Nguyên tắc cơ bản của Heat Transfer Dẫn Conduction truyền nhiệt được giải thích thông qua các chuyển động phân tử trong cấu trúc của chất rắn. Nhiệt được chuyển giao từ một phân tử phân tử kế cận bằng các phương tiện chuyển động rung động. Điều này mô tả cơ bản ra rằng truyền nhiệt thông qua một chất rắn diễn ra hoàn toàn bằng cách dẫn, và cũng có thể nói rằng nó xảy ra với một mức độ hạn chế trong chất lỏng và chất khí bởi vì động phân tử của họ. Việc xây dựng. | 8 Fundamentals of Heat Transfer René Reyes Mazzoco Universidad de las Américas-Puebla Cholula Mexico 1 HEAT TRANSFER MECHANISMS Conduction Conduction heat transfer is explained through the molecular motion in the solid s structure. Heat is transferred from one molecule to the adjacent molecule by means of vibrational motion. This basic description points out that heat transfer through a solid takes place entirely by conduction and also states that it occurs to a limited extent in liquids and gases because of their molecular mobility. The mathematical formulation of conduction heat transfer was proposed by Joseph Fourier while solving heat transfer problems in metal casting and template. The first step for this formulation is the recognition that the amount of heat transferred q W from one point of a metal piece to another point of the same medium continuum is proportional to the temperature difference between those two points. The evaluation of the temperature difference through the derivative in any direction ỉ makes the measurement independent of any two specific points and the distance between them dT 0 - ds 1 Copyright 2002 by Marcel Dekker Inc. All Rights Reserved. For most cases of conduction heat transfer in solids it is possible to change the proportionality relation to an equality defining the proportionality constant called thermal conductivity k W m K . Thus the calculation of the amount of heat transferred per cross-sectional surface area A m2 is obtained from Fourier s first law ì kỉs 2 Measurement of Thermal Conductivity The thermal conductivity is a physical property characteristic of the medium and is defined similarly for the three states of the matter. The expression for the calculation of the amount of heat transferred by conduction is also used to define the thermal conductivity and one procedure for its measurement that is k is calculated after measuring the linear temperature difference between two points the amount of heat .
