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1

Pool boiling for water on surfaces with inclined microchannel

Kaniowski Robert

Archives of Thermodynamics

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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

Survey on the nucleate pool boiling of hydrogen and its limits

Baki Touhami

Journal of Mechanical and Energy Engineering

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2020

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Vol. 4, No 2

157--166

EN

Nucleate pool boiling is a very efficient transfer regime with low temperature gradients, bounded between two heat flux values and which border transitions to other regimes, this phenomenon is well framed with correlations. Our study aims to clarify the applicability of this regime to liquid hydrogen and to develop reliable correlations for a useful and qualitative agreement. An exhaustive review on the nucleate pool boiling of hydrogen and the limits of this regime, whether are the onset nucleate boiling (ONB) and the critical heat flux (CHF) was made, allowing the collection of more than 1400 points from experimental setups, highlighting a variety of parameters. Five predictive correlations were drawn from the literature, graphical and statistical comparisons were made, two in five reveal acceptable results. After analysis of the experimental data, new correlations were developed and compared with the data collected, convincing results were obtained and discussed. A simple form was expressed for the heat flux (...), shows better predicted values; convincing results of the (CHF) have been found on modified correlation, and the CHF value reaches a maximum of 148×103 W/m² for a reduced pressure at 0.35. A nucleate boiling correlation suitable for hydrogen has been developed.

3

Experimental investigation and characteristics of multiwalled carbon nanotube aqua nanofluids from a flat plate heater surface in a pool

Vasudevan D., Senthil Kumar D., Murugesan A., Vijayakumar C.

Bulletin of the Polish Academy of Sciences. Technical Sciences

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2020

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Vol. 68, nr 3

547--554

EN

In this experimental investigation, the critical heat flux (CHF) of aqua-based multiwalled carbon nanotube (MWCNT) nanofluids at three different volumetric concentrations 0.2%, 0.6%, and 0.8% were prepared, and the test results were compared with deionized water. Different characterization techniques, including X-ray diffraction, scanning electron microscopy and Fourier transform infrared, were used to estimate the size, surface morphology, agglomeration size and chemical nature of MWCNT. The thermal conductivity and viscosity of the MWCNT at three different volumetric concentrations was measured at a different temperature, and results were compared with deionized water. Although, MWCNT-deionized water nanofluid showed superior performance in heat transfer coefficient as compared to the base fluid. However, the results proved that the critical heat flux is increased with an increase in concentrations of nanofluids.

4

Method of high heat flux removal by usage of liquid spray cooling

Smakulski P.

Archives of Thermodynamics

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2013

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Vol. 34, no. 3

173--184

EN

High heat flux removal are important issue in many perspective applications such as computer chips, laser diode arrays, or boilers working on supercritical parameters. Electronic microchips constructed nowadays are model example of high heat flux removal, where the cooling system have to maintain the temperature below 358 K and take heat flux up to 300 W/cm2. One of the most efficient methods of microchips cooling turns out to be the spray cooling method. Review of installations has been accomplished for removal at high heat flux with liquid sprays. In the article are shown high flux removal characteristic and dependences, boiling critical parameters, as also the numerical method of spray cooling analysis.

5

Flow controlled critical heat flux: developments in annular flow modelling

Azzopardi B.

Archives of Thermodynamics

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2006

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Vol. 27, no. 2

3-22

EN

Critical heat flux at higher steam qualities is accepted to correspond to the dry out of the wall film in the annular flow pattern where the film is depleted by evaporation and entrainment of liquid into drops and augmented by redeposition of drops. Since the first complete model for annular flow there have been many developments in the understanding and modelling of these flows, which are reviewed here. Latest developments on the rates of entrainment and deposition are described as well as the application of the model to multicomponent mixtures. Another area that has received attention is the start of annular flow and the boundary with churn flow. Applications for more complex geometies, namely annuli, rod bundles, horizontal pipes, Venturis and to the serpentine tubing of fired heaters have been developed and are presented.

6

The Influence of Flame Retardant on the Ignitability of Wood Determined by Cone Calorimeter Method

Helwig M., Wolański P.

Archivum Combustionis

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2002

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Vol. 22 nr 3-4

173-186

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On the mechanistic modeling of forced-convection low-quality boiling

Podowski M. Z.

Zeszyty Naukowe Politechniki Świętokrzyskiej. Mechanika

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1999

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Z. 67

97--111

EN

Practical applications of forced-convection boiling encompass a wide spectrum of industrial systems, including but not limited to, thermal energy generation systems, because of the complexity of phenomena governing boiling heat transfer in general, and subcooled boiling in particular, a commonly used approach to both fundamental and practical problems has traditionally been based on experimental correlations rather than mechanistic models. The recent progress in computational fluid dynamics (CFD), combined with improved experimental techniques in two-phase flow and heat transfer, makes the use of rigorous physically-based models a realistic alternative to the simplistic phenomenological approach which dominated the field in the past. The objective of this paper is to discuss some of the recent accomplishments in the mechanistic modeling of forced-convection low-quality boiling, including both the nucleate boiling regime and the mechanisms governing the departure from nucleate boiling (critical heat flux - CHF).