refer 11th physics book u will get a clear idea about Reynold's number. then 2nd law of thermodynamics comprises 5 basic law that I will tell u simply. first it is impossible to construct a engine which operated in a complete cycle will absorb heat from a single body and convert it completely to work without leaving some changes in the working system 2-impossible to transfer heat from a cold body of a machine without doing some work. 3- efficiency of a machine can never be cent percent 4- if entropy increases there will be a spontaneous. spontaneous means for example in vehicle if entropy increases there will be chance to be accident(spontaneous) .5 the efficiency of heat percentage =output / * 100 entropy s =q/t entropy change ?s and so on...........2nd law of thermodynamics is a big topic so refer 12th u will definitely get a clear idea....