Pure nitrogen dioxide (NO2) has significant economic value and is widely used in many fields, for which condensation technology plays an important role in separation and purification. However, developing cost-effective NO2 condensers remains challenging due to the lack of precise theoretical guidelines and comprehensive understanding of NO2 condensation process. In this work, NO2 condensation at various inlet surface subcoolings, mole fractions of noncondensable gas (NCG), and Re numbers was studied with a visualization experimental system. The influential rules of each parameter on heat transfer coefficients (HTCs) and the NO2 condensate state as the coexistence of droplet, streamlet and film were revealed. A substantial underestimation of experimental data by the classical heat and mass transfer analogy (HMTA) model was quantified. The large discrepancy was found to originate from the uniqueness in heat transfer, mass transfer, and condensate state caused by NO2 dimerization during condensation. A modified HMTA model was developed considering the release heat of dimerization reaction and the promotion of mass transfer by an increased NO2 concentration gradient within the diffusion layer which contribute to improvements of HTCs by ∼6 and ∼49%, respectively. The correction of liquid film roughness regarding potential heterogeneity of dimerization was proposed as a function of the key parameters, contributing to the improvement of HTCs by ∼150%. An accurate theoretical formula for HTCs prediction within an error of ±25% was finally derived, providing the key step for success in practical applications.
© 2022 The Authors. Published by American Chemical Society.