Three Dimensional (3D) Modeling of Heat and Mass Transfer during
Microwave Drying of Potatoes
Huacheng Zhu1,2,Tushar Gulati1 and Ashim K. Datta1
1Department of Biological and Environmental Engineering, Cornell
University, Ithaca, NY 2 Institute of Applied Electromagnetics,
Sichuan University, Chengdu, China
Microwave drying of fruits and vegetables has been found to
result in large textural changes in the product such as puffing,
crack formation and even burning due to the inhomogeneous heating
of the microwaves.
Microwave drying of potatoes is a complex interplay of mass,
momentum and energy transport.
Three phases are considered in the system: solid (skeleton),
liquid (water) and gas (water vapor and air).
Concentration of different species was solved for using the
Transport of Dilute Species module (for liquid water) and
Maxwell-Stefan Diffusion model (for vapor and air) together with
Darcy Law (to calculate Gas Pressure).
Microwave oven worked in 10% power level (Cycle Way). Shrinkage
effects have been ignored.
Modeling Framework
Potatoes treated as a porous material
Transport Model
Conservation of energy Bulk flow Conduction Phase change
Conservation of mass Water: bulk flow, capillary flow
and phase change Gas (air, vapor): bulk flow phase
change, binary diffusion
Conservation of momentum Darcys flow
The microwave oven works in a cycle way
Total samples average water saturation with drying time
Tushar Gulati 175 Riley Robb Hall
Email: [email protected] Ph: 607-255-2871
Ashim Datta 208 Riley Robb Hall
Email: [email protected] Ph: 607-255-2482
Conclusions
A mechanistic approach that predicts the microwave drying
process of potatoes has been developed.
The model could aid in predicting key quality attributes
associated with the microwave drying process.
Geometry & COMSOL Implementation
Results
Boundary Conditions - Forced convection heat
transfer - Moisture loss through
evaporation
COMSOL Implementation - Electromagnetic - Transport of Dilute
Species - Transport of Concentrated Species - Heat Transfer in
Fluids - Darcy Law
The coupled Electromagnetic and Transport Model developed above
was solved in COMSOL Multiphysics 4.3a to obtain the moisture
content and mass fraction of vapor.
Calculated surface mass fraction of vapor in the first microwave
heating cycle
0s 2s 7s 12s 17s 22s
Calculated surface water saturation with drying time
0s 44s 88s 132s 176s 220s
Microwave oven model GE JES738WJ02
Potato Sample size 1cm
Introduction
Electromagnetic Model
Maxwells Equations Faradays Law of Induction Amperes Law Gauss
Law for electricity Gauss Law for magnetism
Power Dissipation Poynting Theorm
Governing Equations
cw
t+ v
w- v
s( ) cw + cwvw = Dwcw( )- I
Conservation of Mass
Water:
cv
t+ v
g- v
s( ) cg + cgvg = jSgC2
rg
MaM
vD
eff ,gx
v
+ I
cg
t+ v
g- v
s( ) cg + cgvg = IGas:
Vapor:
t
i=s,w,v,a
cic
p,iT( )
+
i=w,v,a
vi- v
s( ) cicp,iT( )+ i=w,v,a
cic
p,iT v
i( )- cp,wT Dccw( ) = keffT( )- lI
Conservation of Energy
Darcys Law: (water and gas)
vi- v
s= -
kik
r ,i
Sif
im
i
P
Conservation of Momentum
Maxwells Equation
0 *
( ) 0
0
j
j
E H
H E
E
H
Faradays Law of Induction:
Amperes Law:
Gauss Law for electricity:
Gauss Law for magnetism:
Poynting Theorm:
0
1( , ) ''( *)
2P T x E E
Power Dissipation Huacheng Zhu
175 Riley Robb Hall Email: [email protected]
Ph: 607-255-2871
