Which are the underlying principles of mass and heat transfer?
Many industrial processes generate mass transfer of some sort, i.e. moving mass from one part of the process to another. This may be to separate different substances from each other, change the composition of a mixture, or concentrate a solution. Mass transfer can take place in a number of different processes, e.g:
- absorption - one substance is absorbed by another substance
- adsorption - a gaseous substance or a substance dissolved in a liquid adheres to the surface of another solid or liquid
- evaporation - a substance changes from a solid or liquid state to a gaseous state
Examples of mass transfer processes are flue gas cleaning and stripping.
The following terms are often used in connection with heat transfer:
- temperature - How hot or cold something is compared to a reference point. The temperature of an object depends on how much kinetic energy the object contains, i.e. how fast the particles in the object are moving. Usually temperature is expressed in Celsius, Kelvin or Fahrenheit.
- thermal energy - includes the total kinetic energy of all the particles in an object. The unit of thermal energy is the joule (J)
- heat - is defined as the transfer of thermal energy from one object or system to another
Heat transfer is defined as heat and how thermal energy is transferred from one object or system to another. Thermal energy is transferred from a point of high temperature (high energy) to a point of lower temperature (lower energy).
Heat transfer can occur in a number of different ways:
- conduction (thermal conduction) - heat transfer occurs through direct contact between the particles in the objects
- convection (flow) - A gas or liquid that comes into contact with a hot source changes its density. It rises to a point of lower temperature, which in turn causes the gas or liquid to sink again. This movement is called convection.
- radiation - heat transferred by electromagnetic radiation created by the thermal motion of the particles in the object
- phase transition - a substance undergoes a phase transformation that either transfers the latent energy in that substance to its surrounding or absorbs energy from its surrounding
An example of a heat transfer process is flue gas condensation.