Basics of Thermal Dissipation - Definition, Mechanism, and Equation Explained
Learn more about thermal dissipation and the factors that influence it in this article.
Thermal dissipation is an important concept not only in engineering and industry, but technology and electronic goods. The thermal dissipation of a product can predict whether it is likely to overheat, and poor thermal dissipation can cut service life by half. Many factors can affect heat transfer. In this article we go over the basics of thermal dissipation, as well as the factors that influence it.
What is Thermal dissipation?
Thermal dissipation refers to a form of heat transfer. Heat transfer in this respect occurs from an object that is hotter, to surrounding objects and environment that are cooler. In many industries particularly those involving technology, this can be deleterious as it “corrosion under insulation”. Equipment made of insulated low-carbon steels and insulated carbon are at risk of this, particularly in the presence of water (collecting in the insulation) and oxygen. It can also have negative effects on alloy performance, especially in high temperature environments.
The mode and rate of heat transfer is governed primarily by the temperature difference between an object and its surrounding environment. In order to manage thermal dissipation and help with the selection of appropriate thermal insulation, factors such as operation, environment and design should also be considered.
Difference from similar mechanisms
Thermal dissipation vs. thermal transfer
Thermal dissipation is simply a type of thermal transfer. The “transfer” of thermal energy refers to its movement between objects and the environment while dissipation focuses on the wasting of energy; any energy that is not transferred to useful energy stores is considered wasted. Transfer in this case would be from the object to its cooler surrounding environment.
Thermal dissipation vs. thermal distribution
Both thermal dissipation and distribution are concerned with the movement of heat though “dissipation” is the process of removing excess heat entirely. Thermal distribution, however, is the process of ensuring that excess heat is evenly distributed rather than lost. In both cases, managing the amount of thermal resistance is beneficial for its control. In the case of electronics, thermal dissipation is often preferred to thermal distribution as overheating is less likely.
Thermal dissipation vs. thermal radiation
Thermal radiation refers to the emission of thermal energy in the form of infrared waves, which are emitted by bodies at certain temperatures. Thermal dissipation works in the same way, but only if an object is hotter than its surrounding environment. Any objects with a temperature above absolute zero (−273.15 °C) emit thermal radiation. It is important to note here that thermal dissipation works in many other ways.
Thermal dissipation mechanism
(Ti-Tu) = Qv / (k*A)
Ti - Permitted internal temperature
Tu - Ambient temperature
Qv - Watts to dissipate
k - Heat transfer coefficient
A - Enclosure surface area
Brief explanation of the equation
The above is a rearrangement of the thermal dissipation equation that focuses on the change in temperature. This is important as electronic component failure inside an enclosure is often a result of heat and can cut its service life in half. This equation allows us to calculate the maximum temperature increase relative to the temperature inside the equipment or enclosure; it can be useful to ensure that equipment is not likely to overheat and be damaged. This creates what is known as the “thermal limit”, which is an important factor to consider. The thermal limit demonstrates the maximum temperature an electronic component can reach before it can no longer operate.
Factors such as surface area, types of materials used and ambient temperature can be adjusted to ensure this limit is not reached.
Ambient temperature refers to the air temperature of any environment or object where the equipment is stored. This is particularly important as it has the greatest effect on the rate of dissipation; ideally cooler environments ensure that heat is dissipated outward rather than remaining within the walls of the enclosure. Always double check the temperature used in Kelvin.
Permitted internal temperature
The permitted internal temperature refers to the temperature of the product as opposed to that of its environment (ambient temperature). Just as above, it is best to convert temperature to Kelvin when using this equation for consistency.
Enclosed surface area
This refers to the surface area in regard to the walls of the enclosure. A larger surface area allows better and faster thermal dissipation from the object as a larger surface has more contact with the ambient temperature than a smaller one.
Thermal dissipation materials
To counter the heat produced by electrical components, a variety of materials may be used to help dissipate the heat. These materials include metals, ceramics and graphite. They are often incorporated into installations such as heat sinks, which are needle type structures usually made of metal that allow for greater surface area and better heat dissipation as a result. Other examples of components include graphite sheets, heat pipes, vapor champers, thermally conductive grease (thermal grease) and TIM (thermal interface material) to name a few. Depending on the space available, many installment options to accommodate are available. For example, vapor chambers allow for heat dissipation in miniature high-performance electronic devices because of the thin and sleek build of the devices.
More information about thermal dissipation materials can be found in this article.
Thermal dissipation for electronics
When temperatures rise above the thermal limit, the component burns out and, as discussed, it is one of the most common causes of electronic component failure. With steep advances in technology, thermal management techniques have become increasingly more efficient over time. Liquid cooling technology, for example, is no longer limited to high capacity computing hardware and is found in many consumer goods. Within electronic cooling, many cooling methods are available, such as air cooling, gas cooling, phase transition cooling and liquid cooling.
More information on thermal dissipation for electronics can be found in this article.
Thermal dissipation for laptops
Thermal dissipation is a key determinant of laptops' performance. Efficient thermal dissipation, especially in the limited space inside a laptop, requires well-thought-out thermal countermeasures.On a laptop board, electronic components are neatly and densely mounted, and copper foil wiring connects them. Among the electronic components (i.e., heat sources) used in PCs, the CPUs (Central Processing Units), GPUs (Graphics Processing Units), and SSDs (Solid State Drives) generate the largest amount of heat.
Heat generated by CPUs, GPUs, and SSDs is transferred (dissipated) by “Thermal conduction”, “Convective heat transfer”, and “Thermal radiation”. Of these, thermal conduction through the wiring and circuit boards in contact with the electronic components is said to account for the majority of the heat transferred, with the remainder being the convective heat transfer from the component surface into the air.
Heat from the electronic components mounted on the board in a laptop spreads to the board by thermal conduction and is dissipated from the board to the air by heat transfer.
In order to reduce the temperature of the air inside a laptop, air vents should be provided in the chassis and air flow paths should be created inside, including the layout of the components mounted on the board, and fans should be used to force ventilation. This will increase the efficiency of thermal dissipation of laptops.
More information on thermal dissipation for laptops can be found in this article.
Vapor Chambers for heat dissipation
Vapor Chambers are thin sheet-like heat dissipation components made of metal. They have very high thermal conductivity and their operating principle is the same as that of heat pipes. Generally, Vapor Chambers that employ meshes have a fine capillary structure (wick) contained inside that is filled with a working fluid such as pure water. The internal capillary structure of DNP’s Vapor Chamber, on the other hand, is characterized by having a form that is made to be extremely fine and precise by means of using etching technology.
When one end of a vapor chamber is situated to be in contact with a heat source, its working fluid evaporates, absorbing latent heat in the process, and the resulting vapor moves to a lower temperature area where it releases the heat and returns to liquid form. This working fluid returns to the heat source through the wick by the process of capillary action. This cycle is very short and continuous, and requires not external power.
DNP’s Vapor Chambers
DNP, using in-house ultra-fine precision metal processing technology, has developed a Vapor Chamber with a thickness of 0.20mm, comparable to that of thermally conductive sheets. It is also flexible to some extent and can be applied to curved or graded surfaces. (* Information as of February 2022)