The so-called countercurrent of the plate heat exchanger is the high temperature steam from the upper, the bottom out, the time is basically condensate water, cold water from the bottom into the top out, after coming out is the hot water we need.
The so-called "downstream" is to move from top to bottom and go in one direction.
Also, it should be noted that the plate heat exchanger has four holes, two on top and two on the bottom.
From the heat transfer, the countercurrent is better than the current, and the heat transfer coefficient is high.From the theory and the reality, the countercurrent is better than the current heat transfer effect.