Two-phase flow

Two -phase flow refers to the flow of fluid mechanics of a mixture of two phases. It usually is a liquid and a gaseous phase. A basic distinction between a one-component two-phase flow, this would be an important application, the flow of a mixture of boiling water and water vapor in the energy technology, and the evaporative cooling, and a multi-component two-phase flow, such as water and air. In general, both phases do not flow with the same velocity in the pipe.

Phase distribution

Depending on the velocity and mass flow ratio of the two phases to provide a different characteristic distributions of the phases over the cross section of the flow channel, which is also called flow patterns. For an up- perfused tube can be usually four main groups, namely, bubble flow, piston bubble flow, annular flow and sprinkling stream differ. The adjusting to flow resulting from the pressure prevailing in the flow and acting on each of the phases forces.

Phase distribution of states

H. Brauer has shown appropriate general phase distribution of states for the existing flow directions. In bubble flow, the gas phase is uniformly dispersed in the continuous liquid phase. It can be assumed that the velocity of both phases is equal to (slip = 1). If there is an increase in the proportion of gas, so more and more bubbles grow together and form a gas piston, one observes a piston bladder or piston flow. A further increase of the gas component in the horizontal pipe ultimately leads to the laminar flow. In this case, gas and liquid flow, separated by their density by the layered tube, said small bubbles may be present in the liquid phase. In a vertical tube type of flow this is not observed. This also applies to the shaft and the slug flow, in which the gas stream has a shear stress is transferred to the liquid that causes waves on the assumption of a specific value. At a certain gas flow rate individual wave crests reach such a large amount that they are used as surge pushed through the tube. The plug flow again occurs in the vertical and in the horizontal pipe. Gas plug push through the tube, the liquid surrounding them, and covered the pipe wall. At very high gas flow rates, a film flow, and annular flow is called from. The liquid only forms a film on the tube wall. Usually, the gas flows faster than the liquid (slip > 1). The outer border of the case, two-phase flow is represent those sprinkling stream or mist, the liquid droplets are distributed homogeneously in the gas phase.