in engineering thermodynamics it links to the system and it is recognised how much heat is enter to reach system and how much output is delivered by the system on the basis of system properties taking some assumption it is a macroscopic approach basis but heat transfer exist system boundaries boundaries properties play important role for heat transfer this boundary no meaning for thermodynamic. Thermodynamics have four laws. The zeroth law basis on thermal equilibrium. this law the temperature scales are are there and next door law first law of thermodynamics in that law energy neither created nor destroyed it can transform one form to another form like heat is transform into work and work is transform into heat there is a mutual conversion and that law internal energy is a property of this law so all the high grade energy is works on this law it is a quantitative laws ,next law is second law of thermodynamics is also called nature law basically for heat engine in that there are two statement Kelvin planck statement and clausius statement. Kelvin planck statement says that it is impossible to construct engine which operates in a cyclic manner it takes the heat from one source and to produce only work not reject anything to other source in clausius statement says that it is impossible to construct a reverse engine which can we convey heat from low temperature to high temperature without unaided external work, third law, this is that the entropy of the universe at absolute zero temperature is zero that means all the substance in universe will be in form of Crystal and heat transfer generally represent the heat rate that is existence boundary of the system so how is system boundaries make a good or a bad that it convey more heat to the system I think about such material of the boundaries so the heat is crossing boundaries is basically depends upon thermal conductivity so there are the three mode of heat transfer is conduction convection and radiation.