Entropy & Engine Cyles

Demo: Thermoelectric Cooler Information
This thermoelectric cooler had a cold reservoir and a hot reservoir. There is a metal plate inside of each reservoir connected. The thermoelectric device creates voltage when there is a different temperature at each of the plates. This caused the wheel to spin. 

Here we derived formulas to use in problems involving adiabatic processes. 

The Carnot Engine:

• the performance of useful work is accompanied by heat being transferred 
• most efficient heat engine cycle
• consists of 2 isothermal processes and 2 adiabatic processes
• the engine cycle is reversible
• no change in entropy
• not a possible cycle since no real engine processes are reversible and all real physical processes involve a change in entropy

Diesel Engine:

• similar to Otto Cycle but does not use spark plugs 
• engine cycles include:
• adiabatic compression
• constant pressure process
• adiabatic expansion
• constant volume process
• uses internal combustion

The Stirling Engine:

• operates by cyclical compression and expansion of air or other gas at different temperatures 
• closed cycle regenerative heat engine with a permanent gaseous working fluid
• high efficiency engines
• heat energy source is generated externally
• processes include:
• isothermal expansion
• isochoric heat removal
• isothermal compression
• isochoric heat addition

Otto Engine Cycle:

• internal combustion engine
• simple 4 stroke engine
• intake strokes- piston moves down the cylinder and the pressure will drop causing the air/fuel mixture to be sucked into the cylinder
• compression stroke-cylinder is at max volume and intake valve is closed temperature increases
• power stroke-force drives piston down, volume increased and pressure decreased
• exhaust stroke-exhaust valve is opened, piston moves up cylinder, pressure drops, volume decreased

An example of the otto engine is shown below.

LAWS OF THERMODYNAMICS 

(These Laws were copied from the Online Notes provided)

	Energy cannot be created or destroyed.
	Entropy can be created but not spontaneously destroyed.
	It is the Entropy (not Energy) of a system that goes to zero as the Absolute Temperature goes to zero.

Here we solved for the maximum possible coefficient of performance of a given refrigerator.We also solved for the heat exhausted when it operates at 43% of its max COP. 

 Then we solved for the time it takes for this refrigerator to cool 4.20kg of water from 18.0 degrees celsius to 0.0 degrees celsius. We also solved for the change in entropy.

 Below we found the effectiveness of a heat engine.

Reversible Processes:

• *Reversible processes- states of the process are infinitesimally close to equilibrium states.
• Possible to return system to original state

This problem required us to calculate the final temp of two blocks (same mass and heat capacity but different initial temperatures) that are insulated so no heat is lost to the environment. The calculations are as follows:

 The calculations for the thermal efficiency of the thermal process is shown below.

Summary:

• A thermoelectric device creates voltage when there is a different temperature at each of the plates. 
• A Carnot Engine is the most efficient heat engine cycle and consists of 2 isothermal processes and 2 adiabatic processes.
• The Stirling Engine operates by cyclical compression and expansion of air or other gas at different temperatures. It is a closed cycle regenerative heat engine with a permanent gaseous working fluid. These are high efficiency engines.
• Otto Cycle engines are internal combustion engines with exhaust valves and power strokes.
• The Laws of Thermodynamics are:  
• Energy cannot be created or destroyed.
• Entropy can be created but not spontaneously destroyed.
• It is the Entropy (not Energy) of a system that goes to   zero as the Absolute Temperature goes to zero.
• Reversible processes- states of the process are infinitesimally close to equilibrium states.