Card 9 - MCV Moving Control Volume Fluid Elements

KODE

KODE is the code MCV (or 28)

N1

N1 is an element number, or a group name.

T1

T1 is an element number or 0, which defaults to T1 = N1. If N1 is a group name, T1 must be 0.

T2

T2 is the capacitance flow rate, used for steady-state analysis only. T2 may be blank and is ignored for transient analysis.

Code example

XCAP 3 7 3 
$ ELEMENTS 3 TO 7 HAVE CAPACITANCES OF 3.0
$
MCV 3 7
$ ELEMENTS 3 TO 7 ARE MCV FLUID ELEMENTS.
$ THE FLUID FLOWS FROM ELEMENT 3 TO 4, ETC.

Notes

The MCV card defines the elements N1 through T1 to be MCV fluid elements.

The temperature of an MCV element is calculated by computing its heat balance as it moves downstream to its next location.

The MCV method provides an alternative to the standard stationary control volume (SCV) method for modeling one-dimensional pipe or duct fluid flow.

The SCV method assumes the elements are stationary, and one-way conductances are used to model the heat carried into an element by the moving fluid. One-way conductances can be defined directly with XCOND cards, or are automatically created for hydraulic networks. Where possible, the SCV method should be used to model fluid flow.

The major advantage of the MCV method is that it can model fluid flow with phase change, by defining the phase change properties of the element with PHASE or MAT cards. Otherwise, it is a much more cumbersome technique.

With the MCV method, a special numbering sequence must be used. MCV fluid elements must be sequentially numbered in ascending order in each flow branch. Fluid flows from the lowest to the highest element number.

If transient analysis is performed with MCV cards:

• All elements must be separated by equally spaced time intervals. The integration time step DT specified on Card 2b must be the time it takes for the fluid to flow to the next downstream element.
• Only the -3 forward differencing or the -2 exponential forward differencing techniques may be specified on Card 2b.
• Capacitances must be specified as usual for all MCV elements. Capacitances may be calculated from geometry or specified on XCAP cards. Capacitances are ignored in steady-state analysis.

If steady-state analysis is performed, it is necessary to specify the T2 parameter on the MCV card. T2 must be the mass rate of flow times the specific heat of the fluid (Btu/sec/F or W/C).

Fluid branching may be modeled with MCV elements. The first element in a branch must be connected to the main stream with a XCOND FOLLOWER card.

MCV elements must not be merged or renumbered with Card 7.

MCV elements may not be used with the ILU solver.