HYSTERESIS OF PLANAR DOUBLE SLOT IMPINGING AIR JETS

In present study, the bistability and hysteresis of the non-isothermal flow behind two slot nozzle is numerically investigated. Theoretical review of bistability of isothermal stagnation flow is presented and both flow field patterns that exist in the region of bistability are commented on. Hysteresis is found in number of conducted simulations and effects of various parameter changes are discussed. Moreover, the mechanism of transition from one flow field pattern to another is discussed for both transition directions. In conclusion, validity of 2D simulation results against real 3D problems is of concern and general contribution of this research is discussed. Throughout this work, emphasis is on applications regarding heat transfer.

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Simulation of Acoustic Enhancement of Heat Transfer in a Droplet Heat Exchanger

Volume 4: Turbo Expo 2007, Parts A and B ◽

10.1115/gt2007-27179 ◽

2007 ◽

Author(s):

Melaku Habte ◽

Savas Yavuzkurt

Keyword(s):

Heat Transfer ◽

Flow Field ◽

Acoustic Field ◽

High Intensity ◽

Acoustic Fields ◽

Single Droplet ◽

Enhancement Of Heat Transfer ◽

Nusselt Numbers ◽

2D Simulation ◽

Simulation Results

Enhancement of heat transfer from a droplet exposed to acoustic fields is investigated. Investigation is part of a research project in enhancing the heat transfer in direct contact heat exchangers. Adding high intensity sound to Droplet Heat Exchanger (DHX) design produces relative gas motion around droplets otherwise entrained in the main flow field. Particles do not get fully entrained in the high frequency acoustic field giving rise to relative velocity. This enhances the heat transfer from droplets. Further benefits could be obtained by acoustic agglomeration of small droplets. DHXs have high contact area, no interface losses, low pressure drop and superior heat transfer characteristics compared to standard heat exchangers. With further enhancement of heat transfer by high intensity acoustic field application makes DHXs very attractive in many industrial applications such as droplet/particle reactors, humidifiers, gas scrubbers as well as ground based power generating gas turbines. In this paper, results of simulations of a single droplet exposed to acoustic fields of a range of sound intensity level (SPL) and frequency are presented. Spherical droplets are exposed to high intensity acoustic fields up to 175 dB with frequencies 25–2000Hz. Droplet size considered here is 100μm. Three dimensional (3-D) simulation of an oscillating flow field around a spherical droplet are carried out using FLUENT code. First, simulation results of space-averaged Nusselt numbers for steady flow around a single droplet are compared with available experimental data. Results were within 1–5% of each other. Simulations with acoustic field with and without steady velocity component were carried out and the results were compared with previous two dimensional studies as well as experimental and correlations of the same phenomena. The current simulation results are on average 22% higher than the 2D simulation results indicating the 3D nature of the flow. Space and time-averaged Nusselt numbers were more than 400% higher than the ones obtained without the acoustic field for acoustic Reynolds number 100 and frequency 50Hz and 30% higher than 2D simulation results. Finally, entrainment of droplets in the oscillating flow field was also considered. The result showed insignificant reduction (< 1%) in heat transfer rate compared to the case with no entrainment at all ranges of frequency (50–2000Hz).

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Comparing 2D and 3D numerical simulation results of gas flow velocity in convection reflow oven

Soldering & Surface Mount Technology ◽

10.1108/ssmt-07-2013-0016 ◽

2014 ◽

Vol 26 (4) ◽

pp. 223-230 ◽

Cited By ~ 9

Author(s):

Balázs Illés

Keyword(s):

Heat Transfer ◽

Flow Field ◽

Flow Velocity ◽

Gas Flow ◽

Content Type ◽

Simulation Results ◽

2D And 3D ◽

Gas Flow Velocity ◽

2D Model ◽

Gas Flow Field

Purpose – This paper aims to compare and study two-dimensional (2D) and three-dimensional (3D) computational fluid dynamics simulation results of gas flow velocity in a convection reflow oven and show the differences of the different modeling aspects. With the spread of finer surface-mounted devices, it is important to understand convection reflow soldering technology more deeply. Design/methodology/approach – Convection reflow ovens are divided into zones. Every zone contains an upper and a lower nozzle-matrix. The gas flow velocity field is one of the most important parameters of the local heat transfer in the oven. It is not possible to examine the gas flow field with classical experimental methods due to the extreme circumstances in the reflow oven. Therefore, numerical simulations are necessary. Findings – The heat transfer changes highly along the moving direction of the assembly, and it is nearly homogeneous along the traverse direction of the zones. The gas flow velocity values of the 2D model are too high due to the geometrical distortions of the 2D model. On the other hand, the calculated flow field of the 2D model is more accurate than in the 3D model due to the finer mesh. Research limitations/implications – Investigating the effects of tall components on a printed wiring board inside the gas flow field and further analysis of the mesh size effect on the models. Practical implications – The presented results can be useful during the design of a simulation study in a reflow oven (or in similar processes). Originality/value – The presented results provide a completely novel approach from the aspect of 2D and 3D simulations of a convection reflow oven. The results also reveal the heat transfer differences.

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2D Simulation of the Gas-Solid Two Phase Flow inside the Abrasive Jet (AJ) Nozzle

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.53-54.369 ◽

2008 ◽

Vol 53-54 ◽

pp. 369-373

Author(s):

Rong Guo Hou ◽

Chuan Zhen Huang ◽

Y.S. Feng ◽

Y.Y. Liu

Keyword(s):

Flow Field ◽

Two Phase Flow ◽

Cone Angle ◽

Multiphase Model ◽

Phase Flow ◽

Fatigue Wear ◽

Two Phase ◽

2D Simulation ◽

Jet Nozzle ◽

Simulation Results

The simulation of the gas-solid two phase flow inside the abrasive jet nozzle is studied by the computed dynamic software (CFD)-FLUENT, the velocity field of the two phase flow and the trajectory of the abrasive inside the nozzle are obtained. The Eulerian multiphase model and the DPM model have been used to compute the two-phase flow field. The simulation results express that the velocity of the jet is slow at the inlet, while it will be increased with the area of the section decreasing, the cone angle of the nozzle affects the flow field very much, the flow has low turbulence and the gradient of the velocity is small when the cone angle is small, while the velocity of the flow increased rapidly and the gradient of the velocity is big when the cone angle increasing. The simulation results also express that the arc radius affects the flow field greatly, the flow will move more smoothly when the arc radius is large. The pressure field of the wall expresses that the nozzle will wear rapidly at the corner of the nozzle, the reason is that the pressure is big or changed greatly, the fatigue wear and the blast wear will happen at those place.

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