Heat Transfer Lecture-1 | তাপ সঞ্চালন скачать в хорошем качестве

Heat Transfer Lecture-1 | তাপ সঞ্চালন

The basic requirement for heat transfer is the presence of a temperature difference. There can be no net heat transfer between two bodies that are at the same temperature. The temperature difference is the driving force for heat transfer, just as the voltage difference is the driving force for electric current flow and pressure difference is the driving force for fluid flow. The rate of heat transfer in a certain direction depends on the magnitude of the temperature gradient (the temperature difference per unit length or the rate of change of temperature) in that direction. The larger the temperature gradient, the higher the rate of heat transfer. Heat transfer equipment such as heat exchangers, boilers, condensers, radiators, heaters, furnaces, refrigerators, and solar collectors are designed primarily on the basis of heat transfer analysis. The heat transfer problems encountered in practice can be considered in two groups: (1) rating and (2) sizing problems. The rating problems deal with the determination of the heat transfer rate for an existing system at a specified temperature difference. The sizing problems deal with the determination of the size of a system in order to transfer heat at a specified rate for a specified temperature difference. Joule is best known for his work on the conversion of electrical and mechanical energy into heat and the first law of thermodynamics. The energy unit joule (J) is named after him. The Joule’s law of electric heating that he formulated states that the rate of heat production in a conducting wire is proportional to the product of the resistance of the wire and the square of the electric current. Through his experiments, Joule has demonstrated the mechanical equivalence of heat, i.e., the conversion of mechanical energy into an equivalent amount of thermal energy, which laid the foundation for the conservation of energy principle. Joule, together with William Thomson (later Lord Kelvin), discovered the temperature drop of a substance during free expansion, a phenomenon known as the Joule- Thomson effect, which forms the foundation of the operation of the common vapor-compression refried ration and air conditioning systems. Heat can be transferred in three different modes: conduction, convection, and radiation. All modes of heat transfer require the existence of a temperature difference, and all modes are from the high-temperature medium to a lower-temperature one. Below we give a brief description of each mode.