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.

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 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.

Investigation of Subcooled Flow Boiling Model Under Low Pressure

2010 ◽  
Author(s):  
Fan Pu
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Flow Boiling ◽  
Reactor Core ◽  
Low Pressure ◽  
Nucleate Boiling ◽  
Transfer Model ◽  
Local Flow ◽  
Subcooled Flow Boiling ◽  
Subcooled Flow

Two fluid model integrating a set of closure relationships (such as inter-phase heat transfer model, inter-phase mass transfer model, inter-phase momentum transfer model, mean bubble diameter model, bubble departure diameter model, bubble departure frequency model, onset of nucleate boiling model, wall heat flux partition model) are applied to solve the local flow and heat transfer of subcooled flow boiling under low pressure, and local flow parameters such as volume fraction, liquid velocity, vapor phase etc. are obtained using developed code. The subcooled flow boiling results predicted in this paper are compared to the subcooled flow boiling experimental results of TH Lee etc. in annular channel with inner tube heated uniformly and adiabatic outer tube, and they agree well. The code can also be used to predict the multiphase flow field in power reactor core when the subcooled flow boiling take place and the critical heat flux of Departure Nucleate Boiling (DNB) in reactor core and it is meaningful for reactor core design.

Experimental Investigation of Nucleate Boiling on Capillary Tubes Under PWR Specific Subcooling and Flow Parameters

2012 ◽  
Author(s):  
C. Schneider ◽  
R. Hampel ◽  
A. Traichel ◽  
A. Hurtado ◽  
S. Meissner ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Experimental Investigation ◽  
Critical Heat Flux ◽  
Flow Boiling ◽  
Nucleate Boiling ◽  
Test Facility ◽  
High Heat Flux ◽  
Subcooled Flow Boiling ◽  
Subcooled Flow

During full power operation of Pressurized Water Reactors (PWR), heat transfer phenomena of subcooled nucleate boiling may occur on the surface of the fuel rods. Despite high subcooling, this behavior results from the high heat flux up to 100 W/cm2 where vapor bubbles condensate when they are detached from the rod surface. In case of an accident with disturbance of cooling during transition from bubble to film boiling the critical heat flux (CHF) can be reached. This paper outlines the experimental investigation of heat transfer during subcooled flow boiling on a capillary tube. To investigate the heat transfer processes under these boiling conditions, a test facility for flow boiling with access for optical measuring methods was constructed. The temperature is measured with a thermocouple inside the tube while boiling bubbles are generated on the outside. For different subcooling and flow velocity the heat flux is increased in a range from zero up to approximately 115 W/cm2. The major aims of these investigations are to generate a database for modeling of these dependencies in computational fluid dynamic (CFD) codes and enhance the knowledge of phenomenological effects of subcooled flow boiling. This provides a contribution for the prediction of the critical heat flux with simulation codes.

scholarly journals Numerical Investigation of Successively Nucleating Bubbles During Subcooled Flow Boiling of FC-72 in Microgravity

2021 ◽  
Vol 33 (2) ◽  
Author(s):  
Benjamin Franz ◽  
Axel Sielaff ◽  
Peter Stephan
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Flow Boiling ◽  
Heating Time ◽  
Bubble Nucleation ◽  
Reference Case ◽  
Subcooled Flow Boiling ◽  
System Parameters ◽  
Subcooled Flow ◽  
The Impact

AbstractFor the present study numerical simulations of subcooled flow boiling of FC-72 in microgravity have been conducted to accompany boiling experiments performed in microgravity on the International Space Station (ISS). The numerical domain represents the geometry of the experimental test cell. For all simulations the open source framework OpenFOAM was employed, including extensions to the interFoam solver, which have been developed at the authors’ institute. A reference case has been defined applying intermediate values from the experimental parameter range as system parameters. This case has been examined thoroughly with regards to hydrodynamic phenomena and heat transfer during multiple, successive bubble cycles. Based on this reference case, the system parameters flow velocity, input heat flux, pre-heating time, and subcooling of the liquid bulk have been varied, and the impact of these quantities on bubble growth and movement as well as heat transfer have been studied. It was found, that an increased flow rate as well as increased subcooling lead to smaller bubbles and increased time between subsequent nucleations. A high input heat flux, an increased pre-heating time, and a decreased subcooling lead to a rapid cycle of bubble nucleation and coalescence.

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

2018 ◽  
Author(s):  
Kan Zhou ◽  
Junye Li ◽  
Zhao-zan Feng ◽  
Wei Li ◽  
Hua Zhu ◽  
...  
Keyword(s):  
Heat Flux ◽  
Flow Pattern ◽  
Flow Boiling ◽  
Nucleate Boiling ◽  
Working Fluid ◽  
Inlet Temperature ◽  
Lower Mass ◽  
Subcooled Flow Boiling ◽  
Mass Fluxes ◽  
Subcooled Flow

For improving the functionality and signal speed of electronic devices, electronic components have been miniaturized and an increasing number of elements have been packaged in the device. As a result there has been a steady rise in the amount of heat necessitated to be dissipated from the electronic device. Recently microchannel heat sinks have been emerged as a kind of high performance cooling scheme to meet the heat dissipation requirement of electronics packaging, In the present study an experimental study of subcooled flow boiling in a high-aspect-ratio, one-sided heating rectangular microchannel with gap depth of 0.52 mm and width of 5 mm was conducted with deionized water as the working fluid. In the experimental operations, the mass flux was varied from 200 to 400 kg/m2s and imposed heat flux from 3 to 20 W/cm2 while the fluid inlet temperature was regulated constantly at 90 °C. The boiling curves, flow pattern and onset of nucleate boiling of subcooled flow boiling were investigated through instrumental measurements and a high speed camera. It was found that the slope of the boiling curves increased sharply once the superheat needed to initiate the onset of nucleate boiling was attained, and the slope was greater for lower mass fluxes, with lower superheat required for boiling incipience. As for the visualization images, for relatively lower mass fluxes the bubbles generated were larger and not easy to depart from the vertical upward placed narrow microchannel wall, giving elongated bubbly flow and reverse backflow. The thin film evaporation mechanism dominated the entire test section due to the elongated bubbles and transient local dryout as well as rewetting occurred. Meanwhile the initiative superheat and heat flux of onset of nucleate boiling were compared with existing correlations in the literature with good agreement.

Calcium Carbonate Scale Formation During Subcooled Flow Boiling

1997 ◽  
Vol 119 (4) ◽  
pp. 767-775 ◽  
Author(s):  
S. H. Najibi ◽  
H. Mu¨ller-Steinhagen ◽  
M. Jamialahmadi
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Calcium Carbonate ◽  
Flow Boiling ◽  
Fluid Velocity ◽  
Nucleate Boiling ◽  
Operating Conditions ◽  
Initial Surface ◽  
Subcooled Flow Boiling ◽  
Subcooled Flow

Scale deposition on the heat transfer surfaces from water containing dissolved salts considerably reduces fuel economy and performance of the heat transfer equipment. In general, this problem is more serious during nucleate boiling due to the mechanisms of bubble formation and detachment. In this study, a large number of experiments were performed to determine the effect of fluid velocity, initial surface temperature, and bulk concentration on the rate of calcium carbonate deposition on heat transfer surfaces during subcooled flow boiling. A physically sound prediction model for the deposition process under these operating conditions has been developed which predicts the experimental data with good accuracy. Two previously published models are also discussed and used to predict the experimental data.

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.

Sign in / Sign up

Export Citation Format

Share Document