Heat Transfer Characteristics and Bubble Behaviors During Nucleate Flow Boiling for Sodium Chloride Solution

2019 ◽  
Author(s):  
Junping Gu ◽  
Guoli Tang ◽  
Yuxin Wu ◽  
Junfu Lyu ◽  
Hairui Yang ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Boiling Heat Transfer ◽  
Saline Solution ◽  
Flow Boiling ◽  
Pure Water ◽  
Nucleate Boiling ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Nucleate Boiling Heat Transfer

Abstract Deep understanding of nucleate boiling heat transfer mechanism of saline solution is of great importance for the design and safe operation of steam generation equipment. In this paper, the nucleate flow boiling process of saline solution in a vertical heated pipe was experimentally studied within the concentration range of 0 % ∼ 6 %. In order to realize the visualization, the vertical heated pipe was made of transparent silica glass and a transparent ITO heater was used to provide energy for boiling. The high-speed high-resolution camera was used to capture the vapor-liquid two-phase flow structure. The bubble behaviors such as bubble departure diameter, bubble departure frequency, bubble growth time and waiting time were investigated under different operating conditions. The experimental results showed that the heat transfer deterioration did not occur within the solution concentration of 6% in this work. Under some low heat flux conditions, the heat transfer coefficients of solution can be higher than those of pure water. The reason for this phenomenon can be explained by the different bubble behaviors. Comparing to pure water, the bubble departure diameter of saline solution is bigger and bubble departure frequency is lower. The influences of operating parameters, including concentration, mass flux (200 kg/m2s ∼ 600 kg/m2s), heat flux (30 kW/m2 ∼ 180 kW/m2) and subcooling of fluid (5 K ∼ 35 K), on the nucleate boiling heat transfer coefficients and bubble parameters were comprehensively studied.

scholarly journals Boiling Heat Transfer Performance of Parallel Porous Microchannels

Energies ◽  
2020 ◽  
Vol 13 (11) ◽  
pp. 2970
Author(s):  
Donghui Zhang ◽  
Haiyang Xu ◽  
Yi Chen ◽  
Leiqing Wang ◽  
Jian Qu ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Boiling Heat Transfer ◽  
Flow Boiling ◽  
Nucleate Boiling ◽  
High Heat ◽  
High Heat Flux ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Boiling Process

Flow boiling in microporous layers has attracted a great deal of attention in the enhanced heat transfer field due to its high heat dissipation potential. In this study, flow boiling experiments were performed on both porous microchannels and a copper-based microchannel, using water as the coolant. As the heat flux was less than 80 W/cm2, the porous microchannels presented significantly higher boiling heat transfer coefficients than the copper-based microchannel. This was closely associated with the promotion of the nucleation site density of the porous coating. With the further increase in heat flux, the heat transfer coefficients of the porous microchannels were close to those of the copper-based sample. The boiling process in the porous microchannel was found to be dominated by the nucleate boiling mechanism from low to moderate heat flux (<80 W/cm2).This switched to the convection boiling mode at high heat flux. The porous samples were able to mitigate flow instability greatly. A visual observation revealed that porous microchannels could suppress the flow fluctuation due to the establishment of a stable nucleate boiling process. Porous microchannels showed no advantage over the copper-based sample in the critical heat flux. The optimal thickness-to-particle-size ratio (δ/d) for the porous microchannel was confirmed to be between 2–5. In this range, the maximum enhanced effect on boiling heat transfer could be achieved.

Nucleate Boiling and Critical Heat Flux From Protruded Chip Arrays During Flow Boiling

1993 ◽  
Vol 115 (1) ◽  
pp. 78-88 ◽  
Author(s):  
C. O. Gersey ◽  
I. Mudawar
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Critical Heat Flux ◽  
Single Phase ◽  
Liquid Velocity ◽  
Flow Boiling ◽  
Nucleate Boiling ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Subcooled Flow

The effects of chip protrusion on the forced-convection boiling and critical heat flux (CHF) of a dielectric coolant (FC-72) were investigated. The multi-chip module used in the present study featured a linear array of nine, 10 mm x 10 mm, simulated microelectronic chips which protruded 1 mm into a 20-mm wide side of a rectangular flow channel. Experiments were performed in vertical up flow with 5-mm and 2-mm channel gap thicknesses. For each configuration, the velocity and subcooling of the liquid were varied from 13 to 400 cm/s and 3 to 36° C, respectively. The nucleate boiling regime was not affected by changes in velocity and subcooling, and critical heat flux generally increased with increases in either velocity or subcooling. Higher single-phase heat transfer coefficients and higher CHF values were measured for the protruded chips compared to similar flush-mounted chips. However, adjusting the data for the increased surface area and the increased liquid velocity above the chip caused by the protruding chips yielded a closer agreement between the protruded and flush-mounted results. Even with the velocity and area adjustments, the most upstream protruded chip had higher single-phase heat transfer coefficients and CHF values for high velocity and/or highly-subcooled flow as compared the downstream protruded chips. The results show that, except for the most upstream chip, the performances of protruded chips are very similar to those of flush-mounted chips.

Low Mass Quality Flow Boiling in Microtubes at High Mass Fluxes

2011 ◽  
Vol 3 (4) ◽  
Author(s):  
Mehmed Rafet Özdemir ◽  
Alihan Kaya ◽  
Ali Koşar
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Mass Flux ◽  
Boiling Heat Transfer ◽  
Flow Boiling ◽  
High Mass ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Mass Fluxes ◽  
Wall Superheat

In this article, an experimental study on boiling heat transfer and fluid flow in microtubes at high mass fluxes is presented. De-ionized water flow was investigated over a broad range of mass flux (1000 kg/m2s–7500 kg/m2s) in microtubes with inner diameters of  ∼ 250 μm and ∼685 μm. The reason for using two different capillary diameters was to investigate the size effect on flow boiling. De-ionized water was used as working fluid, and the test section was heated by Joule heating. Heat transfer coefficients and qualities were deduced from local temperature measurements. It was found that high heat removal rates could be achieved at high flow rates under subcooled boiling conditions. It was also observed that heat transfer coefficients increased with mass flux, whereas they decreased with local quality and heat flux. Moreover, experimental heat flux data were compared with partial boiling correlations and fully developed boiling correlations. It was observed that at low wall superheat values, there was only a small inconsistency between the experimental data and the conventional partial boiling prediction method of Bergles, while the subcooled and low quality fully developed boiling heat transfer correlation of Kandlikar could fairly predict experimental results at high wall superheat values.

Enhanced Flow Boiling Over Open Microchannels With Uniform and Tapered Gap Manifolds

2013 ◽  
Vol 135 (6) ◽  
Author(s):  
Satish G. Kandlikar ◽  
Theodore Widger ◽  
Ankit Kalani ◽  
Valentina Mejia
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Transfer Performance ◽  
Flow Boiling ◽  
Nucleate Boiling ◽  
High Heat ◽  
High Heat Flux ◽  
Transfer Performance ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients

Flow boiling in microchannels has been extensively studied in the past decade. Instabilities, low critical heat flux (CHF) values, and low heat transfer coefficients have been identified as the major shortcomings preventing its implementation in practical high heat flux removal systems. A novel open microchannel design with uniform and tapered manifolds (OMM) is presented to provide stable and highly enhanced heat transfer performance. The effects of the gap height and flow rate on the heat transfer performance have been experimentally studied with water. The critical heat fluxes (CHFs) and heat transfer coefficients obtained with the OMM are significantly higher than the values reported by previous researchers for flow boiling with water in microchannels. A record heat flux of 506 W/cm2 with a wall superheat of 26.2 °C was obtained for a gap size of 0.127 mm. The CHF was not reached due to heater power limitation in the current design. A maximum effective heat transfer coefficient of 290,000 W/m2 °C was obtained at an intermediate heat flux of 319 W/cm2 with a gap of 0.254 mm at 225 mL/min. The flow boiling heat transfer was found to be insensitive to flow rates between 40–333 mL/min and gap sizes between 0.127–1.016 mm, indicating the dominance of nucleate boiling. The OMM geometry is promising to provide exceptional performance that is particularly attractive in meeting the challenges of high heat flux removal in electronics cooling applications.

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