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ME 6
Topic : Optimal Design of a Thermoelectric Cooling/Heating for
Date of Submission:
Team Members
Karthik Reddy Peddireddy
Ravi Teja Jogiparthi
Vikas Reddy
ME 6950- Thermoelectric -I (Design)
Summer - II (2015)
Project Report
Optimal Design of a Thermoelectric Cooling/Heating for
Car Seat Comfort
Faculty: Dr. HoSung Lee
Date of Submission: 19th Aug, 2015
WIN ID
Karthik Reddy Peddireddy 781376840
461473289
429383932
Optimal Design of a Thermoelectric Cooling/Heating for
i
ACKNOWLEDGMENTS
I would like to express my sincere thanks to Dr. HoSung Lee, Professor of Mechanical &
Aeronautical Engineering and Alaa M. Attar, for their time and guidance throughout the study
that is continued in this project. It would not have been possible to make this project a better one
without their presences.
I would like to thanks my classmates for the moral support.
Team Work
ii
TABLE OF CONTENTS
ACKNOWLEDGMENT .........................................................................................................i
LIST OF FIGURES .................................................................................................................iii
ABSTRACT .............................................................................................................................iv
1. Introduction ....................................................................................................................1
2. Optimum Design Background .................................................................................2
3. Optimal Design of Cooling/Heating of a Car Seat ...........................................4
3.1 Present Study ........................................................................................................4
4. Application .......................................................................................................................8
5. Conclusion ........................................................................................................................9
6. Reference ...........................................................................................................................10
iii
LIST OF FIGURES
Fig.1.1 a) TEC module with two heat sinks, (b) Schematic of thermoelectric couple ..............1
Fig 3.1 Typical thermoelectric cooler module ...........................................................................4
Fig.3.2 Cooling power (W) and COP vs. element length with the current of I = 4 A used ......5
Fig 3.3 Fluid outlet temperatures vs. Element length (mm) with the current of I = 4 A used ..5
Fig 3.4 Heating power (W) and COP vs. element length (mm) ................................................6
Fig 3.5 Schematic of thermoelectric car seat cooling/heating device ........................................7
Fig. 3.6 Schematic of thermoelectric car seat cooling/heating with a recirculating duct ..........8
iv
Abstract
To improve the performance and system design we optimize new method which include a fan, a
thermoelectric device, under-seat channels, and an optional recirculating duct enveloped in
constant/heating and low power consumption. This work illustrates whether the distributed air is
consumed completely at the end of channels or recirculated using a return duct and impermeable
materials except the perforated holes. Selecting suitable thermoelectric modules from various
commercial modules is quite difficult for the system designers. A typical 1.2 mm thermoelectric
cooler module is intended to decrease the Joule heating also concurrently revokes energy back-
flow by the thermal conduction. By considering five independent dimensionless parameters such
as Nk, Nh, NI, T* and ZT we can predict analysis that indicates the thermoelectric devices must be
designed based on the specific cooling/heating system.
1
1. INTRODUCTION
Moving to the standard vehicle optimal design of car seat is progressively becoming a
competitive issue. Since then early 1960s, it was shown that aerated car seats improved human
comfort (Johnson, 1964). Recent climate chamber tests of different types of seat indicate that
transpiring (perforated) materials with ventilation showed enhanced comfort (Malvicino, 2001).
Thermoelectric devices probably first time applied to car seat comfort (Feher, 1990). Later, seat
climate control for initial startup warming and cooling using thermoelectric devices was reported
(Gallup, 2003). Placing seat temperature control unit in series with automotive HVAC module
for considering humidity control increased body comfort (Kadle, 2007). Recently, compactness
of a novel ventilation system with thermoelectric devices was reported (Bell, 2013).
A simple electrical circuit for thermoelectric cooling (TEC) is shown in Fig.1. The
amount of heat absorbed at the cold junction is associated with the Peltier cooling, the half of
Joule heating, and the thermal conduction. It is determined by net heat removed the cold
junction, such that,
�� = ���� −1
2��� − �∆�
Where ∆T = Th − Tc and � is thermal conductance.
Fig.1.1. a) TEC module with two heat sinks, (b) Schematic of thermoelectric couple
Multiple thermocouples can be used as to increase the cooling capacity and greater
temperature difference can be achieved by operating the cooling unit. An electric insulator is
usually placed between the electric conductor and the cold plate to avoid short circuit.
2
The objective of this work is to optimize design (Lee, 2012) of a thermoelectric device
such as, element length, cross section and number of thermoelements. This method improves the
performance and then an innovative system design a fan, a thermoelectric device, under-seat
channels, and an optional recirculating duct with high efficiency (constant cooling/heating and
low power consumption). This design includes transient startup warming and cooling before the
car (Heating Ventilation and Air-conditioner) HVAC is active in the cabin. Usually the
distributed air of the channels are completely consumed through perforated holes and permeable
seat materials. This study gives an option whether the distributed air is consumed completely at
the end of channels or recirculated using a return duct and impermeable materials except the
perforated holes.
A thin thermoelectric cooler module is considered with element length 1.2 mm and
element area 4.4 mm2 and there exits two thermal resistance between the two hot and cold
junctions and fluids. We perform a non-dimensional analysis for minimizing parameters defining
five independent dimensionless parameters, not conflicting with one another, one of which is Nk
that includes the most important geometric information such as number of thermoelements,
element length and cross section, and thermal conductivity. The next important parameter is
dimensionless current NI which is the ratio of the Peltier cooling power to the thermal
convection. The third dimensionless parameter is Nh, which is the ratio of the cold convection to
the hot convection. The fourth is the ratio of cold inlet fluid temperature to the hot inlet fluid
temperature. Lastly the fifth is called the dimensionless figure of merit ZT, which represent the
quality of materials, the higher is the better. The performance curves is difficult to predict
without the analysis of dimensionless parameters.
2. Optimum Design Background
The dimensionless analysis developed by Lee, (2012) obtains the maximum cooling
power by simultaneously determining the dimensionless current supplied (NI) and the ratio of the
thermal conductance to the convection conductance (NK) for a given set of fixed parameters.
This method converts the four basic heat balance equations, such as
�� = Ƞ�
ℎ���(�∞� − ��) (1)
�� = � ����� −1
2��� +
��
���(�� − ��)� (2)
3
�� = � ����� +1
2��� +
��
���(�� − ��)� (3)
�� = Ƞ�
ℎ���(�� − �∞�) (4)
Qc and Qh are the rate of heat transfer for the cold and hot fluids, and n is the no. of
thermoelectric couples. the thermal resistance of the cold heat sink can be expressed by the
reciprocal of the convection conductance Ƞ�
ℎ��� , where Ƞ�
is the fin efficiency, ℎ� is the
convection coefficient, and �� is the total surface area of the cold heat sink.
��(�∞∗ − ��
∗)
��= ����
∗ −��
�
2��∞�+ (��
∗ − ��∗) (5)
��∗ − 1
��= ����
∗ −��
�
2��∞�+ (��
∗ − ��∗) (6)
��∞�, ��, ��, and �� are defined as the dimensionless figure of merit, convection ratio, the ratio
of thermal conductance to convection conductance, and dimensionless current, respectively. The
dimensionless temperatures are then a function of five independent dimensionless parameters as,
��∗ = �(��∞�, ��, ��, ��, �∞
∗) (7)
��∗ = �(��∞�, ��, ��, ��, �∞
∗) (8)
Then, the dimensionless cooling power QC, heat rejection Qh, input power Pin, and COP can be
defined as,
��∗ =
��
Ƞ�
ℎ����∞� (9)
��∗ =
��
Ƞ�
ℎ����∞� (10)
���∗ =
���
Ƞ�
ℎ����∞� (11)
��� =��
∗
��∗
(12)
Using these equations, where ��∞�, �∞∗, �� are set to be inputs, the dimensionless parameters ��
and �� can be optimized to solve for maximum cooling power.
3. Optimal Design of Cooling/H
A newly developed optimization method is used to improve the performance on the
thermoelectric devices which includes a fan, a thermoelectric device, under
optional recirculating duct. In this the under seat channels contain perforated holes and
permeable seat materials which consume the total distributed air of
design gives an option whether the distributed air is consumed completely at the end of channels
or recirculated using a return duct and impermeable materials except the perforated holes which
can be verified by measurements.
Many manufacturers provide performance curves of the thermoelectric products based on the
ideal conditions that assume no thermal resistances between the junctions and medium which is
indeed unrealistic. Furthermore, the material properties are unknown and e
electrical contact resistances.
3.1 Present Study
This Present work provides a new design which significantly improves the performance of
car seat cooling/heating and indicate that a much lower power consumption almost in half could
be achieved with equivalent cooling/heating.
Fig 3.1. Typical thermoelectric cooler module
The above figure shows a typical thin thermoelectric cooler module. Here an element length
of 1.2mm is used as shown to decrease the joule heating. But we cannot
4
of Cooling/Heating of a Car Seat
A newly developed optimization method is used to improve the performance on the
thermoelectric devices which includes a fan, a thermoelectric device, under-seat channels, and an
optional recirculating duct. In this the under seat channels contain perforated holes and
permeable seat materials which consume the total distributed air of the channels. This optimal
design gives an option whether the distributed air is consumed completely at the end of channels
or recirculated using a return duct and impermeable materials except the perforated holes which
can be verified by measurements.
ny manufacturers provide performance curves of the thermoelectric products based on the
ideal conditions that assume no thermal resistances between the junctions and medium which is
indeed unrealistic. Furthermore, the material properties are unknown and even the thermal and
This Present work provides a new design which significantly improves the performance of
car seat cooling/heating and indicate that a much lower power consumption almost in half could
achieved with equivalent cooling/heating.
Fig 3.1. Typical thermoelectric cooler module
The above figure shows a typical thin thermoelectric cooler module. Here an element length
of 1.2mm is used as shown to decrease the joule heating. But we cannot say that this short length
A newly developed optimization method is used to improve the performance on the
seat channels, and an
optional recirculating duct. In this the under seat channels contain perforated holes and
the channels. This optimal
design gives an option whether the distributed air is consumed completely at the end of channels
or recirculated using a return duct and impermeable materials except the perforated holes which
ny manufacturers provide performance curves of the thermoelectric products based on the
ideal conditions that assume no thermal resistances between the junctions and medium which is
ven the thermal and
This Present work provides a new design which significantly improves the performance of
car seat cooling/heating and indicate that a much lower power consumption almost in half could
The above figure shows a typical thin thermoelectric cooler module. Here an element length
say that this short length
is beneficial until optimization is done.
element length as shown below:
Fig.3.2. Cooling power (W) and COP vs. element length (mm) with the current of I = 4 A used
The above figure shows the graph between cooling power and COP
which provide solution to determine the element length. From the above figure it can be
observed that the optimal element length is near 2.2mm and also the increase of e
from 1.2mm (commercial) to 2.2mm (present) results in 35% increase of cooling power from
28W to 38W with an acceptable decrease in the COP from 1.3 to 1.
Fig 3.3 Fluid outlet temperatures vs. Element length (mm) with the current
5
is beneficial until optimization is done. The Performance of TED is a function of thermoelectri
Cooling power (W) and COP vs. element length (mm) with the current of I = 4 A used
The above figure shows the graph between cooling power and COP vs. element length (mm)
which provide solution to determine the element length. From the above figure it can be
observed that the optimal element length is near 2.2mm and also the increase of e
from 1.2mm (commercial) to 2.2mm (present) results in 35% increase of cooling power from
28W to 38W with an acceptable decrease in the COP from 1.3 to 1.
Fluid outlet temperatures vs. Element length (mm) with the current
The Performance of TED is a function of thermoelectric
Cooling power (W) and COP vs. element length (mm) with the current of I = 4 A used.
element length (mm)
which provide solution to determine the element length. From the above figure it can be
observed that the optimal element length is near 2.2mm and also the increase of element length
from 1.2mm (commercial) to 2.2mm (present) results in 35% increase of cooling power from
Fluid outlet temperatures vs. Element length (mm) with the current of I = 4 A used.
The above figure shows the cold and hot fluid outlet temperatures along with the element
length. A temperature difference of
COP of about 1.0 for cooling in summer.
Fig 3.4 Heating power (W) and COP vs. element length (mm)
The above figure shows the Heating power and COP vs
difference of ∆� = 21�� obtained from cooling power of 80 W and COP of about 2.0 for
heating in winter.
The below diagram in CATIA shows the schematic of commercial model of thermoelectric
car seat cooling/heating. It consists of thermoelectric device sandwiched between Heat sink 1
which is a cold heat sink, Heat sink 2 which is a hot heat sink, where each has 20 fins
space between the fins. This fin design is based on the optimization of heat sink. Conditioned air
is supplied from fan with volume flow rate of 6.3
thickness 0.3 cm which covers occupant seat area o
perforated holes which helps to dissipate hot air or cold air from the heat sinks through seat
channel holes to the seat occupant.
6
The above figure shows the cold and hot fluid outlet temperatures along with the element
length. A temperature difference of ∆T=11�� is obtained from the cooling power of 38W and
COP of about 1.0 for cooling in summer.
Heating power (W) and COP vs. element length (mm)
The above figure shows the Heating power and COP vs. element length. Here a temperature
obtained from cooling power of 80 W and COP of about 2.0 for
iagram in CATIA shows the schematic of commercial model of thermoelectric
car seat cooling/heating. It consists of thermoelectric device sandwiched between Heat sink 1
which is a cold heat sink, Heat sink 2 which is a hot heat sink, where each has 20 fins
space between the fins. This fin design is based on the optimization of heat sink. Conditioned air
is supplied from fan with volume flow rate of 6.3 CFM to the under seat channels (5 channels) of
thickness 0.3 cm which covers occupant seat area of 25cm×20cm. Each channel contain
perforated holes which helps to dissipate hot air or cold air from the heat sinks through seat
channel holes to the seat occupant.
The above figure shows the cold and hot fluid outlet temperatures along with the element
is obtained from the cooling power of 38W and
element length. Here a temperature
obtained from cooling power of 80 W and COP of about 2.0 for
iagram in CATIA shows the schematic of commercial model of thermoelectric
car seat cooling/heating. It consists of thermoelectric device sandwiched between Heat sink 1
which is a cold heat sink, Heat sink 2 which is a hot heat sink, where each has 20 fins with 1 mm
space between the fins. This fin design is based on the optimization of heat sink. Conditioned air
CFM to the under seat channels (5 channels) of
20cm. Each channel contain
perforated holes which helps to dissipate hot air or cold air from the heat sinks through seat
7
Fig 3.5 Schematic of thermoelectric car seat cooling/heating device.
One of the main advantage of using thermoelectric device is heating or cooling can be
achieved just only by changing the polarity of electricity. During cooling the hot air is vented to
the cabin which will be somewhat trouble to occupants but compared to the HVAC the flow rate
is very small.
This below diagram in CATIA shows a design which is modified to utilize the waste
conditioned air by recirculating the air to the inlet of the fan. In this the permeable materials on
the seat channels are replaced with impermeable materials to decrease the air consumption. With
the back flow of air to the fan, part of the total volume flow rate is consumed through the
perforated holes and remaining flow rate is vented to cabin for hot air.
8
Fig. 3.6 Schematic of thermoelectric car seat cooling/heating with a recirculating duct.
4. Applications
Thermoelectric coolers are advantageous than the traditional cooling devices in terms of
compact size, no moving parts and working fluid, compatible with automobile electrical system
voltage, and easily switching between heating and cooling modes. Therefore, thermoelectric
cooler appears to be especially favorable for automotive application. Applications for
thermoelectric modules cover a wide spectrum of product areas. These include equipment used
by military, medical, industrial, consumer, scientific/laboratory, and telecommunications
organizations. Uses range from simple food and beverage coolers for an afternoon picnic to
extremely sophisticated temperature control systems in missiles and space vehicles.
9
5. Conclusion
The presented work show an option whether the distributed air is consumed completely at the
end of channels or recirculated using a return duct and impermeable materials except the
perforated holes. Now an innovative design on top of the design showed in the preceding
paragraphs is implemented into car seat cooling/heating. Suppose that the design is modified to
utilize the waste conditioned air by recirculating the air to the inlet of the fan. In this new design,
the permeable materials should be replaced by impermeable materials to reduce the air
consumption while still having the small holes, where the size can be optimized to be large
enough to provide comfort but small enough to minimize the conditioned air consumption. In
this way, the unused conditioned air is returned to the fan, so that a portion of the total volume
flow rate is consumed through the small holes and simultaneously a portion of the flow rate is
vented to cabin for hot side air. For that reason, the fan has to draw more air than the air
recirculated through the opening (gap) between the return duct and the fan inlet, where the gap
can be determined by experiments. This new design significantly improves the performance of
car seat cooling/heating.
10
6. References
[1] Alaa M. Attar, "Optimal Design of Automotive Thermoelectric Air Conditioner (TEAC)".
Journal of Electronic Materials, Vol. 43, No. 26, 2014.
[2] HoSung Lee, "Optimal Design of thermoelectric devices with dimensional analysis". Applied
Energy, Vol. 106, pp. 79-88, 2013.
[3] HoSung Lee, "The Thomson effect and the ideal equation on thermoelectric coolers". Energy,
Vol. 56, pp. 61-69, 2013.