Heat-transfer mechanism at a gas-fiber boundary

Abstract The onset of nucleate boiling (ONB) is the point at which the heat transfer mechanism in fluids changes and is one of the thermo-hydraulic factors that must be considered when establishing a cooling system operation strategy. Because the high heat flux of several MW/m2, which is loaded within a tokamak, is applied under a one-side heating condition, it is necessary to determine a correlative relation that can predict ONB under special heating conditions. In this study, the ONB of a one-side-heated screw tube was experimentally analyzed via a subcooled flow boiling experiment. The helical nut structure of the screw tube flow path wall allows for improved heat transfer performance relative to smooth tubes, providing a screw tube with a 53.98% higher ONB than a smooth tube. The effects of the system parameters on the ONB heat flux were analyzed based on the changes in the heat transfer mechanism, with the results indicating that the flow rate and degree of subcooling are proportional to the ONB heat flux because increasing these factors improves the forced convection heat transfer and increases the condensation rate, respectively. However, it was observed that the liquid surface tension and latent heat decrease as the pressure increases, leading to a decrease in the ONB heat flux. An evaluation of the predictive performance of existing ONB correlations revealed that most have high error rates because they were developed based on ONB experiments on micro-channels or smooth tubes and not under one-side high heat load conditions. To address this, we used dimensional analysis based on Python code to develop new ONB correlations that reflect the influence of system parameters.

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Methods of Numerically Analyzing and Visually Measuring Transport Phenomena in Chemical Equipment. Numerical Analysis of the Heat Transfer Mechanism in an Arc Furnace for Silica Grass Crucible Production.

KAGAKU KOGAKU RONBUNSHU ◽

10.1252/kakoronbunshu.27.535 ◽

2001 ◽

Vol 27 (5) ◽

pp. 535-539

Author(s):

Yoshihisa Abe ◽

Toshiyuki Kikuchi ◽

Hideo Nakanishi ◽

Takayuki Watanabe

Keyword(s):

Heat Transfer ◽

Numerical Analysis ◽

Transport Phenomena ◽

Chemical Equipment ◽

Transfer Mechanism ◽

Arc Furnace ◽

Heat Transfer Mechanism

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Large Eddy Simulation of Flow and Heat Transfer Mechanism in Matrix Cooling Channel

Volume 5A: Heat Transfer ◽

10.1115/gt2017-63515 ◽

2017 ◽

Author(s):

Yigang Luan ◽

Lianfeng Yang ◽

Bo Wan ◽

Tao Sun

Keyword(s):

Heat Transfer ◽

Flow Field ◽

Large Eddy Simulation ◽

Gas Turbine ◽

Transfer Mechanism ◽

Heat Transfer Mechanism ◽

Longitudinal Vortices ◽

Eddy Simulation ◽

Flow And Heat Transfer ◽

Large Eddy

Gas turbine engines have been widely used in modern industry especially in the aviation, marine and energy fields. The efficiency of gas turbines directly affects the economy and emissions. It’s acknowledged that the higher turbine inlet temperatures contribute to the overall gas turbine engine efficiency. Since the components are subject to the heat load, the internal cooling technology of turbine blades is of vital importance to ensure the safe and normal operation. This paper is focused on exploring the flow and heat transfer mechanism in matrix cooling channels. In order to analyze the internal flow field characteristics of this cooling configuration at a Reynolds number of 30000 accurately, large eddy simulation method is carried out. Methods of vortex identification and field synergy are employed to study its flow field. Cross-sectional views of velocity in three subchannels at different positions have been presented. The results show that the airflow is strongly disturbed by the bending part. It’s concluded that due to the bending structure, the airflow becomes complex and disordered. When the airflow goes from the inlet to the turning, some small-sized and discontinuous vortices are formed. Behind the bending structure, the size of the vortices becomes big and the vortices fill the subchannels. Because of the structure of latticework, the airflow is affected by each other. Airflow in one subchannel can exert a shear force on another airflow in the opposite subchannel. It’s the force whose direction is the same as the vortex that enhances the longitudinal vortices. And the longitudinal vortices contribute to the energy exchange of the internal airflow and the heat transfer between airflow and walls. Besides, a comparison of the CFD results and the experimental data is made to prove that the numerical simulation methods are reasonable and acceptable.

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