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1

An Evaluation of the use of Laser-Vibration Melting to Increase the Surface Roughness of Metal Objects

Grabas B.

Archives of Metallurgy and Materials

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2015

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Vol. 60, iss. 1

33--39

EN

This paper presents preliminary, experimental results of a new, hybrid method of increasing the surface roughness of metal objects. In this new approach, metal objects are melted with a mobile laser beam while they are being rotated. A vibration generator provides circular vibrations with an amplitude of 3 mm, and the vibration plane is perpendicular to the moving laser beam. The melting tests were performed using flat carbon steel samples at a predetermined frequency of circular vibrations. The effects of laser power and laser beam scanning velocity on the melted shapes were studied. All laser melting procedures were performed at a vibration frequency of 105 Hz. The melted samples were subjected to microscopic evaluation and the Ra parameter, which characterises mean roughness, was measured using a profilometer. Melting metal samples with physically smooth surfaces (Ra = 0.21 µm) resulted in surface structures of varied roughness values, with Ra ranging from 5 µm to approximately 58 µm. The studies were undertaken to employ this technology for the purpose of passive heat exchange intensification of heating surfaces in practical applications.

PL

W artykule zaprezentowano wstępne wyniki eksperymentalne nowej hybrydowej metody zwiększania chropowatości powierzchni elementów metalowych. W metodzie tej wykorzystuje się przetapianie ruchomą wiązką laserową elementów metalowych poddanych równocześnie wibracji kołowej. Generator drgań wytwarza wibrację kołową o amplitudzie 3 mm, a płaszczyzna wibracji jest prostopadła do osi przemieszczającej się wiązki laserowej. Próbom przetapiania przy ustalonej częstotliwości wibracji kołowej poddano płaskie próbki ze stali węglowej. Badano wpływ mocy laserowej oraz prędkości skanowania wiązki laserowej na kształt przetopień. Wszystkie przetopienia laserowe wykonywano przy częstotliwości wibracji f = 105 Hz. Otrzymane przetopy poddane zostały obserwacjom mikroskopowym oraz pomiarom profilometrycznym parametru Ra charakteryzującego średnią chropowatość. W wyniku przetapiania technicznie gładkich powierzchni próbek metalowych (Ra = 0,21 µm), uzyskano struktury o zróżnicowanych chropowatościach, dla których Ra mieścił się w przedziale od ok. 5 µm do ok. 58 µm. Badania prowadzono pod kątem potencjalnych możliwości stosowania tej technologii do pasywnej intensyfikacji wymiany ciepła powierzchni płyt grzewczych.

2

Turbulent heat transfer in thin liquid films at low and high heat fluxes

Mikielewicz D., Mikielewicz J.

Journal of Theoretical and Applied Mechanics

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2007

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Vol. 45 nr 3

603-619

EN

In the paper presented are considerations of turbulent heat transfer in thin liquid films at low and high heat fluxes. Postulated have been simple models of heat transfer for laminar and turbulent liquid films formed by impinging jets and exposed to nucleate boiling, namely under high heat fluxes, as well as without nucleate boiling, at low heat fluxes, as a simplified case. Turbulence in such case is strongly modified and difficult to be modelled. Turbulence model due to Prandtl has been applied where, in the case of high heat fluxes, the mixing length is strongly modified. In the case of high heat fluxes, incorporated into the model is a blowing velocity, which models the transverse transport of momentum caused by departing bubbles. Calculated have been the velocity and temperature distributions in the liquid film, which enabled determination of the corresponding heat transfer coefficient and the Nusselt number.

PL

W pracy przedstawiono rozwiązanie turbulentnej wymiany ciepła w cienkich filmach cieczowych przy małych i dużych strumieniach ciepła. Zaproponowano proste modele wymiany ciepła dla przypadków laminarnego i turbulentnego filmu cieczowego wytworzonego uderzającą strugą w warunkach dużych i małych strumieni cieplnych. W takich przypadkach turbulencja jest silnie modyfikowana i z tego względu trudna do modelowania. W pracy zastosowano model drogi mieszania Prandtla i w przypadku dużych strumieni cieplnych droga mieszania jest szczególnie mocno zmodyfikowana. W przypadku dużych strumieni ciepła wprowadzono do modelu tzw. prędkość wzdmuchu, która modeluje wymianę pędu w kierunku poprzecznym do przepływu wywołaną odrywającymi się od ścianki pęcherzykami. Wyznaczono rozkłady prędkości i temperatury w filmie cieczowym, które umożliwiły wyliczenie współczynnika przejmowania ciepła i liczby Nusselta.

3

Modelling and analysis of stochastic and deterministic behaviors of nucleate boiling

Mosdorf R., Zapolnik L.

Archives of Thermodynamics

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2007

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Vol. 28, no. 1

33-50

EN

In the paper two kinds of numerical models of boiling have been investigated (stochastic and deterministic). The nucleate boiling on the horizontal heating surface with randomly located 100 nucleation sites has been considered. The heat fluxes absorbed from heating surface have been calculated for microlayer evaporation, natural convection and transient heat transfer. The impact of stochastic processes of activation and deactivation of nucleation sites on the dynamic properties of heating surface temperature fluctuation has been evaluated. Non-linear methods of data analysis have been applied to analysis of the heating surface temperature changes. In case of single nucleation site a significant difference between character of temperature changes at nucleation site obtained from both models under consideration has been noticed. But in case of 100 nucleation sites randomly located on the heating surface the temperature fluctuations obtained from both models are similar. Results of simulation and analyses of temperature fluctuation show that interaction of deterministic nucleation sites leads to such heating surface temperature fluctuation which is difficult to distinguish from temperature fluctuation generated by the stochastic model. Non-linear methods of data analysis such as largest Lyapunoy exponent and correlation dimension can not recognize the existence of behavior of random activation and deactivation of nucleation sites.

4

Pomiary rozkładu temparatury w żebrach z dodatkowymi pokryciami strukturalnymi

Pastuszko R., Piasecka M.

Pomiary Automatyka Kontrola

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2005

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R. 51, nr 6

27--30

PL

Omówiono wykorzystanie dwóch metod określania rozkładu temperatury dla powierzchni ożebrowanych, oddalających ciepło do wrzącej cieczy. Metoda "ruchomej termopary", umieszczonej wewnątrz żebra, pozwala na określenie zmian temperatury przy dowolnym, zadanym przesunięciu, zależnym od dokładności czujnika położenia. Bezstykowa metoda, wykorzystująca kamerę termowizyjną, umożliwia określenia pola temperatur na odizolowanej od kontaktu z wrzącą cieczą powierzchni żebra. Opisano stanowiska pomiarowe i dokonano porównań przykładowych danych eksperymentalnych z obliczeniami teoretycznymi oraz oszacowano błędy pomiarowe.

EN

The paper discusses the application of two stating temperature distribution on finned surfaces with tunnel structures (TS) and capillary porous covering (CPS), which relase heat into the boiling liquid. The method of "movable thermocouple" located inside a fin makes it possible to specify temperature changes at arbitrary, preset shift dependent on the location sensor accuracy. With the contactless method relying on IR camera, it is possible to state temperature fields on the fin surface isolated from boiling liquid, which makes reference to temperature distribution in the fin intersection. The measurement stand are described, exemplary experimental data are compared with theoretical computation and measurement errors are estimated. Exemplary results obtained with both measurement techniques are included. They require correcting calculations for measured temperatures. That would account for both qualitqtive and quantitative evaluation of temperature distribution on developed surfaces with additional structural coverings.

5

The correlation dimension of attractor reconstructed from the heating surface temperature fluctuations in boiling

Mosdorf R.

Zeszyty Naukowe Politechniki Świętokrzyskiej. Mechanika

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2003

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Z. 77

41-48

EN

In the paper the problem of onfluence of temperature measuring method on the correlation dimension of the attractor reconstructed from the temperature fluctuations has been considered. Two-dimensional heat transfer under simulated nucleation sites has been analysed. It has been shown that when the measurement of averaged volume temperature is located under many nucleation sites then the correlation dimension of the attractor reconstructed from the temperature fluctuations under a single nucleatin site. This result corresponds to experimental results.

6

Temperature field in tho-layer fins immersed in boiling water

Pastuszko R.

Transactions of the Institute of Fluid-Flow Machinery

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2003

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nr 112

103-118

EN

The steady, two-dimensional temperature field for a two-layer fin, composed of copper core and porous covering, filled with boiling water was calculated. Simplified one-dimensional model was also presented. Fin parameters were: height - 10 mm, thickness - 3 mm, porosity - 60%, capillary-porous structure (CPS) layer thickness - 0.6 mm. The modified finite difference method was described. The heat transfer coefficient was assumed to vary with a power-law-type formula. Temperature distribution in the fin vertical section was determined experimentally with a thermovision camera. A reasonable degree of congruence was found to exist between the theoretical and the experimental results.

7

Investigation of interface oscillations during boiling

Kuzma-Kichta Y., Ustinov A. K., Ustinov A. A., Kholpanov L.

Archives of Thermodynamics

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2003

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Vol. 24, no 1

17-23

EN

This paper presents experimental data and simulation of the interface oscillations of bubble growth during pool nucleate boiling. Spectra of acoustic and optical sensors signals are obtained, that show an existence of correlation between interface oscillations and pressure oscillations in liquid during pool nucleate boiling. Several results of simulation of the oscillation process are also presented. Bubble radius changes in time obtained using this model correspond to new experimental data. For the first time, attractors for the system under simulation are obtained.

8

Determination of heat flux for two-layer fins assembly

Poniewski M., Pastuszko R.

Archives of Thermodynamics

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2003

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Vol. 24, no 2

5-17

EN

The paper presents nucleate boiling on the assembly with two-layer fins, composed of a copper core and capillary-porous structure (CPS) covering. The base heat flux for the fin assembly was determined. Two methods of heat flux calculation were described. The constants C and n in the formula[ q=C>T^n ] were determined experimentally on the basis of boiling curves. General relation for heat transfer coefficient was also used to specify the heat flux. Calculated heat fluxes were compared with experimental data for samples of different porosity (47-85%), CPS thickness (0.2-0.7 mm) and fins thickness (1.5-5 mm). A reasonable degree of congruence was found to exist between presented computation models and experimental results.

9

Modelling of heating surface temperature fluctuations in nucleate boiling using two-dimensional model

Mosdorf R.

Archives of Thermodynamics

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2000

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Vol. 21, nr 1-2

29-42

EN

The heating surface temperature fluctuations during nucleate boiling in two-dimensional model have been analysed. Process of bubble generation has been modelled by changing boundary condition on the heating surface. Results of simulation show that when the heat flux absorbed by vapour bubble exceeds the critical heat flux the periodic function of changing the heating surface temperature becomes non-periodical. Calculations of largest Lyapunov exponent show that changes of heating surface temperature have a deterministic chaotic character. Results of calculation of correlation dimension indicated that an atractor created by subsequent values of heating surface temperature is low dimensional. The low dimensional atractors has been observed in experimental investigations. Results of calculations of correlation dimension and largest Lyapunov exponent allow to conclude that heat transfer between heating surface and boiling liquids is one of the processes responsible for chaos generation in boiling.

10

Simple model of spatiotemporal chaos nucleate boiling

Mosdorf R.

Zeszyty Naukowe Politechniki Świętokrzyskiej. Mechanika

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1999

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Z. 67

293--302

EN

The model presented in the paper simulates the changes of the heating surface temperature under 80 nucleate sites. Process of bubble generation has been modelled by changing of boundary condition on the heating surface. Results of simulation show that when the rate of heat flux absorbed by vapour bubble exceeds a critical rate the phenomenon of spatiotemporal chaos is observed. Calculations of largest Lyapunov exponent show that changes of heating surface temperature have deterministic chaos character. Calculations of correlation dimension show that an atractor created by subsequent values of heating surface temperature has correlation dimension equal to D2≈3,5.