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Reliability-oriented design of thermoelectric cooling devices
Section 12. Electrical engineering
Zaikov Vladimir Petrovych, Ukraine, Odesa, Research Institute Shtorm, Head of Sector, Candidate of Technical Sciences.
E-mail: gradan@ua.fm Mescheryakov Vladimir Ivanovych, Ukraine, Odesa, Odessa State Environmental University, Head of Department, Doctor of Technical Sciences.
E-mail: gradan@ua.fm Zhuravlov Yurii Ivanovych, Ukraine, Odesa, Odessa State Environmental University,
applicant. E-mail: zhuravlov.y@ya.ru
Reliability-oriented design of thermoelectric cooling devices
Abstract: This paper studies the design route of high reliability thermoelectric cooling devices. The influence of different combinations of original thermoelectric materials at the same and different efficiency thereof is analyzed. Keywords: reliability, thermoelectric devices, efficiency, temperature, failure rate.
Thermoelectric devices (TED) compared to other cooling devices have smaller dimensions, easy control and performance, higher reliability due to the absence ofmoving parts, pumped liquids or gases. Toughening ofrequirements to operating conditions resulted in reliability degradation. Building reliable systems from the components with ultimate reliability is a fundamental design problem, in particular, the approaches aimed at improving the reliability of heat-loaded elements with TED, are relevant.
When designing TED the following is usually specified: cooling capacity; heat-absorbing junction temperature; selection of such product designs and operating mode that would satisfy the requirements for dimensions and weight, power consumption, operating current value, reliability indices.
Typical operating modes of TED are the following:
Q0 , E , Я .
Although design at maximum cooling capacity Q0max ensures minimum number of thermocouples n, its use is associated with high power consumption, which leads to an increase in heat flow at TED’s heat-removing junctions, increase in surface area of the heat-sink, increase in size and weight of the device, increase in operating current value I, decrease in coefficient of performance E and increase in failure rate.
Design of TED at the maximum coefficient of performance Emax allows minimizing power consumption, but leads to an increase in the number of thermocouples n and, as a consequence, to increase in failure rate Я.
Design of TED at lowest failure rate hmin ensures minimum value of failure rate Я , but at the same time it leads to an increase in the number of thermocouples n , i. e. weight and cost of the TED, as well as a slight increase in energy consumption.
This inconsistency suggests that there are intermediate operating modes other than typical, which can take into account the interference and importance of each factor towards the growth of TED reliability indices.
The aim of this paper is to increase the reliability indices of thermoelectric devices by examining the influence of the efficiency of thermoelectric materials and their combinations on reliability.
The paper [1] studies the influence of thermoelectric efficiency of original materials in TED on reliability indices for various temperature changes AT and operating conditions. The growth of thermoelectric efficiency Zm of original materials leads to an increase in maximum temperature difference AT and, therefore, decrease in relative temperature difference 0, increase in cooling capacity value by one thermocouple, allowing to reduce
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Section 12. Electrical engineering
the number of thermocouples n. All of this leads to a reduction in the failure rate Я and increase in the probability of failure-free operation Р. АЯ/
Fig. 1 shows the dependence of K =
AZ/
value
'Z
from the total temperature difference AT of the singlestage TED for modes Q0max -1 and ЯтП -2 at T = 300K,
=10. The area between characteristic modes Q0max GOOD
and Яш;п is the area where intermediate modes are located.
Dependency analysis shows that the increase in the thermoelectric efficiency of original materials in the module by one percent can reduce the failure rate in mode Q0max: at AT = 40K by 2.6%; at AT = 50K by 2.9%; at AT = 60K by 4.3%; in mode ЯтП : at AT = 40K by 4.2%; at AT = 50Kby 4.3%; at AT = 60Kby 5.0%.
20.0 25.0
АХ/
/ /
Fig. 1. Dependence of K = Kr7 7 value from the total temperature difference AT for modes Q0
AZ/
1 and Ят
XZ
2 at T = 300K; Q0 = 2.0 W; / = 10
Improving TED reliability is inextricably connected with improving the quality of original thermoelectric materials and, first of all, their efficiency. As international practice has shown, currently it is not possible to improve substantially the efficiency of thermoelectric materials [2-4].
At the same time, for the same efficiency of the original materials the following combinations of averaged
parameters can be selected: Seebeck coefficient e and electric conductivity coefficient о, allowing to improve reliability indices [5].
We shall consider possible (obtained experimentally) combinations ofthe parameters oforiginal thermoelectric materials in the module at T = 300K; ZM = 2.4T0-3 1/K;
jS = 10; AT = 0, shown in the table with a view to their possible use for building a high reliability TED.
Table 1. - Possible combinations of original thermoelectric materials
Possible combination number e, мкВ/ /К о, См/ / см х -10 3, Вт/ /см ■ К 2 с ст-104, Вт/ /К2 • см 2 Y= e ctTg2 S/i > Вт
1 250 550 14.3 0.344 0.310
2 210 800 14.7 0.353 0.318
3 200 900 15.0 0.360 0.325
4 180 1200 16.2 0.390 0.351
5 165 1500 17.0 0.410 0.370
The use of e and о as basic significant parameters of thermoelectric materials provides sufficient information about cooling capabilities of the modules assembled based on them. A model of interconnection between TED’s basic characteristics and reliability indices and the parameters of the original
material e and о and the temperature of heat-absorbing junction Т 0 is proposed and considered.
We shall consider calculations of the basic parameters of a single-stage TED and reliability indices for different
f Q Л f Q Л
°perating modes Q0nax; ; -yf ; Яш;п
V 1
\1
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Reliability-oriented design of thermoelectric cooling devices
with the following source data: heat load, Q0 = 2.0 W; heat-removing junction temperature T = 300K; temperature difference AT = 0K; 20K; 40K; 60K; averaged thermoelectric efficiency ZM = 2.4T03 1/K;
= 10; Я0 = 3T0-8 1/h and assembled from various original materials (possible combinations of parameters (1-5) according to the table).
Analysis of calculation results showed the possibility of reducing the failure rate Я for the combination (5) compared with the conventional (3) by 10-11% and up to 15% compared with combination (1) at the same efficiency of original materials in a predetermined temperature range at a predetermined thermocouple
combinations (1, 2) is inappropriate, as this increases the failure rate Я and decreases the probability of failure-free operation Р.
increases
Studies have shown that with increase in temperature difference AT in the single-stage TED:
• the relative value of the failure rate for all operating modes;
• the absolute value of the failure rate Я for mode Emax and ЯтП increases both for combination (3) and for combination (5);
• the value of the failure rate Я in combination (5), compared with (3) decreases for any operating mode at a predetermined temperature difference AT.
14.000
12.000
10,000
8,000
6,000
4.000
2.000 0,000
0,0 1,0 2,0 3,0 4,0 5,0 6,0
АЛ /л,%
AT=0K
/ AT=6( K
i
АЯ
Fig. 3. Dependence of the relative value —
X
i = 4-5 at T = 300K; Q0 = 2.0 W; % =
% of the single-stage TED from the combination of the original material 10 for various temperature differences AT and operating modes
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Section 12. Electrical engineering
Fig. 3 shows the dependence of the relative failure
rate value
^3 ~^5 I3
% from possible combination of the
original material parameters (1-5) for various temperature differences AT and operating mode.
Inner area bounded by the curves AT =0K and AT = 60K (Fig. 3) makes it possible to reduce the failure rate for possible combinations (4, 5) compared with conventional one (3) for any mode and temperature difference within the range.
These calculations allow us to choose possible combination of the original material parameters with increased electrical conductivity to increase
cooling capacity by one thermocouple or to reduce the number of thermocouples, failure rate and increase the probability of failure-free operation. The economic feasibility of the use of original materials with increased electrical conductivity in the design of TED is not only to increase reliability, but also to significantly reduce the cost of TED.
Based on LabView package a computer-aided design subsystem was developed for designing high reliability thermoelectric coolers using the proposed approach to combining different combinations of original thermoelectric materials at a different and the same efficiency.
References:
1. Zaykov V. P., Mescheryakov V. I., Gnatovskaya A. A., Zhuravlev Y. I. (2015). The influence of the thermoelectric efficiency of raw materials on reliability of thermoelectric cooling devices performance. Part 1: Single stage TED. Technology and design of electronic equipment, № 1. P. 44-48.
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3. Sootsman J. R. New and Old Concepts in Thermoelectric Materials [Text]/J. R. Sootsman, D. Y. Chung, M. G. Kanatzidis//Angewandte Chemie International Edition. - 2009. - Vol. 48, № 46. - P. 8616-8639. doi:10.1002/anie.200900598.
4. Brown S. R. Yb 14 MnSb 11: New High Efficiency Thermoelectric Material for Power Generation [Text]/S. R. Brown, S. M. Kauzlarich, F. Gascoin, G. J. Snyder//Chemistry of Materials. - 2006. - Vol. 18, № 7. -
P. 1873-1877. doi:10.1021/cm060261t.
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