heat flux oven temperature baking heat

Heat flux has been found to be the best non-intrusive indicator of the performance of ovens.

Heat Flux


What is Heat Flux?

Heat flux is defined as the amount of energy transferred per unit area per unit time from or to a surface. It has been found to be the best non-intrusive indicator of the performance of ovens during baking in terms of the product.1

Heat flux profile

Heat transfer follows three mechanisms during baking: radiation, convection and conduction; heat flux involves all three of these components. Every product has its own unique mix of heat flux components; therefore each has its own heat flux profile.

Critical to understanding finished product characteristics is knowing the total heat experienced by the product, and the component quantities of radiant and convective heat fluxes. The difference in these components explains why one oven bakes differently than another – and analyzing and controlling these differences are fundamental to product quality.

What factors can influence heat flux?

Heat flux and heat flux profile are determined by air velocity and oven temperature.Airflow plays a big role in the amount of convective heat flux experienced by the product.  The emissivity of the radiating object (oven ceiling) and the temperature difference between the hot object and the cold object (product), play a big role in the amount of radiant heat flux experienced by the product.

How is heat flux measured?

The heat flux sensor is designed to measure convective and radiant heat fluxes at the product level, and to identify which modes of heat transfer are predominant.

Application

Heat flux profiles are often used when trying to produce the same product on two different lines, or when trying to transfer product from one line to another. When the heat flux component profiles are matched, the two lines will produce the same product.

The ratio of heat flux components is an important factor for baked product quality. Even if the same amount of heat flux is delivered to a given product, the convective heat transfer may vary. The variation could affect energy consumption as well as the appearance and quality of the baked product.

For cake baking, cake volume expansion will be reduced significantly when the convection fraction in heat flux is reduced.3 This because the crust will form faster due to the higher radiation mode of heat transfer, thus preventing volume expansion development.

Heat flux profile can also influence the hardness, chewiness, gumminess, and color of baked products. For example, cake will have more uniform top surface appearance with a low convection effect, but remarkable gradient in darkness on the outer surface when baked with a high convection effect.3

References

  1. Zareifard, M.R., et al. “A Method For Balancing Heat Fluxes Validated For A Newly Designed Pilot Plant Oven.” Journal of Food Engineering, vol. 76, no. 3, 2006, pp. 303–312.
  2. Fahloul, D., et al. “Measurements and Predictive Modelling Of Heat Fluxes In Continuous Baking Ovens.” Journal of Food Engineering, vol. 26, 1995, pp 469–479.
  3. Zareifard, M.R., et al. “Bakery Product Characteristics As Influenced By Convection Heat Flux.” Food Research International, vol. 42, 2009, pp. 856–864.