Influence of the meandering channel geometry on the thermo-hydraulic performances of an intensified heat exchanger/reactor

Abstract

In the global context of process intensification, heat exchanger/reactors are promising apparatuses to implement exothermic chemical syntheses. However, unlike heat exchange processes, the implementation of chemical syntheses requires to control the residence time to complete the chemistry. A way to combine the laminar regime (i.e. enough residence time) with a plug flow and the intensification of both heat and mass transfers is the corrugation of the reaction path. In this work, the experimental setup is based on plate heat exchanger/reactor technology. 7 millichannel corrugated geometries varying the corrugation angle, the curvature radius, the developed length, the hydraulic diameter and the aspect ratio have been designed and experimentally characterized (heat transfer, mixing times, pressure drops, RTD). The objectives were to assess their respective performances to derive some correlations depending on the channel design. The results confirmed the benefits of the reaction channel corrugation. Heat and mass transfers have been intensified while maintaining a plug flow behaviour in the usually laminar flow regime. Moreover, whatever the meandering channel's curvature radius, the results highlighted the relevance of considering the Dean number as the scale-up parameter. This dimensionless number, more than the Reynolds number, seems to govern the flow in the wavy channels.

Chemical reaction engineering, process design and scale-up issues at the frontier of synthesis: Flow chemistry

“…In particular, heat exchangers/reactors are promising systems due to improved safety and selectivity control. Fluid flow has been studied as function of channels geometry [104]. By tuning channels configuration one may achieve the formation of vortices, called Dean vortices, due to flow instability even at relatively low values of the Reynolds number (Re).…”

“…where k is the thermal conductivity of the fluid [104] and the subscripts e and i define the two sides across the wall where heat transfer takes place. U normally ranges between 500 and 5000W/m 2 K depending on material, employed fluids, temperature and channel geometry [105].…”

Pressure drop and axial dispersion in industrial millistructured heat exchange reactors

“…9 shows the evolution of Péclet number as a function of Reynolds number for a straight circular pipe using both models (Eqs. (19) and (20)). The length of the reactor is set at L = 2 m and D h = 2 mm which roughly corresponds to the dimensions of the Corning and Chart reactors studied.…”

“…It consists in comparing the outlet signal with an analytical solution provided by a convectiondispersion model [8,17,18] or a succession of perfectly mixed tanks model [19]. These models imply a perfect Dirac injection that is experimentally difficult to perform.…”

Implementation of ‘chaotic’ advection for viscous fluids in heat exchanger/reactors

“…This device combines the benefits of a large heat transfer performance and a plug-flow regime allowing an intensive radial mixing, as a result of the specific design of process channels [4][5][6][7][8][9]. These geometries generate instabilities even in laminar flow regime (50 < Re < 2000).…”