M.Tech Seminar

1. Electrohydrodynamic
Drying of Food
Anas Shaikh (18AG63R07)
First Year M.Tech (Food Process Engineering)
Indian Institute of Technology, Kharagpur,
India

2. Background
 Drying – important unit operation in food processing – aids in preservation
Drying Technique Advantages Shortcomings
Convective, conductive,
radiative heating
- Low moisture
- Microbial & chemical stability
- Energy intensive
(10% of energy used in food industry)
– Undesirable changes in foods
Freeze Drying - Excellent sensory characteristics
- Excellent rehydration properties
- Expensive & difficult implementation
Microwave & Radiofrequency
Drying
- Decreased drying times - Scale-up problems
Osmotic Dehydration - Energy efficient - Longer drying times
 Therefore, there is a need of a drying technique that fulfills the following criteria:
- Less Energy-Intensive
- Minimum Damage to Food Materials
- Enhanced Drying Rates
- Economically feasible
- Environmentally sound
Table 1. Advantages and shortcomings of conventional and some novel drying techniques (Singh, et al., 2012;
Bajgai, et al., 2006)

3. Introduction to Electrohydrodynamic Drying
 Electrohydrodynamics
– Use of air ions in a strong electric field to ↑ heat and mass transfer
 Electrohydrodynamic Drying
-Non-Thermal Processing Technology
 Recently gained attention
– 1st study on drying of foods reported for a Potato slab (Chen & Barthakur, 1991)
 EHD drying
– uses the synergistic effect of high voltage and corona wind velocity
Use of High Voltage
Electric Fields
(HVEF’s)
Various types of
discharges,
Corona Discharge
being one
Corona Discharge
leads to induced
electric flows called
EHD flow
Driving Force for
EHD Drying through
enhanced Mass and
Heat Transfer
Fig 1 Schematic view of design of EHD
drying (Courtesy:Dau, et al., 2016)

4. Corona Wind
Electrons
accelerated by
HVEF
Electrons emitted
from the electrode
(called emitter
electrode)
Transfer of kinetic
energy to neutral
gas molecules
Ionization of gas
molecules
(Townsend effect)
Momentum
transfer with
neutral gas
molecules
via collision
Electrical Energy
 Mechanical Energy
Ion drag phenomenon
(due to friction resistance during collision)
Electric Wind/
Corona Wind
Fig 2 (Left) EHD air-flow generation (Right) Air speed distribution (Courtesy:Defraeye& Martinenko, 2019)

5. Mechanism of EHD Drying
Impingement of
Electric Wind on
food material
Generation of
Impact
Turbulence of Water
(greater just below the
emitter electrode)
Water molecules
acquire sufficient
energy
Phase
Change of
Water from
Liquid to
Vapor
Diffusion of Water from
outer layers to inner
layers
Generation of
concentrationgradient
between the concentric
layers
Drying of entire food
material
Reasons:
 Rapid utilization of the heat of vaporization
 Decrease in Entropy of the water molecules due to their ordered
orientationin presence of electric field
Benefit:
 Food Characteristics are not affected due to thermal damage
 Opens avenues for innovative EHD-assisted freeze drying techniques
Secondary Effect of EHD Drying (Lowering of Temperature of the Food Matrix)
Fig 3 Temperature distribution (Courtesy: Isobe, et al.,
1999)

6. Experimental Set-Up
Fig 4 EHD experimental set-up: 1: desktop computer 2: high voltage power supply 3: multiple-pin electrode 4: grounded plate-type electrode 5: drying chamber 6: digital
balance 7: air blower (Courtesy:Martynenko& Zheng, 2016)

7. Operating Parameters affecting Drying Rate & Energy Consumption
(I) Emitting Electrode configuration
 Type: Point Electrodes (Needles, Pins) or Line Electrodes (Wires)
 Lai and Wong, 2003 reported:
- Performance @ lower voltages: Wire > Needle
- Performance @ higher voltages: Needle > Wire
- Reason: Difference in geometries of the corona generated
(Needle Conical jet; Wire: Slot-type jet) (Kudra & Martynenko, 2015)
 Size of point electrode:
Thin sewing needle > Thick copper needle (Hashinaga, et al., 1999)
 Number of Needles (Multi-point electrode) - Myriad results on drying rates:
- ↑ (Hashinaga, et al., 1999)
- No effect (Bajgai and Hashinaga, 2001)
- ↓ (Dalvand, et al., 2013; Lai & Sharma, 2005)
 Energy consumptionin single and multiple electrode – similar (Singh, et al., 2012)
 Distance between two neighboring electrodes: optimum (Bai, et al., 2011)
Fig 5 Corona wind in different distances between neighboring wires
(Courtesy:Bai, et al., 2011)

8. Operating Parameters affecting Drying Rate & Energy Consumption
(II) Discharge gap
 As discharge gap ↑, electric field strength ↓
 Thus, electric wind velocity ↓, hence drying rate ↓
 An optimum discharge gap – Multi-electrode EHD drying
(Bai, et al., 2011)
(III) Electrode geometry (Shape)
 Water evaporation rate:
Point electrode > Hemispherical > Flat
 Larger the curvature, higher the evaporation rate (Zheng,
et al., 2011)
(IV) Voltage (Electric field intensity)
 Voltage ↑, Current ↑, Ionic wind velocity ↑, Heat transfer ↑,
Drying rate ↑ (Cao, et al., 2004)
𝒗 = 𝑬
𝜺 𝟎
𝝆
- Velocity of Electric Wind (𝑣, m·s-1)
- Electric Field Strength (𝐸, V·m-1)
- Density of air (ρ, kg·m-3)
- Permittivity in vacuum (ε0, 8.854 * 10-2, F·m-1)
Equation given by Cross
(1979)
Fig 6 Corona wind in differentdischarge gaps (Courtesy:Bai, et al., 2011)
𝑬𝒏𝒆𝒓𝒈𝒚 𝑪𝒐𝒏𝒔𝒖𝒎𝒑𝒕𝒊𝒐𝒏 𝜶
𝟏
𝑫𝒓𝒚𝒊𝒏𝒈 𝒓𝒂𝒕𝒆
Influence of the operating parameters on energy
consumptioncan be deduced from the following rule of
thumb:

9. Energy Consumption in EHD Drying
 Low Energy Consumption
– Attractive feature of EHD drying
 Voltage used – high;
but Current involved – very small (µA to mA)
therefore, Power required – insignificant
Electrode
Configuration
Specific Energy
Consumed (kJ/kg)
in EHD drying
Reference
Single needle 100-1,250 (Singh, et al.,
2012)Multiple needle 100-800
Wire electrode 200-5,000
Commodity Specific Energy
Consumed (kJ/kg)
in EHD drying
Reference
Tomato slices
(Multiple needle,
6-10 kV)
4,400-16,500 (Esehaghbeygi
& Basiry, 2011)
Sample Specific Energy
Consumed (kJ/kg) in
spouted bed dryer
Reference
Wheat 3,360-7,683 (Singh, et
al., 2012)Corn 3,290-3,535
Paprika 4,091-6,158
Potato pulp 3,025
Brewery yeast 3,000-3,500
Table 2. Specific Energy Consumption of foods in
spouted bed dryer
Table 3. Specific Energy Consumption of foods in EHD
drying

10. Applications of EHD drying to food materials-I
Food Conditions Parameters Major Findings Reasons and/or Inferences References
Potato
slab
E= 525 kV/m
ρ= 1.293 kg/m3
Electrode
spacing= 1 cm
v(Calc)= 1.37 m/s
v(Meas)= 1.63 m/s
Drying
Kinetics
- Rapid drying rate
- 2 falling rates
instead of constant
rate
- Lowered product
temperature
- Increased heat and mass
transfer by wind
- Rapid evaporation of water
- Rapid dissipation of energy
liberated upon breakage of
intermolecular bonds
- Decreased Entropy
(Chen &
Barthakur,
1991)
Fig 8 (Left) Drying rate as a function of moisture content (Right) Temperature-timecurve for potato slab drying (Courtesy:Chen & Barthakur, 1991)

11. Applications of EHD drying to food materials-II
Food Conditions Parameters Major Findings Reasons and/or
Inferences
Reference
Rice Random
combinations
of:
10-30 kV/m
35-55 mm
(discharge
gap)
25-50 °C
Effect of EHD drying on:
- Rough rice fissuring
- Germination rate
compared to air drying
(@ same temperature)
- No difference in
number of heavy
fissures
- Larger number of
light fissures in EHD
treated rice
- No effect on
germination
characteristics
Considering heavy
fissures-major cause-
loss of Head Rice Yield:
- EHD drying does not
significantly reduce
quality
(Cao, et
al., 2004)
Shrimp 45 kV
9 cm
(discharge
gap)
Comparisonof drying
rate & product
characteristics for:
- EHD drying @ 15 °C
- Air drying @ 15 °C
- Oven drying @ 60 °C
- Drying rates: Oven
(60 °C)> EHD (15 °C)>
Air (15 °C)
- EHD-dried shrimps:
1) Less shrinkage
2) Better rehydration
3) Better color
4) Lower distortion
5) Softer body
- EHD-shrinkage of
muscle fibre-water
loss
- Oven-cell and wall
membrane damage
- Oven-Rehydration
loss-crust formation
& distortion of
muscle structure
- EHD-↓temperature
(Bai &
Sun, 2011)

12. Applications of EHD drying to food materials-III
Food Conditions Parameters Major Findings Reasons and/or
Inferences
Reference
Banana
slices
EHD: 6, 8, 10
kV/cm
MW: 9 & 18
W/g
- Drying time
- Rehydration
ability
- Shrinkage
- Color change
- Energy
consumed
- MW faster than EHD
- EHD better rehydration,
lesser shrinkage &
better appearance
- Specific energy
consumption:
1) EHD: 0.34 kJ/g
2) MW: 9.66 kJ/g
- MW penetrate
deeper into
product
- MW causes cell &
wall membrane
damage
- MW-thermal
effects
(Esehaghbeygi,
et al., 2014)
Fig 9 Color changes of banana slices under various drying conditions: a) Fresh, b) EHD, c) Microwave (Courtesy:Esehaghbeygi, et al., 2014)

13. Concluding Remarks
 Electrohydrodynamic drying is a novel drying technique with higher drying rates as compared to conventional
drying techniques.
 It is an energy efficient technique with reduced power consumption.
 It leads to increased quality retention and lesser quality deterioration of foods.
 Electrohydrodynamically dried food has been found to be free of any foreign species (Bajgai & Hashinga, 2001)–
hence, it is safe & environment friendly.
 The lower energy consumption would lead to reduced costs of drying. However, an economic analysis, which
has not been performed yet, is essential in order to know detailed costs involved.
 Thus, electrohydrodynamic drying proves to be an ideal drying technology with a great potential of applications
in the food industry.
 Therefore, further research on ‘process optimization’ and ‘equipment design’ for the commercialization of EHD
drying is the need of the hour.
 Further innovationssuch as EHD-assisted freeze drying may be possibly explored by exploiting lowered
temperatures during EHD drying.

14. References
Bai, Y. & Sun, B. (2004). Study of electrohydrodynamic (EHD) drying technique for shrimps. Journal of Food Processing and
Preservation, 35(6), 891-897.
Bai, Y., Hu, Y. & Li, X. (2011). Influence of operating parameters on energy consumption of electrohydrodynamic
drying. International Journal of Applied Electromagnetics and Mechanics, 35, 57-65.
Bajgai, T.R. & Hashinaga, F. (2001). Drying of spinach with a high electric field. Drying Technology, 19(9), 2331-2341.
Bajgai, T.R., Raghavan, G.S.V., Hashinaga, F. & Nagadi, M.O. (2006). Electrohydrodynamic drying- a concise overview. Drying
technology, 24(7), 905-910.
Cao, W., Nishiyama, Y., Koide, S. & Lu, Z.H. (2004). Drying enhancement of rough rice by an electric field. Biosystems
Engineering, 87(4), 445-451.
Chen, Y.H. & Barthakur, N.N. (1991). Potato slab dehydration by air ions from corona discharge. International Journal of
Biometeorology, 35(2), 67-70.
Cross, J.A. (1979). Electrostatically assisted heat transfer. In Electrostatistics (pp.191-199). Institute of Physics Bristol and
London.
Dafraeye, T. & Martynenko, A. (2019). Electrohydrodynamic drying of multiple food products: evaluating the potential of emitter-
collecter electrode configurations for upscaling. Journal of Food Engineering, 240, 38-42.
Dalvand, M.J., Mohtasebi, S.S. & Rafiee, S. (2013). Effect of needle number on drying rate of kiwi fruit in EHD drying
process. Agricultural Sciences, 4(1), 1-5.

15. References
Dau, V.T., Dinh, T.H., Terebessy, T. & Tung, B.T. (2016). Bipolar corona discharge based air flow generation with low net
charge. Sensors and Actuators A Physical, 244, 146-155.
Esehaghbeygi, A., Basiry, M. & Sadeghi, M. (2011). Electrohydrodynamic (EHD) drying of tomato slices (Lycopersicon
esculentum). Journal of Food Engineering, 104(4), 628-631.
Esehaghbeygi, A., Pirnazari, K. & Sadeghi, M. (2014). Quality assessment of electrohydrodynamic and microwave dehydrated
banana slices. LWT- Food Science and Technology, 55(2), 565-571.
Hashinaga, F., Bajgai, T.R., Isobe, S. & Barthakur, N. N. (1999). Electrohydrodynamic (EHD) drying of apple slices. Drying
Technology, 17(3), 479-495.
Isobe, S., Barthakur, N., Yoshino, T., Okushima, L. & Sase, S. (1999). Electrohydrodynamic drying characteristics of agar gel. Food
Science and Technology Research, 5(2), 132-136.
Kudra, T. & Martynenko, A. (2015). Energy aspects in electrohydrodynamic drying. Drying Technology, 33(13), 1534-1540.
Lai, F.C. & Wong, D.S. (2003). EHD-enhanced drying with needle electrode. Drying Technology, 21(7), 1291-1306.
Lai, F.C. & Sharma, R.K. (2005). EHD enhanced drying with multiple needle electrode. Journal of Electrostatics, 63(3-4), 223-237.
Martynenko, A. & Zheng, W. (2016). Electrohydrodynamic drying of apple slices: Energy and quality aspects. Journal of Food
Engineering, 168, 215-222.

16. References
Singh, A., Orsat, V. & Raghavan, V. (2012). A comprehensive review on electrohydrodynamic drying and high-voltage electric field
in the context of food and bioprocessing. Drying Technology, 30(16), 1812-1820.
Zheng, D.-J., Liu, H.J., Cheng, Y.-Q. & Li, L.-T. (2011). Electrode configuration and polarity effects on water evaporation
enhancement by electric field. International Journal of Food Engineering, 7(2), 1-12.