Thanks a lot Sir. nSir I have one more doubt regarding buoyancy. As I increase operating pressure of reactor, more eddies starts forming inside reactor and it becomes very difficult for laminar model to converge even if Reynolds number<2300 but if I use K-epsilon model instead solution converges smoothly. Can I use turbulent flow models to deal with buoyancy even if Reynolds number falls in laminar region or there is any method of dealing with this problem using laminar model. (in my reactor gravity is acting opposite to the direction of gas flow i.e. gas flow is from bottom to top and temperature difference between reactor temperature and inlet temperature is large-900C)nRegardsn