How to change the pressure in fluid properties? When I set the operation pressure range, and then go next, the software will automatically defines some pressure points, I tried to change to the pressure I want. But it is not allowed.
Daniel Qi Lou
The reason that it auto-populates ranges on the fluid properites screen is that it is auto-populating the ranges that the fluid can operate in. For instance, if you enter water in as a "liquid" fluid type, it will auto-populate the valid ranges that water is still a liquid for a given P and T. So lets just say you enter 100 kPa as the pressure that this fluid will operate at and maybe 40 C. From there, it will auto generate the min and max for P and T that water will still exist as a liquid. There really is not a reason to change this, it will not affect accuracy if you do.
For a natual gas, it will autopopulate the ranges per the selected standard (AGA 3 or ISO). This again will ensure that it does not invalidly calculate outside the ranges of the selected fluid. This question gets into the fluid characteristics and operating conditions so if I am unclear about any of the following, let me know.
Regards,
Brian
In reply to Brian Fretschel:
It is for customer gas, how the software know which P and T the fluid is still gas not liquid?
In reply to qi lou:
It will depend on what is entered on the next "fluid properties" tab. That will match up what you entered for P and T with the composition of gas. So if it is a custom gas, you must enter in nominal P and T as well as the operating range, click next to the fluid properites tab, and identify the components of the gas. Generally, custom gases are better handled through Rosemount specialist group and they can help you through this process if you get confused. www2.emersonprocess.com/.../index.aspx
Custom liquid works similarly in that you enter a nominal temp and operating temps and then density and compressibility values on the fluid properties screen.
Hi Brian,
What u mean the composition of gas? If I fill the operation P and T range, and normal operation P and T, and the molecular weight, the softare will give out 63 pairs P and T. Does that mean the customer gas will stay at gas phase under the 63 conditions?
Daniel
Cabot Corporation
No, all it is doing there is filling in 63 points between the P and T ranges you have entered in. This is a complex algorithm for how we analyze the state of the gas. For instance if you enter in a Pmin of 20 and Pmax of 100 it will auto-populate 63 points between those two numbers.