Joule effect, heat losses

Corresponding to the charge in the potential of single electrodes which is related to their different overpotentials, a shift in the overall cell voltage is observed. Moreover, an increasing cell temperature can be noticed. Besides Joule-effect heat losses Wj, caused by voltage drops due to the internal resistance Rt (electrolyte, contact to the electrodes, etc.) of the cell, thermal losses WK (related to overpotentials) are the reason for this phenomenon. 

Jahn-Teller distortions 309 ff Japanese separators 264, 267 Joule effect, heat losses 13 jump frequency, solid electrolytes 532 Jungner nickel cadmium batteries 22... 

When ions flow from one side of the electrolyte to the other, there is ohmic loss and generated heat, due to the Joule effect. 

Adiabatic calorimetry is particularly useful for the study of closed adsorption systems at low temperatures (where radiation losses are small) and for temperature scanning experiments. It is the preferred type of measurement for the determination of the heat capacity of adsorption systems, especially in the temperature range 4-300 K (Morrison et al., 1952 Dash, 1975). The temperature scan is obtained by means of the Joule effect applied to the sample container the sample heating coil shown in Figure 3.14 is used for this purpose. 

Also provided by the finite element solver is the source term SQ in the energy balance, eqn. (6). Except within the H2 release zone, the volumetric heat flux corresponds to heat losses by Joule effect in the conducting materials. In zone , the heat dissipated by the irreversible interfacial processes is computed instead. 

In this type of reactor the charge is used as an electrode. It must then be pointed out that the melt is heated by the plasma as in other conflgurations but also heated by Joule effect and electron condensation (anode) (see Sect. 2.3.2.4.) thus enhancing the efficiency of the heat transfer to the reactants and reducing the heat losses to the electrodes. 

Figure 6.3 illustrates the heat losses that occur in a micro-hotplate when operating. The thermal energy, Q, generated by the Joule effect in the microheater, is given by ... 

Fig. 6.18 shows relative contributions through all the possible heat loss mechanisms, as a function of temperature at surface of the die [4]. The temperature evolution in the plungers/sample/die assembly is a reflection of the synergistic effects of Joule heat generation and heat transfer. The heat is lost from the assembly to the loading train and eventually the water-cooled electrodes through thermal conduction and to the wall of the SPS chamber through radiation. It has been... 

In connection with the sign of the ohmic drops, let us highlight the fact that when in power source mode, the ohmic drop decreases the output voltage of the cell. Yet when in electrolyser mode it leads to an increase in the voltage, which must be imposed so as to trigger the reaction(s). In both cases ohmic drops cause energy losses, in the form of heat loss (Joule effect). 

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 process is thermodynamically reversible when an infinitesimal reversal in a driving force causes the process to reverse its direction. Since all actual processes occur at finite rates, they cannot proceed with strict thermodynamic reversibility and thus additional nonrevers-ible effects have to be regarded. In this case, under practical operation conditions, voltage losses at internal resistances in the cell (these kinetic effects are discussed below) lead to the irreversible heat production (so-called Joule heat) in addition to the thermodynamic reversible heat effect. 

As already mentioned, the induced current Ipl heats the plasma due to joule losses which are proportional to the plasma resistance. With increasing temperature the plasma resistance decreases and the ohmic heating becomes less effective. Theoretical analysis shows that the maximum temperature which can be reached in this way is below 2 keV, i.e. the plasma cannot enter the ignition region of 5 keV4. Therefore,... 

It can be concluded from the above equation that the diameter of the capillary has to be reduced to a few hundred /zm, or less, in order to be able to work at the desired high potential of several tens of thousands of V m without a loss in efficiency due to excess temperature in the center of the capillary. The radial temperature profile also causes changes in other physico-chemical paramaters such as mobilities, pH, density, viscosity, etc. with regard to the dependence of mobilities on the temperature (being c. 2% per IK) the strong effect of Joule heat on the dispersion of zones is quite evident [12]. 

Example 1-4. Into a flask containing 100 g of water at I8.0°C, with a small amount of hydrochloric acid dissolved in it, there was poured 100 g of water, also at 18.0°C, containing a small amount of sodium hydroxide. The temperature of the mixed solution increased to 24.5°C. Neglecting the effect of the substances dissolved in the water and the loss of heat to the flask, calculate how much heat (how many joules) was produced by the reaction of the acid and the sodium hydroxide. 

---