Heat Transfer in Furnaces

Heat transfer in a furnace takes place in three ways: radiation, convection, and conduction. The burners are located in a chamber that has tubes on four sides. When the burners are ignited, they transfer heat to the surrounding tubes by radiation. The process heats the fluid that is in the tubes that are close to the source of heat for radiation to occur.

Convection requires the flow of a gas or liquid to carry heat. In a furnace, there are tubes located above the furnace that catch heat as it leaves the heating chamber before it exits through the stack. This process helps maintain the efficiency of the furnace by preventing the waste of heat.

The conduction of heat happens in the furnace where heat is transferred to the tubes. Conduction is the transferring of heat through a solid surface. In the case of a furnace, the tubes are the surface heat is transferred through.

How Furnace Stacks Work

The stack is a chimney or vertical pipe that disperses the hot air or flue gases from the furnace heating process. The emissions from the stack are strictly controlled and monitored to avoid the release of harmful gases into the atmosphere. Flue gases contain a variety of materials, including carbon dioxide (CO2), water vapors, nitrogen, and oxygen. With the rise of environmental concerns, most stacks have contaminating materials filtered through air scrubbing or some other method before release. The high pressure outside the stack is the force that drives the flue gases out.

Inside some stack configurations are damper blades, which are thin metal plates that regulate the flow of air. In large furnaces, dampers have multiple blades designed to protect the stack and prevent materials from entering the furnace. They come in sizes made to fit the diameter of the stack.

Furnaces serve the dual purposes of providing heat and assisting in production. Industrial uses of furnaces tend to center around the annealing, melting, tempering, and carburizing of metals. Though these are critical functions of furnaces, they serve far more purposes and come in designs to fit those differing functions.

Residential furnaces are simple devices designed to provide a sufficient amount of heat. Those designed for industrial use are more complex and provide far greater amounts of heat. The basic designs of the two types are similar but industrial use furnaces are more complex.

The selection of a residential furnace is rather easy since its purpose is to provide heat. In the case of industrial furnaces, there are a variety of parameters to consider, beginning with the purpose of the furnace and its importance in production. Industrial furnaces can be divided between direct contact and indirect contact furnaces.