Entropy generation and sensitivity analysis of R134a flow condensation inside a helically coiled tube-in-tube heat exchanger

Entropy generation analysis is a key to evaluating heat transfer augmentation along with pressure drop in enhanced heat exchangers. In the present study, entropy generation during R134a flow condensation inside a helically coiled tube-in-tube heat exchanger is investigated. In that regard, heat transfer and pressure drop contributions to entropy generation are assessed and compared for such condensers. Also, the influence of variation in geometrical parameters and flow conditions on entropy generation is studied. The findings reveal that larger tube diameters and diameter ratios, higher mass and heat fluxes and inlet vapor qualities, and lower saturation temperatures result in higher entropy generation. Additionally, a sensitivity analysis is conducted to analyze such condensers' sensitivity to changes in geometrical and flow conditions from an entropy generation perspective. The analysis results indicate that at high mass velocities (G >= 300 kg.m(-2).s(-1)) and inlet vapor qualities (x >= 0.5) and low saturation temperatures (T-sat <= 46 degrees C), coils with larger tube diameters are of higher sensitivity to alterations in aforementioned flow conditions, while coils with different coil diameters are of nearly the same sensitivity at both high and low ranges of flow parameters. On the contrary, when heat flux changes, coils with larger coil diameters are seen to be more sensitive to entropy generation, while coils with different tube diameters show virtually the same level of sensitivity. (C) 2021 Elsevier Ltd and IIR. All rights reserved.