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1
Content available remote Operation of pumps in a district heating system supplying a distant major industrial user
Poniewski M., Salij A., Stępień J. C.
Journal of Power Technologies
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2015
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Vol. 95, spec.
68--74
EN
Water pump control methods are presented for the district heating system supplying an industrial heat user. The analysis aimed at determining optimum operating conditions for the system of pumps. The study focused on control parameters of the pumps installed at the heating substation delivering the heated water to the end-user. The chosen method consisted of throttling control of the pump using a control valve in the discharge header. The values of characteristic parameters and control characteristics of the pumps were used to evaluate the performance of the said pump system.
2
Content available Measurements of two-phase flow patterns and local void fraction in vertical rectangular minichannel
Kaniowski R., Poniewski M.
Archives of Thermodynamics
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2013
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Vol. 34, no. 2
3--21
EN
Technology advancements entail a necessity to remove huge amounts of heat produced by today’s electronic devices based on highly integrated circuits, major generators of heat. Heat transfer to boiling liquid flowing through narrow minichannels is a modern solution to the problem of heat transfer enhancement. The study was conducted for FC-72 boiling in a rectangular, vertical and asymmetrically heated minichannel that had depths of 0.5–1.5 mm, a width of 20 mm and a length of 360 mm. The heat flux increased and decreased within the range of 58.3–132.0 kWm-2, the absolute pressure ranged from 0.116 to 0.184 MPa and the mass flux was 185–1139.2 kgm-2s-1. The boiling process took place on a flat vertical heating surface made of Haynes-230 0.1 mm thick acid-proof rolled plate with the surface roughness of 121 μm.
3
Technologia wytwarzania i zastosowania spiekanych proszkowych struktur porowatych
Wójcik T. M., Poniewski M., Dziadoń A., Depczyński W.
Zeszyty Naukowe Politechniki Świętokrzyskiej. Nauki Techniczne
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2008
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Z. 11
321--328
PL
W Politechnice Świętokrzyskiej podjęto prace nad wytworzeniem nowych pokryć porowatych powierzchni grzejnych. Założono, że w wyniku spiekania w atmosferze zdysocjowanego amoniaku proszku miedzi z dodakiem proszku tlenku miedzi powstaną pory pochodzenia dyfuzyjnego, co powinno doprowadzić do rozwinięcia powierzchni wewnątrz struktury i zapewnić dodatkowe ośrodki nukleacji. Podstawowa technologią wytwarzania struktur jest spiekanie proszków miedzianych proszkiem tlenku miedzi o rożnej wielkości cząstek. Drugą proponowaną technologią jest nakładanie pokryć metodą elektrolityczną. Przedstawiono wyniki badań metalograficznych i wpływu parametrów strukturalnych tak wytworzonych pokryć na wymianę ciepła przy wrzeniu. Dla struktury spiekanej uzyskano znaczną intensyfikację wymiany ciepła przy wrzeniu.
EN
In the paper the authors present the results of studies of boiling heat transfer on sintered and galv-ted, porous structures. It was assumed that hydrogen atmosphere sintering of copper powder with an ition of cuprous oxide powder will result in the formation of diffusive pores, which should lead to Irface extension inside the structure and a generation of new nuclcation sites. Sintering of copper powders with different amounts of copper oxide added to them is the basic technology for structure (eneration. Electrolytic deposition is another proposed technology. The paper discusses results of metallographic analysis the effect of prepared covering structural parameters on boiling heat transfer. Significant intensification of boiling heat transfer coefficient (11 x) was obtained for the sintered structure.
4
Wpływ parametrów powierzchni tunelowej na wymianę ciepła przy wrzeniu pęcherzykowym
Kozioł M., Pastuszko R., Poniewski M.
Inżynieria i Aparatura Chemiczna
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2006
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Nr 6s
126-127
EN
The paper deals with the experimental study of nucleate pool boiling heat transfer on tunnel surfaces. The experiments were carried out at atmospheric pressure for the R-123. The influence of foil pores diameter on boiling heat flux was defined.
5
Content available remote The onset of refrigerant R-123 flow boiling in a narrow vertical channel
Piasecka M., Poniewski M.
Archives of Thermodynamics
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2003
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Vol. 24, no 2
19-35
EN
The interest area covered the issues of heat transfer to the subcooled working fluid (refrigerant R-123) flowing upward through a narrow rectangular channel (1 x 40 x 360 mm), vertically oriented with one wall heated uniformly and others approximately adiabatic. Liquid crystals thermography was applied to determine two-dimensional temperature distribution on the heating surface. The current study concentrated on heat transfer transition phenomenon during laminar flow, from single phase convection, to boiling incipience and further, to fully developed nucleate boiling. Particular attention was paid to boiling incipience coditions. Experimental investigations were meant to specify the location of the "boiling front", which demonstrated that the phenomenon callud "nucleation hysteresis" or "zero boiling crisis" took place when the boiling incipience occurred. Observations of the hysteresis phenomena, including the impact of various factors (the liquid subcooling at inflow, flow velocity and pressure) on the incipience boiling in narrow channels were also presented. Results are shown in the form of boiling curves plotted for selected points in the channel where heat flux density depends on the heating surface superheating T[w]-T[sat]. The shapes of the curves, in which "nucleation hysteresis" or "zero boiling crisis" are visible, were analysed. The correlation concerning the determination of heat transfer coefficient for refrigerant R-123 boiling incipience in a narrow vertical channel was put forward.
6
Content available remote Determination of local flow boiling heat transfer coefficient in narrow channel
Piasecka M., Poniewski M., Hożejowska S.
Archives of Thermodynamics
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2003
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Vol. 24, no 2
55-67
EN
In the paper two models of heat transfer through the main parts of the test section with a narrow channel, were proposed and discussed: one- and two-dimensional. The area of interest was the issue of heat transfer into refrigerant 123 flowing through a narrow vertical channel of 1 mm height with one wall heated uniformly and others approximately adiabatic. Experimental investigations dealt with forced convection and particular attention was paid to boiling incipience conditions and hysteresis phenomena. Thermosensivite liquid crystals were used for measuring the two-dimensional temperature distribution on the heating surface. An inverse problem was dealt with as, on the basis of temperature measurement on external side of the heating and the measurement of the electric power supplied to the heater, it is possible to determine local heat transfer coefficients on the surface: the heating foil - the boiling fluid flowing along the narrow channel. The resultant local heat transfer coefficients obtained for two models were compared.
7
Content available remote 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.
8
Content available remote Probabilistic model of boiling heat transfer in thin-layer porous structures
Poniewski M., Wiśniewski M., Wójcik T.
Archives of Thermodynamics
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2000
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Vol. 21, nr 3-4
55-73
EN
There were presented the results of theoretical analysis of boiling heat transfer on heating surfaces covered with thin-layered capillary porous structures. Heat transfer probabilistic model was proposed. It was then compared with experimental results of II type hysteresis. The results of investigations and modeling were obtained for metal, fibrous structures with non-homogeneous distribution of the porous layer cell dimensions. II type hysteresis, termed by the authors "controlled hysteresis", could be applied to surface temperature adjustment.
9
Fractal analysis in two phase flow
Mosdorf R., Poniewski M., Ulbrich R.
Zeszyty Naukowe Politechniki Świętokrzyskiej. Mechanika
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1999
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Z. 67
303--312
EN
The paper presents principles of fractal analysis of measurement signals. The application of such indicators as autocorrelation function. Hurst exponent, the largest Lapunow exponent, correlation dimension. Kołmogorow entropy for the measuring signal analysis are discussed. The fractal analysis of experimental data was used to analyse the results of registration of local changes of gas void fraction in the flow of water-air mixture crosswise to the tube bundle in the shell-side space. The occurrence of low dimensional attractors of correlation dimensions close to D2=1.1 and D2=3.9 was found.
10
Content available remote Experimental investigation of boiling heat transfer hystersis on metal fibrous porous coverings
Poniewski M., Wójcik T.
Archives of Thermodynamics
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1999
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Vol. 20, no 1/2
93-118
EN
Knowledge of thermal characteristics of capillary-porous structures is indispensable for designing and constructing of heat exchangers based on the concept of a heat pipe. The paper presents the results of experimental research in boiling on heating surfaces covered with copper fibrous porous layers that provide a filling for heat pipes. The results of the research pertain to the structures with randam pore size distribution. The research was carried out for pool boiling of distilled water, ethanol and freon-113 for layers with porosity of 40, 70 and 85%. A significant enhancement of heat transfer in comparison to a smooth surface was noted. The heat transfer coefficient and the maximum heat flux depend on the structural parameters of the covering.The boiling curve was determined by increasing and decreasing the heat flux, which for certain sets of structural parameters of the coverings and the physical properties of liquid induce heat transfer hysteresis. Two different types of hysteresis were observed. For For a relatively thick coberings, the hysteresis is characterized by a decrease of the heat transfer coefficient after the flux is reduced (appering after the maximum flux is reached). The second type of hysteresis is characterized by an increase of the heat transfer coefficient when the flux is lowered to below its maximum value. The physical basis of the phenomenon of hysteresis was presented in consideraration of new factors characterizing the mechanism of boiling on a porous covering (intralayer crisis, gradual pore activation, delayed activation of cells within the structure). For the zones of the boiling curve without hysteresis, the experimental results were developed in a form of a correlation for the Nusselt number.
11
Modelowanie wymiany ciepła przy wrzeniu cienkowarstwowych strukturach porowatych
Poniewski M., Wiśniewski M., Wójcik T.M.
Prace Naukowe Instytutu Techniki Cieplnej i Mechaniki Płynów Politechniki Wrocławskiej. Konferencje
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1998
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Vol. 53, nr 9
737-744
PL
Przedstawiono wyniki badań eksperymentalnych i analizy teoretycznej wymiany ciepła przy wrzeniu na powierzchniach grzejnych pokrytych cienkowarstwowymi strukturami kapilarno-porowatymi. Krzywe wrzenia wyznaczano zwiększając i zmniejszając strumień ciepła, co pozwoliło na ujawnienie zjawiska histerezy. Rezultaty badań dotyczą struktury z niejednorodnym rozkładem rozmiarów komórek warstwy porowatej. Przedstawiono probabilistyczny model wymiany ciepła z wynikami obliczeń dla pokryć, dla których występuje histereza II rodzaju.
EN
Results of experimental investigations and theoretical analysis of boiling heat transfer on heating surfaces covered with thin layered capillary porous structures are presented. The boiling curves were determined while increasing and decreasing the heat flux. It allowed revealing the hysteresis phenomena. The results of investigations refer to the structures with stochastic distribution of dimension of cells inside the porous structure. The probabilistic model of boiling hear transfer and results of calculation are presented for the coverings revealing the II kind hysteresis.
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