Experimental study on falling film evaporation heat transfer of R-1233zd(E) on horizontal enhanced tubes for high-temperature industrial heat pump applications

초록

Among various evaporator designs, falling film evaporators have garnered significant interest due to their low refrigerant charge and high heat transfer efficiency. Most previous studies have focused on conventional refrigerants, and reliable heat transfer data for low-GWP (Global Warming Potential) alternatives to replace conventional refrigerants remain limited. This study experimentally investigates the external heat transfer characteristics of enhanced tubes for falling film evaporators using R1233zd(E), a promising low-GWP refrigerant suitable for high-temperature industrial heat pump applications. Three horizontal enhanced tubes with different fin pitches (FPI (Fin Per Inch) = 45, 48, 52) were tested under same saturation and heat flux conditions. The external heat transfer coefficient was evaluated as a function of falling film Reynolds number. Results revealed that the enhanced tubes achieved up to 4.5 times higher heat transfer performance compared to a smooth tube. Based on the experimental data, a Nusselt number correlation incorporating fin geometry was proposed. The developed correlation demonstrated robust predictive capability for high-temperature industrial heat pump applications, accurately estimating 95 % of experimental data within a +/- 18 % error margin. These findings not only offer valuable insights into the heat transfer mechanisms of falling film evaporation using R1233zd(E) but also provide a practical reference for the design and optimization of industrial falling film evaporators operating with next-generation refrigerants.

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