This document summarizes a study on the power efficiency of piezoelectric fans. Piezoelectric fans use alternating electric fields applied to PZT layers to induce vibration in attached fan blades, creating airflow without moving parts. The study experimentally investigates how fan configuration factors like blade thickness and length affect power consumption and heat transfer performance. Total power consumption is separated into parasitic losses in the PZT actuator and useful flow power that correlates to cooling. Results show flow power estimated using aerodynamic damping matches better than linear damping models, and heat transfer performance correlates more closely to flow rather than total power. Ongoing work aims to further optimize blade motion for higher efficiency.
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conference slides_Final
1. Yide Wang
Navid Dehdari Ebrahimi
Advisor: Y. Sungtaek Ju
Department of Mechanical and Aerospace Engineering
University of California, Los Angeles
Power Efficiency of Piezoelectric Fan
2. Overview
• Background
• Introduction to working principles and previous studies
• Experimental setups, devices and techniques
• Experimentally Investigating power efficiency of piezoelectric fan cooling with
different configurations.
1. Different blade thickness
2. Different blade length
• Conclusion
• Ongoing and Future work
3. Background
• Applied alternating electric field on top and
bottom PZT (lead zirconate titanate) layers
induces alternating and opposite deformation.
• Opposite deformation creates bending
moment, causing vibration.
• Vibrating at fan blade’s resonance frequency
to induce maximum air flow.
• Lower power consumption compared to
traditional rotary fan.
• Low noise level.
Three-layer PZT
bimorph actuator
Fan blade (Polyester film)
http://dx.doi.org/10.1016/S0924-4247(99)00231-9
4. Previous Works
http://catalog.pelonistechnologies.com/Asset/Intel%20Piezo%20Report.pdf
• Acikalin et.al thoroughly studied the factors
affecting the piezoelectric fan cooling
including relative position, vibration
amplitude, frequency and etc.
• Wait et.al researched the efficiency of
piezoelectric fan converting electrical energy
into mechanical energy operating at higher
flexural modes.
• Kimber et.al derived correlations obtaining
forced convection coefficients from the
vibration of piezoelectric fan.
However, the lack of systematic study of cooling efficiency in terms of power
consumption needs to be addressed !
5. Power measurement
Function Generator + Amplifier
current and voltage
Output monitoring
signal from amplifier
Data processing
𝑃 =
1
𝑇 0
𝑇
𝑉 𝑡′ 𝐼 𝑡′ 𝑑𝑡 ′
The total power consumption of piezoelectric fan:
7. Power Measurement Result
Total power consumed
• Parasitic power dissipation
• Flow power (correlates
directly to cooling)
Parasitic power dissipated in PZT actuator
• Internal friction
• Dielectric loss
• Heat generation
Need to estimate flow power !
8. Dynamic Model of Piezoelectric Fan
𝑚1 0
0 𝑚2
𝑦1
𝑦2
+
(𝐶1 + 𝐶2) −𝐶2
−𝐶2 𝐶2
𝑦1
𝑦2
+
𝐶1𝑎 0
0 𝐶2𝑎
𝑦1
𝑦2
𝑦1
𝑦2
+
(𝐾1 + 𝑘2) −𝐾2
−𝐾2 𝐾2
𝑦1
𝑦2
=
𝐹0 sin 𝜔𝑡
0
𝐾2, 𝐶2, 𝐶2𝑎𝐾1, 𝐶1, 𝐶1𝑎
𝑚1 𝑚2
After measuring the vibration amplitude of piezoelectric fan
9. Flow power estimation
𝑃𝑓 =
8
3
𝐶2𝑎 𝑦2
3
𝜔2
𝑓
After obtaining the aerodynamic damping coefficient
Flow power at various input voltages Finite amount of power difference
represents the parasitic power
dissipation
Total Power Flow Power
PZT loss
10. Changing Blade Thickness
Configuration blade length (mm)
Rang of Resonance
Frequency (Hz)
Range of Voltage
Applied to Piezo
Actuator (V)
Thickness (mm) Material
I (Changing Thickness) 32 35 - 119 70 - 140 0.127 - 0.508
Kapton sheet
(Ployester)
II (Changing length) 19 - 50 30 - 188 70 - 140 0.254
Kapton sheet
(Ployester)
13. Conclusion
• Using aerodynamic damping (𝑓𝑑~𝑢2
) results in a better match than the linear damping (𝑓𝑑~𝑢)
• The flow power induced by the piezoelectric fan can be estimated by subtracting the power dissipation in
the PZT actuator from the total power consumption.
• Heat transfer Performance of the piezoelectric fan is more relevant to the flow power not the total power.
• Plotting the “forced convection coefficient of the fan” vs. “flow power” gives a convergent curve.
Total Power Flow Power
PZT loss
14. Ongoing and Future Work
• Measuring force on an opposing flat surface due to piezo fan to find out relation
between heat transfer performance and air jet momentum.
• Measuring the flow rate of the air jet to find the relationship between the air
flow rate and heat transfer performance.
• Simulation-based investigation of the relation between tip velocity and vortex
strength.
• Optimizing the blade motion for higher efficiency: Experiment and Simulation
16. References
1. Açıkalın, Tolga, et al. "Characterization and optimization of the thermal performance of miniature piezoelectric
fans." International Journal of Heat and Fluid Flow 28.4 (2007): 806-820.
2. Kimber, Mark, and Suresh V. Garimella. "Measurement and prediction of the cooling characteristics of a generalized vibrating
piezoelectric fan." International Journal of Heat and Mass Transfer 52.19 (2009): 4470-4478.
3. Wait, Sydney M., et al. "Piezoelectric fans using higher flexural modes for electronics cooling applications." IEEE transactions
on components and packaging technologies 30.1 (2007): 119-128.
Notas del editor
Hello everyone. I hope you’ve been having a pleasant day so far.
In this presentation I’m going to introduce our recent project concerning the “power efficiency of piezoelectric fans”.
First, I’m going to introduce the concept of piezoelectric fans, their important merits over conventional rotary fans, and their principal of working.
Secondly, we will review some backgrounds related to this work and some previous works that have been done, their contributions and the motivation of our project.
Next, comes the measurement instruments and techniques that we used.
After that, we will go over the results of a portion of our experiments that lead us to the next part, which is conclusion.
Finally, ongoing and future works.
The piezoelectric fan is composed of 2 parts: piezoelectric actuator and a blade (usually made of polymer).
The piezo actuator consists of two layers of PZT ceramics on top and bottom with a brass shim sandwiched at the middle. By applying an alternating electric field, the piezo-actuator starts to vibrate. When the driving frequency equals the resonance frequency of the fan blade, the maximum vibration amplitude can be obtained, as well as the maximum induced flow that can be employed to create forced convection.
Compared to traditional rotary fans, the piezoelectric fan
****consumes much less power, around 15mW compared to 130mW for an equivalent rotary fan
****introduces less noise in delicate and noise sensitive electronics.
****can be easily scaled down due to its super-simple mechanism.
The above picture is an example of substituting traditional rotary fan by an array of piezo fan in chip cooling application. Some great works studying the piezoelectric fan cooling have been done by others.
For instance, Acikalin and others investigated the effect of various factors on the COOLING performance of the piezoelectric fan like relative position from the heat source, amplitude, frequency etc.
Wait and other coworkers ...
Kimber derived correlations for forced heat transfer coefficient for the piezo electric fan vibration.
In electronics cooling, the power consumption can be a great concern due to limited battery capacity. However, there isn’t much work done in systematic study of the cooling efficiency in terms of power consumption. Therefore, we took a chance to dig a little deeper in the power consumption of piezoelectric fan. As mentioned in the literature, the power consumption of piezoelectric fan can be obtained by measuring its alternating voltage and current and integrate through the time of one period.
In doing so, we have a function generator and an amplifier to drive the piezoelectric fan. The amplifier can output monitoring signal for both voltage and current. The Labview Vi is created to display and record the voltage and current values. Finally, a MATLAB script is created to fit the signal with two sine functions, which eliminates noise, and to do the integration in getting power.
According to previous studies, the power consumption of PZT actuator concentrates on three categories, internal friction, dielectric loss and heat generation. As shown by the plot on the left, the power consumption of solo PZT actuator without the fan blade is linearly proportional to the frequency at a given input voltage. However, the total power consumption of piezoelectric fan shows a peak at the fan blade’s resonance frequency. Clearly, a portion of total power consumption comes from the fan blade, and we believe it is the flow power that the fan blade provides to surrounding air via vibration. To estimate the flow power, we need to create a dynamic model for piezoelectric fan.
The piezoelectric fan is modeled as a 2 DOF mass-spring-damper system with effective mass 𝑚, stiffness 𝐾, linear damping coefficient 𝐶, aerodynamics damping coefficient 𝐶 𝑎 and an excitation force 𝐹 0 . Previous studies only include linear damping in the governing equation. Therefore, we did a comparison between curve fitting the blade’s amplitude by having only linear damping coefficient and aerodynamic damping coefficients.
Plot on the left Includes aerodynamic damping coefficient. the aerodynamic damping of PZT actuator, 𝐶 1𝑎 , is assumed to be zero. Aerodynamic damping of blade, 𝐶 2𝑎 , can then be determined by fitting the measured amplitude.
As shown above, the amplitude obtained from including aerodynamic damping fits the measured amplitude better.
The flow power 𝑃 𝑓 can then be determined based on blade’s vibrating amplitude 𝑦 2 , frequency 𝑓 and aerodynamic damping coefficient 𝐶 2𝑎
As expected, the flow power peaks at the fan blade’s resonance frequency. And if we compare the total power and flow power, shown by the plot on the right, there is a finite difference between them. And this difference represents the parasitic power dissipation in the PZT actuator.
We postulated that the flow power is the portion of power related to heat transfer performance.
In this experiment, we change the configuration of the piezoelectric fan by changing the thickness of the blade by adding layers of polyester, and as a result, the resonance frequency also changes. A maximum number of 4 layers was used by which we could obtain a range of natural frequencies from 35Hz to 119Hz.
We varied the voltage for each configuration from 70V to 140V.
In the left hand side, the power normalized heat transfer performance (as a representative for power efficiency) is shown vs. blade thickness. On the right hand side you see the same curve, this time normalized by flow power.
As it is clear, normalizing by flow power leads to a convergent curve.
