Refrigeration equipment and air-cooling systems are essential elements of everyday life. However, standard refrigerant-based volumetric designs are not suitable for mobile applications such as cooler bags. In such cases, devices based on the operation of the Peltier effect are used, which we will discuss in detail in this material.
The Peltier element or thermoelectric cooler is based on a thermocouple of two elements with p- and n-type conductivity, which are connected by a connecting copper plate. Details in most cases are made of bismuth, tellurium, antimony and selenium. Such devices are used in domestic cooling systems, they also have the ability to generate energy.
Content
What it is
The phenomenon and the term Peltier suggest a discovery made in 1834 by the French scientist Jean-Charles Peltier.The essence of the discovery is that heat is constantly released or absorbed in the area where there is a contact between two differently directed conductors through which an electric current flows.
The classical theory explains this phenomenon in this way: with the help of an electric current, electrons are transferred between metals, accelerating or slowing down, depending on the contact potential difference on metal conductors with different levels of conductivity. Peltier elements thus contribute to the conversion of kinetic energy into heat.
On the second conductor, the opposite effect occurs, where replenishment of energy is necessary based on the fundamental law of physics. This situation occurs due to the process of thermal oscillation, as a result of which the metal of the second conductor is cooled.
With the help of modern technologies, it is possible to manufacture a Peltier module with a maximum thermoelectric effect.
Device and principle of operation
Modern Peltier modules are a design in which there are two insulator plates, and thermocouples are connected between them in strict sequence. The standard scheme of this element for a better understanding of its functioning is shown in the figure.
Designations of structural elements:
- A - contacts, with the help of which the connection to the power source is carried out;
- B - hot surface;
- C - cold side;
- D - copper conductors;
- E is a p-junction semiconductor;
- F is an n-type semiconductor.
The element is made so that both surfaces are in contact with p-n or n-p junctions, based on polarity. Contacts p-n heat up, and n-p temperature decreases.As a result, a temperature difference DT appears at the ends of the element. This effect means that the thermal energy that moves between the elements of the module regulates the temperature regime depending on the polarity. It should also be noted that in the case of a change in polarity, the hot and cold surfaces change.
Specifications
The technical parameters of the Peltier element assume the following values:
- cooling capacity (Qmax) - calculated on the basis of the current limit and the temperature difference between the ends of the module. Unit of measure - Watt;
- limiting temperature difference (DTmax) - measured in degrees, this characteristic is given for optimal conditions;
- Imax is the maximum electric current required to provide a larger temperature difference;
- limit voltage Umax, which is required for the electric current Imax to achieve the maximum temperature difference DTmax;
- Resistance - internal resistance of the device, measured in Ohms;
- COP is the coefficient of efficiency or efficiency of the Peltier module, which reflects the ratio of cooling and power consumption. Depending on the features of the device, for inexpensive devices, the indicator is in the range of 0.3-0.35, for more expensive models it varies up to 0.5.
The advantages of the mobile Peltier element are small dimensions, reversibility of the process, as well as the possibility of using it as a portable electric generator or refrigerator.
The disadvantages of the module are high cost, low efficiency within 3%, high energy costs and the need to constantly maintain the temperature difference.
Application
Even taking into account the low coefficient of efficiency, the plates in the Peltier module are widely used in measuring, computing devices, as well as in portable household appliances. Here is a list of devices in which models are an integral part:
- portable refrigeration devices;
- small generators of electricity;
- cooling complexes in PCs and laptops;
- coolers for heating and cooling drinking water;
- air dryers.
How to connect
You can connect the Peltier module yourself, it will not require much time and effort. The output contacts must be supplied with a constant voltage, which is indicated in the operating instructions for the device. The red wire is connected to positive and the black wire is connected to negative. Note that when the polarity is reversed, the heated and cooled surfaces will switch places.
Before connecting, it is recommended to check the operability of the element. One of the simple and reliable ways to check the device is the tactile method: for this you need to connect the device to an electric current source and touch different contacts. In a normally functioning device, some contacts will be warm, while others will be cool.
You can also check with a multimeter and a lighter. To do this, you need to connect the probes to the contacts of the device, bring the lighter to one side and observe the readings of the multimeter. If the Peltier element is operating in the standard mode, during the heating process, an electric current will be generated on one side, and the voltage data will be displayed on the multimeter screen.
How to make a do-it-yourself peltier element
The Peltier element is impractical to manufacture at home due to the low cost and the need for special knowledge to create a workable element. However, you can assemble an efficient mobile thermoelectric generator with your own hands, which will come in handy in the country or on a camping trip.
In order to stabilize the electrical voltage, you will need to assemble a standard converter on the L6920 IC chip yourself. It is necessary to apply a voltage of 0.8-5.5 V to the input of the device, and at the output it will produce 5 V, this value is enough to charge the battery of mobile devices in standard mode. If a standard electronic Peltier device is used, then it will be necessary to limit the temperature limit of the heated surface to 150 degrees. For ease of temperature control, it is advisable to use a kettle with boiling water, then the model will not heat up over 100 degrees.
Peltier plates are widely used to cool modern household appliances, in air conditioners, the effectiveness of the device has been proven, in particular, to stabilize the thermal regime and cool a powerful processor. On the basis of the Peltier element, effective mobile refrigerators are often made at home for summer cottages or cars, powering the radiator. Due to the reversibility of the process, self-made elements are used as mobile small power plants in areas without a source of electricity.
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