In the one fermenter, the temperature everywhere is not same. And the direction of convection in main fermentation is opposite from secondary fermentation.

1.Main fermentation stage

The beer with high temperature will flow to top. So, in this stage, it should to strengthen the cooling of upside of fermentation tank. Cooled beer will flow to bottom, while beer in higher temperature continue to flow upside.
Keep recycling, it will not end until up to the needed temperature.

2.Secondary fermentation stage

Now, the direction of beer flowing is different from main fermentation stage. Its working principle is similar with water. The water in 4℃ has biggest density. So the when the water temperature is lower than 4℃，water will flow from bottom up. Similarly, beer has biggest density in 2.5℃（Beer in higher concentration has biggest density in 1℃, beer in lower concentration will has biggest density in 3℃）。So, in the secondary fermentation stage, the beer temperature is higher in upside, lower in bottom. So the direction of beer convection is beer in lower temperature flow to top, in higher temperature flow to bottom. So, in secondary fermentation stage, it should strengthen the cooling of bottom of conical fermenter. So it will improve the cooling effect. 
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