Ohmic heating, mechanism

A simple thin film technique has been developed to measure the electrical properties of polyelectrolyte solutions under sinusoidal electric fields of 100-500 v/cm at frequencies of. 10-10 KHz. Ohmic heating is largely avoided by the rapid transfer of heat to the electrodes and by the high surface to volume ratios. The resulting temperature is not sufficient to damage the medium. Current and voltage wave forms are monitored directly so that dispersion and nonlinear phenomena of the medium can be viewed directly as functions of frequency, voltage, and concentration of the solution. Possible mechanisms for the observed phenomena are discussed. 

There are various improvements that can be made to the presented model, some improvements could be accomphshed. Foremost among these possible future-work directions is the inclusion of nonisothermal effects. Such effects as ohmic heating could be very important, especially with resistive membranes or under low-humidity conditions. Also, as mentioned, a consensus needs to be reached as to how to model in detail Schroder s paradox and the mode transition region experiments are currently underway to examine this effect. Further detail is also required for understanding the membrane in relation to its properties and role in the catalyst layers. This includes water transport into and out of the membrane, as well as water production and electrochemical reaction. The membrane model can also be adapted to multiple dimensions for use in full 2-D and 3-D models. Finally, the membrane model can be altered to allow for the study of membrane degradation, such as pinhole formation and related failure mechanisms due to membrane mechanical effects, as well as chemical attack due to peroxide formation and gas crossover. 

Microwave radiation generates heat rapidly inside absorptive materials, and the heat then spreads via conduction through the material. The prime absorption mechanisms are dipolar rotation and electron/anion resistivity that produce ohmic heating (i.e., conductive currents due to the movement of ion or electron charges) [22]. 

An alternative write/erase mechanism that may be exploited to provide a scattering display in smectic liquid crystals [60] relies on the electrothermal reorientation of a material of positive dielectric anisotropy (Fig. 14). The thermal input to the material can be provided either by ohmic heating of stripe electrodes [61] in the cell, or by scanning a visible or infrared laser spot across the device. A dye can with profit be incorporated into the liquid crystal [62] to improve the absorption of the incident light. Typically, the liquid crystal used will pos-... 

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