The isothermal Joule-Thomson coefficient of steam measured from T=313.00 Kto T=413.19 K

A flow calorimeter with an adjustable throttle has been used to measure the isothermal Joule-Tnomson coefficient of water vapour at temperatures from T = 313.00 K to 413.19 K. At each temperature measurements made over a rang e of pressures were extrapolated to zero pressure to obtain the quantity ph i (o), = (B - TdB/dT), where B is the second virial coefficient. At tempera tures above 330 K the measurements are in good agreement with the work of C ollins and Keyes (1937), and if their value at T = 312.09 K is corrected by 3.3 per cent, the amount by which their measurement of the heat capacity o f steam at this temperature is in error, the agreement is within the combin ed experimental error over the whole temperature range. Values of the zero pressure isothermal Joule-Thomson coefficient phi (o) derived from the meas urements are compared with an equation for B(T) proposed by Gallagher which is consistent with the 1984 NBS/NRC steam tables, an equation for B(T) pro posed in 1988 by Hill and MacMillan, and with values of B(T) derived from t he 1995 IAPWS equation of state for steam of Pruss and Wagner. The new meas urements are found to be in agreement with the equation of Hill and MacMill an to within the experimental error. (C) 2000 Academic Press.