Free technical library

Electric welding. How to calculate the radiator. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / welding equipment

 Comments on the article

During operation of a semiconductor device, power is released in its crystal, which leads to heating of the latter. If more heat is released than is dissipated in the surrounding space, then the temperature of the crystal will rise and may exceed the maximum allowable. In this case, its structure will be irreversibly destroyed.

Therefore, the reliability of semiconductor devices is largely determined by cooling efficiency. The most effective is the convective cooling mechanism, in which heat is carried away by the flow of a gaseous or liquid coolant, washing the cooled surface.

The larger the cooled surface, the more efficient the cooling, and therefore powerful semiconductor devices must be installed on metal radiators with a developed cooled surface. Ambient air is usually used as the heat transfer medium.

According to the method of moving the coolant, they distinguish:

• natural ventilation;
• forced ventilation.

In the case of natural ventilation, the movement of the coolant is carried out due to the draft that occurs near the heated radiator. In the case of forced ventilation, the coolant is moved by means of a fan. In the second case, it is possible to obtain higher flow rates and, accordingly, better cooling conditions.

Thermal calculations can be greatly simplified if we use the thermal cooling model (Fig. 18.26) Here the difference between the crystal temperature T_J and ambient temperature T_A causes a heat flow moving from the crystal to the environment through thermal resistances R_JC (crystal - housing), R_CS (housing - radiator) and R_SA (radiator - environment).

Figure 18.26. Thermal cooling model

Thermal resistance has the unit of °С/W. Total maximum thermal resistance R_JA on the site of the crystal - the environment can be found by the formula:

where P_PP - power dissipated on the crystal of a semiconductor device, W.

Thermal resistance R_JC and R_CS indicated in the reference data for semiconductor devices. For example, according to the reference data, for the IRFP250N transistor, its thermal resistance in the crystal-radiator section is R_JC + R_CS \u0,7d 0,24 + 0,94 \uXNUMXd XNUMX ° C / W.

This means that if a power of 10 W is dissipated on the chip, then its temperature will be 9,4 °C higher than the temperature of the heatsink.

Heat sink thermal resistance can be found by the formula:

The following methodology is based on AAVID THERMALLOY's Max Clip System™ Aluminum Radiator Selection Guidelines.

On fig. 18.27 shows a graphical relationship between the perimeter of the section of an aluminum radiator and its thermal resistance for natural (red line) and forced (blue line) airflow cooling.

By default, it is assumed that:

• the radiator has a length of 150 mm;
• difference between heatsink temperature T_S and ambient temperature T_а is ;
• forced cooling flow velocity is 2 m/s.

If the cooling conditions differ from those accepted by default, then the necessary correction can be made using the graphs in Fig. 18.28 - fig. 18.30.

Rice. 18.27. Relationships between the cross section of an aluminum radiator and its thermal resistance

Rice. 18.28. Correction factor for the difference between the temperature of the radiator and the environment

Rice. 18.29. Correction factor for airflow rate

Rice. 18.30. Correction factor for radiator length

For example, let's calculate a radiator that provides cooling for an ERST transistor, consisting of 20 IRFP250N type transistors. The calculation of the radiator can be carried out for one transistor, and then the resulting size can be increased by a factor of 20.

Since the total power dissipated on the key transistor is 528 W, then the power dissipated on each IRFP250N transistor is 528/20 = 26,4 W. The heatsink must ensure the maximum temperature of the transistor crystal is not more than +110 °C at a maximum ambient temperature of +40 °C.

Will find thermal resistance R_JA for one transistor IRFP250N:

Now find heat sink thermal resistance:

Knowing the maximum temperature of the crystal and the thermal resistance in the section of the crystal-radiator, we determine the maximum temperature of the radiator:

According to the graph (Fig. 18.28), we determine the correction factor Kt for the temperature difference between the radiator and the environment:

Used to cool the radiator fan type 1,25EV-2,8-6-3270U4, having a capacity of 280 m3/h. To calculate the flow rate, you need to divide the performance by the cross section of the duct blown by the fan.

If the duct has a cross-sectional area:

then the airflow rate will be:

According to the graph (Fig. 18.29), we determine the correction factor K_v to the actual airflow speed:

Let's assume that we have a large number of ready-made radiators with a section perimeter of 1050 mm and a length of 80 mm. According to the graph (Fig. 18.30), we determine the correction factor K_L for the length of the radiator:

To find the total correction, we multiply all the correction factors:

Subject to amendments, the radiator should provide thermal resistance:

Using the graph (Fig. 18.27), we find that one transistor requires a radiator with a cross-sectional perimeter of 200 mm. For a group of 20 IRFP250N transistors, the radiator must have a cross-sectional perimeter of at least 4000 mm. Since the available radiators have a perimeter of 1050 mm, 4 radiators will have to be combined.

Less power is dissipated on the ERST diode, but for design reasons, a similar radiator can be used for it.

Often, cooler manufacturers indicate the surface area of ​​\uXNUMXb\uXNUMXbthe radiator, and not the perimeter and length.

To obtain the radiator area from the proposed method, it is enough to multiply the radiator length by its perimeter S_P = 400 x 8 = 3200 cm2.

Author: Koryakin-Chernyak S.L.

See other articles Section welding equipment.

Read and write useful comments on this article.

<< Back

Latest news of science and technology, new electronics:

Air trap for insects 01.05.2024

Agriculture is one of the key sectors of the economy, and pest control is an integral part of this process. A team of scientists from the Indian Council of Agricultural Research-Central Potato Research Institute (ICAR-CPRI), Shimla, has come up with an innovative solution to this problem - a wind-powered insect air trap. This device addresses the shortcomings of traditional pest control methods by providing real-time insect population data. The trap is powered entirely by wind energy, making it an environmentally friendly solution that requires no power. Its unique design allows monitoring of both harmful and beneficial insects, providing a complete overview of the population in any agricultural area. “By assessing target pests at the right time, we can take necessary measures to control both pests and diseases,” says Kapil ... >>

The threat of space debris to the Earth's magnetic field 01.05.2024

More and more often we hear about an increase in the amount of space debris surrounding our planet. However, it is not only active satellites and spacecraft that contribute to this problem, but also debris from old missions. The growing number of satellites launched by companies like SpaceX creates not only opportunities for the development of the Internet, but also serious threats to space security. Experts are now turning their attention to the potential implications for the Earth's magnetic field. Dr. Jonathan McDowell of the Harvard-Smithsonian Center for Astrophysics emphasizes that companies are rapidly deploying satellite constellations, and the number of satellites could grow to 100 in the next decade. The rapid development of these cosmic armadas of satellites can lead to contamination of the Earth's plasma environment with dangerous debris and a threat to the stability of the magnetosphere. Metal debris from used rockets can disrupt the ionosphere and magnetosphere. Both of these systems play a key role in protecting the atmosphere and maintaining ... >>

Solidification of bulk substances 30.04.2024

There are quite a few mysteries in the world of science, and one of them is the strange behavior of bulk materials. They may behave like a solid but suddenly turn into a flowing liquid. This phenomenon has attracted the attention of many researchers, and we may finally be getting closer to solving this mystery. Imagine sand in an hourglass. It usually flows freely, but in some cases its particles begin to get stuck, turning from a liquid to a solid. This transition has important implications for many areas, from drug production to construction. Researchers from the USA have attempted to describe this phenomenon and come closer to understanding it. In the study, the scientists conducted simulations in the laboratory using data from bags of polystyrene beads. They found that the vibrations within these sets had specific frequencies, meaning that only certain types of vibrations could travel through the material. Received ... >>

Random news from the Archive Mitsubishi Electric 60" Projection Video Wall Display VS-60HS12U Slim Cube 28.06.2014 Mitsubishi Electric introduced the latest VS-60HS12U Slim Cube video wall display. The VS-60HS12U Slim Cube projection type display is positioned as an alternative to LCD based displays. It has very thin bezels and is designed for long continuous use. The display thickness is 52 cm, which is about a quarter thinner than other similar models in the Mitsubishi Electric range, one of which is shown in the illustration. Moreover, the thickness can be reduced to 38,6 cm in some mounting options. Mitsubishi Electric calculates that video walls assembled from Slim Cube series displays have 85% less bezels between individual screens than LCD video walls. The Slim Cube series displays are designed so that maintenance with full access to the internals of the device is performed from the side of the screen, eliminating the need to access the back of the video wall. Another advantage is the long service life, estimated by the manufacturer at 110 hours or more than 000 years of continuous operation.

Other interesting news:

▪ 1,8" SAS SSD

▪ Innovative modular smartphone from Google

▪ Intent Predictive Headphones

▪ A painted window becomes a solar panel

▪ slow action coffee

News feed of science and technology, new electronics

Interesting materials of the Free Technical Library:

▪ section of the site Stories from the life of radio amateurs. Selection of articles

▪ article History of world and national culture. Crib

▪ article Thanks to whom stores stopped selling goods to different customers at different prices and introduced price tags? Detailed answer

▪ article Stevedoring knot. Travel Tips

▪ article Side Mount Antennas for Trunk Systems. Encyclopedia of radio electronics and electrical engineering

▪ article Automatic supply of the correct phase sequence to a three-phase consumer. Encyclopedia of radio electronics and electrical engineering

Leave your comment on this article:

All languages ​​of this page

Arabic	Hebrew	Polish
Bengali	Hindi	Portuguese
Chinese	Italian	Spanish
English	Japanese	Turkish
French	Korean	Ukrainian
German	Malay	Vietnamese

Home page | Library | Articles | Website map | Site Reviews

www.diagram.com.ua
2000-2024