| Abstract: | Boiling – stabilizer and destabilizer of safe operation. Boiling is used in power- and chemical engineering if large quantities of energy have to be transported and if high heat-flux densities have to be applied. The stabilizing action of boiling, which is already high due to the large heat transfer coefficients and small temperature differences, is further improved by the fact that heat transfer still increases with increasing energy addition. Even if single-phase liquid flow is present under normal operation conditions power fluctuations can be overcome without impermissible temperature rise due to the onset of subcooled boiling. Beyond a critical heat-flux, however, film boiling starts which decreases the heat transfer coefficient by orders of magnitude. In apparatus in which the fluid is transported under conditions of high void fraction it should be ensured that the liquid film at the wall is thick enough to guarantee a sufficient heat transport. Also, under these conditions boiling can stabilize or destabilize the energy transport. |
