Laboratory Ovens and Industrial Ovens described for natural and forced convection ovens.
Many of the industrial and laboratory ovens present the choice between having gravity convection and forced convection. Both types of convection are used to heat samples in the ovens evenly. Convection is a method of heat transfer that occurs from the motion of a fluid, in ovens the fluid is air.
Natural convection, or gravity or free convection, is convection that occurs when air is heated and the warmer, less dense air rises above the cooler, more dense air. As the warmer air rises, the cooler air sinks and becomes warmer so that it, in turn, rises. This creates a current where the cooler, more dense air sinks, warms up and becomes less dense, rises, and cools and becomes more dense. It is sometimes called gravity convection because without gravity to move the cool, dense air down, the current would not be created.
Forced convection is convection that occurs when air is moved using any type of external source, such as a fan. The warmer air is forced over cooler air by a fan. The fan, or fans, can be set up to provide either a vertical current similar to natural convection or a horizontal current. A few ovens offer a third option, mixed convection. This is a convection current that has both a natural and a forced component. Usually, the fans will blow from the sides, creating a horizontal current, while there is a natural convection current in the center of the oven with a vertical current. Forced convection assures a more even temperature distribution.
Which is right for you? That depends on the amount of material located in the oven and how important the accuracy of the temperature is at every location.