Demos. Shuttle Tile and Oven Mohair fuzz Candle Fire Syringe Deck of Cards Pasco Cylinder and Temp Sensor Bicycle Tire and Digital Thermometer Steam Engine and generator + bulb Stirling Engine DI Water , Ethanol. Thermodynamics, Heat Energy, and how we benefit from it. Outline.
Thermo means “heat" and Dynamics relates to "movement"; in essence thermodynamics studies the movement of heat energy and how that energy makes mechanical movement (i.e. does work).
Thermodynamics is a science about the effects of changes in temperature, pressure, and volume and how these changes effect a physical system.
(e.g. a car engine, an air conditioner)
Heat Energy is a type of kinetic energy
Heat Energy relates to Thermal Energy (or internal energy)
Thermal Energy is the sum of the kinetic energy, ½ mv2 , of ALL the individual atoms in a system or object.
Heat is the energy that flowsfrom one object to anotherdue to a temperature difference.
When Energy flows from a hot object to a cold object, the energy is called Heat
James Joule’s experiment proved that heat was a form of energy. In this experiment the kinetic energy of the paddle is transferred to thermal energy in the water, as measured with a sensitive thermometer.
Fast moving atoms with a lot of random motion collide with slower moving atoms.
As kinetic energy is transferred from the fast moving atoms to the slower moving atoms, we say that the warmer side gave up heat to the colder side and that heat was transferred.
Temperature is a measurement of the average thermal energy of the particles in a substance.
Heat flows due to temperature differences.
No heat is transferred between two objects that are at the same temperature (i.e. in thermal equilibrium).
A cup of boiling water is at the same temperature as a gallon of boiling water, but the gallon of boiling water has more thermal energy than the cup.
The measure of the heat energy required to increase the temperature of a unit quantity of a substance by one degree.
Copper 0.385 Joule/gr oC
Dry Air 1.0035 Joule/gr oC
Humid Air 1.0102 Joule/gr oC
Water 4.1813 Joule/gr oC
Concrete 0.88 Joule/gr oC
Sand 0.42 Joule/gr oC
Second highest specific heat, next to Ammonia
McGill University, Montreal – Solar Decathlon 2007
Both Objects are at the same temperature, but the metal feels colder, why?
You are at a higher temperature than any non-living object in the room, therefore heat is transferred from your body to both the wood and the metal.
The metal conducts heat better than the wood because there are a lot of free electrons in metals, therefore mobile electrons take heat from your hand faster than wood.
Shuttle Tile white-hot at 2300 oF
The tile is 10% pure silica fibers and 90% air. The high percentage of air makes the tiles very lightweight.
Tile has very low thermal conductivity due to trapped air and the low conductivity of long glass fibers.
Heat energy is transmitted table…
by collisions from neighboring atoms/molecules.
Buoyancy forces cause bulk movement of the water.
Rising hot air and falling cool air sets up convection cells.
Heat from the earth’s core comes from ancient energy left from earth’s formation and radioactive elements which decay and release heat.
Heat from the earth’s core causes slow moving convection cells in the earth’s mantle. The earth’s crust spreads at mid-ocean ridges by 2-3 cm per year.
Northern Atlantic cold water sinks. This pulls in warmer water from the Gulf Stream. This heat transfer phenomenon determines how warm or cool European climates will be.
Fresh water is less dense than salt water. As Greenland’s ice fields recede more fresh water enters the North Atlantic possibly impacting normal oceanic convection patterns.Oceanic Convection
A fan circulates the air so hot air is not trapped at the top of the oven. More cookies can be baked at one time and all will cook at the same rate.
www.sleekhome.com water from the Gulf Stream. This heat transfer phenomenon determines how warm or cool European climates will be.Ceiling Fans
In both hot and cold weather, ceiling fans are useful for circulating air to force convection.
Rooms with high ceilings are a problem during the winter as the hot air rises and moves away from the floor area.
All objects with thermal energy emit Infrared Radiation (even ice)
Infrared radiation is invisible to our eyes but we can feel it as heat
Non-ionizing radiation is everywhere and is considered to not be harmful.
If two objects are in thermal equilibrium with a third object, then they are also in thermal equilibrium with each other.
Thermal equilibrium means an objects temperature, pressure, and volume are not changing.
http://www.cafemakers.com electron off an atom)
A cooling cup of coffee is NOT in thermal equilibrium with the room.
/www.wentapottery.com electron off an atom)
If two cups of coffee are at thermal equilibrium with the room, then the two cups are in thermal equilibrium with each other.
The two cups of coffee have the same temperature.
If the two cups are put in contact with each other no heat will flow.
First Law of Thermodynamics: electron off an atom)
(The good news!)
Energy is Conserved. Energy can not be destroyed.
In an isolated system, the total energy stays the same.
Energy can be converted from one form to another.
Thermal Energy can be converted into another form of energy!
Entropy = total disorder of an object/system
Disorder is the sum of the thermal energy plus the physical disorder.
Entropy always increases with time!
Wikipedia.com electron off an atom)
www.wiley.comExamples of increasing entropy
Playing “52 pick up”
+ electron off an atom)
Heat, light, ash, particulates, gases
Heat, light, ash, particulates, gases
Energy flows in one direction electron off an atom) – towards a more disordered state
The Second Law of Thermodynamics: electron off an atom)
(The bad news!)
An isolated system gets more disordered with time.
Entropy always increases with time.
When a fluid is compressed, work is done on the fluid.
This work/energy is converted into thermal energy within the fluid.
Each molecule has more kinetic energy so the temperature of the fluid increases.
www.grannysstore.com electron off an atom)Fire Piston
As air is rapidly compressed, it can reach 400-500 degrees, allowing tinder to ignite.
The compressed air is the heat source as well as the oxygen needed to ignite the tinder.
Fire piston are thought to be prehistoric fire starting devices, used in South East Asia and South Pacific.
For more info see:
The modern match evolved during the 1800’s. Prior to 1900, fires had to be maintained or started by creating heat through friction.
Many people used flintlock guns.
The Bow and Drill used by Native Americans
A cycling machine/engine that converts thermal energy into mechanical energy (also known as work)
4-stroke engine (OTTO Cycle)
A boiler is used to heat water to create steam. This high pressure fluid in turn does work on the pistons.
Working fluid (steam) is heated through a heat exchanger. Fuel is external to working fluid.
About 6% efficient
Click for animation
Briggs and Stratton Website
The Power Piston lags the Displacer by 90 pressure fluid in turn does work on the pistons.o
Click for animation
Diesel engines do not have spark plugs because similar to the fire piston, the compression of the gas and air mixture is great enough to automatically ignite the fuel.
Gas is injected into cylinder after air is compressed. This allows for greater compression, and higher efficiency.
Click for animation
Make Magazine Vol#3
Stanley Steam Car 1912
Thomas Edison circa 1900
Morrison’s 4-horse power EV with a range of 50 miles.
Waverley Automobile Co.
Detroit Electric Carriage - 1912
Karl Benz was the first to commercialize a gas powered motorwagon in 1885
Huntington Beach 1928 pressure fluid in turn does work on the pistons.
Beaumont, Texas on Spindletop Hill
Heat flows into fluid
Heat leaves the fluid, heating the kitchen floor and condensing the fluid.
http://physics.bu.edu pressure fluid in turn does work on the pistons.
The compressor on the bottom compresses the working fluid raising its temperature.
In the condenser coils, heat leaves the fluid and enters the room. This condenses the fluid into a liquid.
When allowed to expand, the temperature of the liquid drops dramatically. This cold fluid absorbs heat from the inside of the refrigerator, causing the fluid to evaporate and turn back into a gas.
External Combustion – the fluid doing the work (working fluid) is heated externally.
Internal Combustion – the fluid doing the work is heated by burning a fuel internally inside a cylinder pushing down on a piston