In this paper we focus on diamond film hot-filament chemical vapor deposition reactors where the only reactant ishydrogen so as to study the formation and transport of hydrogen atoms. Analysis of dimensionless numbers forheat and mass transfer reveals that thermal conduction and diffusion are the dominant mechanisms for gas-phaseheat and mass transfer, respectively A simplified model has been established to simulate gas-phase temperature andH concentration distributions between the filament and the substrate. Examination of the relative importance ofhomogeneous and heterogeneous production of H atoms indicates that filament-surface decomposition of molecularhydrogen is the dominant source of H and gas-phase reaction plays a negligible role. The filament-surface dissociationrates of H_2 for various filament temperatures were calculated to match H-atom concentrations observed in the literature or derived from power consumption by filaments. Arrhenius plots of the filament-surface hydrogen dissociationrate In this paper we focus on diamond film reactors where the only reactant ishydrogen so as to study the formation and transport of hydrogen atoms. Analysis of dimensionless numbers forheat and mass transfer reveals that thermal conduction and diffusion are the dominant mechanisms for gas-phaseheat and mass transfer, respectively A simplified model has been established to simulate gas-phase temperature and H concentration distributions of H Molecular hydrogen is the dominant source of H and gas-phase reaction plays a negligible pink. Molecular Weight is found in the literature or derived from power consumption by filaments. Arrhenius plots As the background of the hydrogels n dissociationrate