Effect of tube diameter on pressure drop characteristics of refrigerant–oil mixture flow boiling inside metal-foam filled tubes

The objective of this study is to analyze the effect of tube diameter on pressure drop characteristics of refrigerant–oil mixture flow boiling in metal-foam filled tubes. Experiments on metal-foam filled tubes with an inner diameter of 7.9 mm were performed, and the analysis of the diameter effect was done based on the experimental data of 7.9 mm tubes together with those of 13.8 mm and 26.0 mm from literature. The research results show that, the pressure drop increases with increasing PPI, and the impact of PPI becomes insignificant as the tube diameter decreases. When the diameter decreases from 13.8 mm to 7.9 mm, the pressure drop decreases due to the incomplete cells and randomly chopped ligaments nearby tube wall, and the maximum decrements are 22% and 35% for 5 PPI and 10 PPI metal-foam filled tubes, respectively. A new pressure drop correlation was developed, and it agrees well with the experimental data for different diameter tubes.