The heat exchanger without phase change only considers sensible heat exchange, that is, temperature difference is the driving force. The heat exchanger with phase change will change its phase state. If the temperature of the heat exchanger wall is lower than the dew point temperature of the air, the water vapor in the air will condense and condense into water on the heat exchanger (assuming that it is a film, i.e. a layer of water film). This layer of water film will transfer the heat released from condensation (condensation heat) to the heat exchanger wall to realize heat exchange, because the heat of condensation heat is very large, and water The heat transfer coefficient is larger than that of air, so the heat transfer effect is good and the heat transfer is also large. Therefore, the heat exchange effect of heat exchanger with phase change is good.
The condensation heat transfer in phase change heat transfer is divided into film condensation and bead condensation. These two heat transfer are better than the second, but film condensation is often encountered in engineering. Although the second kind of condensation is expected to happen, but the technology is difficult, so when it comes to film condensation heat transfer, in order to achieve better heat transfer, it is necessary to thin the film thickness and remove non condensable gas, etc The heat transfer effect of turbulent film is better than that of laminar film
In fact, it's very wonderful. I can't understand what I said in depth. (Tucao: Next: professional words are not spelled out, and they make complaints about each other.