Question Description: The science of thermodynamics deals with the amount of heat transfer as a system undergoes a process from one equilibrium state to another and makes no reference to how long the process will take. But in engineering, we are often interested in the rate of heat transfer. In order to determine the rate of heat transfer, one must know the mechanisms/mode of heat transfer. a) State three (3) modes of heat transfer. b) List one example for each type of heat transfer stated in (a).
Course Hero Answer & Explanation:
Heat: It is the form of energy which can be transferred from a substance at high temperature to another substance at a low temperature due to the difference in temperature.
Thermodynamics is deal with the amount of heat transfer when a system undergoes a process from one equilibrium state to another equilibrium state.
Heat Transfer is deal with the rate heat transfer per unit time per unit area due to difference in temperature.
The transfer of energy as heat is always from the higher-temperature medium to the lower-temperature one. Heat transfer stops when the two mediums reach at the same temperature and the equilibrium in temperature is occurs.
In general, there are three different modes of heat transfer:
(1) Conduction: The conduction heat transfer mainly occurs in solid substances where the heat (energy) transfers one particle of a substance to another adjacent particle in direct contact. Heat is a transfer by molecules/atoms of the particle that are in contact with each other.
Example: (1) Melting of an ice cube when holding it in hand. The heat is being conducted from hand into the ice cube.
(2) Hot food will heat a stoneware or porcelain plate for a time.
(2) Convection: In the convection mode of heat transfer, the is a transfer from a solid surface to the adjacent liquid or gas medium is in motion. Convection is the combination of conduction and fluid motion. The rate of heat transfer increases with increasing the motion of the fluid.
Example: (1) Boiling of water in a vessel.
(2) Melting of Ice when leave into the open air.
(3) Radiation: In the radiation mode of heat transfer, the heat is transfer through electromagnetic waves. Both conduction and convection heat transfer occurs through medium while the radiation does not require any medium as it transfers the heat by means of electromagnetic waves. In general, the radiation heat transfer appears at a very high temperature.
Example: (1) Heat transfer by Sunlight.
(2) Heat transfer in boiler furnaces.