| Abstract: | A new thermoelectric, matching-heater, flow calorimeter has been constructed for fast and accurate enthalpy measurements. Energy is removed from the calorimeter at a constant rate by a current-regulated cooling module. Prior to introducing a flowing fluid, the energy removed by the cooling module is matched by the addition of electrical energy so as to maintain the temperature of the calorimeter constant to ±0.002 K at the reference temperature (usually 298.15 K). Upon starting flow of the fluid at a known rate and inlet temperature, power supplied to the matching-heater is adjusted to maintain the reference temperature constant. The change in electrical power is equal to the rate of removal of the enthalpy of the fluid in the calorimeter. The standard deviation of liquid enthalpy measurement is 0.6 J g⁻¹. Water was used to test the performance of the apparatus and the agreement with steam tables is 0.3% and a bias of--0.08% for temperatures between 328 to 455 K and pressures up to 120 bar. After the apparatus was automated and tested, we measured enthalpies of trichlorofluoromethane (R-11) and dichlorodifluoromethane (R-12) at temperatures from 240 to 420 K, and at pressures up to 66 bar, and only two measurements on chlorotrifluoromethane (R-13) at 241 and 253 K at 41.8 bar. Measurements on three refrigerant mixtures were performed: (R-11+R-12, x[subscript R-11] = 0.5024), (R-11+R-13, x[subscript R-11] = 0.4946), and (R-11+R-22, x[subscript R-11] = 0.8294 and 0.8310), where R-22 is chlorodifluoromethane. The temperature range for these measurements was from 230 to 475 K and at pressures up to 67 bar. |
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