Design Of The Ohmic Heater

The ohmic heater column typically consists of four or more electrode housings machined from a solid block of poly(tetrafluoroethylene) (PTFE) and encased in stainless steel, each containing a single cantilever electrode (Fig. 2). The electrode housing are connected using stainless steel interconnecting tubes lined with an electrically insulating plastics liner. Suitable lining materials include poly(vinylidene difluoride) (PVDF) and glass. These flanged tube sections are bolted together and sealed with flat food-grade rubber gaskets.

The column is mounted in a vertical or near vertical position with the flow of product in an upward direction. A vent valve positioned at the top of the heater ensures the column is always full. The column is configured such that each heating section has the same electrical impedance; hence, the interconnecting tubes generally increase in length toward the outlet. This is because the electrical

Product outlet

Product outlet

Ohmic Heaters

Figure 2. Design of an ohmic heater column.

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Ohmic Heating Food Processing

Alternating current power supply

Figure 1. Principle of ohmic heating.

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Alternating current power supply

Figure 1. Principle of ohmic heating.

Figure 2. Design of an ohmic heater column.

conductivity of food products usually increases with increase in temperature; indeed, for aqueous solutions of ionized salts there is a linear relationship between temperature and electrical conductivity. This phenomenon is attributed to increased ionic mobility with increase in temperature and also applies to most food products. Exceptions could be products in which viscosity increases markedly at higher temperatures such as those containing ungelled starches.

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