Analysis of microscale inner-grooved tubes during condensation of low-GWP R1234ze(E): Flow regime visualization and enhancement factors

Abstract

Abstract In an attempt to attenuate the global warming contribution in the refrigeration industry, several regulations have been legislated. HydroFluoroOlefins (HFOs) could be construed as feasible candidates from which R1234ze(E) with GWP approximately equal to unity for various applications has been subjected to experimental investigations. Owing to its prevalence in many industrial applications, flow condensation and boiling inside tubes have received particular attention in such experimental campaigns. The current experimental investigation aims at determining the degree of augmentation of the thermal performance with the usage of inner grooved tubes. In this case, tubes with various geometrical properties are employed for flow condensation of R1234ze(E) at a saturation temperature of 30°C. Measuring the experimental heat transfer coefficient (HTC) allows obtaining the enhancement factor of the enhanced tube which is defined as HTC of an inner grooved tube to that of a conventional smooth tube of the same diameter. Furthermore, since the efficacy of enhanced surfaces is directly linked to prevailing flow patterns, for different operating conditions (G = 100 to 400 m−2 s−1, x = 0.01 to 0.95) the flow pattern has been identified with the aid of a high-speed camera. Lastly, results of flow pattern visualizations and enhancement factors are provided on a non-dimensional graph of EF (enhancement factor) versus JG (non-dimensional gas velocity) that allows a comprehensive performance analysis of enhanced surfaces.