model comparisons

Comparisons of Steam and Water Formulations

SteamTab Quad gives us the ability to generate water and steam properties using any one of the following formulations:

1. The IAPWS Formulation for General and Scientific Use (IAPWS-95)
2. The IAPWS Formulation for Industrial Use (IAPWS-IF97)
3. The NBS/NRC Formulation; approved by the IAPS for General and Scientific Use in 1984 (NBS/NRC-84)
4. The IFC 1967 Formulation for Industrial Use; also known as the "ASME Steam Tables" (IFC-67)

A question that our clients have repeatedly asked us is: What is the difference between these formulations? With the help of SteamTab Quad, we can now answer this question. The following sections describe the differences in the computed values of enthalpy, entropy, density, etc as computed by these 4 formulations.

Many SteamTab users find it is necessary to use more than one set of steam property formulations to determine whether steam system performance issue is related to steam properties or equipment or relying the assessment of plant performance based on the most accurate set of formulation and conducting commercial transactions with another contractually agreed set of formulation.

Results for additional parameters will be published here as soon as they are completed. If you wish us to examine any specific parameters or scenarios, please email your request to clc.support@chemicalogic.com.

 

Comparing Fundamental Constants

One source of difference among these formulations is the use of different fundamental constants of water, such as the critical properties. A comparison of the fundamental constants is presented here.

Comparing Vapor Pressure

This sections presents the results of the difference between the various formulations for the vapor pressure of steam, calculated from the triple point to the critical point.

Comparing Latent Heat of Vaporization

Some of the largest deviations occur in the computation of the latent heat of vaporization, especially near the critical region. This section summarizes these results.

Comparing Saturated Densities

While specific density is not typically used by engineers, it is an extremely important property as the scientific formulations are explicit in temperature and density from which other properties are derived.