Peltier Cooling Theory

peltier

The theme of cooling PC components is of concern to many users. The majority of them are limited to standard air coolers, individual enthusiasts are assembling CPU (a CbO stepping). And what’s next? For sure, those who were seriously interested in overclocking, have heard about the Peltier modules (or thermoelectric modules, hereinafter referred to as TEC, Thermoelectric Cooler) and their use as heat outlets for the strong-warming elements of the computer.

However, often even basic information on the correct use of these amazing devices is difficult to find, hence the numerous mistakes of those who first encounter them. By the way, cooling system manufacturers are also experimenting with Peltier modules, sometimes presenting very curious concepts to the public. How do TECs work, are they really so necessary in computer SBs, how to collect uncomplicated coolers on their own and avoid the simplest mistakes that are typical for beginners? We will tell about all this in this material.

A bit of theory

What is the Peltier effect or module? It is an effect of cooling of one junction and the heating of the other when an electric current is sandwiched in a circuit consisting of two different conductors. In a circuit consisting of a battery joined by two lines of electric copper-wire to a bismuth, a temperature rise occurs at the junction where the current passes from copper-wire to bismuth (heat or cold, depending on the direction of current flow), as a result, a drop in temperature occurs at the junction where the current passes from bismuth to copper-wire. This effect was discovered by the French scientist named Jean Charles Athanase Peltier, in the year 1834. The colling/heating effect, known by his name – PELTIER, is used in devices for measuring temperature and, with the discovery of new conducting materials, mainly for refrigerator or computer units. In short. The essence of this process is the occurrence of a temperature difference in the place of contact of materials when electric current flows through them.

We will not go into details of the history of the discovery and scientific substantiation of the specific nature of the work of the TEC, since this topic can be devoted to a whole thesis. However, we will mention general concepts.

Thermoelectric Cooler device
Basic scheme of Thermoelectric Cooler Device

Peltier elements consist of two conductive materials (semiconductors) with different levels of electron energy in the conduction band. The physics of the flow of current through such substances is such that for the transition of electrons they require a certain make-up obtained at the moment of passage of the current through the spike. In such a case, it is possible to move the particles into the high-energy conduction band from one material to another. The place of contact of semiconductors at the moment of energy absorption is cooled. Changing the direction of the current or moving electrons from the more energy zone to the less saturated leads to heating of the contact point. In addition, the Peltier modules observe a thermal effect characteristic of any substances through which electric current is passed. In general, the processes inherent in TECs also appear at the point of contact of ordinary metals, However, to determine them without complex instruments is almost impossible. Therefore, semiconductors are the basis for the modules.

The Peltier element consists of one or more pairs of semiconductor parallelepipeds of various types (as in diodes or transistors, n- and p-type). The modern industry for these purposes most often chooses germanium silicon and telluride bismuth. Semiconductors are connected in pairs by metal bridges from low-melting substances. The latter perform the role of thermal contacts and directly touch the ceramic plate or stand. The pairs of semiconductors are connected in series, different types of conductivity are in contact with each other. On one side of the module there are only n -> p transitions, on the other hand, p -> n. The current flow causes cooling and heating of the opposite groups of contacts. Therefore, we can talk about the transfer of thermal energy from one side of the Peltier module to another and, as a consequence, the occurrence of a temperature difference on the plate. Correct application of the modules allows you to extract some benefits for industrial, including computer, SO. By the way, the elements can also be used as power generators – based on the same principles of work, the physics of the processes occurring inside is explained by the Seebeck effect (relatively speaking, the same Peltier effect with the “opposite sign”).

Pros and cons of TEC application

Often, the merits of Peltier modules include:

  • relatively small overall dimensions;
  • the ability to work for both cooling and heating of the system;
  • absence of moving parts, mechanical components, subject to wear.

At the same time TEC have a number of disadvantages, significantly limiting their widespread practical use. Among them are the following:

  • low efficiency of modules;
  • the need for a source of current for their operation;
  • The power of the large consumption to achieve appreciable temperature difference and, consequently, a substantial thermal isolation;
  • limited dimensions and useful characteristics.

However, despite the negative characteristics of the Peltier modules, they have found their application in a number of products. TECs are advantageous in the first place where the energy efficiency of the cooler is uncritical, the smaller – the better. Elements serve to cool devices with charge communication in digital cameras, allowing to achieve a noticeable reduction of thermal noise during long exposures. Peltier modules are often used for cooling and thermostating diode lasers in order to stabilize the wavelength of their radiation. It is possible to use several TECs, composed in series in the form of cascades (the cold side of one cools the hot of the other) so that it is really possible to reach very low temperatures for devices that have low heat release. Elements Peltier – the basis of compact refrigerators, primarily automotive. They are used in miniature souvenirs from the field of computer peripherals, and in productive COs as basic or auxiliary components. It is about the latter version that we will talk in more detail.

Peltier modules in PC: practice

water block and a copper buffer plate
The Peltier element is placed between the water block and a copper “buffer” plate

When moving to the practical implementation of JI on the basis of TEC, several reservations must be made that will make it possible to correctly select the parameters of the final designs. Often the experiments of newcomers end badly: either the temperatures on the “cold” side of the modules during operation are higher than on the hot ones, or the systems demonstrate frankly weak results even in comparison with the stock coolers without Peltier elements. The reasons are often hidden in the wrong calculation (or at random). The fact is that any TEC has its own characteristics, usually two values are distinguished (consider them for example TEC1-12709 module with the declared maximum power of 136 W), for example, write that ?Tmax Qcmax = 0 (° ?) 66 and Qcmax ?Tmax = 0 (W). 89.2. To paraphrase this expression: the module is able to provide the maximum temperature difference between the sides, equal to 89.2 º? in the absence of a thermal load and 0 º?, if any, to the “cold” side of 66 W. Thus, the payload of the module lies in the range from 0 to 66 W, ideally – the smaller – the better and the greater the temperature difference will be provided by the TEC. At the same time, any module has a different characteristic – the maximum power consumption, which must also be taken away from it by means of a cooling system. For the TEC1-12709 considered, Umax (B) is equal to 15.2 V, I max is 9 A. Consequently, with the indicated parameters, we have an energy consumption of 136.8 W, which is quite agreeable. At the same time, any module has a different characteristic – the maximum power consumption, which must also be taken away from it by means of a cooling system. For the TEC1-12709 considered, Umax (B) is equal to 15.2 V, I max is 9 A. Consequently, with the indicated parameters, we have an energy consumption of 136.8 W, which is quite agreeable. At the same time, any module has a different characteristic – the maximum power consumption, which must also be taken away from it by means of a cooling system. For the TEC1-12709 considered, Umax (B) is equal to 15.2 V, I max is 9 A. Consequently, with the indicated parameters, we have an energy consumption of 136.8 W, which is quite agreeable.

TEC1-12709 module
The cooling system must successfully remove heat directly from the module (providing the highest possible low temperature of the “hot” side) and PC components. You can calculate the approximate efficiency of such a system – with a useful component of 150-200 watts (approximately so many modern overclocked CPUs allocate) to get at least some visible results, you will need to spend at least 600-800 watts of electrical power and allocate at least a kilowatt of heat. That is why productive POs based on Peltier modules have not received wide distribution. However, the precedents of the relatively successful implementation of hybrid coolers are known, and we will try to create our own – low-power and optimal. To avoid limitations in the form of insufficient heat dissipation, on the “hot” side of the TEC we place productive water blocks connected to the circuit of the water heaters. By the way, Peltier modules can not be installed directly on the core / heat distribution cover of chips – a thin ceramic lining is not capable of maintaining effective heat transfer to all semiconductor pairs making up the TEC. For this purpose, an intermediate “buffer” is best – a copper plate 5-7 mm thick, completely covering the surface of the module. By the way, the optimal mode of operation of Peltier elements is provided at reduced voltage and current consumption. Approximation of these parameters to the maximum significantly increases the heat output of the plate, but not so tangibly – a useful component. making TEC. For this purpose, an intermediate “buffer” is best – a copper plate 5-7 mm thick, completely covering the surface of the module. By the way, the optimal mode of operation of Peltier elements is provided at reduced voltage and current consumption. Approximation of these parameters to the maximum significantly increases the heat output of the plate, but not so tangibly – a useful component. making TEC. For this purpose, an intermediate “buffer” is best – a copper plate 5-7 mm thick, completely covering the surface of the module. By the way, the optimal mode of operation of Peltier elements is provided at reduced voltage and current consumption. Approximation of these parameters to the maximum significantly increases the heat output of the plate, but not so tangibly – a useful component.

 

We decided to cool the graphics chip of the Radeon HD 4350 and the CPU Core 2 Duo E8500 to the maximum, trying to overclock these components. To remove heat from the GPU we used the already mentioned TES1-12709 (maximum power consumption – 136 W) and a homemade copper waterblock, paired with the processor worked TES1-12726 (395 W) and one of the best industrial waterblocks Swiftech Apogee GT. The modules were connected directly to the computer PSU in a 12-volt circuit. The application of a kilowatt is quiet! Dark Power PRO BQT P6PRO-1000W gave every reason not to worry for the lack of power to power the PC and the elements of the cooling system. Two “double” radiators for 120 mm fans and a Hydor Seltz L30 pump (with a capacity of 1200 l / h at idle) worked in the circuit of the heat and power plant.

In the case of cooling components to temperatures below room temperature (in particular, below the “dew point”), condensation on supercooled surfaces should be expected. It is clear that water in this form is the main enemy of the user, and its allocation must be warned. This is done by careful thermal insulation of any surfaces (parts of the PCB, space on both sides of the board, the TEC proper, the heat spreader of the processor and the GPU) with materials that do not allow air to pass through. The best standard for these purposes is a standard thermal insulation material for water supply pipes (based on foamed rubber), special putty, some kinds of foam rubber supplied with PC components, at worst thermal paste and paper napkins. In the latter case, PC operation is permissible only for short-term benching sessions.

The resulting temperatures, obtained in different modes of operation of the components, and their comparison with those provided exclusively by the water cooling system, are shown in the diagram. As you can see, Peltier modules allowed to lower the temperature of the components significantly below room temperature (depending on the load). Under such conditions, it was not difficult to overclock the processor to 4.3 GHz with an increase in the supply voltage to 1.35 V, and the GPU was forced to operate at 800 MHz (the nominal value was 600 MHz). At the same time, we got a noticeable heating CO of the test bench (in the case, the situation would have worsened more significantly) and a sharp increase in the level of power consumption of the PC (in fact, the whole design consumes more than a single computer based on the components of the test stand). Such a solution is definitely useful in the winter,

Are you ready for such sacrifices in order to achieve relatively low temperatures on PC components? Decide for yourself, but remember the basic tips given in this part of the material – they will help correctly apply the Peltier modules in practice. The use of TEC-based cooling systems is reasonable and justifiable in the case of low-power components (chipsets of motherboards, GPU of low- and medium-level video cards). Do not forget about the thermal insulation of the cooling elements – in fact, condensate is the main enemy of the system during the experiments with TEC.

conclusions

Summing up the above concerning the peculiarities of Peltier modules operation and the expediency of their practical application, let us repeat: TECs have the above-mentioned advantages and disadvantages, which do not allow to give an unambiguous answer to the question: “Is it worth …?” Their use is justified for eliminating insignificant heat loads compact refrigerators, thermostated lasers, and CO for low-power components of the PC-chipsets and individual GPUs).

Based on Peltier elements, you can create various homemade cooling and heating devices, there are examples of successful implementation of low-power generators. But before you engage in the manufacture of such structures, read all the same with the theoretical component – preliminary preparation will save errors and save time at the time of practical implementation of projects.

To talk about the use of Peltier modules in a PC should be rather cautious: after reading about getting low temperatures on cooled elements, beginners often forget about the considerable consumed and allocated power of such CO, do not take into account the parameters and the “margin of safety” of a particular design. TEC will be of interest primarily to overclockers, for which any winning degree and every megahertz are important. The elements in question are an intermediate link between classical water cooling systems and chillers or freons, operating on the principle of phase transition. However, the use of TEC is by no means simple, so before weighing serious experiments, carefully weigh all the pros and cons.

Ready-made SB based on TEC

Peltier modules are used by manufacturers of cooling systems for PCs as the main and auxiliary components of coolers. Sometimes it turns out effective effective devices, sometimes everything does not go as smoothly as originally intended. We decided to recall the main SBs that use TEC, which they named the role of revolutionaries of their time.

Thermaltake SubZero4G

Thermaltake SubZero4G

One of the first coolers with an element of Peltier, made relatively much noise in the cooling of the CPU (2003). However, a low margin of safety, a significant energy consumption at the time, a cumbersome design and noise in the work did not allow it to gain a foothold in the market. Appear this model for a year or two before – perhaps everything would turn out differently.

Titan Elena

Titan Elena

Supercooler for video cards built on the same principle as Titan Amanda: one half of the radiator works directly to remove heat from the GPU, the other cools the hot side of the TEC. At one time it turned out to be one of the best during the testing of CO for graphics adapters. (We wrote about it in “Home PC” in 2007.)

Swiftech MCW6500-T

Swiftech MCW6500-T

The most powerful modern CPU cooling solution that uses the Peltier element. It is a productive water block that removes heat from the TEC (about 400 W of consumed electric power), which, in turn, creates the optimal temperature regime of the processor. This system is capable of providing Core i7 operation at a frequency of about 4 GHz at a temperature of about 0 ° C (idle mode) and 20-30 ° C in the maximum load mode.

Swiftech MCW60-T

Swiftech MCW60-T 

Similar to the processor solution is a high-performance water block for the graphics adapter, supplemented by the Peltier module. Depending on the TDP, the video chip is capable of keeping its temperature at room temperature or below.

Cooler Master V10

Cooler Master V10 

Peltier elements of this CO cool part of the heat pipes. The approach is quite interesting and correct, the use of modules allows to knock down a couple of degrees on the processor. However, the economic feasibility of such a move – a big question, because the V10 at a significant price is not able to overtake the best air super coolers. Most likely, the design features and insufficient power of the TEC are to blame.

Titan Amanda

Titan Amanda 

A series of quite modern CPU super-coolers on heat pipes using a thermoelectric module (2007-2008). A part of the radiator removed heat directly from the TEC, while the other half cooled the heating component. Such an approach to design avoids a sharp overload of CO due to exceeding the heat limits of the Peltier module. The coolers of the Amanda line showed excellent results with processors that have a relatively low TDP.

Peltier modules conclusion

Depending on the type of connection of the TECs to the circuit, they allow a little lowering of the temperature of the coolant, and when creating powerful COs even provide a coolant temperature close to zero.

The principle of operation of the system is quite simple: the Peltier modules (8 TECs with a maximum power consumption of 136 W each) cooled from two sides large copper water block, and themselves, in turn, are cooled by the same water blocks. The “cold” and “hot” contours of the SBO are completely separated. To supply an amount of TEC during the first run are used two computer PD with total capacity of 1200 watts stated, as a coolant “hot” circuit LSS performed with two radiators under two 120 mm fans each pumped powerful pump. However, even such SVO was not enough, and the radiators had to be purged by high-performance industrial fans. The “cold” circuit were connected to the pump Hydor L20 II and waterblock Swiftech Apogee GT, played a large cooler water block, which contacts the “cold” side of the TEC. As a result of the first experiment was able to achieve water temperature in the order of 5-7 ° C contour, wherein as a load for the system used Core i7 965 processor Extreme Edition, clocked to a frequency of 4 GHz.

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