Free(Natural) Convection \TE) P a>0 <0 <0 dx Unstable Stable, Bulk fluid motion No fluid motion Grashofnumber in natural convection is analogous to the reynolds number in forced convection G2=8B(7,-Tm)3 Buoyancy forces Viscous forces Natural Natural Rel convection can Re 2 convection be neglected L dominates Heat Transfer Su Yongkang School of Mechanical EngineeringHeat Transfer Su Yongkang School of Mechanical Engineering # 9 Free (Natural) Convection • Grashof numberin natural convection is analogous to the Reynolds number in forced convection Unstable, Bulk fluid motion Stable, No fluid motion ( ) Viscousforces Buoyancy forces 2 3 = − =   g  T T L Gr s L 1 Re2  L GrL 1 Re2  L GrL Natural convection dominates Natural convection can be neglected