sandeep thermo ppt

PREPARED BY

SANDEEP KUMAR SHARMA ASSISTANT PROFESSOR DEPT OF MECHANICAL ENGINEERINGDr.C V RAMAN UNIVERSITY, KARGI ROAD KOTA BILASPUR C.G.

The 0th Law (discovered 4th) The 1st Law (discovered 2nd) The 2nd Law (discovered 1st) The 3rd Law (discovered 3rd)

If: Objects A and B are the same temperature Objects B and C are the same temperature

Then: Objects A and C are the same temperature

Just the transitive property of mathematics.

The total sum of all energy in an isolated system will never increase or decrease.

“Law of conservation of energy.”

Energy cannot be created or destroyed, only transfer forms.

If two objects are not the same temperature then:

Heat will always flow from high to low temperatures.o Hot object will decrease in temperature andcold object will increase in temperatureuntil they are both the same temperature.

Entropy is randomness, i.e., disorder, spread out,

lack of structure, messiness, etc.Entropy must increase (unless controlled by an intelligence). Means that:Machines cannot be 100% efficient.Heat flows from hot to cold.

Examples: What happens to these if left alone?a.) A stack of lumber in the forest.b.)Your bedroom.

Anyone know how the steam engines on trains of the 1800’s worked?

Please describe it?

Talk about the steam engines on trains in the 1800’s.

Cold water

Heated water

2.) Water Tank. Cold water enters, heated by fire box, exits to steam turbine.Heat lost to non insulatedwater tank and pipes.

1.) Fire box. Some heat rises up to heat water, but most escapes to air around box.

3.) Steam Turbine More heat wasted on Friction at joints.

Heat Loss

Fire

© Jake Burkholder 2012

Talk about the steam engines on trains in the 1800’s.

Heat Loss?

Where does the lost heat go to?What does it do?

© Jake Burkholder 2012

Talk about the steam engines on trains in the 1800’s.

Heat Loss: goes where?

Heat is lost to air. It increases thetemperature of the air molecules, which means the speed of the air molecules increase, which makes them more random, i.e., it increases the entropy of air.

© Jake Burkholder 2012

Talk about the steam engines on trains in the 1800’s.

So how efficient are engines?

Efficiency is Work Out = Work Out

Work In Q In

if you get 1000J of work producedgoing out and put 4000J of heat in, you have a 1000J/4000J = 25% efficient engine.

© Jake Burkholder 2012

Talk about the steam engines on trains in the 1800’s.

Cold water

Heated water

Heat Loss

Fire

1.) Fire box. If only 2/7 of heat goes up to water, best efficiency is 28% (=2/7). More of the heat is lost from the hot water tank and due to friction in the turbine. These 1800 train engines were only 5 to 10% efficient.

Modern car engines are about 30% efficient. They best that modern cars can achieve is about 37% efficient.

© Jake Burkholder 2012

Talk about the steam engines on trains in the 1800’s.

Cold water

Heated water

Heat Loss

Fire

2nd Law of Thermo leads to:Machines cannot be 100% efficient which means that 1.) you cannot build a perpetual motion machine and 2.) You cannot create energy, (i.e., efficiency cannot exceed 100%)

© Jake Burkholder 2012

“S” is for “Entropy”S = Q/T

Internal Energy / Temperature (absolute) Joule/Kelvin

This system starts with same pressure and temperature on both sides. Then heat is applied to the left side. Which way will the boundary move? (What happens to the pressure on the left side when heated?)

The boundary will move, and temperatures and pressure will even out. 2 Actions: Increasing left pressure will push the boundary towards the right until pressures are the same. At the same time, the unequal temps will affect each other until they are equal.

Entropy is a measure of disorder.

In this low entropy state, there will be a net force, since there is more movement to the right than to the left.

Operating principle of a steam engine. Some of the heat in the hot gas was turned into work done on the cold gas.

Can I get any more work out of these gasses?

I would need to find a third gas sample at a lower temp to get more useful work.

Or supply my own energy to create another temperature difference.

Entropy is a measure of how evenly spread out the energy is.

Entropy is a measure of energy that is no longer “useful,” or “workable.”

Work is change in energy. It won’t change anymore if it’s spread out evenly. (Work won’t change anymore if the temperature is spread out evenly.)

States where energy is not spread out evenly will evolve into states where energy is spread out more evenly.

Chemistry people? What is Gibbs Energy?

“Absolute zero” is a state of zero motion. This means absolutely no entropy. So it can’t be reached.

THANK YOU