Application of Computational Fluid Dynamics in cooling systems design for special purpose objects

U ovom radu, na primeru projektovanja sistema za hlađenje elektro-opreme, smeštene u kontejner kranske dizalice MK-46 - 'GOŠA FOM', prikazana je osnovna problematika CFD (Computational Fluid Dynamics) pristupa rešavanju problema izbora odgovarajućeg rashladnog sistema, te određivanja optimalnog položaja, broja i veličine otvora za hlađenje. Pokazano je da numerička mehanika fluida, sa svojom mogućnošću, da i pre izgradnje samog objekta pruži precizne trodimenzionalne slike o brzinskim i temperaturnim poljima u fluidu, kao i da predvidi promene ovih polja koje bi nastale pri promeni geometrije, graničnih i prostornih uslova (otvora za ventilaciju i ubacivanje i izbacivanje vazduha, pojedinih zidova i pregrada), predstavlja superioran pristup projektovanja ovih sistema.The paper illustrates the basic methodology and principal problems of CFD (Computational Fluid Dynamics) approach in designing a proper cooling system (capacity of cooling, determination of optimal position, number and size of openings for cooling, etc.) in special purpose objects. Taking as an example the design of the cooling for electrical equipment placed in a container of crane MK-46 - 'GOSA FOM', the problem of the selection of proper cooling system was demonstrated. It has been shown that the numerical fluid dynamics represents a superior approach to the design of these systems., with its ability to, provide precise three-dimensional images of velocity and temperature field in the fluid even before the construction of the facility, as well as to predict the changes of those fields that would appear with modification of geometry, boundary and spatial conditions (opening for injection and exhausting of air, position of the walls and obstacles)

Application of Computational Fluid Dynamics in cooling systems design for special purpose objects

U ovom radu, na primeru projektovanja sistema za hlađenje elektro-opreme, smeštene u kontejner kranske dizalice MK-46 - 'GOŠA FOM', prikazana je osnovna problematika CFD (Computational Fluid Dynamics) pristupa rešavanju problema izbora odgovarajućeg rashladnog sistema, te određivanja optimalnog položaja, broja i veličine otvora za hlađenje. Pokazano je da numerička mehanika fluida, sa svojom mogućnošću, da i pre izgradnje samog objekta pruži precizne trodimenzionalne slike o brzinskim i temperaturnim poljima u fluidu, kao i da predvidi promene ovih polja koje bi nastale pri promeni geometrije, graničnih i prostornih uslova (otvora za ventilaciju i ubacivanje i izbacivanje vazduha, pojedinih zidova i pregrada), predstavlja superioran pristup projektovanja ovih sistema.The paper illustrates the basic methodology and principal problems of CFD (Computational Fluid Dynamics) approach in designing a proper cooling system (capacity of cooling, determination of optimal position, number and size of openings for cooling, etc.) in special purpose objects. Taking as an example the design of the cooling for electrical equipment placed in a container of crane MK-46 - 'GOSA FOM', the problem of the selection of proper cooling system was demonstrated. It has been shown that the numerical fluid dynamics represents a superior approach to the design of these systems., with its ability to, provide precise three-dimensional images of velocity and temperature field in the fluid even before the construction of the facility, as well as to predict the changes of those fields that would appear with modification of geometry, boundary and spatial conditions (opening for injection and exhausting of air, position of the walls and obstacles)

Computational study of smoke flow control in garage fires and optimization of the ventilation system

With the aim of evaluating capabilities of a ventilation system to control the spread of smoke in the emergency operating mode, thereby providing conditions for safe evacuation of people from a fire-struck area, computational fluid dynamics simulation of a fire in a semi-bedded garage was conducted. Using the experimental results of combustion dynamics of a passenger car on fire, optimal positions of ventilation openings were determined. According to recommendations by DIN EN 12101 standard, the operating modes of a ventilation system were verified and optimal start time of the smoke extraction system was defined

Numerical study of smoke flow control in tunnel fires using ventilation systems

Sa ciljem procenjivanja mogućnosti jednog tunelskog ventilacionog sistema, da u incidentnom radnom režimu kontroliše širenje dima i da tako obezbedi uslove za bezbednu evakuaciju ljudi iz vatrom zahvaćenog prostora, izvršena je CFD (Computational Fluid Dynamics) simulacija požara u jednom dvocevnom tunelu. Korišćenjem eksperimentalnih rezultata, o dinamici sagorevanja zapaljenog automobila i prema preporukama PIRAC-a određenih radnih režima ventilatora, izvršena je provera kritične brzina strujanja vazduha kojom će se sprečiti prodor dima u evakuacione hodnike, te izvršena provera potrebnog broja i rasporeda ventilatora u tunelskim cevima.With the aim of evaluating capabilities of a tunnel ventilation system to control the spread of smoke in the emergency operating mode, thereby providing conditions for safe evacuation of people from a fire-struck area, a CFD (Computational Fluid Dynamics) simulation of a fire in a double tube tunnel was done. By the use of experimental results regarding the combustion dynamics of a passenger car, that is truck on fire and ventilation system operating modes determined according to PIRAC recommendations, a check of critical air velocity required to prevent smoke penetration into the evacuation hallways was performed, as well as the check of the optimum number and positions of ventilators in the tunnel tubes

Numerical study of smoke flow control in tunnel fires using ventilation systems

Sa ciljem procenjivanja mogućnosti jednog tunelskog ventilacionog sistema, da u incidentnom radnom režimu kontroliše širenje dima i da tako obezbedi uslove za bezbednu evakuaciju ljudi iz vatrom zahvaćenog prostora, izvršena je CFD (Computational Fluid Dynamics) simulacija požara u jednom dvocevnom tunelu. Korišćenjem eksperimentalnih rezultata, o dinamici sagorevanja zapaljenog automobila i prema preporukama PIRAC-a određenih radnih režima ventilatora, izvršena je provera kritične brzina strujanja vazduha kojom će se sprečiti prodor dima u evakuacione hodnike, te izvršena provera potrebnog broja i rasporeda ventilatora u tunelskim cevima.With the aim of evaluating capabilities of a tunnel ventilation system to control the spread of smoke in the emergency operating mode, thereby providing conditions for safe evacuation of people from a fire-struck area, a CFD (Computational Fluid Dynamics) simulation of a fire in a double tube tunnel was done. By the use of experimental results regarding the combustion dynamics of a passenger car, that is truck on fire and ventilation system operating modes determined according to PIRAC recommendations, a check of critical air velocity required to prevent smoke penetration into the evacuation hallways was performed, as well as the check of the optimum number and positions of ventilators in the tunnel tubes

Improvement of cfd models of tunnel fire development based on experimental data

This paper, dealing with the problems of mathematical description of the tunnel fire development process with the use of experimental data, outlines the procedure of correction of the existing and obtaining of an improved CFD model package. The improved CFD model was developed on the basis of detailed analysis and comparison of experimental and numerical results, through consideration of the physical structure of all processes affecting combustion. During the analysis it was noticed that the existing CFD model in the part covering combustion based on the so-called steady laminar flamelet model, treats the combustion process almost as a direct correlation between the processes of mixing gasses and heat release rate. This potential deficiency has been overcome by correction of the model in the section defining boundary condition for the burning surface and by establishing a direct correlation between the measured value of the fuel mass change rate and the amount of heat released from burning surface. In this way a modification of complex stoichiometric combustion processes was avoided, while providing the model that better describes and predicts the course of events in this type of complex, anisotropic and turbulent flow of gases in the tunnel

Development of a new near-wall reynolds stress turbulence model for jet impingement heat transfer prediction

U ovom radu je predstavljen nov naponski model (model drugog reda) turbulentnih napona. Ovaj novi naponski model nastao je pretvaranjem "standardnog" IP (high-Reynolds) naponskog modela u odgovarajući naponski model kojim je moguće vršiti proračune i u oblastima strujanja sa malim vrednostima Rejnoldsovog turbulentnog broja (low-Reynolds model), kao i sa popravkom tog modela u vidu dopunskog člana nagle preraspodele turbulentnih napona usled prisustva zida *R II, w τ, ij. Pretvaranje IP modela iz njegove high-Reynolds u njegovu low-Reynolds verziju, izvršeno je uključivanjem prethodno zanemarenog uticaja molekularne difuzije na procese prenošenja, tj. sa uvođenjem odgovarajućih članova i funkcija u jednačinu "prenošenja" Rejnolsovih napona i jednačinu "prenošenja" disipacije turbulentne kinetičke energije. Novi, dopunski član nagle preraspodele turbulentnih napona usled prisustva zida *R II, w τ, ij, koji je modeliran u skladu sa realnom fizičkom situacijom, obuhvatio je netipičan takozvani efekat eha pritiska, tj. netipičan proces preraspodele turbulentnih napona koji se javlja u strujnom polju pri udaru mlaza o ploču u blizini zaustavne tačke. Nasuprot "standardnim" linearnim dvojednačinskim modelima turbulentnih napona, predloženi naponski model daje kvalitativno bolja predviđanja polja kinetičke energije turbulencije i značajno bolja predviđanja lokalnih vrednosti Nuselovog broja. U poređenju sa "standardnim" high-Reynolds naponskim modelima, predloženi model pokazuje značajno bolja predviđanja turbulentnih napona u zaustavnoj zoni udara mlaza, nešto bolja predviđanja polja osrednjenih brzina, a i omogućava predviđanje lokanih vrednosti Nuseltovog broja.The newly proposed Reynolds-stress turbulence model (second moment closure) was created by transforming the "standard" high-Reynolds Isotropisation-of-Production turbulence model into its low-Reynolds version and by introducing a new additional wall-reflection term, *R II, w τ, ij Transformation from high- to low-Reynolds turbulence model was carried out by including the previously neglected influence of molecular diffusion i.e. by introducing the appropriate terms and functions into Reynolds stress and turbulent dissipation rate transport equation. The new additional "rapid" wall-reflection term *R II, w τ, ij, that was modeled in accordance to the real physical situation, encompassed the "atypical" so-called pressure-echo effect, i.e. the "atypical" redistribution of turbulent stress in the vicinity of the stagnation point of an impinging jet. In contrast to "standard" linear near-wall two-equation turbulence models, the newly proposed Reynolds-stress turbulence model gives essentially better predictions of turbulent kinetic energy field and considerably better predictions of local Nusselt number. Compared with the "standard" high Reynolds turbulence stress models, the proposed turbulence model demonstrates considerably better prediction of turbulent stress field in the vicinity of impinging jet stagnation point, slightly better prediction of mean velocity field, and also enables prediction of local Nusselt number

Development of a new near-wall reynolds stress turbulence model for jet impingement heat transfer prediction

U ovom radu je predstavljen nov naponski model (model drugog reda) turbulentnih napona. Ovaj novi naponski model nastao je pretvaranjem "standardnog" IP (high-Reynolds) naponskog modela u odgovarajući naponski model kojim je moguće vršiti proračune i u oblastima strujanja sa malim vrednostima Rejnoldsovog turbulentnog broja (low-Reynolds model), kao i sa popravkom tog modela u vidu dopunskog člana nagle preraspodele turbulentnih napona usled prisustva zida *R II, w τ, ij. Pretvaranje IP modela iz njegove high-Reynolds u njegovu low-Reynolds verziju, izvršeno je uključivanjem prethodno zanemarenog uticaja molekularne difuzije na procese prenošenja, tj. sa uvođenjem odgovarajućih članova i funkcija u jednačinu "prenošenja" Rejnolsovih napona i jednačinu "prenošenja" disipacije turbulentne kinetičke energije. Novi, dopunski član nagle preraspodele turbulentnih napona usled prisustva zida *R II, w τ, ij, koji je modeliran u skladu sa realnom fizičkom situacijom, obuhvatio je netipičan takozvani efekat eha pritiska, tj. netipičan proces preraspodele turbulentnih napona koji se javlja u strujnom polju pri udaru mlaza o ploču u blizini zaustavne tačke. Nasuprot "standardnim" linearnim dvojednačinskim modelima turbulentnih napona, predloženi naponski model daje kvalitativno bolja predviđanja polja kinetičke energije turbulencije i značajno bolja predviđanja lokalnih vrednosti Nuselovog broja. U poređenju sa "standardnim" high-Reynolds naponskim modelima, predloženi model pokazuje značajno bolja predviđanja turbulentnih napona u zaustavnoj zoni udara mlaza, nešto bolja predviđanja polja osrednjenih brzina, a i omogućava predviđanje lokanih vrednosti Nuseltovog broja.The newly proposed Reynolds-stress turbulence model (second moment closure) was created by transforming the "standard" high-Reynolds Isotropisation-of-Production turbulence model into its low-Reynolds version and by introducing a new additional wall-reflection term, *R II, w τ, ij Transformation from high- to low-Reynolds turbulence model was carried out by including the previously neglected influence of molecular diffusion i.e. by introducing the appropriate terms and functions into Reynolds stress and turbulent dissipation rate transport equation. The new additional "rapid" wall-reflection term *R II, w τ, ij, that was modeled in accordance to the real physical situation, encompassed the "atypical" so-called pressure-echo effect, i.e. the "atypical" redistribution of turbulent stress in the vicinity of the stagnation point of an impinging jet. In contrast to "standard" linear near-wall two-equation turbulence models, the newly proposed Reynolds-stress turbulence model gives essentially better predictions of turbulent kinetic energy field and considerably better predictions of local Nusselt number. Compared with the "standard" high Reynolds turbulence stress models, the proposed turbulence model demonstrates considerably better prediction of turbulent stress field in the vicinity of impinging jet stagnation point, slightly better prediction of mean velocity field, and also enables prediction of local Nusselt number

Experimental determination of thermophysical characteristics of soil as a heat source for geothermal heat pumps

Prilikom projektovanja sistema grejanja sa geotermalnom toplotnom pumpom tipa zemlja-voda, podaci o toplotnoj provodljivosti zemljišta i njenoj temperaturi su ključni parametri pri dimenzionisanju spoljašnjeg dela sistema - vertikalno uronjenih izmenjivača toplote. U ovom radu opisana je jedna od metoda za eksperimentalno određivanje ovih parametara, tzv. test toplotnog odziva. U prilogu opisa eksperimentalne procedure i instalacije, prikazivanjem eksperimentalnih podataka, u radu je data i teorijska osnova metode kao i glavni ograničavajući faktori za njenu primenu.When designing the geothermal heat pump heating system of the ground-water type, data on thermal conductivity of soil and its temperature are key parameters for dimensioning the outer part of the system - vertically buried heat exchanges. In this paper, one of the methods of experimental determination of these parameters, a so-called thermal response test, is presented. In addition to the description of the experimental procedure and installation, through the presentation of experimental data, the paper describes theoretical basis of the method, and presents its main limitations

Simulation of solar water heating system

U radu je prikazan matematički model rada solarnog sistema za zagrevanje vode. Analizirani solarni sistem sadrži ravne solarne kolektore, dva akumulaciona rezervoara za vodu, spoljašnji razmenjivač toplote i dopunski izvor energije. Primenjeni model omogućava simulaciju rada i određivanje odgovarajućih energetskih pokazatelja rada sistema i njegovih elemenata za različite lokacije (klimatske uslove), orijentaciju kolektora, termičkih karakteristika komponenata sistema, kao i različitu dinamiku korišćenja tople vode. Rezultati simulacije su prikazani za dane tipične meteorološke godine za Beograd i dnevni profil korišćenja tople vode. Prikazana je analiza energetskih karakteristika sistema. Rezultati dobijeni numeričkom simulacijom su poređeni sa rezultatima dobijenim primenom f-chart metode proračuna.The paper presents a mathematical model of the solar water heating system. The analyzed solar system consists of flat collectors, two water storage tanks, outer heat-exchanger and a source of auxiliary energy. The implemented model enables simulation of system operation and determination of appropriate energy characteristics of the system and its elements for different locations (climatic data), orientations of collectors, thermal characteristics of system components, as well as different dynamics of hot water consumption. Results of the simulation are presented for the days of a typical meteorological year for Belgrade and the daily profile of hot water consumption. The analysis of the energy performances of the system is presented. The results obtained by simulation were compared with the results obtained with the -chart method of calculation