IntroductionModule 1 - Lecture 01When there is temperature difference heat flows from region of high temperature to low temperature. The subject dealing with the rate at which this heat flow occurs is called Heat Transfer.When any system undergoes heat and work interactions, the system goes from one equilibrium state to another equilibrium state. The system attains certain state which is described by temperature pressure etc.In thermodynamics, generally we don't ask how much time goes in that process, i.e., rate at which heat interaction takes place is not our concern.In the heat transfer we study the rate at which heat transfers occurs. Once we have the laws which govern the process of heat transfer, we can design the equipment where heat transfers occurs.If there is concentration difference, mass transfers from region of high concentration to region of low concentration.There are three modes of transfers, viz., Conduction, Convection and Radiation.Conduction is the flow of heat in a substance due to exchange of energy between molecules having more energy and molecules having less energy. The transfer of energy by conduction happens by the virtue of lattice vibrations. The vibrations in higher temperature region is higher than the vibrations in lower temperature region.Another mode of mechanism by which conduction happens in solids is by the motions of free electrons.In liquids or gas the conduction process happens due to collision of molecules.In addition to random motion fluids can be made to move by various processes, like creating temperature differences which in turn creates density difference. The transfer of energy from one region to another due to macroscopic motion in a fluid, added on to the energy transfer by conduction is called heat transfer by convection.In forced convection, fluid motion caused by an external agency. In natural convection, fluid motion occurs due to density variations caused by temperature variations.All physical matter emits thermal radiation in the form of electromagnetic waves because of vibrational and rotational movements of the molecules and atoms which make up the matter.The rate of emission increases with temperature level. Unlike conduction and convection, this mode does not require a material medium for energy transfer to occur.