Radiative‐CFD Analysis of Laminar Continuous‐Flow Water in Coil and Annular Quartz Reactors Under External Broadband Heating

ABSTRACT Continuous‐flow quartz reactors under external radiative heating are central to emerging photochemical and thermal processes, yet geometry selection is often guided by heuristics rather than quantified thermo‐hydrodynamic and thermodynamic criteria. This study presents a comparative computational fluid dynamics (CFD) analysis of helical coil and annular quartz reactors handling laminar water flow ( Re ≈ 280–320, Tin = 300 K) subjected to 100 W broadband external radiation. Coupled conjugate heat transfer and discrete ordinates (DO) radiative modelling were applied in semi‐transparent quartz and water, and the simulations were validated against analytical correlations, infrared thermography, and micro‐PIV velocity measurements. The annular geometry provided a high outlet bulk temperature (85.3°C vs. 78.1°C), 36.8 times higher length averaged Nusselt number (5.24 vs. 3.83) and 20 times better thermal efficiency (65.1 vs. 53.7) at the same residence time, lowering pressure drop (12.1 Pa vs. 18.2 Pa) and These tendencies are due to the fact that the annular reactor facilitates more uniform radiative absorption and almost one dimensional thermal evolution and the Dean vortex causes the secondary flows within the coil, although locally increasing heat transfer and radial mixing, augmenting viscous dissipation and increasing pumping power requirements. An integrated evaluation of Bejan number and thermo‐hydrodynamic merit index indicates that the annular arrangement is largely dominated by the heat transfer imposed irreversibilities and a higher degree of useful heat transfer per unit pumping energy than the coil. As a result, the current radiative CFD model provides physics‐based, entropy‐informed design criteria in the choice of coil/annular quartz reactor in energy‐efficient continuous flow photochemical, catalytic, and radiative heating processes in which thermal performance and hydrodynamic penalties need to be quantitatively trade‐off.