Convection & Buoyant Force

By Ross Nuechterlein
Convection is the movement of molecules
within fluids and is one of the major modes of
heat and mass transfer in liquids and gas.
Buoyancy is an upward
acting force exerted by a
fluid , that opposes an
object's weight.
Buoyancy = weight of
displaced fluid.
A change in Temperature, Salinity or Density causes
a fluid parcel to have vertical tendencies until a great
enough force is achieved. Until then:
Transport takes place horizontally till the downward
force becomes greater than the rising force below.
Natural Convection
Gravitational Convection
 Forced Convection
 Granular Convection
 Thermo magnetic
Occurs due to temperature differences affecting
density resulting in buoyancy (more or less
This leads to bulk fluid movement.
More rapid movement between two fluids of
large density differences.
Larger acceleration occurs through greater
Induced by buoyancy variations resulting from
material properties other than temperature.
Variable salinity in water is a frequent cause of
ocean convection.
Dependant on the effects of gravity and does
not occur in micro gravity environments
Solar radiation warms
the oceans near the
Equator, driving warm
water toward the poles.
Cold polar water
replaces displaced
warm water at the
equator creating
Density differences also drive ocean convection
due to varying salinity. This is known as
Thermohaline convection.
In some cases warm saline water may sink
being replaced by cooler fresher water which
rises. This reverses the transport of heat.
Deep Ocean circulation is important because it
determines the vertical stratification of the
ocean and because it also modulates climate.
This circulation is caused by the convection
processes discussed.
Stewart, R. H., 2002. Introduction to Physical
Open ocean convection: observations, theories,
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