Effective cooling of electronic equipment requires selecting suitable solutions, but also making necessary adjustments in terms of efficiency and technical parameters. Manufacturers offer solutions that are tailored to specific needs and extremely stringent requirements. This article discusses the solutions available on the market and their key advantages.
Cutting-Edge Electronic Systems and Related Challenges
As a result of technology development, computers must process more and more data. They are required to perform complex tasks, while at the same time manufacturers strive to miniaturise electronic equipment, ideally to a pocket size. Computers that once took up entire rooms were only tasked with simple calculations. Modern computers fit in the palm of your hand and their capabilities seem almost infinite. However, the issues connected with heat generation by electronic circuitry remain unchanged. Moreover, the increasing amount of computing power brings with it a proportional increase in heat to be dissipated. It won’t come as a surprise to anybody that excess heat is one of the greatest enemies of electronic systems. It greatly accelerates the wearing of such electronic components as transistors, resistors or relays. In special cases, high temperatures can even damage control systems irreparably. A device repair cost may then exceed the profitability threshold. While comparing computers designed a few decades ago to those of today, we need to remember that the 20th century devices equipped with extensive cooling systems in fact operated under much more favourable conditions.
Nowadays, electronic systems set the pace for human life, help provide safety and streamline further technology advancements. To ensure their faultless operation at the maximum efficiency, adequate cooling and protection against overheating must be provided. The challenges faced by consumer mobile devices or advanced industrial systems force manufacturers to go to great lengths to find the best way to maintain the most sensitive components at safe temperatures.
Tailor-Made Cooling Systems
There are several common cooling and heat-dissipation systems for electronic circuits. They differ primarily in size, which is one of the main criteria for selecting a cooling system for a specific application; other differences include a coolant selected or heat dissipation efficiency offered. Therefore, in order to decide which one is the most suitable solution, it is necessary to learn a bit about their characteristics and most important advantages.
When it comes to selecting a cooling system, the following are the most popular solutions:
A fan is a basic cooling device present in each household or industrial facility. The first and most common application of fans in electronic devices is to dissipate heat. They are installed both in desktop computers and in laptops. We usually become aware of their presence when we run some demanding software or game. Then, our computer operates at its maximum capacity, which results in higher heat energy generation. When this happens, a fan automatically extracts heat from the device enclosure to allow the process to continue uninterrupted and protect all heat-sensitive electronics.
Fans are equipped with motors driving the impeller blades. Convection air movements forced by impeller rotations dissipate and remove the heat generated in an electronic device. The heat energy is extracted through the grilles located in the computer enclosure. The fan movement is triggered by a Temperature Sensor. After a certain setpoint is exceeded, the fan impeller starts rotating to facilitate device circuitry cooling. The mass of air flowing through a fan is specified in square metres per hour m3/ℎ.
A fan also plays another important role, i.e. acts as a “dust cleaner” inside a computer unit. To ensure its trouble-free operation, dust must be removed from the impeller blades on a regular basis.
It is also worth noting that fans currently offered by the leading manufacturers undergo rigorous noise level tests. Therefore, their operation does not cause computer users’ fatigue. However, the noise level increases in proportion to the size of a fan and the amount of air it has to push.
Using the active cooling feature causes a risk of damaging certain components, e.g. the drive system or the driven impeller itself. This risk is eliminated when using the passive cooling feature mentioned below.
A heat sink is another element that is often encountered in cooling systems. It is a finned metal element most often used in conjunction with the fans described above to increase heat dissipation efficiency. It is usually made of aluminium.
Now, a question arises: how can such a component influence the process of extracting heat from electronic parts? As per the heat exchange process principles, the greater the surface area absorbing thermal radiation, the higher the cooling capacity. In a heat sink design, properly shaped fins maximise the heat exchange surface area. It is obvious that the larger the heat sink, the more intensive the cooling process is. Still, the size of the device for which the component is to be used is the biggest limitation for its performance. The distance between the heat sink and the heated component is another very important aspect. The smaller the distance, the more efficient the heat dissipation is. In order to maximally intensify the temperature transfer process, thermally conductive plates are placed in the contact area between both surfaces.
In a fan/heat sink assembly, the latter accepts hot air masses pushed by fan impeller blades, and dissipates the heat into the surroundings.
Peltier modules provide an interesting solution for electronic circuit cooling. They are made of parallel ceramic plates, between which type N and type P semiconductors are alternately placed. Direct contact between these plates is ensured by using copper sheets to transfer electrons. A current flow forces temperature changes in the places of contact between dissimilar semiconductors. Fault-free operation, a relatively small and compact design and no need to use a coolant are the main advantages of this cooling system. Another important aspect is the possibility of expanding and increasing the capacity of a Peltier cell by adding additional modules. Then, the “hot” side of the first module is connected with the “cold” side of another one. Therefore, the heat collection capability depends on the available space and current intensity.
These cells are a perfect solution for harsh environmental conditions, e.g. locations where large amounts of dust are present. Examples of everyday applications for Peltier modules include portable car refrigerators or much more sophisticated equipment systems requiring precise temperature control, for example, high-power generators.
Effective heat dissipation in state-of-the-art high-power electronic systems requires high cooling capacity. Note that the thermal capacity of air, i.e. the amount of energy that air is capable of storing is approx. 1 kJ/m3, whereas the thermal capacity of water is 4000 kJ/m3.
Therefore, demanding electronic systems benefit from liquid cooling systems. “Water blocks” are based on water (or another cooling liquid) flowing around the heat sink in a sealed enclosure. A pump system ensures liquid circulation. Liquid cooling systems require a high degree of manufacturing precision. This results from the necessity to avoid contact of electrically powered systems with water. Even if a system is filled with an non-conductive substance and simple contact with this substance will not destroy the device, the coolant loss will disrupt the cooling process. Such solutions are implemented, for example, in computers designed to perform complex calculations or simulations for the research and engineering industry.
A Heat Tube is a simple device transferring heat in line with the convection principle.
Despite the fact that this technology was known already in the 1940s, it was not commonly used in industry until approximately 20 years later. Currently, heat tubes are used in numerous fields of application, from cooling and heating solutions, through cutting-edge computers, to the space industry.
A heat tube is divided into three zones:
- evaporation zone (evaporator);
- intermediate zone – heat transfer without exchange with the surroundings (adiabatic);
- condensation zone (condenser).
Heat is absorbed in the evaporator in which the liquid medium is evaporated. The pressure in the evaporator space is higher than the pressure in the condenser space. This pressure difference forces the movement of vapour to the condensing space where it is condensed and transfers heat to the upper source.
The heat tube technology is applied in space vessels and chemical or power engineering industry.
The Importance Of Cooling For Electronic System Operation
Excessive heat in equipment reduces its service life, adversely impacts its performance and often results in inevitable electronic system failures. Proper selection of cooling elements helps avoid all of these negative effects. It is a considerable challenge for designers, as numerous factors, such as key technical parameters and dimensions of devices, have to be taken into account. Correct calculations are also necessary. Note, however, that despite installing high-end heat dissipation systems, it is still the users who have great impact on equipment life time by providing adequate space for air circulation and using it only in line with its intended purpose.