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

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).

scholarly journals HYSTERESIS OF PLANAR DOUBLE SLOT IMPINGING AIR JETS

2018 ◽  
Vol 180 ◽  
pp. 02109
Author(s):  
Tomáš Tisovský ◽  
Tomáš Vít
Keyword(s):  
Heat Transfer ◽  
Flow Field ◽  
Isothermal Flow ◽  
Field Pattern ◽  
Stagnation Flow ◽  
Slot Nozzle ◽  
Air Jets ◽  
2D Simulation ◽  
Field Patterns ◽  
Simulation Results

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.

Flow and Heat Transfer Characteristics in Rectangular Channels With Staggered Transverse Ribs on Two Opposite Walls

2007 ◽  
Vol 129 (12) ◽  
pp. 1732-1736 ◽  
Author(s):  
Rong Fung Huang ◽  
Shyy Woei Chang ◽  
Kun-Hung Chen
Keyword(s):  
Heat Transfer ◽  
Flow Field ◽  
Turbulence Intensity ◽  
Flow Characteristics ◽  
Channel Height ◽  
Primary Concern ◽  
Height Ratio ◽  
Nusselt Numbers ◽  
Characteristic Flow ◽  
Rectangular Channels

The flow characteristics and the heat transfer properties of the rectangular channels with staggered transverse ribs on two opposite walls are experimentally studied. The rib height to channel height ratio ranges from 0.15 to 0.61 (rib height to channel hydraulic diameter ratio from 0.09 to 0.38). The pitch to rib height ratio covers from 2.5 to 26. The aspect ratio of the rectangular channel is 4. The flow characteristics are studied in a water channel, while the heat transfer experiments are performed in a wind tunnel. Particle image velocimetry (PIV) is employed to obtain the quantitative flow field characteristics. Fine-wire thermocouples imbedded near the inner surface of the bottom channel wall are used to measure the temperature distributions of the wall and to calculate the local and average Nusselt numbers. Using the PIV measured streamline patterns, various characteristic flow modes, thru flow, oscillating flow, and cell flow, are identified in different regimes of the domain of the rib height to channel height ratio and pitch to rib height ratio. The vorticity, turbulence intensity, and wall shear stress of the cell flow are found to be particularly larger than those of other characteristic flow modes. The measured local and average Nusselt numbers of the cell flow are also particularly higher than those of other characteristic flow modes. The distinctive flow properties are responsible for the drastic increase of the heat transfer due to the enhancement of the momentum, heat, and mass exchanges within the flow field induced by the large values of the vorticity and turbulence intensity. Although the thru flow mode is conventionally used in the ribbed channel for industrial application, the cell flow could become the choice if the heat transfer rate, instead of the pressure loss, is the primary concern.

Numerical Simulation of Heat and Flow of Liquid Through Minichannels

2006 ◽  
Author(s):  
Heming Yun ◽  
Lin Cheng ◽  
Liqiu Wang ◽  
Shusheng Zhang
Keyword(s):  
Heat Transfer ◽  
Numerical Simulation ◽  
Reynolds Number ◽  
Aspect Ratio ◽  
Flow Region ◽  
Resistance Coefficient ◽  
Equivalent Diameter ◽  
Nusselt Numbers ◽  
Friction Factors ◽  
Simulation Results

In this paper the heat transfer and flow in minichannels was investigated by using CFD methods. The numerical simulation results show that the equivalent diameter has little influence on resistance coefficient in the laminar region. In the turbulent flow region, the resistance coefficient decreases with the increasing of the equivalent diameter. In all computation region, the friction factors increases with increasing of the aspect ratio, and the friction factors decreases obviously with increasing of Reynolds number. The numerical simulation results show that the equivalent diameter has little influence on heat transfer Nusselt number in laminar flow region. In turbulent region, the Nusselt numbers are larger than those in macro channels. The Nusselt numbers increase with decreasing of equivalent diameter and the aspect ratio for a given Reynolds number.

A Comparison Between Computational Simulation and Measurement of Acoustically Enhanced Heat Transfer

2005 ◽  
Author(s):  
Yool-Kwon Oh ◽  
Ho-Dong Yang
Keyword(s):  
Heat Transfer ◽  
Acoustic Field ◽  
Ultrasonic Transducer ◽  
Computational Simulation ◽  
Acoustic Streaming ◽  
Ultrasonic Waves ◽  
Structural Vibration ◽  
Computational Simulations ◽  
Enhancement Of Heat Transfer ◽  
Fortran Language

The strong upward flow called as “acoustic streaming”, when ultrasonic waves were applied in a medium, occurred near to ultrasonic transducer and enhanced the heat transfer. That is, applying ultrasonic waves in a medium may cause the flow velocity of the medium to increase: an effect known as acoustic streaming promotes heat transfer through convection and affects the thermal boundary layer. So, this study was compared with the pressure variations and enhancement of heat transfer by computational simulations and experiments in acoustic field. For the computational simulations, structural vibration simulator (SVS) programmed with a fortran language and based on a coupled finite element-boundary element method (coupled FE-BEM) was used. The results of this study reveal that the acoustic pressure is higher near two ultrasonic transducers than other points where no ultrasonic transducer was installed. The enhancement trend of heat transfer is similar with the profile of the pressure variations. It is concluded that the pressure variations are related to the enhancement of heat transfer in acoustic field.

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

2014 ◽  
Vol 26 (4) ◽  
pp. 223-230 ◽  
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.

Heat Transfer and Flow Characteristics of Two-Pass Parallelogram Channels With Attached and Detached Transverse Ribs

2016 ◽  
Author(s):  
Tong-Miin Liou ◽  
Shyy-Woei Chang ◽  
Yi-An Lan ◽  
Shu-Po Chan ◽  
Yu-Shuai Liu
Keyword(s):  
Heat Transfer ◽  
Flow Field ◽  
Flow Characteristics ◽  
Height Ratio ◽  
Differential Heat ◽  
Flow Measurements ◽  
Full Field ◽  
Performance Factors ◽  
Nusselt Numbers ◽  
Design Activities

The full-field endwall Nusselt number (Nu) distributions and flow field are presented respectively using steady-state infrared thermography and particle image velocimetry (PIV) for the two-pass parallelogram channels with attached and detached transverse ribs. These square transverse ribs on two opposite channel endwalls are in-line arranged with rib-height to duct-height ratio of 0.1 and rib-pitch to rib-height ratio of 10. For the detached ribs, the detached distance between rib and channel endwall is 0.38 rib height. With the measurements of Fanning friction factor (f), heat transfer distributions and flow field features, the thermal performance factors (TPF) for the attached and detached rib cases are comparatively examined. A set of Nu, f and TPF results with the associated flow measurements at the test conditions of 5,000≤Re≤20,000 is selected to disclose the differential heat transfer enhancement mechanisms and heat transfer efficiencies between the attached and detached ribbed channels. Empirical correlations evaluating the endwall area-averaged Nusselt numbers (Nu) and f factors are devised to assist the relevant design activities.

A Model of the Enhancement of Coal Combustion Using High-Intensity Acoustic Fields

1991 ◽  
Vol 113 (4) ◽  
pp. 277-285 ◽  
Author(s):  
S. Yavuzkurt ◽  
M. Y. Ha ◽  
G. Koopmann ◽  
A. W. Scaroni
Keyword(s):  
Mass Transfer ◽  
Heat And Mass Transfer ◽  
Acoustic Field ◽  
High Intensity ◽  
Coal Combustion ◽  
Sound Pressure ◽  
Pulverized Coal ◽  
Acoustic Fields ◽  
Coal Particles ◽  
Sound Pressure Levels

A model for the enhancement of coal combustion in the presence of high-intensity acoustic fields has been developed. A high-intensity acoustic field induces an oscillating velocity over pulverized coal particles otherwise entrained in the main gas stream, resulting in increased heat and mass transfer. The augmented heat and mass transfer coefficients, expressed as space and time-averaged Nusselt and Sherwood numbers for the oscillating flow, were implemented in an existing computer code (PCGC-2) capable of predicting various aspects of pulverized coal combustion and gasification. Increases in the Nusselt and Sherwood numbers about 45, 60 and 82.5 percent at sound pressure levels of 160, 165 and 170 dB for 100-μm coal particles were obtained due to increase in the acoustic slip velocity associated with the increased sound pressure levels. The main effect of the acoustic field was observed during the char combustion phase in a diffusionally controlled situation. A decrease in the char burn-out length (time) of 15.7 percent at 160 dB and 30.2 percent at 170 dB was obtained compared to the case with no sound for the 100-μm coal particles.

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

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.

An Analytical Model of External Streaming and Heat Transfer for a Levitated Flattened Liquid Drop

2008 ◽  
Vol 130 (9) ◽  
Author(s):  
Sungho Lee ◽  
S. S. Sadhal ◽  
Alexei Ye. Rednikov
Keyword(s):  
Heat Transfer ◽  
Flow Field ◽  
Acoustic Field ◽  
Thermophysical Properties ◽  
Liquid Drop ◽  
Thermocapillary Flow ◽  
Heat Transfer Analysis ◽  
Thermal Stimulus ◽  
Steady Streaming ◽  
Stokes Layer

We present here the heat-transfer and fluid flow analysis of an acoustically levitated flattened disk-shaped liquid drop. The interest in this work arises from the noncontact measurement of the thermophysical properties of liquids. Such techniques have application to liquids in the undercooled state, i.e., the situation when a liquid stays in a fluidic state even when the temperature falls below the normal freezing point. This can happen when, for example, a liquid sample is held in a levitated state. Since such states are easily disrupted by measurement probes, noncontact methods are needed. We have employed a technique involving the use of acoustically levitated samples of the liquid. A thermal stimulus in the form of laser heating causes thermocapillary motion with flow characteristics depending on the thermophysical properties of the liquid. In a gravity field, buoyancy is disruptive to this thermocapillary flow, masking it with the dominant natural convection. As one approach to minimizing the effects of buoyancy, the drop was flattened (by intense acoustic pressure) in the form of a horizontal disk, about 0.5mm thick. As a result, with very little gravitational potential, and with most of the buoyant flow suppressed, thermocapillary flow remained the dominant form of fluid motion within the drop. This flow field is visualizable and subsequent analysis for the inverse problem of the thermal property can be conducted. This calls for numerical calculations involving a heat-transfer model for the flattened drop. With the presence of an acoustic field, the heat-transfer analysis requires information about the corresponding Biot number. In the presence of a high-frequency acoustic field, the steady streaming originates in a thin shear-wave layer, known as the Stokes layer, at a surface of the drop. The streaming develops into the main fluid, and is referred to as the outer streaming. Since the Stokes layer is asymptotically thin in comparison to the length scale of the problem, the outer streaming can be formally described by an effective slip velocity at the boundary. The presence of the thin Stokes layer, and the slip condition at the interface, changes the character of the heat-transfer mechanism, which is inherently different from the traditional boundary layer. The current analysis consists of a detailed semianalytical calculation of the flow field and the heat-transfer characteristics of a levitated drop in the presence of an acoustic field.

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