Thermal Energy

Objectives 6.1 Compare and contrast the transfer of thermal energy by conduction, convection, and radiation. 6.1 Differentiate between conductors and insulators 6.1 Explain how insulation affects the transfer of energy.

Objectives 6.2 Explain how solar energy can be used to heat buildings. 6.2 Explain the differences between passive and active solar heating systems. 6.3 Describe how internal combustion engines and external combustion engines work.

Objectives 6.4 Explain how a heat mover can transfer thermal energy in a direction opposite of that to its natural environment. 6.4 Explain how differences in temperatures can be used to operate a heat engine that changes thermal energy to mechanical energy. Discuss advantages/disadvantages of using ocean thermal power

Energy Transfer Conduction: Direct contact – Molecules come in direct contact, the fast moving particle makes the slow moving particle speed up – You touch a hot stove Convection: Mass movement of material – Weather front, currents in rivers and oceans Radiation: Waves – Light, in all forms (radio  Gamma) – Your microwave

Differences Conduction transfers energy from one object to the other, convection doesn’t. – Energy moves, matter doesn’t Convection only occurs with fluids. Solids can’t move themselves Radiation can be transferred without material in the middle

Energy Flow Insulators: Do not allow heat to move easily through them – Wood, plastic, glass, air – Most insulation you buy, is air. Pockets of air inside the insulation provide the insulation – Your winter coats use the same concept, filled with air

Energy Flow Conductors: Allow the movement of thermal energy through them – Metals, others?

Insulation Ratings – R-Values When you talk about your attic, a value is given to say how much insulation you have (Ie R-30) – The R-Value is calculated by The Thickness of the material times the R- Value of the material – A brick’s R-Value is 0.08/cm. A brick that is 3 cm thick has a R-Value of 0.24.

Insulation Ratings Brick: 0.08/cm Wood Siding: 0.60/cm Aluminum Siding: 0.01/cm Loose Foam: 1.89/cm Air Space: 1.82 – 3.56/cm 1 cm of foam has as much insulation as each of the others?

Insulation Double paned windows: Provide extra insulation by putting an air space in the middle If the gap gets too big, what type of energy transfer becomes a problem?

Heating your house Radiators: Heat house by conduction/convection – Have a large surface area to increase the contact with air (conduction) – This hot air then creates a convection current throughout the room

Force Air-Systems Also called Central Heating or Central Air conditioning Air is heated in furnace, and then the fan creates a convection current to move the air through the vents

Solar Heating – Utilizes the sun’s energy – Two types Passive Solar Heating: No mechanical devices used to transfer heat from one place to another – Example: Big window allows sunlight to heat a room. That is passive – Some houses are designed to maximize the amount of sunlight and energy absorbed – New paints used to keep houses cool (reflect solar energy)

Solar Heating Active Solar Heating: Use Mechanical Devices – Examples include: Solar panels, water tanks that get heated and then pumped through the house

Heat Engines Convert thermal energy into mechanical energy – Use combustion, They burn stuff Internal Combustion Engine: Burn the fuel inside the engine (in cylinders) – Cars and trucks are examples of this

Engines: How do they work? 4 Steps

Engines: How do they work? 1 st Step: Intake: Air in/Gas in, piston down 2 nd Step: Compression: Piston pushes up, compressing the air/gas mixture 3 rd Step: Power (Ignition): Spark plug lights, causing the gas to ignite, the explosion pushes the piston down (Diesel doesn’t need spark) 4 th Step: Exhaust: Piston rotates back up and pushes out the exhaust (burned gas)

External Combustion Engines Fuel is burned outside the engine – Examples include: Steam engines (old trains), steam boats

Heat Movers Moves thermal energy from one location to another – Examples include: Your fridge and air conditioner. If you keep your fridge open, does your kitchen get warm or cold?

Cooling the Human Body Sweat is a key part of the body cooling down (as water evaporates from skin, it takes energy from you) – Did you know that some people can’t sweat very well? Research more about it if you want – Dogs don’t sweat (except between toes). Need to pant to cool down Like a radiator, surface area matters – What parts of body cool down fastest?

Energy from Oceans? Can use the waves energy to spin turbines Can use the temperature differences Is this a good idea?