me 6950- thermoelectric -i (design) summer - ii (2015 ...homepages.wmich.edu/~leehs/me695/car seat...

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


thermoelectric devices which includes a fan, a thermoelectric device, under-seat channels, and an


permeable seat materials which consume the total distributed air of the channels. This optimal



can be verified by measurements.

ny manufacturers provide performance curves of the thermoelectric products based on the


indeed unrealistic. Furthermore, the material properties are unknown and even the thermal and



achieved with equivalent cooling/heating.

Fig 3.1. Typical thermoelectric cooler module


of 1.2mm is used as shown to decrease the joule heating. But we cannot say that this short length


seat channels, and an


the channels. This optimal



ny manufacturers provide performance curves of the thermoelectric products based on the


ven the thermal and




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)


observed that the optimal element length is near 2.2mm and also the increase of e


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)


observed that the optimal element length is near 2.2mm and also the increase of element length


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


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


which is a cold heat sink, Heat sink 2 which is a hot heat sink, where each has 20 fins


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


channel holes to the seat occupant.


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


which is a cold heat sink, Heat sink 2 which is a hot heat sink, where each has 20 fins with 1 mm


CFM to the under seat channels (5 channels) of

20cm. Each channel contain


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.

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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.

me 6950- thermoelectric -i (design) summer - ii (2015 ...homepages.wmich.edu/~leehs/me695/car seat...

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