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The effects of submergence ratio and gas flow rate on the performance and hydrodynamic behavior of air–liquid two-phase flow have been investigated during liquid lifting in the developed bubble-generator-type airlift pump system. Here, a mechanistic model was also developed to predict the performance of the bubble-generator-type airlift pump system on the basis of pressure balance with considering the intake angle of the injector, and the suction pipe length. A developed image processing technique was implemented to determine the hydrodynamic behaviors including gas slug velocity, water slug velocity, slug length, and gas hold up under the various submergence ratio and gas flow rate. The submergence ratio is the ratio between the static lift and the sum of static lift and static head. The experimental result was found that the minimum air flow rate for removing water is reduced by 19.17% when the airlift pump is combined with an orifice-type bubble generator. The decrease in submergence ratio causes the lower the efficiency at the critical point of airlift pump-bubble generator. Under the same submergence ratio, an increase in the supplied air superficial velocity increased the hydrodynamic parameter. A mechanistic model from pressure balance and dimensional analysis have a maximum error of 11.97% and 3.33%, respectively. [ABSTRACT FROM AUTHOR]

An experimental study on the contact angle dynamic during the impact of single water droplet onto a hot flat practical stainless steel surface under medium weber number was performed. The tested solid material was practical stainless steel of SUS 304. The surface roughness of the hot surface, the static contact angle at ambient pressure, and the diameter of the solid materials were respectively Ra = 0.2 µm, 85.7o, and 30 mm. The surface temperatures were varied from (60–200) oC. The liquid droplet diameter was 2.4 mm. The Weber numbers were 52.1, 57.6, and 63.1. The dynamic contact angles of single droplet during the impact were determined by implementing the developed image processing technique of the obtained video images from experiments. As a result, it was found that (1) the time needed to reach a maximum diameter of single droplet on a flat hot solid surface decreases with the increase of surface temperature, (2) the increase of the Weber number will postpone the spreading of the droplet from its receding, (3) there are three regions of the dynamic contact angle during the liquid evaporation, those are transient spreading region (region 1), a quasi-mechanical equilibrium region (region 2), and transient evaporation region (region 3), and (4) The contact angle in quasi-mechanical equilibrium region the under the nucleate boiling is insensitive to the surface temperature. [ABSTRACT FROM AUTHOR]

The effects of the wettability of a droplet impacting onto a hot solid surface under medium Weber numbers were studied experimentally. The Weber numbers used in the present experiment were 52.1, 57.6, and 63.1. Three kinds of solid surfaces with different wettability were used. These were normal stainless steel (NSS), TiO coated NSS, and TiO coated NSS radiated with ultraviolet rays. The surface temperatures were varied from 60 to 200 °C. The image of side the view and 30° from horizontal were taken to explain the spreading and the interfacial behavior of a single droplet during impact the hot solid surfaces. It was found that under medium Weber numbers, the surface wettability plays an important role on the droplet spreading and evaporation time during the impact on the hot solid surfaces. The higher the wettability, the larger the droplet spreading on the hot surface, and the lower the evaporation time. [ABSTRACT FROM AUTHOR]