Page 145 - WCS - Electrical

WORKSHOP CALCULATION & SCIENCE - CITS

Units of Heat

The SI unit for heat is the joule (J), while the most commonly used unit for heat in everyday contexts is the calorie
(cal).
- The relation between heat and temperature change is given by the formula Q = mcΔT, where Q is the heat
transferred, m is the mass of the substance, c is the specific heat capacity, and ΔT is the change in temperature.
There are three units of measure of heat
Calorie: The amount of heat required to raise the temperature of one gram of water through 1°C

BTU: It is the quantity of heat required to raise 1 pound of water through
1°F. (British thermal unit).
1 B.T.U. =252 calories
C.H.U: (Centigrade Heat Unit) It is the quantity of heat required to raise 1 pound of water

Through 1°C. Relation
1 B.T.U. =252 calories
1 C.H.U = 453.6 calories
1 C.H.U. = 1.8 B.T.U.
Joule: S.I. Unit (1 Calorie = 4.186 joule)

Thermal Equilibrium
- Thermal equilibrium occurs when two objects in contact reach the same temperature, and there is no net heat
flow between them.
- This principle is essential for understanding heat transfer in various systems and processes.

Concepts and Differences
- Heat is a form of energy that transfers between objects or systems due to the temperature difference between
them. It flows from hotter objects to colder ones until thermal equilibrium is reached.

- Temperature is a measure of the average kinetic energy of the particles in a substance. It determines the
direction of heat flow, with heat flowing from higher to lower temperatures.
- In summary, heat is the transfer of energy, while temperature is a measure of the intensity of heat in a substance.
Temperature Measuring Scales

- The most commonly used temperature scales are Celsius (°C), Fahrenheit (°F), and Kelvin (K).
- The Celsius scale is based on the freezing and boiling points of water (0°C and 100°C, respectively).
- The Fahrenheit scale uses a different zero point (32°F) and different degree size compared to Celsius.
- Kelvin scale is an absolute temperature scale with the zero point (absolute zero) at -273.15°C. It’s commonly
used in scientific contexts.
Transference of Heat
Conduction

- Conduction is the transfer of heat through a substance by the collision of molecules. It occurs primarily in
solids.
- Materials with higher thermal conductivity conduct heat more efficiently.
Convection

- Convection is the transfer of heat through the movement of fluids (liquids or gases). It involves the transfer of
heat through the movement of heated particles within the fluid.

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CITS : WCS - Electrical - Exercise 12