Measurement of the specific enthalpy of vaporization on 1,1,1,2-tetrafluoroethane in the temperature range 180--240 K
- Physikalisch-Technische Bundesanstalt, Braunschweig (Germany)
An apparatus is described which is capable of measuring the enthalpy of vaporization in the temperature range from 100 to 250 K. The sample (134a; purity, at least 99.999%) is located in the measuring cell at the saturated vapor pressure, p = p{sub s}. A control circuit allows p to be kept constant by opening a motor-operated valve to a weighing cylinder after having switched on the electrical measuring cell heater. During the experiment, the temperature is kept constant within a 10 mK. In the range 180 to 230 K, the data for R134a are compared with calculated values from the fundamental equation given by Tillner-Roth and Baehr, which is recommended by Annex 18 of the International Energy Agency (IEA) as an international standard. Good agreement within a standard uncertainty of 1.6 {times} 10{sup {minus}3} is obtained. At temperatures of only 10 K above the triple-point temperature, the enthalpy of vaporization calculated from the Clausius-Clapeyron equation shows considerable uncertainty due to the determination of the small vapor pressure. It is chiefly in this range that it is advantageous to have the new apparatus.
- OSTI ID:
- 675541
- Report Number(s):
- CONF-970629-; ISSN 0195-928X; TRN: IM9833%%150
- Journal Information:
- International Journal of Thermophysics, Vol. 19, Issue 3; Conference: 13. symposium on thermophysical properties, Boulder, CO (United States), 22-27 Jun 1997; Other Information: PBD: May 1998
- Country of Publication:
- United States
- Language:
- English
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