Effects Of Pipe Diameter And Dynamic Load On The Flow And Heat Transfer Characteristcs Of Two-phase Boiling Flow

A rotation platform is used to create dynamic load. An experiment system of two-phase flow has been fixed on the platform. Single-phase water flow and boiling two-phase flow was obtained by means of electric heating. There are three layouts to place the test pipes, i.e. along the circumferential direction, or in the radial direction of the rotating platform, in which the flow direction can be from the edge of the platform to the center, or form the center to the edge of the platform. Though above layouts, three kinds of dynamic loads in side, same and converse directions comparing with the flow direction are created. The parameters such as heat flux, pressure, temperature, void fraction, and ratational speed are measured. The comparison tests for single-phase water flow and boiling flow in the pipes with three diameters under dynamic load were conducted respectively, so that the effects of dynamic load and diameter on their flow and heat transfer characteristics were investigated. The two-phase flow patterns in test pipe under rotation condition were obtained with a video camera.The results show that acceleration and diameter significantly influence the two-phase flow patterns, but the effect of dynamic load on flow pattern in its lower region and higher region are different. Under lower load and smaller diameter, steam-phase controls the patterns, and its symmetrical characteristic is destroyed. For higher load and bigger diameter, the water-phase controls the flow patterns, which appears symmetrical. A new kind of flow pattern, interface flow, was found under dynamic load whose direction is the same as the flow direction. The results show that the dynamic load has great influence on flow and heat transfer. The greater the dynamic load, the higher pressure drop, and the slug flow easily appears. Under this condition, it has a great challenge for the water to be heated or cooled steadily. The greater the dynamic load, the higher the heat emission, and the lower the flow rate, the void fraction, the fluid temperature and the heat flux. Pipe diameter also has great influence on Renolds number, pressure and heat emission. In summary, dynamic load impedes fluid flow and enhances heat emission, and the pipe with smaller diameter has larger flow resistance, and good heat exchange ability.