CFD modelling of continuous baking tunnel ovens
File(s)
Author(s)
Avalos Patino, Jorge
Type
Thesis
Abstract
Physically, biscuits baking can be described as a process of simultaneous heat and mass transport, within the product as well as in the environment inside the baking chamber. At the industrial scale, biscuits are baked in direct-fired continuous ovens. These ovens are typically linear tunnels fitted with gas burners located above and below the conveyor belt that transports the biscuit dough and with exhaust ducts and chimneys for the extraction of the flue gases and water vapour. The oven operation is often by trial and error, with a resultant lack of understanding of optimum settings.
Previous studies related to modelling industrial baking have focused on bread baking. The bread baking process differs from biscuit baking in different aspects. Bread baking is carried out using indirect-fired ovens, therefore, there is no direct interaction between the flames and the product during the baking process and gas radiation is not as relevant to bread baking as it is to biscuits baking. Another important aspect is the range of length scales in direct-fired continuous tunnel ovens for baking biscuits, which are up to 100 metres long and the flame slots of gas burners are 1.5 centimetres in width. Moreover, none of the previous studies developed a CFD model incorporating air flow patterns and radiative heat transfer in continuous tunnel ovens for baking biscuits.
These aspects introduce two main challenges for modelling biscuits baking: (i) modelling radiative heat transfer, considering the effect of inhomogeneous participating media, including flue gases and water vapour, and (ii) resolving velocity fields, considering the range of length scales involved, while preserving reasonable computational cost.
This thesis aims to develop the methods and models required to address these challenges, resulting in the first CFD model of a continuous tunnel oven for baking biscuits. For modelling radiative transfer, a new global gas radiation model for inhomogeneous unsteady participating media was developed. This gas radiation model improves the performance of numerical solvers for the radiative transfer equation in terms of accuracy and computational cost. For modelling turbulence across a wide range of scales, a new parameter-free turbulence model for anisotropic mesh adaptivity was developed. This model allows for achieving good accuracy with reasonable computational cost and introduces a new vortex identification method allowing for the visualisation of the flow structures responsible for advection. Given that these methods allow for balancing accuracy and computational cost, they can be applied to different real applications involving radiative heat transfer and turbulence across wide ranges of scales, hence becoming a powerful tool for industrial applications.
The CFD model of a continuous tunnel oven for baking biscuits was validated using real data from a biscuits manufacturer, demonstrating good agreement between experimental data and calculations using the model. Moreover, the simulations using the model bring to light aspects that had been unknown, including the detailed description of the flow inside the oven and its effect on the heat distribution, allowing the identification of features in heat and mass transport processes that lead to inefficiencies in the baking process or defects in the product. This validation demonstrates that the CFD model provides a new understanding of the baking process that was not available until now.
Previous studies related to modelling industrial baking have focused on bread baking. The bread baking process differs from biscuit baking in different aspects. Bread baking is carried out using indirect-fired ovens, therefore, there is no direct interaction between the flames and the product during the baking process and gas radiation is not as relevant to bread baking as it is to biscuits baking. Another important aspect is the range of length scales in direct-fired continuous tunnel ovens for baking biscuits, which are up to 100 metres long and the flame slots of gas burners are 1.5 centimetres in width. Moreover, none of the previous studies developed a CFD model incorporating air flow patterns and radiative heat transfer in continuous tunnel ovens for baking biscuits.
These aspects introduce two main challenges for modelling biscuits baking: (i) modelling radiative heat transfer, considering the effect of inhomogeneous participating media, including flue gases and water vapour, and (ii) resolving velocity fields, considering the range of length scales involved, while preserving reasonable computational cost.
This thesis aims to develop the methods and models required to address these challenges, resulting in the first CFD model of a continuous tunnel oven for baking biscuits. For modelling radiative transfer, a new global gas radiation model for inhomogeneous unsteady participating media was developed. This gas radiation model improves the performance of numerical solvers for the radiative transfer equation in terms of accuracy and computational cost. For modelling turbulence across a wide range of scales, a new parameter-free turbulence model for anisotropic mesh adaptivity was developed. This model allows for achieving good accuracy with reasonable computational cost and introduces a new vortex identification method allowing for the visualisation of the flow structures responsible for advection. Given that these methods allow for balancing accuracy and computational cost, they can be applied to different real applications involving radiative heat transfer and turbulence across wide ranges of scales, hence becoming a powerful tool for industrial applications.
The CFD model of a continuous tunnel oven for baking biscuits was validated using real data from a biscuits manufacturer, demonstrating good agreement between experimental data and calculations using the model. Moreover, the simulations using the model bring to light aspects that had been unknown, including the detailed description of the flow inside the oven and its effect on the heat distribution, allowing the identification of features in heat and mass transport processes that lead to inefficiencies in the baking process or defects in the product. This validation demonstrates that the CFD model provides a new understanding of the baking process that was not available until now.
Version
Open Access
Date Issued
2022-12-01
Date Awarded
01/08/2023
Advisor
Neethling, Stephen
Piggott, Matthew
Sponsor
Ministerio de Ciencia, Tecnología e Innovación, MinCiencias
Grupo Nutresa (Firm)
Publisher Department
Earth Science & Engineering
Publisher Institution
Imperial College London
Qualification Level
Doctoral
Qualification Name
Doctor of Philosophy (PhD)