Rotary Fan Research Articles

Development and numerical optimization of a cylindrical wire-fin-type integrated ionic wind heat sink for cooling high-power LEDs

Light-emitting diodes (LEDs) are becoming increasingly high-power and compact, which makes rotary fans incompetent in some cooling situations. The ionic wind technique can compensate for the shortcomings of rotating fans, owing to its benefits of no moving parts and compact structure. Integrating the ionic wind generator with heat dissipation fins can effectively reduce the size of LED devices, but research in this area is still insufficient. In this study, an integrated ionic wind heat sink is designed for cooling LEDs. The multi-physical characteristics of discharge, flow, and heat transfer are numerically studied. The geometric parameters’ impact degree and mechanism on the multi-physical characteristics are analyzed. The performance optimization of the integrated heat sink is realized and verified. The fin length, flow channel center angle, and relative position of the fin have a large influence on the average velocity of ionic wind. The relative position of the wire electrode determines the electric field strength distribution, and it has the greatest influence on the ionic wind performance. The emitting electrode being placed at the inlet edge of the collecting electrode produces a high ionic wind flow rate. The integrated ionic wind heat sink designed in this study exhibits an outstanding cooling performance and temperature uniformity. This device can cool down the surface of a heat source with a power of 200 W to below 91 °C and make the average heat transfer coefficient reach 18.6 W/(m2·K). This study proposes a valuable method to optimize the integrated ionic wind heat sink for cooling high-power electronic devices.

Investigations on Five PMMA Closed Types of Piezo Actuators as a Cooling Fan

There are five closed types of piezo actuators (closed type of PA, closed PA) as a cooling fan relative to those different PAJs of the previous work (open type of PAJ, open PAJ) for analysis in the present study. Closed PA was composed of circular piezoelectric ceramics (PCs) and acrylic (PMMA) plates and investigated on five different types at operating conditions. The results show that the noise of the closed PA is quieter than that of the open PAJ by about 10 dB. When the closed PA is deposed at a suitable distance of 10 to 20 mm from the heat source, averting sucking back the high-temperature fluids around that, the thermal convection coefficient is above 120% more than that of the conventional rotary fan. The cooling performances of these five closed PAs were evaluated by thermal analysis technique, and the convection thermal resistance of the best closed PA can be decreased by over 15%. In terms of energy consumption, a monolithic closed PA was less than 10% than that of a rotary fan. Among these five closed PAs, the best one has the essential qualities that the diameter of the piezoelectric sheet is 41 mm, the opening length is 4 mm, and the outer opening length is 10 mm. Moreover, the best operating conditions are a voltage frequency of 300 Hz and a release distance of 15 mm in the present study.

Numerical study on channel-flow convection heat transfer enhancement with piezoelectric fans under various operating conditions

Piezoelectric fans have been widely considered for electronics cooling as a stand-alone cooling device with its advantages over conventional rotary fans, such as low power consumption, low noise level, and small form factor. However, the application of the piezoelectric fans as a supplemental device in an existing forced-convection condition is rare in the literature. In this study, a transient numerical simulation is carried out to investigate the impacts of the piezoelectric fan, operating at various conditions and locations, on the convection heat transfer of a heated surface in an airflow channel. The mean-to-peak displacements and the operating frequencies of the piezoelectric fan are varied from 3.4 to 7.8 mm and from 90.3 to 180.6 Hz, respectively, for case studies. As a result, when the piezoelectric fan is operated at the front-end location with its maximum displacement and frequency, about 70 % of heat transfer improvement is achieved over the channel flow condition without the piezoelectric fan operation. Furthermore, the Q-criterion analysis is used to visualize vortical structures generated by the piezoelectric fan operating at three relative locations from a heated surface. It is found that the vortical structures carry most of the kinetic energy, creating a significant enhancement of the convective heat transfer in the channel.

Design and Testing of a Bearing less Piezo Jet Micro Heat Sink

The present study utilized piezoelectric ceramics (PC) as actuators to design five new piezoelectric heatsinks and preliminarily investigated the different design types and their operating conditions, such as the frequency, placement distance, thickness between piezoelectric sheets, piezoelectric sheet size, and noise produced. The results showed that when the micro heatsink bearingless piezo jet was placed too close to the heat source, the high temperature sucked back the surrounding fluids, causing the fluid chamber temperature to rise and the cooling effect to be reduced. Therefore, the heatsink should be placed between 10 and 20 mm from the heat source. With the proper distance, the heat convection coefficient was 200% greater than that of a traditional rotary fan. The cooling effect of the five heatsinks was calculated using the thermal analysis method, and the results indicated that the convection thermal resistance of the best heatsink could be reduced by about 36%, and the frequency, flow velocity, and noise were all positively correlated. When the supplied piezoelectric frequency was 300 Hz, the noise level was similar to that of a commercial rotary fan. The tested heatsinks had one of two volumes depending on the size of the piezoelectric sheet, including 3150 mm3 or 4050 mm3, respectively. An array of 25 to 32 micro heatsinks of the same size were connected in series. The power consumption of any single heatsink was 10% of that for a rotary fan. Among the five types of heatsinks, the best type had a piezoelectric sheet diameter of 41 mm, a piezoelectric thickness of 2 mm, and an opening length of 4 mm. Furthermore, the best operating conditions were found at a frequency of 300 Hz and a placement distance of 20 mm.

Effect of Impact and Bearing Parameters on Bird Strike with Aero-Engine Fan Blades

Bird strikes are one of the most dangerous incidents occurring to aircraft engines and can inflict heavy casualties and economic losses. In this study, a smoothed particle hydrodynamics (SPH) mallard bird model has been used to simulate bird impact to rotary aero-engine fan blades. The simulations were performed using the finite element method (FEM) by means of LS-DYNA. The reliability of the material model and numerical method was verified by comparing the numerical results with Wilbeck’s experimental results. The effects of impact and bearing parameters, including bird impact location, bird impact orientation, initial bird velocity, fan rotational speed, stiffness of the bearing, and the damping of the bearing on the bird impact to aero-engine fan blade are studied and discussed. The results show that both the impact location and bird orientation have significant effects on the bird strike results. Bird impact to blade roots is the most dangerous scenario causing the impact force to reach 390 kN. The most dangerous orientation is the case where the bird’s head is tilted 45° horizontally, which leads to huge fan kinetic energy loss as high as 64.73 kJ. The bird’s initial velocity affects blade deformations. The von Mises stress during the bird strike process can reach 1238 MPa for an initial bird velocity of 225 m/s. The fan’s rotational speed and the bearing stiffness affect the rotor stability significantly. The value of bearing damping has little effect on the bird strike process. This paper presents a procedure for evaluating the strength of fan blades against bird strike in the design stage.

PMMA Application in Piezo Actuation Jet for Dissipating Heat of Electronic Devices

The present study utilizes an acrylic (PMMA) plate with circular piezoelectric ceramics (PC) as an actuator to design and investigate five different types of piezo actuation jets (PAJs) with operating conditions. The results show that the heat transfer coefficient of a device of PAJ is 200% greater than that of a traditional rotary fan when PAJ is placed at the proper distance of 10 to 20 mm from the heat source, avoiding the suck back of surrounding fluids. The cooling effect of these five PAJs was calculated by employing the thermal analysis method and the convection thermal resistance of the optimal PAJ can be reduced by about 36%, while the voltage frequency, wind speed, and noise were all positively correlated. When the supplied piezoelectric frequency is 300 Hz, the decibel level of the noise is similar to that of a commercial rotary fan. The piezoelectric sheets had one of two diameters of 31 mm or 41 mm depending on the size of the tested PAJs. The power consumption of a single PAJ was less than 10% of that of a rotary fan. Among the five types of PAJ, the optimal one has the characteristics that the diameter of the piezoelectric sheet is 41 mm, the piezoelectric spacing is 2 mm, and the length of the opening is 4 mm. Furthermore, the optimal operating conditions are a voltage frequency of 300 Hz and a placement distance of 20 mm in the present study.

The Effects of Inlet Blockage and Electrical Driving Mode on the Performance of a Needle-Ring Ionic Wind Pump.

The thermal management of microelectronics is important because overheating can lead to various reliability issues. The most common thermal solution used in microelectronics is forced convection, which is usually initiated and sustained by an airflow generator, such as rotary fans. However, traditional rotary fans might not be appropriate for microelectronics due to the space limit. The form factor of an ionic wind pump can be small and, thus, could play a role in the thermal management of microelectronics. This paper presents how the performance of a needle-ring ionic wind pump responds to inlet blockage in different electrical driving modes (direct current), including the flow rate, the corona power, and the energy efficiency. The results show that the performance of small needle-ring ionic wind pumps is sensitive to neither the inlet blockage nor the electrical driving mode, making needle-ring ionic wind pumps a viable option for microelectronics. On the other hand, it is preferable to drive needle-ring ionic wind pumps by a constant current if consistent performance is desired.

Stress–strain behavior of discontinuous blades for axial mine fans

The study is aimed at designing of blades such that preserve strength at the tip sped not higher than 140 m/s. Because of high rotary speeds, cast blades lack the wanted strength. Thus, it is necessary to design light-weight blades to increase rotary velocity fans. Using the finite element method in ANSYS, strength calculations are performed for blades of varied cellular structures; the stress and strain patterns versus rotor speed are obtained. The cellular structure blades made of aluminium alloy AK7 allows 1.8 times increase in the rotor speed and delivery of an axial fan series VOD.

Effects of Electrical Driving Mode on Pressure and Flow Rate of Wire-Rod Electrohydrodynamic Pumps

Forced convection is the most common thermal management practice and is usually implemented by airflow-generating devices, such as rotary fans. Working based on electrohydrodynamics (EHDs), EHD pumps are emerging airflow-generating devices that have no moving parts, work quietly, and are geometry flexible. The curves showing static pressure versus flow rate (PQ curves) represent the characteristics of an airflow-generating device. This article, experimentally and statistically, presents how PQ curves of a wire-rod EHD pump respond to the electrical driving mode with respect to the numbers of the corona and the collector electrodes. The results show that when the EHD pump is driven by constant corona voltage, both the static pressure and the flow rate are sensitive to the number of corona electrodes. On the other hand, when the EHD pump is driven by constant corona current, both the static pressure and the flow rate are highly responsive to the level of the applied corona current.

Thermal Analysis of Radial Piezoelectric-Magnetic Fan (RPMF) for Electronics Cooling

Application of piezoelectric fan in electronic cooling system has been proven that it is more efficient than natural convection with least power consumption and has high potential to replace existing rotary fan for its simplicity and longer life. An integration of piezoelectric fan with magnet is to widen the cooling coverage area with similar power consumption and cost of running a single piezoelectric fan. By optimizing the repulsive magnetic force generated in between the magnets, the overall fans oscillate with significant average amplitude. The purpose of this paper is to investigate the performance of multiple piezoelectric-magnetic fan and its significance in reducing temperature while enhance the heat transfer. The parameters under investigation are the distance between magnets and fans orientation. In this study four magnetic fans were activated by a piezoelectric fan. It is found that at distance between magnets is 14 millimeters; the average amplitude is largest at highest resonant frequency. The multiple fans is better to be arranged in radial orientation for its ability to produce larger repulsive magnetic force to oscillate the adjacent fans. The distribution of repulsive magnetic force in radial orientation is five times better than array orientation. Therefore, radial piezoelectric-magnetic fan (RPMF) produces larger average amplitude of fans which is 111%. 30% of power consumption per unit coverage area is secured. RPMF generates average wind velocity of 0.4m/s compared to array orientation 0.17m/s.

Effect of arbitrary yaw/pitch angle in bird strike numerical simulation using SPH method

The influences of arbitrary attitude angles on bird strike on a fixed rigid flat plate and a rotary jet-engine fan are studied. A verified realistic bird model and a hemispherical-ended cylinder substitute bird model are modeled by using the smoothed particle hydrodynamics (SPH) method. Since birds can strike aircraft engine from any orientations, simulations of bird models striking a rigid flat plate at random attitude angles are first done as a validation test. Results show that different attitude angles of bird model have distinct effect on the response of bird strike. As the attitude angle increases, the peak impact force becomes larger and the bird model loses more energy. By considering the rotation of the jet-engine fan ignored before, the impact behavior of realistic bird models striking on rotating engine blades from arbitrary attitude angles is investigated. Effects of the attitude angle on the most concerned impact force, kinetic energy and von Mises stress of blade roots are discussed. It is concluded that considering attitude angles of real bird and rotation of the jet-engine fan in bird strike simulation has practical significance on structural tolerant design.

Mechanisms of power dissipation in piezoelectric fans and their correlation with convective heat transfer performance

Piezoelectric fans offer an intriguing alternative to conventional rotary fans for thermal management of portable and wearable electronics due to their scalability, low power consumption and simple mechanical construct. We report a combined experimental and modeling study to help elucidate power dissipation mechanisms in piezoelectric fans. To analyze contributions from these different mechanisms, mathematical models that account for mechanical hysteresis, dielectric loss and viscous damping from generated air flows are used in conjunction with vibration amplitudes and power consumption data obtained experimentally from piezoelectric fans of different blade lengths, thicknesses and mass distributions. In parallel, we perform experiments on convective heat transfer coefficients and aerodynamic forces acting on surfaces that are oriented perpendicular with respect to fan-induced air flows. These experiments establish that the portion of power dissipation ascribed to air flows correlates well with the heat transfer performance and aerodynamic force. A power ratio, defined as the fraction of the air flow power to the total power dissipation, is then proposed as a useful indicator of the power efficiency of the piezoelectric fans. We show that the power efficiency exhibits a peak at a particular bias voltage amplitude, and provide a guideline to determine this optimum voltage. Lastly, we relate the air flow power to the blade’s geometrical parameters to facilitate systematic optimization of the blades for both cooling performance and power efficiency.

The Design of The Monitoring Tools Of Clean Air Condition And Dangerous Gas CO, CO2 CH4 In Chemical Laboratory By Using Fuzzy Logic Based On Microcontroller

There are many phenomena that human are exposed to toxins from certain types such as of CO2, CO2 and CH4 gases. The device used to detect large amounts of CO, CO2, and CH4 gas in air in enclosed spaces using MQ 135 gas sensors of different types based on the three sensitivity of the Gas. The results of testing the use of sensors MQ 135 on the gas content of CO, CO2 and CH4 received by the sensor is still in the form of ppm based on the maximum ppm detection range of each sensor. Active sensor detects CO 120 ppm gas, CO2 1600 ppm and CH4 1ppm "standby 1" air condition with intermediate rotary fan. Active sensor detects CO 30 ppm gas, CO2 490 ppm and CH4 7 ppm "Standby 2" with low rotating fan output. Fuzzy rulebase logic for motor speed when gas detection sensor CO, CO2, and CH4 output controls the motion speed of the fan blower. Active sensors detect CO 15 ppm, CO2 320 ppm and CH4 45 ppm "Danger" air condition with high fan spin fan. At the gas level of CO 15 ppm, CO2 390 ppm and CH4 3 ppm detect "normal" AC sensor with fan output stop spinning.

Development of a radial-flow multiple magnetically coupled fan system with one piezoelectric actuator

In recent years, piezoelectric fans and their feasibility for use in cooling electronic devices have been widely studied. However, there are few studies that address using a single piezoelectric actuator to generate radial air flow. In this study, a radial-flow multiple fan system (RMFS) was developed for the thermal management of high power LEDs. This system only used one piezoelectric actuator and a magnetic repulsive force to activate up to 20 fans, which featured low power consumption and a large cooling area. The RMFS was mounted in a circular heat sink to evaluate its thermal performance. To find the optimal design for the RMFS, the influence of some geometric parameters was investigated. The performance of different designs was compared with a commercially available axial fan. The results showed that design E had the best thermal performance among the designs because of its relatively large frequency and amplitude. The thermal resistance and percentage improvement under a 35W heat flux were 0.86K/W and 36.9%, respectively. In addition, a coefficient of performance (COP) was defined. The COP of design E was approximately 3.7 times that of the rotary fan. For the power consumption aspect, the RMFS is more efficient than the rotary fan.

Electrostatic Fluid Accelerator under High‐Speed Free Air Stream

AbstractThe electrostatic fluid accelerator (EFA) generates ionic wind with a simple structure that barely obstructs the free air stream or produce excessive noise. This paper presents the velocity characteristics of an EFA under a high speed free air stream to simulate an EFA‐powered propulsor. The results show that when the EFA generates identical velocity to the free air stream, the EFA contributes 25% of the resultant velocity. When the EFA is replaced by a rotary fan that generates identical velocity to the free air stream, the fan contributes only 13.4% of the resultant velocity. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Effect of bird geometry and impact orientation in bird striking on a rotary jet-engine fan analysis using SPH method

A numerical investigation was performed to further understand the physical significance of bird striking on a rotary jet-engine fan. A new numerical bird model considering more geometric characteristics than traditional ones was established first, during which the smooth particles hydrodynamic (SPH) method and an equation of state (EOS) were employed. The numerical method and material model were indicated to be reasonable by a validation analysis. Then, a preliminary study of a rigid target struck by a realistic bird from four different orientations including head, tail, bottom and wing sides as well as a traditional hemispherical-ended cylinder model were simulated. It was found that bird geometry and impact orientation had significant effects on impact response and kinetic energy loss of the bird. Furthermore, the same load conditions were conducted on a rotary jet-engine fan and followed by a series of parametric studies, including impact force history, kinetic energy loss of the bird, deformations of the blade tips and von Mises stresses of the blade roots. The results showed that both bird geometry and impact orientation had significant and non-ignorable influence on bird striking on a rotary jet-engine fan and bottom side was the most dangerous case. Considering more geometric characteristics of the bird and impact orientation in studies of bird strike problems was proved to be meaningful and necessary.

Investigation of a double oscillating-fan cooling device using electromagnetic force

This study proposes a double oscillating-fan cooling device using electromagnetic force. The device consists of two oscillating-fans. It requires only one electromagnet and two fan sheets with one magnet on each of them. The electromagnet and fan sheets are situated on a base and arranged accordingly. The electromagnetic force generated by the electromagnet can actuate the fan sheets. The main advantage of the device is its simple structure because there is no bearing and motor in the device. The driving current can be either DC PWM (Pulse width modulation) or AC (Alternating current) within 3–12V so it is compatible with most electronic devices. The dimensions of the proposed model are 50mm∗50mm∗15mm during operation. Concerning flow rate, sound pressure, power consumption and resonant frequency tests, a comparison between the proposed model and different type of cooling devices has been completed. The result shows that the model can provide cooling ability similar to a rotary fan while consuming 40% of the power of the rotary fan. It shows not only a good cooling ability but also a great potential for structural reliability and design flexibility.

Cooling Performance Evaluation of Synthetic Jet Based Thermal Solution Module

The convective thermal resistance which represents the heat removal from the heat sink surface of a heat pipe/heat sink module to mean coolant flow temperature is often a dominant contributor to the overall thermal resistance of a heat pipe/heat sink module or remote heat exchange (RHE). RHE is a thermal solution module composed of a heat spreader, thin flattened heat pipe with low profile heat sink which is widely used for the thermal management of compact portable electronic devices. Minimizing the convective thermal resistance at the heat sink of RHE as well as thickness reduction is often an important objective for the thermal designers. Recently, an alternate air mover system which operates based on piezoelectricity is developed. This device is called dual cooling jet (DCJ) in short which can be fabricated with very small thickness down to 1.0 mm. Thin DCJ as a synthetic jet generates air jet with more than 7 m/s air flow velocity which is promising for the increasing demands of thinner next generation portable electronic devices. DCJ is a promising device to dissipate the heat from the heat sink of a RHE. In this work, the performance of RHE is evaluated when heat is dissipated from its heat sink by DCJ. The results are compared with conventional rotary fan. The results show that more than 12 W of heat can be dissipated by DCJ which can easily compete with some commercialized rotary mini blowers while having much smaller thickness. Various configuration of heat sink–DCJ combinations as well as size and shape of both heat sink and DCJ are tested and based on thermal resistance data, cooling effectiveness of DCJ is studied.

Thin Profile Fan Using the Generation Principle of Travelling Space between Two Resonantly-Driven Plates

As the size of electronic mobile devices decreases, the size reduction of cooling components becomes valuable. Because of rotation radius, conventional rotary fans occupy columnar space with some thickness. This occupation is an issue for size reduction of electronic devices. This paper proposes a fan that uses the generation principle of travelling space between two resonantly-driven plates. As the profile of this fan is parallelepiped and thin, the fan can be efficiently inserted in small and thin space of parallelepiped devices. This paper also addresses a realization method of the proposed fan principle. The principle needs two plates and excitation of a sine-shaped mode on each plate. Therefore desired excitation conditions and relative position of the two plates were clarified. Then the principle was realized by an experimental apparatus, and consequently airflow with pulsation was confirmed.

Fluent Based Numerical Analysis of Eliminating Ultra-Limit Gas in Upper Corner by Using Rotary Jet Fan

For the problem of gas accumulation in upper corner of "U" type ventilation system mining face, a new approach to eliminating gas accumulation in upper corner of coal mining face by using high-speed rotating jet is proposed based on flow law of rotary jet and actual environment of coal mining face. The numerical simulation with Fluent software is carried out. The results show that when fan is mounted close to the wall, the high-speed rotating jet has good Coanda effect, little impact on air flow structure of coal mining face, and is significantly effective to deal with gas accumulation in upper corner. FLUENT based numerical simulation provides a theoretical basis for actual application of rotary jet fan in coal mining face.This template explains and demonstrates how to prepare your camera-ready paper for Trans Tech Publications. The best is to read these instructions and follow the outline of this text.