•A three-dimensional non-isothermal model of HT-PEMFC was developed.•Thickness and porosity of gas diffusion layer were studied.•Flow uniformity, diffusion flux and ohmic resistance were ...examined.•Optimal values of thickness and porosity were proposed.•A performance increment of 7.7% was achieved.
Wide ranges of thickness (e.g. 100–400 μm) and porosity (e.g. 30–70%) of gas diffusion layer (GDL) in a high temperature proton exchange membrane fuel cell (HT-PEMFC) are available in the literature. However, the effects of GDL porosity and thickness on electron conduction and gas distribution uniformity (under the rib and under the channel) are unclear. In this study, a numerical non-isothermal 3D model was developed. After model validation, parametric analyses were performed to investigate the effects of thickness and porosity on flow uniformity (under the rib and under the channel), diffusion flux and ohmic resistance. It is found that both the flow uniformity and ohmic resistance increase with increasing thickness and porosity. However, the thickness and porosity have opposite influence on diffusion flux, which decreases with increasing GDL thickness but increases with increasing porosity. Unlike the previous research suggesting thin GDL with high porosity, optimal GDL thickness and porosity are found in the present study. The appropriate GDL thicknesses for anode and cathode are 80–120 μm and 140–170 μm respectively while the optimal value for GDL porosity is 35–45%. This study clearly demonstrates that we can further achieve a performance increment of 7.7% by carefully controlling the thickness and porosity of GDL.
•20-kHz sonicator systems were investigated under various geometric conditions.•Sonochemical oxidation activities and SCL images were compared in large-scale vessels.•The change in the probe position ...could change sonochemical activity significantly.•The enhancement of activity could be attributed to strong reflections at the bottom and side wall.
The 20-kHz probe-type sonicator systems were investigated for the enhancement of the cavitational oxidation activity under various geometric conditions including vertical and horizontal probe positions and vessel sizes/volumes as a following study to our previous study. The sonochemical oxidation activity (mass-based I3- ion generation rate) increased significantly for all vessel size conditions as the probe was placed close to the vessel bottom, owing to the expansion of the sonochemical active zone induced by the reflections of ultrasound at the bottom and the reactor wall. A concentric circular active zone is observed at positions close to the bottom. The highest sonochemical activity was obtained at 1 cm (vertical position) in the 20 cm vessels (input power: 50 %). At the vertical positions of 11 cm to 7 cm, no significant difference in the sonochemical activity was observed for all input power conditions (25, 50, and 75 %) because no meaningful reflections occurred. Higher sonochemical activities were obtained at an input power of 75 % owing to the increased power and strong reflection. The highest cavitational yield considering the energy efficiency was obtained at 6 cm (vertical position) for 75 % of all power and geometric conditions. Horizontal probe position tests showed that the asymmetric formation of the sonochemical active zone could significantly enhance the sonochemical activity. The highest activity was obtained at 1 cm (vertical position) and 2.5 cm (horizontal position) in the 20 cm vessel.
•Improved thermal models for Floating Photovoltaic systems is proposed.•The performances of used software tools have been verified experimentally.•The optimal geometrical configurations of floating ...photovoltaics are investigated.•A comparison of monofacial or bifacial Photovoltaic modules in floating systems is considered.
The aim of this study is to create usable commercial simulation software tools for photovoltaic (PV) systems even in the case of floating applications. Using the experimental data of a plant installed at the “Enel Innovation Lab” in Catania (IT), adequate heat exchange coefficients of the software's thermal models were found, which allowed us to take into account the thermal effects for these types of installations. An optimization of the sizes for mono- and bifacial floating systems was carried out. The simulated data for a ground system were compared with the floating data through performance indices. In addition, monofacial models were compared with bifacial. The optimized variables are the tilt angle and the pitch, whereas for the bifacial systems, the module elevation is also considered. The albedo is a sensitive factor mainly for the bifacial modules, so it was considered a parameter in the different design solutions. The simulations were performed by two specialized commercial software programs, where different PV system models are implemented. The normalized annual energy yield was chosen as a meaningful parameter with which to compare the different solutions. As the analysis of PV systems is highly site dependent, the study was developed for two locations, characterized by different diffuse and albedo solar irradiance components, specifically at high latitudes (Frankfurt, DE) and at intermediate latitudes (Catania, IT).
Micro pin-fin heat sink, characterized by low thermal resistance, compact structure and uniform temperature distribution along the flow direction, is effective and valuable for thermal management of ...electronic devices. To enhance the cooling performance of the micro square pin-fin heat sink, a geometry optimizing method changing pin-fin porosity and pin-fin located angle is proposed in this paper. The flow and heat transfer characteristics were studied numerically and the geometry of the micro square pin-fin heat sink was optimized. To reveal the characteristics and advantages of the micro square pin-fin heat sink, the comparison between the square pin-fin and the column pin-fin was made. Numerical results indicate that both the pin-fin porosity and located angle are important for the cooling capacity and thermal performance of the micro square pin-fin heat sink; the optimal porosity and located angle for thermal performance are 0.75 and 30° respectively. Furthermore, micro heat sinks with the optimized square pin-fin present better thermal performance than micro column pin-fin heat sinks, which implies that there is great potential to employ micro square pin-fin heat sinks for thermal management on electronic devices with high energy density.
•An optimization method on geometry is proposed for micro square pin-fin heat sink.•Pin-fin porosity and pin-fin located angle are important on thermal performance.•Heat sinks with optimized square pin-fin hold higher cooling capacity than column pin-fin.
We present a canonical way to turn any smooth parametric family of probability distributions on an arbitrary search space X into a continuous-time black-box optimization method on X, the ...information-geometric optimization (IGO) method. Invariance as a major design principle keeps the number of arbitrary choices to a minimum. The resulting IGO flow is the flow of an ordinary differential equation conducting the natural gradient ascent of an adaptive, time-dependent transformation of the objective function. It makes no particular assumptions on the objective function to be optimized. The IGO method produces explicit IGO algorithms through time discretization. It naturally recovers versions of known algorithms and offers a systematic way to derive new ones. In continuous search spaces, IGO algorithms take a form related to natural evolution strategies (NES). The cross-entropy method is recovered in a particular case with a large time step, and can be extended into a smoothed, parametrization-independent maximum likelihood update (IGO-ML). When applied to the family of Gaussian distributions on R^d, the IGO framework recovers a version of the well-known CMA-ES algorithm and of xNES. For the family of Bernoulli distributions on {0, 1}^d, we recover the seminal PBIL algorithm and cGA. For the distributions of restricted Boltzmann machines, we naturally obtain a novel algorithm for discrete optimization on {0, 1}^d. All these algorithms are natural instances of, and unified under, the single information-geometric optimization framework. The IGO method achieves, thanks to its intrinsic formulation, maximal invariance properties: invariance under reparametrization of the search space X, under a change of parameters of the probability distribution, and under increasing transformation of the function to be optimized. The latter is achieved through an adaptive, quantile-based formulation of the objective. Theoretical considerations strongly suggest that IGO algorithms are essentially characterized by a minimal change of the distribution over time. Therefore they have minimal loss in diversity through the course of optimization, provided the initial diversity is high. First experiments using restricted Boltzmann machines confirm this insight. As a simple consequence, IGO seems to provide, from information theory, an elegant way to simultaneously explore several valleys of a fitness landscape in a single run.
•Effects of geometric and operational factors were investigated in a 20-kHz sonicator system.•Optimal conditions for the highest sonochemical activity were suggested.•Formation of circular-shaped ...active zone is required for the highest sonochemical activity.
The use of a 20-kHz probe-type sonicator irradiating downward in a 500 mL vessel was optimized for the enhancement of the sonochemical activity in terms of the geometric and operational factors. These factors included the probe immersion depth (the vertical position of the probe), input power, height of the liquid from the bottom, horizontal position of the probe, and thickness of bottom plate The sonochemical oxidation reactions were investigated both quantitatively and qualitatively using calorimetry, KI dosimetry, and luminol (Sonochemiluminescence, SCL) techniques. The sonochemical activity was very positively affected by the vertical boundaries. The highest sonochemical activity was obtained when the probe was placed close to the bottom of the vessel (immersion depth of 60 mm), with a high input power (input power of 75%), and optimal liquid height condition (liquid height of 70 mm). The SCL image analysis showed that the cavitational activity zone gradually expanded around the probe body and changed into a circular shape as the experimental conditions were optimized, and consequently the sonochemical activity increased. The formation of a large bright circular-shaped activity zone could be attributed to the strong reflections of the ultrasound firstly, at the vessel bottom and secondly, at the liquid surface. On the other hand, the cavitational activity zone and the sonochemical activity were negatively affected by the horizontal boundaries when the probe was placed close to the side wall of the vessel. In addition, it was found that the sonochemical activity was also significantly affected by the thickness of the support plate owing to the reflection and transmission of the ultrasound at the boundary between the liquid and the solid media.
•LegUp robot enables the motion of the lower limb in the sagittal and coronal planes.•The mathematical models for legup are representative for the rehabilitation task.•Numerical optimizations lead to ...a singularity-free operational workspace.
The paper presents the mathematical modeling and analysis of LegUp, a novel parallel robotic system for lower limb rehabilitation of bedridden patients. The operational workspace of the robotic system is defined based on a set of parameters that describe the motion of the lower limb joints, which is natural in the rehabilitation task. To comply with this representation of the operational workspace, the parallel robot kinematic models describe the dependency between the robotic system actuators and the lower limb joints. Furthermore, the singularity analysis is achieved in the joint space, which shows whether the operational workspace is singularity-free. To achieve a feasible mechanical design for the prescribed operational workspace and to ensure safe operation, the design parameters of the parallel robotic system are determined based on a multi-objective optimization problem. Numerical simulations show that the operational workspace is singularity-free for the selected design parameters, which are then used to construct the experimental model of LegUp.
Recently, several kinds of variable cross-section legs have been reported to improve the performance of thermoelectric generators (TEGs). This work further proposes an optimization study to maximize ...the output power of variable cross-section TEGs for solar energy utilization by coupling finite element method (FEM) and optimization algorithm. Six geometric variables along with the external load resistance are optimized by genetic algorithm (GA) and particle swarm optimization (PSO). Besides, Joule heating, Peltier effect, and Thomson effect are considered in the numerical model to improve the simulation accuracy. Optimization results show that distributions of the thermal resistance and the electrical resistance are significantly changed when the volumes of thermoelectric material remain constant. The optimized leg shape increases the temperature gradient in the high figure of merit (ZT) region by reducing the cross-section area. Although internal resistances of optimal TEGs are greater than those of rectangular TEGs, the improvement in electromotive force results in the enhancement of electrical performance. At heat flux of 35000 W m−2, 40000 W m−2, 45000 W m−2, and 50000 W m−2, temperature differences of optimal TEGs are increased by 12.77%, 18.36%, 41.93%, and 73.14%, while output powers are improved by 1.45%, 2.13%, 9.33%, and 20.13%, respectively.
Flow field designs for the bipolar plates of the proton exchange membrane fuel cell are reviewed; including the serpentine, parallel, interdigitated, mesh type or their mixtures, furthermore 2D ...circular and 3D tubular geometries, porous, fractal, and biomimetic flow fields. The advantages/disadvantages and tendencies from field optimizations are discussed. The performance of each flow field design is compared to the conventional serpentine flow field. Good flow field plates give uniform gas distributions, low pressure drop for transport, and sufficient rib area to provide high electronic conductivity. A good field should also prevent water condensation, remove water efficiently, and provide sufficiently high moisture content in the membrane. The demands on design are sometimes contradictory. Future work should aim for a flow field geometry and topology that produces uniform gas delivery at a low pressure-drop, and at the same time has an optimal channel shape for better water removal. It is concluded that for an area-filling gas distributor, the developments should aim to find a flow field in accordance with minimum entropy production, making an emphasis on multi-criteria optimization methods.
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