Large eddy simulation of tubular reactors with spherical dimples

Abstract

Spherical dimples are implemented in heat exchanger channels to enhance heat transfer at a low pressure drop penalty. This combination of enhanced heat transfer and low pressure drop is also valuable for reactive applications such as steam cracking as this allows to increase product selectivity and reduce fouling. Large eddy simulations (LES) show the presence of asymmetric vortex structures inside the spherical dimples if they are implemented in a tubular reactor for steam cracking. Of all investigated geometric parameters, dimple depth and phase difference between consecutive rows is seen to have the greatest impact on the flow behavior. Spherical dimples in a tube enhance heat transfer up to 43% and increase pressure drop by only 54% relative to a bare tube. Relative to a ribbed tube, spherical dimples in tubes can reduce the pressure drop by half without impacting the heat transfer capabilities of the tube. The impact of these enhancements on product yields and run length is assessed via reactive simulations, benchmarking dimpled reactors against a non-enhanced reactor and industrially applied ribbed reactors. These simulations show the superior performance of dimpled reactors: the reduced fouling allows to increase the run length by up to 40% without a significant impact on product selectivities.