Calculation of Steam Volume Fraction in Subcooled Boiling

1968 ◽  
Vol 90 (1) ◽  
pp. 158-164 ◽  
Author(s):  
S. Zia Rouhani
Keyword(s):  
Heat Transfer ◽  
Relative Velocity ◽  
Single Phase ◽  
Volume Fraction ◽  
Subcooled Boiling ◽  
Vapor Generation ◽  
Subcooled Liquid ◽  
Limiting Value

An analysis of subcooled boiling is presented. It is assumed that heat is removed by vapor generation, heating of the liquid that replaces the detached bubbles, and to some extent by single-phase heat transfer. Two regions of subcooled boiling are considered and a criterion is provided for obtaining the limiting value of subcooling between the two regions. Condensation of vapor in the subcooled liquid is analyzed and the relative velocity of vapor with respect to the liquid is neglected in these regions. The theoretical arguments result in some equations for the calculation of steam volume fraction and true liquid subcooling.

Heat Transfer Enhancement Using Ultrasonic Waves in Presence of Liquid: A Basic Research for Cooling Electronic

2013 ◽  
Vol 464 ◽  
pp. 163-170 ◽  
Author(s):  
F. Baffigi ◽  
C. Bartoli
Keyword(s):  
Heat Transfer ◽  
Free Convection ◽  
Single Phase ◽  
Cooling System ◽  
Basic Research ◽  
Horizontal Cylinder ◽  
Ultrasonic Waves ◽  
Department Of Energy ◽  
Subcooled Boiling ◽  
Joule Effect

This work collects the experimental results obtained in the Thermal Fluid Dynamics Lab at the Department of Energy, Systems, Land and Constructions Engineering at the University of Pisa, concerning a basic physics research on the influence of ultrasounds in single phase free convection and in subcooled boiling, at atmospheric pressure. The ultrasounds are applied at the set frequency of 40 kHz, with a transducer output changing from 300 to 500W, on a circular horizontal cylinder heated by Joule effect, immersed in distilled water. The tests in single phase free convection, without ultrasonic waves, are validated by means of the classical correlations reported in literature, but they do not produce distinctive augmentation of the heat transfer. The enhancement of the heat transfer coefficient is maximum in subcooled boiling conditions (about 57%). In this regime a detailed investigation was performed to optimize the variables involved, such as the ultrasound generator power, the position of the cylinder and, especially, the subcooling degree. This paper, makes clear systematically the effects of ultrasounds on the heat transfer and shows as they could be very useful as cooling system for the last generation electronic components.

Numerical Simulation of Taylor Flow in Micro Circular Tubes

2015 ◽  
Author(s):  
Jingzhi Zhang ◽  
Wei Li
Keyword(s):  
Heat Transfer ◽  
Liquid Film ◽  
Single Phase ◽  
Volume Fraction ◽  
Flow Characteristics ◽  
Constant Heat Flux ◽  
Bulk Temperature ◽  
Capillary Tubes ◽  
Taylor Flow ◽  
Gas Volume

Heat transfer and flow characteristics of Taylor flow in micro capillary tubes have been investigated numerically with the Volume of Fluid (VOF) method. A constant heat flux (32kwm−2) is adopted at the tube wall. All seven computational cases have the same Reynolds number (Re=280), Capillary number (Ca=0.006) and homogenous void fraction (β=0.51), while the inlet gas volume fraction varies from 0.2 to 0.8. The results indicate that liquid slug length (Ll), gas slug length (Lg) and cell length (Lc) vary with α, while liquid film thickness δ remains constant. The friction factor f of Taylor flow is higher than single phase flow. The simulation results agree well with the correlation proposed by Kreutzer et al.. The Local Nusselt number (Nux) gets its peak value at the liquid film region, where the temperature difference between wall temperature (Tw) and fluid bulk temperature (Tbx) is smallest. The average Nu (Nuav) is about 2.8 times of single phase. This means that Taylor bubble can enhance the heat transfer coefficient in micro capillary tubes.

Experimental and Numerical Investigation of Flow of Nanofluids in Microchannels

2010 ◽  
Author(s):  
Pawan K. Singh ◽  
P. V. Harikrishna ◽  
T. Sundararajan ◽  
Sarit K. Das
Keyword(s):  
Heat Transfer ◽  
Pressure Drop ◽  
Single Phase ◽  
Volume Fraction ◽  
The Body ◽  
Particle Migration ◽  
Phase Model ◽  
Channel Cross Section ◽  
Navier Stokes Equation ◽  
Discrete Phase

The current study investigates the flow of nanofluids in microchannels experimentally and numerically. For this purpose, two microchannels of hydraulic diameters of 211 and 300 μm are used with alumina(45nm)-water nanofluids. The nanofluids with the concentrations 0.25, 0.50 and 1 vol% are used to observe the effect of volume fraction in the present analysis. With regard to the numerical simulation of nanofluids in microchannels, two approaches have been chosen in the current work. First one considers the nanofluids as single phase fluid and applies the mixture rule for evaluating properties for the simulation. The second type of modeling is done using the discrete phase approach which involves Eulerian-Lagrangian considerations. The fluid phase is assumed to be continuous and governed by Navier-Stokes equation. The movement of discrete nanoparticles is determined by the Newton’s second law which takes into account the body force, hydrodynamic forces, the Brownian and thermophoresis forces. The predictions are validated against experimental results obtained for nanofluid flow in a chemically etched silicon wafer channel. It is found that the discrete phase modeling is more accurate with regard to the prediction of nanofluids behavior in microchannels, as compared to the single phase model. The results also show the non-uniformity of nanoparticle distribution across the channel cross-section. This non-uniformity in distribution can be attributed to the shear induced particle migration. This can also be the reason for the difference in pressure drop and heat transfer from the single phase model. The pressure drop with 0.25 and 0.5 vol% of alumina is more or less same as that of water and thus, makes it a suitable cooling liquid. However, an enhancement in heat transfer is observed from the computational predictions.

Comparison of Single and Two-Phase Models for the Study of Mixed Convection Flows With Nanofluids

2010 ◽  
Author(s):  
Mahmood Akbari ◽  
Amin Behzadmehr ◽  
Nicolas Galanis
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Mixed Convection ◽  
Single Phase ◽  
Volume Fraction ◽  
Solid Particles ◽  
Two Phase ◽  
Prediction Ability ◽  
Numerical Predictions ◽  
Phase Models

The single phase and three different two phase models (Volume of fluid, Mixture and Eulerian) are used to analyse laminar mixed convection flow of Al2O3-water nanofluids in a horizontal tube, in order to evaluate their prediction ability. The flow is considered steady and developing. The fluid’s physical properties are temperature dependent whereas those of the solid particles are constant. A uniform heat flux is applied at the fluid-solid interface. Two different Reynolds numbers and three different volume fractions have been considered. The governing three-dimensional partial differential equations are elliptical in all directions and coupled. Predicted convective heat transfer coefficients, velocity, and temperature profiles, as well as secondary flow’s velocity vectors and temperature contours are compared at different axial positions. To validate the comparisons and verify the accuracy of the results, the numerical predictions are compared with corresponding experimental data. There are essentially no differences between the predictions of the two-phase models; however their results are significantly different from those of the single-phase approach. Two-phase model results are closer to the experimental data, but they show an unrealistic increase in heat transfer for small changes of the particle volume fraction. Hydrodynamically, the two-phase and single-phase approaches perform almost the same but their thermal predictions are quite different.

scholarly journals Heat Transport Improvement and Three-Dimensional Rotating Cone Flow of Hybrid-Based Nanofluid

2021 ◽  
Vol 2021 ◽  
pp. 1-11
Author(s):  
Azad Hussain ◽  
Qusain Haider ◽  
Aysha Rehman ◽  
M. Y. Malik ◽  
Sohail Nadeem ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Single Phase ◽  
Volume Fraction ◽  
Liquid Fraction ◽  
Current Model ◽  
Velocity Ratio ◽  
Three Dimensional ◽  
Temperature Fields ◽  
Physical Parameters ◽  
Diverse Range

The current research aims to study the mixed convection of a hybrid-based nanofluid consisting of ethylene glycol-water, copper (II) oxide (CuO) and titanium dioxide (TiO2) in a vertical cone. A hybrid base blend model is used to examine the nanofluid’s hydrostatic and thermal behaviors over a diverse range of Reynolds numbers. The application of mixed nanoparticles rather than simple nanoparticles is one of the most imperative things in increasing the heat flow of the fluids. To test such a flow sector, for the very first time, a hybrid-based mixture model was introduced. Also, the mixture framework is a single-phase model formulation, which was used extensively for heat transfer with nanofluids. Comparison of computed values with the experimental values is presented between two models (i.e., the model of a mixture with the model of a single-phase). The natural convection within the liquid phase of phase change material is considered through the liquid fraction dependence of the thermal conductivity. The predicted results of the current model are also compared with the literature; for numerical results, the bvp4c algorithm is used to quantify the effects of nanoparticle volume fraction diffusion on the continuity, momentum, and energy equations using the viscous model for convective heat transfer in nanofluids. Expressions for velocity and temperature fields are presented. Also, the expressions for skin frictions, shear strain, and Nusselt number are obtained. The effects of involved physical parameters (e.g., Prandtl number, angular velocity ratio, buoyancy ratio, and unsteady parameter) are examined through graphs and tables.

Numerical Simulation of Dynamics and Heat Transfer Associated With a Single Bubble in Subcooled Boiling and in the Presence of Noncondensables

2011 ◽  
Vol 133 (4) ◽  
Author(s):  
Jinfeng Wu ◽  
Vijay K. Dhir
Keyword(s):  
Heat Transfer ◽  
Thermocapillary Convection ◽  
Bubble Dynamics ◽  
Bubble Diameter ◽  
Saturation Temperature ◽  
Subcooled Boiling ◽  
Bubble Liquid ◽  
Subcooled Liquid ◽  
Noncondensable Gases ◽  
Induced Flow

During phase change at the bubble-liquid interface, under subcooled boiling conditions, noncondensable gases dissolved in the liquid will be injected into the bubble along with vapor. Due to heat transfer into subcooled liquid, vapor will condense in the upper regions of the bubble while noncondensables will continue to accumulate. Subsequently, thermocapillary convection caused by nonuniform saturation temperature at the interface may occur. The aim of this work is to investigate the effects of noncondensables on heat transfer and bubble dynamics. The numerical results show that the effects of noncondensables on 5°C subcooled boiling of water are minor in terms of the equilibrium bubble diameter and overall Nusselt number. However, induced flow pattern around the bubble is altered, especially under reduced gravity conditions.

Gas Phase Distribution Effects on Heat Transfer in Upward Vertical Bubbly Channel Flows

2016 ◽  
Author(s):  
Haden Hinkle ◽  
Deify Law
Keyword(s):  
Heat Transfer ◽  
Gas Phase ◽  
Bubble Size ◽  
Single Phase ◽  
Volume Fraction ◽  
Phase Distribution ◽  
Vertical Channel ◽  
Channel Flows ◽  
Two Phase ◽  
Ansys Fluent

Two-phase (non-boiling) flows have been shown to increase heat transfer in channel flows as compared with single-phase flows. The present work explores the effects of gas phase distribution such as volume fraction and bubble size on the heat transfer in upward vertical channel flows. A two-dimensional (2D) channel flow of 10 cm wide by 100 cm high is studied numerically. Numerical simulations are performed using the commercial computational fluid dynamics (CFD) code ANSYS FLUENT. The bubble size is characterized by the Eötvös number. The volume fraction and the Eötvö number are varied parametrically to investigate their effects on Nusselt number of the two-phase flows. All simulations are compared with a single-phase flow condition.

scholarly journals Numerical Study of Heat Transfer Enhancement for Laminar Nanofluids Flow

2018 ◽  
Vol 8 (12) ◽  
pp. 2661 ◽  
Author(s):  
Ramon Ramirez-Tijerina ◽  
Carlos Rivera-Solorio ◽  
Jogender Singh ◽  
K. Nigam
Keyword(s):  
Heat Transfer ◽  
Single Phase ◽  
Volume Fraction ◽  
Numerical Study ◽  
Dispersion Model ◽  
Constant Heat Flux ◽  
Process Conditions ◽  
Straight Tube ◽  
Wide Range ◽  
Laminar Forced Convection

The laminar forced convection has been investigated for the flow of nanofluids in conventional straight tube (L = 5.34 m, dt = 10 mm) and straight microtube (L = 0.3 m, dt = 0.5 mm) under the constant temperature and constant heat flux conditions, separately. A wide range of the process parameters has been studied by varying three different type of base fluids including water, ethylene glycol and turbine oil with five different type of nanoparticles viz. Al2O3, TiO2, CuO, SiO2 and ZnO. Six different combinations of the geometries, base fluids and nanoparticle concentrations are considered in the present study. In addition to the single-phase model (SPH), the single-phase dispersion model (SPD) has been also used for effectiveness of the computed results. The results showed that Nusselt number (Nu) increases with increase in Reynolds number (Re). Further, the Nu considerably enhanced (up to 16% at volume fraction ϕ b = 4%, Re = 950) with increase in nanoparticle concentrations. Heat transfer correlations are developed for the flow of nanofluids in conventional straight tube and straight microtube over a wide range of process conditions (25 < Re < 1500, 0 < ϕ b < 10, 6 < Pr < 500) to enable a large number of engineering applications.

Subcooled Boiling Data From Rod Bundles

2004 ◽  
Author(s):  
Zeses E. Karoutas ◽  
Yixing Sung ◽  
Yutung R. Chang ◽  
Gennady A. Kogan ◽  
Paul F. Joffre
Keyword(s):  
Heat Transfer ◽  
Enhancement Factor ◽  
Single Phase ◽  
Phase Flow ◽  
Subcooled Boiling ◽  
Rod Bundles ◽  
Two Phase ◽  
Spacer Grids ◽  
Rod Bundle ◽  
Test Conditions

This paper provides single and two phase rod bundle data to support verification of heat transfer models being used in steaming rate and crud model predictions for rod bundles. The effort to summarize this work was supported by the EPRI Robust Fuel Program and is defined in more detail in EPRI report 1003383. Subcooled boiling tests were performed by Combustion Engineering (CE) in early 1980s to provide insight on heavy crud deposits and fuel failures observed on peripheral rods for bundles in Maine Yankee cycle 4. Two 5×5 tests were performed at the Columbia University Heat Transfer Research Facility simulating the peripheral region of adjacent CE 14×14 fuel bundles for two different perimeter strip geometries. The test conditions were at typical reactor pressure, temperature, and heat flux. The rods were 7’ in heated length and were electrically heated with a uniform axial power shape. There were no mixing vanes on the spacer grids. Thermocouples were placed on the hot rod in the center of the test section and on an adjacent rod at 4 different axial levels. Thermocouples were also located in the center of the subchannels at the end of the test section. Boiling curves were generated over a range of test conditions (system pressure, inlet temperature, and flow rate) by plotting rod surface temperature versus heat flux. The boiling curves covered single phase, subcooled boiling, bulk boiling and DNB conditions. The data from the boiling curves were reduced and evaluated with the VIPRE thermal hydraulic code. Clad temperature predictions were made with VIPRE based on available heat transfer correlations for comparison to clad temperature measurements. These heat transfer correlations include the Dittus Boelter correlation for single phase flow, the Jens Lottes, Thom and Chen correlations for two phase flow conditions (subcooled boiling). The VIPRE predictions of the hot rod average surface temperature, based on the Dittus-Boelter correlation with a grid enhancement factor for single-phase forced convection and the Thom correlation for nucleate boiling, gave the best agreement with the rod bundle test data among all the available modeling options. It was concluded that current heat transfer models used in TH codes, are adequate for average steaming rate calculations supporting Axial Offset Anomalies (AOA) evaluations, as long as the appropriate grid enhancement factor is utilized for the spacer grids in the analysis. However, further testing and modeling may be needed to simulate local grid effects and hot spots downstream of spacer grids.

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