Active Heat Transfer Enhancement in Single-Phase Microchannels by Using Synthetic Jets

2013 ◽  
Vol 5 (1) ◽  
Author(s):  
Ruixian Fang ◽  
Jamil A. Khan
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Enhancement ◽  
Heat Sink ◽  
Heat Transfer Performance ◽  
Synthetic Jets ◽  
Transfer Performance ◽  
Microchannel Flow ◽  
Transfer Enhancement ◽  
Pressure Dynamics ◽  
A Minor

The present work experimentally investigates the effect of synthetic jets on the heat transfer performance in a microchannel heat sink. The heat sink consists of five parallel rectangular microchannels measuring 500 μm wide, 500 μm deep, and 26 mm long each. An array of synthetic jets with 100 μm diameter orifices is placed right above the microchannel with a total of eight jet orifices per channel. Microjets are synthesized from the fluid flowing through the microchannel. Periodic disturbances are generated when the synthetic jets interact with the microchannel flow. Heat transfer performance is enhanced as local turbulence is generated and penetrates the thermal boundary layer near heated channel wall. The effects of synthetic jets on microchannels heat transfer performance are studied for several parameters including the channel stream flow rate, the synthetic jets strength and operating frequency. It shows that the synthetic jets have higher heat transfer enhancement for microchannel flow at lower channel flow rates. A maximum of 130% heat transfer enhancement is achieved for some test cases. The pressure dynamics introduced by the synthetic jets are also investigated. The synthetic jets cause a minor increase in the pressure drop.

Enhancing Heat Transfer of Air-Cooled Heat Sinks Using Piezoelectrically-Driven Agitators and Synthetic Jets

2011 ◽  
Author(s):  
Youmin Yu ◽  
Terrence Simon ◽  
Min Zhang ◽  
Taiho Yeom ◽  
Mark North ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Enhancement ◽  
Heat Sink ◽  
Heat Transfer Performance ◽  
Single Channel ◽  
Synthetic Jets ◽  
Heat Sinks ◽  
Transfer Performance ◽  
Transfer Enhancement ◽  
Enhancing Heat Transfer

Air-cooled heat sinks prevail in microelectronics cooling due to their high reliability, low cost, and simplicity. But, their heat transfer performance must be enhanced if they are to compete for high-flux applications with liquid or phase-change cooling. Piezoelectrically-driven agitators and synthetic jets have been reported as good options in enhancing heat transfer of surfaces close to them. This study proposes that agitators and synthetic jets be integrated within air-cooled heat sinks to significantly raise heat transfer performance. A proposed integrated heat sink has been investigated experimentally and with CFD simulations in a single channel heat sink geometry with an agitator and two arrays of synthetic jets. The single channel unit is a precursor to a full scale, multichannel array. The agitator and the jet arrays are separately driven by three piezoelectric stacks at their individual resonant frequencies. The experiments show that the combination of the agitator and synthetic jets raises the heat transfer coefficient of the heat sink by 80%, compared with channel flow only. The 3D computations show similar enhancement and agree well with the experiments. The numerical simulations attribute the heat transfer enhancement to the additional air movement generated by the oscillatory motion of the agitator and the pulsating flow from the synthetic jets. The component studies reveal that the heat transfer enhancement by the agitator is significant on the fin side and base surfaces and the synthetic jets are most effective on the fin tips.

scholarly journals Enhanced heat transfer characteristics of conjugated air jet impingement on a finned heat sink

2017 ◽  
Vol 21 (1 Part A) ◽  
pp. 279-288 ◽  
Author(s):  
Shuxia Qiu ◽  
Peng Xu ◽  
Liping Geng ◽  
Arun Mujumdar ◽  
Zhouting Jiang ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Enhancement ◽  
Heat Sink ◽  
Heat Transfer Performance ◽  
Cooling System ◽  
Flow Characteristics ◽  
Jet Impingement ◽  
Transfer Performance ◽  
Transfer Enhancement ◽  
Air Jet

Air jet impingement is one of the effective cooling techniques employed in micro-electronic industry. To enhance the heat transfer performance, a cooling system with air jet impingement on a finned heat sink is evaluated via the computational fluid dynamics method. A two-dimensional confined slot air impinging on a finned flat plate is modeled. The numerical model is validated by comparison of the computed Nusselt number distribution on the impingement target with published experimental results. The flow characteristics and heat transfer performance of jet impingement on both of smooth and finned heat sinks are compared. It is observed that jet impingement over finned target plate improves the cooling performance significantly. A dimensionless heat transfer enhancement factor is introduced to quantify the effect of jet flow Reynolds number on the finned surface. The effect of rectangular fin dimensions on impingement heat transfer rate is discussed in order to optimize the cooling system. Also, the computed flow and thermal fields of the air impingement system are examined to explore the physical mechanisms for heat transfer enhancement.

Experimental Heat Transfer Enhancement in Single-Phase Liquid Microchannel Cooling With Cross-Flow Synthetic Jet

2010 ◽  
Author(s):  
Ruixian Fang ◽  
Wei Jiang ◽  
Jamil Khan ◽  
Roger Dougal
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Enhancement ◽  
Heat Transfer Performance ◽  
Synthetic Jet ◽  
Driving Voltage ◽  
Transfer Performance ◽  
Microchannel Flow ◽  
Transfer Enhancement ◽  
Synthetic Jet Actuator ◽  
Phase Liquid

The present study experimentally investigated a new hybrid cooling scheme by combination of a microchannel heat sink with a micro-synthetic jet actuator. The heat sink consisted of a single rectangular microchannel measured 550 μm wide, 500 μm deep and 26 mm long. The synthetic jet actuator with a 100 μm diameter orifice was placed right above the microchannel and 5 mm downstream from the channel inlet. Micro jet is synthesized from the fluid flowing through the microchannel. Periodic disturbance is generated when the synthetic jet interacts with the microchannel flow. Heat transfer performance is enhanced as local turbulence is generated and propagated downstream the microchannel. The scale and frequency of the disturbance can be controlled by changing the driving voltage and frequency of the piezoelectric driven synthetic jet actuator. The effects of synthetic jet on microchannel heat transfer performance were studied based on the microchannel flow Reynolds number, the jet operating voltage and frequency, respectively. It shows that the synthetic jet has a greater heat transfer enhancement for microchannel flow at lower Reynolds number. It also shows that the thermal effects of the synthetic jet are functions of the jet driving voltage and frequency. We obtained around 42% heat transfer enhancement for some test cases, whereas the pressure drop across the microchannel increases very slightly. The paper concludes that the synthetic jet can effectively enhance single-phase liquid microchannel heat transfer performance and would have more promising enhancements if multi-jets are applied along the microchannel.

Heat Transfer Enhancement by Synthetic Jet Arrays in Air-Cooled Heat Sinks for Use in Electronics Cooling

2012 ◽  
Author(s):  
Longzhong Huang ◽  
Terrence Simon ◽  
Min Zhang ◽  
Youmin Yu ◽  
Mark North ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Enhancement ◽  
Channel Flow ◽  
Heat Sink ◽  
Jet Flow ◽  
Synthetic Jet ◽  
Synthetic Jets ◽  
Transfer Enhancement ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients

A synthetic jet is an intermittent jet which issues through an orifice from a closed cavity over half of an oscillation cycle. Over the other half, the flow is drawn back through the same orifice into the cavity as a sink flow. The flow is driven by an oscillating diaphragm, which is one wall of the cavity. Synthetic jets are widely used for heat transfer enhancement since they are effective in disturbing and thinning thermal boundary layers on surfaces being cooled. They do so by creating an intermittently-impinging flow and by carrying to the hot surface turbulence generated by breakdown of the shear layer at the jet edge. The present study documents experimentally and computationally heat transfer performance of an array of synthetic jets used in a heat sink designed for cooling of electronics. This heat sink is comprised of a series of longitudinal fins which constitute walls of parallel channels. In the present design, the synthetic jet flow impinges on the tips of the fins. In the experiment, one channel of a 20-channel heat sink is tested. A second flow, perpendicular to the jet flow, passes through the channel, drawn by a vacuum system. Surface- and time-averaged heat transfer coefficients for the channel are measured, first with just the channel flow active then with the synthetic jets added. The purpose is to assess heat transfer enhancement realized by the synthetic jets. The multiple synthetic jets are driven by a single diaphragm which, in turn, is activated by a piezoelectrically-driven mechanism. The operating frequency of the jets is 1250 Hz with a cycle-maximum jet velocity of 50 m/s, as measured with a miniature hot-film anemometer probe. In the computational portion of the present paper, diaphragm movement is driven by a piston, simulating the experimental conditions. The flow is computed with a dynamic mesh using the commercial software package ANSYS FLUENT. Computed heat transfer coefficients show a good match with experimental values giving a maximum difference of less than 10%. The effects of amplitude and frequency of the diaphragm motion are documented. Changes in heat transfer due to interactions between the synthetic jet flow and the channel flow are documented in cases of differing channel flow velocities as well as differing jet operating conditions. Heat transfer enhancement obtained by activating the synthetic jets can be as large as 300% when the channel flow is of a low velocity compared to the synthetic jet peak velocity (as low as 4 m/s in the present study).

Effect of Protuberances in the Heat Transfer Enhancement in Mini-Channels

2021 ◽  
Author(s):  
Ariel Cruz Diaz ◽  
Gerardo Carbajal
Keyword(s):  
Heat Transfer ◽  
Numerical Simulation ◽  
Pressure Drop ◽  
Heat Transfer Enhancement ◽  
Heat Transfer Performance ◽  
Heat Removal ◽  
Working Fluid ◽  
Transfer Performance ◽  
Transfer Enhancement ◽  
Mini Channels

Abstract This study presents the effects of adding an array of protrusions in a microchannel for heat transfer enhancement. The presence of mini-channels increases the overall heat transfer area and boosts the mixing development near the solid-fluid interaction; therefore, it can remove more heat than conventional mini-channels without protuberances. A numerical study proved that protuberances in a mini-channel increase the heat transfer performance by disturbing the relative fluid motion near the solid wall. The numerical simulation was performed with three different protuberances arrays: aligned, staggered, and angular. Each array consists of a thin flat plate with a hemispherical shape; the working fluid and the solid materials were water and copper. The study also includes the effect of different Reynolds numbers: 1,000, 1,500, and 2,000. Three heat inputs were applied in the numerical simulation; these were 1W, 3W, and 5W. The study was compared with a simple microchannel with non-protuberances to analyze the microchannel performance regarding heat removal and pressure drop. For heat transfer performance, the best array was the staggering array with a maximum heat removal increase of 5.26 percent. In terms of pressure drop performance, the best array was the aligned array, with a maximum increase of 34.73 percent.

Heat transfer performance of steam/air flow in inverted V-shaped rib-roughened channels

2021 ◽  
pp. 095765092110161
Author(s):  
Chao Ma ◽  
Bing Ge
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Heat Transfer Enhancement ◽  
Heat Transfer Performance ◽  
Air Flow ◽  
Transfer Performance ◽  
Transfer Enhancement ◽  
Ribbed Channel

The heat transfer performance of steam and air flow in a rough rectangular channel with different inverted V-shaped ribs was investigated by infrared thermal imaging technology. Under the conditions that the Reynolds number is in the range of 4000–15,000, the effects of the rib angle on the heat transfer enhancement of the two coolants were obtained. The rib pitch ratio of the flow channel is 10, the ratio of the rib height to the channel hydraulic diameter is 0.078, and the inverted V-shaped rib angle varies from 45° to 90°. The results show that in the inverted V-shaped ribbed channel, the Nu number on both sides of the channel is greatly increased, while the Nu number in the middle of the channel is lower. The local Nu distribution on the surface of the ribbed channel is highly related to the shape of the rib. For different medium cooling, the value and unevenness of the heat transfer coefficient are different, but the shape of the high and low heat transfer coefficient distribution is hardly affected. The heat transfer of both coolants increases as the rib angle decreases from 90° to 45°. Compared with air flow, steam flow cooling shows higher convective heat transfer enhancement. For rib angles of 45°, 60°, 75°, and 90°, under the operating condition of the Reynolds number = 12,000, the area-averaged Nusselt numbers of the steam flow is 23.6%, 27.4% and 13.9% higher than that of the air flow, respectively. Based on the experimental heat transfer data, the correlation in terms of the Reynolds number and the rib angle was developed, which is used to estimate the Nu number for steam and air cooling in the inverted V-shaped rib-roughness channels.

Convective Heat Transfer Enhancement Using Carbon Nanofibers (CNFs): Influence of Amorphous Carbon Layer on Heat Transfer Performance

2013 ◽  
Author(s):  
T. J. Taha ◽  
L. Lefferts ◽  
T. H. Van der Meer
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Convective Heat Transfer ◽  
Heat Transfer Enhancement ◽  
Surface Area ◽  
Carbon Nanofibers ◽  
Amorphous Carbon ◽  
Heat Transfer Performance ◽  
Transfer Performance ◽  
Transfer Enhancement

In this work, an experimental heat transfer investigation was carried out to investigate the combined influence of both amorphous carbon (a-C) layer thickness and carbon nanofibers (CNFs) on the convective heat transfer behavior. Synthesis of these carbon nano structures was achieved using catalytic chemical vapor deposition process (CCVD) on a 50 μm nickel wire at 650°C. Due to their extremely high thermal conductivity, CNFs are used to augment/modify heat transfer surface. However, the inevitable layer of a-C that occurs during the synthesis of the CNFs layer exhibit low thermal conductivity which may result in insulating the surface. In contrast, the amorphous layer helps in supporting and mechanical stabilizing of the CNFs layer attachment to the polycrystalline nickel (Ni270) substrate material. To better understand the influences of these two layer on heat transfer, the growth mechanism of the CNFs layer and the layer of carbon is investigated and growth model is proposed. The combined impact of both a-C and CNFs layer on heat transfer performance is studied on three different samples which were synthesized by varying the deposition period (16 min, 23min and 30 min). The micro wire samples covered with CNF layers were subjected to a uniform flow from a nozzle. Heat transfer measurement was achieved by a controlled heat dissipation through the micro wire to attain a constant temperature during the flow. This measurement technique is adopted from hot wire anemometry calibration method. Maximum heat transfer enhancement of 18% was achieved. This enhancement is mainly attributed to the surface roughness and surface area increase of the samples with moderate CNFs surface area coverage on the sample.

Ultrasonic Effect on Heat Transfer Performance of Oscillating Heat Pipes

2015 ◽  
Vol 137 (9) ◽  
Author(s):  
Nannan Zhao ◽  
Benwei Fu ◽  
Hongbin Ma ◽  
Fengmin Su
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Enhancement ◽  
Heat Input ◽  
Heat Transfer Performance ◽  
Operating Temperature ◽  
Heat Pipes ◽  
Transfer Performance ◽  
Transfer Enhancement ◽  
Ultrasonic Effect ◽  
Ultrasonic Sound

The ultrasonic effect on the heat transfer performance in oscillating heat pipes (OHPs) was investigated experimentally. Ultrasonic sound was applied to the evaporating section of the OHP by using electrically controlled piezoelectric ceramics. The heat pipes were tested with or without the ultrasonic effect. The effects of heat input, filling ratio, orientation, operating temperature, and working fluids (water and acetone) were investigated. The experimental results showed that ultrasonic sound can affect the oscillating motions and enhance the heat transfer performance of an OHP. However, the heat transfer enhancement mainly occurs at low heat input. In addition, it was found that heat transfer enhancement of the ultrasonic effect depends on the working fluid and operating temperature. At an operating temperature of 20 °C, the enhancement percentage of the water OHP is higher than acetone OHP. However, when the operating temperature was increased to 40 °C, the enhancement percentage of the water OHP was lower than the acetone OHP.

Heat Transfer Enhancement in Microchannel Using Nanofluids

2013 ◽  
Vol 465-466 ◽  
pp. 536-540
Author(s):  
Khairul Afif Fadzin ◽  
Ann Lee
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Enhancement ◽  
Thermal Performance ◽  
Heat Transfer Performance ◽  
Volume Concentration ◽  
Pure Water ◽  
Transfer Performance ◽  
Transfer Enhancement ◽  
Particle Volume ◽  
Better Than

Numerical investigation of heat transfer enhancement in two-dimensional microchannel heat sink (MCHS) using Al2O3-water, CuO-water and TiO2-water was conducted. The effect of different type of nanoparticles at particle volume concentration of 1%, 2% and 5% on the thermal performance in the MCHS was examined. The thermal performance is increased when nanofluids with high thermal conductivity and low dynamic viscosity was used. As the particle volume concentration increases, the heat transfer performance also improved. The result shows that the heat transfer performance of all the nanofluids used in this study was better than that of pure water. Overall, nanofluids with Al2O3-water at 5% particle volume concentration show the best cooling performance.

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