Heat transfer problems with a temperature difference greater than the critical temperature difference

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This post was last edited by kaminocmyhc on 2009-9-3 08:49. There are certain limits on the heating temperature difference for the reboiler, the amount of condensation of the heating steam, and the cooling temperature difference of the condenser; these values must not exceed the critical temperature differences. Generally, as the temperature difference increases, the number of vaporization nuclei and the rate at which bubbles grow also increase. When a certain temperature difference is exceeded, a large number of bubbles accumulate in the heated surface layer, forming a steam film. Heat must be transferred from this film into the liquid, and due to the low thermal conductivity of steam, heat transfer becomes difficult, resulting in a decrease in the film coefficient. At this point, the temperature difference at which nucleate boiling transitions to film boiling is the critical temperature difference. May I ask, how large is this critical temperature difference generally? If the bottom of the tower needs to be heated to 120 degrees, and only steam at 150 degrees is available, how can it be ensured that the heating temperature difference remains below the critical value?