Full installation with Gas updates now available!
Download Version 11.112 Gas Update – Full installation
Explanation of issue in versions 11.001 through 11.110.
When the code in 11.001 was modified to address the flow conversion factor issue (see “Prior to 11.001” below), the standard density pertaining to air (roughly 0.076) was inadvertently used instead of using the standard density pertaining to the gas being modeled. When the specific gravity specified by the user is 1 it implies air, otherwise a different gas. The above modified exe file computes the density at standard temperature (60F or 20C) and standard pressure taking into account the specific gravity value specified.
Contact Technical Support with any questions, Jana Faith, 812-619-1901, [email protected]
Prior to 11.001
The gas analysis engine uses mass flow units for all internal calculations (as in lbm/s). Therefore, it needs to convert flows (demands) specified in other units into this standard internal flow units. However, the engine has been using “hard coded” conversion factors for converting non-standard flowrates to standard flowrates. These conversion factors make use of gas density. The gas density used with these conversion factors is based on room temperature of 62F. For example, it is 0.076 lb/ft^3 for air at room temperature, while it is 0.071 lb/ft^3 for air at 100F.
The Reference density (density at standard atmospheric conditions but at user specified temperature) was computed based on the user specified temperature.
The conversion from Cv to K employs the air density value, more specifically the reference density value. Once again, till this point, the calculations are consistent – flow coefficient tool computes the Cv value based on user specified temperature (100F for example), and the K value is derived from this Cv value making use of reference density which is also computed at 100F.
The problem is with mismatch between flowrate conversion which was done using density at ROOM Temperature and standard atm pressure and the Cv to K conversion using density at USER SPECIFIED temperature and standard density.
We can verify this with the following example, where the Cv value is computed with 60F temperature and with 60F as temperature input in system data for the P2K model. We get the exact pressure drop of 0.425 inch water, with Cv value of 3161.
Change in version 11.001
The solution added is to adjust the flowrate conversion factor with a computed reference density at user specified temperature.
This would affect models where user specified temperature is NOT same as room temperature AND where the flow units are anything other than Lb/sec. Same with SI units.
This is the improved way of handling the gases that are not at room temperature.
