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The effects of concentration on electrical conductivity of orange juice concentrates during ohmic heating

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Abstract

Ohmic heating is an alternative heating technique, using an electrical current passing through the food product. It can be specially used in pumpable food lines as an alternative heating unit. In this study, orange juice concentrates having 0.20–0.60 mass fraction soluble solids were ohmically heated by using five different voltage gradients (20–60 V/cm). The dependence of electrical conductivity on temperature, voltage gradient and concentration were measured. The ohmic heating system performance coefficients were calculated by using the energies given to the system and taken by the orange juice samples. The mathematical model results, taking system performance coefficients into account, were compared with experimental ones. The predictions of the mathematical model were found to be very accurate.

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Abbreviations

A:

Heat transfer area based on outer surface of test tube (m2)

Ae:

Area of cross-section of the electrodes (m2)

B1:

Empirical temperature constant (S/mK), Table 3

B2:

Empirical temperature constant (S/mK), Eq. 13

B3:

Empirical temperature constant (S/mK), Eq. 14

B4:

Empirical temperature constant (S/mK), Eq. 15

C1:

Empirical constant (S/m), Table 3

C2:

Empirical constant (S/m), Eq. 13

C3:

Empirical constant (S/m), Eq. 14

C4:

Empirical constant (S/m), Eq. 15

conc:

Total soluble solid concentration of the orange juice (mass fraction)

Cp:

Specific heat capacity (J/kg K)

D1:

Empirical voltage gradient constant (S/m(cm/V)−N1), Eq. 13

D2:

Empirical voltage gradient constant (S/m(cm/V)−N2), Eq. 15

\( {\mathop {E_{{{\text{loss}}}} }\limits^ \bullet } \) :

Rate of energy loss (W)

E:

Amount of heat (J)

E1:

Empirical concentration constant (S/m (mass fraction×100)−N2), Eq. 14

E2:

Empirical concentration constant (S/m (mass fraction×100)−N2), Eq. 15

h:

Heat transfer coefficient (W/m2K)

I:

Current (Ampere)

k:

Thermal conductivity of the sample (W/mK)

Kc:

Cell constant (1/m)

L:

Distance between the electrodes (m)

m:

Mass of the sample (kg)

Q:

Amount of heat (J)

R:

Resistance of the sample (m)

t:

Time (s)

T:

Temperature (°C)

\( {\mathop u\limits^ \bullet } \) :

Internal energy generation (W/m3)

v:

Volume of the sample (m3)

V:

Voltage applied (V)

Xw:

Weight fraction of the water in the sample

ρ:

Density of the sample (kg/m3)

σ:

Specific electrical conductivity (S/m)

acc:

Accumulated

amb:

Ambient

exp:

Experimental

fin:

Final temperature

gen:

Generated

in:

Initial temperature

nc:

Natural convection

P:

Predicted assuming Qloss to be equal to zero

T:

Temperature dependent

TC:

Temperature and concentration dependent

TV:

Temperature and voltage gradient dependent

w:

At wall

N1:

Constant in Eq. 13

N2:

Constant in Eq. 14

N3:

Constant in Eq. 15

N4:

Constant in Eq. 15

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Acknowledgement

This study was partially supported by Ege University Science-Technology Research and Application Center (EBILTEM) Project No: 2001/BIL/002, Ege University Scientific Projects Fund Project No: 2001/MUH/03, ETAP Agricultural and Food Products Packaging SA Turkey and Pinar Dairy Products SA Turkey.

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Author notes

  1. Coskan Ilicali

    Present address: Department of Process and Food Engineering, Faculty of Engineering, Universiti Putra Malaysia, 43400 UPM, Serdang, Selangor, Malaysia

Authors and Affiliations

  1. Food Engineering Department, Engineering Faculty, Ege University, 35100, Bornova- Izmir, Turkey

    Filiz Icier & Coskan Ilicali

Authors
  1. Filiz Icier
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  2. Coskan Ilicali
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Correspondence to Filiz Icier.

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Icier, F., Ilicali, C. The effects of concentration on electrical conductivity of orange juice concentrates during ohmic heating. Eur Food Res Technol 220, 406–414 (2005). https://doi.org/10.1007/s00217-004-1043-x

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  • DOI: https://doi.org/10.1007/s00217-004-1043-x

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