APPENDIX 2.B

TYPES OF CALORIMETERS EMPLOYED IN STUDIES


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  1. Isothermal (isoperibolic or heat leak). The cell is immersed in a constant temperature bath (at Tb) sometimes separated from it by a vacuum jacket or other material to control the rate of heat conduction from the cell to the bath. The temperature of the the cell, Tc, which is always at a higher temperature than the bath, is monitored.

    ISO A. The heat flow from the cell to the bath is determined from the temperature difference, Tc - T b and the heat transfer coefficient, determined by periodically calibrating the cell with an internal heater in the cell, by Newton's law of cooling. In this type of cell, TC varies and increases as the power output of the cell increases.

    ISO B. The cell is maintained at a constant temperature by varying the power to the heater (heat substitution method). The cell is first brought to a given steady state temperature, Tc by the heater operating at a given power, Ph. The electrolysis cell is then turned on and the heater power decreased to a level, Phc, to maintain the cell temperature at Tc. The power generated by the electrolysis is calculated as Pc = Ph - P hc.

  2. Isothermal, heat flow (ISO C). Power that flows between the cell and the external constant temperature bath is detected by a multitude of thermocouples connected in series and completely surrounding the cell chamber. The system is calibrated at different power levels by a heater in the cell chamber.

  3. Flow Calorimeter. The cell is surrounded by a chamber cooled by a constant flow of water or other fluid. The inlet temperature of the fluid, Tin, and the outlet temperature, Tout, are monitored and the power evolved in the cell calculated from the difference in temperatures, the flow rate, and the heat capacity of the fluid.

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