13.2 Types of heat transfer: The IREKS Compendium of Baking Technology

Schematische Darstellung Wärmestrahlung — Illustration 13.4: Schematic representation of heat radiation

Heat radiation takes place by means of heat rays (waves), which are passed from the top area of the baking chamber to the goods for baking and which heat these. Heat radiation mainly occurs in deck ovens and tunnel ovens.

Schematische Darstellung Wärmeleitung — Illustration 13.5: Schematic representation of heat conduction

Heat conduction describes the transfer of the heat via a body from a higher to a lower temperature level. Heat conduction is used when baked goods are to be baked directly on the oven plate. Heat conduction can only take place if two bodies of a different temperature touch one another directly.

Schematische Darstellung Konvektion Wärmeströmung — Illustration 13.6: Schematic representation of convection/heat convection

Convection/Heat convection is the movement of hot air or hot steam around the goods for baking. Here, the air movement is caused by a recirculating fan. Convection is characteristic for rack ovens and convection shop ovens. Also the introduction of hot steam causes a certain movement of air in the baking chamber.

Schematische Darstellung Kondensation — Illustration 13.7: Schematic representation of condensation

Condensation takes place when hot steam condenses on the dough piece. By the change in the aggregate state of the steam from gas to liquid on the upper surface of the dough piece, a lot of energy is released. As a result, a rapid transfer of heat to the dough piece takes place.

Depending on the oven system used, the types of heat transfer can be distinctly different. While mainly heat radiation is used in the deck oven, heat convection or convection dominates in the rack oven. Trolley ovens is the name for ovens heated by thermal oil into which a trolley is rolled, but does not turn. Several horizontally arranged radiators, through which the thermal oil flows, are found in the trolley oven. The trays of the trolley are directly above the radiators. In addition to convection, the heat radiation above all is responsible for the heat transfer in trolley ovens.

Percentage shares of the total heat output for different furnace systems — Illustration 13.8: Percentages of the total heat output in the case of various oven systems (cf. MIWE impulse XV 2011)

Due to their economic viability, mostly oil and gas are used to heat the different oven systems. Electrically heated ovens are less frequently in use as a result of their higher energy costs. In rare cases, coal, wood or wood pellets are used for heating.