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%.

Force Analysis of Bubble Dynamics in Flow Boiling Silicon Nanowire Microchannels

2016 ◽  
Author(s):  
Tamanna Alam ◽  
Wenming Li ◽  
Fanghao Yang ◽  
Ahmed Shehab Khan ◽  
Yan Tong ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Surface Tension ◽  
Bubble Growth ◽  
Bubble Dynamics ◽  
Flow Boiling ◽  
Silicon Nanowire ◽  
Bubble Nucleation ◽  
Force Analysis ◽  
Vapor Interface ◽  
Liquid Vapor

In microchannel flow boiling, bubble nucleation, growth and flow regime development are highly influenced by channel cross-section and physical phenomena underlying this mechanism are far from being well-established. Relative effects of different forces acting on wall-liquid and liquid-vapor interface of a confined bubble play an important role in heat transfer performances. Therefore, fundamental investigations are necessary to develop enhanced microchannel heat transfer surfaces. Force analysis of vapor bubble dynamics in flow boiling Silicon Nanowire (SiNW) microchannels has been performed based on theoretical, experimental and visualization studies. The relative effects of different forces on flow regime, instability and heat transfer performances of flow boiling in Silicon Nanowire microchannels have been identified. Inertia, surface tension, shear, buoyancy, and evaporation momentum forces have significant importance at liquid-vapor interface as discussed earlier by several authors. However, no comparative study has been done for different surface properties till date. Detailed analyses of these forces including contact angle and bubble flow boiling characteristics have been conducted in this study. A comparative study between Silicon Nanowire and Plainwall microchannels has been performed based on force analysis in the flow boiling microchannels. In addition, force analysis during instantaneous bubble growth stage has been performed. Compared to Plainwall microchannels, enhanced surface rewetting and critical heat flux (CHF) are owing to higher surface tension force at liquid-vapor interface and Capillary dominance resulting from Silicon Nanowires. Whereas, low Weber number in Silicon Nanowire helps maintaining uniform and stable thin film and improves heat transfer performances. Moreover, force analysis during instantaneous bubble growth shows the dominance of surface tension at bubble nucleation and slug/transitional flow which resulted higher heat transfer contact area, lower thermal resistance and higher thin film evaporation. Whereas, inertia force is dominant at annular flow and it helps in bubble removal process and rewetting.

Aero-Thermal Coupled Throughflow Method With Cooling Model Based on Flow Network Analysis

2017 ◽  
Author(s):  
Wei Ba ◽  
Xiaodong Ren
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Network Analysis ◽  
Flow Rate ◽  
Film Cooling ◽  
Cooling Effect ◽  
Flow Network ◽  
Model Based ◽  
Film Cooling Holes ◽  
Cooling Model

The aero-thermal coupled phenomenon is significant in the modern cooled turbine, and it is necessary to consider the cooling effect in the throughflow design phase. A new cooling model based on flow network analysis for the aero-thermal coupled throughflow method was developed to consider the film cooling effect and predict the blade wall temperature downstream of the film cooling holes. The flow network analysis is introduced into the cooling model to determine the flow rate of each cooling hole. The mixing loss caused by film cooling is investigated as local total pressure loss, and the heat transfer influence caused by film cooling is considered by the film cooling effectiveness estimated by empirical correlation. The blade heat transfer downstream the film cooling holes is calculated from pressure and suction surfaces separately, based on main flow parameters calculated by the streamline curvature method. The experimental data of the C3X profile is selected for the cooling model verification. The film cooling flow rate calculated by the flow network analysis agrees well with the experimental data, and the calculated temperatures of both the pressure and suction surfaces downstream the film cooling holes are also in accordance with the experimental data. Therefore, aero-thermal coupled throughflow method with this cooling model can be a powerful tool for preliminary design of cooled turbine.

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.

Fuzzy Modeling to Simulate Surface Roughness in CNC Turning of AISI 1045 Steel

2011 ◽  
Vol 486 ◽  
pp. 262-265
Author(s):  
Amit Kohli ◽  
Mudit Sood ◽  
Anhad Singh Chawla
Keyword(s):  
Experimental Data ◽  
Surface Roughness ◽  
Process Parameters ◽  
Fuzzy Model ◽  
Fuzzy Modeling ◽  
Cnc Machine ◽  
Model Based ◽  
Aisi 1045 Steel ◽  
Aisi 1045 ◽  
1045 Steel

The objective of the present work is to simulate surface roughness in Computer Numerical Controlled (CNC) machine by Fuzzy Modeling of AISI 1045 Steel. To develop the fuzzy model; cutting depth, feed rate and speed are taken as input process parameters. The predicted results are compared with reliable set of experimental data for the validation of fuzzy model. Based upon reliable set of experimental data by Response Surface Methodology twenty fuzzy controlled rules using triangular membership function are constructed. By intelligent model based design and control of CNC process parameters, we can enhance the product quality, decrease the product cost and maintain the competitive position of steel.

scholarly journals Experimental analysis and ANN prediction on performances of finned oval-tube heat exchanger under different air inlet angles with limited experimental data

Open Physics ◽  
2020 ◽  
Vol 18 (1) ◽  
pp. 968-980
Author(s):  
Xueping Du ◽  
Zhijie Chen ◽  
Qi Meng ◽  
Yang Song
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Heat Exchanger ◽  
Correlation Equation ◽  
Tube Heat Exchanger ◽  
Flow Friction ◽  
Air Inlet ◽  
Comparison Results ◽  
Wide Range ◽  
Oval Tube

Abstract A high accuracy of experimental correlations on the heat transfer and flow friction is always expected to calculate the unknown cases according to the limited experimental data from a heat exchanger experiment. However, certain errors will occur during the data processing by the traditional methods to obtain the experimental correlations for the heat transfer and friction. A dimensionless experimental correlation equation including angles is proposed to make the correlation have a wide range of applicability. Then, the artificial neural networks (ANNs) are used to predict the heat transfer and flow friction performances of a finned oval-tube heat exchanger under four different air inlet angles with limited experimental data. The comparison results of ANN prediction with experimental correlations show that the errors from the ANN prediction are smaller than those from the classical correlations. The data of the four air inlet angles fitted separately have higher precisions than those fitted together. It is demonstrated that the ANN approach is more useful than experimental correlations to predict the heat transfer and flow resistance characteristics for unknown cases of heat exchangers. The results can provide theoretical support for the application of the ANN used in the finned oval-tube heat exchanger performance prediction.

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