Heat Exchanger

Heat Exchanger is a device that transfers heat from one medium to another, without allowing them to mix. This transfer of heat is used to cool liquids.

Example: Heat exchanger used to warm up the car during chilly days works such that it absorbs heat from the warm fluid flowing in the tubes and supplies it to the fan. This results in cooling of the Liquid. This kind of heat exchanger is termed as Liquid-to-air heat exchanger.

Peltier Effect

Peltier Effect is the production or absorption of heat at the junction of two metals on the passage of a current. Heat is produced or absorbed depending on the direction and amount of current flow.

This thermal energy process was first observed in 1834 by Jean Peltier, a French watchmaker and part-time physicist, who was investigating thermal energy flows between dissimilar metal junctions.

Example: Thermoelectrics based on Peltier effect could be used to cool liquids.

Phase Transitions

Phase Transition is change from one state (solid or liquid or gas) to another, without a change in chemical composition. This concept is used in liquids such that, when a liquid is cooled, it changes it's phase to solid.

Example: Water when cooled beyond freezing temperature forms ice. Hence, the phase transition from liquid to solid.

Ranque Effect

Ranque Effect states that, whenever any mass of gas, whatever its initial density and temperature, is caused to rotate axially, via exogenous and/or endogenous effects, it will gradually cool in the area near the axis of rotation and will warm in the external areas. This was discovered by French physicist Georges Ranque.

Thermomagnetic Effect

Thermomagnetic Effect occurs when two dissimilar metals are connected in a loop, such that the ends of the wire are connected to each other, and when one junction was heated and the other cooled, then a magnetic field is observed. Reverse thermomagnetic effect is used in cooling liquids where the coller end of the junction of metals is immersed in liquid to be cooled.

Conduction

Conduction is transmission of electric charge or heat through a conducting medium, without perceptible motion of the medium itself. This phenomena is used to cool a substance.

Example: Hot tea cools easily by stirring action of the spoon by transferring the heat to the spoon. The handle of the spoon that extends out of the tea heats up by conduction in turn cooling the tea.

Convection

Convection is a process of transfer or transmission, as of heat or electricity, by means of currents in liquids or gases, resulting from changes of temperature and other causes in a medium.

Convection is the transfer of heat by the circulation or movement of heated parts in a liquid or gas. Convection is also the circulatory motion that occurs in a fluid, which is at a non-uniform (or varying) temperature caused by the variation of the density of liquid at different temperatures and the action of gravity.

Example: Suppose that you remove the hot tea from the microwave oven, and then you pour some cream into the water, since water and cream are fluids, the method of heat transfer between them is convection. As the cream heats up and the tea cools down slightly, a flow develops and the cream mixes with the tea.

Addition of ice cubes into juice results in flow of heat from juice to ice cubes to bring them into thermal equilibrium.

Air-flow

Air-Flow is continuous supply of air. When such a continuous supply of air is applied on a hot object, the air absorbs the heat inturn cooling the object.

Example: A radiator is designed to transfer heat from the hot coolant that flows through it to the air blown through it by the fan. The coolant flows from the inlet to the outlet through many tubes mounted in a parallel arrangement. The fins conduct the heat from the tubes and transfer it to the air flowing through the radiator.