Multiple Synthetic Jet Research Articles

Flow and heat transfer analysis of submerged multiple synthetic jet impingement in a square channel with forced-flow

This study experimentally and numerically investigated the flow and heat transfer of submerged multiple synthetic jet impingement in forced crossflow in a square-section channel with a constant heat flux on the bottom surface. In the forced channel flow, effects on heat transfer of six synthetic jets placed diagonally in the main flow have four different amplitudes and six different frequencies at various Reynolds numbers (6000 ≤ Re ≤ 40000) were examined. Jets were submerged vertically into the main flow and their effects on heat transfer in the turbulent regime of the main flow were analyzed. Temperature measurements were made using thermocouples placed at the channel entrances and exits on the target surface. The Nusselt numbers (Nu) were calculated using the measured temperatures. The results indicate that at Re = 6000, the target surface temperature decreases significantly with increasing amplitude and frequency, and the effects of amplitude and frequency on surface temperatures decreased at increasing Reynolds numbers. It was observed that the THP values increased with increasing amplitude and frequency for all Reynolds numbers tested. For a constant jet parameter (Ao = 0.88 and Wo = 27), the highest THP was determined as 2.06 at Re = 6000.

Flow and heat transfer characteristics of single and multiple synthetic jets impingement cooling

In this paper, the comparison between synthetic jet actuator with single axisymmetric orifice and multiple axisymmetric orifices is presented. The aim of this paper is to compare the flow and heat transfer characteristics of single and multiple synthetic jet impingements cooling. The multiple orifice configurations had a central orifice and a satellite orifices placed in the pitch circle. The synthetic jet actuator had central orifice with 0, 3, 4, 5 and 6 orifices placed in the diameters of the relative pitch circle p/d = 2.5, 3 and 4. A total of 13 various geometric configurations were tested experimentally. In the multiple orifice configurations, the total cross-section area was approximately equal to the cross-section area of the single orifice configuration. The input power delivered to the synthetic jet actuator was maintained constant and equal to 3.00 W. The synthetic jet actuator energetic efficiency, Reynolds number, equivalent Reynolds number, radial and axial distributions of pressure coefficient, and heat transfer characteristic were presented. The synthetic jet issuing from multiple orifice plate merged at some axial distance, creating a single axisymmetric jet. The merging jet axial distances were determined for all investigated configurations. In the present paper, the integral quantities averaged over all orifices cross section area, or over impingement plate much larger than total orifices area, were analyzed for the purpose of objective comparison. From all various investigated parameters obtained from five different and independent experimental methods, the following conclusion may be made: if the total orifice cross section area in the case of single and multiple orifice synthetic jet is similar and real power deliver to the SJA is maintained at the same level the resulting equivalent Reynolds number and equivalent dimensionless stroke length achieved similar values and the impinging jet equivalent Nusselt number also achieved comparable values and distributions.

Influence of Strouhal number and phase difference on the flow behavior of a synthetic jet array

A computational study is presented to characterize the flow behavior of independently controlled multiple synthetic jet actuators (SJA). For fixed geometric configuration and Reynolds number (Re) 300, the influence of Strouhal number (St=0.028–0.172) and phase difference (∅=0°–180°) between the actuators on the evolution, and interaction of the vortices are highlighted. Directivity plots are employed to illustrate the effect of ∅ on the vectoring behavior of a synthetic jet array (SJ array). It has been observed that a high jet vectoring angle (β) is achieved while operating the SJ array at low St. The vectoring angle seems to be independent of ∅ for the low and high St. However, for an intermediate St=0.086, the vectoring angle varies with the ∅. The phase averaged vorticity contour for St=0.028 reveals that the evolution of the anti-clockwise vortex from the leading actuator (SJA1) decides the vectoring of the jet. By contrast, for higher Sts(0.115 and 0.13), the remnant vortices play a significant role in vectoring the jets toward the leading actuator. Based on the cross-stream distribution of time-averaged streamwise velocity, three distinct flow regimes are characterized: near-field, intermediate-field, and far-field. The strength of the jet is quantified by the downstream distribution of the jet momentum flux. Proper evolution of the vortices results in the enhancement of the jet momentum flux. It is recommended to operate the SJ array at an intermediate St (0.086) to vary the jet vectoring angle with phase differences as well as to achieve maximum jet momentum flux.

Nanofluid heat transfer in a microchannel heat sink with multiple synthetic jets and protrusions

This study focuses on the innovative integration of different cooling techniques to maximize the thermal performance in a 3D microchannel heat sink (MCHS). The paper discusses nanofluid flow and thermal fields in the MCHS with protrusions subjected to double synthetic jets (SJs). A validated multiphase mixture model is used to study the effect of Al2O3 particles in water. The effect of particle concentration, orifice spacing, orifice height, oscillation frequency, membrane amplitude, and phase actuation on convective and conductive heat transfer is analyzed. Heat transfer is significantly influenced by the particle concentration in both active and inactive SJs. Overall, 180° out-of-phase jet configurations show better performance in terms of convective heat transfer, while in-phase jet arrangements are more efficient in conductive heat transfer enhancement. In terms of thermal performance, 180° out-of-phase cases show a higher figure of merit (FOM) than in-phase SJs. Increasing the frequency and amplitude enhances the heat transfer. In the case of nanofluids, the maximum degree of convective enhancement of 1.23 demonstrates the effectiveness of SJs and protrusions. However, the maximum degree of overall thermal enhancement of 54% is obtained at in-phase actuation under the same conditions.

Optimization of nanofluid heat transfer in a microchannel heat sink with multiple synthetic jets based on CFD-DPM and MLA

This study uses a combination of computational fluid dynamics consisting of the discrete phase model (CFD-DPM) coupled with support vector regression-particle swarm optimization (SVR-PSO) techniques to maximize the cooling performance of Al2O3water nanofluids in a microchannel heat sink (MCHS) with multiple synthetic jets (SJs). First, a CFD parametric study is carried out to understand the effect of influential parameters, including orifice spacing, particle volume fraction, orifice height, diaphragm length, phase actuation of jets, frequency and amplitude of oscillating diaphragms. A hybrid SVR-PSO algorithm is then adopted to predict the optimum values of the influential parameters for the maximum homogeneous heat transfer. The results predicted by the machine learning algorithm (MLA) are also compared to CFD findings. 0.15% and 3.5% deviations are found between predicted and actual values for the minimum average temperature and temperature uniformity, respectively. The parametric study reveals that heat transfer increases when the two jets are placed apart from each other. Based on the parametric study, the average temperature drops by 4.3 K as the membrane length increases from 0.95 mm to 1.96 mm. The highest heat transfer is obtained at a particle volume fraction of 5% in both jet arrangements. It is found that increasing the amplitude and frequency of the membranes results in better cooling performance. The results also confirm that larger orifice heights allow the creation of longer and stronger flows in the orifices that propagate the furthest in the microchannel. Overall, in-phase jet configurations show more uniform and lower temperatures (e.g., better heat transfer) at higher particle concentrations compared to the 180° out-of-phase jet arrangements.

Experimental investigation on heat transfer enhancement of air-cooled heat sink using multiple synthetic jets

The heat transfer enhancement of air-cooled heat sink using multiple synthetic jets is investigated experimentally. A heat sink is located inside synthetic jet actuator cavity in order to reduce space occupied by the cooling device. It has been observed that heat sink located inside the synthetic jet actuator cavity dissipates heat in a manner similar to the heat sink cooled by impinging synthetic jet. The thermal resistance of the heat sink depends on the synthetic jet Reynolds number and dimensionless stroke length. The paper presents experimental results of synthetic jet Reynolds number, dimensionless stroke length as well as the heat sink thermal resistance and coefficient of performance. The value of the heat sink thermal resistance of 0.22 K/W was measured during operation of synthetic jest cooling while the thermal resistance of the heat sink without loudspeaker was found to be 1.4 K/W. A correlation of thermal resistance as a function of Reynolds number and dimensionless stroke length based on the experimental results is presented and discussed.

Experimental study on the flow interaction between two synthetic jets emanating from a dual round orifice

Multiple orifice synthetic jet devices are becoming widely utilized for active flow control and jet impingement cooling, due to its mixing performance resulting from the vortices and jet interaction. Therefore, understanding the flow interaction between multiple synthetic jets is crucial in maximizing the potential for many industrial applications. In the present study, an experimental investigation on flow interaction between two synthetic jets generated from a dual-orifice device is performed. The influence of dimensionless orifice spacing (s/D = 1.2, 2.0, and 3.0) and stroke length (L0/D = 13.7, 18.6, and 27.5) is analyzed at a fixed Reynolds number of Re0 = 3700. Phase-locked particle image velocimetry (PIV) is used to obtain time- and phase-averaged flow fields. The jet interaction is enhanced as the orifice spacing and stroke length decrease, resulting in shorter distances for the merging and combining points. In addition, the inner vortices between the two jets are deformed and cancelled due to the jet interaction, which leads to the inner and outer vortices merging into a single vortex. The vortex interactions and merging are delayed as the orifice spacing increases, while the advection speed of vortices is increased without change of flow structure as the stroke length increases.

Heat transfer enhancement of a heated cylinder with synthetic jet impingement from multiple orifices

This study proposed and investigated a method to enhance the heat transfer performance of a heated cylinder with synthetic jet impingement from multiple orifices. A synthetic jet has a flow with alternately changing orientations at its exit and eventually generates a periodic flow in constant orientation in the area far from the exit. First, the flow characteristics of synthetic jets generated from the multiple orifices on a piccolo tube were investigated in detail with a hot-wire anemometer. Next, the heat transfer of a heated cylinder was enhanced with multiple synthetic jets. The Nusselt number of the heated cylinder was calculated using the temperature variation of the cylinder with time. The heat transfer rate enhanced with multiple synthetic jets was 2–3 times higher than that without jets. The results also showed that the heat transfer rate with upward-oriented jets from the piccolo tube located below the heated cylinder was higher than that with downward-oriented jets from the tube located above the cylinder. We also compared synthetic jets to continuous jets generated with a high-pressure air source. The results showed that the effects of the synthetic jets were valid at greater distances than those of the continuous jets.

A computational approach to the simulation of controlled flows by synthetic jets actuators

The paper focuses on the integration of a non-linear one-dimensional model of Synthetic Jet (SJ) actuator in a well-assessed numerical simulation method for turbulent compressible flows. The computational approach is intended to the implementation of a numerical tool suited for flow control simulations with affordable CPU resources. A strong compromise is sought between the use of boundary conditions or zero-dimensional models and the full simulation of the actuator cavity, in view of long-term simulation with multiple synthetic jet actuators. The model is integrated in a multi-domain numerical procedure where the controlled flow field is simulated by a standard CFD method for compressible RANS equations, while flow inside the actuator is reduced to a one-dimensional duct flow with a moving piston. The non-linear matching between the two systems, which ensures conservation of the mass, momentum and energy is explained. The numerical method is successfully tested against three typical test cases: the jet in quiescent air, the SJ in cross flow and the flow control on the NACA0015 airfoil.

Liquids mixing enhanced by multiple synthetic jet pairs at low Reynolds numbers

In this paper, the effect of three synthetic jet pairs on the mixing between two fluid streams in a planar mixing channel is examined at a net flow Reynolds number of 2. They are mounted transversely to the incoming flow and operated 180° out-of-phase. The PLIF technique is used to provide a visual impression of the effect of synthetic jets on mixing as their operating condition varies, whereas PIV is used to provide the complementary information about the flow structures produced by the synthetic jets and their role in promoting mixing. Our experimental results demonstrate that this inline fluid mixer with a simple design produces an excellent mixing at low Reynolds numbers. It is found that such a good mixing is the result of a significantly increased interfacial area created by these synthetic jet pairs. Based on the degree of mixing deduced from the PLIF data at some distances downstream of the synthetic jets, a functional relationship between the synthetic jet actuation frequency and amplitude is also obtained. This functional relationship can be used for selecting the synthetic jet operating conditions to ensure a good mixing for a scaled version of this fluid mixer.

Flow and heat transfer characteristics under synthetic jets impingement driven by piezoelectric actuator

Synthetic jet is a novel flow technique which synthesizes stagnant air to form a jet, and is potentially useful for cooling applications. An experimental measurement utilizing particle image velocimetry (PIV), hot-wire anemometer and infrared camera on the synthetic jet impingement cooling driven by piezoelectric actuator was carried out in the present investigation. The flow and heat transfer characteristics of impinging synthetic jets formed from a single cavity but with different orifices, such as single-slot, single-hole, three-slots and three-holes, were explored. The synthetic jet output from the piezoelectric actuator reaches a peak value when it is excited at its optimum frequency. The synthetic jet output from the piezoelectric actuator reaches a peak value when it is excited at its optimum frequency. For single-hole synthetic jet, the optimum frequency is nearly the same as that of single-slot orifice given the same orifice exit area. But the optimum frequency for the multi-orifices is lower than that of single-orifice synthetic jet. In general, the synthetic jet originated from the single-slot orifice introduces a stronger entrainment and more vigorous penetration in relative to that from the single-hole orifice, performing better than the single-hole synthetic jet orifice. And the multiple synthetic jets exhibit complex influence on the heat transfer by comparison to single synthetic jet for a given actuator cavity and a single actuator. Only when the multi-slots or multi-holes are arranged in their optical mode, the multiple synthetic jets could achieve competitive heat transfer capacity with the single synthetic jet.

INFLATABLE EAR DEVICE

A diaphonic valve utilizing the principle of the Synthetic Jet is disclosed herein. A diaphonic valve pump is provided for the inflation of an in-ear balloon. More complex embodiments of the present invention include stacks of multiple synthetic jets generating orifices as well as an oscillating, thin polymer membrane. In one or more embodiments of the present invention, a novel application is provided for the creation of static pressure to inflate or to deflate an inflatable member (balloon). In addition, sound can be utilized to inflate or deflate an inflatable member in a person's ear for the purpose of listening to sound.

Heat transfer enhancement in micro-channel with multiple synthetic jets

A three-dimensional computational model has been developed to investigate the effect of multiple synthetic jets interaction with cross-flow in micro-channel on the cooling of microchip. Studies were performed with the use of two micro jets being in-phase and 180° out-of-phase at two different operating frequencies and a fixed diaphragm amplitude. The addition of one synthetic jet was shown to achieve greater mixing of flow in the micro-channel than those with single synthetic jet. Greater heat transfer enhancement was achieved with double synthetic jets. Results showed that greater cooling enhancement could be achieved with the out-of-phase flow configuration at oscillating frequency of 560Hz compared with the in-phase flow configuration. However, the effect of the actuation phase at a frequency of 1120Hz was found to be insignificant. With double synthetic jet actuators operating out-of-phase, a mere 0.1K reduction was achieved in maximum silicon temperature compared with in-phase flow jets. The greater the mixing of flow in the micro-channel in either in-phase or out-of-phase flow configuration due to higher jets Reynolds number resulted in the constraint in further cooling enhancement despite having different phases of the flow configuration.

Contribution to the Understanding of Flow Interactions Between Multiple Synthetic Jets

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