Convection
Summary
- Convection is the transfer of heat by the flow of a fluid.
- Spontaneous convection…
- is caused by the buoyancy 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
- is caused by the buoyancy differences between
- Forced convection…
- is aided by fans, blowers, impellers, lung power, etc.
- is described by newton's law of cooling
P = dQ = hA(T − T0) dt P = dQ/dt = the 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