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  Numarul 4/2021

Volumul 12 (2021), Nr. 4 - Vizualizare numar complet

Influenta iluminarii si a trasoarelor asupra masuratorilor de velocimetrie a imaginii particulelor pe canalele de curgere deschise
Influence of illumination and tracers on Particle Image Velocimetry measurements on open flow channels
Ilinca Nastase, Mihnea Sandu, Marius Iliescu, Amjed Albaiyati

Within the study of free surface flows, measurements in the vertical planes of the flow are desired. Using Particle Image Velocimetry, usually measurements are performed with the laser sheet through the bottom of the channel in order to avoid the optical perturbations on the laser light sheet, generating light scattering and measurement artefacts. There are however a number of cases where this is not possible since the transparence of the bottom cannot be ensured. In the present study we wanted to check the influence of the illumination on the velocity fields distribution, through the bottom of the channel or through the free surface, on a very simple flow on a plane plate placed on the bottom of a circular channel. We also checked the influence on using conventional silver hollow glass spheres and fluorescent particles. The results allowed us to conclude that in the cases where the study is focused on the boundary layer close to the solid surface and the observed perturbations of the free surface are not important, top illumination of the open channel might be considered as an option if perturbations of the free surface are not observed.

Keywords: PIV, free surface flows, optical techniques

Transfer constant de caldura prin convectie naturala (libera) si radiatie, pentru o teava circulara orizontala inconjurata de aer, folosind software-ul Mathcad®
Steady heat transfer by natural (free) convection and radiation, for a horizontal circular pipe surrounded by air, using the Mathcad® software

Lucrarea prezinta un studiu privind transmiterea caldurii in regim termic stationar, prin convectie termica libera si radiatie, de la o conducta cu sectiune circulara catre aerul inconjurator. Cu ajutorul aplicatiei software Mathcad®, a fost implementata pe calculator procedura de calcul pentru coeficientii de transfer termic superficiali prin convectie, radiatie si combinat, precum si determinarea valorii fluxului termic unitar raportat la unitatea de lungime transmis mediului ambiant, avand in vedere diverse valori ale temperaturii pe suprafata exterioara a conductei. Rezultatele studiului indica faptul ca neglijarea transferului de caldura prin radiatie termica, chiar in cazul unor temperaturi avand valori cuprinse in intervalul 40°C…90°C, poate conduce la erori tehnice relativ ridicate privind estimarea pierderilor de caldura ale conductelor, fiind necesar a lua in calcul in aceste situatii transferul termic combinat prin convectie si radiatie.

Cuvinte cheie: transfer, caldura, stationar, convectie termica, libera, radiatie termica, Mathcad

The paper presents a study on the heat transfer in steady state, by natural convection and radiation, from a circular pipe to the surrounding air. Using the Mathcad® software application, the calculation procedure for the average heat transfer coefficient on the surface by convection, radiation and combined was implemented on the computer, as well as the determination of the heat flux density (the rate of heat transfer per unit time per unit length) taking into account various values of the outer surface temperature of the pipe. The results of the study show that neglecting the heat transfer by thermal radiation, even for low temperatures with values in the range of 40°C...90°C, can lead to relatively high technical errors in estimating the heat loss of pipes. In these situations, is necessary to take into account the combined heat transfer by natural convection and thermal radiation.

Keywords: heat, transfer, steady state, natural convection, radiation, Mathcad

Aspecte teoretice privind eficienta energetica in refrigerarea si congelarea alimentelor
Theoretical aspects regarding energy efficiency in foods refrigeration and freezing
Alina GIRIP, Razvan CALOTA, Madalina NICHITA, Anica ILIE

This paper presents a technical study on energy consumption and performance of a refrigeration system used for food products refrigeration and congelation. The authors compared the two-stage refrigeration system with the cascade refrigeration system. The analysis was based on the thermodynamic cycles corresponding to each one of the proposed solutions. For the booster system several refrigerants were considered in the analysis for the upper loop, respectively R717, R404A, R407C and R417A. Based on the total energy consumption of the installation (compressor, fans, recirculation pumps), the overall performance coefficient of the installation was determined. The study showed that the lowest electrical energy consumption corresponds to the cascade refrigeration system with R717-R744 and the two-stage compression refrigeration system with R717. The difference between the 2 optimal variants is only 4.6%. Therefore, it is recommended that the choice of the final scheme to be made on the basis of an LCC (Life cycle cost) analyze, which takes into account the refrigerant charge, the initial investment cost, the operating costs and the electricity cost.

Keywords: ammonia, carbon dioxide, power consumption, coefficient of performance

Analiza in situ si de laborator a solului marin tratat prin metode de consolidare
In-situ and Laboratory Analysis of Treated Marine Soil by Consolidation Methods

The methods of improvement of vibroflotation (VF), dynamic compaction (DC) and the preloading took a scale in Algeria these last years, they are applied at the port of DjenDjen in Jijel province, object of our study, in the framework of its extension and its development, in order to improve the support soil which will receive the foundations of the protections structures and the container terminal in caissons. The main objective is to understand and apprehend these techniques, as well as the sensitivity of the intervening factors on its realization, and their effect on the behavior of the soil during and after its implementation. In addition, this treatment to minimize the risk of liquefaction and instability of the protective structure, However, the advantage of speed of execution and reasonable cost compared to the importance of the project, thus no negative effects have been reported on the environment. The effectiveness of these soil treatment methods has been demonstrated by the results of the available in-situ tests, in particular the SPT tests which made it possible to check the capacity of the support soil before and after its completion, as well as the settlement surveys confirm the efficiency of these techniques in terms of improving the bearing capacity of the seabed.

Keywords: Harbours, Vibroflottation, Dynamic compaction, Preloading, Soil improvement

O revizuire cu privire la recuperarea caldurii din apele uzate
A Review Regarding the Heat Recovery from Wastewater
Amjed Albaiyati

One of the main challenges in the world today is reducing energy consumption and CO2 footprint in existing buildings without major construction work. Many of these buildings represent heritage buildings and the intervention constraints on the original building are much more restrictive for these particular cases. The building sector is one of the world's largest energy consumers, so it is important to seek out and use recovery energies for individual consumers. The main component of energy consumption in buildings is heating, but the demand for the domestic hot water is also very high, especially when daily consumption is high and especially for specific applications ( hotels or laundries for example) This is why the implementation of technologies using renewable energy and recovery sources for water heating[1] has become very important and one of these technologies involves the recovery of the thermal energy from wastewater. Usually, heat recovery from wastewater is designed to recover residual energy from the hot drainage water and this recovered energy is used to preheat incoming cold water or to heat pumps.

Keywords: wastewater, energy recovering, heat exchanger

Programe software utilizate in proiectarea tablourilor electrice de distribuiie de joasa tensiune
Software programs used in designing of low voltage electrical distribution panels
Cristina Gabriela Saracin, Diana Paraipan

This paper presents the ABB Doc and Schrack Design programs used in the design of voltage electrical distribution panels. The consumers' power supply depends on the correct choice of the protection and switching equipment and the correct size of the distribution panel. Therefore, the paper exemplifies and compares these software applications used successfully in the size of distribution cabinets. Therefore, the paper exemplifies and compares these software applications used successfully in the size of distribution cabinets. Dimensions of the switchboard are obtained by choosing and correctly positioning the electrical equipment in the switchboard. Schrack Design program allows the manufacturing of electrical panels without calculating the necessary parameters choices of protection and switching equipment. The choice of electrical equipment and electrical distribution panels is made exclusively by the user. It can make component selections from the manufacturer's database or add electrical equipment from other companies to this database. Once the options have been selected, the program generates the single-wire or multi-wire circuit diagram. The validation of the chosen solutions involves the thermal calculation of the electrical distribution panels which is done with the help of the Schrack Design program.

Keywords: electrical distribution panels, ABB Doc program, Schrack Design program

Modelarea contractiei prin uscare a betoanelor structurale
Modeling the Drying Shrinkage of Structural Concretes
Abderraouf Kebir, Abdelmalek Brahma

Shrinkage in hydraulic materials is a complex time-dependent process. For standard concretes, one of the most significant parts of shrinkage is drying shrinkage. In fact, to predict deformations of concrete due to shrinkage, various predictive models have been developed; most of them use many numbers of factors that can affect shrinkage such as concrete strength, concrete age at loading, curing conditions type, ambient conditions, type of cement and aggregates, water to cement ratio, concrete mix, member shape and size, loading duration and type. A such number of parameters increases the complexity of using these models lead to some prediction imperfections; thence a new simplified model is needed. The main target of the current paper is to formulate a novel and simplified model with a minimum of factors that affect drying shrinkage behaviour as like as relative humidity and volume to area ratio of the concrete element (V/S). To achieve this goal, we had developed a prediction model based on probability density function and a small number of parameters that influence shrinkage like relative humidity and volume to surface ratio of the element. A huge database has been used to calibrate our model's parameters using the most recent studies and researches to validate the model.

Keywords: hydraulic materials, drying shrinkage, modelling, prediction, concrete deformation, structural concrete

Analiza implementarii masurilor de aparare impotriva incendiilor in cladiri civile
Analysis of the implementation of fire protection measures in civil buildings
Conf.univ.dr.ing. Aurel Trofin, Drd.ing. Mihai Ciprian Mitrea

Implementarea masurilor de aparare impotriva incendiilor in contextul legislatiei actuale, presupune identificarea unui set de masuri legislative si norme tehnice specifice domeniului de activitate si implementarea standardizata in toate etapele de proiectare, executie, punere in functiune si exploatare a cladirilor civile. Totodata, factorii de decizie pentru fiecare etapa enumerata anterior raspund de modul de implementare a normelor tehnice si a masurilor necesare asigurarii securitatii la incendiu a tuturor lucratorilor si utilizatorilor din constructiile civile.

Cuvinte cheie: lucrator, loc de munca, incendiu, masuri specifice, interventie

Implementing the fire protection measures in the context of current legislation, involves the identification of a set of legislative measures and technical rules specific to the field of activity and standardized implementation in all stages of design, execution, commissioning and operation of civil buildings. At the same time, the decision makers for each stage listed above are responsible for the implementation of technical rules and measures necessary to ensure fire safety of all workers and users of civil buildings.

Keywords: worker, job, fire, specific measures, intervention

Metoda eficienta de incalzire cu microunde pentru fabricarea spumei de sticla din deseu de sticla
Effective microwave heating method for manufacturing glass foam from glass waste
Lucian Paunescu, Sorin Mircea Axinte, Marius Florin Dragoescu, Bogdan Valentin Paunescu

In lucrare este prezentata o tehnica originala de fabricare a spumei de sticla prin sinterizarea la temperatura inalta a deseului de sticla datorita incalzirii cu microunde. Incalzirea materiei prime este realizata predominant direct si partial indirect utilizand un tub ceramic din SiC cu o grosime optima a peretelui de 2,5 mm. Aceasta metoda contribuie la reducerea semnificativa a consumului specific de energie, a vitezei de incalzire si a duratei procesului comparativ cu tehnicile conventionale de incalzire. Caracteristicile spumei de sticla sunt similare cu acelea ale spumelor fabricate conventional si pot fi utilizate ca inlocuitori ai materialelor de constructie existente.

Cuvinte cheie: spuma de sticla, microunda, incalzire predominant directa, agent de spumare, eficienta energetica

An original technique for manufacturing glass foam by high temperature sintering of glass waste due to the microwave heating is presented in the paper. The heating of the raw material is performed predominantly direct and partially indirect by using a SiC ceramic tube with an optimal wall thickness of 2.5 mm. This method contributes to the significant reduction of the specific energy consumption, the heating rate and the process duration compared to the conventional heating techniques. The characteristics of glass foam are similar to those of conventionally manufactured foams and can be used as replacements for existing building materials.

Keywords: glass foam, microwave, predominantly direct heating, foaming agent, energy efficiency

Expandarea deseului de sticla prin dublul efect al agentilor de spumare lichid si solid pentru fabricarea pietrisului din spuma de sticla (CGG) intr-un cuptor cu microunde de 10 kW
Expansion of glass waste by the double effect of liquid and solid foaming agents for manufacturing the cellular glass gravel (CGG) in a 10 kW-microwave oven
Lucian Paunescu, Sorin Mircea Axinte, Marius Florin Dragoescu, Bogdan Valentin Paunescu

O reteta de fabricare industriala a pietrisului din spuma de sticla (CGG) din deseu de sticla printr-o tehnica originala neconventionala utilizand simultan un agent de spumare lichid si solid (glicerina si carbonat de calciu) a fost testata intr-un cuptor cu microunde de 10 kW. Utilizand un creuzet ceramic de mari dimensiuni din carbura de siliciu, in interiorul caruia a fost introdusa o matrita metalica continand amestecul de materie prima fin macinata si presata, a fost produsa o cantitate mult mai mare de produs spumat. Caracteristicile probelor de CGG au fost densitatea in vrac de 0,20-0,25 g/cm3, conductivitatea termica de 0,062-0,070 W/m·K si rezistenta la compresiune de 7,1-7,4 MPa.

Cuvinte cheie: pietris din spuma de sticla, incalzire cu microunde, deseu de sticla, glicerina, carbonat de calciu

An industrially manufacturing recipe of cellular glass gravel (CGG) from glass waste by an original unconventional heating technique using simultaneously a liquid and solid foaming agent (glycerol and calcium carbonate) was tested on a 10 kW-microwave oven. Using a large silicon carbide ceramic crucible, inside which a metal mold containing the finely ground pressed raw material mixture was inserted, a much higher amount of foamed product was produced. The characteristics of CGG samples were bulk density of 0.20-0.25 g/cm3, thermal conductivity of 0.062-0.070 W/m·K and compressive strength of 7.1-7.4 MPa.

Keywords: foam glass gravel; microwave heating; glass waste; glycerol; calcium carbonate.

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