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Basic Explanation about PELTIER ELEMENTS
          basic explanation as pdf-file
Peltier elements are thermal electric modules, that can work as an heat pump. It is suitable for cooling as well as for heating. If direct current (DC) flows a module the heat will be transferred from one side of module to the other. As a result one side of the module cools and the other side heats. The value of temperature difference can achieve up to 73°C in a single stage and more than 100°C in a multistage module.
After the German physicist Thomas Johann Seebeck (1770 – 1831) has detected the thermoelectricity in the year of 1821 thus making possible the well known temperature measurement with thermal elements, the French physicist Jean Peltier (1785 – 1845) detected in the year 1834 the inversion of the thermoelectricity.
If you connect two wires with different electric conductivity at both end and one of the connecting point has an other temperature than the second one, an electric voltage will arise between the two points. This effect (Seebeck) is used for measurement of temperature. This Elements are so called thermal elements. If you put a voltage in the assembly, an electric current will flow transporting heat from the one connection point to the other. The one junction heats the other one cools. The heat transport is caused by the flow of electrons. These devices are the so called Peltier elements (the law of nature of the intermediary metals and of the intermediary temperatures).
Suitable materials for PE are those with a high electric conductivity and a low thermal conductivity. Since the most of the electric conductors have a coexistent high thermal conductivity, endowed semiconductors are used for a high degree of efficiency. Bismuth Telluride (Bi2Te3), Antimony Telluride (Sb2Te3), Bismuth Selenium (Bi2Se3) and other materials are applied. In n-semiconductors the heat flows reverse to electric current, in p-semiconductors in the same direction as the electric current.
What kind of advantages may be achieved using thermoelectric modules:
  • Ecological cleanliness and safety due to the absence of any gas or liquid agents.
  • No noise or vibration
  • Cooling or heating operation mode by simple change of the current flow direction
  • Practically unlimited possibility of miniaturising
  • Work capability in any position relative to gravitation field including weightlessness
  • Direct Power generation from heat
  • And a lot more...
Quality from Peltier-Elements
  • Research and development will provide a high technical standard of Quick-Ohm products
  • Thus a current adaptation to customers requirements is guaranteed
  • The best thermoelectric material with high mechanical strength helps to eliminate failure of modules during transportation, assembly and exploitation
  • Quick-Ohm gives the utmost attention to reliability. Especially for this purpose modified modules (M-Series) have been developed and introduced in production. These elements have a very high cycling reliability which exceeds the figure for standard modules more than dozen of times
  • Taking into account specific conditions, modules are forced to work in, Quick-Ohm can offer to customers a few levels of protection against moisture and condensation.
  • Only the best raw materials, ceramic substrates, spare parts and so from the largest world-wide suppliers are used
  • All stages of manufacturing are thoroughly checked. 100 % of modules shipped to our customers are passed through the utmost care tests of electrical, thermoelectric parameters, appearance and subjected to ultrasonic diagnostics and thermal screening. Such close examination allows to provide total conformity with the quality certificate that is submitted to each customer
  • The specially developed technology of package, using new modern wrapper, prevents delicate modules against vibration, shocks, atmosphere precipitation and sharp temperature drops during transportation from any damages or failures.

HIGH RELIABLE M-SERIES MODULES:
The M-series were especially developed in order to solve two most important problems: (1) the long term operation in thermal cycling applications, and (2) the capability to withstand a high mechanical loads during the installation and operation.
Thermal cycling reliability:
Thermal cycling operation of modules like the ON/OFF cycles is the main factor which significantly reduces a module lifetime and TE modules can be reliably exploited in a more or less continuous mode of operation only. To solve this problem we introduced special GM assembling technology which provides the drastic improving of cycling reliability due to several construction features.
The so-called test 40/90 (40°C for 3 minutes then 90°C for 3 minutes, then again 40°C for 3 minutes) was conducted to verify the cycling reliability of standard modules and modified modules (M-series) assembled by GM-technology. The arrangement of test 40/90 involving current reversal burn-in is shown in Fig. 1. The test results, represented in the Table for module QC-127-1.4-6.0, demonstrate approximately 70x life-time increasing.
Mechanical strength of a module:
The well-known origin of module failure during the operation has to do with latent damages arising in the process of installation by the clamping method. Besides, properly mounted module is subjected to shock and vibration in exploitation period and it may lead to failure, too. The main factors caused the failures are the mechanical strength of TE material and the features of module assembling technology.
TE material with improved mechanical properties was specifically developed for M-series modules. Its Application combined with GM assembling technology provides a considerable module strengthening.
The chosen shock test shown in Fig. 2 consists of the set of shocks against the assembly with clamped module for simulating the module behaviour in a real device. The test has successfully confirmed the efficiency of made innovations (see the table).
TECHNOLOGY 40/90 TEST SHOCK TEST
  Time before failure (hours) Number of cycles before failure Number of shocks before failure
Standard module
QC-127-1.4-6.0
49,2
649
352
Modified module
QC-127-1.4-6.0M
3795
45002
7756
Note: The module failure criterion - 5% resistance change.
Choosing an appropriate module
PE module is a device suitable for operating in various number of different working conditions nevertheless most of the applications are as follows:
The mode of maximum energy efficiency is characterised by minimum energy expenses necessary to receive targeted portion of cold, i.e. the maximum value of Coefficient of Performance (COP);
The mode of maximum cooling capacity is of the utmost interest. On base of it the method of required module selection is built on the module operation in mode of maximum cooling capacity. There are two necessary parameters for proper TE module selection:
1.According to thermal load onto a module
2. According to temperature difference at which heat is taken from an object to be cooled.
The total heat load consists of a power dissipation of the object to be cooled and various kinds of inflow heat from environment due to convection, radiation and thermal conductivity of mounting elements. The temperature difference is determined as a difference between the temperature at which heat dissipation takes place and the temperature of the object to be cooled. Using the below-stated table select the minimum number of stages to meet the required temperature difference:
DT max in a vacuum, °C
Number of Stages
72
1
94
2
110
3
117
4
If the required temperature difference does not exceed 50°C, the number of stages more than one is reasonable to apply.
A proper PE module selection
Using a ratio of operating parameter results to maximum values together with the graph one can determine parameters of selected module.
Performance Graph
The diagonal optimum Qo/Qmax corresponds to maximum cooling capacity to be obtained by selected module. On the performance graph the point of intersection of the horizontal line corresponding DT/DTmax and the diagonal Qo/Qmax line is the optimum value of Qo/Qmax. The point of intersection of the horizontal line and the vertical axis is the maximum value of Qo/Qmax.

To determine optimum and maximum values of cooling capacity for needed module divide value of calculated total load by corresponding relative values from the performance graph

 
Installation of PE modules
A thermoelectric (TE) module of any application contains comparatively fragile semiconductor material that demands a strict execution of certain operations and their sequence when assembling. Non fullflillment of any operation leads to the modules efficiency decreasing or failure.

A TE module in the real device should not be used as a supporting member for the same reason. The mounting surfaces of the module to be installed should be without any dirt and have unflatness and nonparallel not more than 0,020 mm. If two modules or more are installed in the device their height tolerance should not exceed 0,050 mm.

How to install PE modules Widely used method of module assembling consists of the location of the modules between heat sink and cold plate to be clamped. To install the module accomplish the following operations:
1. Coat a layer of thermal conductive grease as thin as possible onto the seat place of the heat sink. Locate a module in the suitable position and using gentle pressure with fingers move the module back and forth to squeeze out the excess of thermal grease.

Notice: Don’t use common thermal grease containing aluminium oxide, due the filler seasons and the thermal resistance will grow up. The result is an exceeding heating of the PE. This may lead to an untimely destruction of the PE.

Before installation all contact surface should be cleared and removed from fat.

2. Coat a thermal grease on the appropriate place of cold plate and locate the plate onto the module. Squeeze out the excess of thermal grease as described previously

3. Regardless of qty of 2,3 or 4 (clamping) screws, clamping force should be approx. 13 – 15 kg/cm². Under such conditions the thermal resistance of a conductive grease is minimised. After reaching the demanded value (see: calculation E.g.) of torque leave the assembly for an hour. Check the torque and retighten if it is necessary.

Additional information: Using the recommended clamping force, thermal resistance of thermal grease with thickness above 0,03 mm will be in range 0,03 – 0,05°C/W for a coverage area of 40 x 40 mm. Of course this value depends on the type of grease.

E.g. remarks:

QC-127-1.4-6.0M (Quick-Cool general specification) should be clamped under 21 – 240 kg force.

If you install the elements with modern thermal grease you should know that temperature losses at the hot side can make 2,7 °C.

If you use 2 clamping screws with diameter 4 mm, the torque per screw should be 0,11 – 0,12 kg x m.

If you use 4 clamping screws with diameter 4 mm, the torque per srew should be 0,05 – 0,06 kg x m.

If you know the desired clamping efforts for a module, you can calculate a torque per screw as below:

Beispiel:
QC-127-1.4- 6.0M (QUICK-COOL Allgemein-Spezifikation) sollte der Anpressdruck 210 - 240 kg sein. Werden die Elemente mit moderner Wärmeleitpaste montiert, dann können die Temperaturverluste auf der warmen Seite 2,7°C betragen.
Werden 2 Klemmschrauben mit 4 mm Ø eingesetzt, sollte das Drehmoment 0,11 -0,12 kpm betragen. Wenn die erforderlichen Klemmkräfte für ein Element bekannt sind, kann man das Drehmoment pro Schraube berechnen:

Where:
p = desirable clamping force (kg)
d = diameter or screw (mm)
n = quantity of clamping screws.

Corrosion protection of PE

Corrosion protection proposes a prevention of corrosion process flow in solder junctions under moisture influence in case if undershoot the dew point. Besides destructive impact of corrosion phenomena accumulated water create thermal bridges between ceramic substrates leading to reduction of module efficiency.

Our Research and Development team has elaborated the following methods of module moisture protection different in terms of efficiency and production expenditure.

1. Method of internal protection (Coating)

Coating as internal protection method is recommended for PE modules that operate at negative and short time positive temperatures below the dew point.

Coating is introduced to cover all parts inside the module protection specially pellet-pad solder junctions. Long-term examinations in different environments of modules coated with corrosion protection varnish show that such type of protection can be used in wide temperature range of module operation: from – 50°C to + 140°C. Furthermore coating does not reduce module efficiency due to the absence of strong thermal bridges.

Coating is considered as the initial protection method for most PE module Application cases. If coating is chosen as moisture protection option suffix “C“ should be added to the module marking while specifying the type.

2. Method of external protection (sealing)

Sealing as the external protection method is performed along PE module perimeter with Application of epoxy or silicone materials.

Silicone type of protection can be used within the following temperature range of PE module operation: from – 40°C to + 180°C. Silicone sealant due ist good elastic properties is preferable for cycling applications and low temperature condition.

Epoxy sealant provides module exploitation in a mode with intensive vapour condensation and ca be applied within the following temperature range of PE module operation: from – 50°C to + 150°C.

If silicone sealing is chosen as moisture protection option suffix “S“ should be added to the module marking while specifying the type. If epoxy sealing is chosen as moisture protection option suffix “X“ should be added to the module marking while specifying the type.

Most of the corrosion protecting sealants used in the thermoelectric Industry have good adhesion to the coating varnish an can be applied as an additional protection barrier. Upon customer special request Quick-Ohm is ready to proceed with double corrosion protection: Coating plus silicon or epoxy sealant.

Corrosion protection index:

• coating.....................“C“
• silicone sealing.........“S“
• epoxy sealing............“X“

If combined method is chosen as moisture protection option suffix “CS“ or “CX“ should be added to the module marking while specifying the type.
Remarks about module feeding

Thermoelectric modules are devices of direct current. If there are current ripples in power source of a TE module then characteristics go down as illustrated in the formular below:

DT/DTmax = 1/ (1+K²); where K - ripples factor.
E.g. at DC feeding and DTmax =72° pulsation of power source is K = 0.2 (20%), then
DT/DTmax = 1/(1+0.22) = 0.96;
DT = 0.96
DTmax = 69°;
Quick-Cool recommends K =0,1 ( 10% ):
At using impulse power source the current ripples factor can be calculated in accordance with the formula given below:
K = I(Imp)/I(DC) x T(Imp)/T, where:
I(Imp), T(Imp) - amplitude and duration of current impulse;
I(DC) - value of direct current; T - pulse period.

Presence of short-time impulses in feeding circuit with T=1 x 10 sec even of big amplitude up to ten of I (max) provides no negative influence upon economic life-time of TE module.
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