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Heat Transfer
Published in Irving Granet, Jorge Luis Alvarado, Maurice Bluestein, Thermodynamics and Heat Power, 2020
Irving Granet, Jorge Luis Alvarado, Maurice Bluestein
In this chapter, we have surveyed the three mechanisms of heat transfer: conduction, convection, and radiation. We studied conduction through a simple plane wall and a wall consisting of several resistances. Using the electrical analogy where Ohm’s law is compared to Fourier’s law, it was found that the treatment of resistances in series and parallel could be handled readily. The same reasoning was used when conduction in a hollow cylinder was considered. In convection heat transfer, there is motion of a fluid relative to a body. It therefore becomes necessary to consider the character of the flow of the fluid. That is, is the flow laminar or turbulent, and is the flow due to natural or forced convection? Because of the complexity of the subject, we could only treat several common cases in a rather simplified manner. Radiation heat transfer differs from the other modes of heat transfer in that a medium is not required to transfer the heat. Using the concept of a blackbody and the Stefan–Boltzmann equation, we were able to calculate the radiation heat transfer and to combine it with the other modes of heat transfer. We studied heat exchangers and the application of Newton’s law of cooling to the calculation of their performance. When different modes of heat transfer are available, they can be combined into an overall heat transfer coefficient. Heat-transfer principles were also applied to the cooling of electronic equipment and to heat pipes. Finally, the usage of fins to enhance the rate of heat transfer was introduced.
Definitions and Terminology
Published in Frank Vignola, Joseph Michalsky, Thomas Stoffel, Solar and Infrared Radiation Measurements, 2019
Frank Vignola, Joseph Michalsky, Thomas Stoffel
Convection is the movement of heat by a gas or a liquid from one place to another. A more apt description of the processes of concern is advection, taking heat away from a surface and then having the gas or fluid move the heat by convection. An example of advection is wind blowing air molecules across a surface with heat transferred from the surface to the air. Thus, the air carries away the heat from the surface by convection. Newton’s law of cooling states that the rate of change in temperature of an object is proportional to the temperature difference between the object and the fluid or gas taking away, or adding, heat. () dQdt=hA(Ts−Tg)
Non-equilibrium Thermodynamics
Published in Jeffrey Olafsen, Sturge’s Statistical and Thermal Physics, 2019
Newton’s law of cooling states that the rate of heat loss by an object to its surroundings is proportional to the temperature difference between the object and those surroundings. This version of Newton’s law of cooling assumes a constant heat transfer coefficient (so independent of the object’s temperature). However, similar to the form of the Stefan-Boltzmann law, the surface area of the object (the area of heat transfer between the object and its surrounding environment) plays a role in the heat flux, so that: () đQdt=chA[T(t)−Ta],
Selection of cross-seasonal heat collection/storage media for wood solar drying
Published in Drying Technology, 2020
Xiang Chi, Jing Xu, Guangping Han, Wanli Cheng, Bing Liu, Xinyuan Du, Haoyu Chen
According to Newton’s law of cooling,[23] when the system cools naturally, the temperature T of the experimental system is higher than the ambient temperature θ, and the difference between T and θ is small, the rate of heat loss through the surface of the system is proportional to (T – θ). where K0 is the heat dissipation coefficient, T is the medium temperature, and θ is the ambient temperature. After loss of heat dQ, the temperature changes by dT, and dQ = CsdT.
Structural damage identification using an enhanced thermal exchange optimization algorithm
Published in Engineering Optimization, 2018
TEO is a physically inspired algorithm that uses Newton’s law of cooling. Newton’s law of cooling states that the rate of heat loss of a body is proportional to the difference in temperatures between the body and its surroundings.