I heard about radial fans are better when cooling printed objects. But I couldn't find one from local stores. so I thought about make one from an ordinary fan.
Break your 50mm fan, sand it, and glue it with printed parts.
Try this at your own risk. There is so much chance to make your fan useless. Glue it carefully and make sure that there is no interference at all.
Also note that it is not performing well. Wind is not strong enough as I expected. I can even feel airs turning back from inlet. Definitely for my bad design.