Effects of Heat Flux, Mass Flux, Inlet Fluid Subcooling, and Channel Orientation on Subcooled Flow Boiling in a High-Aspect-Ratio Rectangular Microchannel

2020 ◽  
Vol 142 (8) ◽  
Author(s):  
Wei Li ◽  
Zengchao Chen ◽  
Junye Li ◽  
Kan Zhou ◽  
Zhaozan Feng
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Aspect Ratio ◽  
Mass Flux ◽  
Flow Boiling ◽  
Bubbly Flow ◽  
Nucleate Boiling ◽  
Bubble Nucleation ◽  
Rectangular Microchannel ◽  
Subcooled Flow Boiling

Abstract An experimental investigation of subcooled flow boiling in a high-aspect-ratio, one-sided heating, silicon-based rectangular microchannel was conducted utilizing de-ionized water as the working fluid. The microchannel was 5.01 mm wide and 0.52 mm high, having a hydraulic diameter of 0.94 mm and an aspect ratio (AR) of 10. The heat flux, mass flux, and inlet fluid subcooling were in the ranges of 0–30 W/cm2, 200–500 kg/m2 s, and 5–20 °C, respectively, while the orientations were vertical and horizontal. Parametric study on heat transfer characteristics including the onset of nucleate boiling (ONB), heat transfer coefficient (HTC), and critical heat flux (CHF) was carried out combined with flow visualization. Significant appearance of ONB without boiling hysteresis was observed in the boiling curve, accompanied with bubble nucleation. Nucleate boiling occurred first near the exit, where the HTC increased more sharply, while easier bubble nucleation was found near the sides. Unique time-dependent flow pattern consisting of isolated bubbly flow, elongated bubbly flow, partial dry-out, and rewetting process was observed. More nucleation sites were activated at higher heat flux, while higher initial heat flux and wall superheat for ONB as well as higher CHF value were obtained at higher mass flux and inlet subcooling. Compared to the vertical channel, higher wall temperature and pressure drop with larger oscillation amplitudes were found for the horizontal counterpart, where the merged bubbles agglomerated in the heating section, resulting in earlier dry-out which deteriorated heat transfer.

Flow Pattern Analysis and Heat Transfer Characteristics During Subcooled Flow Boiling in a Rectangular Microchannel on ZnO Microrod Surface

2021 ◽  
Vol 143 (12) ◽  
Author(s):  
Yuhao Lin ◽  
Junye Li ◽  
Jia Sun ◽  
Wei Li ◽  
Yanlong Cao
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Flow Pattern ◽  
Titanium Surface ◽  
Flow Boiling ◽  
Bubbly Flow ◽  
Heat Transfer Characteristics ◽  
Rectangular Microchannel ◽  
Subcooled Flow Boiling ◽  
Subcooled Flow

Abstract The combination of microstructured surface and microchannel flow boiling is expected to solve the thermal management problems of high-heat-flux devices. In this study, the experimental investigation of subcooled flow boiling in a high aspect ratio, one-sided heating rectangular microchannel was conducted with de-ionized water as the working fluid. ZnO microrods were synthesized on the titanium surface to be used as the heated surface compared with the bare titanium surface. A facile image tool is utilized to process the flow patterns photographed by a high-speed camera, which is analyzed with the heat transfer characteristics. The flow pattern of isolated bubbly flow reveals the large number of nucleation sites formed on the microrod surface but the heat transfer performance deteriorates with increasing mass flux because of the smaller bubble area and weaker nucleation. With increasing heat flux, the flow pattern changes from isolated bubbly flow to alternating bubbly/slug flow and alternating slug/annular flow. The latter flow pattern is confirmed to bring a higher heat transfer coefficient due to the larger area of thin-film evaporation. Compared with the bare surface, a higher heat transfer coefficient is achieved on the ZnO microrod surface for up to 37% due to the more nucleate sites and strengthened convective evaporation. Therefore, this surface might be suitable for heat dissipation in the watercraft or aerospace industry considering the low density, strong intensity, and corrosion resistance of titanium.

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.

scholarly journals Experimental Investigation on Flow Boiling Heat Transfer and Pressure Drop of a Low-GWP Refrigerant R1234ze(E) in a Horizontal Minichannel

Energies ◽  
2021 ◽  
Vol 14 (18) ◽  
pp. 5972
Author(s):  
Yu Xu ◽  
Zihao Yan ◽  
Ling Li
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Experimental Investigation ◽  
Pressure Drop ◽  
Mass Flux ◽  
Flow Boiling ◽  
Saturation Pressure ◽  
Nucleate Boiling ◽  
Vapor Quality ◽  
Frictional Pressure Drop

To protect the environment, a new low-GWP refrigerant R1234ze(E) was created to substitute R134a. However, its flow boiling performances have not received sufficient attention so far, which hinders its popularization to some extent. In view of this, an experimental investigation was carried out in a 1.88 mm horizontal circular minichannel. The saturation pressures were maintained at 0.6 and 0.7 MPa, accompanied by mass flux within 540–870 kg/m2 s and heat flux within 25–65 kW/m2. For nucleate boiling, a larger heat flux brings about a larger heat transfer coefficient (HTC), while for convective boiling, the mass flux and vapor quality appear to take the lead role. The threshold vapor quality of different heat transfer mechanisms is around 0.4. Additionally, larger saturation pressure results in large HTC. As for the frictional pressure drop (FPD), it is positively influenced by mass flux and vapor quality, while negatively affected by saturation pressure, and the influence of heat flux is negligible. Furthermore, with the measured data, several existing correlations are compared. The results indicate that the correlations of Saitoh et al. (2007) and Müller-Steinhagen and Heck (1986) perform best on flow boiling HTC and FPD with mean absolute deviations of 5.4% and 10.9%.

Experimental Study on Flow Boiling of HFE-7100 in Wavy Copper Microchannels

2020 ◽  
Author(s):  
Peilin Cui ◽  
Zhenyu Liu
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Flow Boiling ◽  
Thin Liquid Film ◽  
Bubbly Flow ◽  
Nucleate Boiling ◽  
Inlet Temperature ◽  
The Heat Transfer Coefficient

Abstract This study experimentally investigated the flow boiling of HFE-7100 in wavy copper microchannel heat sink (20 mm × 10 mm), which was fabricated with the ultrafast laser micromachining approach, consisting of 20 wavy microchannels with wavelength of 2000 μm and wave amplitude of 100 μm with triangular cross section (200 μm × 573 μm). The experiment was conducted with the mass fluxes of 330.07–550.11 kg/(m2·s) and heat flux of 14.5–411.3 kW/m2 at an inlet temperature of 15°C. Four flow patterns including bubbly flow, slug flow, churn flow and annular flow were captured with the visualization technique. Several confined bubbles with irregular shape were observed. In the low heat flux region, the dominant flow regime of heat transfer in the microchannels is the nucleate boiling and the heat transfer coefficient increases with increasing heat flux. With the nucleate boiling suppressed gradually, the evaporation of thin liquid film begins to dominate and the heat transfer coefficient decreases with the increase of heat flux. The heat flux has a significant effect on heat transfer coefficient compared with the mass flux and vapor quality.

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.

Flow Boiling in Minichannels of Copper, Brass, and Aluminum Round Tubes

2004 ◽  
Author(s):  
K. H. Bang ◽  
W. H. Choo
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Mass Flux ◽  
Boiling Heat Transfer ◽  
Flow Boiling ◽  
Nucleate Boiling ◽  
Wall Heat Flux ◽  
Vapor Quality ◽  
Transfer Coefficients ◽  
Flow Boiling Heat Transfer

The past work on flow boiling heat transfer in minichannels ranging one to three millimeters of hydraulic diameter has indicated that the local heat transfer coefficients are largely independent of mass flux and vapor quality, but mainly a function of wall heat flux. The present work is a revisit of flow boiling in minichannels by conducting experiment using 1.67 mm inner diameter tubes of three different materials; aluminum, brass, and copper, to investigate an effect of the tube inner surface conditions with the focus on an effect on nucleate boiling. Tests were conducted for R-22, a fixed mass flux of 600 kg/m2s, 5∼30 kW/m2 of wall heat flux, 0.0∼0.9 of local vapor quality. The present experimental data confirmed that the flow boiling heat transfer coefficient in a minichannel varies only by heat flux, independent of mass flux and vapor quality. The effect of tube material was found small for the tubes used in the present work. The present data were well predicted by the correlation proposed by Tran et al. (1996).

Heat Transfer Characteristics and Flow Pattern Visualization for Flow Boiling in a Vertical Narrow Microchannel

2019 ◽  
Vol 141 (3) ◽  
Author(s):  
Kan Zhou ◽  
Hua Zhu ◽  
Wei Li ◽  
Junye Li ◽  
Kuang Sheng ◽  
...  
Keyword(s):  
Heat Flux ◽  
High Speed ◽  
Heat Dissipation ◽  
Flow Boiling ◽  
Nucleate Boiling ◽  
Working Fluid ◽  
Inlet Temperature ◽  
Rectangular Microchannel ◽  
Subcooled Flow Boiling ◽  
Subcooled Flow

Recently, microchannel heat sinks have been emerged as a kind of high performance cooling scheme to meet the heat dissipation requirement of electronics packaging and integration. In this study, an experimental investigation of subcooled flow boiling in a high-aspect-ratio rectangular microchannel was conducted with de-ionized water as the working fluid. In the experimental operations, the mass flux was varied from 200 to 400 kg/m2s and the imposed heat flux from 3 to 20 W/cm2 while the fluid inlet temperature was regulated constantly at 90 °C. The boiling curves, onset of nucleate boiling (ONB), and flow patterns of subcooled flow boiling were investigated with the aid of instrumental measurements and a high-speed camera. The slope of the boiling curves increased sharply once the superheat needed to initiate the onset of nucleate boiling was attained, with lower superheat required of boiling incipience for lower mass fluxes. Meanwhile, the initiative superheat and heat flux of onset of nucleate boiling were compared with the existing correlations in the literature with good agreement. As for the flow visualization images, slug flow and reverse backflow were observed, where transient local dryout as well as rewetting occurred. A facile image processing tool was developed to profile the transient development and progression of the liquid–vapor interface and partial dryout patches in microchannels, which proved that the physical quantities of bubble dynamics for the elongation period during subcooled boiling could be well detected and calculated.

Investigations on Effect of Lift and Wall Lubrication Forces on the Subcooled Flow Boiling

2020 ◽  
Vol 6 (4) ◽  
Author(s):  
Sai Raja Gopal Vadlamudi ◽  
Arun K. Nayak
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Flow Boiling ◽  
Nucleate Boiling ◽  
Eulerian Model ◽  
Subcooled Flow Boiling ◽  
Void Fractions ◽  
Subcooled Flow ◽  
Flux Partitioning ◽  
The Impact

Abstract Subcooled flow boiling is widely used as a mode of heat transfer in many industries, especially in nuclear reactors. Despite its advantages, the heat transfer is hampered beyond a certain flux due to a phenomenon known as departure from nucleate boiling (DNB). It is important to determine the void fraction profiles, especially the near-wall void fractions, to evaluate the limiting heat flux conditions. The two-fluid Eulerian model, coupled with the heat flux partitioning model, is widely used to predict subcooled flow boiling characteristics. Over the years, many researchers have not considered lift and wall lubrication forces in their modeling of subcooled flow boiling. Few researchers have considered the Tomiyama model for lift force; however, their results were not encouraging. Moreover, there is no systematic study in evaluating the impact of lift and wall lubrication forces on subcooled flow boiling. In this paper, various lift and wall lubrication models are compared to understand the implications of these forces on void distribution. The advantages and limitations of the models are discussed in detail.

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