Departure and Lift-Off Point of Bubbles at Heating Wall in Vertical Channel

2006 ◽  
Author(s):  
Liang-Ming Pan ◽  
De-Qi Chen ◽  
De-Wen Yuan ◽  
Ying-Qing He ◽  
Li Zhang
Keyword(s):  
Buoyancy Force ◽  
Vertical Channel ◽  
Hydrodynamic Pressure ◽  
Surface Tension Force ◽  
Inertia Force ◽  
Pressure Force ◽  
Heating Wall ◽  
Departure Point ◽  
Lean Angle ◽  
Lift Off

This paper proposed a theoretical model involving in conditions of bubble departure point and lift-off point, the principle and estimating method of individual forces have been proposed as well. The forces acted on growing bubble are, namely, surface tension force Fs, growth force of bubbles Fdu, shear lift force FsL, drag force of flow Fqs, hydrodynamic pressure force Fh, contact pressure force Fcp, buoyancy force Fb and bubble acceleration inertia force d(mvc)/dt as well. Horizontal and vertical momentum equations are presented according to forces balance of bubble, meanwhile, the estimating method of lean angle of bubble before departure also has been discussed.

Development of Bubble Departure Diameter Model Based on Force Analysis

2017 ◽  
Author(s):  
Ye Tian ◽  
Wei Huang ◽  
Pengfei Li ◽  
Simin Cao ◽  
Yan Sun
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Drag Force ◽  
Bubble Dynamics ◽  
Hydrodynamic Pressure ◽  
Surface Tension Force ◽  
Force Analysis ◽  
Pressure Force ◽  
Model Based ◽  
Unsteady Drag Force

Bubble departure diameter has significant effect on bubble dynamics and heat transfer in boiling system, and it is difficult to be measured in a boiling system. Therefore, a method to predict bubble departure diameter is necessary to study of bubble dynamics and heat transfer in boiling system. A new theoretical model based on force analysis is proposed for the prediction of bubble departure diameter in vertical boiling system in this paper. Surface tension force, unsteady drag force, quasi-steady drag force, shear lift force, buoyancy force, hydrodynamic pressure force and contact pressure force are taken into account to build the model. Chen’s experimental data is used to validate the model, the averaged relative deviation between the predict results of the model and the experimental data is less than ±14.8%.

5A 1300V Trenched and Implanted 4H-SiC Vertical JFET

2012 ◽  
Vol 229-231 ◽  
pp. 824-827 ◽  
Author(s):  
Gang Chen ◽  
Xiao Feng Song ◽  
Song Bai ◽  
Li Li ◽  
Yun Li ◽  
...  
Keyword(s):  
Ohmic Contact ◽  
Field Effect ◽  
Field Effect Transistor ◽  
Vertical Channel ◽  
Drain Current ◽  
Gate Bias ◽  
Blocking Voltage ◽  
Drain Bias ◽  
Effect Transistor ◽  
Lift Off

A silicon carbide (SiC) vertical channel junction field effect transistor (VJFET) was fabricated based on in-house SiC epitaxial wafer with lift-off trenched and implanted method. Its blocking voltage exceeds 1300V at gate bias VG = -6V and forward drain current is in excess of 5A at gate bias VG = 3V and drain bias VD = 3V. The SiC VJFET device’s current density is 240A/cm2 at VG= 3V and VD = 3V, with related specific on-resistance 8.9mΩ•cm2. Further analysis reveals that the on-resistance depends greatly on ohmic contact resistance and the bonding spun gold. The specific on-resistance can be further reduced by improving the doping concentration of SiC channel epilayer and the device’s ohmic contact.

scholarly journals Flow Reversal of Fully Developed Mixed Convection in a Vertical Channel with Chemical Reaction

2013 ◽  
Vol 2013 ◽  
pp. 1-4 ◽  
Author(s):  
Habibis Saleh ◽  
Ishak Hashim ◽  
Sri Basriati
Keyword(s):  
Mixed Convection ◽  
Chemical Reaction ◽  
Buoyancy Force ◽  
Vertical Channel ◽  
Critical Values ◽  
Flow Reversal ◽  
Governing Equations ◽  
Reversed Flow ◽  
Exothermic Chemical Reaction

The present analysis is concerned with the criteria for the onset of flow reversal of the fully developed mixed convection in a vertical channel under the effect of the chemical reaction. The governing equations and the critical values of the buoyancy force are solved and calculated numerically via MAPLE. Parameter zones for the occurrence of reversed flow are presented. The exothermic chemical reaction is found to enhance the flow reversal and made flow reversal possible for symmetrical walls temperature.

Improved Taylor analogy breakup and Clark models for droplet deformation prediction

2017 ◽  
Vol 233 (2) ◽  
pp. 767-775 ◽  
Author(s):  
Zhenlong Wu ◽  
Benyin Lv ◽  
Yihua Cao
Keyword(s):  
Leading Edge ◽  
Surface Tension Force ◽  
Aerodynamic Characteristics ◽  
Viscous Force ◽  
Pressure Force ◽  
Droplet Deformation ◽  
Deformation Prediction ◽  
Clark Model ◽  
Improved Model ◽  
Breakup Model

The deformation of rain droplet at the leading edge of a wing is critical to the aerodynamic characteristics of the aircraft under heavy rainfall and icing conditions. This study introduces the improvement of the Taylor analogy breakup and Clark models for prediction of droplet deformation near the leading edge of an airfoil. The slip velocity is considered as time-variant in the improved Taylor analogy breakup model. The viscous force is optimized in the improved Clark model. The prediction results suggest that the Clark models predict better results than the Taylor analogy breakup models. Besides, the improved Clark model has the highest prediction accuracy. However, considering the Clark model is derived based on a two-dimensional model, even the improved model still has some unavoidable deviations from the real situation. In addition, the simplified surface area in the surface tension force and the approximation of the pressure force in the original Clark model are very effective, thus are kept the same in the improved Clark model.

scholarly journals UNSTEADY MHD FLOW OF RADIATING CASSON FLUID THROUGH A PERMEABLE CHANNEL WITH SLIP, BUOYANCY FORCE AND HEAT SOURCE

2020 ◽  
Vol 50 (4) ◽  
pp. 315-320
Author(s):  
Om Prakash Verma ◽  
Oluwole Daniel Makinde ◽  
R. L. Monaledi
Keyword(s):  
Heat Transfer ◽  
Heat Source ◽  
Skin Friction ◽  
Buoyancy Force ◽  
Fluid Velocity ◽  
Vertical Channel ◽  
Wall Slip ◽  
Mhd Flow ◽  
Casson Fluid ◽  
Left Wall

Analytical investigation is performed into an unsteady Magnetohrodynamics mixed convective Casson fluid flow and heat transfer characteristics with thermal radiation, wall slip, heat source and buoyancy force in a permeable vertical channel. The fluid is injected into the left wall of the channel and sucked out at right wall. The governing momentum and energy balance equations are achieved and tackled analytically. The effects of numerous thermophysical parameters on the temperature profiles, velocity, Nusselt number as well as skin friction are presented graphically and discussed qualitatively. The results show that a temporal decline in the pressure gradient causes both the temperature and fluid velocity to decrease. Moreover, the enhancement in heat transfer due to wall injection/suction also causes the skin friction to decrease.

scholarly journals Bubble departure diameter determination for pool boiling on surface with microchannels

2018 ◽  
Vol 70 ◽  
pp. 02008
Author(s):  
Robert Kaniowski ◽  
Robert Pastuszko ◽  
Joanna Kowalczyk ◽  
Łukasz Nowakowski
Keyword(s):  
Atmospheric Pressure ◽  
Buoyancy Force ◽  
Pool Boiling ◽  
Surface Tension Force ◽  
Copper Sample ◽  
Heat Fluxes ◽  
Force Balance ◽  
Saturated Water ◽  
Open Microchannel ◽  
Parallel Microchannels

The paper presents visualization investigations into pool boiling heat transfer for open microchannel surfaces. The experiments were carried out with saturated water, ethanol, FC-72 and Novec-649 at atmospheric pressure. Parallel microchannels fabricated by machining copper sample were about 0.2 to 0.5 mm wide and 0.2 to 0.5 mm deep. The diameter of departing bubble was calculated for the microchannel surface on the basis of buoyancy force and surface tension force balance. The visualization carried out was aimed at determining the diameters of the departing bubbles at various heat fluxes for four working fluids.

scholarly journals Prediction of Bubble Departure in Forced Convection Boiling with a Mechanistic Model That Considers Dynamic Contact Angle and Base Expansion

Energies ◽  
2019 ◽  
Vol 12 (10) ◽  
pp. 1950 ◽  
Author(s):  
Hamed Setoodeh ◽  
Wei Ding ◽  
Dirk Lucas ◽  
Uwe Hampel
Keyword(s):  
Bubble Dynamics ◽  
Flow Boiling ◽  
Mechanistic Model ◽  
Dynamic Contact Angle ◽  
Dynamic Contact ◽  
Contact Angles ◽  
Force Balance ◽  
Heating Wall ◽  
System Pressure ◽  
Lift Off

A mechanistic model for bubble dynamics in flow boiling that is based on a force balance approach for a growing bubble is introduced. It considers the evaporation of the microlayer underneath the bubble, thermal diffusion and condensation around the bubble cap as well as dynamic inclination and contact angles between the bubble and the heating wall. It requires no recalibration of parameters to predict the bubble growth. Validation against different experimental flow boiling data was carried out with no case-dependent recalibration and yielded good agreement. The simulations confirmed the dependency of bubble departure and lift-off diameters on different parameters such as heat flux, liquid properties, subcooling temperature, system pressure, inclination angle of channel, channel geometry and mass flow rate.

scholarly journals Bubble Departure Diameter Prediction Uncertainty

2012 ◽  
Vol 2012 ◽  
pp. 1-7 ◽  
Author(s):  
Marko Matkovič ◽  
Boštjan Končar
Keyword(s):  
Prediction Accuracy ◽  
Buoyancy Force ◽  
Lift Force ◽  
Bubble Dynamics ◽  
Flow Boiling ◽  
Surface Tension Force ◽  
Experimental Accuracy ◽  
Mechanistic Modelling ◽  
Boiling Process ◽  
Heat Partitioning

This paper presents quality assessment of a mechanistic modelling for bubble departure diameter prediction during pool boiling condition. In contrast to flow boiling process only buoyancy force with opposing surface tension force was considered as the responsible mechanisms for bubble departure. Indeed, inertia from the fluid flow around the bubble and the growth force, which describes momentum change due to the evaporation at the bubble base and condensation at the top of the bubble, were all neglected. Besides, shear lift force and quasi-steady drag force as the dominant inertia driven forces were also neglected in the assessment. Rather than trying to model bubble dynamics as precise as possible by properly addressing all the relevant mechanisms available, the work focuses on prediction accuracy of such approach. It has been shown that inlet boundary conditions with realistic experimental accuracy may lead to a significant uncertainty in the prediction of bubble departure diameter, which is intrinsically connected to the uncertainty of most heat partitioning and CHF models.

Bearing Characteristic Parameters to Estimate the Optimum Counterweight Mass of a 6-Cylinder In-Line Engine

2001 ◽  
Author(s):  
Richard E. Stanley ◽  
Dinu Taraza
Keyword(s):  
Critical Speed ◽  
Engine Speed ◽  
Inertia Force ◽  
Maximum Pressure ◽  
Operating Parameters ◽  
Cylinder Pressure ◽  
Characteristic Parameters ◽  
Pressure Force ◽  
Bearing Load ◽  
Bearing Characteristic

Abstract Two dimensionless relationships that estimate the maximum and average bearing load of a 6-cylinder 4-stroke in-line engine have been found. These relationships may assist the design engineer in choosing a desired counterweight mass. It has been demonstrated that: 1) the average bearing load increases with engine speed and 2) the maximum bearing load initially decreases with engine speed, reaches a minimum, then increases quickly with engine speed. This minimum refers to a critical speed at which the contribution of the inertia force overcomes the contribution of the maximum pressure force to the maximum bearing load. The critical speed increases with an increase of counterweight mass and is a function of maximum cylinder pressure and the operating parameters of the engine.

Photographic Study on Bubble Motion in Subcooled Pool Boiling

2009 ◽  
Author(s):  
Tomio Okawa ◽  
Takahiro Harada ◽  
Yuta Koutsusa
Keyword(s):  
Surface Tension ◽  
Contact Angle ◽  
Pool Boiling ◽  
Surface Tension Force ◽  
Nucleate Boiling ◽  
Tension Force ◽  
Test Fluid ◽  
Static Contact ◽  
Short Period ◽  
Lift Off

Using a static contact angle as a main experimental parameter, photographic study was carried out to investigate the dynamics of vapor bubbles during subcooled pool boiling on a vertical heated surface. Test fluid was distilled water and the experiments were performed under the atmospheric pressure; liquid subcooling was set to around 5 K. To enable clear observation of bubble behavior with a high speed camera, the experiments were conducted in an isolated bubble regime near the onset of nucleate boiling. Distinctly different bubble behaviors were observed on hydrophobic and hydrophilic surfaces: the bubbles were adhered to the surface for a long period of time when the contact angle was large while lifted off the surface within a short period of time after the nucleation when the contact angle was small. Since buoyancy does not remove the bubble from a vertical surface, mechanisms of lift-off were investigated. It was shown that the change in bubble shape induced by the surface tension force, unsteady growth force and local liquid flow induced by heterogeneous condensation around the bubble are considered to promote the bubble lift-off and the surface tension force acting on the three-phase common line prevents the lift-off. Dependences of bubble size and time at lift-off and the condensation rate on the surface wettability were also investigated.

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