this slide contains basic knowledge on ohmic heating wid a case study

1. Presented by :
ANJALI
SUDHAKAR
(01 PFE/15)
OHMIC HEATING
Assignment under the course :
ADVANCED FOOD PROCESS ENGINEERING
PFE (503)

2. OUTLINES
o Introduction
o Principle
o Parts of ohmic heating
o Mechanism
o Advantage
o Application
o Disadvantage
o Suggestion for improvements
o Case study

3. INTRODUCTION
 Ohmic heating, a thermal electrical heating
method, is also termed as resistance heating.
 Ohmic heating is direct heating method
where food is in contact with the electrodes.
 The concept of ohmic heating is quite simple.
The passage of electric current through an
electrically conductive food material obeys
Ohm’s law (V = IR); and heat is generated
due to the electrical resistance of the food.

4.  Almost all electric power is transformed
into heat.
 It is possible to heat the product containing
large particles upto 2.5 cm in size which
would be damaged in conventional
equipment, to sterilization temperature of
upto 140°C in less than 90 sec.
 It is regarded as Green process.

5. PRINCIPLE
Ohmic heating works on the principle of
Ohm’s law of electricity.
Where V is the voltage (volts)
I is the amperage (amperes)
R is the resistance (ohms)
V = I * R

6. MAIN PARTS OF OHMIC HEATING SYSTEM
Contains mainly 3 parts:
1. Power supply
2. Heater assembly
3. Control panel

7. OHMIC HEATING PROCESS DIAGRAM

8. MECHANISM
Food product (k)
Conducts electricity
Collision of molecules
Momentum transfer to these
molecules
Increase in kinetic energy thereby
heating product

9. The interaction between the local field strength and
local electrical conductivity will govern the local heat
generation according to
Where Q is heat generation rate per unit volume (W/m³)
E is the electric field strength (V/cm)
k is the electrical conductivity (S/m)
λ is the resistivity (ohm-meter)
J is the current density (A/m²)
Q = E²k = λJ²

10. The actual heating rate for the substance
can then be calculated from the equation:
Where T is temperature in degree Celsius
t is the time in second
ρ is the density (kg/m³)
C is the specific heat capacity(kJ/kg-
C)
ρC is the volumetric heat capacity
dT /dt = Q/ ρC

11. FACTORS INFLUENCING HEAT GENERATION RATE
 Electrical field strength
- can be adjusted by changing voltage.
 Electrical conductivity
- practically possible only between the range of
(0.01 -10 S/m) and it works optimally in the range
(0.1 - 5 S/m).
 Temperature
- depend on the electrical conductivity.

12. ADVANTAGES
 Temperature required for UHT processing can
be achieved.
 No problem of surface fouling or over heating
of the product.
 Useful in pre-heating products before
canning.
 Energy conversion efficiencies are very high.
 Suitable for continuous processing.
 Lower capital investment as compared to
microwave heating and conventional heating.

13.  Large-scale process can be carried out in
heavy-duty ohmic cookers or batch ohmic
heaters.
 It has a high solid-loading capacity.
 Causes less nutrient loss.
 It provides rapid, uniform treatment of liquid
and solid phases with minimal heat damage.
 Less maintenance cost.
 Eco-friendly.

14. APPLICATIONS
.
BLANCHING EXTRACTION
DEHYDRATION
FERMENTATION EVAPORATION

15.  The ohmic heating system allows for the production
of new, high-added-value, shelf-stable products with
a quality previously unattainable with alternative
sterilization techniques, especially for particulate
foods.
 Ohmic methods offer a way of processing particulate
food at the rate of HTST processes, but without the
limitation of conventional HTST on heat transfer to
particulates.

16. MICROBIAL INACTIVATION DURING OHMIC HEATING
Microbial
inactivation
Non-thermal
Mechanical
(disruption of cell
membrane)
Chemical
(Formation of free
radicals and
metals ions )
Thermal
Kill bacillus
subtilis spores

17. PHYSICAL AND CHEMICAL CHANGES
 Nutritional effect
Larger particle
(smaller surface
to volume ratio)
Shorter time
Reduction in
solute loss

18.  Protein Coagulation / Denaturation
- High molecular weight proteins are
more susceptible to heating.
- Coagulate protein and partially purify
proteolytic enzymes in fish.
- Mild ohmic heating (55°C for 3 min at 90
volt) is the efficient step for
concentrating the proteinase.

19. SPECIFIC FOOD PRODUCTS
Meat
Fish
Milk
•Complex
food
•Muscle fiber
•Uniform
heating
•No change
in water
soluble
protein
•Effective
pasteurization
with no additional
protein
destruction

20. Fruits
Vegeta
bles
Egg
•Juice
extraction
•Juice
preservation Blanching
•Pasteurize
egg
•Reduce
fouling

21. ECONOMICS OF OHMIC PROCESSING
Economically attractive &
sustainable
Practical benefits
> 90% energy efficiency

22. DISADVANTAGES
o Lack of generalized information.
o Requested adjustment according to the
conductivity of dairy products.
o Narrow frequency band.
o Difficult to monitor and control.
o Complex coupling between temperature and
electrical field distribution.
o Limited to DC current.

23. SUGGESTIONS FOR IMPROVEMENT
 Develope predictive, determinable and reliable
models of ohmic heating.
 Reliable feedback control to adjust the supply power
according to the conductivity change of the dairy
liquid.
 Developing real time-temperature monitoring
techniques for locating cold-spots and overheated
regions during ohmic heating.
 Developing adequate safety and quality-assurance
protocols in order to commercialization of ohmic
heating technology.

24. CASE STUDY
Tomato peeling by ohmic heating with lye-salt
combinations:
Effects of operational parameters
on peeling time and skin diffusivity
The Ohio State University, Department of Food, Agricultural and Biological
Engineering, 590 Woody Hayes Drive, Columbus,
OH 43210, USA

25. CONTENTS
 Introduction
 Objective
 Materials and methods
 Results and discussion
 Conclusion

26. INTRODUCTION
 Base (NaOH/KOH).
 Provides smooth surface of peeled tomato.
 Generate environmental problem.
 Difficult and costly to treat.
LYE

27. OBJECTIVE
1. To determine the effects of field strength
and salt-lye composition on the time
required for peeling, and
2. To determine the effect of electric field and
temperature on the diffusivity of sodium
hydroxide through tomato peel.

28. MATERIALS AND METHOD
1). Experimental setup
 Power supply- 60 Hz , 0-1000 volt
 Ohmic heater- L= 0.201 m, D= 0.051 m
 Titanium electrode- gap= 6.2 cm
 Thermocouple
 Data logger

29. 2. Experimental procedure
Receive local tomato of same
variety
Heating starts at 25±1°C/
record parameters
Power supply off when peel
cracked
Tomato was peeled by washing
in water

30. 2.1. Effect of electric field strength and type of fluid medium
NaCl / NaOH
Mixture(%w/v
)
0.01/0.01 _ _ _ _ _ 3230 4840 6450
0.01/0.05 _ _ _ _ _ 3230 4840 5650
0.01/0.1 _ _ _ 1610 2420 3230 _ _
0.01/0.5 _ _ 1210 1610 _ _ _ _
0.01/1.0 645 806 1130 1450 _ _ _ _
0.03/0.01 _ _ _ _ _ 3230 4840 _
NaCl / KOH
mixture
0.01/0.5 _ 806 1210 1610 2020 _ _ _
0.01/1.0 _ 806 1130 1290 _ _ _ _
Field strength (V/m)
Table: Experimental treatments for studying effects of electric field strength, and
concentrations of NaCl/NaOH and NaCl/KOH mixtures on tomato peeling.

31. 2.2. Diffusion analysis during tomato lye and ohmic peeling
Peel preparation
(t= 0.02 cm, d=1.8cm)
Check cell leakage/
Kept in water bath
Kept in diffusivity cell
(2 reservior : 1250cm³)
Pour 950 cm³ pre-
heated 7% NaOH and
0.01% NaCl .
Pre-assigned temp.
(50º & 65ºC) is
recorded
Continuously stir
solution
Withdraw 5 ml of NaCl
at every 1 minute
Continue it until
diffusivity rate gets
steady
Diffusivity is measured
by a software FLUENT

32. RESULTS AND DISCUSSION
Effects of electric field strength and concentrations of media NaCl/NaOH mixture

33. Relationships between the total amounts of NaOH diffusing through the tomato
skin (Q) and time (t) during ohmic and control treatments
(At 50ºC)
(At 65ºC)

34. Diffusivity values of NaOH diffusing through the tomato skin over time during
ohmic and control treatments
(At 50ºC)
(At 65ºC)

35. CONCLUSION
 Ohmic tomato peeling treatments of 0.01/0.5% NaCl/NaOH
at 1610 V/m and 0.01/1.0% NaCl/NaOH at 1450 V/m were
the conditions that required the shortest time for cracking.
 For NaCl/KOH mixtures, 0.01/0.5% NaCl/KOH at 2020 V/m
and 0.01/1.0% NaCl/KOH at 1450 V/m required the shortest
time for cracking.
 Following an initial period, diffusivities for lye peeling with
ohmic heating were greater than those without ohmic
heating at both 50 and 65 C.
 The electric field enhances the diffusion of NaOH through
the tomato skin during the peeling process.

36. REFERENCE
 Nagasri, Pisit Wongas & Sastry, Sudhir.K., (2016). “Tomato
peeling by ohmic heating with lye-salt combinations: Effects
of operational parameters on peeling time and skin
diffusivity.” Journal of Food Engineering. 186: 10-16.
 Andrew Proctor, 2011. “Alternatives to Conventional Food
Processing”. Royal Society of Chemistry. 307-334.

37. Thank you