scholarly journals Convective flow boiling heat transfer in an annular space: N-heptane/water case in a bubbly sub-cooled flow

2020 ◽  
Vol 3 (2) ◽  
pp. 33
Author(s):  
M. M. Sarafraz ◽  
H. Arya
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Flow Rate ◽  
Boiling Heat Transfer ◽  
Flow Boiling ◽  
Heating Surface ◽  
Nucleate Boiling ◽  
Subcooled Flow Boiling ◽  
Subcooled Flow ◽  
Flow Boiling Heat Transfer

The subcooled flow boiling heat transfer characteristics of n-heptane and water is conducted for an upward flow inside the vertical annulus with an inner gap of 30 mm, in different heat fluxes up to 132kW.m-2, subcooling max.:30C, flow rate: 1.5 to 3.5lit.min-1 under the atmospheric pressure. The measured data indicate that the subcooled flow boiling heat transfer coefficient significantly increases with increasing liquid flow rate and heat flux and slightly decreases with decreasing the subcooling level. Although results demonstrate that subcooling is the most effective operation parameter on onset of nucleate boiling such that with decreasing the subcooling level, the inception heat flux significantly decreases. Besides, recorded results from the visualization of flow show that the mean diameter of the bubbles departing from the heating surface decreases slightly with increasing the flow rate and slightly decreases with decreasing the subcooling level. Meanwhile, comparisons of the present heat transfer data for n-heptane and water in the same annulus and with some existing correlations are investigated. Results of comparisons reveal an excellent agreement between experimental data and those of calculated by Chen Type model and Gungor–Winterton predicting correlation.

Subcooled Flow Boiling Inception and Heat Transfer of Water in a Circular Tube Under Pulsatile Flow

2018 ◽  
Author(s):  
Hongsheng Yuan ◽  
Sichao Tan ◽  
Kun Cheng ◽  
Xiaoli Wu ◽  
Chao Guo ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Steady Flow ◽  
Flow Rate ◽  
Flow Boiling ◽  
Nucleate Boiling ◽  
Nucleation Site ◽  
Subcooled Flow Boiling ◽  
Average Heat ◽  
Subcooled Flow

The flow rate can fluctuate in offshore nuclear power systems which are exposed to wind and waves, as well as in loops where flow instabilities occur, resulting in different thermal-hydraulic characteristics compared with that under steady flow. Among the thermal-hydraulic characteristics, onset of nucleate boiling (ONB) model determines whether the fluid is boiling, and boiling heat transfer is crucial to equipment performance and safety, both being key issues in subcooled flow boiling. Therefore, an experimental study was conducted to investigate how an imposed periodic flow oscillation affects the boiling inception and heat transfer of subcooled flow boiling of water in a vertical tube. The experiments were conducted under atmospheric pressure with the average flow rate ranging from 96kg/m2s to 287kg/m2s and heat flux ranging from 10kW/m2 to 197kW/m2. The relative pulsatile amplitude range is 0.1–0.3 and pulsatile period range is 10s-30s. Photographic images and thermal parameters such as temperatures and flow rate were recorded. The lack of nucleation site on the heated surface of the test section results in high wall superheat at ONB. The effects of pulsatile amplitude and period on superheat at boiling onset and average heat transfer were analyzed. The results show that the superheat at boiling inception is decreased when the average heat flux is lower than the heat flux at boiling inception of the corresponding steady flow, and the superheat at boiling onset is increased when the average heat flux is higher than the heat flux at boiling onset of the corresponding steady flow. The above effect of flow rate pulsation on superheat increases with increasing amplitude and decreasing period, and the mechanism can be explained by boiling nucleation theory. The lack of large active nucleation site also affects the boiling heat transfer. By comparing the contribution of nucleate boiling to heat transfer with the widely used Cooper’s pool boiling correlation, the subcooled flow boiling was found suppressed by convection. The average heat transfer of both the intermittent flow boiling and the single phase flow is influenced by flow oscillation.

scholarly journals Alumina Nanoparticle Pre-Coated Tubing Enhancing Subcooled Flow Boiling Critical Heat Flux

2009 ◽  
Author(s):  
Bao Truong ◽  
Lin-wen Hu ◽  
Jacopo Buongiorno ◽  
Thomas McKrell
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Critical Heat Flux ◽  
Mass Flux ◽  
Boiling Heat Transfer ◽  
Flow Boiling ◽  
Subcooled Flow Boiling ◽  
Nanoparticle Deposition ◽  
Subcooled Flow ◽  
Flow Boiling Heat Transfer

Nanofluids are engineered colloidal dispersions of nano-sized particle in common base fluids. Previous pool boiling studies have shown that nanofluids can improve critical heat flux (CHF) up to 200% for pool boiling and up to 50% for subcooled flow boiling due to the boiling induced nanoparticle deposition on the heated surface. Motivated by the significant CHF enhancement of nanoparticle deposited surface, this study investigated experimentally the subcooled flow boiling heat transfer of pre-coated test sections in water. Using a separate coating loop, stainless steel test sections were treated via flow boiling of alumina nanofluids at constant heat flux and mass flow rate. The pre-coated test sections were then used in another loop to measure subcooled flow boiling heat transfer coefficient and CHF with water. The CHF values for the pre-coated tubing were found on average to be 28% higher than bare tubing at high mass flux G = 2500 kg/m2 s. However, no enhancement was found at lower mass flux G = 1500 kg/m2 s. The heat transfer coefficients did not differ much between experiments when the bare or coated tubes were used. SEM images of the test sections confirm the presence of a nanoparticle coating layer. The nanoparticle deposition is sporadic and no relationship between the coating pattern and the amount of CHF enhancement is observed.

Experimental Study on Al2O3/H2O Nanofluid Flow Boiling Heat Transfer Under Different Pressures

2016 ◽  
Author(s):  
Y. Wang ◽  
K. H. Deng ◽  
B. Liu ◽  
J. M. Wu ◽  
G. H. Su
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Flow Rate ◽  
Boiling Heat Transfer ◽  
Volume Concentration ◽  
Flow Boiling ◽  
Heating Surface ◽  
Nanofluid Flow ◽  
Flow Boiling Heat Transfer ◽  
Heat Transfer Capacity

In present work, Al2O3/H2O nanofluid was prepared by ultrasonic oscillation. Furthermore, nanofluid flow boiling heat transfer in a vertical cube is experimentally studied, with 0.1% and 0.5% volume concentration and 20nm diameter. Some factors are under consideration, including heat flux on the heating surface (48∼289kW·m−2), pressure (0.2∼0.8MPa) and mass flow rate (400∼1100 kgm−2s−1). The results confirm that the flow boiling heat transfer of Al2O3/H2O nanofluid is improved mostly about 86% compared with pure water. And the average Nusselt number enhancement rate of nanofluid compared with deionized water is 35% in the range of this work. Moreover, the heat transfer capacity of nanofluid increase with the heat flux on the heating surface, pressure and the volume concentration of nanoparticle. It is proved that nanoparticle deposited on the heating surface by SEM observations, and TEM observations for nanoparticle confirm that nanoparticle have not obviously changed after boiling. In addition, the enhancement rate of nanofluid flow boiling heat transfer capacity increase with the pressure, and the influence of mass flow rate is negligible. In conclusion, this work is a supplement for nanofluid flow boiling heating transfer, especially for the influence of pressure.

Subcooled Flow Boiling Heat Transfer of Nanofluids in a Microchannel

2009 ◽  
Author(s):  
Saeid Vafaei ◽  
Dongsheng Wen
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Temperature Distribution ◽  
Boiling Heat Transfer ◽  
Flow Boiling ◽  
Subcooled Boiling ◽  
Subcooled Flow Boiling ◽  
Surface Temperature Distribution ◽  
Subcooled Flow ◽  
Flow Boiling Heat Transfer

This work investigates the subcooled flow boiling of aqueous based nanofluids in a 510 μm single microchannel with a focus on the effect of nanoparticles on the critical heat flux (CHF). The surface temperature distribution along the pipe, the inlet and outlet pressures and temperatures are measured simultaneously for different concentrations of alumina nanofluids and dionized water. The experiment shows a remarkable increase ∼ 31% in the CHF under very low nanoparticle concentrations (∼0.1v%) and a nonlinear influence of nanoparticles on the subcooled boiling heat transfer.

Enhanced Subcooled Flow Boiling Heat Transfer in Microchannel With Piranha Pin Fin

2017 ◽  
Vol 139 (11) ◽  
Author(s):  
X. Yu ◽  
C. Woodcock ◽  
Y. Wang ◽  
J. Plawsky ◽  
Y. Peles
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Boiling Heat Transfer ◽  
Flow Boiling ◽  
Nucleate Boiling ◽  
Heat Fluxes ◽  
Subcooled Flow Boiling ◽  
Subcooled Flow ◽  
Flow Boiling Heat Transfer

An experimental study on subcooled flow boiling with engineering fluid HFE-7000 in a microchannel fitted with piranha pin fins (PPFs) is presented. Heat fluxes of up to 735 W/cm2 were achieved and mass fluxes ranged from 618 kg/m2s to 2569 kg/m2 s. It was found that the flow boiling heat transfer was significantly enhanced with PPFs. The heat transfer coefficient with flow boiling was double the corresponding single-phase flow. Correlations for two-phase heat transfer coefficient and pressure drop in the nucleate flow boiling regime were developed based on the boiling, Weber, and Jakob numbers. The onset of nucleate boiling (ONB) and the critical heat flux (CHF) conditions were determined through visualization and was typically initiated from the last row of fins where temperatures were highest and flow rates lowest.

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