Condensation Heat Transfer and Pressure Drop of R134A in Horizontal Micro-Scale Enhanced Tube

This study was performed to investigate the heat transfer and pressure drop of R134A during condensation inside a stainless steel micro-scale enhanced surface tube (EHT tube) and smooth tube. The tests were conducted at a saturation temperature of 45°C, over the mass fluxes range of 100 to 200 kg/m2s, the heat fluxes of 14–25 kW/m2, an inlet vapor quality of 0.8 and outlet vapor quality of 0.2. The heat length and inner diameter of the tested tube were 2 m and 11.5 mm. The micro-scale enhanced surface tube has complex surface structures composed of dimples and petal arrays background patterns. It can be observed the condensation heat transfer coefficients of the EHT tube is about 1.6–1.7 times higher than that of a stainless steel smooth tube. Enhancement of the EHT tube was achieved due to disruption of the boundary layer, secondary fluid generation, increasing fluid turbulence and heat transfer area. In addition, considering the friction pressure drop, the EHT tube produces the larger friction pressure drop, which is 1.05–1.20 times as compared to the smooth tube. Finally, the performance factors were performed to evaluate the enhancement effect of the EHT tube based on heat transfer coefficient-pressure drop evaluation criteria value (η1) and heat transfer coefficient-area evaluation criteria value (η2).

Study on the Influence of the Heaving Condition on the Pressure Drop Characteristics of the Two-Phase Flow in the Circular Tube

The experimental study on the pressure drop characteristics of the gas-liquid two-phase flow under heaving condition is carried out. The influence of the heaving condition on the transient and time-averaged two-phase pressure drop is obtained. On this basis, the calculation model of two-phase transient pressure drop under heaving condition is constructed, which is in good agreement with the experimental results. According to the experimental data and the results of the model calculation, the influence of heaving condition on the pressure drop components is analyzed. It is found that the transient total pressure drop is fluctuating periodically, while the time-averaged value is nearly the same as that under static condition. Further analysis shows that the friction pressure drop and the gravity pressure drop are basically the same under heaving condition. The fluctuation of additional pressure drop introduced by heaving motion is the reason for the periodic fluctuation of the total pressure drop.