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Convection
Summary
- Convection is the transfer of heat by the flow of a fluid.
- Spontaneous convection …
- is caused by the boyancy differences between
- warmer, less dense fluid and
- cooler, more dense fluid
- is also caused by differences in surface tension between
- hotter regions with less surface tension and
- cooler regions with more surface tension
- can be summarized in two simple rules
- hot fluid rises
- cold fluid sinks
- will result in the formation of closed loops of circulating fluid called convection cells
- Forced convection …
- is aided by fans, blowers, impellers, lungpower, etc.
- is described by newton's law of cooling
where …
P = dQ/dt is rate at which heat is transferred
h = convection heat-transfer coefficient (or film coefficient or film conductance)
A = exposed surface area
T = temperature of the immersed object
T0 = temperature of convecting fluid
- heat-transfer coefficients are determined experimentally
