The Investigation Of The Gas-liquid Interfacial Phenomenon And Two-phase Pressure Drop In Minichannel

Due to the high performance in heat and mass transfer and high level of integration of the minichannel, it is widely used in many fields such as microelectronics, bio-medical, cryogenic refrigeration, chemical industry, power engineering and aerospace industries. However the minichannel is quite different from the conventional channel in many aspects, when the two-phase pressure drop and flow pattern models derived from the conventional channel are applied for the prediction of the two-phase pressure drop and flow patterns, poor results are obtained. So further investigation on the two-phase flow patterns and pressure drop are necessary. This paper did experimental and numerial research on the two-phase flow in minichannel, and the influences of void fraction(the liquid mass flux, the gas flow rate), different gas-phase working fluids and different inner diameters were taken into account.According to the visual experimental study and numerical simulation results, as for the channel with 2 mm inner diameter, under given gas flow rate, with increasing initial liquid mass flux, the pressure drop increases linearly and only elongated slug flow was observed, while with increasing gas-phase flow rate when the initial liquid mass flux is keep constant, the variation of pressure drop is not linear any more, and only elongated slug flow was observed. For the slug observed in this paper, there were smooth slug, bubble-slug and slug-slug interface morphologies, and intense fluctuation were observed in the three interface morphologies. The gas-liquid two-phase interface morphologies observed in these working comditions agreed well with the simulation resluts.For different gas phases with 2 mm inner diameter, under given liquid mass flux, the time-averaged bubble lengths of carbon dioxide and nitrogen increase along with the increasing gas flow rate; while the time-averaged bubble lengths of argon and air increase first then decrease and increase finally and the time-averaged bubble length of carbon dioxide is the shortest. The time-averaged gap for air, nitrogen, and argon between two consecutive bubbles decreases with the increasing gas flow rate, while the time-averaged gap for carbon dioxide decreases first and then increases later.With nitrogen as gas phase, water as liquid phase, under given liquid mass flux and gas flow rate, the flow patterns observed in the channels with 1 mm、2 mm、6 mm inner diameters were elongated slug flow, elongated slug flow and elongated bubble flow respectively. Along with the increasing inner diameter, Mo number was constant, while Eo number increased indicating that the influence of surface tension on the two-phase interface was weaker and weaker comparing with that of gravity. The fluctuation of the gas-liquid interface become intenser while the pressure drop and mass flux fluctuation become mild with the increasing inner diameter.