Effect of the surface texture on the heat transfer coefficient in nucleate boiling of aqueous lithium bromide solution at low heat fluxes

2015 ◽  
Vol 21 (3) ◽  
pp. 258-266
Author(s):  
Florian Menhart ◽  
Manuel Riepl ◽  
Stefan Natzer
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Surface Texture ◽  
Lithium Bromide ◽  
Nucleate Boiling ◽  
Heat Fluxes ◽  
Bromide Solution ◽  
Lithium Bromide Solution ◽  
Aqueous Lithium Bromide ◽  
The Heat Transfer Coefficient

scholarly journals Experimental Study of Nucleate Boiling of Flammable, Environmentally Friendly Refrigerants

Energies ◽  
2019 ◽  
Vol 13 (1) ◽  
pp. 160 ◽  
Author(s):  
Bartosz Gil ◽  
Beata Fijałkowska
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Nucleate Boiling ◽  
Heat Fluxes ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
New Correlation ◽  
Boiling Process ◽  
The Heat Transfer Coefficient

This paper investigates the nucleate boiling process of dimethyl ether and selected hydrocarbons. The main goal of this study is to measure the heat transfer coefficients of RE170, R600a, and R601, and to compare them with R134a. The experiments were carried out for heat fluxes up to 70 kW/m2. Experimental results have shown a typical trend that the heat transfer coefficient of flammable refrigerants increases as the heat flux increases. Among the tested fluids, the highest values of heat transfer coefficient were obtained for RE170. Available correlations describing this coefficient showed a deviation of up to 93%, as compared to the data obtained. The new correlation was developed by regression analysis taking into account dimensionless variables affecting the boiling process.

Heat Transfer Mechanisms of Propane Boiling on Horizontal Steel Tubes With Smooth and Enhanced Surfaces

2010 ◽  
Author(s):  
A. Luke ◽  
Bjo¨rn C. F. Mu¨ller
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Mild Steel ◽  
Transfer Coefficient ◽  
Steel Surface ◽  
Bubble Formation ◽  
Nucleate Boiling ◽  
Heat Fluxes ◽  
Mild Steel Surface ◽  
The Heat Transfer Coefficient

The trend towards a better understanding of the fundamentals of nucleate boiling in re-entrant cavities is supported by the variation of the heating surface’s characteristics and the identification of parameters influencing the heat transfer at enhanced tubes. The optimized surface of enhanced evaporator tubes supports the bubble formation by providing stable nucleation sites, which are cavities that trapped the necessary amount of vapor to generate the next bubble. The optimal size of the cavities for bubble formation depends on various thermodynamic properties of the fluid and the wall material. The knowledge of these physical mechanisms is important for the further optimization. The influence of micro- and macrostructures on the overall heat transfer coefficient is investigated with the refrigerant R134a and the hydrocarbon propane (R290) boiling in a wide range of reduced pressures (p* = ps/pc = 0.03 to 0.5) and heat fluxes (0.05 to 100 kW/m2). The measurements are carried out using a standard apparatus and a horizontally positioned, electrically heated surface with various wall materials. Two different materials — copper and mild steel — with the same surface preparation by polishing are investigated. Furthermore, heat transfer measurements are carried out on a plain mild steel tube and on an industrially manufactured surface of the GEWA-PB type. The polished surfaces demonstrate a deterministic microstructure, the roughness parameters depends strongly on the measurement direction. The heat transfer coefficient as function of the heat flux of the polished copper tube can be described by the correlation of the VDI Heat Atlas, while the mild steel surface differ from former investigations due to the deep re-entrant cavities remaining from the drawn surface. The onset of boiling is nearly the same of both materials because of these cavities on the mild steel surface. As presented in the recent years, the heat transfer of nucleate boiling at tubes with subsurface channels can be divided into different domains, each influenced by different parameters like wettability, the product of vapor density and evaporation enthalpy. The identification of parameters influencing the bubble formation is done by heat transfer measurements, high-speed-video recording and photographic documentation. The experimental results of this work are compared to results of the polished surfaces. The heat transfer coefficient increases drastically for the enhanced tube, especially for beginning nucleation. The same α-q-relationship as on plain tubes is observed for higher pressures and heat fluxes but for three times higher values of the heat transfer coefficient α.

scholarly journals Systematic heat transfer measurements in highly viscous binary fluids

2021 ◽  
Author(s):  
Ann-Christin Fleer ◽  
Markus Richter ◽  
Roland Span
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Volatile Component ◽  
Test Tube ◽  
Heat Fluxes ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Low Viscosity ◽  
The Heat Transfer Coefficient

AbstractInvestigations of flow boiling in highly viscous fluids show that heat transfer mechanisms in such fluids are different from those in fluids of low viscosity like refrigerants or water. To gain a better understanding, a modified standard apparatus was developed; it was specifically designed for fluids of high viscosity up to 1000 Pa∙s and enables heat transfer measurements with a single horizontal test tube over a wide range of heat fluxes. Here, we present measurements of the heat transfer coefficient at pool boiling conditions in highly viscous binary mixtures of three different polydimethylsiloxanes (PDMS) and n-pentane, which is the volatile component in the mixture. Systematic measurements were carried out to investigate pool boiling in mixtures with a focus on the temperature, the viscosity of the non-volatile component and the fraction of the volatile component on the heat transfer coefficient. Furthermore, copper test tubes with polished and sanded surfaces were used to evaluate the influence of the surface structure on the heat transfer coefficient. The results show that viscosity and composition of the mixture have the strongest effect on the heat transfer coefficient in highly viscous mixtures, whereby the viscosity of the mixture depends on the base viscosity of the used PDMS, on the concentration of n-pentane in the mixture, and on the temperature. For nucleate boiling, the influence of the surface structure of the test tube is less pronounced than observed in boiling experiments with pure fluids of low viscosity, but the relative enhancement of the heat transfer coefficient is still significant. In particular for mixtures with high concentrations of the volatile component and at high pool temperature, heat transfer coefficients increase with heat flux until they reach a maximum. At further increased heat fluxes the heat transfer coefficients decrease again. Observed temperature differences between heating surface and pool are much larger than for boiling fluids with low viscosity. Temperature differences up to 137 K (for a mixture containing 5% n-pentane by mass at a heat flux of 13.6 kW/m2) were measured.

Effect of Open Micro-Channels on External Condensation Heat Transfer

2016 ◽  
Author(s):  
Brandon Hulet ◽  
Andres Martinez ◽  
Melanie Derby ◽  
Amy Rachel Betz
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Film Thickness ◽  
Transfer Coefficient ◽  
Heat Fluxes ◽  
Condensation Heat Transfer ◽  
Dropwise Condensation ◽  
Micro Channels ◽  
Lower Heat ◽  
The Heat Transfer Coefficient

This research experimentally investigates the heat transfer performance of open-micro channels under filmwise condensation conditions. Filmwise condensation is an important factor in the design of steam condensers used in thermoelectric power generation, desalination, and other industrial applications. Filmwise condensation averages five times lower heat transfer coefficients than those present in dropwise condensation, and filmwise condensation is the dominant condensation regime in the steam condensers due to a lack of a durable dropwise condensation surface. Film thickness is also of concern because it is directly proportional to the condenser’s overall thermal resistance. This research focuses on optimizing the channel size to inhibit the creation of a water film and/or to reduce its overall thickness in order to maximize the heat transfer coefficient of the surface. Condensation heat transfer was measured in three square channels and a plane surface as a control. The sizes of the square fins were 0.25 mm; 0.5 mm; and 1 mm, and tests were done at a constant pressure of 6.2 kPa. At lower heat fluxes, the 0.25mm fins perform better, whereas at larger heat fluxes a smooth surface offers better performance. At lower heat fluxes, droplets are swept away by gravity before the channels are flooded. Whereas, at higher heat fluxes, the channels are flooded increasing the total film thickness, thereby reducing the heat transfer coefficient.

Preparation of cellulose-chitosan foams using an aqueous lithium bromide solution and their adsorption ability for Congo red

Cellulose ◽  
2018 ◽  
Vol 25 (4) ◽  
pp. 2615-2628 ◽  
Author(s):  
Ung-Jin Kim ◽  
Dabum Kim ◽  
Jungmok You ◽  
Joon Weon Choi ◽  
Satoshi Kimura ◽  
...  
Keyword(s):  
Congo Red ◽  
Lithium Bromide ◽  
Adsorption Ability ◽  
Bromide Solution ◽  
Lithium Bromide Solution ◽  
Aqueous Lithium Bromide

Experimental Investigation on Onset of Nucleate Boiling in Tube-Bundle Channels

2009 ◽  
Author(s):  
Guangyao Lu ◽  
Junsheng Ren ◽  
Guisheng Zhao ◽  
Wenyuan Xiang ◽  
Huaning Ai
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Experimental Investigation ◽  
Heat Transfer Coefficient ◽  
Tube Bundle ◽  
Nucleate Boiling ◽  
Visualization Experiment ◽  
Inclined Tube ◽  
Good Accordance ◽  
The Heat Transfer Coefficient

Experiments are carried out to investigate the Onset of Nucleate Boiling (ONB) of refrigerant R-113 through vertical and inclined tube-bundle channels. Several methods are adopted to ascertain ONB in the experiments, and their differences are analyzed. The experiments show that the results of ONB estimation from the visualization experiment, ONB estimation from the wall temperature and that from the heat transfer coefficient are uniform. The influences of heat flux, mass flow rate, the geometric dimensions and inclination angle of the tube-bundle channels on the ONB height are explored in detail. On the foundation of the comparisons and analyses, an equation is put forward for calculating the ONB height in tube-bundle channels, which has a good accordance with the experimental results.

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