31 replies to this topic

[marchem]

It may be that Khuram has to define the proper regional settings for separators in Excel,

I have had a similar problem with macros interpreted as text,  The solution was simply to change separators from ";" to "," and macros began to work as expected :-)

[frpe]

yes, I had a similar problem with Excel,  another problem was Excel 32 installed on Windows 8 64, now I have Excel 64 and it works fine.

I have a quetion, too,  PRODE PROPERTIES has a nice Excel page which allows to design and rate safety vales with different methods for both single phase and two phases (HEM, HEN etc.) but there is not a Excel page for control valves,

I know which is possible to model a control valve with a constant enthalpy flash and there are examples in operating manual,  I have some valves on liquid mixtures flashing,  can you suggest a procedure for these cases ?

[marchem]

I know some simple methods and
a few complex methods,

for an idea of a complex method see the paper
"Sizing of throttling Device for Gas/Liquid
Two-Phase Flow" by Diener and Schmidt,
the paper illustrates applications of
the HNE-DS method for sizing control valves,
by the way a procedure which applies HNE-DS
is included in PRODE PROPERTIES,

however my preference in common practice
is to identify the initial condition for flashing
(easy with the set of flash operations
included in PRODE PROPERTIES) and adopt
that value as the equivalent of the
critical differential pressure discussed
in ISA 75.01 formulation,


I do apply classical methods
(as the sum of calculated CV for diferent states)
since I suspect they can originate large errors

Edited by marchem, 06 November 2013 - 06:20 AM.

[frpe]

thanks, I have found a paper about HNE-DS applied to control valves, author Schmidt, it is based on a variant of Omega method, I would prefer HEM method, could you help with details ?

[PaoloPemi]

frpe,

yes, HNE-DS is derived from Omega model,

to model thermodynamics you shouldn't have problems with PRODE PROPERTIES

(there is a complete set of flash operations, not available in other simulators)

the problem which I see is about fluid dynamics (i.e. fluid flow inside the valve),

I do not know of any simple and accurate general purpose models for that,

most models require specific parameters which are not easy to evaluate.

[frpe]

thanks Paolo,

I would model the valve with specified pressure and enthalpy flash,

do you suggest a different operation ?

(PRODE includes specific models as those for PSV which perhaps could be utilized)

[serra]

you have different alternatives,

the most obvious is H-P flash

another option could be HEM or HNE modesl

PRODE allows to solve directly HEM while

for solving HNE a procedure could be that described in the paper Sizing of throttling device for gas/liquid two‐phase flow part 2: Control valves, orifices, and nozzles

by Diener and Schmidt,

also with PRODE you have a rigorous HNE model.