Joule heat

The narrow bore of the capillary column and the relative thickness of the capillary s walls are important. When an electric field is applied to a capillary containing a conductive medium, such as a buffer solution, current flows through the capillary. This current leads to Joule heating, the extent of which is proportional to the capillary s radius and the magnitude of the electric field. Joule heating is a problem because it changes the buffer solution s viscosity, with the solution at the center of the... 

Other perturbations have been demonstrated. The pressure,, jump, similar to the T-jump in principle, is attractive for organic reactions where Joule heating may be impractical both because of the solvent being used and because concentrations might have to be measured by conductivity. Large (10 —10 kPa) pressures are needed to perturb equiUbrium constants. One approach involves pressurizing a Hquid solution until a membrane mptures and drops the pressure to ambient. Electric field perturbations affect some reactions and have also been used (2), but infrequentiy. 

The term j(t is the rate of dissipation of energy per unit volume by joule heating. This occurs within the working fluid, and so represents a departure... 

In 1857, Thomson (Lord Kelvin) placed the whole field on firmer footing by using the newly developing field of thermodynamics (qv) to clarify the relationship between the Seebeck and the Peltier effects. He also discovered what is subsequently known as the Thomson effect, a much weaker thermoelectric phenomenon that causes the generation or absorption of heat, other than Joule heat, along a current-carrying conductor in a temperature gradient. 

The primary thermoelectric phenomena considered in practical devices are the reversible Seebeck, Peltier, and, to a lesser extent, Thomson effects, and the irreversible Eourier conduction and Joule heating. The Seebeck effect causes a voltage to appear between the ends of a conductor in a temperature gradient. The Seebeck coefficient, L, is given by... 

Zone electrophoresis is defined as the differential migration of a molecule having a net charge through a medium under the influence of an electric field (1). This technique was first used in the 1930s, when it was discovered that moving boundary electrophoresis yielded incomplete separations of analytes (2). The separations were incomplete due to Joule heating within the system, which caused convection which was detrimental to the separation. 

Studies show that the production of 1kg dry biomass requires 2.0 kg sugar, 0.7 kg oxygen, 0.1 kg ammonia, with the liberation of 12,300 k Joules heat. A typical continuous fermentation operates at a dilution rate (D) = 0.2 h 1, with sugar concentration of 3% (w/v) in the incoming medium. With a fermentor of 50 m3 capacity and 90% utilisation of carbohydrate [ie 0.3% (w/v) sugar in the outgoing medium] what would be ... 

For collision frequencies large compared with the frequency of the electric field, the current remains in phase with the electric field in the reverse case, the current is 90° out of phase. The in-phase component of the current gives rise to an energy loss from the field (Joule heating loss) microscopically, this is seen to be due to the energy transferred from the electrons to the atoms upon collision. 

Hoiiuchi K, Dutta P (2004) Joule heating effects in electroosmotically driven microchannel flows. 

Gidon, S., Lemonnier, O., Rolland, B., Bichet, O., and Dressier, C., Electrical Probe Storage Using Joule Heating in Phase Change Media, Appl. Phys. Lett., Vol. 85, 2004, pp. 6392-6394. 

Micro reactors are seen to have smaller inhomogeneities of the electrical field and less temperature rise in the reaction medium due to the Joule heating effect between the electrodes [70]. Submillimeter interelectrode gaps are expected to reduce the ohmic loss. 

A high electric field inside the capillary generates heat. This so-called Joule heat can destroy the efficiency of separation. An electric field corresponds to a well defined current value for a specific electrolyte system. An ohm plot can be constructed for each electrolyte system by measuring the current at increasing electric fields. For an ideal system, the ohm plot is a... 

Figure 5 Ohm plots and the development of Joule heating of the same buffer system using different cooling methods.

The actual temperature of separation is determined by internal and external factors. The internal factor, as it was mentioned earlier, is the generated Joule heat. The external factor is the temperature control applied by the cooling system. A temperature increase decreases the viscosity of the electrolyte and increases the diffusion of the sample, resulting in zone broadening and a decrease in efficiency. 

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