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

Subwavelength hole arrays with nanoapertures fabricated by scanning probe nanolithography

Owing to their surface plasmon-based operation, arrays of subwavelength holes show extraordinary electromagnetic transmission and intense field localizations of several orders of magnitude. Thus they were proposed as the basic building blocks for a number of applications utilizing the enhancement of nonlinear optical effects. We designed and simulated nanometer-sized subwavelength holes using an analytical approach. In our experiments we used the scanning probe method for nanolithographic fabrication of subwavelength hole arrays in silver layers sputtered on a positive photoresist substrate. We fabricated ordered nanohole patterns with different shapes, dispositions and proportions. The smallest width was about 60 nm. We characterized the fabricated samples by atomic force microscopy

Numerical methods for generation and characterization of disordered aperiodic photonic lattices

We introduce numerical modeling of two different methods for the deterministic randomization of two-dimensional aperiodic photonic lattices based on Mathieu beams, optically induced in a photorefractive media. For both methods we compare light transport and localization in such lattices along the propagation, for various disorder strengths. A disorder-enhanced light transport is observed for all disorder strengths. With increasing disorder strength light transport becomes diffusive-like and with further increase of disorder strength the Anderson localization is observed. This trend is more noticeable for longer propagation distances. The influence of input lattice intensity on the localization effects is studied. The difference in light transport between two randomization methods is attributed to various levels of input lattice intensity. We observe more pronounced localization for one of the methods. Localization lengths differ along different directions, due to the crystal and lattice anisotropy. We analyze localization effects comparing uniform and on-site probe beam excitation positions and different probe beam widths

Analytical and experimental determination of the temperature field on the surface of wall heating panels

This paper presents experimental verification of the accuracy and acceptability of Faxen-Rydberg-Huber analytical expression for determining thermal characteristics of the heating panels. The verification of accuracy of the Faxen-Rydberg-Huber expression, which describes the 2-D temperature field in the wall with series of embedded heated pipes having uniform temperature, was performed by comparing the temperatures on the surface of three types of heating wall panels, differing in structure and geometric characteristics. The analysis of results has shown high accuracy of Faxen-Rydberg-Huber expression in describing the temperature field. Also, it was noted that small changes in heating fluid temperature, occurring along the pipe in the heated panel, have a negligible influence on the accuracy of prediction by the expression. This confirmed that the Faxen-Rydberg-Huber expression can be used to describe the temperature field in the wall heating panels. At the same time, this expression has proven to be extremely sensitive primarily to thermophysical characteristics of the panel layers, as well as to the geometric parameters of the panels

Analytical and experimental determination of the temperature field on the surface of wall heating panels

This paper presents experimental verification of the accuracy and acceptability of Faxen-Rydberg-Huber analytical expression for determining thermal characteristics of the heating panels. The verification of accuracy of the Faxen-Rydberg-Huber expression, which describes the 2-D temperature field in the wall with series of embedded heated pipes having uniform temperature, was performed by comparing the temperatures on the surface of three types of heating wall panels, differing in structure and geometric characteristics. The analysis of results has shown high accuracy of Faxen-Rydberg-Huber expression in describing the temperature field. Also, it was noted that small changes in heating fluid temperature, occurring along the pipe in the heated panel, have a negligible influence on the accuracy of prediction by the expression. This confirmed that the Faxen-Rydberg-Huber expression can be used to describe the temperature field in the wall heating panels. At the same time, this expression has proven to be extremely sensitive primarily to thermophysical characteristics of the panel layers, as well as to the geometric parameters of the panels

Low temperature hydronic heating system with radiators and geothermal ground source heat pump

Upotreba grejnog sistema s toplotnom pumpom i zemljom kao izvorom energije bez obzira na relativno nisku temperaturu raspoloživog "izvora" geotermalne energije (temperatura vode ili tla ne mora biti viša od 12°C), omogućava da se 50-80% energije potrebne za grejanje preuzme od zemlje, a da se ostatak nadomeštava električnom energijom. Ovaj udeo geotermalne energije, u ukupnoj energiji potrebnoj za grejanje, zavisi pre svega od sistema njene dalje raspodele (radijatorski sistem, sistem grejanja pomoću fancoil-a ili zidno i podno grejanje), a tek potom i od temperature vode, odnosno tla. U radu je data uporedna analiza termičke efikasnosti dva sistema centarlnog grejanja sa radijatorima kao grejnim telima, visokotemperturnog kotlovskog sistema grejanja (90°C/70°C) i niskotemperaturnog sistema sa toplotnom pumpom i zemljom kao izvorom energije (65°C/55°C, 55°C/45°C ili 50°C/45°C).The use of a system with a geothermal ground source heat pump, regardless of the relatively low temperature of the available source of geothermal energy (water or ground temperature does not need to exceed 12°C), allows 50-80% of the energy required for heating to be taken from the ground, while the remaining amount is provided by electrical energy. This share of geothermal energy, in the total energy required for heating, primarily depends on the system of its further distribution (radiator system, fan coil heating system or wall and floor heating), and secondarily on water and ground temperature. The paper deals with the comparative analysis of thermal efficiency of two water central-heating systems with radiators, a conventional high-temperature heating system with a boiler (90°C/70°C) and a low-temperature heating system with a geothermal ground source heat pump ( 65°C/55°C, 55°C/45°C or 50°C/45°C)

Plasma and Sol-Gel Technology for Creating Nanostructured Surfaces of Fibrous Polymers

For a modification of natural and synthetic fibrous polymers low-pressure ICRF plasma and liquid repellent sol-gel fluoroalkyl-functional siloxane precursor were used. Plasma induced surface chemical and morphological changes on fluorinated poly(ethylene terephthalate) and cellulose were analysed using X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). Wettability properties of sol-gel functionalized polymers were determined by the goniometric water contact angles and water sliding angle measurements. After plasma treatment the oxygen content on the surface of both polymers increased (increase of O/C ratio) and a nanostructured surface roughness appeared. Plasma ablation caused partially defluorinated nanostructured surface of fluorinated poly(ethylene terephthalate) polymer and increased its hydrophilicity. Plasma activation and etching of cellulose polymer contributed to the creation of highly adhesive and wash resistant sol-gel coating with superhydrophobic, oleophobic and self-cleaning properties. When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/3539

Low temperature hydronic heating system with radiators and geothermal ground source heat pump

Upotreba grejnog sistema s toplotnom pumpom i zemljom kao izvorom energije bez obzira na relativno nisku temperaturu raspoloživog "izvora" geotermalne energije (temperatura vode ili tla ne mora biti viša od 12°C), omogućava da se 50-80% energije potrebne za grejanje preuzme od zemlje, a da se ostatak nadomeštava električnom energijom. Ovaj udeo geotermalne energije, u ukupnoj energiji potrebnoj za grejanje, zavisi pre svega od sistema njene dalje raspodele (radijatorski sistem, sistem grejanja pomoću fancoil-a ili zidno i podno grejanje), a tek potom i od temperature vode, odnosno tla. U radu je data uporedna analiza termičke efikasnosti dva sistema centarlnog grejanja sa radijatorima kao grejnim telima, visokotemperturnog kotlovskog sistema grejanja (90°C/70°C) i niskotemperaturnog sistema sa toplotnom pumpom i zemljom kao izvorom energije (65°C/55°C, 55°C/45°C ili 50°C/45°C).The use of a system with a geothermal ground source heat pump, regardless of the relatively low temperature of the available source of geothermal energy (water or ground temperature does not need to exceed 12°C), allows 50-80% of the energy required for heating to be taken from the ground, while the remaining amount is provided by electrical energy. This share of geothermal energy, in the total energy required for heating, primarily depends on the system of its further distribution (radiator system, fan coil heating system or wall and floor heating), and secondarily on water and ground temperature. The paper deals with the comparative analysis of thermal efficiency of two water central-heating systems with radiators, a conventional high-temperature heating system with a boiler (90°C/70°C) and a low-temperature heating system with a geothermal ground source heat pump ( 65°C/55°C, 55°C/45°C or 50°C/45°C)

Phytochemical, Antioxidant and Antimicrobial Profiles of Extracts of Daphne alpina (Thymelaeaceae) L Leaf and Twig from Mt Kopaonik (Serbia)

Purpose: To investigate the phytochemical composition, as well as antioxidant and antimicrobial activities of the leaf and twig extracts of Daphne alpina L. (Thymelaeaceae).Methods: The dry chloroform and methanol extracts of the leaf and twigs of Daphne alpinа were used for analysis. Total phenolic and flavonoid contents were determined by established procedures. Antioxidant potential was investigated by several methods. The antimicrobial properties of the extracts were obtained by microdilution method. High performance liquid chromatography (HPLC) was employed for the identification of the most abundant metabolites, present in D. alpina extracts.Results: The total phenolics of the extracts ranged from 78.98 to 88.98 mg GA/g while total flavonoids were in the range 28.09 to 34.65 mg GA/g of fresh weight. HPLC analysis of the extracts showed the presence 4-hydroxybenzoic acid, 7,8-dihydroxycoumarine and 7-hydroxycoumarine. Total antioxidant capacity ranged from 69.71 μg AA/g for the methanol leaf extract to 73.55 μg AA/g for the chloroform twig extract. All the extracts showed DPPH radical scavenging activity (21.57 - 25.45 μg/mL), inhibitory activity against lipid peroxidation (26.79 - 35.24 μg/mL), ferrous ion chelating ability (21.57 - 45.45 μg/ml) and hydroxyl radical scavenging activity (87.98 - 98.86 μg/mL). Minimum inhibitory concentration (MIC) was in the range 15.62 - 125 μg/mL.Conclusion: The extracts possess moderate antioxidant and antimicrobial activities due probably to the phenolic compounds in the extracts.Keywords: Daphne alpina, Coumarines, 4-Hydroxybenzoic Acid, Phenols, Flavonoids, Antimicrobial Activity, Antioxidant Activit