Radiators for LEDs. Easy calculation of heat sink area for power transistors and thyristors Radiator for transistor designation

In small-signal circuits, transistors rarely dissipate more than 100mW of power. The distribution of heat along the conductors and convection from the body of the transistor into the surrounding air are sufficient to avoid overheating of the /?-and-junction.

High power dissipation transistors - in the emitter followers of high power supplies and in the output stages of power amplifiers - require special means of heat dissipation. Usually heat sinks(heatsinks) are used with transistors that are adapted to work with heatsinks. On fig. 9.35 am a shows a corrugated metal heatsink that doubles the heat dissipation of a transistor in a T05 package, such as the BFY50 transistor. A powerful transistor (Fig. 9.35, b) in the TOZ package is mounted on a massive ribbed heatsink. The transistor thus mounted allows a power dissipation of 30 W; without a heat sink, power dissipation is limited to 3W.

Rice. 9.35. Radiators.

Electrical isolation

The heatsink housing is usually screwed directly to a grounded metal chassis or instrument housing, or in some cases the chassis itself can act as a heat sink. In all these cases, it must be remembered that the transistor body is usually connected to the collector, and therefore electrical isolation is necessary between the transistor body and the heatsink. Mica or lavsan washers provide insulation without significantly reducing thermal conductivity. Silicone grease applied to each side of the washer ensures good thermal contact.

Thermal resistance

The quality of heat removal is usually expressed by the value of thermal resistance, which takes into account the fact that the rate of heat propagation is proportional to the temperature difference between the heat source and the external environment (compare with electrical resistance, in which the speed of charge movement is proportional to the potential difference. [Only with a very big stretch can we liken electric current of charge movement speed. Note. transl.]).

As is often the case with physical concepts, the unit of thermal resistance (degrees Celsius per watt) provides a good idea for its formal definition, which looks like this:

In other words, a heatsink housing with a thermal resistance of 3 °C/W, with a power dissipation of 30 W, will heat up to a temperature of 3 x 30 °C = 90 °C above the ambient temperature.

A complete picture of the established thermal equilibrium between the transistor and the environment is given by the thermal diagram shown in fig. 9.36. The thermal power P released by the transistor is considered as a "thermal current generator", which creates a temperature difference at various thermal resistances in the system.

The maximum allowable p-n junction temperature is usually 150 °C, and the ambient temperature can be taken equal to 50 °C - this is the temperature at which general-purpose electronic equipment is allowed to operate.

Transistor manufacturers specify a safe maximum case temperature for their transistors (often 125°C), in which case in, with

Rice. 9.36. Thermal diagram of the transistor and its environment.

is excluded from our calculations, and we go down one rung down the ladder of resistors in Fig. 9.36. In addition, the thermal conductivity from the transistor case to the heatsink is usually so good that 6CS 6SA , so that the thermal resistance between the heatsink and the air 6SA is the dominant factor in most calculations. Knowing the power P dissipated by the transistor, it is easy to find the case temperature T casc , assuming an ambient temperature of 50°C:

By referring to the manufacturer's data, we can now tell if this transistor can dissipate the required power at the found case temperature. If this is not the case, then the 6 SA thermal resistance must be reduced by using a larger heatsink.

Large finned heatsinks for power transistors typically have a temperature resistance of 2 to 4°C/W, which can be reduced to 1°C/W by forced cooling. On the other hand, small heatsinks designed for transistors in the T05 package have an average thermal resistance of about 50 ° C / W, and with their help, the allowable power dissipation of medium power transistors such as BFY50 or 2N3053 increases from 0.8 to 1.5 W.

Radiators for semiconductor devices

During operation, powerful semiconductor devices emit a certain amount of heat into the environment. If you do not take care of their cooling, transistors and diodes can fail due to overheating of the working crystal. Ensuring the normal thermal regime of transistors (and diodes) is one of the important tasks. To properly solve this problem, you need to have an idea about the operation of the radiator and its technically competent design.

As you know, any heated object, cooling, gives off heat to the environment. As long as the amount of heat released in the transistor is greater than that given off by it to the environment, the temperature of the transistor case will continuously increase. At a certain value, the so-called thermal balance occurs, that is, the equality of the amounts of dissipated and released heat. If the temperature of the heat balance is less than the maximum allowable for the transistor, it will work reliably. If this temperature is higher than the allowable maximum temperature, the transistor will fail. In order for the heat balance to occur at a lower temperature, it is necessary to increase the heat transfer of the transistor.

Three methods of heat transfer are known: Thermal conduction, Radiation and Convection. The thermal conductivity of air is usually low - this value can be neglected when calculating the radiator. The proportion of heat dissipated by radiation is significant only at high temperatures (several hundred degrees Celsius), so this value can also be neglected at relatively low operating temperatures of transistors (no more than 60-80 degrees). Convection is the movement of air in the zone of a heated body, due to the difference in temperature between the air and the body. The amount of heat given off by a heated object is proportional to the temperature difference between the object and air, the surface area and the speed of the air flow washing the body.

In my youth, I came across an original solution for removing heat from powerful output transistors. Transistors (then transistors of the P210 type were used to build amplifiers) on long wires were outside the case. Two plastic jars of water were screwed to the case, and the transistors were in them. Thus, "water" effective cooling was provided. When the water in the jars was heated, it was simply replaced with cold water ... Instead of water, you can use mineral (liquid) or transformer oil ... Now the industry has begun to mass-produce water cooling systems for processors and video cards of computers - on the principle of car radiators (but this is already , in my opinion, exotic ...).

To ensure efficient heat removal from the semiconductor crystal, heat sinks (radiators) are used. Let's get acquainted with some of the designs of radiators.

The device and principles of operation of the radiator for LEDs. Rules for choosing the material and area of ​​the part. We make a radiator with our own hands quickly and easily.

The common belief that LEDs do not heat up is a misconception. It arose because low-power LEDs do not feel hot to the touch. The thing is that they are equipped with heat sinks - radiators.

The principle of operation of the heat sink

The main consumer of the heat generated by the LED is the ambient air. Its cold particles approach the heated surface of the heat exchanger (radiator), heat up and rush upward, making room for new cold masses.

When colliding with other molecules, heat is distributed (dissipated). The larger the surface area of ​​the heatsink, the more intensely it will transfer heat from the LED to the air.

Read more about the principles of operation of LEDs.

The amount of heat absorbed by the air mass per unit area does not depend on the material of the radiator: the efficiency of a natural "heat pump" is limited by its physical properties.

Materials for manufacturing

Radiators for cooling LEDs vary in design and material.

Ambient air can take no more than 5-10 W from a single surface. When choosing a material for the manufacture of a radiator, the following condition should be taken into account: its thermal conductivity must be at least 5-10 W. Materials with a smaller parameter will not be able to transfer all the heat that air can take.

Thermal conductivity above 10 W will be technically excessive, which will entail unjustified financial costs without increasing the efficiency of the radiator.

For the manufacture of radiators, aluminum, copper or ceramics are traditionally used. Recently, products made of heat-dissipating plastics have appeared.

Aluminum

The main disadvantage of an aluminum radiator is the multi-layer design. This inevitably leads to the appearance of transient thermal resistances, which have to be overcome by using additional heat-conducting materials:

• adhesive substances;
• insulating plates;
• materials that fill air gaps, etc.

Aluminum radiators are the most common: they are well pressed and cope with heat dissipation quite tolerably.

Aluminum Heatsinks for 1W LEDs

Copper

Copper has a higher thermal conductivity than aluminum, so in some cases its use for the manufacture of radiators is justified. In general, this material is inferior to aluminum in terms of lightness of construction and manufacturability (copper is a less pliable metal).

It is impossible to manufacture a copper radiator by pressing - the most economical - method. And cutting gives a large percentage of waste of expensive material.

Copper radiators

Ceramic

One of the most successful options for a heat sink is a ceramic substrate, on which current-carrying traces are pre-applied. LEDs are soldered directly to them. This design allows you to remove twice as much heat compared to metal radiators.

Bulb with ceramic heatsink

Heat-dissipating plastics

Increasingly, there is information about the prospects for replacing metal and ceramics with thermally dissipating plastic. Interest in this material is understandable: plastic costs much less than aluminum, and its manufacturability is much higher. However, the thermal conductivity of ordinary plastic does not exceed 0.1-0.2 W / m.K. It is possible to achieve acceptable thermal conductivity of plastics through the use of various fillers.

When replacing an aluminum radiator with a plastic one (of equal size), the temperature in the temperature supply zone increases by only 4-5%. Given that the thermal conductivity of heat-dissipating plastic is much less than aluminum (8 W/m.K versus 220-180 W/m.K), we can conclude that the plastic material is quite competitive.

Bulb with thermoplastic heatsink

Design features

Structural radiators are divided into two groups:

• needle;
• ribbed.

The first type is mainly used for natural cooling of LEDs, the second - for forced cooling. With equal overall dimensions, a passive needle radiator is 70 percent more efficient than a ribbed one.

Needle type heatsinks for high power and smd LEDs

But this does not mean that plate (finned) radiators are only suitable for working in tandem with a fan. Depending on the geometric dimensions, they can also be used for passive cooling.

LED lamp with ribbed heatsink

Pay attention to the distance between the plates (or needles): if it is 4 mm - the product is designed for natural heat removal, if the gap between the radiator elements is only 2 mm - it must be equipped with a fan.

Both types of radiators can be square, rectangular or round in cross section.

Radiator area calculation

Methods for accurately calculating the parameters of a radiator involve taking into account many factors:

• ambient air parameters;
• scattering area;
• radiator configuration;
• properties of the material from which the heat exchanger is made.

But all these subtleties are needed for a designer developing a heat sink. Radio amateurs most often use old radiators taken from end-of-life radio equipment. All they need to know is what is the maximum power dissipation of the heat exchanger.

F \u003d a x Sx (T1 - T2), where

• Ф – heat flux (W);
• S is the surface area of ​​the radiator (the sum of the areas of all fins or needles and the substrate in sq. m). When calculating the area, it should be borne in mind that the fin or plate has two heat removal surfaces. That is, the heat sink area of ​​a rectangle with an area of ​​1 cm2 will be 2 cm2. The surface of the needle is calculated as the circumference (π x D) multiplied by its height;
• T1 is the temperature of the heat-removing medium (boundary), K;
• T2 is the temperature of the heated surface, K;
• a is the heat transfer coefficient. For unpolished surfaces it is assumed to be 6-8 W/(m2K).

There is another simplified formula obtained experimentally, which can be used to calculate the required radiator area:

S = x W, where

• S is the heat exchanger area;
• W - input power (W);
• M is the unused power of the LED.

For finned radiators made of aluminum, you can use the approximate data provided by Taiwanese experts:

• 1 W - from 10 to 15 cm2;
• 3 W - from 30 to 50 cm2;
• 10 W - about 1000 cm2;
• 60 W - from 7000 to 73000 cm2.

However, it should be noted that the above data is inaccurate, since they are indicated in ranges with a fairly large range. In addition, these values ​​are determined for the climate of Taiwan. They can only be used for preliminary calculations.

You can get the most reliable answer about the optimal way to calculate the radiator area in the following video:

DIY

Radio amateurs rarely take up the manufacture of radiators, since this element is a responsible thing that directly affects the durability of the LED. But in life there are different situations when you have to make a heat sink from improvised means.

Option 1

The simplest design of a homemade radiator is a circle cut out of an aluminum sheet with notches made on it. The resulting sectors are slightly bent (it turns out something that looks like a fan impeller).

4 antennae are bent along the axes of the radiator to fasten the structure to the lamp body. The LED can be fixed through the thermal paste with self-tapping screws.

Option 1 - homemade aluminum radiator

Option 2

The radiator for the LED can be made with your own hands from a piece of rectangular pipe and an aluminum profile.

Necessary materials:

• pipe 30x15x1.5;
• press washer with a diameter of 16 mm;
• hot glue;
• thermal grease KTP 8;
• profile 265 (W-shaped);
• self-tapping screws.

To improve convection, three holes with a diameter of 8 mm are drilled in the pipe, and holes with a diameter of 3.8 mm are drilled in the profile for its fastening with self-tapping screws.

The LEDs are glued to the pipe - the base of the radiator - with hot glue.

At the joints of the radiator parts, a layer of KTP 8 thermal paste is applied. Then the structure is assembled using self-tapping screws with a press washer.

Methods for attaching LEDs to a radiator

LEDs are attached to heatsinks in two ways:

• mechanical;
• gluing.

You can glue the LED on hot glue. To do this, a drop of adhesive mass is applied to the metal surface, then an LED sits on it.

To obtain a strong connection, the LED must be pressed down with a small load for several hours - until the glue is completely dry.

However, most radio amateurs prefer the mechanical fastening of LEDs. Special panels are now being produced with which you can quickly and reliably mount the LED.

Some models have clips for secondary optics. Installation is simple: an LED is installed on the radiator, on it is a socket, which is attached to the base with self-tapping screws.

But not only radiators for the LED can be made independently. Fans of plants are advised to familiarize themselves with the LED.

High-quality cooling of the LED is the key to the durability of the LED. Therefore, the selection of a radiator should be approached with all seriousness. It is best to use ready-made heat exchangers: they are sold in radio stores. Radiators are not cheap, but they are easy to install and the LED protects more reliably from excess heat.

One of the most important issues of creating comfortable living conditions in a house or apartment is a reliable, correctly calculated and installed, well-balanced heating system. That is why the creation of such a system is the main task when organizing the construction of your own house or when carrying out a major overhaul in a high-rise apartment.

Despite the modern variety of heating systems of various types, the proven scheme still remains the leader in popularity: pipe contours with a coolant circulating through them, and heat exchange devices - radiators installed in the premises. It would seem that everything is simple, the batteries are under the windows and provide the required heating ... However, you need to know that heat transfer from radiators must correspond to the area of ​​\u200b\u200bthe room and a number of other specific criteria. Thermal engineering calculationsbased on the requirements of SNiP is a rather complicated procedure performed by specialists. Nevertheless, you can do it on your own, of course, with an acceptable simplification. This publication will tell you how to independently calculate heating batteries for the area of ​​\u200b\u200bthe heated room, taking into account various nuances.

But, for starters, you need to at least briefly familiarize yourself with the existing heating radiators - the results of the calculations will largely depend on their parameters.

Briefly about the existing types of heating radiators

• Steel radiators of panel or tubular design.
• Cast iron batteries.
• Aluminum radiators of several modifications.
• Bimetal radiators.

Steel radiators

This type of radiator has not gained much popularity, despite the fact that some models are given a very elegant design. The problem is that the disadvantages of such heat exchange devices significantly exceed their advantages - low price, relatively small weight and ease of installation.

The thin steel walls of such radiators do not have enough heat capacity - they heat up quickly, but also cool down just as quickly. Problems can also arise during hydraulic shocks - welded joints of sheets sometimes leak at the same time. In addition, inexpensive models that do not have a special coating are susceptible to corrosion, and the service life of such batteries is short - usually manufacturers give them a rather short warranty on the duration of their operation.

In the vast majority of cases, steel radiators are a one-piece structure, and they do not allow varying heat transfer by changing the number of sections. They have a nameplate thermal power, which must immediately be selected based on the area and characteristics of the room where they are planned to be installed. An exception - some tubular radiators have the ability to change the number of sections, but this is usually done on order, during manufacture, and not at home.

Cast iron radiators

Representatives of this type of batteries are probably familiar to everyone from early childhood - it was these accordions that were previously installed literally everywhere.

It is possible that such batteries MS -140-500 did not differ in particular elegance, but they faithfully served more than one generation of residents. Each section of such a radiator provided heat transfer of 160 watts. The radiator is prefabricated, and the number of sections, in principle, was not limited by anything.

Currently, there are a lot of modern cast-iron radiators on sale. They are already distinguished by a more elegant appearance, even smooth outer surfaces that facilitate cleaning. Exclusive versions are also produced, with an interesting relief pattern of cast iron casting.

With all this, such models fully retain the main advantages of cast iron batteries:

• The high heat capacity of cast iron and the massiveness of the batteries contribute to long-term preservation and high heat transfer.
• Cast iron batteries, with proper assembly and high-quality sealing of joints, are not afraid of water hammer, temperature changes.
• Thick cast-iron walls are not very susceptible to corrosion and abrasive wear. Almost any coolant can be used, so such batteries are equally good for autonomous and central heating systems.

If we do not take into account the external data of old cast-iron batteries, then among the shortcomings we can note the fragility of the metal (accented blows are unacceptable), the relative complexity of installation, associated to a greater extent with massiveness. In addition, not all wall partitions can withstand the weight of such radiators.

Aluminum radiators

Aluminum radiators, having appeared relatively recently, very quickly gained popularity. They are relatively inexpensive, have a modern, rather elegant appearance, and have excellent heat dissipation.

High-quality aluminum batteries are able to withstand a pressure of 15 or more atmospheres, a high temperature of the coolant - about 100 degrees. At the same time, the heat output from one section in some models sometimes reaches 200 watts. But at the same time they are small in weight (section weight - usually up to 2 kg) and do not require a large volume of coolant (capacity - no more than 500 ml).

Aluminum radiators are available for sale as a set of batteries, with the ability to change the number of sections, and solid products designed for a certain power.

Disadvantages of aluminum radiators:

• Some types are highly susceptible to oxygen corrosion of aluminum, with a high risk of gassing. This imposes special requirements on the quality of the coolant, so such batteries are usually installed in autonomous heating systems.
• Some non-separable aluminum radiators, the sections of which are made using extrusion technology, can, under certain unfavorable conditions, leak at the connections. At the same time, it is simply impossible to carry out repairs, and you will have to change the entire battery as a whole.

Of all the aluminum batteries, the highest quality ones are made using metal anodic oxidation. These products are practically not afraid of oxygen corrosion.

Outwardly, all aluminum radiators are approximately similar, so you need to read the technical documentation very carefully when making a choice.

Bimetal heating radiators

Such radiators compete with cast-iron radiators in terms of their reliability, and with aluminum ones in terms of heat output. The reason for this lies in their special design.

Each of the sections consists of two, upper and lower, steel horizontal collectors (pos. 1) connected by the same steel vertical channel (pos. 2). The connection into a single battery is made by high-quality threaded couplings (pos. 3). High heat transfer is ensured by the outer aluminum shell.

Steel inner pipes are made of metal that is not subject to corrosion or has a protective polymer coating. Well, the aluminum heat exchanger does not under any circumstances come into contact with the coolant, and corrosion is absolutely not terrible for it.

Thus, a combination of high strength and wear resistance with excellent thermal performance is obtained.

Prices for popular heating radiators

Heating radiators

Such batteries are not afraid of even very large pressure surges, high temperatures. They are, in fact, universal and suitable for any heating systems, however, they still show the best performance in conditions of high pressure of the central system - they are of little use for circuits with natural circulation.

Perhaps their only drawback is the high price compared to any other radiators.

For ease of perception, there is a table that shows the comparative characteristics of radiators. Symbols in it:

• TS - tubular steel;
• Chg - cast iron;
• Al - ordinary aluminum;
• AA - aluminum anodized;
• BM - bimetallic.

Video: recommendations for choosing heating radiators

You may be interested in information about what is

How to calculate the required number of heating radiator sections

It is clear that the radiator installed in the room (one or more) should provide heating to a comfortable temperature and compensate for the inevitable heat loss, regardless of the weather outside.

The base value for calculations is always the area or volume of the room. By themselves, professional calculations are very complex, and take into account a very large number of criteria. But for domestic needs, you can use simplified methods.

The easiest way to calculate

It is generally accepted that 100 watts per square meter is enough to create normal conditions in a standard residential area. Thus, you should only calculate the area of ​​\u200b\u200bthe room and multiply it by 100.

Q = S× 100

Q- the required heat transfer from heating radiators.

S- the area of ​​the heated room.

If you plan to install a non-separable radiator, then this value will become a guideline for selecting the required model. In the case when batteries are installed that allow a change in the number of sections, one more calculation should be carried out:

N = Q/ Qus

N- the calculated number of sections.

Qus- specific thermal power of one section. This value must be indicated in the technical data sheet of the product.

As you can see, these calculations are extremely simple, and do not require any special knowledge of mathematics - a tape measure is enough to measure a room and a piece of paper for calculations. In addition, you can use the table below - there are already calculated values ​​\u200b\u200bfor rooms of various sizes and certain capacities of heating sections.

Section table

However, it must be remembered that these values ​​\u200b\u200bare for a standard ceiling height (2.7 m) of a high-rise building. If the height of the room is different, then it is better to calculate the number of battery sections based on the volume of the room. For this, an average indicator is used - 41 V t t thermal power per 1 m³ of volume in a panel house, or 34 W in a brick house.

Q = S × h× 40 (34 )

where h- the height of the ceiling above the floor level.

Further calculation is no different from the one presented above.

Detailed calculation taking into account the features premises

Now let's move on to more serious calculations. The simplified calculation method given above can present a “surprise” to the owners of a house or apartment. When the installed radiators will not create the required comfortable microclimate in the living quarters. And the reason for this is a whole list of nuances that the considered method simply does not take into account. And meanwhile, such nuances can be very important.

So, the area of ​​\u200b\u200bthe room is again taken as the basis and all the same 100 W per m². But the formula itself already looks a little different:

Q = S× 100 × A × B × C ×D× E ×F× G× H× I× J

Letters from BUT before J coefficients are conditionally indicated, taking into account the features of the room and the installation of radiators in it. Let's consider them in order:

A - the number of external walls in the room.

It is clear that the higher the contact area of ​​​​the room with the street, that is, the more external walls in the room, the higher the total heat loss. This dependence is taken into account by the coefficient BUT:

• One outer wall A = 1.0
• Two outer walls A = 1.2
• Three outer walls A = 1.3
• All four walls are external - A = 1.4

B - orientation of the room to the cardinal points.

Maximum heat loss is always in rooms that do not receive direct sunlight. This is, of course, the northern side of the house, and the eastern side can also be attributed here - the rays of the Sun come here only in the mornings, when the luminary has not yet “come out at full power”.

The southern and western sides of the house are always warmed up by the Sun much more strongly.

Hence, the values ​​of the coefficient AT :

• Room facing north or east B = 1.1
• South or West rooms - B = 1, that is, may not be taken into account.

C - coefficient taking into account the degree of insulation of the walls.

It is clear that the heat loss from the heated room will depend on the quality of the thermal insulation of the external walls. Coefficient value FROM are taken equal to:

• Medium level - the walls are laid out in two bricks, or their surface insulation is provided with another material - C = 1.0
• External walls are not insulated C = 1.27
• High level of insulation based on thermal engineering calculations - C = 0.85.

D - features of the climatic conditions of the region.

Naturally, it is impossible to equate all the basic indicators of the required heating power “one size fits all” - they also depend on the level of winter negative temperatures characteristic of a particular area. This takes into account the coefficient D. To select it, the average temperatures of the coldest decade of January are taken - usually this value is easy to check with the local hydrometeorological service.

• - 35° FROM and below - D= 1.5
• – 25h – 35° FROM – D= 1.3
• up to – 20 ° FROM – D= 1.1
• not lower - 15 ° FROM – D=0.9
• not lower than – 10 ° FROM – D=0.7

E - the coefficient of height of the ceilings of the room.

As already mentioned, 100 W / m² is an average value for standard ceiling heights. If it differs, a correction factor must be entered. E:

• Up to 2.7 m – E = 1,0
• 2,8 – 3, 0 m – E = 1,05
• 3,1 – 3, 5 m – E = 1, 1
• 3,6 – 4, 0 m – E = 1.15
• More than 4.1 m - E = 1.2

F is a coefficient that takes into account the type of premises located above

Arranging a heating system in rooms with a cold floor is a pointless exercise, and the owners always take action in this matter. But the type of room located above often does not depend on them. Meanwhile, if there is a residential or insulated room on top, then the total need for thermal energy will significantly decrease:

• cold attic or unheated room - F=1.0
• insulated attic (including insulated roof) - F=0.9
• heated room - F=0.8

G is the coefficient for taking into account the type of installed windows.

Different window structures are subject to heat loss differently. This takes into account the coefficient G :

• conventional wooden frames with double glazing – G=1.27
• windows are equipped with a single-chamber double-glazed window (2 glasses) - G=1.0
• single-chamber double-glazed window with argon filling or double-glazed window (3 glasses) — G=0.85

H is the coefficient of the glazing area of ​​the room.

The total amount of heat loss also depends on the total area of ​​the windows installed in the room. This value is calculated on the basis of the ratio of the area of ​​​​the windows to the area of ​​\u200b\u200bthe room. Depending on the result obtained, we find the coefficient H:

• Ratio less than 0.1 – H = 0, 8
• 0.11 ÷ 0.2 – H = 0, 9
• 0.21 ÷ 0.3 – H = 1, 0
• 0.31÷ 0.4 – H = 1, 1
• 0.41 ÷ 0.5 – H = 1.2

I - coefficient taking into account the scheme of connecting radiators.

From how the radiators are connected to the supply and return pipes, their heat transfer depends. This should also be taken into account when planning the installation and determining the required number of sections:

• a - diagonal connection, supply from above, return from below - I = 1.0
• b - one-way connection, supply from above, return from below - I = 1.03
• c - two-way connection, both supply and return from below - I = 1.13
• d - diagonal connection, supply from below, return from above - I = 1.25
• e - one-way connection, supply from below, return from above - I = 1.28
• e - one-sided bottom connection of return and supply - I = 1.28

J is a coefficient that takes into account the degree of openness of the installed radiators.

Much also depends on how open the installed batteries are for free heat exchange with the room air. Existing or artificially created barriers can significantly reduce the heat transfer of the radiator. This takes into account the coefficient J :

a - the radiator is located openly on the wall or not covered by a window sill - J=0.9

b - the radiator is covered from above with a window sill or shelf - J=1.0

c - the radiator is covered from above by a horizontal protrusion of the wall niche - J= 1.07

d - the radiator is covered from above by a window sill, and from the front sides — partschno covered with a decorative cover J= 1.12

e - the radiator is completely covered with a decorative casing - J= 1.2

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Well, finally, that's all. Now you can substitute the required values ​​\u200b\u200band the coefficients corresponding to the conditions into the formula, and the output will be the required thermal power for reliable heating of the room, taking into account all the nuances.

After that, it remains either to select a non-separable radiator with the desired thermal output, or to divide the calculated value by the specific thermal power of one section of the battery of the selected model.

Surely, for many, such a calculation will seem excessively cumbersome, in which it is easy to get confused. To facilitate the calculations, we suggest using a special calculator - it already contains all the required values. The user only needs to enter the requested initial values ​​or select the desired positions from the lists. The "calculate" button will immediately lead to an accurate result with rounding up.

= ([Temperature at the hot spot, °C] - [Temperature at the cold point, °C]) / [Dissipated power, W]

This means that if a thermal power of X W is supplied from a hot spot to a cold one, and the thermal resistance is Y cg / W, then the temperature difference will be X * Y cg.

Formula for calculating the cooling of a force element

For the case of calculating the heat removal of an electronic power element, the same can be formulated as follows:

[Power element crystal temperature, GC] = [Ambient temperature, °C] + [Dissipated power, W] *

where [ Total thermal resistance, Hz / W] = + [Thermal resistance between the case and the radiator, Hz / W] + (for the case with a radiator),

or [ Total thermal resistance, Hz / W] = [Thermal resistance between the crystal and the case, Hz / W] + [Thermal resistance between the case and the environment, Hz / W] (for case without heatsink).

As a result of the calculation, we must obtain such a crystal temperature that it is less than the maximum allowable value indicated in the reference book.

Where can I get the data for the calculation?

Thermal resistance between die and package for power elements is usually given in the reference book. And it is marked like this:

Do not be confused by the fact that the units of measurement K / W or K / W are written in the reference book. This means that this value is given in Kelvin per Watt, in Hz per W it will be exactly the same, that is, X K / W \u003d X Hz / W.

Usually, reference books give the maximum possible value of this value, taking into account the technological spread. We need it, since we must carry out the calculation for the worst case. For example, the maximum possible thermal resistance between the crystal and the case of the power field effect transistor SPW11N80C3 is 0.8 c/W,

Thermal resistance between case and heatsink depends on the case type. Typical maximum values ​​are shown in the table:

Insulating pad. In our experience, a properly selected and installed insulating pad doubles the thermal resistance.

Thermal resistance between case/heatsink and environment. This thermal resistance, with an accuracy acceptable for most devices, is quite simple to calculate.

[Thermal resistance, Hz / W] = [120, (gC * sq. cm) / W] / [The area of ​​the radiator or the metal part of the element body, sq. cm].

This calculation is suitable for conditions where elements and radiators are installed without creating special conditions for natural (convection) or artificial airflow. The coefficient itself is chosen from our practical experience.

The specification of most heatsinks contains the thermal resistance between the heatsink and the environment. So in the calculation it is necessary to use this value. This value should be calculated only if tabular data on the radiator cannot be found. We often use used heatsinks to assemble debug samples, so this formula helps us a lot.

For the case when heat is removed through the contacts of the printed circuit board, the contact area can also be used in the calculation.

For the case when heat is removed through the leads of an electronic element (typically diodes and zener diodes of relatively low power), the area of ​​the leads is calculated based on the diameter and length of the lead.

[Lead area, sq. cm.] = Pi * ([ Length of the right output, see] * [Right outlet diameter, see] + [Length of the left output, see] * [Left outlet diameter, see])

An example of calculating heat removal from a zener diode without a radiator

Let the zener diode have two terminals with a diameter of 1 mm and a length of 1 cm. Let it dissipate 0.5 watts. Then:

The output area will be about 0.6 sq. cm.

The thermal resistance between the case (terminals) and the environment will be 120 / 0.6 = 200.

The thermal resistance between the crystal and the body (terminals) in this case can be neglected, since it is much less than 200.

Let us assume that the maximum temperature at which the device will be operated will be 40 °C. Then the temperature of the crystal = 40 + 200 * 0.5 = 140 °C, which is acceptable for most zener diodes.

Online calculation of heat sink - radiator

Please note that for plate radiators, the area of ​​\u200b\u200bboth sides of the plate must be calculated. For PCB tracks used for heat dissipation, only one side needs to be taken, since the other does not come into contact with the environment. For needle radiators, it is necessary to approximately estimate the area of ​​\u200b\u200bone needle and multiply this area by the number of needles.

Online calculation of heat dissipation without a radiator

Several elements on one radiator.

If several elements are installed on one heat sink, then the calculation looks like this. First, we calculate the temperature of the radiator using the formula:

[Radiator temperature, gc] = [Ambient temperature, °C] + [Thermal resistance between the radiator and the environment, Hz / W] * [Total power, W]

[Crystal temperature, c] = [Radiator temperature, gc] + ([Thermal resistance between the crystal and the body of the element, Hz / W] + [Thermal resistance between the body of the element and the radiator, Hz / W]) * [Power dissipated by the element, W]