While a considerable body of research exists regarding enhancements of the heat transfer using nanofluids, the basic hydraulic phenomenon of a nanofluid has not been investigated as much. Several studies were reported related to the pressure drop of nanofluid flow and a few researches on the hydraulic characteristics of two-phase nanofluid flow were conducted. Even though there is much attention towards the heat transfer performance of nanofluid, it is also required to identify the basic hydraulic phenomenon of nanofluid especially in the two-phase flow region. For the pre-analysis of the two-phase flow analysis, CFD analysis of the vertically upward two-phase flow in a helical wire inserted tube was performed. Based on the various turbulence models and interphase momentum transfer models, vertically upward two-phase air-water flow was analyzed in Part Ⅰ. And the two-phase flow experiment, especially using nanofluids, were conducted in Part Ⅱ and results were analyzed using the models which were studied in Part Ⅰ.
PartⅠ. Two-phase Flow Analysis in a Helical Wire Inserted Tube using CFD Code
An analysis on the two-phase flow in a helical wire inserted tube using commercial CFD code, CFX11.0, was performed in bubbly flow and annular flow regions. The analysis method was validated with the experimental results of Keishi Takeshima. Bubbly and annular flows in a 10 mm inner diameter tube with varying pitch lengths and inserted wire diameters were simulated using the same analysis methods after validation. The geometry range of p/D was 1-4 and e/D was 0.08-0.12.
The results show that the inserted wire with a larger diameter increased swirl flow generation. An increasing swirl flow was seen as the pitch length increased. Regarding pressure loss, smaller pitch lengths and inserted wires with larger diameters resulted in larger pressure loss. The average liquid film thickness increased as the pitch length and the diameter of the inserted wire increased in the annul...