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Development of industrial prototype
of microwave technology for drying
of agricultural products
M. Nisoa and Pr. Kerdtongmee
Plasma technology for agricultural applications
research laboratory
School of Science, Walailak University
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Topics
• Microwave interaction with bio-materials
• Applications of microwave heating
• Advantages of microwave drying
• Laboratory prototype system
• Small industrial prototypes
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Microwave and its interaction with bio-materials
Maxwell’s equations𝜵 × 𝑬 = −
𝜕𝑩
𝜕𝑡
𝜵 × 𝑯 = 𝑱 +𝜕(𝜀𝑬)
𝜕𝑡
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Microwave and its interaction with bio-materials
Dielectric heating
materials
Dipole molecules
j
Selective heating
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Applications of microwave heating
Microwave
Heating
T < 100o C
T < 180o C
T < 60o C
T > 300o C
Cooking
Processing of materials
Extraction
Drying
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Advantages of microwave drying
• Alternative use during rainy season
• Fast and energy efficiency
• Preserve good qualities
• Bulk heating
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Advantages of microwave drying
Fast and energy efficiency
Dried materials Methods SEC(MJ/kg)
Okara (Product from
soymilk) Jet spouted bed with hot air 1.6 – 4.1
vegetable starch solutions
Jet spouted bed with hot air 3 - 5
Rice grain Fluidized-bed drying with hot air 4.7-7.0
Barley FIR – convection 12.1 – 20.3
Oion Osmo – convective drying 7.2 – 12.6
Carrot Microwave 0.4 – 1.4
Pumpkin Microwave – air drying 0.1 – 0.6
Specific energy consumption SEC =Total energy supplied in drying process
Amount of water removed during dryingkJ/kg
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Advantages of microwave drying
Preserve good qualities (Leaves of Coccinia grandis)
Fresh
1 h microwave drying
8 h solar drying
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Laboratory prototype system
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Laboratory prototype system
Control of microwave power
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Laboratory prototype system
Control of microwave power
Power efficiency is about 67%
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Laboratory prototype system
Door’s choke configuration for leakage suppression
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Laboratory prototype system
Typical drying curve
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Laboratory prototype system
Nonlinear drying effect
Run away heating
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Laboratory prototype system
Food chemistry
e
a
b
c
d
0.0
0.5
1.0
1.5
2.0
C 10 W 15 W 20 W 25 W
Fre
e fa
tty
aci
d c
on
ten
t (g
/100 g
lip
id)
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Laboratory prototype system
Sensory test
123456789
Colour
Appear
ance
Odor
Hardnes
sTas
teTex
ture
Overall
liking
Attributes
Scale
(1-9
)
Microwave
Sun dry
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Small industrial prototype
Multi-magnetron
And power controlMulti-modes cavity
Leakage’s shielding
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Small industrial prototype
1
2
3
4
5
6
Uniformity of the microwave field
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Small industrial prototype
Uniformity of the microwave field
Capacity 60×70×160 cm3
Microwave power 4.8 kW, 6 magnetrons
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Small industrial prototype
Drying of graviola leaf
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Small industrial prototype
Drying of cardamom
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Small industrial prototype
Drying of coix seed
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Small industrial prototype
Drying of surimi
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Small industrial prototype
Drying of salmon fish’s skin
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Small industrial prototype
Drying of fish
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Small industrial prototype
Thawing frozen fishes
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Small industrial prototype
Conveyor microwave food processing
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Small industrial prototype
Weevill control in rubber wood for children’s toys
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ขนาด: ไม ้1000 kg/10นาทีก าลงั: 72 kW (50 magnetrons)
Small industrial prototype
Weevill control in rubber wood for children’s toys
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Power 72 kWCapacity: 200 cm x 200 cm x 200 cm
Treatment 1 ton within 20 minutes
Small industrial prototype
Weevill control in rubber wood for children’s toys
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Small industrial prototype
Drying of rubber block STR20
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Petty patent
1.ไดรั้บการคุม้ครองอนุสิทธิบตัรเร่ือง เคร่ืองใหค้วามร้อนเมลามีนก่อนข้ึนรูป (Preheat)ดว้ยคล่ืนไมโครเวฟ
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Petty patent
2.ยืน่จดอนุสิทธิบตัรเร่ือง เคร่ืองใหค้วามร้อนวสัดุผสมยางดว้ยคล่ืนไมโครเวฟ
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Petty patent
3. ยืน่จดอนุสิทธิบตัรเร่ือง เคร่ืองอบลูกเดือนก่อนการแปรรูปดว้ยคล่ืนไมโครเวฟ
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Patent
4. ยืน่จดสิทธิบตัรเร่ือง เคร่ืองอบรังนกแอ่นความดนัต ่าดว้ยคล่ืนไมโครเวฟ
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การถ่ายทอดเทคโนโลยใีหภ้าคเอกชนในเชิงพานิชย์
1. การถ่ายทอดเทคโนโลยกีารอบแหง้และควบคุมก าลงัไมโครเวฟ ใหก้บั ภาคเอกชน บ.ไซโนเทค จ าจดั วงเงิน 600,000 บาท ระยะเวลา 5 ปี
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การถ่ายทอดเทคโนโลยใีหภ้าคเอกชนในเชิงพานิชย์
2. การถ่ายทอดเทคโนโลยีการควบคุมก าลังไมโครเวฟ ให้กับ ภาคเอกชน บ.ประดู่ เอ็นจเินียริ่ง จ าจัด วงเงิน 450,000 บาท++ ระยะเวลา 5 ปี
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Thank you very much
Questions and Comments
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The 20th International Drying Symposium (IDS 2016)
Gifu, JAPAN, 7-10 August 2016
DEVELOPMENT OF INDUSTRIAL PROTOTYPE OF MICROWAVE
TECHNOLOGY FOR DRYING OF AGRICULTURAL PRODUCTS
Mutorlep NISOA1* and Priwan KERDTONGMEE2
1Plasma agricultural application research laboratory, Walailak University
222 Taiburi, Tasala, Nakhon-si-thammarat,80160, Thailand
Tel.:+66-75-672-006, E-mail: [email protected]
2Center for scientific and technological equipment, Walailak University
222 Taiburi, Tasala, Nakhon-si-thammarat, Thailand, 80161
Tel.:+66-75-673-248, E-mail: [email protected]
Abstract: The conventional method for drying agricultural products, such as fish, chili,
fruits and herbs, is by hot air circulation. Normally, it will take long time and high energy
consumption for finishing products. An alternative drying method by using microwave
energy has been developed at Walailak university. Because of strong interaction between
dielectric dipoles of water molecules and microwave field, the drying time of the
agricultural products can be reduced drastically. We have developed a novel microwave
heating system for the efficient drying of the products. The system utilizes a phase control
high-voltage power supply so that the magnetron can generate a microwave field
continuously, and its output power can be adjusted for each magnetron. Door chokes have
been carefully investigated by simulation and experiment for safety of microwave
leakage. The experimental results reveal that heat produced by the microwave system
causes evaporation of moisture from the products at low temperature, making it possible
to produce high quality dried foods and herbs. The prototypes of various microwave
drying systems for different agricultural products have been developed and used by local
industries and communities. These prototypes have high-potential for foods and herbs
business in the future.
Keywords: agricultural products, microwave drying, dielectric dipole, industrial prototype,
Door choke
INTRODUCTION
The conventional drying process of agricultural
products around the world utilizes heat from the sun
in the dry season or heat from burning wood or gas
during the rainy season as energy sources. Such
natural energy sources unfortunately require long
period of time for drying, and may lead to
contamination from dust and pathogens.
Consequently, it is very difficult to control the
quality of the dried products. Microwave technology,
developed for RADAR application in the 2nd World
War: (ET Thostenson and TW Chou,1999), has long
been known as an effective energy source for the
drying of agricultural products: (JM Osepchuk,
2002). Microwaves are electromagnetic waves with a
frequency ranging from 300 MHz to 300 GHz.
Typically, microwaves at 2.45 GHz are used for
processing food products because these materials
contain a lot of water molecules which can absorb
energy from microwave field very effectively: (AK
Datta, E Sun and A Solis, 1995). The dried products
can preserve good qualities of nutrition, colour,
texture and aroma. Although microwave drying has
shown proven advantage, utilization of microwave
drying for businesses, industry or small and medium-
sized enterprises, are quite limited: (M. Zhang, J.
Tang, A.S. Mujumdar and S. Wang, 2006). To
promote microwave drying technology, scaling up of
the microwave oven, as shown in Fig. 1, is necessary.
In the paper we will we will present the development
of industrial prototype of microwave technology for
drying of agricultural products.
C-4-3
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Fig. 1. Scaling up of the microwave oven
DEVELOPMENT OF INDUSRTRIAL
PROTOTYPE
Fig. 2. Drawing of the industrial prototype
microwave drying system
The industrial prototype microwave drying system
shown in Fig. 2 has dimension of 60×70×160 cm3,
powered by six magnetrons, mounted vertically on
the same cavity surface. There are twenty rotatable
trays for placing agricultural products. The picture of
the prototype is shown in Fig. 3.
Fig. 3. Picture of the prototype
Phase control high-voltage power supply
Fig. 4. Diagram of phase controlled magnetron
circuit
Fig. 5. Dependence of microwave power on phase
angle
Microwave oven utilizes on-off power control
scheme for delivering microwave energy to the loads.
During the on duration whereas maximum
microwave power is radiated, serious damages, such
as burning, run away heating, arcing, may occur to
the materials. It is quite difficult to obtain high-
quality dried product by on-off microwave oven.
Phase control microwave power has advantage of
adjustable power for suitable drying of various kinds
of agricultural products. Therefore dried product will
preserve its original properties. The diagram of the
phase controlled circuit to power magnetron is shown
in Fig. 4. Triac is a power electronic device that will
function as switch to control the flow of electric
current. Therefore variable waveform, depending on
the phase angle, will supply to the high-voltage(HV)
transformer which resulted in different microwave
power as shown in Fig. 5. The microwave power is
generated by magnetron when biasing by high-
voltage and heating its filament. The threshold high-
voltage is about 3.5 kV for minimum microwave
power output, whereas maximum high-voltage is
about 7 kV, to generate highest microwave power
about 800 W. Each magnetron is separately
controlled to generate microwave power.
Cavity Cavity
Magnetrons
Trays
y
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Multi-modes, multi-magnetron cavity
Fig. 6. Distribution of microwave power in the cavity
The uniformity of the microwave power in the cavity
is shown in Fig. 6. The microwave power density is
measured by using water load placed on the trays
along the vertical y axis.
Performance of the system
Fig. 7. Diagram of phase controlled magnetron
circuit
To evaluate the drying performance of the system,
fresh leaves of Coccinia grandis are placed on the
each tray as shown in Fig. 7 to heat by microwave
radiation. The experiments show that drying of 400
grams of Coccinia grandis take only about 1 hour as
shown in Fig. 8 and Fig. 9.
Fig. 8. Decreasing of mass of Coccinia grandis
leaves on time
Fig. 9. Drying rate of Coccinia grandis leaves at
different times.
Microwave power can be appropriately chosen to
preserve their original color. The color is better
preserved than color of those drying by sunlight and
by on-off power control household microwave oven
as shown in Fig. 10 and Fig. 11
Fig. 10. Dried leaves obtained by on-off control of
microwave power.
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Fig. 11. Dried leaves obtained by phase control of
microwave power.
CONCLUSIONS
The experimental results reveal that heat produced by
the microwave system causes evaporation of
moisture from the products at low temperature,
making it possible to produce high quality dried
foods and herbs. The prototypes of various
microwave drying systems for different agricultural
products have been developed and used by local
industries and communities. These prototypes have
high-potential for foods and herbs business in the
future.
ACKNOWLEDGEMENTS
We would to Thailand Excellent center in
Physics(ThEP) and the institute of research and
development, Walailak University, for their funding
support.
REFERENCES
Datta, A.K.; Sun, E.; Solis, A. Food Dielectric
Property Data and Their Composition-Based
Prediction: Engineering Properties of Foods;
Marcel Dekker Inc.; New York, 1995, p. 457-494.
Osepchuk, J.M. Microwave power applications.
IEEE Transactions 2002, 50, 975-985 .
Thostenson, E.T.; Chou, T.W. Microwave
processing: fundamentals and applications.
Composites: Part A 1999. 30, 1055-1071.
Zhang, M.; Tang, J.; Mujumdar, A.S.; Wang, S.
Trends in microwave related drying of fruits and
vegetables. Trends in Food Science &
Technology 2006, 17, 524-534