thermodynamics

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First Law open system

Thermodynamics, the study of the relationships between heat and mechanical energy

Thermodynamics (from the Greek θερμη, therme, meaning “heat” and δυναμις, dunamis, meaning ” power”) is a branch of physics and is used extensively in chemistry. Thermodynamics studies the effects of changes in temperature, pressure, and volume on physical systems at the macroscopic scale by analysing the collective motion of their particles using statistics. Roughly, heat means “energy in transit” and dynamics relates to “movement”; thus, in essence thermodynamics studies the movement of energy and how energy instills movement. Historically, thermodynamics developed out of need to increase the efficiency of early steam engines.

Thermodynamics studies the effects of changes in temperature, pressure, and volume on physical systems. Thermodynamics studies the movement of energy and how energy instills movement. Historically, thermodynamics developed out of need to increase the efficiency of early steam engines.

Thermodynamics uses the concepts of science that deal with transfer of heat and work which are used to solve engineering problems. Engineers use thermodynamics to calculate energies in chemical processing, to calculate the fuel efficiency of engines, and to find ways to make more efficient systems, be they rockets, refineries, or nuclear reactors. For example, a mechanical engineer would have used “thermo” extensively in the design of an “alternative energy vehicle” that uses natural gas.

Heat and Thermodynamics covers a range of topics – internal energy, temperature, heat transfer, thermal expansion, conduction, radiation, and relative humidity

  • Entropyis a measure of the random activity in a system. The entropy of a system depends on your observations at one moment. How the system gets to that point doesn’t matter at all. If it took a billion years and a million different reactions doesn’t matter. Here and now is all that matters in entropy measurements.

Thermal Mechanics

Heat transfer

CFD – computational

Thermodynamics systems – Classical thermodynamics deals with systems in equilibrium. The equilibrium state is defined by the values of observable quantities in the system. These are called system properties.

  • system – The minimum number of variables required to describe the system depends on the complexity or degrees of freedom of the system. Degrees of freedom refer to the number of properties that can be varied independently of each other in a system. Some of the common system variables are pressure, temperature, and density, though any other physical properties may be used.
  • process – A change in the system state is called a process.

thermodynamic cycle – consists of a collection of thermodynamic processes transferring heat and work, while varying pressure, temperature, and other state variables, eventually returning a system to its initial state. In the process of going through this cycle, the system may perform work on its surroundings, therefore acting as a heat engine.

  • external combustion
  • internal combustion
  • refrigeration
Physical layout of the four main devices used in the Rankine cycle

External combustion engines – Steam turbines use the Rankine cycle – an idealised thermodynamic cycle of a heat engine that converts heat into mechanical work.

Diagram showing the basic layout of a Rankine cycle; Fluid is pumped to high pressure going from state 1 to 2. Heat is added in the boiler by the burning of fuel (although heat can be added by any method) boiling the fluid to state 3. The vapour expands through the turbine dropping significantly in pressure and temperature to state 4. Finally the vapour is condensed back to a liquid and fed back in the pump.

The heat is supplied externally to a closed loop, which usually uses water as the working fluid. The Rankine cycle, in the form of steam engines generates about 90% of all electric power used throughout the world,[1] including virtually all solar thermal, biomass, coal and nuclear power plants.

Thermodynamic temperature
Work (thermodynamics)

Entropy
First law of thermodynamics
Heat
Second law of thermodynamics
Statistical mechanics
Third law of thermodynamics
Universe
Work (thermodynamics)

Some other examples and applications

  • Internal combustion engines follow the Otto cycle – an idealized thermodynamic cycle which describes the functioning of a typical spark ignition reciprocating piston engine, the thermodynamic cycle most commonly found in automobile engines.
  • Air conditioning
  • Heat pump
  • steam engines

What’s the problem?

  • Ask – How is heat used to do work?
  • Imagine – How have ideas like steam engines been modified for modern use?
  • Design, Build What are some example of thermodynamics that are around us?
  • Improve

Engineering ideas

  • heat transfer, pressure, vapor, condense, heat pump, absorption, thermometer

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