Condensation of ammonia and high-temperature-glide ammonia/water zeotropic mixtures in minichannels – Part I: Measurements

In this two-part study, a comprehensive investigation of the condensation of pure and zeotropic mixtures of ammonia and ammonia/water is conducted and improved models for condensation are developed. In Part I, condensation heat transfer experiments were conducted on ammonia and ammonia/water mixtures. Data for pure ammonia were obtained for varying tube diameters (0.98 < D < 2.16 mm), mass fluxes (75 < G < 225 kg m⁻² s⁻¹), and saturation conditions (30 < T_sat < 60 °C). Experiments on zeotropic ammonia/water mixtures were conducted for multiple tube diameters (0.98 < D < 2.16 mm), mass fluxes (50 < G < 200 kg m⁻² s⁻¹), and bulk ammonia mass fractions (x_bulk = 0.8, 0.9 and >0.96). For zeotropic mixtures, the apparent heat transfer coefficient showed a different trend from the pure ammonia heat transfer coefficient, with strong degradation observed in quality ranges with large temperature glides. At low quality ranges (i.e., low temperature glides and smaller mixture effects), the pure ammonia heat transfer coefficient and zeotropic mixture apparent heat transfer coefficient were in good agreement. In Part II of this study, a new model for predicting condensation heat transfer for pure ammonia in mini- and microchannels is introduced.