Condensation of ammonia and high-temperature-glide zeotropic ammonia/water mixtures in minichannels – Part II: Heat transfer models

Abstract

In this two-part study, a comprehensive experimental investigation of the condensation of pure ammonia and zeotropic mixtures of ammonia/water is conducted and improved models for predicting condensation heat transfer are developed. In Part I, condensation heat transfer experiments were conducted with ammonia and ammonia/water mixtures. In Part II, a heat transfer model is developed for condensation of ammonia in mini/microchannels. The model is validated with data and shows a significantly improved predictive capability (AAD=12.8% for all ammonia data) compared to models and correlation developed for different classes of fluids and channel geometries. Using the insights derived from the pure ammonia model, an improved zeotropic condenser design method for high-temperature-glide ammonia/water mixtures in small diameter channels, based on the non-equilibrium film theory, is introduced. The key features of the improved model are the consideration of annular and non-annular flow effects on liquid film transport, including condensate and vapor sensible cooling contributions, and accounting for mini/microchannel effects through the new liquid film correlation.