Introduction to Engineering: Mechanical

THERMODYNAMICS & ENERGY

Created by The North Carolina School of Science and Math. Copyright 2012. North Carolina Department of Public Instruction.

Thermodynamics is the study of the connection between heat and work and the conversion of one into the other.

Applications:Internal combustion enginesRefrigeratorsHVAC systemsSteam Power Plants

WHAT IS THERMODYNAMICS?

By Duk (Own work) [GFDL (http://www.gnu.org/copyleft/fdl.html) or CC-BY-SA-3.0 (http://creativecommons.org/licenses/by-sa/3.0/)], via Wikimedia Commons

KEY TERMSEnergy – ability to do work.Work – amount of energy transferred

by a force exerted over a distance. Heat – a transfer of energy due to

thermal contactTemperature – a relative term

reflecting how vigorously the atoms of a substance are moving and colliding.

Efficiency – the percentage of energy converted into work

UNITS OF HEATCalorie

The amount of heat required to raise the temperature of one gram of water 1oC.

Joule 4.184J of heat energy is required to raise

the temperature of one gram of water from 0oC  to 1oC. 

1 J (Joule) = 9.478 10-4 BTU BTU (British Thermal Unit)

The amount of energy needed to heat one pound of water one degree Fahrenheit

TYPES OF ENERGY

MechanicalKineticPotentialSound

Thermal

• Chemical• Electromagneti

c• Electrical• Nuclear Energy

MECHANICAL ENERGY EXAMPLES

Potential

KineticBy Stefan Scheer (Own work) [CC-BY-SA-3.0-2.5-2.0-1.0 (http://creativecommons.org/licenses/by-sa/3.0)], via Wikimedia Commons

By Thierry from Le Plessis Robinson, France (Thunder of Zeus) [CC-BY-2.0 (http://creativecommons.org/licenses/by/2.0)], via Wikimedia Commons

ELECTROMAGNETIC, CHEMICAL, AND THERMAL ENERGY EXAMPLES

Electromagnetic Energy Chemical Energy Thermal Energy

See Notes for photo attributions

ELECTRICAL AND NUCLEAR ENERGY EXAMPLES

Electrical

Nuclear

See notes for photo attributions

WHAT TYPE OF ENERGY IS SHOWN BELOW?

Chemical EnergyImage from: “Wagon Lane Park Bench” by Flickr user philwhin http://www.flickr.com/photos/phil123/52092643/sizes/o/

Creative Commons CC BY 2.0/

WHAT TYPES OF ENERGY ARE SHOWN BELOW?

Electrical, Mechanical, and ElectromagneticRemote control photo by Flickr user espensorvik http://www.flickr.com/photos/28478778@N05/5728486437/sizes/l/

Creative Commons CC BY 2.0

HEAT TRANSFERThe transition of thermal energy

from a hotter to a cooler objectForms: conduction, convection, and radiation. Conduction and convection refer to

transfer of thermal energy.Radiation is a conversion of energy to

a different form.

Conduction, Convection, Radiation

http://www.spectrose.com/modes-of-heat-transfer-conduction-convection-radiation.html

CONDUCTIONThe "diffusion" of thermal energy (heat) through a

substance, which occurs because of a temperature gradient

Metals are excellent conductors of heat energy, whereas things like wood or plastics are not good conductors of heat.

Those that are not so good conductors are called insulators.

CONVECTIONThe transfer of heat energy by the

movement of a substance, such as a heated gas or liquid from one place to another.

Example: hot air rising to the ceiling There are two major types of convection:

Forced convectionNatural (Free) convection

RADIATIONRadiation refers the transfer of heat energy

through empty space. The source of this radiation is the thermal

energy of the materialsExample: standing in front of a fireplace