Implement the complete equation for R11-24.

Implement Z, pKwG and pKw for computing the ionization constant.

src/iapws_r1124.f90

@@ -1,4 +1,4 @@
-module iapws__g704
+module iapws__r1124
     !! Module for IAPWS R11-24.
     use iapws__common
     implicit none
@@ -15,17 +15,49 @@ module iapws__g704
 
 contains
 
-pure elemental Z(T, rhow)result(res)
+pure elemental function Z(T, rhow)result(res)
     !! Empirical function in Bandura–Lvov model, g.cm^{-3}
 
-    !! Arguments
+    ! Arguments
     real(dp), intent(in) :: T     !! Temperature in K.
     real(dp), intent(in) :: rhow  !! Mass density, g.cm^{-3}
 
-    !! Returns
+    ! Returns
     real(dp) :: res               !! Empirical value of temperature and water density
 
     Z = rhow * exp(a0 + a1/T + a2/T**2.0_dp*rhow**(2.0_dp/3.0_dp))
 end function
 
+pure elemental function pKwG(T)result(res)
+    !! Equilibrium constant of the ionization reaction in the ideal-gas state.
+
+    ! Arguments
+    real(dp), intent(in) :: T     !! Temperature in K.
+
+    ! Returns
+    real(dp) :: res
+    res = 0.61415 + 48251.33/T + 67707.93/T**2.0_dp + 10102100.0_dp/T**3.0_dp
+
+end function
+
+pure elemental function pKw(T, rhow)result(res)
+    !! Ionization constant of water.
+    !! Validity range 273.13 K <= T <= 1273.15 K and 0 <= p <= 1000 MPa.
+
+    ! Arguments
+    real(dp), intent(in) :: T     !! Temperature in K.
+    real(dp), intent(in) :: rhow  !! Mass density in g.cm^{-3}.
+
+    ! Returns
+    real(dp) :: res
+
+    res = ieee_value(1.0_dp, ieee_quiet_nan)
+
+    if(T>=Tlim1) .and. (T<=Tlim2)then
+        res = -2*n* ( &
+        log10(1+Z(T, rhow)) - Z(T, rhow)/(Z(T, rhow)+1) * rhow *(b0+b1/T+b2*rhow) &
+        ) + pKwG(T) + 2*log10(Mw/1000.0_dp)
+    endif
+end function
+
 end module iapws__r1124