Introduction to Heat Transfer | Heat Transfer | ME

Introduction to Heat Transfer This lecture is short description of the subject of heat transfer. It gives an idea of the scope of the subject, its applications and discusses a basic difference between the three mechanisms of heat transfer through examples. Scope: Heat Transfer vs. Thermodynamics Whenever a process occurs, it involves some kind of interaction between a system and its surroundings. These interactions are in form of mass, heat and work transfer. Particularly speaking of heat transfer, the subject of Thermodynamics gives its definition as well as the total amount of transfer by comparing the initial and final states of the system. However the subject of Thermodynamics does not give any information about 1. Mechanism of heat transfer: Micro and macro level activities responsible for transfer of            heat 2. Factors affecting the mechanism 3. Instantaneous Rate of Heat transfer between system and its surroundings & 4. Temperature field The study which deals with all these aspects is that of Heat Transfer. It provides the laws which incorporate in themselves the mechanisms and corresponding factors. These laws are experiment based observations and are used for mathematical modelling and solving of real world problems. Applications 1. Design of • Power plant equipment • Air conditioners and Refrigerators • IC Engines and air compressors • House hold appliances: cooking range, utensils, fans, motors etc. • Electronic equipment etc. 2. Parameterization of processes in • Chemical industries • Food processing • Manufacturing processes (Heat Treatment, Casting and Injection Molding, Machining etc.) Mechanisms of Heat Transfer 1. Conduction • Transfer of heat through a medium as a result of micro level activities with in the medium • These activities are lattice vibration and free electron transfer in solids and diffusion with intermolecular collision in fluids. • Though conduction is possible through solids, liquids as well as gases but it is most significant in solids. • Examples: heating up of free end of a spoon dipped in hot liquid, transfer of heat through a wall etc. 2. Convection • Transfer of heat as a result of bulk motion of fluid mass. • Transfer of heat between a solid surface and adjacent fluid is a result of convection and involves conduction in a very thin layer adjacent to solid surface followed by advection (fluid motion) and diffusion in farther layers. • Example: boiling of water in a pan, cooling the hot food in spoon by blowing air etc. 3. Radiation • Heat propagation in form of Electro Magnetic waves; Infrared, light and Ultra violet rays in particular. • These waves are combination of perpendicular electric and magnetic fields propagating in the third direction. • These waves do not require any medium for propagation and can transmit through gases, liquids as well as solids. However liquids and solids are generally opaque to radiation heat transfer. • Example: Heat transfer from sun to earth. The syllabus is based on the laws related to these mechanisms and mathematical solutions to corresponding engineering problems.
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