The property routines described here are for the aqueous salt mixture LiBr/H2O. These routines were developed primarily as a part of the Sorption Systems Consortium at the University of Maryland. The basic rotuines are provided in an external library named LiBrSSC.dll. The routines available in this library are listed in Table 1. The units of the properties must be as specified.

Table 1. Summary of LiBrSSC Routines

See details on units in procedure description Input Units: Tc - K, X – mass fraction of LiBr %, P – kPa

The transport property correlations included were derived from an examination of available data. This was done as part of the SSC efforts but was unpublished [1]. Details of the correlations are summarized here

$$lnμ=A_0+A_1X^2+\frac{B_0}{T}+\frac{B_1X^2}{T}+\frac{C_0}{T}+\frac{C_1X^2}{T}$$

where the units are μ (cP), T (K), X (mass fraction LiBr) and the constants are

This equation yields a $R^2$ value of 0.984073 across all of the data sets used. Example calculation: T = 25°C (298.15 K), X = 50% ➡ μ = 3.807 cP.

$$k=A_0+A_1X+B_0T+B_1TX+C_0T^2+C_1T^2X+D_0T^3+D_1T^3X$$

where k = W/m-K, T = K & X = mass fraction LiBr

Our “best fit” produced an R2 value of 0.9844 and the most well behaved curve over a broad range of the independent parameters. There were equations that had higher R2 values but the one shown above had the best combination of properties. Example calculation: T = 25°C (298.15 K), X = 50% k = 0.444 W/m-K.

The index of refraction of aqueous lithium bromide can be calculated from the correlation of Bostick et al. [2]

$$N=N_1X^2+N_2X+N_3T+N_4$$

where

Units: T - °C, x – mass fraction LiBr in %

The crystallization temperature is calculated from a curve fit to the data of Boryta [3]. $$x=A_0+A_1T+A_2T^2$$

Units: T - °C, x – mass fraction LiBr in %

The thermodynamic properties include volume, enthalpy, specific heat, entropy and chemical potential as well as the saturation properties temperature and pressure. All of these properties are derived from a Gibbs function fitted to a broad set of data for the mixture. The advantage of this approach is that any thermodynamic property of interest can be easily derived from the Gibbs function. And a corollary is that all of the derived properties will be thermodynamically consistent (up to the precision of the calculation). The details of the Gibbs function are available in the literature [4, 5]. It provides excellent fidelity with the available data over the full concentration range from pure water up to crystallization and from 0 – 300°C.

$$g_w=u_w=g-x(\frac{∂g}{∂x}){p,T}$$ $$g_s=u_s=g+(100-x)\frac{∂g}{∂x}{p,T}$$

Example calculation: T = 25°C (298.15K), X = 50% LiBr, P = 0.8071 kPa ➡ g = -2.337 J/g, dg/dx=3.785 J/g, gw = - 191.6 J/g, gs = 186.9 J/g.

One of the aspects of partial properties is that you can sum them up to obtain the mixture property as $$g=\frac{(100-x)g_w+xg_s}{100}$$

$$h_w=h-x(\frac{∂h}{∂x}){p,T}$$ $$h_s=h+(100-x)\frac{∂h}{∂x}{p,T}$$

Example calculation: T = 25°C (298.15K), X = 50% LiBr, P = 0.8071 kPa ➡ h = 52.92 J/g, dh/dx=1.944 J/g, hw = - 44.25 J/g, hs = 150.1 J/g.

One of the aspects of partial properties is that you can sum them up to obtain the mixture property as $$h=\frac{(100-x)h_w+xh_s}{100}$$

$$s_w=s-x(\frac{∂s}{∂x}){p,T}$$ $$s_s=s+(100-x)\frac{∂s}{∂x}{p,T}$$

Example calculation: T = 25°C (298.15K), X = 50 % LiBr, P = 0.8071 kPa ➡ s = 0.1853 J/g-K, ds/dx=-0.006176 J/g-K, hw = 0.4942 J/g-K, ss = -0.1235 J/g-K.

One of the aspects of partial properties is that you can sum them up to obtain the mixture property as $$s=\frac{(100-x)s_w+xs_s}{100}$$

$$v_w=v-x(\frac{∂v}{∂x}){p,T}$$ $$v_s=v+(100-x)\frac{∂v}{∂x}{p,T}$$

Example calculation: T = 25°C (298.15K), X = 50% LiBr ➡ v = 0.6523 cm3/g, dv/dx=-0.006976 cm3/g, vw = 1.001 cm3/g, vs = 0.3033 cm3/g.

One of the aspects of partial properties is that you can sum them up to obtain the mixture property as $$v=\frac{(100-x)v_w+xv_s}{100}$$

• Psat = libr_p(x,T)
• Tsat = libr_t(x,p)
• Xsat = libr_x(T,p)

Example calculation: T = 25°C, X = 50% ➡ P = 0.8052 kPa

Note: The overall mass, LiBr mass and energy balances are all satisfied

1. SSC, Transport Property Data for Aqueous Lithium Bromide, in SSC Unpublished Report1998.
2. Bostick, D.A., Klatt, L.N., Perez-Blanco, H., Fiber optics refractometer for absorption machines, 1987.
3. Boryta, D.A., Solubility of Lithium Bromide in Water Between -50°C and 100°C (45 to 70% Lithium Bromide). J. Chem. Eng. Data,, 1970. 15(1): p. 142-144.
4. Yuan, Z. and K.E. Herold, Thermodynamic properties of aqueous lithium bromide using a multiproperty free energy correlation. HVAC&R Research, 2005 11(3): p. 377-393.
5. Yuan, Z. and K.E. Herold, Specific heat measurements on aqueous lithium bromide. HVAC&R Research, 2005. 11(3): p. 361-375.