*2.3.2 Forced circulation*

 The circulation of water in such boiler is provided by the feed pumps [21]. This circulation allows great liberty in circuit design, since circulation is always assured. In addition, the diameter of the tubes may be smaller than in natural circulation boilers. In forced circulation boilers, the water vaporized in totality by the unstable film evaporation regime and then by stable film is established necessarily in the final parts of the circuit; it must then be controlled that the speed of the emulsion is sufficient to ensure the cooling of the tube. Forced circulation boiler can be used for all subcritical and supercritical pressures.
