Final Superheater Heating Surface

However, this advantage of austenitic over martensitic materials generally apphes only to base-load operation of the steam generator. In case of operation with daily start-ups and shutdowns, the austenitic steels can show worse corrosion properties than the martensitic ones. The resulting higher corrosion rates can be explained by the large difference between the thermal expansion coefficients of the austenitic tube material and of the oxide deposits, which lead to spaHing of the oxide layer and thus result in an increased corrosive attack. 

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Figure 10 presents the interface shape of the rivulet for wall superheat as 0.5 K and Re = 2.5. Here also presented the data on pressure in liquid and heat flux density in rivulet cross-section. The intensive liquid evaporation in near contact line region causes the interface deformation. As a result the transversal pressure gradient creates the capillarity induced liquid cross flow in direction to contact line. Finally the balance of evaporated liquid and been bring by capillarity is established. This balance defines the interface shape and apparent contact angle value.For the inertia flow model, the solution is obtained from a non-stationary system of equations, i.e., it is time-dependable. In this case the disturbances in flow interface can create the wave flow patterns. The solutions of unsteady state liquid spreading on heat transfer surface without and with evaporation are presented on Fig. 11. When the evaporation is not included (for zero wall superheat) the wave pattern appears on the interface. When the evaporation includes, the apparent contact angle increase immediately and deform the interface. It causes the wave suppression due to increasing of the film curvature.

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