heat transfer, forced convection...?

Question

how does it affect the system if the fluid is laminar or turbulent?

Answer 1

Heat transfer in cases of convection is referring to heat moving from (or to) one material and a fluid.

For instance, a person standing out in the wind is having heat transfered from himself, into the colder wind. If the wind is blowing slowly, the flow of air across the person might be laminar in some places. In that case the air would move steadily across from one place to another.

Imagine a cold wind blowing on a window of a heated room. If the flow of air is laminar, the air would contact the window at one edge and that same bit of air would move all the way across the window heating up as it goes. By the end of trip across the window the air has heated a lot and is no longer pulling as much heat from the room and window.

With turbulent flow, the air contacts the window at one edge but the "stirring" effect of the turbulent flow almost immediately moves that bit of air away and brings new fully cold air into contact with the window.

You can see that turbulent fluid will cause much higher heat transfer than laminar flowing fluid.