Validated CFD experimental study of heat transfer in water bath heaters at city gate stations

This study develops and validates a conjugate computational fluid dynamics (CFDs) framework to quantify heat-transfer paths in indirect water-bath heaters used at city-gate stations and to assess the influence of atmospheric-burner settings. A full 3-D model of a station heater-resolving the fire-tube, water bath, and process-gas coil-was built and solved with RANS turbulence and coupled solid-fluid heat transfer at two representative operating loads (20,000 and 40,000 m³ h^-1). Grid-independence was demonstrated (change in coil-outlet temperature <0.5% beyond ∼1.67 M cells), and integral energy balances closed within the prescribed tolerances. The validated solution shows a buoyancy-driven bath with a warm cap beneath the top head and a cooler descending core through the coil bundle (mean bath ≈48°C; characteristic bath speeds ≤0.05 m s^-1). In the coil, the gas warms monotonically from ∼10°C to the station setpoint (∼35°C-36°C), with most duty delivered on the first pass; local velocity peaks (∼6 m s^-1) occur at elbow inner radii. On the fire side, the premixed jet forms an upward-lifting hot core (peak ≈880°C), producing a top-wall hot streak that concentrates heat flux but elevates wall metal temperature. Analysis indicates that high excess-air operation-typical of atmospheric burners-penalizes efficiency mainly through stack sensible losses rather than bath-side limitations. The model highlights practical levers for improvement-moderating excess air and tuning the primary/secondary split, gentle bath recirculation or baffling, and coil-pass placement-which can be screened numerically before field implementation.