1. Proceedings of the 1st Thermal and Fluid Engineering Summer Conference, TFESC
August 9-12, 2015, New York City, USA
TFESC-12963
*Corresponding Author: mlk53@pitt.edu
1
FULL FIELD THERMAL PERFORMANCE OF A SIDE MOUNTED
PIEZOELECTRIC FAN
Juliana M. Said1
, Nick Jean-Louis1
, Ashwin P. Iyer1
, John Bates1
, Mark L. Kimber2*
1
University of Pittsburgh, Pittsburgh, PA 15213, USA
2
Assistant Professor, 636 Benedum Hall, 3700 O’Hara St, Pittsburgh, PA 15213, USA
ABSTRACT
Piezoelectric fans are a potential low power thermal management solution for handheld and low profile electronic
devices. Their design is simple and adaptable, enables noiseless operation, and makes use of resonance conditions
which allow for a highly energy efficient cooling device. It has been shown that piezoelectric fans oscillating at
their resonance frequency have the capability to significantly increase heat transfer over natural convection, but
many of the fundamental studies have focused on an impingement orientation, one where the fan is positioned
normal to the heated surface. This requires a significant amount of space to implement, and hence precludes many
low profile applications, where volume usage must be as efficient as possible. In this study, the full field heat
transfer coefficients maps are experimentally found for a piezoelectric fan oscillating parallel to the heated surface
using infrared thermography. The effect of the distance between the fan blade and heater is explored by considering
three different values for gap: 1 mm, 3 mm, and 5 mm. For these experiments, the oscillation amplitude is held
constant at 10 mm. Results show that these small changes in gap can have a large impact on the heat transfer
coefficient distributions. A gap of 1 mm yields the largest impact zone for thermal enhancement over natural
convection, and produces wing-like contours. For the largest gap considered (5 mm), the impact zone become
more localized near the fan tip and provides peak heat transfer performance higher than the 1 mm gap. At the
intermediate gap, the contours are qualitatively similar to the 5 mm gap results, but with an improvement in heat
transfer coefficient. Optimal performance is dependent on the intended target size of the heat source. The full field
convection coefficient maps are analyzed in detail to produce optimization approaches for the design engineer.
This includes gap and placement of the vibrating fan with respect to the heated target.
KEY WORDS: Piezoelectric fan, Heat transfer enhancement, Electronics cooling, Cantilever beam
1. INTRODUCTION
As technology decreases in size, there is an increasing pressure to continually improve cooling methods. A
current research focus for cooling is on the implementation of piezoelectric fans. A piezoelectric fan consists
of a piezoelectric material bonded to one end of a cantilever beam. Sending an alternating current through a
piezoelectric material causes it to expand and contract which then causes the cantilever beam to oscillate.
When the fan is usually run at the resonance frequency of the beam, the oscillations reach their maximum for
the given signal. These large oscillations cause fluid flow which significantly increases the heat transfer when
compared to natural convection. Additionally, low power consumption, ability to be noiseless, and simplicity in
design are all attributes that make piezoelectric fans an effective method of cooling.
In order to effectively use the fan, research has been conducted on some parameters directly related to the fan’s
function. Sheu et al. [1] ran tests on fans with different types of bonding between the cantilever blade and the
piezoelectric material itself. Another parameter tested was the length of the piezoelectric material on the blade. It
was found that a higher Young’'s modulus as well as larger lengths of piezoelectric materials on the blade would
increase the fan's displacement. Fairuz et al. [2] conducted experiments to determine whether the resonance

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frequency, the first mode shape, of the cantilever blade was the best frequency to run the fan at. The frequency
was changed to first, second, and third mode shapes and it was found that as the mode of vibrations increased, the
airflow velocity decreased and therefore lower heat transfer coefficients were found.
There has also been research on the flow fields generated by piezoelectric fans. Analysis of the flow field from a
single piezoelectric fan was found by Kim et al. [3] who found that vortices were shed at twice the vibration
frequency with maximum fluid velocities at approximately four times the maximum fan tip velocity. Açikalin et
al. [4] found models describing the fluid flow generated by a single piezoelectric fan. Among the first to model
the flow caused by piezoelectric fans was Toda [5]. In the tests, a heated surface was targeted with a fan in order
to predict the vibration and flow behavior.
Toda [6] also conducted experiments in which he placed two fans on either side of a power transistor panel of a
television receiver which resulted in a 17°C decrease in temperature on the surface of the panel. Açikalin et al. [7]
investigated the thermal performance of the piezoelectric fan over a heat sink in a cell phone and the areas of
stagnant airflow in a laptop, finding that there was an additional temperature drop of 6°C in the laptop with the
piezoelectric fans when compared with the rotary fan alone.
Research has also been conducted to analyze the effect of combining heat sinks and piezoelectric fans. Li et al. [8]
compared vertical to horizontal orientations when cooling a heat sink. The width and amplitude of the fans and
the number of fins in the heat sink were changed in these tests. The best positioning for vertically and horizontally
oriented fans were determined for the different heat sinks. Gilson et al. [9] looked at both fluid and thermal
performance of a piezoelectric fan array and its application to electrical machine cooling. The impact of fan
geometry, orientation, aspect ratio, and fin geometry were investigated for two specific sections of the array: the
fin base and the fin side walls. Although distances to both walls and the amplitude of the fan were changed, no
optimum cooling conditions were found.
Açikalin et al. [10] conducted tests changing the fan amplitude, length, frequency from resonance, and offset from
the center of the heat source as well gap between the fan and the heat source. It was found that the determining
factors of heat transfer were the frequency, with resonance the best case, as well as gap distance, and amplitude.
Kimber and Garimella [11] analyzed the piezoelectric fan in order to characterize and predict the heat transfer of
a generalized vibrating piezoelectric fan. By targeting a heated surface with the fan mounted normal to the face of
the heated surface and accounting for all other heat transfer, they were able to gain data on the performance of the
fan based on amplitude and distance from the heated surface, concluding that the maximum performance of any
given fan can simply be described in terms of vibration frequency and oscillation amplitude, similar to what
Açikalin et al. [10] had concluded. Kimber et al. [12] conducted tests changing the fan amplitude and gap distance
from heat source and found different contours of heat transfer found at different gaps and amplitudes. An optimum
gap distance and amplitude correlation was found for a fan in an orthogonal orientation to the heat source.
In this study, the effect of gap distance on the heat transfer performance of the piezoelectric fan is analyzed.
With the data from the heat transfer map, assessment of trends and correlations for effective heat transfer of
heated surfaces can be made.
2. EXPERIMENT SETUP AND PROCEDURES
The experiment consists of a flat steel sheet in the vertical orientation which is exposed to ambient conditions
on both sides. Both sides of the sheet is coated in a Krylon #1602 paint with a known emissivity of 0.95 [13].
On one side of the sheet is a piezoelectric fan oriented in a parallel plane to the sheet. The fan is mounted on
a linear stage which allows the gap between the fan and the sheet to be accurately adjusted. The vertical
oscillation of the fan tip is measured with a Keyence laser displacement sensor model LK-G157 placed above
the fan. On the opposite side of the sheet to the fan, thermal images are captured by a FLIR SC5000 IR camera
with a resolution of +/-2°C. Ambient temperatures are measured using type T thermocouples with a resolution
of +/-1°C. This setup is enclosed by a 60 cm x 70 cm x 30 cm plexiglass enclosure to keep the system isolated
from possible currents in the room.

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Figure 1 Experiment setup and vertical sheet setup respectively.
The steel sheet is stretched across two 25.4 mm diameter copper rods connected to a power supply thus acting as
busbar terminals. The sheet has dimensions of 0.051 mm thickness and 101.6 mm length. The separation of the
busbars gives the sheet a width of 203.2 mm providing a heated surface area of 101.6 mm x 203.2 mm. Beyond
the copper busbars, the sheet is held taught by spring-loaded mounting plates. Voltage measurements are made in
the unheated gap region behind the busbars and before the mounting plates. This setup is based on the setup done
previously by Kimber et al. and can be seen in the second figure of Figure 1 [12].
Table 1 Piezoelectric fan setup parameters
Case (Hz) A (mm) G (mm)
1 60 10 1
2 60 10 3
3 60 10 5
The local heat transfer coefficients at each pixel was first measured under natural convection conditions to serve
as a reference. The piezoelectric fan was then set into place and run at its resonance frequency of 60 Hz and at a
set amplitude A. Forced convection data was taken and analyzed for the local heat transfer coefficients at each
pixel. Comparing the forced and natural convection heat transfer coefficients, the performance of the piezoelectric
fan can then be analyzed. The parameter changed in the experiments was the gap between the fan and the heat
source and can be quantified as seen in Table 1.
3. RESULTS
The heat transfer performance was analyzed between 3 gaps of distances 1 mm, 3 mm and 5 mm away from
the heated surface. The heat transfer coefficients for each distance were found to have distinct contours. For a
gap distance of: 1 mm has a bird shaped pattern, 3 mm has a bell shaped pattern, and 5 mm has a thinner bell
shaped pattern. The piezoelectric fan heat transfer coefficients are displayed in Figure 2. For all analysis and
figures, it is important to note that the origin is placed at the location of the fan tip when it is not moving. From
observing these maps it is seen that out of the three, the best performance comes from a gap distance of 3mm.
It is interesting to note that the best performance does not result from the smallest gap distance of 1 mm as
observed from the horizontal centerline trace in Figure 3.
All three gap distances follow similar trends in their centerline plots, however there are differences that can be
analyzed. For example, the 1 mm gap test has values that peak further upstream compared to the other gaps.
While its peak is at a relatively low convection coefficient, it covers a wider area than the other two distances.
This suggests that the smaller the gap distance the greater the area of coverage. In turn it can be said that for
surface areas that require a great amount of fluid flow but a small amount of convection, an application of a
1mm gap would be suitable. Comparing the remaining two gaps, the 3 mm gap has a higher peak of heat

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transfer than a gap of 5 mm. As the 3mm gap is closer to the surface than the 5 mm gap, it has a higher
concentration of fluid flow toward the surface next to it while the 5mm gap has more fluid flow downstream.
This change in concentration of convection is seen at the distance of 40 mm away from the tip of the fan,
where the 3mm and 5mm lines in Figure 3 intersect.
Figure 2 Piezoelectric fan convection coefficient maps with fan gap distances of 1mm (a), 3mm (b), and 5mm
(c). Colorbar is in [W/m2
K] and x and y axes are in [mm] with the origin at the fan tip.
Figure 3 Horizontal centerline traces for 1 mm, 2 mm, and 3 mm gaps.
Further analysis was done to find optimum x direction heater placement and the resultant average heat transfer
coefficient of the fan for the heater at that location. These can be seen as contours in Figure 4. The analysis is
done given that heater placement in the y direction would be symmetrically aligned with the fan.

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Figure 4 Left column gives optimum placement from the tip of the fan of a X x Y dimensioned heater. Right
column gives expected heat transfer coefficients for the given heater.
For example, given a heater size of 20 x 15 mm and a gap of 1 mm from Figure 4 we find that the heater should
be placed approximately 4 mm downstream of the fan tip and that the fan’s heat transfer coefficient would be
approximately 45.4 W/m2
K. For the same heater, a gap of 3 mm should be placed at the fan tip for cooling of
approximately 53 W/m2
K, and a gap of 5 mm should be placed approximately 3.5 mm downstream of the fan
tip for cooling of approximately 48.7 W/m2
K. From this analysis it can be seen that for the best cooling of a
20 x 15 mm heat surface, a fan with a 3 mm gap positioned as stated above is best.
G = 1
G = 3
G = 5

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As seen in Figure 4, the only heater size region at which a gap of 3 mm is not most fitting is around 60 x 50
mm dimensions, at which a gap distance of 1 mm provides the best cooling. However as you decrease the x or
y dimension, a gap of 3 mm quickly becomes the optimum gap distance. This follows what was said before
about the 1 mm gap having better performance further downstream compared to the other gaps. It is also noted
that the 3 mm and 5 mm gaps have similar curve plots and the heat transfer coefficients are also similar with
3 mm giving higher values. Furthermore, for the 5 mm gap distance, a larger x direction heater distance is
needed to reach these similar values when compared to the 3 mm gap curves. In fact, it is only for the 3 mm
gap orientation that a heater position upstream of the fan tip is seen.
4. CONCLUSION
Local heat transfer coefficients are found for a single piezoelectric fan in a parallel orientation to a heated
surface at three different gaps. The centerline plots show that a 1 mm gap while providing the largest spread
in cooling does not provide the best cooling which occurred at a 3 mm gap. This is reinforced by the
optimization curves which showed that the best cooling mostly occurs at a 3 mm gap with only the farthest
region from the fan tip showing better cooling at a 1 mm gap. Further tests may be conducted to find where
the optimum gap distance actually resides between 1 and 5 mm. Changing the amplitude is also
recommended for future studies.
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transfer characteristics,” Int. Communications in Heat Mass Transf., 52, pp. 140-151, (2014).
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Physics of Fluids, 16, pp. 145-164, (2003).
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