The growth of thick epitaxial 4H-SiC layers with low defect density is an essential step for the fabrication of SiC based devices. A hot-wall reactor using silane and propane diluted in hydrogen were used in this study. The typical growth temperature range is 17001900 K and total pressure range 10-100 kPa. The resulting epilayers of 2" wafers exhibit low background doping, low defect density and good thickness uniformity. One problem is that it is difficult to ensure a good uniformity of deposition and doping over several wafers. A 3D simulation approach of heat and mass transfer was used with two objectives. The first one is to evaluate the electrical, thermal, transport and kinetic databases. The second one is to have a visualization and a quantification of the flow, temperature and gaseous species fields under some conditions for a better understanding of some of the engineering problems at elevated temperatures.