A flame-wall interaction model for combustion and heat transfer in S.I. engines

Surface heat transfer and skin friction enhancements, as a result of free-stream turbulence levels between 10 percent < Tu > 20 percent, have been measured and compared in terms of correlations given throughout the literature. The results indicate that for this range of turbulence levels, the skin friction and heat transfer enhancements scale best using parameters that are a function of turbulence level and dissipation length scale. However, as turbulence levels approach Tu = 20 percent, the St′ parameter becomes more applicable and simpler to apply. As indicated by the measured rms velocity profiles, the maximum streamwise rms value in the near-wall region, which is needed for St′, is the same as that measured in the free stream at Tu = 20 percent. Analogous to St′, a new parameter, Cf′, was found to scale the skin friction data. Independent of all the correlations evaluated, the available data show that the heat transfer enhancement is greater than the enhancement of skin friction with increasing turbulence levels. At turbulence levels above Tu = 10 percent, the free-stream turbulence starts to penetrate the boundary layer and inactive motions begin replacing shear-stress producing motions that are associated with the fluid/wall interaction. Although inactive motions do not contribute to the shear stress, these motions are still active in removing heat.

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A Thermal Model to Predict Tool Temperature in Machining of Ti-6Al-4V Alloy With an Atomization-Based Cutting Fluid Spray System

Volume 1: Processing ◽

10.1115/msec2016-8595 ◽

2016 ◽

Cited By ~ 3

Author(s):

Asif Tanveer ◽

Deepak Marla ◽

Shiv G. Kapoor

Keyword(s):

Heat Transfer ◽

Interaction Model ◽

Spray Cooling ◽

Droplet Surface ◽

Cutting Fluid ◽

Design Parameters ◽

Transfer Model ◽

Tool Temperature ◽

Spray System ◽

Heat Transfer Phenomenon

In this study a heat transfer model of machining of Ti-6Al-4V under the application of atomization-based cutting fluid spray coolant is developed to predict the temperature of the cutting tool. Owing to high tool temperature involved in machining of Ti-6Al-4V, the model considers film boiling as the major heat transfer phenomenon. In addition, the design parameters of the spray for effective cooling during machining are derived based on droplet-surface interaction model. Machining experiments are conducted and the temperatures are recorded using the inserted thermocouple technique. The experimental data are compared with the model predictions. The temperature field obtained is comparable to the experimental results, confirming that the model predicts tool temperature during machining with ACF spray cooling satisfactorily.

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Effect of Spray-Wall Interaction On Thermoacoustic Instability Prediction by Flame Transfer Function and the Convective Time Delay Method

Journal of Engineering for Gas Turbines and Power ◽

10.1115/1.4051639 ◽

2021 ◽

Author(s):

Sheng Meng ◽

Man Zhang

Keyword(s):

Time Delay ◽

Transfer Function ◽

Numerical Models ◽

Time Lag ◽

Interaction Model ◽

Phase Lag ◽

Thermoacoustic Instability ◽

Spray Flame ◽

Wall Interaction ◽

Definition Of

Abstract This study numerically investigates the effect of spray-wall interactions on thermoacoustic instability prediction. The LES-based flame transfer function (FTF) and the convective time delay methods are used by combining the Helmholtz acoustic solver to predict a single spray flame under the so-called slip and film spray-wall conditions. It is found that considering more realistic film liquid and a wall surface interaction model achieves a more accurate phase lag in both of the time lag evaluations compared to the experimental results. Additionally, the results show that a new time delay exists between the liquid film fluctuation and the unsteady heat release, which explains the larger phase value in the film spray-wall condition than in the slip condition. Moreover, the prediction capability of the FTF framework and the convective time delay methodology in the linear regime are also presented. In general, the instability frequency differences predicted using the FTF framework under the film condition are less than 10 Hz compared with the experimental data. However, an underestimation of the numerical gain value leads to requiring a change in the forcing position and an improvement in the numerical models. Due to the ambiguous definition of the gain value in the convective time delay method, this approach leads to arbitrary and uncertain thermoacoustic instability predictions.

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Numerical Simulation Of A Microchannel For Microelectronic Cooling

Jurnal Teknologi ◽

10.11113/jt.v46.278 ◽

2012 ◽

Cited By ~ 1

Author(s):

Wai Hing Wong ◽

Normah Mohd. Ghazali

Keyword(s):

Heat Transfer ◽

Numerical Simulation ◽

Heat Flux ◽

Aspect Ratio ◽

Three Dimensional ◽

Large Temperature ◽

Rectangular Microchannel ◽

Numerical Work ◽

Solid Region ◽

Wall Interaction

Kertas kerja ini membincangkan simulasi berangka ke atas sinki haba saluran mikro dalam penyejukan alatan mikroelektronik. Model Dinamik Bendalir Berkomputer (CFD) tiga dimensi dibina menggunakan pakej komersil, FLUENT, untuk mengkaji fenomenon aliran bendalir dan pemindahan haba konjugat di dalam suatu sinki haba segi empat yang diperbuat daripada silikon. Model ditentusahkan dengan keputusan daripada uji kaji dan pengkajian berangka yang lepas untuk lingkungan nombor Reynolds kurang daripada 400 berdasarkan diameter hidraulik 86 mm. Kajian ini mengambil kira kesan kelikatan bendalir yang bersandaran dengan suhu dan keadaan aliran pra–membangun dari segi hidrodinamik dan haba. Model memberi maklumat tentang taburan suhu dan fluks haba yang terperinci di dalam sinki haba saluran mikro. Kecerunan suhu yang tinggi dicatat pada kawasan pepejal berdekatan dengan sumber. Fluks haba paling tinggi didapati pada dinding tepi saluran mikro diikuti oleh dinding atas dan bawah. Purata pekali pemindahan haba yang lebih tinggi bagi silikon menjadikan ia bahan binaan sinki haba saluran mikro yang lebih baik berbanding dengan kuprum dan aluminium. Peningkatan nisbah aspek saluran mikro yang bersegi empat memberi kecekapan penyejukan yang lebih tinggi kerana kelebaran saluran yang berkurangan memberi kecerunan halaju yang lebih tinggi dalam saluran. Nisbah aspek yang optimum yang diperoleh adalah dalam lingkungan 3.7 – 4.1. Kata kunci: Saluran mikro, CFD, FLUENT, simulasi berangka, penyejukan mikroelektron The paper discusses the numerical simulation of a micro–channel heat sink in microelectronics cooling. A three–dimensional Computational Fluid Dynamics (CFD) model was built using the commercial package, FLUENT, to investigate the conjugate fluid flow and heat transfer phenomena in a silicon–based rectangular microchannel heatsink. The model was validated with past experimental and numerical work for Reynolds numbers less than 400 based on a hydraulic diameter of 86 mm. The investigation was conducted with consideration of temperaturedependent viscosity and developing flow, both hydrodynamically and thermally. The model provided detailed temperature and heat flux distributions in the microchannel heatsink. The results indicate a large temperature gradient in the solid region near the heat source. The highest heat flux is found at the side walls of the microchannel, followed by top wall and bottom wall due to the wall interaction effects. Silicon is proven to be a better microchannel heatsink material compared to copper and aluminum, indicated by a higher average heat transfer. A higher aspect ratio in a rectangular microchannel gives higher cooling capability due to high velocity gradient around the channel when channel width decreases. Optimum aspect ratio obtained is in the range of 3.7 – 4.1. Key words: Microchannel, CFD, FLUENT, numerical simulation, microeletronics cooling

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On the Maxwell gas-wall interaction model for micro/nano gas flows

10.1063/1.4769674 ◽

2012 ◽

Author(s):

Tengfei Liang ◽

Qi Li ◽

Wenjing Ye

Keyword(s):

Interaction Model ◽

Gas Flows ◽

Wall Interaction ◽

Maxwell Gas

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A Numerical Model for the Mist Dynamics and Heat Transfer at Various Ambient Pressures

Journal of Fluids Engineering ◽

10.1115/1.1976743 ◽

2005 ◽

Vol 127 (4) ◽

pp. 631-639 ◽

Cited By ~ 8

Author(s):

Roy J. Issa ◽

S. C. Yao

Keyword(s):

Heat Transfer ◽

Numerical Model ◽

Test Data ◽

Model Simulation ◽

Droplet Size Distribution ◽

Atmospheric Conditions ◽

Single Stream ◽

Wide Range ◽

Wall Interaction ◽

Uniform Droplets

A numerical model is developed to simulate the dynamics of the droplet-wall interaction and heat transfer mechanisms at sub-atmospheric to elevated ambient pressures, and for surface temperatures ranging from nucleate to film boiling. This is the first time a general model is developed to study these phenomena over a wide range of ambient pressures. The model provides insight to the optimal flow conditions, and droplet size distribution for best heat transfer enhancement. Simulations are provided for single stream droplet impactions, and for full conical sprays using nozzles that dispense a spectrum of non-uniform droplets. The model simulation was compared against available test data for single stream of droplets at non-atmospheric conditions, and the simulation compared favorably well with the test data.

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Heat Transfer to Horizontal Gas-Solid Suspension Flows

Journal of Heat Transfer ◽

10.1115/1.3449649 ◽

1970 ◽

Vol 92 (1) ◽

pp. 77-82 ◽

Cited By ~ 15

Author(s):

C. A. Depew ◽

E. R. Cramer

Keyword(s):

Heat Transfer ◽

Pressure Drop ◽

Solid Loading ◽

Airflow Rate ◽

Nusselt Numbers ◽

Glass Spheres ◽

Significant Difference ◽

Solid Suspension ◽

Bottom Side ◽

Wall Interaction

Heat transfer and pressure-drop characteristics of a gas-solid suspension flow in a horizontal circular tube were investigated using glass spheres of two sizes, 30 and 200 micron. The airflow rate was held constant at three different values in a 0.71-in-ID tube such that Reynolds numbers of 10,000, 15,000, and 30,000 were produced. Solid loading ratios on a mass basis were as large as 7. The purpose of the investigation was to observe the effect of stratification on the heat transfer characteristics of the system. The pressure-drop results indicate that the solids were suspended in all cases, but the heat transfer data slum significant difference between the temperature of the tube wall at the top and bottom with the small particles. Nusselt numbers were as much as 2-1/2 times larger on the bottom side than on the top side. No such effect was produced with the large particles. The pressure-drop data indicate significant wall interaction for the large size, but not for the small size.

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