Development of Conjugate Heat Transfer models to study the behavior of heat exchange in gaseous microflows. At the scales considered, rarefaction effects play a relevant role so that the need to involve slip flow boundary conditions is fundamental. The wide development of MEMS application, the very fast development in microfabrication technologies, and the increasing industrial applications of microfluidic systems, which are all taking place and evolving in the last decades, require a better knowledge of the behavior of microfluidic systems, especially of gases, which haven’t been yet understood as well as liquid ones have. Flows that are involved in this realm have characteristic dimensions of the order of tens of micrometers. The object of this work is essentially the investigation, and evaluation, of the characteristics and performances of forced convection in micro channels and of Micro Heat Exchangers. A general correlation for the local Stagnation Nusselt number is derived, which is in good agreement with all the results obtained in the study, and it has been proven that it works for the convection heat transfer cases with compressibility effects in the Micro Heat Exchanger