Four types of heat transfer: conduction, convection, radiation, evaporation, and condensation.
Examples are very important.
Transfer of energy directly from direct contact of hot and cold molecules.
Examples:
Pot on a stove: heat from the burner to the pot, then to the water.
Ventilator heater (hospital setting): plate of heater touches the plate of the device on top, transferring heat to warm the water.
Touching cold metal: body heat transfers to the metal, making it feel cold.
High thermal conductivity metals quickly draw heat away from the skin, creating a feeling of cold.
Involves fluid molecules at different temperatures mixing.
Examples:
Infant incubator: air is warmed in one location and circulated to carry heat.
Forced air heating in houses: air molecules mix and warm the air.
Convective oven: molecules heat up and circulate around the food.
Heat transfer occurs without direct physical contact.
Examples:
Sunlight: radiant heat warms objects without direct contact.
Radiant heat warmer for babies: heat comes from above without direct contact.
Kerosene or electric heater: heat radiates across the room.
According to the first law of thermodynamics, energy must come from the surroundings.
Bulk storage of oxygen: Compressed liquid oxygen is exposed to ambient temperatures and vaporized into gaseous form.
Heat is taken from the air surrounding the liquid, cooling the air.
Example: Sweating - liquid sweat evaporates and cools the skin.
The opposite of evaporation; heat is given back to the surrounding air, warming it.
Example: Refrigerator - Food cools as energy is passed through the walls of the refrigerator into the pipes, warming the refrigerant which is carried into the atmosphere.
Heat always moves from hot objects to colder ones.
Materials impact heat transfer.
Conduction: Good conductors (copper, silver, iron, steel) vs poor conductors (wood, styrofoam, paper, air).
Convection: Up and down movement of gases and liquids; warmer rises, cooler falls, creating a convection current.
Radiation: Electromagnetic waves transfer heat to objects.
Melting: Changing from a solid to a liquid; it takes heat.
Latent heat of fusion: The number of calories required to change from a solid to liquid without changes in temperature.
1$$1$$ gram of solid into a liquid without changing temperature.
Freezing: Changing from a liquid to a solid
Requires a large amounts of externally applied energy
Freezing returns energy to its surroundings.
Transition from a solid to a vapor without becoming a liquid.
Example: Dry ice - it sublimates from its solid form into a gas CO2$$CO_2$$ without first melting and becoming a liquid.
Two forms:
Boiling
Evaporation
A liquid can also change into a gas at temperatures lower than its boiling point and called evaporation.
Liquid is the temp at which the vapor pressure exceeds atmospheric pressure
Boiling occurs earlier with lower atmospheric pressure and at lower temperatures.
A liquid can also change into a gas at temperatures lower than its boiling point through a process called evaporation.
Water is a good example of that.
The amount of water vapor in the atmosphere involving the kinetic energy of molecules in the air.
The actual weight or amount or weight of the water vapor in the air.
Can be measured by weighing the water vapor extracted from air.
Fully saturated or partially saturated
Air is fully saturated with the water vapor at 37 degrees Celsius and 760 millimeters of mercury, which is 43.8$$43.8$$ milligrams per liter.
Percent saturated ∗$$*$$ water vapor content (43.8$$43.8$$).
Ratio of the actual water vapor content to its saturated capacity at a given temperature.
RH=CapacityContent∗100$$RH = \frac{Content}{Capacity} * 100$$
Heat Transfer Notes
Four types of heat transfer: conduction, convection, radiation, evaporation, and condensation.
Examples are very important.
Transfer of energy directly from direct contact of hot and cold molecules.
Examples:
Pot on a stove: heat from the burner to the pot, then to the water.
Ventilator heater (hospital setting): plate of heater touches the plate of the device on top, transferring heat to warm the water.
Touching cold metal: body heat transfers to the metal, making it feel cold.
High thermal conductivity metals quickly draw heat away from the skin, creating a feeling of cold.
Involves fluid molecules at different temperatures mixing.
Examples:
Infant incubator: air is warmed in one location and circulated to carry heat.
Forced air heating in houses: air molecules mix and warm the air.
Convective oven: molecules heat up and circulate around the food.
Heat transfer occurs without direct physical contact.
Examples:
Sunlight: radiant heat warms objects without direct contact.
Radiant heat warmer for babies: heat comes from above without direct contact.
Kerosene or electric heater: heat radiates across the room.
According to the first law of thermodynamics, energy must come from the surroundings.
Bulk storage of oxygen: Compressed liquid oxygen is exposed to ambient temperatures and vaporized into gaseous form.
Heat is taken from the air surrounding the liquid, cooling the air.
Example: Sweating - liquid sweat evaporates and cools the skin.
The opposite of evaporation; heat is given back to the surrounding air, warming it.
Example: Refrigerator - Food cools as energy is passed through the walls of the refrigerator into the pipes, warming the refrigerant which is carried into the atmosphere.
Heat always moves from hot objects to colder ones.
Materials impact heat transfer.
Conduction: Good conductors (copper, silver, iron, steel) vs poor conductors (wood, styrofoam, paper, air).
Convection: Up and down movement of gases and liquids; warmer rises, cooler falls, creating a convection current.
Radiation: Electromagnetic waves transfer heat to objects.
Melting: Changing from a solid to a liquid; it takes heat.
Latent heat of fusion: The number of calories required to change from a solid to liquid without changes in temperature.
1 gram of solid into a liquid without changing temperature.
Freezing: Changing from a liquid to a solid
Requires a large amounts of externally applied energy
Freezing returns energy to its surroundings.
Transition from a solid to a vapor without becoming a liquid.
Example: Dry ice - it sublimates from its solid form into a gas CO2 without first melting and becoming a liquid.
Two forms:
Boiling
Evaporation
A liquid can also change into a gas at temperatures lower than its boiling point and called evaporation.
Liquid is the temp at which the vapor pressure exceeds atmospheric pressure
Boiling occurs earlier with lower atmospheric pressure and at lower temperatures.
A liquid can also change into a gas at temperatures lower than its boiling point through a process called evaporation.
Water is a good example of that.
The amount of water vapor in the atmosphere involving the kinetic energy of molecules in the air.
The actual weight or amount or weight of the water vapor in the air.
Can be measured by weighing the water vapor extracted from air.
Fully saturated or partially saturated
Air is fully saturated with the water vapor at 37 degrees Celsius and 760 millimeters of mercury, which is 43.8 milligrams per liter.
Percent saturated ∗ water vapor content (43.8).
Ratio of the actual water vapor content to its saturated capacity at a given temperature.
RH=CapacityContent∗100