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1
Content available Pool boiling for water on surfaces with inclined microchannel
Kaniowski Robert
Archives of Thermodynamics
|
2024
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Vol. 45, no 2
41--49
EN
The heat transfer measurements were conducted during pool boiling of water on surfaces with microchannels. Parallel grooves were made on a copper surface with widths ranging from 0.2 mm to 0.5 mm at intervals of 0.1 mm. The inclination angle of the grooves to the horizontal was set at 30° and 60°, and the depth of the microchannel grooves was 0.3 mm. The achieved heat flux ranged from 25 kW/m² to 1730 kW/m², and the heat transfer coefficients ranged from 12 kW/(m²K) to 475 kW/(m²K). The influence of geometric parameters such as width, inclination angle of the microchannel, surface extension, and Bond number on heat exchange efficiency was examined. A nearly sixfold increase in α (heat transfer coefficient) and a twofold increase in critical heat flux were observed compared to a smooth surface.
2
Content available Subatmospheric pool boiling of water at very low liquid levels
Hałon Tomasz, Kaczmarek Dominika, Lada Wiktoria, Zajączkowski Bartosz
Archives of Thermodynamics
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2023
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Vol. 44, no 4
447--461
EN
The paper discusses how the vapour bubbles growing during boiling under the near-triple point pressure influence the heat transfer coefficient when the refrigerant level is lower than the bubble departure diameter. The experiments were carried out for liquid levels of 0.57 to 1.89 cm, saturated pressure range between 0.9 and 4 kPa (saturation temperatures between 5.5 and 29◦C). Boiling occurred on a plain surface with wall heat flux densities between 0.43 and 5.93 Wcm−2. We determined boiling curves for the low-pressure process and analyzed the changes in wall superheat for different filling levels. The experimentally obtained heat transfer coefficient (HTC) was compared with the theoretical values produced by the most popular mathematical expressions used at higher pressures. We also prepared the boiling map, where we specified two boiling regimes: the regime of convection or small popping bubbles and the regime of isolated bubbles. The results indicate that the level of liquid can be neglected within the heat flux range analyzed in this study. The main mechanism of heat transfer under measured conditions is heat convection and conduction, rather than evaporation. The experimentally determined difference between the heat transfer coefficients for different levels of liquid is under 100 Wm−2K−1 (for the same heat flux and pressure at the wall).
3
Content available Comparison of pool boiling heat transfer coefficients for surfaces with open microchannels of variable and constant depths
Bedla-Pawlusek Milena, Pastuszko Robert, Kaniowski Robert
Journal of Machine Construction and Maintenance - Problemy Eksploatacji
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2019
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no. 1
59--67
EN
Experimental studies of pool boiling heat transfer on open microchannels of variable and constant depth were conducted. Microchannels of variable depth from 0.05 to 2.8 mm and a width from 0.2 and 0.5 mm were uniformly spaced on base surfaces with a pitch of 0.4 and 1.0 mm. Reference surfaces with microchannels with a constant depth were 0.2 or 0.4 mm wide and 0.2 or 0.5 mm deep. The experiment was conducted for three liquids, i.e. water, ethanol, and Novec-649, at atmospheric pressure. A comparison of heat transfer coefficients (HTCs) for surfaces with microchannels of constant and variable depths was made. The highest values of the heat transfer coefficient for boiling water were obtained for microchannels with a constant depth at heat flux above 350 kW/m2 . At the boiling of ethanol, the highest HTCs were achieved at a heat flux above 150 kW/m2 for narrow microchannels with variable depths. A high speed camera and photo camera were used to record images of the entire sample surface. Visualization investigations were aimed at identifying nucleation sites and determining the bubble growth cycle.
PL
Przeprowadzono eksperymentalne badania wymiany ciepła przy wrzeniu w mikrokanałach o zmiennej i stałej głębokości. Mikrokanały o zmiennej głębokości od 0,05 do 2,8 mm i szerokości 0,2 i 0,5 mm były równomiernie rozmieszczone na powierzchni podstawy z podziałką 0,4 i 1 mm. Powierzchnie referencyjne wykonano w postaci mikrokanałów o stałej głębokości 0,2 lub 0,5 mm oraz szerokości 0,2 lub 0,4 mm. Eksperyment był prowadzony dla następujących czynników wrzących: wody, etanolu i Novec-649, będących pod ciśnieniem atmosferycznym. Najwyższe wartości współczynnika przejmowania ciepła podczas wrzenia wody uzyskano dla mikrokanałów o stałej głębokości przy gęstości strumienia ciepła powyżej 350 kW/m2 , natomiast przy wrzeniu etanolu najwyższe wartości współczynnika przejmowania osiągnięto przy zastosowaniu wąskich mikrokanałów o zmiennej głębokości, dla gęstości strumienia ciepła powyżej 150 kW/m2 . Do zarejestrowania obrazów na całej powierzchni próbki użyto kamery o wysokiej prędkości i aparatu cyfrowego. Badania wizualizacyjne miały na celu zarejestrowanie obrazów miejsc tworzenia, wzrostu i oderwania się pęcherzyków.
4
Content available Numerical investigation of pool nucleate boiling in nanofluid with lattice Boltzmann method
Rostamzadeh A., Jafarpur K., Rad E. G.
Journal of Theoretical and Applied Mechanics
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2016
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Vol. 54 nr 3
811--825
EN
Due to significant improvement of thermal performance and other properties of nanofluids, this group of liquids is in high demand. According to the literature, the effect of nanoparticles on boiling heat transfer enhancement or degradation is not the same among different investigations. In the present article, the pseudo-potential multiphase lattice Boltzmann method is used to simulate nucleate pool boiling with two different fluids: a pure liquid and a nanofluid. The current results indicate that the contact angle is the same for both the fluid and nanofluid when the vapor bubble detachment occurs. Also, bubble departure diameter is greater in the base liquid while bubble release frequency is higher in the nanofluid. In brief, the present results demonstrate that using a nanofluid instead of its base fluid will increase the boiling heat transfer coefficient.
5
Content available Study of heat transfer during pool boiling on minifins surface coated with carbon nanotubes
Strąk E., Pastuszko R., Kłosowiak R., Urbaniak R.
Transactions of the Institute of Fluid-Flow Machinery
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2015
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nr 128
59--72
EN
The article describes the study of heat transfer during pool boiling on minifins surface coated with nanostructure. This is a molecular level technology used in engineering or mechanical factory. A surface with carbon nanotubes (CNTs) is highly effective in reducing the superheat incipience and enhancing both the heat flux and heat transfer coefficient. The paper focuses on the comparison of the surfaces, on which pool boiling heat transfer occurs, i.e., on minifins coated with carbon nanotubes (MF+N) with surfaces formed by sintering the woven copper wire mesh to the minifins tips (MF+M) and with plain minifins surface (MF). The experiments were carried out for two boiling fluids: water and ethyl alcohol. The purpose of the presented study was to find out which of those tested surfaces and fluids could be the best alternative for use in the cooling of electronic devices and which surfaces could be used as thermosyphon or heat pipe evaporator.
6
Content available Pool boiling of nanofluids on rough and porous coated tubes: experimental and correlation
Cieśliński J. T., Kaczmarczyk T. Z.
Archives of Thermodynamics
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2014
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Vol. 35, no. 2
3--20
EN
The paper deals with pool boiling of water-Al2O3 and water-Cu nanofluids on rough and porous coated horizontal tubes. Commercially available stainless steel tubes having 10 mm outside diameter and 0.6 mm wall thickness were used to fabricate the test heater. The tube surface was roughed with emery paper 360 or polished with abrasive compound. Aluminium porous coatings of 0.15 mm thick with porosity of about 40% were produced by plasma spraying. The experiments were conducted under different absolute operating pressures, i.e., 200, 100, and 10 kPa. Nanoparticles were tested at the concentration of 0.01, 0.1, and 1% by weight. Ultrasonic vibration was used in order to stabilize the dispersion of the nanoparticles. It was observed that independent of operating pressure and roughness of the stainless steel tubes addition of even small amount of nanoparticles augments heat transfer in comparison to boiling of distilled water. Contrary to rough tubes boiling heat transfer coefficient of tested nanofluids on porous coated tubes was lower compared to that for distilled water while boiling on porous coated tubes. A correlation equation for prediction of the average heat transfer coefficient during boiling of nanofluids on smooth, rough and porous coated tubes is proposed. The correlation includes all tested variables in dimensionless form and is valid for low heat flux, i.e., below 100 kW/m2.
7
Content available Enhancement of the pool boiling heat transfer coefficient using the gas injection into the water
Sarafraz M.M., Peyghambarzadeh S.M., Alavi Fazel S.A.
Polish Journal of Chemical Technology
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2012
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Vol. 14, nr 4
100-109
EN
In this paper, a new method for enhancing the pool boiling heat transfer coefficient of pure liquid, based on the gas injection through the liquids has been introduced. Hence, the effect of gas dissolved in a stagnant liquid on pool boiling heat transfer coefficient, nucleation site density, and bubble departure diameter has experimentally been investigated for different mole fractions of SO2 and various heat fluxes up to 114 kW/ m2. The presence of SO2 in captured vapor inside the bubbles, particularly around the heat transfer surface increases the pool boiling heat transfer coefficient. The available predicted correlations are unable to obtain the reasonable values for pool boiling heat transfer coefficient in this particular case. Therefore, to predict the pool boiling heat transfer coefficient accurately, a new modified correlation based on Stephan-Körner relation has been proposed. Also, during the experiments, it is found that nucleation site density is a strictly exponential function of heat flux. Accordingly, a new correlation has been obtained to predict the nucleation site density. The major application of the nucleation site density is in the estimating of mean bubble diameters as well as local agitation due to the rate of bubble frequency.
8
Content available The effect of pressure on heat transfer during pool boiling of water-A1[2]0[3] and water-Cu nanofluids on stainless steel smooth tube
Cieślinski J.T., Kaczmarczyk T.Z.
Chemical and Process Engineering
|
2011
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Vol. 32, nr 4
321-332
EN
Experimental investigation of heat transfer during pool boiling of two nanofluids, i.e. water-Al203 and water-Cu has been carried out. Nanoparticles were tested at the concentration of 0.01%, 0.1%, and 1% by weight. The horizontal smooth stainless steel tubes having 10 mm OD and 0.6 mm wall thickness formed the test heater. The experiments have been performed to establish the influence of nanofluids concentration on heat transfer characteristics during boiling at different absolute operating pressure values, i.e. 200 kPa, ca. 100 kPa (atmospheric pressure) and 10 kPa. It was established that independent of nanoparticle materials (A1203 and Cu) and their concentration, an increase of operating pressure enhances heat transfer. Generally, independent of operating pressure, sub- and atmospheric pressure, and overpressure, an increase of nanoparticle concentration caused heat transfer augmentation.
9
Content available Fenomenologiczna ocena tworzenia się struktur wodno-olejowych podczas wrzenia w objętości
Troniewski L., Filipczak G., Witczak S.
Inżynieria i Aparatura Chemiczna
|
2009
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Nr 6
188-189
PL
W pracy przedstawiono wyniki badań i analiz dotyczących warunków wnikania ciepła podczas wrzenia mieszaniny cieczy wzajemnie nierozpuszczalnych. Eksperymenty przeprowadzono w dużej objętości i pod ciśnieniem atmosferycznym, wykorzystując jako czynniki robocze wodę oraz oleje o różnych właściwościach. Scharakteryzowano warunki wnikania ciepła przy różnej zawartości obu składników mieszaniny.
EN
Experimental results of heat transfer during pool boiling of two immiscible liquids are presented. The experiments were carried out under atmospheric pressure. Water and various oil mixtures were used as working liquids. The conditions of heat transfer for a different content of both liquids in the mixture were characterized.
10
Content available remote Study of pool boiling and critical beat flux enhancement in nanofluids
Kim S.J., Bang I.C., Buongiorno J., Hu L.W.
Bulletin of the Polish Academy of Sciences. Technical Sciences
|
2007
|
Vol. 55, nr 2
211-216
EN
The pool boiling characteristics of dilute dispersions of alumina, zirconia and silica nanoparticles in water were studied. These dispersions are known as nanofluids. Consistently with other nanofluid studies, it was found that a significant en-hancement in Critical Heat Flux (CHF) can be achieved at modest nanoparticle concentrations ( <0.1% by volume). Buildup of a porous layer of nanoparticles on the heater surface occurred during nucleate boiling. This layer significantly improves the surface wettability, as shown by a reduction of the static contact angle on the nanofluid-boiled surfaces compared with the pure-water-boiled surfaces. CHF theories support the nexus between CHF enhancement and surface wettability changes. This represents a first important step towards identification of a plausible mechanism for boiling CHF enhancement in nanofluids.
11
Content available remote Formation of bubbles from a single nucleation site
Cieśliński J., Polewski J., Szymczyk J.
Archives of Thermodynamics
|
2002
|
Vol. 23, no 3
59-77
EN
A systematic study on nucleate pool boiling from single artificial nucleation site to saturated, distilled water and methanol under atmospheric pressure is reported. Electrically heated sections have been employed to produce vapour bubbles. The cavities were drilled on a flat end of the copper rod. The diameter of the cavities was 0.25 mm and 1.0 mm, and the depth was approximately 0.40 mm and 1.6 mm, respectively. Laser-photodiode system coupled with a digital oscilloscope or a PC-audio card has been utilised for measurement of release frequency. An exposure technique for measurement of bubble size has been developed. The images of the bubbles were recorded with a CCD video camera and analysed using a commercial software.
12
An approach to modelling nucleate pool boiling heat transfer from horizontal tubes at low heat flux density
Cieśliński J. T., Dominczak P. R.
Zeszyty Naukowe Politechniki Świętokrzyskiej. Mechanika
|
1999
|
Z. 67
195--204
EN
An experiment on nucleate pool boiling heat transfer from horizontal cylinders to saturated, distilled water under atmospheric pressure is reported. Experiments of nucleate pool boiling were conducted using stainless steel tubes with OD: 8.15 mm and 18.04 mm and active length about 250 mm. In particular, measurements have been performed of inside circumferential temperature. Three component model of nucleate pool boiling outside horizontal tube has been proposed. The proposed mechanisms of heat transfer that have contribution in total heat flux are: free convection, evaporation to sliding bubbles and nucleate boiling.
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