21 thermodynamics

THERMODYNAMICSHeat and Temperature

HEAT

HEAT is energy (thermal) in transit, energy that transfers from one body to another because of temperature difference.

Heat flows from an area of high temperature to an area of low temperature (unless an external work is done).

Heat is measured with the following SI units:joules (J); calorie (cal); kilocalorie (kcal or Cal)where: 1 cal = 4.184J and 1 Cal = 1000cal

SOURCES OF HEAT

A. NATURAL SOURCES 1. the Sun 2. interior of the Earth

 B. ARTIFICIAL SOURCES

1. chemical action 2. mechanical energy 3. electrical energy

4. nuclear energy

THERMAL ENERGY AND TEMPERATURETHERMAL ENERGY

- also called Internal Energy - the total energy in a system or body; the sum of kinetic and potential energy of the atoms or molecules of a body

 TEMPERATURE

- measure of the degree of hotness or coldness of a body - the average kinetic energy of the molecules of a body

How can you measure temperature??

Touching- Very easy to use

- However, it is unreliable and has limitations

types of thermometer

*Liquid-in-glass*thermocouple*Rotary*Liquid crystal thermometer

Liquid-in-glass- A liquid inside a glass tube expands and contracts with a change in temperature

Thermocouple- Uses circuits to measure changes in electric current due to changes in temperature

Rotary- Uses a coiled bimetallic strip

Liquid Crystal- Uses a strip of liquid crystals that changes color with temperature

Temperature Scales

*Fahrenheit, °F*Celsius, °C*Kelvin, K

METHODS OF HEAT TRANSFER

1. CONDUCTION – heat transfer through solids*Thermal conductivity – ability of a material to allow heat to pass through* Kinds of material based on thermal conductivity: a. conductors – allow heat to pass through b. insulators – resist heat transfer

2. CONVECTION – heat transfer through fluids (liquids

and gases), which involves currents/flow 3. RADIATION – heat transfer through empty space,

through electromagnetic radiation, such as light, microwave, etc.

HEAT TRANSFER