Understanding Heat Transfer and Temperature Scales

Heat Transfer

Heat is the transfer of energy from one part of a body to another, or between bodies that are at different temperatures. Heat is energy in transit and always flows from hotter bodies to those with a smaller temperature. Temperature is the quantity that tells us how hot or cold an object is in comparison with a reference.

Temperature Scales

• Celsius: The most used international unit for ordinary temperature measurements.
• Fahrenheit: The temperature unit proposed by Gabriel Fahrenheit, which is fixed at zero and one hundred for the freezing and boiling temperatures of ammonium chloride in water, respectively.
• Kelvin: The temperature unit scale established by William Thomson, based on the degree Celsius, with the absolute zero point set while keeping the same dimension.

Units of Heat

• kcal (kilocalorie)
• Joule
• Calorie

Methods of Heat Transfer

• Conduction: The propagation of heat through a solid body due to the collision between its molecules.
• Convection: Characterized because it is produced through a fluid that transports heat between areas with different temperatures.
• Radiation: The propagation of heat through electromagnetic waves that spread, even in a vacuum.

Thermal Expansion

Dilation is the change in volume, length, or some other metric dimension that a physical body undergoes due to a change in temperature.

• Linear Expansion: The increase or decrease in length that a solid undergoes with increasing temperature.
• Linear Expansion Coefficient: The increment in length that a rod of a determined substance, with an initial length of one meter, has when its temperature rises one degree Celsius.
• Superficial Expansion or Contraction: Linear expansion or contraction in two dimensions.
• Cubic Expansion: Involves a change in the dimensions of a body: length, width, and height. Cubic expansion differs from linear dilation because it also implies an increase in volume.
• Cubic Expansion Coefficient: The increment in volume that a body of a given substance experiences, with a volume equal to unity, when its temperature is raised by 1°C.

Specific Heat and Heat Exchange

• Specific Heat: Of a substance is equal to the heat capacity of the substance divided by its mass.
• Heat Released and Absorbed: In any heat exchange made, heat is transferred and absorbed. In other words, heat lost equals heat gained.