Thermal analysis is defined as “the study of the relationship between a property of a sample and its temperature while the sample is heated or cooled in a controlled manner”. Definition approved in 2006 by the International Confederation for Thermal Analysis and Calorimetry (ICTAC). We routinely deal with thermal studies with application to solve engineering problems in ATS. Some common thermal problems are: cooling of a computer chip, cooling or heating of thermal loads, mass of material, of an oven, heat transfer by radiation and convection in a boiler, furnace, or in an oven. The thermal comfort conditions of industrial, office or aircraft environments are also evaluated.
At high temperatures, above 300 ˚C, radiation begins to predominate over the effects of convection on heat transfer. Tools like CFD can be used to calculate the form factors of infrared radiation between complex surfaces. This is an advantage, as the tables available in the literature do not represent with the same accuracy the real surfaces present in the industry. Even when natural convection is predominant, radiation is also important, which can account for 50% of a body's total heat transfer.
Conduction thermal analysis is performed by applying the First Law of Thermodynamics to solids, liquids or gases, being more predominant in solids. If there is flow over one of the solid's surfaces, there can be convective heat transfer to heat or cool the solid with a temperature distribution. Coupling heat transfer by conduction and convection is called conjugate heat transfer. In addition to convection, there can be radiative exchanges in the infrared range between surfaces, which can cool or heat exposed surfaces.
Heat exchangers are a special application of conjugate heat transfer, where convection and conduction are important for their effectiveness. One type of heat exchanger is fins, which are extended surfaces to improve the exchange of body heat with a fluid through natural or forced convection. Other types of exchangers are shell-tube, finned tubes, plate, tube-plate, for example. Exchangers can be concurrent or countercurrent.
Analysis to assess thermal comfort is a service that has been in increasing demand over the past three decades. There is global comfort, which tells if the person has the thermal balance in a range of satisfaction and local comfort, which tells if any part of the person's body is exposed to an influence of a hot or cold heat source. A thermal comfort analysis can be performed for transport vehicles, automobiles, aircraft, ships and trains, or for industrial and urban buildings.
The thermal insulation design has to consider the material properties of the body or duct and the insulation material. It is often used to prevent internal runoff from decaying or rising in temperature or to protect the material from structural damage, such as in the case of building fires. There is an ideal thickness of insulation, in which heat transfer to the environment is reduced.
Despite the low speeds, ventilation systems face challenges such as pressure drop, but mainly flow distribution. For example, a well-balanced air conditioner will cool the heat load or the environment more evenly.
Thermal analysis can be done analytically using tools specifically developed for solving the problem in Excel or Python. When the geometry has a complex three-dimensional shape, thermal analysis is done using CFD software, which accurately calculates conjugate heat transfer and infrared radiation, estimating all radiative form factors between surfaces. Analytical models are used to perform a sanity check of CFD++ results.
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