Experimental Air Impingement Crossflow Comparison and Theoretical Application to Photovoltaic Efficiency Improvement

The photovoltaic cell temperature is a key factor in solar energy harvesting. Solar radiation raises temperature on the cell, lowering its peak efficiency. Air jet impingement is a high heat transfer rate system and has been previously used to cool the back surface of photovoltaic modules and cells. In this work, an experimental comparison of the cooling performance of two different air jet impingement crossflow schemes was performed. Crossflow is defined as the air mass interacting with a certain jet modifying its movement. This leads to a change in its heat exchange capabilities and is related with the inlet-outlet arrangement of the fluid. In this work, zero and minimum crossflow schemes were compared. The main contribution of this work considered the consumption of the flow supplying devices to determine the most suitable system. The best configuration increased the net power output of the cell by 6.60%. These results show that air impingement cooling can play a role in increasing photovoltaic profitability. In terms of uniformity, on small impingement plates with a low number of nozzles, the advantages expected from the zero crossflow configuration did not stand out.This work was funded by the Regional Development Agency of the Basque Country (SPRI) [grant number KK-2018/00109]

jBAY Modeling of Vane-Type Vortex Generators and Study on Airfoil Aerodynamic Performance

The increased demand for wind power is related to changes in the sizes of wind turbines and the development of flow control devices, such as vortex generators (VGs). In the present study, an analysis of the vortices generated by a vane-type VG is performed. To that end, the aerodynamic performance of a DU97W300 airfoil with and without VG is evaluated. The jBAY source term model was implemented for simulation of a triangular-shaped VG and the resolution of the fully meshed computational fluid dynamics (CFD) model. Reynolds-averaged Navier–Stokes (RANS) based simulations were used to calculate the effect of VGs in steady state, and the detached eddy simulation (DES) method was used for angles of attack (AoAs) around the stall situation. All jBAY based numerical simulations were carried out with a Reynolds number of Re = 2 × 106 to analyze the influence of VGs with AoAs between 0 and 20° and were validated versus experimental wind tunnel results. The results show that setting up a VG device on an airfoil benefits its aerodynamic performance and that the use of the jBAY model for simulation is accurate and efficient.The authors are grateful to the government of the Basque Country and the University of the Basque Country UPV/EHU through the SAIOTEK (S-PE11UN112) and EHU12/26 research programs, respectively

2D PIV/PTV–3D uRANS RSM Investigation on the Combined Effect of Iron Filings Filtering Techniques in a Backward Facing Step Flow

The presence of suspended particles in liquid fluids is one of the main reasons for hydraulic system failure. Metallic impurities in particular increase the presence of toxic substances in wastewater; therefore, it is vital to study and address the behaviour of such particles in water flows. The current literature lacks studiees approaching the combined effect of different filtering techniques in backward-facing step (BFS) flows. This work aims to analyse the behaviour of iron filings within a BFS system, making use of a combined experimental 2D PIV/PTV–3D uRANS computational approach. Experiments and computations are performed at a Reynolds number ReH=3684.63. Computational measurements are performed in several planes whereas the experimental campaign is focused on the dynamics of the particles through the streamwise middle plane. A half plane reattachment length of Xr=11.73h is measured for an inlet flow turbulence intensity of about 1%. The trajectories of the iron filings under the influence of an external magnetic field are examined. A comparison with their paths under the influence of no attractive forces elucidates that the presence of an external magnetic field alters their elliptical trajectories. Moreover, a more forward magnet placement reveals greater trajectory disruptions.Open Access funding provided thanks to the CRUE-CSIC agreement with Springer Nature. The authors are thankful to the government of the Basque Country for the ELKARTEK21/10 KK-2021/00014 and ITSAS-REM IT1514-22 research programs, respectively

Refrigeración mediante impacto de chorro de aire de dispositivos de alto flujo térmico

xxv, 143 p.El impacto de chorro es una tecnología de gran potencial para tareas de gestión térmica. Sin embargo, el análisis del estado actual de la técnica ha confirmado la existencia de una serie de condicionantes que dificultan su implementación en ciertas aplicaciones. Por un lado, faltan metodologías completas de diseño y optimización que faciliten la implantación de esta tecnología como pueden existir para otros sistemas de refrigeración, como intercambiadores de calor o disipadores. En segundo lugar, pese a presentar las tasas de transferencia de calor más elevadas para sistemas de convección forzada, requiere elevados caudales para su funcionamiento, lo cual compromete su uso en configuraciones donde la eficiencia energética sea un factor diferencial. La focalización de anteriores investigaciones en la mejora del coeficiente de transferencia de calor deja de lado el coste energético asociado a este beneficio. Por último, la experimentación y simulación de placas de chorros requiere de conocimientos e instrumentación avanzada. El compromiso entre eficiencia de recursos y precisión en los resultados es fundamental al analizar aplicaciones prácticas con geometrías complejas y otros retos técnicos. En estetrabajo se pretende dar respuesta a estos problemas con una clara orientación hacia el ámbito de la ingeniería. Cada una de estas cuestiones ha sido abordada individualmente en cada capítulo. Como resultado final del trabajo de investigación, se obtiene: una metodología completa de cálculo y optimización; la determinación de una geometría y condiciones que permiten el incremento de la eficiencia neta de un sistema aplicando esta técnica de refrigeración y, en último lugar, una técnica experimental que aporta suficiente información para la optimización de detalle

Source Term Modelling of Vane-Type Vortex Generators under Adverse Pressure Gradient in OpenFOAM

An analysis of the generation of vortices and their effects by vane-type vortex generators (VGs) positioned on a three-dimensional flat plate with a backward-facing ramp and adverse gradient pressure is carried out. The effects of a conventional vortex generator and a sub-boundary layer vortex generator are implemented by using a source term in the corresponding Navier-Stokes equations of momentum and energy according to the so-called jBAY Source Term Model. The influence of the vortex generator onto the computational domain flow is modelled through this source term in the Computational Fluid Dynamics (CFD) simulations using the open-source code OpenFOAM. The Source Term Model seems to simulate relatively well the streamwise pressure coefficient distributions all along the flat plate floor as well as certain parameters studied for vortex characterization such as vortex path, decay and size for the two vane-type vortex generators of different heights studied. Consequently, the implementation of the Source Term Model represents an advantage over a fully Mesh-Resolved Vortex Generator Model for certain applications as a result of a meaningful decrease in the cell number of the computational domain which implies saving computational time and resources

Multi-Objective Particle Swarm Based Optimization of an Air Jet Impingement System

Air jet impingement systems have proven to be a very efficient way of heat transfer in single phase flows, which has allowed them to be applied in several industries. However, the complexity of the physical phenomena that take place in the cooling or heating processes makes the task of designing and sizing a system of this type very difficult. The objective of this work is to develop a methodology for the optimization of the impingement plate for electronic components cooling systems. The component chosen to exemplify this work is an insulated gate bipolar transistor (IGBT) such as those employed in photovoltaic inverters. The proposed methodology is divided into the thermo-hydraulic calculation process and the optimization of the system. This optimization is carried out using a multi-objective particle swarm optimization (PSO) algorithm that seeks the best compromise between two variables: Component temperature and manufacturing time of the impingement plate. The result is a calculation tool that can quickly find the solution that meets the requirements of the designer without the need to evaluate all possible solutions

High power factor in isovalently substituted Ca3Co4O9 ceramic through a rapid preparation method

Resumen del trabajo presentado a la XVII Conference Ceramics in Europe, celebrada en Krakow (Poland), del 10 al 14 de julio de 2022.N

ANN-Based Stop Criteria for a Genetic Algorithm Applied to Air Impingement Design

Artificial Neural Networks (ANNs) have proven to be a powerful tool in many fields of knowledge. At the same time, evolutionary algorithms show a very efficient technique in optimization tasks. Historically, ANNs are used in the training process of supervising networks by decreasing the error between the output and the target. However, we propose another approach in order to improve these two techniques together. The ANN is trained with the points obtained during an optimization process by a genetic algorithm and a flower pollination algorithm. The performance of this ANN is used as a stop criterion for the optimization process. This new configuration aims to reduce the number of iterations executed by the genetic optimizer when learning the cost function by an ANN. As a first step, this approach is tested with eight benchmark functions. As a second step, the authors apply it to an air jet impingement design process, optimizing the surface temperature and the fan efficiency. Finally, a comparison between the results of a regular optimization and the results obtained in the present study is presented

Efecto de las condiciones de procesado en la microestructura y propiedades del Ca3Co4O9

Resumen del trabajo presentado al XVI Congreso Nacional de Materiales, celebrado en Ciudad Real del 28 de junio al 1 de julio de 2022.N