Ohmic Heating Assisted Turmeric Curing ; Performance Evaluation

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Figure 2 : Ohmic heating setup

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Figure 3 : Stainless steel electrode plate

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Figure 4 : Teflon Ohmic heating Chamber

METHODOLOGY

Design consideration for development of Ohmic heating chamber

The heating chamber of the assembly is fabricated as discussed by Darvishi et al., (2013) and Olivera et al., (2014) with some modifications. The experiments were carried out in lab scale ohmic heating chamber. The system consist of a Teflon cylindrical chamber, transformer, thermocouple, digital ammeter and voltmeter that are attached with the system. The capacity of the heating chamber is around 600±5 ml. The heating chamber includes two stainless steel circular disc electrode. The stainless steel and Teflon provide unique ability to resist corrosion, less heat loss, heat damage, chemically reactive and having high mechanical strength. The processing of particulate materials is considered as very complex in view of the many parameters that can play a role, such as different phases (solid, liquid and gas), particle size distributions, different particle shapes, often high concentrations causing particle-particle interactions, etc. keeping this in mind we have considered a wide opening at top of the chamber to operate particulate food material which will be further helpful for handling of the material. A single-phase power supply from the AC mains (220 V, 50 Hz) was used in the experimental set-up. An important consideration in the designing of the power supply system was personal and equipment safety to avoid unforeseen accidents.

Performance Evaluation of Ohmic Heating Chamber

After fabrication of ohmic heating chamber for particulate material like rice, peas, Maize, fruits and vegetables, grains etc. performance evaluation is conducted base of Electric Conductivity. For the ohmic heating purpose a supply of 240V/50Hz is used for the study, to achieve the different levels of electric field strength through a varaic transformer (0-500V) is used. The real time data of current, voltage, power consumption and temperature during the experiment are collected.

The present study involves on the development and functional analysis of ohmic heating chamber based on the principle of electrical resistance induced in the food. Experiments were carried out with 0.1% NaCl solution at an Electric fields (25, 30, 35 V/cm) at 95·C. In this study of ohmic heating fabricated chamber specifically for particulate material and based on electrical conductivity of the product the performance evaluation is determined. Turmeric rhizomes which is a particulate material is cured by ohmic heating. The sample is cut into pieces of 1cm. The solid and NaCl solution is varied and given in table 1 . To evaluate the process applicability for solid foods, turmeric rhizomes was heated with 0.1% NaCl solution in the experimental ohmic heating setup.

Table 1 : Different Solid water Ratio

Solid : water Ratio

Solid(g)

Water(g)

1:1

150

150

1:0.75

171.43

128.67

1:0.50

200

100

1:0.25

240

60

Electrical conductivity (σ) values were obtained as a function of temperature. After each 10sec interval till the temperature of sample reached at 95◦C readings were taken.

Electrical Conductivity was calculated according to the following equation:

σ= …….……………………………. (3.1)[pic 8]

Where I is the current intensity (A), V is the voltage (V), L is the gap between the electrodes (m) and A is the electrode surface area (m2). (F. Marra et al. 2008).

Model for performance evaluation

For the steady state case, the voltage distribution within a conductor developed by combining Ohm’s law and the continuity equation for electric current is:

∇(σ∇V)=0 …………………………………. (3.2)

For a stationary medium, with negligible internal heat conduction resistance, the energy balance may be written as:

ův=mCp+Ėloss …………………………………. (3.3)[pic 9]

The volumetric heat generation rate is:

ů=|∇V|2σ ..………………………………… (3.4)

The average voltage gradient assuming that the voltage only changes in the axial direction can be written as:

∇V= ………………………………….. (3.5)[pic 10]

The energy given to the system was calculated by using the current and voltage values recorded during the heating experiments:

Egiven=ΣΔV/t ………………………..…..…… (3.6)

The heat required to heat the sample to a prescribed temperature was calculated as:

Qtaken=m Cp (Tfin – Tin) ………………..……… (3.7)

The specific heat capacities of the orange juice concentrates were assumed to be independent of temperature. The energy given to the system will be equal to the energy

Required to heat the sample plus the energy loss:

Egiven= Qtaken + Eloss ………………………….. (3.8)

The energy loss term in Eq. 3.8 represents