Abstract

In a typical practical monolith reactor implementation, turbulent flow in a large pipe or inlet header enters small monolith channels. After some distance the flow becomes fully developed laminar flow. It has been shown that the distance over which the turbulence transitions to laminar flow is significant. This paper reports results of investigation into the value of the Nusselt number in the entry region of a circular tube under conditions of decaying turbulence. Large Eddy Simulations (LES) are used to model the flow. LES simulations show that the Nusselt number is significantly larger in the entry region compared to the classical case of developing laminar flow. The entry length Nu number depends not only on the inverse Graetz number, but also independently on the Reynolds number, turbulence length scale and upstream turbulence intensity. A general correlation is developed that relates the Nu number in the entry region to the inverse Graetz number, Reynolds number, inlet turbulence intensity and turbulence length scale.