Convective boiling for horizontal tubes
Phase change heat transfer Flow boiling

For reasons of compactness and size, horizontal tubes are sometimes used, for example in refrigeration machine evaporators. Near-horizontal tubes are also used in coaxial spiral evaporators. In multi-tube evaporators with vertical tubes, the connecting elbows are also horizontal tube sections.

In such a flow configuration, the effect of gravitational forces on two-phase flow is not symmetrical and can lead to a separation of the liquid and vapor phases: stratification. The upper part of the tube is then dried out, and boiling can only occur on a limited portion of the tube cross-section wetted by the liquid.