Nelu-Cristian Cherecheş

Gheorghe Asachi Technical University of Iași

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Sebastian Valeriu Hudişteanu

Gheorghe Asachi Technical University of Iași

FȚ

Florin-Emilian Țurcanu

Gheorghe Asachi Technical University of Iași

Marina Verdeş

Gheorghe Asachi Technical University of Iași

Cătălin George Popovici

Gheorghe Asachi Technical University of Iași

Cătălin-George Popovici

Gheorghe Asachi Technical University of Iași

Vasilică Ciocan

Gheorghe Asachi Technical University of Iași

Ana Diana Ancaş

Gheorghe Asachi Technical University of Iași

Monica Cherecheş

Institutul Naţional de Cercetare-Dezvoltare in Construcţii Urbanism şi Dezvoltare Teritorială Durabilă

Theodor Mateescu

Gheorghe Asachi Technical University of Iași

Cătălin Popa

University of Craiova

Cooperative Institutions

Gheorghe Asachi Technical University of Iași

Université de Reims Champagne-Ardenne

Institutul Naţional de Cercetare-Dezvoltare in Construcţii Urbanism şi Dezvoltare Teritorială Durabilă

Institut de Thermique, Mécanique, Matériaux

Alexandru Ioan Cuza University

Centre National de la Recherche Scientifique

Grigore T. Popa University of Medicine and Pharmacy

"Dunarea de Jos" University of Galati

Technical University of Cluj-Napoca

Transylvania University of Brașov

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Numerical Study of Cooling Solutions Inside a Power Transformer

Energy Procedia (2017)

Nelu-Cristian Cherecheș Monica Cherecheş Livia Miron Sebastian Valeriu Hudişteanu

In this paper we study the fluid flow and heat transfer by convection in a thermo-convective circuit with several cooling channels and different inlet fluid velocities. A numerical study has been conducted in steady state for a step-down 3-phase power transformer in columns immersed in a mineral oil bath inside of a tank. Our main objective is the cooling optimization of the power transformer. An obstacle is used at the inferior part of the transformer in order to conduct the oil to the hottest surface. In order to study the influence of the different parameters on both the heat transfer and the fluid flow we have made use of the highest and the bulk temperature as well as the volume flow rate and dimensionless numbers Re and RiRe in every channel. The obtained results show an optimal velocity where the temperatures are kept below the limits.

10.1016/j.egypro.2017.03.1103

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Citations (26)

Effect of cooling on power generated by photovoltaic panels

IOP Conference Series Materials Science and Engineering (2021)

Sebastian Valeriu Hudişteanu Nelu-Cristian Cherecheș Cătălin George Popovici Marina Verdeş Vasilică Ciocan

Abstract The paper presents a numerical analysis of the operation of photovoltaic (PV) panels integrated in fixed position on the roofs or facades of the buildings. Knowing that the efficiency of photovoltaic panels is temperature-dependent, and due to fixed PV panel position, the possibility of the improving the conversion is analysed from the point of view of the temperature of the PV cells. The model is simulated using TRNSYS software and the main functioning parameters assessed are the operating temperature of the cells, open circuit voltage, maximum power generated and conversion efficiency. The solution proposed for cooling consists in using water heat exchangers attached to the backside of the photovoltaic panel. The results highlight the direct dependence of the photovoltaic efficiency with the temperature of the panel for different positions in the same geographical location. The energy gain during the cooling interval is about 26.9 Wh/m2 (vertical), 81.9 Wh/m2 (inclined) and 81.7 Wh/m2 (horizontal), which represents an increase of 5.8%, 9.3% and 9.2% respectively, compared to the normal operating conditions.

TRNSYS

Maximum power principle

10.1088/1757-899x/1141/1/012008

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Reliability and Sustainability of Water Transport Systems

Advances in civil and industrial engineering book series (2022)

Ana Diana Ancaş Florin-Emilian Țurcanu Marina Verdeş Valeriu Sebastian Hudişteanu Nelu-Cristian Cherecheș

The development of populated centers has as a consequence the corresponding increase of the consumption of resources, first of all of the consumption of energy necessary for the transport of the additional flows of water. Their often-limited character materializes the desire to redistribute existing resources in time and space, in accordance with the requirements of the uses served. The widespread introduction, due to competitive prices, of composite pipes, but for which there is insufficient information on their behavior over time, has led to the need to research the sustainability and reliability of new systems in development for water transport. This chapter aims to provide an efficient tool for those interested in managing water supply systems with direct reference to the reliability and sustainability of water transport systems: supply and distribution networks.

Water Transport

Water consumption

Consumption

10.4018/978-1-7998-9810-8.ch005

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Analysis of an innovative water-cooling solution for photovoltaic-thermal systems

IOP Conference Series Earth and Environmental Science (2021)

Valeriu Sebastian Hudişteanu Nelu-Cristian Cherecheș Marina Verdeş Vasilică Ciocan Cătălin George Popovici

Abstract The research is focused on realizing a comparative analysis regarding the parameters of an active water-cooling solution for improving the efficiency of monocrystalline silicon photovoltaic (PV) panels. The efficiency of the photovoltaic panels is dependent on the climatic conditions, varying especially with the change of the intensity of the solar radiation and of the operating temperature. The cooling of the photovoltaic panels is a viable solution for both fixed and variable positions of the system. Numerical modelling was carried out on a photovoltaic panel integrated into the façade of a buildings. The water-cooling solution consist in using a water film heat exchanger attached on the backside of the PV panel. The parameters of the heat agent analysed were the temperature, velocity and width of the water film. The optimal water film heat exchanger solution was obtained for a thickness of 3 mm of water film, a velocity of 0.01 m/s and an operating temperature of 20 °C. In this case, the thermal power extracted by the film exchanger reaches values of 140.8 W, with an overall heat exchange coefficient of 48.6 W/m 2. K. During the study, the global heat transfer coefficient and the raise off efficiency is determined for each case.

Coefficient of performance

10.1088/1755-1315/664/1/012025

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Citations (4)

System for Monitoring Electrical Cables Condition in Building Installation

2021 International Conference on Electromechanical and Energy Systems (SIELMEN) (2023)

George Bălan Nelu-Cristian Cherecheș Dorin Dumitru Lucache

The monitoring and diagnosis of electric cables it was a constant concern in installations of medium and high voltage networks, but nowadays it becomes important also for buildings. Electrical installations in an office building, hospitals or commercial enterprises must operate without technical deviations on a normal operating day. Different techniques can be used for monitoring and diagnosis, but the chosen solution must comply with the specificity of building and cables in use, and also with the budget available for monitoring and maintenance. The paper presents a system conceived for monitoring the operational and environmental factors that could lead to cables aging and for providing real-time alerts when a possible fault can occur. The results of testing the system on a simulated cable installation are presented.

Condition Monitoring

Electrical equipment

Electrical wiring

10.1109/sielmen59038.2023.10290783

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Contribution à l'optimisation de circuits thermoconvectifs

Nelu-Cristian Cherecheş

L'ecoulement du fluide ainsi que le transfert de chaleur par convection mixte sont analyses dans le circuit thermoconvectif a plusieurs canaux de refroidissement d'un transformateur electrique de puissance triphase en colonnes immerge dans un bain d'huile minerale a l'interieur d'une cuve. Les objectifs de ce travail sont l'optimisation du transfert de chaleur et la limitation de la temperature du point chaud tout en assurant une bonne comprehension des phenomenes thermiques et dynamiques mis en jeu a l'interieur du transformateur electrique. Dans un premier temps, differentes configurations geometriques ont ete concues et etudiees afin de choisir la meilleure solution pour le refroidissement du transformateur lorsque celui-ci est soumis a un regime permanent de fonctionnement. L'etude comparative des resultats a montre qu'un ecoulement dirige de l'huile par un obstacle place a l'entree du fluide est une bonne solution dans un systeme multicanaux. Ensuite, les approximations faites dans la modelisation ont ete validees par des mesures effectuees sur un transformateur reel fonctionnant en regime permanent. L'etude realisee en regime transitoire a mis en evidence que l'hypothese d'une densite de flux imposee sur les parois du noyau et des enroulements n'est plus valable et que l'utilisation d'une source interne de chaleur est necessaire. Dans un deuxieme temps, afin d'approfondir l'analyse, en se basant sur un calcul semi-analytique une etude a ete faite sur un seul canal entre deux plaques planes verticales afin de determiner l'espacement optimal et de trouver des criteres pour distinguer les differents regimes convectifs.

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Analyse du comportement thermodynamique pour deux systèmes de chauffage solaire – murs échangeurs de chaleur

Deleted Journal (2011)

Cătălin Grigoraş Theodor Mateescu Nelu-Cristian Cherecheș

Le but de ce travail est d’effectuer une nouvelle recherche dans le domaine du chauffage solaire passif et actif an etudiant le comportement thermodynamique de deux types de murs capteurs solaires et en meme temps d’essayer d’encourager l’etude et la construction de maisons qui utilisent l’energie solaire.

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Energy Improvement Study of a Double-Skin Façade in Winter Conditions

Advanced engineering forum (2017)

Theodor Bratosin Eugen Iavorschi Nelu-Cristian Cherecheș Cătălin Popa

A numerical study of a natural convection flow coupled with radiation was carried out in a double-skin façade. The solar radiation flux to which the double-skin façade is subjected has been chosen for a cold season month (φ = 66.9 W/m 2 ). The double-skin façade is installed on a building whose interior temperature is 293 K given that the temperature at the inlet in winter conditions is 255 K. This study focuses on 5 different widths of the double-skin façade (4, 6, 8, 10 and 12 cm). Three-dimensional numerical simulations have been carried out for a steady and turbulent flow. Transport equations of mass, momentum and energy are solved numerically using finite volume method. Velocity and temperature profiles show the differences between all the above mentioned 5 cases in order to highlight the optimal width of the double-skin façade.

Momentum (technical analysis)

10.4028/www.scientific.net/aef.21.453

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Flow visualization of natural convection in a vertical channel with asymmetric heating

International Communications in Heat and Mass Transfer (2012)

Dan Ospir Cătălin Popa Nelu-Cristian Cherecheș Guillaume Polidori S. Fohanno

Aspect ratio (aeronautics)

Secondary flow

10.1016/j.icheatmasstransfer.2012.02.005

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Citations (45)

NUMERICAL STUDY OF HEAT TRANSFER INSIDE A COOLING FLUID IN A POWER TRANSFORMER

Nelu-Cristian Cherecheş Alina Marinescu Jacques Padet Nadim El Wakil

In this paper we study the heat transfer and fluid flow in a step-down 3-phase power transformer. In order to simplify the study we choose an element composed of two windings wound around a core. The Joule effect and the Foucault currents produce an undesirable heat in the different components of the transformer. From an economical and security point of view, there is a need to cool the transformer to preserve it from destruction. Our main objective is the cooling optimization of the power transformer. A numerical study has been conducted for six different geometric configurations with six different flow rates of the cooling oil at the entrance. The physical properties of the fluid are supposed to be function of the temperature. The control volume method has been used to resolve the continuity, the momentum and the energy equations in the steady state. The obtained results show that the structure of the flow is somehow complex and according to the case some rolls appear at the top and the bottom of the windings; these rolls contribute to a good mixing of the fluid leading to a nearly homogenous temperature. The hot temperature is located inside the cooling channels crossing the primary and the secondary windings. These channels are very narrow ones, and the fluid has a difficulty to flow through them, so its preference goes to those separating the different elements. To reduce these high temperatures, there is a need to force the fluid to go in these narrow channels by using a directed flow.

Quadrature booster

10.1615/ichmt.2004.cht-04.200

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