Study of continuous cake pre-baking in a rectangular channel using ohmic heating

摘要

An original device dedicated to additive manufacturing was developed to pre-bake cake batter. Its originality lies in the fact that pre-baking is ensured by ohmic heating implemented in a rectangular channel equipped with two parallel electrodes. Experiments and numerical studies were carried out and benchmarked. The rheological properties of the cake batter (non-Newtonian power-law fluid) and the influence of voltage and temperature on electrical conductivity were accommodated in the numerical model. Due to the low velocities of the very viscous products near the solid-liquid interface, it was found that the heterogeneity of the temperature at the nozzle outlet under continuous ohmic heating could lead to nozzle clogging when high temperatures are reached. Hot spots were identified in different areas of the channel, such as corners where the electric field is high and velocity is close to zero. A parametric study was performed on the impact of the thermophysical properties of the batter, showing that specific heat has a much greater impact than thermal conductivity on the accuracy of the temperatures computed. Analysis of the process parameters showed that a stronger electric field leads to a higher temperature gradient in the nozzle section. The temperature gradient decreases with electrode distance (delect) and nozzle width (l). This model could be used to optimize the ohmic heating nozzle configuration, with the objective of obtaining a continuous flow of pre-baked cake batter, while preventing clogging. Such a system could be used as 3D printing head. Industrial relevance: Conventional 3D printing of bakery products is based on the deposition of a batter, followed by a baking. This study proposes an innovative approach based on a printing nozzle equipped with ohmic heating, with the objective of achieving a uniform temperature distribution and of obtaining high mass flow rate. Despite a significant temperature gradient in the baked batter at the exit of the nozzle, the obtained results showed that adjusting the nozzle geometry allows a reduction of the gradient. Further investigations are thus needed to reduce the temperature gradient and to accommodate expansion of the batter in the case of formulation using baking powder. The transfer of such concept for industry application may be doable in a close future.