State-of-the-art assessment-based review of boiling heat transfer and friction factor correlations for NH3–H2O, NH3–LiNO3 and NH3–LiNO3–H2O mixtures in a plate heat exchanger

Abstract

The increasing demand for energy-efficient and environmentally sustainable cooling technologies has led to a renewed focus on ammonia and lithium nitrate-based absorption refrigeration systems, particularly those utilizing Plate Heat Exchangers (PHEs). Despite their importance, reliable predictive models for boiling heat transfer and frictional pressure drop in PHEs using ammonia and lithium nitrate mixtures, such as NH<inf>3</inf>–LiNO<inf>3</inf> and NH<inf>3</inf>–LiNO<inf>3</inf>–H<inf>2</inf>O, remain limited and often suffer from structural deficiencies. This study provides a comprehensive evaluation of existing correlations for boiling heat transfer and friction factor in PHEs, specifically focusing on ammonia-based mixtures (NH<inf>3</inf>–H<inf>2</inf>O, NH<inf>3</inf>–LiNO<inf>3</inf>, and NH<inf>3</inf>–LiNO<inf>3</inf>–H<inf>2</inf>O). More than 20 correlations for boiling heat transfer coefficient and friction factor were critically analysed and adjusted to account for the unique thermophysical behaviors of multi-component salt mixtures. The study reveals that many correlations fail to accurately predict boiling heat transfer in NH<inf>3</inf>–H<inf>2</inf>O mixtures due to inadequate sensitivity to heat flux. Scaling these correlations led to notable improvements in prediction accuracy, underlining the significance of appropriate scaling for different PHE configurations. Additionally, the study validates the assumption that lithium nitrate remains in the liquid phase in NH<inf>3</inf>–LiNO<inf>3</inf> and NH<inf>3</inf>–LiNO<inf>3</inf>–H<inf>2</inf>O mixtures, supporting its exclusion from latent heat calculations. Friction factor correlations that include positive exponents for Reynolds and Weber numbers were found to be structurally inconsistent, resulting in inaccurate predictions. The analysis further highlights that many correlations are overly empirical or based on narrow experimental conditions, limiting their applicability to diverse heat exchanger geometries. A key contribution of this work is the unique visual comparison of the correlations, providing a detailed depiction of their structural characteristics and offering more precise insights than those available in previous studies. © The Author(s) 2025.