Energy Efficiency of Low Form Factor Cooling Devices

2007 ◽  
Author(s):  
Mehmet Arik ◽  
James Petroski ◽  
Avram Bar-Cohen ◽  
Mehmet Demiroglu
Keyword(s):  
Heat Transfer ◽  
Energy Efficiency ◽  
Electronics Cooling ◽  
Thermodynamic Characteristics ◽  
Synthetic Jets ◽  
Coefficient Of Performance ◽  
Thermal Engineering ◽  
Wide Range ◽  
Cooling Devices ◽  
Science Community

With increasing attention to the energy efficiency of consumer and commercial products, thermal engineering and science community is devoting greater effort and attention to the design and implementation of energy-efficient cooling solutions. This study focuses on the cooling potential and Coefficient of Performance, (COP), achievable with three distinct meso-scale cooling technologies, applicable to a wide range of electronics cooling challenges. The thermo-fluid and thermodynamic characteristics of synthetic jets, piezo-driven vibrating blades, and compact muffin fans will be addressed. We are dedicating this paper to Prof. Kakac for his contributions to heat transfer science and technology, developing young scientists, writing highly valuable heat transfer textbooks, and most importantly for his kindness and friendship.

Analysis of Parallel Microchannels for Flow Control and Hot Spot Cooling

2013 ◽  
Vol 5 (4) ◽  
Author(s):  
Stephen A. Solovitz
Keyword(s):  
Heat Transfer ◽  
Power Law ◽  
Hot Spots ◽  
Hot Spot ◽  
Electronics Cooling ◽  
Flow Distribution ◽  
Reynolds Numbers ◽  
Heat Fluxes ◽  
Cooling Devices ◽  
Parallel Microchannels

Microchannel heat transfer is commonly applied in the thermal management of high-power electronics. Most designs involve a series of parallel microchannels, which are typically analyzed by assuming a uniform flow distribution. However, many devices have a nonuniform thermal distribution, with hot spots producing much higher heat fluxes and temperatures than the baseline. Although solutions have been developed to improve local heat transfer, these are advanced methods using embedded cooling devices. As an alternative, a passive solution is developed here using analytical methods to optimize the channel geometry for a desired, nonuniform flow distribution. This results in a simple power law for the passage diameter, which may be useful for many microfluidic systems, including electronics cooling devices. Computational simulations are then applied to demonstrate the effectiveness of the power law for laminar conditions. At low Reynolds numbers, the flow distribution can be controlled to good accuracy, matching the desired distribution to within less than 1%. Further simulations consider the control of hot spots in laminar developing flow. Under these circumstances, temperatures can be made uniform to within 2 °C over a range of Reynolds numbers (60 to 300), demonstrating the capability of this power law solution.

Predicting Heat Transfer From Unsteady Synthetic Jets

2012 ◽  
Vol 134 (8) ◽  
Author(s):  
Mehmet Arik ◽  
Tunc Icoz
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Jet Impingement ◽  
Synthetic Jet ◽  
Synthetic Jets ◽  
Operating Conditions ◽  
Small Scale ◽  
Wide Range ◽  
The Heat Transfer Coefficient

Synthetic jets are piezo-driven, small-scale, pulsating devices capable of producing highly turbulent jets formed by periodic entrainment and expulsion of the fluid in which they are embedded. The compactness of these devices accompanied by high air velocities provides an exciting opportunity to significantly reduce the size of thermal management systems in electronic packages. A number of researchers have shown the implementations of synthetic jets on heat transfer applications; however, there exists no correlation to analytically predict the heat transfer coefficient for such applications. A closed form correlation was developed to predict the heat transfer coefficient as a function of jet geometry, position, and operating conditions for impinging flow based on experimental data. The proposed correlation was shown to predict the synthetic jet impingement heat transfer within 25% accuracy for a wide range of operating conditions and geometrical variables.

scholarly journals GENERAL MODEL OF RADIATIVE AND CONVECTIVE HEAT TRANSFER IN BUILDINGS: PART I: ALGEBRAIC MODEL OF RADIATIVE HEAT TRANSFER

2019 ◽  
Vol 59 (3) ◽  
pp. 211-223
Author(s):  
Tomáš Ficker
Keyword(s):  
Heat Transfer ◽  
Convective Heat ◽  
Radiative Heat Transfer ◽  
General Model ◽  
Radiative Heat ◽  
Algebraic Method ◽  
Algebraic Model ◽  
Thermal Engineering ◽  
Algebraic Equations ◽  
Wide Range

Radiative heat transfer is the most effective mechanism of energy transport inside buildings. One of the methods capable of computing the radiative heat transport is based on the system of algebraic equations. The algebraic method has been initially developed by mechanical engineers for wide range of thermal engineering problems. The first part of the present serial paper describes the basic features of the algebraic model and illustrates its applicability in the field of building physics. The computations of radiative heat transfer both in building enclosures and also in open building envelopes are discussed and their differences explained. The present paper serves as a preparation stage for the development of a more general model evaluating heat losses of buildings. The general model comprises both the radiative and convective heat transfers and is presented in the second part of this serial contribution.

Sweeping Flow Heat Transfer With Piezoelectric Fans Over Vertical Flat Surfaces

2009 ◽  
Author(s):  
Mehmet Arik ◽  
Mehmed S. Ulcay
Keyword(s):  
Heat Transfer ◽  
Electrical Power ◽  
Electronics Cooling ◽  
Synthetic Jets ◽  
Operating Conditions ◽  
Flat Surfaces ◽  
Resonance Frequencies ◽  
Transfer Behavior ◽  
Meso Scale ◽  
Piezoelectric Fans

Piezoelectric fans have been investigated for electronics cooling over the last several decades. The primary usage of these meso scale-vibrating fans has been to create sweeping flows over the heated surfaces. In this paper, an experimental study to understand the heat transfer behavior of a thin piezo fan with 7.5 cm length and 1 cm width has been performed for a range of operating conditions and fan-to-heater distance. Results showed that piezo fans consume very small amount of electrical power in return providing considerable COPs. Heat transfer enhancements were found to be over 12 at the resonance frequencies. Later, attention was turned to comparison of this technology with other meso scale cooling devices such as synthetic jets and rotary fans. Volumetric COP and heat transfer characteristics are compared for a range of conditions.

Meso Scale Pulsating Jets for Electronics Cooling

2005 ◽  
Vol 127 (4) ◽  
pp. 503-511 ◽  
Author(s):  
Jivtesh Garg ◽  
Mehmet Arik ◽  
Stanton Weaver ◽  
Todd Wetzel ◽  
Seyed Saddoughi
Keyword(s):  
Heat Transfer ◽  
Synthetic Jet ◽  
Synthetic Jets ◽  
Coefficient Of Performance ◽  
Small Scale ◽  
Driving Voltage ◽  
Driving Frequency ◽  
Air Velocity ◽  
Maximum Heat ◽  
Meso Scale

Microfluid devices are conventionally used for boundary layer control in many aerospace applications. Synthetic jets are intense small-scale turbulent jets formed from periodic entrainment and expulsion of the fluid in which they are embedded. The jets can be made to impinge upon electronic components thereby providing forced convection impingement cooling. The small size of these devices accompanied by the high exit air velocity provides an exciting opportunity to significantly reduce the size of thermal management hardware in electronics. A proprietary meso scale synthetic jet designed at GE Global Research is able to provide a maximum air velocity of 90m∕s from a 0.85 mm hydraulic diameter rectangular orifice. An experimental study for determining the cooling performance of synthetic jets was carried out by using a single jet to cool a thin foil heater. The heat transfer augmentation caused by the jets depends on several parameters, such as, driving frequency, driving voltage, jet axial distance, heater size, and heat flux. During the experiments, the operating frequency for the jets was varied between 3.4 and 5.4 kHz, while the driving voltage was varied between 50 and 90VRMS. Two different heater powers, corresponding to approximately 50 and 80 °C, were tested. A square heater with a surface area of 156mm2 was used to mimic the hot component and detailed temperature measurements were obtained with a microscopic infrared thermal imaging technique. A maximum heat transfer enhancement of approximately 10 times over natural convection was measured. The maximum measured coefficient of performance was approximately 3.25 due to the low power consumption of the synthetic jets.

An Experimental Study of Impinging Synthetic Jets for Heat Transfer Augmentation

2015 ◽  
Vol 23 (03) ◽  
pp. 1550024 ◽  
Author(s):  
Omidreza Ghaffari ◽  
Muhammad Ikhlaq ◽  
Mehmet Arik
Keyword(s):  
Heat Transfer ◽  
Experimental Study ◽  
Vertical Surface ◽  
Synthetic Jet ◽  
Synthetic Jets ◽  
Coefficient Of Performance ◽  
Stroke Length ◽  
Cooling Performance ◽  
Circular Jets ◽  
Number Formula

According to recent trends in the field of miniature electronics, the need for compact cooling solutions compatible with very thin profiles and small footprint areas is inevitable. Impinging synthetic jets are recognized as a promising technique for cooling miniature surfaces like laptops, tablets, smart phones and slim TV systems. Effect of jet to cooled surface spacing is crucial in cooling performance as well as predicting Nusselt number for such spacing. An experimental study has been performed to investigate the cooling performance of two different synthetic jets actuated with piezoelectric actuators cooling over a vertical surface. Results showed that a major degradation of heat transfer when jets are close to the surface is occurred. Slot synthetic jets showed a better performance in terms of coefficient of performance (COP) than semi-confined circular jets for small jet to surface spacing. Later, a correlation is proposed for predicting Nu number for a semi-confined circular synthetic jet accounting the effects of Re number ([Formula: see text]), jet-to-surface spacing ([Formula: see text] and [Formula: see text]) and the stroke length ([Formula: see text] and [Formula: see text]). It is found that correlation can provide predictions with an [Formula: see text] value of over 98%.

scholarly journals Heat Transfer Behaviour and Flow Field Characterisation of Impinging Synthetic Jets for a Wide Range of Parameters

2010 ◽  
Author(s):  
Rayhaan Farrelly ◽  
Alan McGuinn ◽  
Tim Persoons ◽  
Darina Murray
Keyword(s):  
Heat Transfer ◽  
Flow Field ◽  
High Speed ◽  
Local Heat Transfer ◽  
Field Measurements ◽  
Local Heat ◽  
Synthetic Jet ◽  
Synthetic Jets ◽  
Flow Measurements ◽  
Wide Range

Impinging synthetic jets are considered as a potential solution for convective cooling, in applications that match their main characteristics (high local heat transfer rates, zero net mass flux, scalability, active control). Nevertheless the understanding of heat transfer to synthetic jets falls short of that available for steady jets. To address this, this paper uses detailed flow field measurements to help identify the main heat transfer mechanisms in impinging synthetic jets. Local heat transfer measurements have been performed for an impinging round synthetic jet at a range of Reynolds numbers between 1000 and 3000, nozzle to plate spacings between 4D and 16D and stroke lengths (L0) between 2D and 32D. The heat transfer results show evidence of distinct regimes in terms of L0/D and L0/H ratios. Based on appropriate scaling, four heat transfer regimes are identified which justifies a detailed study of the flow field characteristics. High speed particle image velocimetry (PIV) has been employed to measure the time-resolved velocity flow fields of the synthetic jet to identify the flow structures at selected L0/H values corresponding to the identified heat transfer regimes. The flow measurements support the same regimes as identified from the heat transfer measurements and provide physical insight for the heat transfer behaviour.

Experimental Investigation of Heat Transfer in Coated Microchannels for MEMS Applications

2015 ◽  
Vol 813-814 ◽  
pp. 782-786
Author(s):  
C. Anbumeenakshi ◽  
M.R. Thansekhar ◽  
M. Satheeshkumar ◽  
R. Vishnu Gayathri
Keyword(s):  
Heat Transfer ◽  
Electronics Cooling ◽  
High Heat ◽  
Thermal Design ◽  
Heat Transfer Characteristics ◽  
Rectangular Microchannel ◽  
Transfer Characteristics ◽  
Viable Solution ◽  
Cooling Devices ◽  
Microchannel Cooling

The microchannel cooling technique appears to be a viable solution to high heat rejection requirements of today’s high-power electronic devices. The thermal design of the small electronics cooling devices is a key issue that needs to be optimized in order to keep the system temperatures at certain levels. Thus the need of microchannel became vital. This present work investigates the experimental work conducted in a coated rectangular microchannel heat sink of hydraulic diameter of 0.763 mm for a heat input of 250 to 1020 Watt with water to study the heat transfer characteristics with two types of header arrangement such as rectangular header and trapezoidal header. The header plays a significant role in distributing the water in to the channels. The uniform distribution of water leads to uniform heat transfer in microchannels. From the experimental results carried with two types of header arrangements, it was found that coated rectangular microchannel with trapezoidal header gives better heat transfer characteristics for the range of heat inputs.

Heat Transfer Enhancement of a Heat Sink by Inclined Synthetic Jets for Electronics Cooling

2013 ◽  
Author(s):  
Arya Ayaskanta ◽  
Longzhong Huang ◽  
Terrence Simon ◽  
Taiho Yeom ◽  
Mark North ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Enhancement ◽  
Heat Sink ◽  
Electronics Cooling ◽  
Synthetic Jet ◽  
Synthetic Jets ◽  
Thermal Dissipation ◽  
Transfer Enhancement ◽  
Resonance Frequencies ◽  
Jet Array

Rising thermal dissipation from modern electronics has increased the challenge of cooling using conventional heat sinks. In addition to fans and blowers, focus is turning to active cooling devices for augmenting performance. A piezoelectrically-actuated synthetic jet array is one under consideration. Synthetic jets are zero-net–mass-flow jets realized by a cavity with an oscillating diaphragm on one side and an orifice or multiple orifices on the other side. They generate highly unsteady jetting flows that can impinge upon heated surfaces and enhance cooling. However, the synthetic jet actuation components might interfere with other components of the electronics module, such as the fan, requiring a displacement of the cavity center from the jet array center. Herein, heat transfer enhancement by an inclined piezoelectrically-actuated synthetic jet arrangement in a heat sink for electronics cooling has been experimentally and numerically studied. A wedge-shaped platform is designed to introduce the jets with an inclined configuration into the finned channels of the heat sink. The unit is inclined to avoid interference with other components of the module. The penalty is described in terms of velocities of jets emerging from this wedge-shaped platform, compared to those from an aligned cavity-orifice design. Effects on heat transfer performance for the heat sink are documented. The jets are arranged as wall jets passing over heat sink fins. The experimental study is complemented with a numerical analysis of flow within the synthetic jet cavity. Optimization is done on the number of jets against the penalty on jet velocity for obtaining maximum cooling performance. The jets are driven by piezoelectric actuators operating at resonance frequencies of 700–800 Hz resulting in peak jet velocities of approximately 35m/s from 92, 0.9 mm × 0.9 mm orifices. The results give guidance to those who face a similar interference problem and are considering displacement of the synthetic jet assembly.

Piezoelectric Fans: Heat Transfer Enhancements for Electronics Cooling

2008 ◽  
Author(s):  
James Petroski ◽  
Mehmet Arik ◽  
Mustafa Gursoy
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Flow Field ◽  
Heat Sink ◽  
Three Dimensional ◽  
Electronics Cooling ◽  
Coefficient Of Performance ◽  
Three Dimensional Flow ◽  
Dimensional Flow ◽  
Piezoelectric Fans

Piezoelectric fans have been investigated for electronics cooling over the last decade. The primary usage or method has been to place the vibrating fan near the surface to be cooled. The piezofan used in the current study is composed of a piezo actuator attached to a flexible metal beam. It is operated at up to 120VAC and at 60 Hz. While most of the research in the literature focused on cooling bare surfaces, larger heat transfer rates are of interest in the present study. A proposed system of piezoelectric fans and heat sink is presented as a more efficient method of system cooling with these fans. In this paper, a heat sink and piezoelectric fan system demonstrated a capability of cooling an area of about 75 cm2 (about 1 C/W) where electronic assemblies can be mounted. The heat sink not only provides surface area, but also flow shaping for the unusual three-dimensional flow field of the fans. A volumetric coefficient of performance (COPv) is proposed, which allows a piezofan and heat sink system volume to be compared against the heat dissipating capacity of a similar heat sink of the same volume for natural convection. A piezofan system is shown to have a COPv of five times of a typical natural convection solution. The paper will further discuss the effect of nozzles in flow shaping obtained via experimental and computational studies. A three-dimensional flow field of the proposed cooling scheme with a piezofan is obtained via laser Doppler anemometry (LDA) flow visualization method. Velocities at the heat sink in the order of 1.5 m/s were achieved through this critical shaping. Finally, the overall system characterization to different heat loads and fan amplitudes will be discussed.

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