What happens in a convection cell?

In the field of fluid dynamics, a convection cell is the phenomenon that occurs when density differences exist within a body of liquid or gas. The colder, denser part of the fluid descends to settle below the warmer, less-dense fluid, and this causes the warmer fluid to rise.

Explanation:

When density differences exist within a body of liquid or gas,

v=ir = 3x15 =45 v