hypothesized that royal knifefish would generate high power strikes by utilizing large neurocranial elevation, vertebral column extension and epaxial shortening. As predicted, C. blanci generated high suction expansion power compared with the other three species studied to date (up to 160 W), which was achieved by increasing both the rate of volume change and the intraoral subambient pressure. The large epaxial muscle (25% of body mass) shortened at high velocities to produce large neurocranial elevation and vertebral extension (up to 41deg, combined), as well as high muscle mass-specific power (up to 800 W kg-1). For the highest power strikes, axial muscles generated 95% of the power, and 64% of the axial muscle mass consisted of the epaxial muscles. The epaxial-dominated suction expansion of royal knifefish supports our hypothesis that postcranial morphology may be a strong predictor of suction feeding biomechanics.

The metabolic cost of turning right side up in the Mediterranean spur-thighed tortoise (Testudo graeca)

Armoured, rigid bodied animals, such as Testudines, must self-right should they find themselves in an inverted position. The ability to self-right is an essential biomechanical and physiological process that influences survival and ultimately fitness. Traits that enhance righting ability may consequently offer an evolutionary advantage. However, the energetic requirements of self-righting are unknown. Using respirometry and kinematic video analysis, we examined the metabolic cost of self-righting in the terrestrial Mediterranean spur-thighed tortoise and compared this to the metabolic cost of locomotion at a moderate, easily sustainable speed. We found that self-righting is, relatively, metabolically expensive and costs around two times the mass-specific power required to walk. Rapid movements of the limbs and head facilitate successful righting however, combined with the constraints of breathing whilst upside down, contribute a significant metabolic cost. Consequently, in the wild, these animals should favour environments or behaviours where the risk of becoming inverted is reduced.

Performance enhancement of polymer electrolyte membrane fuel cell by PtCo3 nanoporous film as high mass-specific power density catalyst using laser deposition and processing

This study demonstrates the performance of polymer electrolyte membrane fuel cell (PEMFC) can be significantly enhanced with laser deposited and processed PtCo3 nanoporous film as the catalyst layer. The PtCo3 nanoporous film is fabricated by first depositing a thin film of stacked PtCo3 nanoparticles on gas diffusion layer using pulsed laser deposition and then subjecting the film to scanning continuous-wave laser processing. The heating by the scanning laser beam increases electrochemical surface area substantially, which could be ascribed to formation of Pt skin on each nanoparticle via Pt surface segregation. Furthermore, the durability of the catalyst under accelerated degradation test is greatly enhanced, which may be attributed to inhibition of Co leaching by the Pt skin and strengthening of the contacts between nanoparticles caused by concomitant sintering effect. Application of such catalyst to the cathode of a PEMFC exhibits a 2.4-fold increase in current density with respect to that without laser processing, raising the cathode mass-specific power density to 8.79 kW g−1 with 1 atm oxygen and 12.0 kW g−1 with 1.5 atm oxygen.

Power requirements for the hovering flight of insects with different sizes

Winged insects vary greatly in size, from tiny wasps (0.015 mg) to large moths (1.6 g). Previous studies on the power requirements of insect flight focused on relatively large insects; those of miniature insects remain relatively unknown. In this study the power requirements of a series of miniature insects were calculated, and changes with size across a range of insect sizes were investigated. Aerodynamic power was computed by numerically solving the Navier–Stokes equation, and inertial power was computed analytically. Comparison analysis was then conducted on the power requirements of miniature and large insects. Despite a 100,000-fold weight difference, the required power per unit insect mass, referred to as mass-specific power, was approximately equal for all the insects examined. This finding is explained as follows. Power is approximately proportional to the product of the wing speed and the wing drag per unit weight (i.e., “drag-to-lift ratio”). When insect size decreased, wing speed decreased (due to reduced wing-length), while wing drag increased (due to increased air-viscosity), resulting in an approximately unchanged mass-specific power. For large or small insects, flight power is derived from the same type of muscles (striated). Assuming that the mean power per unit muscle mass is the same under the same type of muscle, the above size/specific-power relation indicates that the ratio of flight-muscle mass to insect mass is the same for different sized insects.

The relationship between body size and flight power output in the mango stem borer (Batocera rufomaculata)

Adult body size in insects can be influenced by environmental conditions during larval growth. The effect of such intraspecific variation in body mass on flight performance is poorly understood. In Batocera rufomaculata, a large tree boring beetle, adults emerging from larvae that developed in a dying host tree, and therefore, under nutrient-deprived diet conditions, are smaller but have an elevated long-distance flight capability compared to larger conspecifics that developed in viable host trees. The improved endurance for long-distance flight in the smaller individuals appears to contradict the interspecific trend in flying animals of a decrease in Cost of Transport (CoT) with increased body mass. To explore the relationship between intraspecific variation in body size and power expended during steady forward flight, we flew these beetles tethered in a wind tunnel and compared the flapping kinematics and power output of individuals varying in body mass (1–7 gr). Concurrently, we measured the forces the insects applied on the tether allowing us to evaluate the tethering effects and correct for them. From the flapping kinematics we estimated the mechanical power expended using a quasi-steady blade-element model. We found that muscle mass-specific power did not differ between small and large individuals flying at the same wind (flight) speed in the tunnel. Consequently, the CoT of B. rufomaculata does not vary with body mass. Such invariance of mass-specific power with body mass may aid the dispersal of smaller individuals from deteriorating host trees to new ones.

Temperature effects on the contractile performance and efficiency of oxidative muscle from a eurythermal versus a stenothermal salmonid.

ABSTRACTWe compared the thermal sensitivity of oxidative muscle function between the eurythermal Atlantic salmon (Salmo salar) and the more stenothermal Arctic char (Salvelinus alpinus; which prefers cooler waters). Power output was measured in red skeletal muscle strips and myocardial trabeculae, and efficiency (net work/energy consumed) was measured for trabeculae, from cold (6°C) and warm (15°C) acclimated fish at temperatures from 2 to 26°C. The mass-specific net power produced by char red muscle was greater than in salmon, by 2-to 5-fold depending on test temperature. Net power first increased, then decreased, when the red muscle of 6°C-acclimated char was exposed to increasing temperature. Acclimation to 15°C significantly impaired mass-specific power in char (by ∼40–50%) from 2 to 15°C, but lessened its relative decrease between 15 and 26°C. In contrast, maximal net power increased, and then plateaued, with increasing temperature in salmon from both acclimation groups. Increasing test temperature resulted in a ∼3- to 5-fold increase in maximal net power produced by ventricular trabeculae in all groups, and this effect was not influenced by acclimation temperature. Nonetheless, lengthening power was higher in trabeculae from warm-acclimated char, and char trabeculae could not contract as fast as those from salmon. Finally, the efficiency of myocardial net work was approximately 2-fold greater in 15°C-acclimated salmon than char (∼15 versus 7%), and highest at 20°C in salmon. This study provides several mechanistic explanations as to their inter-specific difference in upper thermal tolerance, and potentially why southern char populations are being negatively impacted by climate change.

Heat exchanger design based on earthen materials

We propose herein the design of a heat exchanger based on clay materials in order to reduce the energy consumed due to data center cooling. Our Thermal Energy Storage (TES) system is to be placed upstream of the CRAC (Computer Room Air Conditioner) unit. A direct contact heat exchanger is thereby built as a vertical packed bed, composed of earthen spheres whose imposed heating/cooling cycles comply with ASHRAE (American Society of Heating, Refrigerating and Air-Conditioning Engineers) standards. A raw earthen material has been chosen owing to its hygrothermal characteristics, which are recognized as relevant for indoor thermal regulation, in addition to a low embodied energy required for manufacturing. Results show that the pore Reynolds number and sphere diameter exert significant effects on the energy buffering capacity. A simple relationship is thus proposed to link the mass-specific power of the energy storage system, the internal heat exchanger architecture and the pore Reynolds number for purposes of designing raw earth bricks at an elevated scale.