Mechanisms of Energy Transfer (Heating): (Heat describes energy flow - - PowerPoint PPT Presentation

Mechanisms of Energy Transfer (Heating):

(Heat describes energy flow from hot -> cold, not amount of energy and object has) Conduction: Transfer of kinetic or vibrational energy by direct molecular

• collisions. What could maximize

conduction efficiency? Convection: Spontaneous transfer of thermal energy by turbulent mixing in

• fluids. What conditions might

maximize convection? Radiation: Transfer of energy by electromagnetic waves. Only mechanism that doesn’t need a medium for transfer. What could prevent radiative transfer?

?

How does direct radiation from the sun warm a cup of water (PS 2) ?

T mc Q

a) (power/are density radiation solar incoming

2

m W A P

Q(in J)=Total Energy= Power x time x area P( in W) = Power = Energy / time

1

A t A P Q c m A t A P T

1

Simple Thermodynamic Relationships

Assumptions in calculating Temp. warming:

• No significant net heat lost by conduction, convection, or radiation

(this is BS except for rare special circumstances)

• All incident solar radiation is absorbed

(or reduced by known albedo)

• Uniform temperature of object

Substance Phase cp J g−1 K−1 Air (Sea level, dry, 0 °C) gas 1.0035 Air (typical room conditionsA) gas 1.012 Aluminium solid 0.897 Ammonia liquid 4.700 Copper solid 0.385 Diamond solid 0.5091 Gasoline liquid 2.22 Gold solid 0.1291 Graphite solid 0.710 Iron solid 0.450 Lead solid 0.127 Lithium solid 3.58 Magnesium solid 1.02 Mercury liquid 0.1395 Nitrogen gas 1.040 Oxygen gas 0.918 Paraffin wax solid 2.5 Silica (fused) solid 0.703 Uranium solid 0.116 Water gas (100 °C) 2.080 liquid (25 °C) 4.1813 solid (0 °C) 2.114

Typical Heat Capacities:

Average Emitted infrared radiation

Incoming solar radiation for August

Solar radiation absorbed yesterday

August solar radiation absorbed by surface

Sea Surface Temperatures

Sea Surface Temperature Anomaly