Microwave Cooking Modeling Heat and moisture transport Andriy Rychahivskyy
Outline What is a microwave? Nature of microwave heating Goals of the project Model description Results Conclusions and recommendations
Scheme of a microwave oven
H ─electric field ─ electric field ─ magnetic field ─ wavelength (12.2 cm for 2.45 GHz) H What is a microwave?
Microwave cooking principle Microwaves act on salt ions 1) salt ions to accelerate them; water molecules 2) water molecules to rapidly change their polar direction + +
Microwave cooking principle Microwaves act on salt ions 1) salt ions to accelerate them; water molecules 2) water molecules to rapidly change their polar direction Food’s water content heats the food due to molecular “friction”
Goal of the project Design a model of microwave cooking predicting temperature and moisture distribution within the food product
Phenomena to model Electromagnetic wave distribution Heat transport within the product Mass (water and vapor) transport
Governing equations and laws Maxwell’s equations Energy balance equation Water and vapor balance equations Ideal gas law Darcy’s law for a flow in a porous medium
Porous medium water vapor solid particle
Porous medium water vapor solid particle
Geometrical model MW cavity C MW cavity food product M food product waveguide G waveguide top bottom
Heat source –electromagnetic properties: ε, σ –electromagnetic properties: ε, σ (control how a material heats up) ε = ε* + i ε** –radial frequency: ω = 2 *2.45 GHz
Heat source Electric field intensity
Heat source Electric field intensity
Heat source Electric field intensity Heat source
Convection-diffusion equation heat capacity : heat capacity : (how much heat the food holds) thermal conductivity: (how fast heat moves) latent heat: (absorbed due to evaporation) interface mass transfer rate:
Boundary and initial conditions thermal conductivity: (how fast heat moves) heat transfer coef.: (thermal resistance) latent heat: (absorbed due to evaporation)
One-dimensional model with at
Numerical results /without mass transport/
Numerical results /general 1D model/
Interpretation of results
Conclusions Electromagnetic source is constant Heating-up of the product until 100 o C develops linear in time T at the boundary >> T in the kernel Moisture loss occurs only in a boundary layer
Recommendations Validate the results Extend our implementation Perform a parameter study