Calculation and Analysis of Heat Transfer Coefficients and Temperature Fields of Air-Cooled Large Hydro-Generator Rotor Excitation Windings

2011 ◽  
Vol 26 (3) ◽  
pp. 946-952 ◽  
Author(s):  
Li Weili ◽  
Zhang Yu ◽  
Chen Yuhong
Keyword(s):  
Heat Transfer ◽  
Temperature Fields ◽  
Transfer Coefficients ◽  
Generator Rotor ◽  
Heat Transfer Coefficients

The Effect of Regulating Elements on Convective Heat Transfer along Shaped Heat Exchange Surfaces

2013 ◽  
Vol 34 (1) ◽  
pp. 5-16 ◽  
Author(s):  
Jozef Cernecky ◽  
Jan Koniar ◽  
Zuzana Brodnianska
Keyword(s):  
Heat Transfer ◽  
Heat Exchange ◽  
Cfd Simulation ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Temperature Fields ◽  
Transfer Coefficients ◽  
Heat Transfer Intensification ◽  
Heat Transfer Coefficients ◽  
Forced Air

Abstract The paper deals with a study of the effect of regulating elements on local values of heat transfer coefficients along shaped heat exchange surfaces with forced air convection. The use of combined methods of heat transfer intensification, i.e. a combination of regulating elements with appropriately shaped heat exchange areas seems to be highly effective. The study focused on the analysis of local values of heat transfer coefficients in indicated cuts, in distances expressed as a ratio x/s for 0; 0.33; 0.66 and 1. As can be seen from our findings, in given conditions the regulating elements can increase the values of local heat transfer coefficients along shaped heat exchange surfaces. An optical method of holographic interferometry was used for the experimental research into temperature fields in the vicinity of heat exchange surfaces. The obtained values correspond very well with those of local heat transfer coefficients αx, recorded in a CFD simulation.

Flow Dynamics Over Two Cylinders in Tandem Subjected to Different Heating Cases

2021 ◽  
Author(s):  
Rami Homsi ◽  
MD Islam ◽  
Yap Yit Fatt ◽  
Isam Janajreh
Keyword(s):  
Heat Transfer ◽  
Cross Flow ◽  
Temperature Fields ◽  
Circular Cylinders ◽  
Transfer Coefficients ◽  
Extended Body ◽  
Heat Transfer Coefficients ◽  
Velocity Magnitude ◽  
Fluid Properties ◽  
Limiting Case

Abstract Heated and unheated flows with forced convection over two fixed circular cylinders in tandem are studied numerically for 80 ≤ Re ≤ 250 and 1 ≤ T* ≤ 2.3. Three different spacing ratios (L/D) = [2, 4, 8] are considered under three heating conditions. The scenarios considered are (1) heated upstream and unheated downstream cylinders, (2) unheated upstream and heated downstream cylinders and (3) heated upstream and downstream cylinders. These scenarios represent the limiting case for a cross-flow heat exchanger, where the downstream tubes are at increasingly lower or higher temperature for cooling or heating, respectively. The global aerodynamic forces on the cylinder as vortices shed was investigated. The flow is visualized by plotting the streamlines, temperature fields, and velocity magnitude contours for the different spacing ratios and compared to the flow regimes in literature namely, Extended-body, Reattachment, and Co-shedding regimes. The drag and surface heat transfer coefficients are analyzed for different scenarios. The effect of heating on the fluid properties and the resulted wakes in the flow are found to be strongly influenced by Re and L/D. The scenario of heated upstream and unheated downstream cylinders was found to increase the mean drag coefficient Cd on the upstream cylinder for L/D = 2 & 4 but is not as evident for the downstream cylinder. The heat transfer coefficient h on the upstream cylinder remained approximately the same regardless of a heated or unheated downstream cylinder. In contrast, h of the downstream cylinder decreases for the scenario of heated upstream and downstream cylinder.

Numerical Simulation on the Temperature Field of Steel 1045 Quenched by Different Hardening Media

2013 ◽  
Vol 444-445 ◽  
pp. 1222-1228
Author(s):  
Jian Bin Xie ◽  
Chang Chang Wu ◽  
Jing Fan ◽  
Miao Fu ◽  
Deng Feng Hu
Keyword(s):  
Heat Transfer ◽  
Finite Element ◽  
Temperature Field ◽  
Temperature Fields ◽  
Cooling Curves ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Heat Transfer Theory ◽  
Quenching Process ◽  
Estimate Method

Based on the experimental measured cooling curves and the boiling heat transfer theory, the inverse problem of nonlinear heat conduct equation for Steel 1045 quenched by different hardening media was established by functional analysis and finite element method, and the surface heat-transfer coefficients in continuous cooling during quenching were calculated by nonlinear estimate method. Then the constitutive model of Steel 1045 during quenching was established subsequently. Finally, the temperature field of Steel 1045 cylinder quenched by different hardening media was simulated by Finite Element Methods (FEM). Results show that the calculated temperature fields agree with the practical quenching process.

An Experimental Study of Sister Holes Film Cooling With Various Secondary-to-Primary Hole Diameter Ratios

2020 ◽  
Vol 143 (1) ◽  
Author(s):  
Rui Zhu ◽  
Enci Lin ◽  
Terrence Simon ◽  
Gongnan Xie
Keyword(s):  
Heat Transfer ◽  
Film Cooling ◽  
Diameter Ratio ◽  
Hole Diameter ◽  
Temperature Fields ◽  
Thermochromic Liquid Crystal ◽  
Transfer Coefficients ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Heat Transfer Coefficients

Abstract For increased specific thrust and efficiency, more effective film-cooling schemes are developed with each successive gas turbine design. Adding secondary film-cooling holes to each primary film-cooling hole represents such improvement without significantly increasing cost. Presented is an experimental investigation on the effects of secondary-to-primary hole diameter ratio on film-cooling performance and flow structure in the coolant-to-passage flow merge zone. Film-cooling effectiveness values and heat transfer coefficients are measured in the vicinity of the hole by the thermochromic liquid crystal (TLC) technique. Measured in-flow temperature fields in the coolant emerging zone identify flow makeup, whether coolant or passage. Furthermore, complementary flow and thermal fields are numerically documented. The Reynolds number based on mainstream velocity and primary hole diameter is 20,300, a representative value. Performance features are compared at three blowing ratios (0.5, 1.0, and 1.5) and two mass flow ratios (3.43% and 5.15%). Secondary holes improve film-cooling effectiveness, especially when blowing rate is high. Secondary holes create an “antikidney vortex structure” that weakens the main kidney vortex pair which helps keep coolant attached to the surface, allowing more effective laterally spreading. However, adding secondary holes increases heat transfer coefficients, especially at high blowing rates. The secondary-to-primary hole diameter ratio is an important parameter. Larger secondary holes can counteract the detrimental effects of having higher blowing ratios, but with increased blowing ratios this improvement subsides. An optimum diameter ratio is sought.

Temperature Field Analysis of Directional Solidification of Multi-Crystalline Silicon

2013 ◽  
Vol 750 ◽  
pp. 96-99 ◽  
Author(s):  
Yan Hu ◽  
Hai Hao ◽  
Xiao Teng Liu
Keyword(s):  
Heat Transfer ◽  
Temperature Field ◽  
Solar Cells ◽  
Directional Solidification ◽  
Crystalline Silicon ◽  
Cost Effective ◽  
Field Analysis ◽  
Temperature Fields ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients

A cost effective directional solidification (DS) technique is one of the main methods to produce multi-crystalline silicon (mc-Si) ingots for solar cells. A detailed understanding of the DS process is very important to control the formation and distribution of impurities, precipitates, thermal stress and dislocation defects in an ingot. All these factors have direct effects on the solar cells efficiency. The quality of crystal grown by DS is largely determined by the temperature field. In order to optimize the technique parameters and obtain high quality silicon ingots, the temperature fields with different heat transfer coefficients at different positions have been calculated during the silicon DS process. The influence of the heat transfer coefficients at the ingot top(ht), the ingot bottom (hb), and between ingot and crucible (hs) on the DS process of mc-Si have been analyzed. The calculation results may provide important theoretical basis for optimizing technological recipe in the productive practice.

Turbulent flow and heat transfer in pipes with buoyancy effects

1979 ◽  
Vol 94 (2) ◽  
pp. 383-400 ◽  
Author(s):  
A. M. Abdelmeguid ◽  
D. B. Spalding
Keyword(s):  
Heat Transfer ◽  
Turbulent Flow ◽  
Dissipation Rate ◽  
Flow Resistance ◽  
The Other ◽  
Temperature Fields ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Flow And Heat Transfer ◽  
Velocity And Temperature Fields

A finite-difference procedure, is employed to predict the turbulent flow and heat transfer in horizontal, inclined and vertical pipes when influenced by buoyancy. The flow is treated as parabolic; and the turbulence model used involves the solution of two differential equations, one for the kinetic energy of turbulence and the other for its dissipation rate. Results are presented for the velocity and temperature fields, and the associated flow-resistance and heat-transfer coefficients. The predictions for horizontal and vertical pipes have been compared with the available experimental results, and the agreement obtained is good.

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