EN
Global existence of regular solutions to the Navier-Stokes equations for velocity and pressure coupled with the heat convection equation for temperature in a cylindrical pipe is shown. We assume the slip boundary conditions for velocity and the Neumann condition for temperature. First we prove long time existence of regular solutions in [kT,(k+1)T]. Having T sufficiently large and imposing some decay estimates on $||f(t)||_{L₂(Ω)}$, $||f_{,x₃}(t)||_{L₂(Ω)}$ we continue the local solutions step by step up to a global one.