THE POWER CONVERSION EFFICIENCIES OF A THERMOGALVANIC CELL OPERATED IN 3 DIFFERENT ORIENTATIONS

Power conversion efficiency (PCE) measurements were carried on a thermogalvanic cell containing the ferricyanide/ ferrocyanide couple in an aqueous background electrolyte of KCl and using two planar platinum electrodes. The PCE was found to be 0.031% which is ca. 0.50% of the Carnot maximum for the two electrode temperatures of 293.1 and 313.1 K. Three different electrode orientations were used, viz: parallel vertical electrodes and parallel horizontal electrodes with, in the latter case, either the cold electrode above the hot electrode or with the hot electrode above the cold electrode. In all three orientations, the open-circuit potential (E(oc)) of the cell did not change significantly with time. The latter two orientations showed negligible drop in the PCE and short-circuit current (I-sc) with time, However, over a 55 min period in the first orientation, I-sc fell to ca. 40% of its initial value and the PCE fell to 68% of its initial value. It was concluded that the horizontal electrode orientation with the cold above the hot electrode and the vertical electrode orientation provide the best convective arrangements for continuous power production. The power outputs from these two orientations were found to be mainly limited by the ohmic resistances of the cells whereas the output from the cell with the hot above the cold electrode was initially limited by ohmic resistance but mass-transport limitations became increasingly important during continuous operation.