Joule heating

Among the applications are: James Prescott Joule first published in December 1840, an abstract in the Proceedings of the Royal Society, suggesting that heat could be generated by an electrical current.

Joule heating is caused by interactions between charge carriers (usually electrons) and the body of the conductor.

The oscillations of the ions are the origin of the radiation ("thermal energy") that one measures in a typical experiment.

It forms the basis for the large number of practical applications involving electric heating.

The use of high voltages in electric power transmission systems is specifically designed to reduce such losses in cabling by operating with commensurately lower currents.

) is:[6] Assuming the element behaves as a perfect resistor and that the power is completely converted into heat, the formula can be re-written by substituting Ohm's law,

The differential form of the Joule heating equation gives the power per unit volume.

Those power lines have a nonzero resistance and therefore are subject to Joule heating, which causes transmission losses.

Joule heating is a flash pasteurization (also called "high-temperature short-time" (HTST)) aseptic process that runs an alternating current of 50–60 Hz through food.

[8] This heating method is best for foods that contain particulates suspended in a weak salt-containing medium due to their high resistance properties.

[4][8] Heat is generated rapidly and uniformly in the liquid matrix as well as in particulates, producing a higher quality sterile product that is suitable for aseptic processing.

[11] This heating method is best for foods that contain particulates suspended in a weak salt containing medium due to their high resistance properties.

[10] Ohmic heating is beneficial due to its ability to inactivate microorganisms through thermal and non-thermal cellular damage.

[9][10][11] Although ohmic heating has not yet been approved by the Food and Drug Administration (FDA) for commercial use, this method has many potential applications, ranging from cooking to fermentation.

[11] There are different configurations for continuous ohmic heating systems, but in the most basic process,[11] a power supply or generator is needed to produce electrical current.

[11] The current continues to flow to the second electrode and back to the power source to close the circuit.

[10] The electrical field strength and the residence time are the key process parameters which affect heat generation.

[11] The efficiency by which electricity is converted to heat depends upon on salt, water, and fat content due to their thermal conductivity and resistance factors.

[11] This prevents overheating of the liquid matrix while particles receive sufficient heat processing.

[9] Table 1 shows the electrical conductivity values of certain foods to display the effect of composition and salt concentration.

[11] The high electrical conductivity values represent a larger number of ionic compounds suspended in the product, which is directly proportional to the rate of heating.

[9][11][12] Microbial inactivation in ohmic heating is achieved by both thermal and non-thermal cellular damage from the electrical field.

[11][13][14] Decreased processing times in ohmic heating maintains nutritional and sensory properties of foods.

[9] Ohmic heating inactivates antinutritional factors like lipoxigenase (LOX), polyphenoloxidase (PPO), and pectinase due to the removal of active metallic groups in enzymes by the electrical field.

[9] Changes in electrical conductivity limit ohmic heating as it is difficult to model the thermal process when temperature increases in multi-component foods.

[9][10] The potential applications of ohmic heating range from cooking, thawing, blanching, peeling, evaporation, extraction, dehydration, and fermentation.

[10] Prospective examples are outlined in Table 2 as this food processing method has not been commercially approved by the FDA.

[10] Since there is currently insufficient data on electrical conductivities for solid foods, it is difficult to prove the high quality and safe process design for ohmic heating.

The definition of the efficiency of a heating process requires defining the boundaries of the system to be considered.

When heating a building, the overall efficiency is different when considering heating effect per unit of electric energy delivered on the customer's side of the meter, compared to the overall efficiency when also considering the losses in the power plant and transmission of power.