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  Numarul 4/2019

Volumul 10 (2019), Nr. 4

Mărirea eficienței energetice la sistemele electroenergetice eoliene funcționând la viteze ale vântului variabile în timp Partea a II-a
Increasing energy efficiency in wind power systems operating at variable wind speeds over time. Part II
Lucian CRIȘAN, Simona POPA-ALBU, Meda Alexandra LAZĂR, Daniel BREBENARIU, Cristian MURĂRESCU, Marius DUDU, Ioan BORZA, Marius BABESCU

În prezenta lucrare, se propune o metodă de mărire a eficienței energetice la un sistem electroenergetic eolian, SEE, format dintr-o turbină de vânt, TV și un generator sincron cu magneți permanenți, GSMP, la viteze ale vântului variabile semnificativ în timp. Valoarea maximă a puterii TV, PTV(ω), se obține la funcționarea la viteza unghiulară mecanică, VUM, optimă, ωOPTIM, a cărei valoare depinde direct proporțional de viteza vântului. Energie electrică obținută, în intervalul de timp t, de la un SEE depinde de cele 2 mărimi funcționale de bază: 1) valorile vitezei vântului, V, în intervalul de timp t și 2) valorile VUM, ω, respectiv variația sa în timp. Problema fundamentală în realizarea unei eficiențe energetice maxime, la momentul de timp t, este corelarea valorii VUM curente, ω, cu valoarea vitezei vântului de la momentul de timp respectiv. Prin măsurarea a două mărimi de bază: viteza vântului V și VUM curentă, ω, se analizează posibilitatea captării unei energii eoliene maxime la SEE din locația MinAna-zona Dobrogea. Pentru a realiza o funcționare în punctul de putere maximă, MPP, trebuie ca VUM curentă să fie ωOPTIM.

This paper proposes a method of increasing the energy efficiency of a wind power system, SEE, consisting of a wind turbine, TV and a synchronous synchronous generator with permanent magnets, GSMP, at variable wind speeds over time. The maximum power of TV, PTV (ω), is obtained when operating at the mechanical angular velocity, VUM, optimum, ωOPTIM, the value of which depends directly on the wind speed. Electricity obtained over time t from an EEA depends on the two basic functional sizes: 1) Wind velocity values, V, in the time interval Δt, and 2) VUM, ω, respectively its variation over time. The fundamental problem in achieving the maximum energy efficiency at time t is to correlate the current VUM value ω with the value of the wind speed at that time. By measuring two basic sizes: wind speed V and current VUM, ω, the possibility of capturing a maximum wind energy in the EEA from the MinAna-Dobrogea area is analyzed. To perform at the MPP maximum power point, the current VUM must be OPTIM.

Comportamentul termic dinamic al unei pompe de caldura functionand intre 2 rezervoare de acumulare
The dynamic thermal behavior of a heat pump operating between 2 storage tanks
Florin IORDACHE, Alexandru DRAGHICI, Mugurel TALPIGA

In lucrare se propune o metoda aproximativa de evaluare a performantelor energetice pe care le ofera un sistem de utilizare a surselor regenerabile folosind pompa de caldura cu comprimare mecanica (de vapori). Alaturi de bilantul energetic aferent pompei de caldura se prezinta si bilanturile termice in regim nestationar ale mediilor sursa si consumator reprezentate in lucrarea de fata de cate un rezervor de acumulare a apei, din care pompa de caldura extrage flux termic si respectiv livreaza flux termic. Relatiile teoretice de lucru permit evaluarea dinamica a performantelor energetice ale sistemului ceea ce ajuta la alegerea unei capacitati potrivite pentru pompa de caldura in concordanta cu necesarul de caldura al consumatorului

Cuvinte cheie: pompa de caldura, surse regenerabile

In the paper is proposed an approximate method of evaluation of the energy performance offered by a system that uses renewable sources by means of a vapor mechanical compression heat pump. Along with the energy balance of the heat pump, is presented also the non-stationary thermal balance of the source and consumer environments, each represented in the present work by a water storage tank, from which the heat pump extracts the thermal flux and respectively supplies heat flux (flow). Theoretical working relationships allow the dynamic evaluation of the energy performance of the system, which aids the selection of a suitable capacity for the heat pump, in concordance with the demand heat of the consumer.

Keywords: heat pump, renewable sources

Aspecte privind predicția coroziunii electrozilor de pământare în solul municipiului Timișoara Partea a II-a. Teste ceață salină
Aspects regarding the prediction of corrosion of earth electrodes in the soil of Timișoara municipality Part II. Saline fog tests
Ștefan PAVEL,Ioan-Bogdan PASCU,Bogdan-Ovidiu ȚĂRANU, Oana-Alexandra GRAD, Romeo NEGREA

Predicția coroziunii electrozilor de pământare instalați în solul din orașul Timișoara

Cuvinte cheie: sol, electrod de împământare, coroziune, predicție

Corrosion prediction of galvanized steel ground electrodes in the soil of Timisoara

Keywords: soil, earth electrode, corrosion, prediction

The effect of nature the granulate on the evolution of the thermal conductivity of an epoxy based concrete exposed to high temperatures
BENOUDJAFER imane, BENOUDJAFER ibtissam, KUKHTA Alexander

The knowledge of the thermal conductivity properties of concrete is essential in studying the behavior of concrete at high temperatures. This knowledge is so essential to feed the thermal behavior patterns and correctly simulate the temperature field developing in a concrete element in any type of heating. In this context, this work aims to follow the influence of the nature of the granulate on the evolution of the thermal conductivity of epoxy-based concretes. The experimental results obtained show that the mineralogical nature of the granulate great affects the conductivity of the concrete.

Keywords: resin concrete, the granulate, high temperature, thermal conductivity

Procedura de evaluare a indicatorilor de performanta pentru masini frigorifice sau pompe de caldura
Procedure for evaluating performance indicators for refrigeration machines or heat pumps
Florin IORDACHE, Alexandru DRAGHICI

Lucrarea are ca obiectiv prezentarea unei proceduri de evaluare a indicatorilor energetici aferenti masinilor frigorifice cu comprimare mecanica, folosite pentru extragerea caldurii (EER) sau furnizarea acesteia (COP) in mediul consumatorului. Procedura are ca date de intrare temperatura mediului rece si a mediului cald in care se gasesc vaporizatorul, respectiv condensatorul instalatiei, tinand totodata seama de randamentul motorului electric aferent compresorului si de randamentul izentropic de comprimare a agentului frigorific. In cadrul simularilor de functionare realizate in programul CoolPack, eficienta masinii frigorifice la comprimare izentropica este utilizata ca indicator energetic de baza.

Cuvinte cheie: masini frigorifice, comprimare mecanica

This paper presents a numerical procedure for evaluating the energetical indicators of the refrigeration systems with mechanical compression, that can be used to extract (EER) or to supply heat (COP) to the consumer. The procedure uses as input data the temperature values of the cold environment (where the frigorific evaporator is installed) and warm environment (surrounding the frigorific condenser). The electric and isentropic efficiencies of the compressor are also taken into account. Within the functional simulation developed in CoolPack software, the evaporator efficiency at isentropic compression is used as a fundamental energetical indicator.

Keywords: refrigeration machines, mechanical compression

Spectrografia în infraroșu. Oportunități, domenii și limite de aplicare
Infrared Spectrography. Opportunities, areas and limits of application
Claudiu JIPA, Mihai DIMA, Vlad IORDACHE

Aplicarea cu performanțe maxime a acestei procedurii depinde de înțelegerea corectă a fenomenului (legile fizice care îl guvernează, condițiile, avantajele și limitele examinării in infrarosu-IR) atât în ceea ce privește captarea imaginilor, cât mai ales în analiza și interpretarea acestora. Există riscul unor determinări cu erori de peste 150 % în cazul aplicării sau interpretării greșite. Prezenta lucrare își propune să detalieze principiile metodei și să constituie un instrument util adresat specialiștilor pentru o alegere optima a echipamentului termografic corespunzător domeniului de interes analizat.

Cuvinte cheie: Termografie, Radiație infraroșu, Echipament termografic.

The maximum performance of this procedure depends on the correct understanding of the phenomenon, both in capturing IR images and in their analysis and interpretation. In the case of mis-application or mis-interpretation, there are risks for determinations of over 150%. This paper aims to detail the principles of the method and to be a useful tool for specialists in choosing thermographyc equipment corresponding to the area of interest analyzed.

Keywords: Thermography, Infrared radiation, Thermographyc equipment

Thermographic inspection for building diagnosis
Andrei PREDA, Lelia Letitia POPESCU, Stefan Razvan POPESCU

Thermography (infrared thermal imaging) is one of the non-destructive methods by which surface temperature variations can be determined on the surface of a building. By this method one can exemplify, at one time, the heat loss through the surface of the building. Thermovision consists of scanning the building with infrared, using a special camera. This allows us to identify the hottest areas where the greatest heat loss occurs. On the basis of the information obtained, the optimal solutions for reducing energy losses can be established, resulting in a better environment for buildings and lower costs in terms of thermal energy, and not only. Thermal camera recordings are converted into color images. The range of colors and color intensity give us insights into temperature differences from the surface of the building under test. All of this creates an overview of the entire building, so construction specialists can make a fair interpretation and offer the most appropriate solution for the issue.

Keywords: thermography, thermovision

Determination of stresses the interface of a rigid eccentric footing, accounting for the effect of soil mechanical characteristics and footing geometrical parameters
Benayad Slimane, Kadri Fatima, Yousfi Aimen

As footings are the most important elements in any construction, it seems judicious to dwell on the sizes that condition these dimensions, as well as soil quality on which these footings will be constructed, especially that they often subject to eccentric loads caused by catastrophic natural phenomena (earthquakes, land pressures, wind, etc. It is therefore important to know, with the largest possible approximation, stresses distribution under the footing, and therefore to what extent the structure can remain stable. The study presented herein examines stresses distribution at soil-footing interface for different combinations of soil properties, foundation geometry and applied load eccentricity using 2D finite element modeling. The FEM evaluation is accomplished by using COMSOL software program. The results prove importance and effect of these mechanical and geometrical characteristics on stress distribution at the interface while theoretical solutions strongly ignore some of them.

Keywords: Eccentric footing, finite element method, soil behavior, soil-footing interaction, stress distribution

Transparent Concrete
Georgia Alexandra COVALEOV

Reinforced concrete was invented and developed simultaneously by several people in the mid-nineteenth century. Besides versions "classical" fiber reinforced concrete (by using steel bars, whatever "style" of them), there are new ways to further concrete strength. Transparent concretes (translucent) is gaining much ground in the construction of the West Europe. "Light Transmitting Concrete" is a concrete-like product, which is translucent due to the mixture of fiber glass, plus a combination of finely divided crushed stone, cement and water. After the strengthening of composition, blocks of various shapes are obtained, with features of concrete and glass. Transparent concrete is a translucent material created by the combination of concrete and thousands of optical fiber wires acting as a filler.

Keywords: transparent concrete, fiber glass

Analiza energetica privind dimensionarea si evaluarea performantelor energetice ale instalatiilor utilizand captatoarele solare termice
Energy analysis regarding the dimensioning and evaluation of the energy performance of the installations using solar thermal collectors
Florin IORDACHE

In cadrul lucrarii se stabileste o relatie de evaluare a gradului de acoperire energetica a necesarului de caldura pentru incalzirea spatiilor sau prepararea a apei calde. In cadru acestei relatii se identifica o serie de 3 parametrii de configurare energetica a siatemului consumator – instalatie solara dar si un indicator energetic climatic important in special din punct de vedere al locatiei de amplasare a consumatorului. Se ofera astfel posibilitatea de a se pune in balanta atat influentele parametrilor de configurare constructiva ai sistemului cat si indicatorul energetic climatic in vederea optimizarii sistemului sursa functie de locatia de amplasare a consumatorului.

Cuvinte cheie: captatoare solare termice, incalzire

In the paper a relationship is established for assessing the degree of energy coverage of the heat demand for space heating or the preparation of hot water. Within this relationship we identify a series of 3 parameters of the energy configuration of the consumer - solar installation and also an important climatic energy indicator especially in terms of the location of the consumer location. This provides the possibility of balancing both the influences of the constructive configuration parameters of the system and the climatic energy indicator in order to optimize the source system according to the location of the consumer's location.

Keywords: solar thermal collectors, heating

 
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