Geometry-Induced Intensification of Coupled Flow, Heat Transfer, and Reaction in Isobutyric Anhydride Pyrolysis

Abstract Thermal pyrolysis of isobutyric anhydride (IBAN) to dimethylketene (DMK) requires a rapid and uniform heat supply at high temperature and short residence time. A three-dimensional CFD model coupling flow, heat transfer, and reaction compared a circular tube (CT), twisted elliptical tubes (TETs), and sinusoidally corrugated tubes (SCTs) at identical length and hydraulic diameter. A larger TET aspect ratio or smaller twist pitch improved conversion and yield with moderate pressure-drop penalties. A larger SCT amplitude gave greater yield gains but higher hydraulic costs. At t = 0.8 s, a representative SCT (T = 50 mm, A = 4 mm) raised the DMK yield from 41.57% for the CT to 60.35% at 98.78% selectivity. At comparable yields, TETs required a lower pressure drop than SCTs. TETs sustain inter-section exchange through noncircularity and twisting, whereas SCTs renew near-wall fluid through periodic contraction and expansion. SCTs suit yield-prioritized designs; TETs suit designs that balance enhancement and hydraulic cost.