Critical Analysis

Critical Analysis

Critical Analysis

Introduction

Electrical and electro-thermal methods such as microwave, Ohmic heating and pulsed electric field are extremely interesting processes in foods and bio materials processing. Ohmic heating is a novel direct heating method as electrical currents pass through apricots to heat them. Most of The foods contain ionic components such as salts and acids. Although Ohmic heating has shown significant promise in a number of food processes such as sterilization and pasteurization but, there sufficiently are no published scientific evidences to indicate temperature values within a particle during a continuous process. Ohmic heating occurs due to energy dissipation when a current passes through a food product. Alternative Conducting (AC) voltage is applied to the electrodes at both ends of the product body.

The rate of Ohmic heating is directly proportional to the square of the electric field strength and the electrical conductivity. The critical property, which affects on, the Ohmic heating, is the electrical conductivity of the food. Variation of the salinity, pH and applied electrical power during the Ohmic heating may alter the electrical conductivity Several models have been developed based on Ohmic heating of solid, liquid mixtures and experimentally validated for single particle in a static heater There are some models for multiple particle systems in both static and continuous flow of Ohmic heaters The objectives of this study were to investigate the effective parameters on Ohmic heating technology especially to check the quality and shelf life of apricots used in syrups.

In these models effects of particles distribution, particles size, effect of electrical conductivity on heating, overall heating of mixture and effect of salt concentration on heating rate were investigated. Equations of the model were solved with finite element method.

Modeling

In order to generate heat in an Ohmic heating system, an electric field should be applied. The electric field (voltage distribution) is a function of the electrode and system geometry, electrical conductivity and the used voltage (Gregory, 1996).

Temperature distribution in a heater which contains a static medium and particle is governed by thermal conduction with internal energy generation. The thermal heat balances for a static medium In order to heat the food using Ohmic heating technology, electrical current through should pass. The heat generated in the food (apricots) (u proportional to the square of its intensity.Discussion

Particle distribution in the field

Looking at the particle distribution of apricots using in syrups, it was found that, salt level has increased the solution electrical conductivity in this process. It also increased internal heat generation and decreased temperature enhancement time. Temperature profile showed that preheating process will effect on the Ohmic heating process and causes distribution uniformity (Oliveira, 1998).

Temperature distribution profiles in a cross section (radial direction) have been shown. It shows salt effect on temperature distribution profile. Particle-liquid mixture temperature increased with time. High values of electrical conductivity of fluid and particle cause more quick temperature enhancement. It reveals that temperature increment increased the electrical conductivity. Therefore, more uniformity in Ohmic heating process with time was observed. Temperature distribution profiles in a cross section for two systems containing pure starch 4 % and starch solution 4 % with salt 1 %. Temperature distribution profiles versus the radial coordinate in the sample planar centre for starch solution 4 % with salt 1 % according to the time Electrical conductivity affected on heat transfer resistance and controlled Ohmic heating rate. An increment in electrolytic content of solution increased the electrical conductivity, widely. Electrical conductivity increases with temperature. Its reason is due to moving ions in conductive solution. These results were supported by Assiry et ...