Why are mosquito coils in a whirlpool shape?
This is a combination of the word 渦 meaning "whirlpool" and 巻く meaning "to roll." A rolling whirlpool is still a whirlpool, just a really violent one.
This is a combination of the words 渦 and 巻く. 巻く becomes 巻き and you just add 渦 to it. So reading this should be pretty simple.