INVESTIGATION OF THERMAL-HYDRODYNAMIC HEAT TRANSFER PERFORMANCE OF R-1234ZE AND R-134A REFRIGERANTS IN A MICROFIN AND SMOOTH TUBE

This research is based on R-1234ze that is considered a substitute for R-134a due to its low global warming potential in a microfin tube with outer diameter 9.52 mm, the number of fins 70, and fin height 0.17 mm. In comparison, a smooth tube with similar geometries was used to study pressure drop and heat transfer coefficients related to the two fluids. The microfin tube was brazed inside a stainless steel tube and heated electrically. T-type thermocouples were used to measure the temperature distribution during the phase change process. The experimental saturation temperatures and refrigerant mass velocities varied from 10-20 degrees C and 50-300 kg/m(2) s, respectively. The vapor quality ranged from 0.1 to 0.9 and heat flux from 5 to 11 kW/m(2). The results showed that heat transfer performance of R-134a in both microfin and a smooth tube was better than R-1234ze, especially at mass velocities above G = 100 kg/m(2) s. However, R-1234ze yielded better heat transfer coefficients at mass velocities lower than G = 100 kg/m(2) s. The pressure gradient of R-1234ze was markedly higher than that of R-134a at all mass flow rates.