Describe from the mechanical engineering point of view. What are the uses of these fans in the ventilation systems?

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The axial-flow fans have blades that force air to move parallel to the shaft about which the blades rotate. Axial fans blow air across the axis of the fan
It is generaly...

heat loss through inverters and other thing is 5 kw & temp. rise in panel is around 10 deg.c
i want to calculate the air flow required and the static pressure to select the fan.can anybody help me?

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See:
http://www.hoffmanonline.com/product_cat alog/tech_resources.aspx?cat_1=34&ca t_2=137&SelectCatID=137&CatId=13 7

about half way down the page under thermal management

I'm looking for an axial fan with the following to life a home-made hovercraft:

operates on 12V batteries
has 2 fan-blades counter rotating so there is no torque on the craft
is roughly .5kg or less
is between 30-70