Imperial Journal of Interdisciplinary Research (IJIR)
Vol-3, Issue-1, 2017
ISSN: 2454-1362, http://www.onlinejournal.in
Material Processing With Microwave
Neha Gupta
M.Tech Student ,Electronics And Communication Engineering
Abstract: For enhancing the properties as well as
economy, microwave processing is new technique
that saves energy and accelerate product
development. Conventional methods of material
processing have some difficulties but it can be
resolved by microwave. Some of the advantage of
using the microwave is controlled electric field
distribution, penetration radiation rapid heating,
self limiting reactions and selective and volumetric
heating. The most important process in the
manufacturing is heating. Microwave heating is
ability is ability of material to absorb microwave
energy and convert it to heat. Microwave heating is
used in industrial application. KEYWORDS:
material processing, dielectric, microwave heating.
INTRODUCTION: Heating is very important in
manufacturing industry like food chemical, textile
and engineering industries for drying, promoting
chemical or physical change and much other
purpose. Ability of material to absorb high
frequency electromagnetic energy (microwave) and
convert it to heat is called microwave heating.
Microwave heating is caused due to chemical
bonding and in presence of high frequency electric
field they are realigned. Realignment occur million
of time per second due to high frequency which
causes internal friction of molecules causing
volumetric heating of material.
1- Energy usage is 70% less than conventional
heating method as it has high energy densities
2- 20% small size system than conventional system
because of direct absorption of energy
and high
energy density.
3-Material can be volumetrically heated and
processed at low temperature so product quality is
improved
4-Due to dielectric properties and applicator design
energy absorption is selective.
5-Microwave energy have deep penetration in any
material which cause bulk heating and heats to
improved throughput.
6-Instantenous control.
7-Clean transfer of energy to product being heated
and increase energy efficiency causes environment
pollution to reduced.
DISADVANTAGES
1-Material with ionic or metallic conductivity can
be efficiently processed when present in bulk due
to inadequate penetration of microwave energy.
Based on their interaction with microwave material
are classified into:
2-It is difficult to heat insulator from room
temperature to required temperature due to low
dielectric loss.
1-OPAQUE OR ELECRICAL CONDUCTORS:
Material in which microwaves are reflected and do
not penetrate.
3-During processing some material have loss
factor due to temperature leads to hot spots and
thermal runway.
2-TRANSPARENT OR LOW DIELECTRIC
LOSS MATERIAL: Material in which microwave
are neither reflected nor absorbed but transmitted
through the material with little attenuation.
EVOLUTION OF MICROWAVE MATERIAL
PROCESSING:
For
material
processing
microwave energy has been used for nearly sixty
years. It has many advantages over conventional
heating method such as faster throughput, small
size, less energy usage. In early stage microwave
heating in not excepted relatively with fossil fuel
heat which is inexpensive. Dependency of
industrialist on inexpensive fossil fuel and other
conventional method of heating causes slow growth
of microwave heating industry .In 60’s many
microwave
heating equipment
has been
manufactured but their were no technical expert to
use it can’t satisfy the customer. In 70’s
3-ABSORBERS OR HIGH DIELECRIC LOSS
MATERIAL: Material which absorb microwave
energy to a certain degree based on value of the
dielectric loss factor and convert it heat.
ADVANTAGE AND DISADVANTAGE OF
USING
MICROWAVE
PROCESSING
ADVANTAGE:
Imperial Journal of Interdisciplinary Research (IJIR)
Page 285
Imperial Journal of Interdisciplinary Research (IJIR)
Vol-3, Issue-1, 2017
ISSN: 2454-1362, http://www.onlinejournal.in
professional engineer provide appropriate sale
service. In 70’s due to crisis of fossil fuel
manufacturer of microwave equipment ensure that
they will meet the challenge of shortage of fossil
fuel .In 80’s microwave application are used in
many firms and industry.
of a kilowatt. Now microwave come in megawatt
.Microwave processing system has wide range and
large amount of money effort have been spent on
this.
Band
designation
FUNDAMENTALS OF MICROWAVES
4
VLF
3KHz-30KHz
Microwaves are part of the electromagnetic
spectrum that extends from low frequency
alternating currents to cosmic rays.
5
LF
30KHz-300KHz
6
MF
300KHz-3MHz
Frequency bands reserved for industrial application
are 915MHz, 2.45GHz, 5.8GHz and 24.124GHz.
At customary domestic frequency of 2.45GHz, the
magnetrons are the workhorse.
7
HF
3MHz-30MHz
8
VHF
30MHz-300MHz
9
UHF
300MHz-3GHz
10
SHF
3GHz-30GHz
11
EHF
30GHz-300GHz
Material processing falls into this category .In
every kitchen magnetron tubes are used in
conventional microwave oven with power of order
frequency limit
MICROWAVE SYSTEM FOR MATERIAL PROCESSING EXPERIMENTAL DETAILS
Microwave heating apparatus consist of three main
components:
1- Microwave source such as magnetrons in which
microwave are generated.
2- Applicator in which the microwave energy is
transferred to the material.
3- Transmission lines or waveguide which are used
to couple energy of microwave source to the
applicators.
Microwave applicators are generally classified into
single mode cavities.
SINGLE
MODE
MICROWAVE
APPLICATORS AND APPLICTAION:
Single mode microwave applicators are used to
focus the microwave field precisely at given
Imperial Journal of Interdisciplinary Research (IJIR)
location with help of proper design. In single mode
cavities which are designed either rectangular or
circular cross section transverse electric and
transverse magnetic waves are commonly used. In
direction of propagation electrical intensity is zero.
For different configuration different TE and TM
waves are different for a waveguide which are
derived
from
mathematical
solution
of
electromagnetic waves either in rectangular or
cylindrical waveguide. Configuration of field is
called mode.
1-ENVIRONMENT
AND
PROCESSING APPLICATIONS:
MINERAL
Microwave assisted process employing single
mode cavity were used for environmental
application such as hydrolysis of oil contaminated
drill cutting gas stripping operation single mode
microwave system of varying power 0-1KW was
Page 286
Imperial Journal of Interdisciplinary Research (IJIR)
Vol-3, Issue-1, 2017
ISSN: 2454-1362, http://www.onlinejournal.in
used. High microwave power level and high
electric field strength were two major factors to
determine mechanism of oil removal of
polyaromatic hydrocarbon from contaminated soil
can be activated with help of microwave heating
under moderate processing condition. In mineral
Microwave sintering of nanocrystalline alumina
and titanium compacts were successfully
performed in single mode microwave set up
operated at frequency of 2.45 GHz. Microwave
processing has advantages over conventional
sintering w.r.t. sintering time, production cycle
time and energy consumption. Different materials
have different magnetic (H) and electric (E) heating
effect. Heating effect due to H field was more
effective than E field for high electric conductivity.
For example powdered metal. Heating effect due to
E field was more effective than H for low
conductivity sample. For Example pure ceramic.
MULDIMODE
APPLICATION:
MICROWAVE
Multimode microwave applicators are closed
volume, totally surrounded by conducting walls
and have large cavity to permit more than one
mode of electric field. For processing bulk material
or array of discrete material multimode microwave
application. Multimode use less sensitive to
position or geometry, adaptable to batch or
continuous flow and are suited for hybrid heating.
1-APPLICATION IN FOOD PROCESSING: Used
as household application for food preparation and
reheating applications. It is used in microwave
oven. Thawing time was found to increase linearly
with the volume and effective increase in the
thawing rate was observed with decrease in load
aspect ratio.
2-CERAMIC AND POLYMER APPLICATION:
Microwave sintering of ceramic material such as
alumina/zirconium system and mullite/zirconium
system were carried out in a 900w, 2.45GHz
Which provides a good approximation for
microwave propagation for semi-infinite samples
whereas Maxwell’s equation provides the exact
solution for microwave propagation within
samples. Barringes performed a comparative
analysis of microwave power and temperature
profiles for thin slab between experimentally
measured value and predicted value based on
Lambert’s law Maxwell’s field equation and a
combined equation. They found the Lambert’s law
and combined equation. They found the Lambert’s
law and combined equation predicted a much
slower heating rate. While Maxwell’s field
equation gave a much more accurate prediction.
Imperial Journal of Interdisciplinary Research (IJIR)
processing microwave heating used in purification
of single wave carbon nanotubes at different
temperature.
2-CERAMIC AND METAL SINTRING
APPLICATION:
microwave oven and it was found that the
densification was enhanced up to 46% due to
addition
of
zirconium.
Enhancement
in
densification up to 60% was observed with
microwave sintering of amorphous alumina
powder.
3-VARIABLE FREQUENCY MICROWAVE
PROCESSING: Processing system was developed
in order to overcome the nonuniformity in
microwave power within multimode cavities,
which result in multiple hotspot. Variable
frequency microwave furnace consist of travelling
wave tube amplifier capable of sweeping frequency
of microwave field which result in time averaged
power uniformity within the microwave cavity.
Due to time averaged heating process variable
frequency microwave eliminate arising and
localized heating problem.
THEORITICAL
INVESTIGATION
AND
MODELLING
APPROCHES:
Microwave
heating
involves
the
propagation
of
electromagnetic waves within the sample medium.
The heat generation within materials is due to
dipole interaction via dielectric loss heat transport
is governed by conduction for solid substance and
convective transport is important for liquid heating.
LAMBERT’S
LAW
VS
MAXWELL’S
EUATION: Most of work during 1970 and 1980
were based on Lambert’s law for formulation of
power absorption but later during earily 1995
Ayappa and co-workers established the theoretical
foundation on combined electromagnetic and
thermal transport using Maxwell’s equation.
Lambert’s
law
based
on
transmission
Lambert’s
law
require
easier
analytical
manipulation whereas the solution of Maxwell
equation coupler with the heat transfer equation
and further increases the computational effort many
times.
RESONANCE IN POWER ABSORPTION: In
power absorption resonance occur during
microwave heating as average power absorption
within the sample may have local maxima at
resonant condition. Greater heating effect within
sample is attributed by greater power absorption
within a sample and maxima in power is termed as
‘resonance’. Resonance occur due to the
constructive interference between transmitted and
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Imperial Journal of Interdisciplinary Research (IJIR)
Vol-3, Issue-1, 2017
ISSN: 2454-1362, http://www.onlinejournal.in
reflected waves within the sample and significant
amount of research has been devoted on analysis of
resonance and its effect on microwave power
absorption within samples.
NONUNIFORMITY ON HEATING RATES:
HOT SPOTS/ THERMAL RUNWAY: One of
most significant challenges for microwave assisted
processing of materials is to control heating rate
which arises due to ‘hot spot’ and / or ‘thermal
runway’ within samples. Localized area of high
temperature that develop during microwave
radiation is called hot spot. Hot spot are
undesirable for sintering of ceramics which leads to
product damage whereas in smelting process hot
spots are desirable to quicken the process. So it is
necessary to predict condition under which hot spot
arises so their occurrence can be either avoided or
utilized. In order to predict condition under which
hot spot a mathematical model for microwave
heating based on forced heat equation with dual
reciprocity boundary element method (DRBEM)
was developed and it may be concluded that the
condition of hot spot could be accurately predicted
with DRBEM.
MICROWAVE/MATERIAL INTERACTION:
The material properties of greatest importance in
microwave processing of dielectric are the complex
relative permittivity
∈= ∈′ −
′′
� ∈ ′′ and the loss tangent
tan� =∈ /∈ ′. The
real parts of permittivity ∈ ′ sometimes called
dielectric constant mostly determines how much of
incident energy is reflected at the air sample
interface and how much enters the sample. The
most important property in microwave processing
is the loss tangent ���� or dielectric loss, which
predicts the ability of material to convert the
incoming energy into heat. For optimum
microwave coupling a moderate value of ∈ ′ to
enable adequate penetration should combined with
high value of ∈′′ and ���� to convert microwave
energy into thermal energy. Microwave heat
material internally and the depth of penetration of
energies varies in different material. The depth is
controlled by dielectric properties. Penetration
depth is also controlled by dielectric properties.
Penetration depth is defined as depth which
approximately 1/e (36.79%) of energy has been
absorbed. It is also approximately given by
4.8
√∈′ /∈ ′′ Dp is in cm , f is in GHz and
�� =
�
∈ ′ is the dielectric constant and ∈ ′′ is the
dielectric loss. ∈ ′ and ∈ ′′ dependent on both
temperature and frequency the extent of which
depends on the material. In material with very high
loss tangent the microwave energy density reduces
with distance of penetration into the material.
Imperial Journal of Interdisciplinary Research (IJIR)
During microwave processing microwave energy is
absorbed by material. Some of energy is absorbed
by material and converted to heat which in turn
raises the temperature of material such that the
interior part of material are hotter than surface
since the surface loses more heat to the
surrounding. The characteristic has potential to heat
large section of material uniformity. The reverse
thermal effect in microwave heating does provide
some advantage:
1- Rapid heating of material without overheating
the surface.
2- Reduction in surface degradation when drying
wet material because of lower surface temperature.
3-Removal of gases from porous material without
cracking.
4- Improvement in product quality .
5-Synthesis of new material.
On other negative effect is formation of hotspot and
cracking. Microwave can be transmitted through
much loss; the applicator can therefore be remote
from the power source.
INTERACTION OF MICROWAVE WITH
MATERIALS
APPLICATION
OF
MICROWAVE
HEATING:
1-It is used in power processing.
2-It is used in foodstuff processing.
3-It is used in baking industries.
4-It is used in textile industry.
5-Manufacture of paper and cardboard, drying
starch and paper board is a very important process.
6-Used in automobiles.
7-Used in aerospace.
8-Used in medicine.
9-Used in biomedical.
10-Hyperthermal apparatus for cancer treatment.
11- Processing of biocompatible ceramic implants
using microwaves.
Page 288
Imperial Journal of Interdisciplinary Research (IJIR)
Vol-3, Issue-1, 2017
ISSN: 2454-1362, http://www.onlinejournal.in
12-Development of a passive microwave
radiometer for non contact medical and industrial
thermograph application.
CONCLUSION
The use of microwave heating in material
processing has been reviewed with a significant
number of theoretical and experimental result and
applications .It can be inferred from the above
discussion that the microwave heating is a
promising alternative for conventional heating due
to its high heating rates and significant cost and
energy savings. These are two important factor
employing microwave processing of material and
these are knowledge of dielectric properties and
penetration or skin depth. Dielectric properties
material subjected to microwave irradiation need to
be investigated over range of temperature and
frequency and hence with the knowledge of
dielectric properties ,high dielectric loss material
may be effectively coupled with microwave
whereas low dielectric loss material may be
effectively coupled with microwave whereas low
dielectric loss material are combined with
microwave susceptors to form hybrid microwave
heating. Microwave generated with single mode
cavities overcome these disadvantages. The
uniformity of microwave field in a domestic
microwave oven can be improved by providing
either rotating turns table. Similarly with suitable
design aspects such as increasing the cavity size or
operating at high frequency, uniformity of
microwave heating based on Lambert’s law and
Maxwell’s electromagnetic field equation have
been renewed along with their application. The
system of equation along with appropriate
boundary condition can be solved either by finite
difference or finite element methods. The solution
obtained by Maxwell’s equation can be used to
predict the temperature distribution and power
absorption at various frequencies. Spatial and time
dependent analysis of Maxwell’s equation can be
used to predict the temperature distribution for
various food and ceramic material. In ceramic
processing there models can be used to predict
densification and grain size distribution. In addition
resonance is power absorption due to microwave
heating has been analysed as function of sample
length and dielectric property of material.
In past two decades microwave heating has found
tremendous application in various areas such as
food processing, ceramics, glass, minerals,
polymer, chemical reacting system, environmental
engineering,
biomedical
and
biosciences.
Microwave heating is widely used in food
processing such as cooking, drying, sterilizing,
pasteurizing, thawing temperature, and blanching
of food products .Microwave sintering of ceramics
and metal power showed better heating results and
mechanical properties than conventional. Sintering
can increase reaction rate and polymerization rate
were observed during microwave heating of
chemical reactant and polymer respectively. Thus
Microwave heating is proved to be a better
alternatives than conventional heating due to its
high heating rates reduced processing time and
reduced cost and energy saving.
REFERENCES:
Imperial Journal of Interdisciplinary Research (IJIR)
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