A new formula for saturated water steam pressure within the temperature range -25 to 220C

• Published in: Izvestiya. Atmospheric and oceanic physics 2009-12, Vol.45 (6), p.799-804
• Main Author: Romanov, N P
• Format: Article
• Language: English
• ISSN: 0001-4338; 1555-628X
• DOI: 10.1134/S0001433809060139

Instead of approximation formula ln(E(t)/E(0)) = [(a - bt)t/(c + T)] commonly used at present for representing dependence of pressure of saturated streams of liquid water E upon temperature we suggested new approximation formula of greater accuracy in the form ln(E(t)/E(0)) = [(A - Bt + Ct super(2))t/T], where t and T are temperature in C and K respectively. For this formula with parameters A = 19.846, B = 8.97 10 super(-3), C = 1.248 10 super(-5) and E(0) = 6.1121 GPa with ITS-90 temperature scale and for temperature range from 0C to 110C relative difference of approximation applying six parameter formula by W. Wagner and A. Pruss 2002, developed for positive temperatures, is less than 0.005%, that is approximately 15 times less than accuracy obtained with the firs formula. Increase of temperature range results in relative difference increasing, but for even temperature range from 0C to 220C it does not higher than 0.1%. For negative temperatures relative difference between our formula and a formula of D. M. Murphy and T. Koop, 2005, is less than 0.1% for temperatures higher than -25C. This paper also presents values of coefficients for approximation of Goff and Grach formula recommended by IMO. The procedure of finding dew point T sub( d ) for known water steam pressure e sub( n ) based on our formula adds up to solving an algebraic equation of a third degree, which coefficients are presented in this paper. For simplifying this procedure this paper also includes approximation ratio applying a coefficient A noted above, in the form T sub( d )(e sub( n )) = $$ \frac{{AT_0 }} {{A - \varepsilon }} $$ + 0.0866 super(2) + 0.0116 super(10/3), where = ln(e sub( n )/E(T sub(0))). Error of dew point recovery in this ratio is less than 0.005 K within the range from 0 to 50C.