The experimental and numerical study of the vertical gas movement in the cylindrical channel

Abstract

The detailed experimental and theoretical studies of the vertical gas movement through a layer of liquid (water, molten tin) placed in a cylindrical channel (10 cm diameter) were performed. It was shown that during the gas passage through a single opening (the diameter of 8 mm) its movement at a small flow takes place as single bubbles, whose diameter becomes greater as they move towards the free surface of the liquid. Increase in the diameter at identical gas and liquid temperatures is explained by the decreasing liquid pressure in the upstream direction. If the gas temperature is lower than the liquid temperature, the diameter of bubbles increases also due to gas heating, thus resulting in the increase of its pressure in the bubble. As the gas flow increases, the number of bubbles which then merge into the uniform mass in the upper part of the channel without reducing their diameter, becomes greater. When passing the gas though the diaphragm with a high number of openings (80 openings of 1 mm in diameter), the amount of bubbles becomes higher, however their diameter in the upper part of the channel practically does not increase. When using multiple strainer diaphragms arranged at small distances from each other along the channel height, the diameters of bubbles become considerably reduced, which is connected with their periodic fragmentation when passing through each subsequent strainer. Furthermore, the bubbles get the smallest diameter when they pass through the last strainer, after which the liquid and the gas make a uniform gas and liquid emulsion in the form of a mist. The analysis of the results of air passage thought the molten tin (at a temperature of 300°C) allows concluding on considerable increase in the bubble diameter as compared to the experiments with water, which is explained by gas heating in the bubbles due to a sufficiently high temperature of tin and, as a result, the increase of pressure in them. Experimental studies applicable to small-diameter cylindrical channel (2 cm) were also performed. Their analysis allows concluding about a considerable divergence of the obtained results as compared to the greater diameter channel (10 cm) at the same gas flow. For the small-diameter channel, numerical calculations were also performed (e.g. tin) in a vertical cylindrical channel (reactor) [5 – 8]. The amount of hydrogen obtained at the reactor outlet depends on the intensity of methane heating to the pyrolysis temperature. It is known that methane passes through the molten tin in the form of bubbles, whose diameter increases as they move towards the upper part of the reactor, which is connected with the reduction of upstream pressure of liquid metal as well as the increase of gas pressure in bubbles resulted from its heating. The increase in the bubble diameter makes it heating to the pyrolysis temperature difficult as a result of low heat conductivity of methane. In this regard, measures should be taken to decrease their diameter.