Convection cooling occurs when the gas stove’s flame is turned off and heat starts to come out of the pan.
Convection cooling is any heat transfer that occurs from fluid motion. Both liquids and gases can be cooled by convection, and the effect can be natural or forced. Natural cooling occurs from heat transfer due to changes in fluid density, such as warm air rising and cooler air falling. Forced convection occurs when any external force is added to move the fluid, such as a fan moving air or a spoon stirring a liquid.
Tectonic plate movement is caused by convection cooling.
Heat transfer occurs mainly by conduction and convection. Conduction is a transfer of heat through any material, without material movement. An example of conduction is a metal pan heated by a flame on a gas stove. The gas flame heats the bottom of the pan and the conduction transfers the heat to the rest of the pan. When the heat is turned off, the convection cools the pan as the heat transfers and rises to the air around the pan.
Cooling by natural convection occurs in the Earth’s atmosphere and oceans. The air is heated by the heating of the earth and rises. As the air rises, it cools and returns to the surface, creating global air circulation and weather patterns. Ocean currents transport warm water to cooler oceans, and cooler water sinks and moves to warmer regions. Sunlight adds energy by heating air or water, and the Earth’s rotation imparts some energy, but the movement is considered natural rather than forced.
Convection cooling also takes place inside the Earth. The molten core, heated by the decay of radioactive elements, rises towards the outer crust of our planet. Convection cools the molten core material and it slowly moves back to the center. This motion causes our continents to move slowly over the molten core, a phenomenon called tectonic plate movement.
Forced cooling is common in homes and businesses. Air conditioning and heating systems used forced air convection to move heat into or out of a building. Fans inside electronic equipment used forced convection cooling to move air over electronic components. Refrigeration systems use fans to remove heat from the condenser coils, but also to cool the compressor and move air within the refrigerated compartment.
Cooling fans have demonstrated convection effects for centuries. With the invention of electricity, electric motors could be used to drive table and ceiling fans. Sophisticated ceiling fans containing thermostats to automatically control their functions have been available since the late 20th century. All rely on the same cooling principle as the human body, moving air through the skin.
Convection can be combined with evaporation to improve cooling performance. Evaporative cooling systems, which use forced air passed through a wet evaporative pad to cool indoor spaces, are popular in very low humidity areas. These systems cool the interior space by removing heat from the incoming air through evaporation. The resulting airflow is cooler but contains more moisture. Evaporative systems do not work well in areas of higher relative humidity, because cooling will not occur and the interior can be quite humid.