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When there is a phenomenon of heat transfer, there are many variables that are subject to curiosity, to be studied by science and engineering, we must keep in mind that science studies the phenomena and laws that govern physical behavior, then put all these achievements in the hands of engineering, and that this is responsible for applying all that science in benefits for humanity.
That is why all these experimental studies on heat transfer have had to transcend and go above all the knowledge that thermodynamics can give us. For this science evolved to create a section where you can agglomerate all the knowledge that involves the phenomena of heat transfer, the transfer of heat to the first and second principles of thermodynamics, by providing additional experimental rules that can be used to establish the laws that govern the phenomena of energy transfer speed. We say then that there is an energy transfer, since there is a displacement or trajectory to move a quantity of heat from one point to another.
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To understand a bit because heat transfer phenomena are studied by another branch different from thermodynamics, we can ask ourselves the following question:
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Will all the physical parameters that originate in the transfer of heat be covered?
To answer this question, consider the different types of problems that are treated by thermodynamics and heat transfer, consider the cooling of a hot steel rod that is placed in a container with water.
Thermodynamics can be used to predict the final equilibrium temperature of the combination of the steel bar and water. Thermodynamics will not tell us how long it will take to reach this equilibrium condition or what the bar temperature will be after a certain time has elapsed before the equilibrium condition is reached.
This limitation makes us think about having to develop a knowledge parallel to thermodynamics, which helps us to have results separately, and not in a totality of the phenomenon. The transfer of heat as an independent science of thermodynamics means that we can understand and study the final temperature states of the two components, that is, the steel bar and the water, the speeds in the heat transfer, the magnitudes of the trajectory traveled by this transfer, and even by means of equations developed by different laws we can find the type of material that conducts and / or transfers this heat from one body to another.
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Transport modes for heat transfer.
Heat transfer by conduction.
Experience has shown that when there is a temperature gradient in a body, there is an energy transfer from the high temperature region to the low temperature region. We say that energy is transferred by conduction and that the rate of energy transfer per unit area is proportional to the normal temperature gradient:
q: represents the total heat transfer
A: is the area of the material that is involved in heat transfer
K: is the thermal conductivity of the material.
It is important to evaluate and analyze what this equation represents, first this equation is the result of experimental studies carried out by the French mathematical physicist Joseph Fourier, which expresses by means of this equation an equality in which the thermal conductivity K is defined , where the heat flow is expressed in watts per meter per degree Celsius, all belonging to the international system.
There are other forms of heat transfer, which are convection and radiation, modes of heat transfer by convection and radiation will be treated in subsequent publications, with the intention of not making this publication as extensive.
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Importance of the study of heat transfer in engineering.
Almost all industrial processes at small and large scale heat transfer phenomena occur, which makes us think that energy costs, the unit cost for heat generation, especially in parts where it is very cold is usually very expensive, it is therefore the importance of the study of heat transfer, because by means of its various laws, for example in the heat transfer by conduction we can choose to choose the material that makes me perform a high heat transfer in the shortest time and least possible cost, that within the engineering involves optimized design, in my particular case I am aware that to graduate in the field of Food Engineering is one of the branches of the processes that most attracts my attention, and the that I think I will give my biggest contribution.
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Book consulted: Heat transfer. J. P. Holman.Mcgraw Hill. Mexico. 1999.
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