Question

For free convection from a surface to the ambient fluid, an increase in Grashof number

a. may cause the flow to change from turbulent to laminar.
b. always causes the flow to change to laminar if the flow is turbulent. c. always causes the flow to change to turbulent if the flow is laminar. d. may cause the flow to change from laminar to turbulent.

Answer 1

Answer: Option(d) is the correct option

Step-by-step explanation:

Grashof number (Gr) is the ratio that is between buoyant force to viscous force persist on fluid on layer of velocity boundary.It is in dimensionless form.

According to the question ,

Laminar flow has
`10^(3)` < (Gr) <
`10^(6)`as range of boundary layer for free convection.

For transition to take place into turbulent form, it has range of
`10^(8) < Gr < 10^(9)` in terms of free convection.

So, if Grashof number (Gr) is increased then it might tend to change flow from laminar form into turbulent form for free convection.

Other options are incorrect because increasing in Grashof number does not always change the flow mechanism from laminar to turbulent or vice versa neither may cause to laminar flow. Therefore, the correct option is option(d).