Peltier heating

Voltage measurement have been made at very low temperatures using a superconductor as one leg of a thermocouple. Eor a superconductor, S is zero, so the output of the couple is entirely from the active leg. The Thomson heat is then measured at higher temperatures to extend the absolute values of the Seebeck coefficients (7,8). The Thomson heat is generally an order of magnitude less than the Peltier heat and is often neglected in device design calculations. 

Besides the reversible production of heat at the junctions, there is an evolution of heat all round the circuit due to frictional resistance, this Joule s heat being proportional to the square of the current, and hence not reversed with the latter. There is also a passage of heat by conduction from the hotter to the colder parts. But if the current strength is reduced, the Joule s heat, being proportional to its square, becomes less and less in comparison with the Peltier heat, and with very small currents is negligible. We shall further assume that the reversible thermoelectric phenomena proceed independently of the heat conduction, so that the whole circuit may be treated as a reversible heat... 

The direct measurements of Jahn (1888, 1893) and of Gill (1890) show that the latent heat A arises at the surfaces of contact of the electrodes and electrolyte and is fully accounted for by these Peltier heats at the junctions of conductors. The equation of 197 ... 

Specific resistance, Thermal conductivity, Peltier heat against lead, Thomson heat,... 

Meckler, M., "Use Peltier Heat Pumps to Improve Process Separation Availability," in Proceedings of the 14th Intersociety Energy Conversion Conference, Vol. 2, pp. 1780-1787, ACS, Washington, D.C. (1979). 

Electrochemical calorimetry — is the application of calorimetry to thermally characterize electrochemical systems. It includes several methods to investigate, for instances, thermal effects in batteries and to determine the -> molar electrochemical Peltier heat. Instrumentation for electrochemical calorimetric studies includes a calorimeter to establish the relationship between the amount of heat released or absorbed with other electrochemical variables, while an electrochemical reaction is taking place. Electrochemical calorimeters are usually tailor-made for a specific electrochemical system and must be well suited for a wide range of operation temperatures and the evaluation of the heat generation rate of the process. Electrochemical calorimeter components include a power supply, a device to control charge and discharge processes, ammeter and voltmeter to measure the current and voltage, as well as a computerized data acquisition system [i]. In situ calorimetry also has been developed for voltammetry of immobilized particles [ii,iii]. 

Electrochemical Peltier heat - molar electrochemical Peltier heat... 

Molar electrochemical Peltier heat (II) — accounts for the amount of heat absorbed or released when an electrochemical reaction takes place under isothermal and reversible conditions and one mol of electric charge or ions is transferred from one phase to another. The molar electrochemical Peltier heat n comprises two contributions one comes directly from the entropy of the reaction taking place at the electrode and another is provided by the movement of ions in solution by migration (-> transport entropy S or -> Eastmans entropy). By convention the molar electrochemical Peltier heat is considered positive for an exothermic anodic reaction. For... 

Peltier heat — is the amount of heat absorbed or released when electrically charged particles (i.e., -> electrons or -> ions) are transferred from one phase to another under isothermal and reversible conditions [i]. See also -> molar electrochemical Peltier heat. 

Seebeck effect — is the potential difference that results when the joins of two different metals are at different temperatures and induces a movement of charge through the conductors. The Seebeck effect is the opposite of the Peltier effect (see - Peltier heat). 

In 1834, Peltier observed that the passage of electric current/through a bimetallic circuit caused the absorption of heat at one junction and rejection of heat at the other junction. The heat flow per unit current at constant temperature was called the Peltier heat qPe, and defined by... 

Figure 7.5 shows a composed of a bimetallic couple metal wires a and b with one junction maintained at temperature T and the other maintained at T+ dT. An electromotive force E causes a current / to pass through the wires. A Peltier heat qpe(T + dT) per unit current will be absorbed at the warm junction and an amount of heat qpe(T) will be given off at the cool junction. To maintain a temperature gradient, Thomson heat (q l h i)(dT) must be supplied to the metal a, and an amount of heat (r/Th h)(c/7 j must be removed from b, since the current is in the opposite direction in metal wire b. In a closed work cycle, the electric energy is fully converted to heat. Therefore, the energy balance per unit current by the first law of thermodynamics is... 

Consider the Peltier effect where a heat flow accompanies a current under isothermal conditions. Figure 7.6 shows the junction between metals a and b at which the Peltier heat is absorbed. After applying Eq. (7.288) to both metals a and b we have... 

The heat flows passing the two metals are TJS. a and 7.7sb and are not equal, since the Peltier heat must be absorbed at the junction to maintain constant temperature. Therefore,... 

Therefore, using Eqs. (7.302), through (7.304), the Peltier heat, its variation with temperature, and the Thomson specific heats may be estimated. 

Figure 12.23 Photon energy input and heat losses for a photoelectrode/Uquid junction. (1) Photonic energy input (2) relaxation loss (3) drift loss (4) recombination loss (5) liberation of Peltier heat at the back contact (6) relaxation loss and liberation of Peltier heat at the electrolyte contact.

Figure 12.25 Example of plot of eq. 12.23 for the determination of the internal quantum efficiency (from the slope) and Peltier heat (from the intercept on the potential axis).

Rappich J. and Dohrmann J. K. (1989), pH-dependence of the internal quantum efficiency and of the Peltier heat for photoanodic water oxidation at flame-oxidized titaninm—an in-situ photoaconstic and photoelectrochemical study , J. Phys. Chem. 93, 5261-5264. 

Thermo-electricity.—If we denote by Q the Peltier heat and by e the potential difference between two metals, we have the well-known equation (analogous to (169))... 

Thermoelectric effects demonstrate the existence of coupling between electrical and thermal phenomena and include the well-known Seebeck effect and Peltier heat, which are explained shortly in the next sections. 

---