RELEASE
NOTES
SINDA/FLUINT Version 4.5
Conductor HR Values
The absolute value of the
heat rate through a conductor is now available as the parameter ¡°HR.¡± This
output variable may be accessed in logic or expressions. Note that because an
absolute value is used, there is no dependence of HR on direction: no ¡°from
node¡± nor ¡°to node.¡±
Builtin Sonic Limits
(Choking)
By default, almost all paths
(including tubes) are now checked for sonic limits in their throats (AFTH), and
if such limits are detected they are automatically modeled.
This new system makes the
CHOKER and CHKCHP routines obsolete, and to avoid confusion their use is
discouraged though still accepted for backward compatibility. Users are
encouraged to delete those calls from their models, and replace them with
appropriate MCH and HCH values.
Unfortunately, this new
default (checking for choking everywhere and applying nonequilibrium expansions
if needed) stresses many fluid property descriptions, hitting lower limits or
requesting offchart thermodynamic properties. The user may need to selectively
or globally turn off such choked flow modeling (using MCH=0) if improvements to
the underlying fluid properties cannot be made and if choking is deemed to be
irrelevant to the problem at hand. In other words, the default was chosen as a
safety measure, and it may be irrelevant or disruptive in some
models.
Expanded Heat Pipe
Modeling
A new routine, HEATPIPE2,
has been introduced to extend the prior HEATPIPE routine to cover pipes with
strong circumferential gradients: 2D heat pipe models using more than one
circumferential node, noncircular heat pipes, and flatplate vapor chamber
fins. Other improvements include the ability to disregard incorrectly
sized/charged VCHPs, greater flexibility of input units (HPUNITS), and a new
routine (HPGLOC) is available to extract the gas front location from previous
HEATPIPE or HEATPIPE2 calls.
Heat pipe users are urged to
review recent FloCAD®
enhancements specifically designed for heat pipe modeling inside 3D FEM/FDM
thermal models.
Miscellaneous
Improvements
 Many model size limits have been relaxed or even
eliminated (for versions based on Fortran 90/95 compilers, which currently
includes all PC versions).
 More complex syntax is now
allowed for conditional operators inside of spreadsheetlike expressions. For
example, ¡°heat = ( (sub.t1 > 300) && (sub.t1 <= 400) )? on : off¡±
meaning ¡°if the temperature of node 1 in submodel sub is above 300 degrees but
less than or equal to 400 degrees, set the register heat to on, otherwise set it
to off.¡±
 Routines for sizing and/or
simulating Peltier devices, including Thermoelectric Coolers (TECs) are now
available.
 A new connector device has
been added to simplify modeling of common orifices: the ORIFICE connector.
Builtin correlations for sharpedged and long orifices are available, or the
user can provide their own coefficients. The resistance of the orifice is
estimated, as well as the prediction of its vena contracta for the purposes of
choked flow detection and modeling.
 A new connector device has
been added to allow users to specify how a component behaves (pressure drop
versus flowrate characteristics) using tables input as ARRAY data: the TABULAR
connector. The tables can use a variety of units for pressure/head and flow.
Either a single curve can be input, or a family of parametric curves based on a
userdefined independent parameter. While intended to assist in the modeling of
valves and other devices using vendorsupplied data, TABULAR devices represent a
generalpurpose means of describing a flow resistance for a variety of
components.
 Much greater flexibility
now exists for defining units for pump curves, enabling users to apply vendor
data directly without conversions.
 To avoid any confusion, the
PRVLV and BPRVLV connectors have been renamed to UPRVLV and DPRVLV connectors,
respectively. The older designations are still accepted in input files, but are
no longer documented to discourage their continued use.
 A new utility routine,
REPATH, has been added to allow users to easily estimate the Reynold¡¯s number
for any tube or STUBE.
 Double precision is now on
by default. The user can return to single precision by
specifying
SINGLEPRECISION (or simply SINGLEPR) in OPTIONS DATA.
 The values of ITHOLD and
ITHLDF now default to zero: the temporary suspension of submodels during steady
states (an attempt at speed savings that is not universally successful) will no
longer be performed by default.
 The COMPLQ routine has been
extended slightly to apply a proportioned compliance to twophase tanks.
Previously, COMPLQ only applied compliance to hardfilled liquid
tanks. This
change avoids a discontinuity at the saturated liquid line.
 A new option (YTHUSH
routine) is available to eliminate fatal errors when the wyetee
(converging/diverging flow) routines such as YTKALG and YTKALI encounter
conditions for which their correlations do not apply. Use of this option means
the user accepts the burden of checking the final results, but permits both
steadystate excursions (temporarily reversed flow directions, for example) as
well as extrapolations of the correlations.
 A change has been made to
the PID controller routines formulation: they now return values of the control
variable (CV) instead of changes to the control variable (CV). This change is
not backward compatible with previous models.
Significant External
Program Improvements
 An Excelbased utility for
reading and plotting SAVE files (all the binary files produced
by the SAVE,
RESAVE, SAVEDB etc. routines) is now available as part of the
EZXY®
installation.
 FloCAD® has been
significantly expanded to include ¡°pipe¡± methods for drawing 1D
lines
representing fluid ducts and heat pipes, and for attaching these to Thermal
Desktop®
surfaces and solids. These improvements make FLUINT modeling
significantly easier for
common pipeflow and heatpipe problems.
 C&R Thermal Desktop®
now features native finite difference solids for enhanced
parametric
modeling.
SINDA/FLUINT Version 4.4
High Speed and
Compressible Flow
Although FLUINT
always handled the full thermodynamic and momentum effects associated with
compressible flow (including choking), it previously made the assumption of
kinetic energy being negligible compared to thermal energy (enthalpybased or
advective transport). Kinetic energy transport is now included in the flow
solutions, such that certain high speed flow phenomena (e.g., Fanno line flow,
etc.) can be modeled.
While this
enhancement is mostly transparent to the user, there are a few subtle changes
and cautions required. First, all paths now have a definable flow area (AF) and
throat area (AFTH), although their use is optional for many connector device
types. If a path has no defined flow area, then kinetic energy cannot be taken
into account and the flow will ¡°stagnate¡± upstream of that path, perhaps to be
accelerated again downstream. Also, the optional choking calculations (CHOKER,
CHKCHL, etc.) no longer assume that the upstream lump represents stagnation, and
therefore an expansion process need only be included if the throat area is less
than the flow area (AFTH < AF). Finally, any lump in which velocities should
be assumed zero can be marked as such using a new ¡°LSTAT=STAG¡± option in lump
subblocks. This designation affects not only choking and kinetic energy
calculations, it will also automatically add an accelerational entrance loss
(equivalent to FK=1.0) to any appropriate path (tube, STUBE, loss, etc.)
attached to and flowing out of that stagnant lump.
Miscellaneous Improvements
 Previously, simultaneous
(sparse matrix based) thermal solutions could be invoked on a submodel by
submodel basis using MATMET=1. Submodels that are tightly coupled can now be
combined into a single matrix using MATMET=2 (Section 4.4.1). Other values of
MATMET retain their original meaning: MATMET=0 means iterative, and MATMET=1
means simultaneous (per submodel).
 A network connectivity
checker has been added that detects isolated groups of nodes: nodes having no
connection to a boundary node in steady states, and arithmetic nodes having no
connection to either boundary or diffusion nodes in transients.
 Model size limits have been greatly
increased.
 In an attempt to avoid
confusion for new users, the builtin spell checker, controlled by the NODEBUG
(Options Data) and DEBOFF and DEBON (logic blocks) options, may
now be
controlled using the SPELLON and SPELLOFF commands instead. The old options are
still available but have become undocumented.
 In connector subblocks,
general path inputs (FR= ..., DUP = ... , STAT = ... etc.) are now tolerated
following the ¡°DEV=¡± specification.
 Defaults now exist for
NLOOPS, OUTPUT, and OUTPTF to avoid aborted runs. The default for EXTLIM has
been reduced from 50 to 5 to avoid instabilities in models with fluid systems,
heat pipes, etc.
 SINDA now tolerates nodes
with zero (or absent) conductors as long as ties are present.
 The FORTRAN reserved word
list has been expanded to include many f90/f95 keywords (¡°WHILE¡±, ¡°ENDDO¡±). This
prevents these names from being used as registers, named control data,
etc.
 RESTAR, RESPAR, RESTDB,
etc. now check the input record number for validity.
 A new routine, HEATPIPE,
has been added to assist in simulating fixed (constant) conductance heat pipes
and variable conductance heat pipes.
 CSGFAC can now be used as a
CSGMIN divisor for time step control in FWDBCK (¡°Transient¡±) as well as FORWRD.
In FWDBCK, use of negative DTIMEI is now taken to mean overriding of the default
(DTIME=0) internal time step control, using instead a time step equal to
CSGMIN/CSGFAC. Positive DTIMEI retains its original meaning as the directly
specified time step.
SINDA/FLUINT
Version 4.3
Reliability Engineering
A new toplevel module has
been added that enables analysts to treat unknowns and uncertainties
statistically, estimating the chances of exceeding arbitrarily complex failure
limits. Dimensions, properties, boundary conditions, usage scenarios, etc. are
normally not fixed quantities, but can assume different values within a
prescribed range. Margins and safety factors are normally used to deal with such
uncertainties, stacking up worstcase scenarios and minimum/maximum values to
produce conservative designs. The Reliability Engineering module allows the
degree of over or underdesign to be quantitatively measured by predicting the
chances that the design will pass muster: the reliability of the design.
Combined with the Solver, it can be used to synthesize a design that meets
reliability requirements up front, intelligently balancing cost against risk.
FluidtoFluid Heat Transfer
Ties
Heat can flow directly
between lumps using "fties", a new network element. Advective transport of
energy is usually always dominant over conductive transport within a fluid.
However, in systems with very slow flowrates or that use highly conductive
fluids (such as liquid metals), neglecting conductive transport may not be
acceptable. Another use of fties is modeling thinwalled heat exchangers between
two sections of the same fluid system (e.g., regenerators). Fties may be applied
with a constant or uservarying conductance ("UF"), or with a constant or
uservarying heat flux ("QF"), or as a companion to a tube or STUBE connector
that automatically updates the ftie conductance to take into account the current
fluid flow within those paths. In fact, such an "AXIAL" ftie can easily be
generated along with any tube or STUBE connector.
Auxiliary routines (WETWICK,
PLAWICK, CYLWICK) are available to calculate and apply ftie conductances for
flows through conductive porous media.
Twinned Tanks
Whenever the assumption of
perfect mixing in twophase control volumes (equal temperatures and pressures
between liquid and vapor) is inappropriate, tanks can be twinned. When twinned,
the code will use one tank to model the vapor and one tank to model the liquid
within the control volume, analogous to the way twinned paths may be used to
solve separate momentum equations for each phase. In fact, twinned paths may be
used in combination with twinned tanks for full nonhomogeneous nonequilibrium
modeling. Other elements such as ties and fties may also be twinned to
facilitate their application to twinned tanks. Twinned tanks use fties and
ifaces between each pair, and also apply a new concept called a superpath to
handle mass transfer between them. Most of these calculations and manipulations
are transparent to the user when default options are used. However, in order to
provide full access and control for custom solutions, the number of new
variables and features is considerable. Twinned tanks make use of the NONEQ
family of routines obsolete. These routines are still available, but are now
undocumented. Users are encouraged to migrate to twinned tanks, which (unlike
the NONEQ routines) can be used within LINE and HX macros, can be used with
twinned paths, and can handle dissolution/evolution phenomena. The NONEQ
routines will eventually become unavailable.
FlowRegime Mapping
Default
Because of the preponderance
of options requiring flowregime mapping in modern SINDA/FLUINT, the prior
default of IPDC=1 (homogeneous pressure drop, unmapped regime) has been changed
to IPDC=6 (automatic regime selection and pressure drops and other calculations
based on regime). This may cause twophase models built for prior versions to
give difference results.
QDOT No Longer an Input
Variable
In previous versions, a
heating rate, QDOT, could be applied to a lump, or QDOT could be calculated
automatically if ties were attached to it. To allow for the expansions
associated with fties, and to permit users to add an additional source onto a
tied lump, the prior meaning of QDOT as both an input and output variable has
been split. A new input variable, "QL", now defines the heat applied to a lump
in addition to heat flowing to it from nodes (via ties) and from other lumps
(via fties).
QDOT retains its original
meaning as the total power applied to a lump, but can no longer be used as an
input variable: it is now strictly an output variable. This means that
occurrences of "QDOT =" in FLOW DATA sections will now cause a preprocessor
abort. They must be changed to "QL =" and the user must assure that this power
is intended as an additional dissipation (if positive) if ties are present on
that lump to get the same results as before. Each occurrence of QDOT in
logic and expressions must be examined to see whether it is appropriate to refer
to the applied power QL, or to the total resulting power QDOT.
Miscellaneous
Improvements
 Thermal Desktop and RadCAD
calculations can now be made dynamically from within PC (4.3L or 4.3D)
SINDA/FLUINT launched from within Thermal Desktop. This major expansion enables
parametric analyses, sensitivity studies, optimization, correlation, reliability
estimation, and robust design activities to include variations in geometry,
optical properties, thermophysical properties, insulation, contact conductance,
orbital parameters, etc. The traditional separation of Thermal Math Modeling
(TMM) and Geometric Math Modeling (GMM) has been eliminated. Refer to the
Thermal Desktop User¡¯s Manual for more information, or contact C&R.
 An intimate link with
Engineous¡¯ iSIGHT® software has been created. iSIGHT provides optimization,
reliability engineering, and robust design within a multidisciplinary
environment. Refer to the Engineous Software, Inc. website (www.engineous.com) for more information on
iSIGHT, and contact C&R for information on how to exploit SINDA/FLUINT¡¯s
intimate link with iSIGHT.
 Psychrometric utilities
have been added for convenience in dealing with the dew points and relative
humidities in air/water mixtures (as well as other mixtures of condensibles and
noncondensibles).
 PID controller simulation
utilities are now available.
 By default, SINDA/FLUINT
now checks array data to see if mixed integer and real data have been input
within a single array. This prevents the common mistake of forgetting the
decimal point for a real value. This option can be overridden (e.g., when
bivariate or trivariate arrays are input) by specifying MIXARRAY in OPTIONS
DATA.
 Pump and fan curves may now
be nonmonotonic: they may include regions with a negative slopes in the head
vs. volumetric flowrate curve.
 On PC f90/f95 versions
(4.3D and 4.3L) and on the Sun ULTRA 64bit f90 version (4.3U), memory is
allocated dynamically for sparse matrix solutions (which are used for all FLUINT
solutions as well as any SINDA submodels using MATMET=1). This eliminates
excessive allocations, aborted runs, and any need to use the NWORK or NWORKS
options. No user involvement is required to use this feature.
 A replacement of the
INCLUDE command, the INSERT command, has been introduced. INCLUDE will still be
accepted and is documented but no longer recommended. INSERT works the same as
INCLUDE, except that an INSERTed file can also contain another INSERT command:
INSERT commands can be nested indefinitely.
 The use of negative signs
on the multiplication factors (¡°F¡±) of SIV and SPV conductors has been
historically used as a signal to use a Node A¡¯s temperature instead of an
average temperature of the two endpoint nodes. New conductor options (SIVM,
SIVA, etc.) have been introduced to avoid conflicts with more modern usage
(expressions, FEM conversions).
 A routine, PUTPAT, has been
introduced to allow paths to be relocated between lumps.
 A new routine, CHGEXP,
allows the expressions defining parameters to be added or changed dynamically
(during processor execution).
 A new utility, QFLOW,
exists for reporting the heat flows from one or more nodes to any other
collection of nodes. Nodes defining each group (¡°to¡± or ¡°from¡±) may be specified
individually, by submodel, or as arbitrary lists.
 Auxiliary modeling tools
have been added to make modeling of wyes and tees (merging and diverging flows)
more convenient, and to make manifold modeling more accurate. These tools
include correlation routines (YTKALI, YTKALG) and a Kfactor conversion utility
(YTKONV).
 A variation of the SUMFLO
routine, SUMDFLO, has been introduced. Unlike SUMFLO, SUMDFLO takes into account
path duplication factors when calculating total network mass, volume, etc.
 A new routine, HTRNOD,
allows any arithmetic or diffusion node to temporarily become a heater node (a
type of boundary node). The action is released by RELNOD. These actions may be
performed on all arithmetic and/or diffusion nodes within a submodel using
HTRMOD and RELMOD.
 The HEATER (thermostatic
heater) routine has been expanded to function during steady states using an
internal call to HTRNOD.
 A new proportional heater
routine, PHEATER, is now available.
 Multiple header blocks of
the same type will no longer cause errors as long as they are syntactically
identical. If encountered, such redundant blocks will be joined into a single
block before preprocessing.
 Shortcut commands now
exist to build all available thermal or fluid submodels into the current
configuration: BUILD ALL, BUILDF ALL. Also, all current thermal models can be
removed from the current configuration using ¡°BUILD NONE¡±, as can all fluid
submodels using ¡°BUILDF NONE.¡±
 An empty (fake) ¡°HEADER
NODE DATA¡± is no longer required for conductoronly submodels.
 SAVE, RESAVE, and SVPART
now accept a minus flag syntax meaning ¡°save all except the following.¡±
 For the convenience of new
users, the most commonly used steadystate routine (FASTIC) may now be referred
to using the alias ¡°CALL STEADY.¡± The most commonly used transient routine
(FWDBCK) may now be referred to using the alias ¡°CALL TRANSIENT.¡±
 Internal improvements have
been made in the Solver algorithms, especially for METHO=2 in constrained
problems.
 Slight nonconservation of
mass and energy in transients due to unavoidable numeric truncation and similar
causes has been rectified by accumulating error terms and folding them back into
the solution, improving the accuracy of the predictions over several time steps.
(Refer to the new RMFRAC control constant.)
 A new control constant,
FRAVER, has been added to allow the FLUINT user to denote a characteristic
average flowrate for a loop such that it can better decide what level of flow
can be neglected as zero and what amount of change in flowrate is negligible per
time step.
 A variation of USRFIL
called USRFIL2 is available that does not abort if it can¡¯t open a file.
Instead, it returns an error flag.
SINDA/FLUINT
Version 4.1
Expressions: Miniature Logic
Blocks
Spreadsheetlike registers
and registercontaining expressions continue to be a popular and powerful
feature of the code. Expressions, which can be used to define almost any value
in SINDA/FLUINT, have been tremendously expanded. First, the user can refer to
processor variables such as "fred.T33" or "abszro" or "drlxcc" or "timen" in the
expressions, completing the spreadsheet capabilities by allowing inputs to be
declared functions of not only other inputs, but also of output (response)
variables. Together with the ability to use conditional operators (IF/THEN/ELSE
type logic), each expression can be as powerful as a logic block, and in fact
many traditional input options and applications of logic blocks are now largely
obsolete (although still supported).
Soluble Gases
Mixture properties can be
extended to include the effects of gases dissolving into liquids and evolving
out of them. Multiple solutes and solvents can be defined. These effects can be
included during either steadystate or transient solutions. Applications include
noncondensible gases in single and twophase thermal transport loops and vapor
compression cycles, pressurant gases in liquid propulsion and in fire retardant
delivery systems, and water quality assessments.
Interface Elements
A new pathlike FLUINT
network element, the "iface," is available for specialized fluid system modeling
needs such as subdividing control volumes (including nonequilibrium control
volumes or thermally stratified vessels), and for modeling springs, bellows,
pistons, servocontrol valves, and wicks.
Simultaneous Thermal
Solutions
Simultaneous (sparse matrix
solution) methods may now be applied to thermal submodels to replace or augment
traditional iterative methods in both steady state and transients. Matrix
methods are particularly suited to conductively dominated problems (such as
translated finite element models from structural meshes) including those in
which large conductors are unavoidable. By default, during each iterative pass
of STDSTL, FASTIC, and FWDBCK, nodes are solved one at a time treating other
nodes temporarily as boundary conditions. In problems with large conductors,
with long conductive paths, and with poor initial conditions, such iterative
methods can be slow or can stall (as noted by the "ENERGY STABLE BUT NOT
BALANCED" caution message) despite the accelerations attempted via EXTLIM and
ITERXT. As an alternative, all the nodes in a submodel can be solved
simultaneously using a sparse matrix solver. Although convergence of
conductancedominated problems is normally tremendously accelerated by this
approach, the cost per iteration is higher than with iterative methods and
several iterations (each using a simultaneous solution in FASTIC and STDSTL) are
still required to adjust for radiation, temperaturedependent conductivities and
sources, and other user logic manipulations.
Miscellaneous
Improvements

The propagation of spreadsheet (register and
processor variable) changes is now performed automatically via internal calls to
UPREG. These automatic updates can be regulated, supplemented, or even globally
turned off using the NOUPDATE command in OPTIONS DATA.
 With the advent of ifaces, the stability and
accuracy of nonequilibrium (NONEQ) options have been greatly improved. Also, the
BELACC option has been obsoleted by the introduction of SPRING ifaces. BELACC is
available but undocumented.
 A new phase change material (PCM) simulation
routine, FUSION, is now available for modeling latent energy within a diffusion
node.
 An improved method has been added for predicting the
density of liquid mixtures: the assumption of additive volumes has been
supplanted with the modified HankinsonBrobstThomson method. Therefore, the PVF
parameter has been globally replaced with MF, the molar fraction (a real,
floating point variable).
 Negative values of IPDC may be used to impose a
userspecified flow regime (turning off the automatic selection available when
IPDC=6).
 Pressure regulating values and backpressure
regulators are now available as PRVLV and BPRVLV connectors.
 NEADCC has been obsoleted. The code always adds an
extra constituent equation to assure accurate tracking of trace species.
 As a convenience in switching between junctions and
tanks, junctions now have volumes ("VOL"). These volumes are ignored by most
program options, important exceptions being the SUMFLO routine and several gas
dissolution/evolution options.
 A routine exits for estimating irrecoverable
(Kfactor) losses in reducers and expanders: FKCONE.
 Two new SINDA output routines are available: HRPRINT
for printing heat rates through conductors, and NODTAB for tabulationstyle
summaries of nodal attributes including energy imbalances.
 CONSTRAINT DATA, part of the Solver, now accepts
"unnamed" constraints to simplify the implementation of common constraints. For
example, the user can specify "sub1.T15 <= 200.0" directly in CONSTRAINT DATA
rather than first defining a constraint variable (e.g., "THEAT <= 200.0") and
then updating that constraint variable later in logic blocks (e.g., THEAT =
sub1.T15).
 CONTRN, NODTRN, INTCON, and INTNOD dynamic
translation routines for nodes and conductors have been rewritten to execute
much faster, especially for repeat calls. This enhancement is transparent to the
user.
 Sparse matrix inversion underlying FLUINT solutions
(and now optionally applied to SINDA solutions as well) have been expanded to
include an ordering optimization which reduces both run times and memory
requirements. This enhancement is transparent to the user.
 The model size limits (number of nodes, etc.) have
been increased to 100000 nodes and 500000 conductors.
 A new INSERT option, analogous to the INCLUDE
option, can be nested: INSERTed files can themselves include Inserted
files.
 A new QFLOW routine allows energy flows between
groups of nodes (including whole submodels) to be calculated.
SINDA/FLUINT Version 4.0
Thermal modelers take note!
Version 4.0 introduces powerful functionality not just to FLUINT but to all
aspects of SINDA usage. Understanding these improvements will change not
only the way you use SINDA, but also the problems to which you apply it.
Dynamic Registers
Version 4.0 completes the
integration of spreadsheet functionality into SINDA/FLUINT by enabling changes
in the values of registers (spreadsheet variables) to propagate through
a model even during processor execution. This enables you to make sweeping model
changes with minimal effort, greatly reducing the need for user logic and
rendering many traditional SINDA techniques obsolete. Parametric analyses and
sensitivity studies are now quite easy to perform. The user has tremendous
flexibility over when and what changes are made to the model when changes are
propagated.
If you are unfamiliar with
Registers, additional information is available in the release notes of SINDA/FLUINT Version 3.2, below.
Version 4.0 enables the
analyst to perform parametric variations within a single run with minimal user
logic through the use of dynamic registers.
In Version 4.0, the
processor remembers every place that a register was used in the definition of a
model, and knows how to propagate changes to registers throughout the model while the solution is proceeding.
Registers can be used in the
definition of nodes, conductors, source terms, fluid system variables, and even
array data. Almost every data value in SINDA/FLUINT can be defined as an
algebraic expression, and in Version 4.0 sweeping model changes can be made with
just a few lines of logic.
Registers themselves can be
changed by providing a new expression instead of a fixed value, and registers
can be updated independently from the model if desired. There are many
traditional features in SINDA/FLUINT that attempt to provide such functionality,
such as the use of number user constants in SIV nodes/conductors and source
data. However, they do so in a relatively clumsy and confusing fashion compared
to the new registerbased methods.
For example, if a register
named "DIAMETER" were used throughout a model to signify a key dimension, then
changing that value throughout the model (conductances, inner diameters, flow
areas, etc. etc.) is as easy as:
DIAMETER = 0.375
CALL UPREG $ (Note: UPREG is
optional in Version 4.1)
The Solver
Not only does the user have
the ability to make sweeping changes of the model while it is executing, in
Version 4.0 the code itself can be tasked to perform those changes
automatically, perhaps to achieve a special design goal or simulation need.
The most significant
enhancement is the introduction of a new highlevel solution routine, the
Solver, with which you can direct SINDA/FLUINT to change selected registers as
needed to achieve some modeling purpose.
Dynamic registers provide a
convenient means by which the user can manipulate an entire model using a few
central parameters such as key dimensions, properties, etc. SINDA/FLUINT may now
be used for
 Goalseek. SINDA/FLUINT has traditionally served as
a point design simulator. Given X, SINDA/FLUINT returns Y. Using the goal
seeking capabilities, the user can easily invert the problem and have
SINDA/FLUINT return X given Y. For example, the user might want the outlet
temperature of a heat exchanger to be a certain value, SINDA/FLUINT will adjust
the design (perhaps flow rates, dimensions, or materials, etc.) subject to
arbitrarily complicated constraints, until the desired value is achieved.
 Optimize. Instead of just matching a single
variable, the Solver can be used to perform design optimization of an arbitrary
number of design variables and constraints. For example, it can be used to find
the cross section of a fin that maximizes fin efficiency while not exceeding a
weight threshold. Using these features, SINDA/FLUINT can participate even in the
very early stages of a design, or can be used to refine an existing design.
 Correlate to Test Data. Just as a design can be
optimized to suit a particular purpose, the model of that design can be
optimized to best fit steadystate or transient test data. As often happens in
thermal/fluid systems, key uncertainties such as contact conductances, surface
optical properties, and natural convection coefficients can dominate
predictions. Thus, correlation of the model against a few tests is required,
making the model an intelligent extrapolator of known test data. This time
consuming task can be automated in Version 4.0, yielding bestfit models
(perhaps defined by leastsquares fit, or minimized maximum error, etc.) as well
as insight into the magnitude of uncertain values.
The Solver works at a higher
level than simply calling for a transient or steadystate run. In essence, using
the Solver can program a series of SINDA/FLUINT runs as needed to automatically
perform some modeling task.
In many ways, the Solver
represents a convenient means of setting up a series of SINDA/FLUINT runs to
perform a highlevel task or to achieve a complicated analysis goal.
Traditionally, SINDA/FLUINT
was a point design analysis tool, now it determines the inputs for a desired
result. For example, in the past, SINDA provided the temperature of a node based
on the input dimensions and surface properties. Now, SINDA will determine the
dimensions and surface properties that will result in the desired temperature.
Or FLUINT will determine the mass flow rate of a pump to provide the required
downstream temperature in a fluid system.
Additional information is
available on the Solver in the form of training notes.
SpeciesSpecific
Suction
Users can now specify which
species should be extracted from tanks as needed to simulate various mass
transfer processes or perhaps chemical reactions.
Miscellaneous
Improvements
Other improvements include
(1) new nodal convergence parameters and algorithms for faster steadystate
executions, such as automatically calculated over and underrelaxation factors;
(2) an option to neglect phase change within throats for choked flow modeling;
(3) modeling of trace species; (4) negative Kfactors; (5) improved convergence
in the STUBE connectors; (6) assistance modeling loop heat pipes (LHPs); (8)
additional auxiliary routines, including monitoring heat flow through a
conductor; and new functionbased dynamic translation routines for thermal
submodels.
SINDA/FLUINT Version
3.2
SINDA/FLUINT, the popular
and powerful network style thermal/fluid analyzer, has now become even more
powerful. This subsection describes the new features in Version 3.2
Registers and
Expressions
In past years, some users
employed spreadsheets as model generators for SINDA, exploiting the ability to
define a model algebraically such that a few changes would propagate
consistently throughout the input file. When it was first introduced in 1992,
SinapsPlus contained such spreadsheetlike expressions and user
variables (registers), and these quickly became one of its most popular
features.
Version 3.2 of SINDA/FLUINT
now accepts registers and, equally important, complex expressions used to define
data. A new Header Register Data block has been added for this purpose. For
example, in past versions, to define the radial conductance in a tube from node
1 to node 2, one might input (given a conductivity of 15, a length of 10, an
outer radius of 0.05, and an inner radius that is half that
value):
1,1,2,2.*3.14*15.*10./0.69
which leaves little or no
selfdocumentation for engineers who inherit the model. Changes to the
dimensions must be made manually in all places using them.
In Version 3.2, one can
define up front:
HEADER REGISTER DATA
con = 15.0
len = 10.0
Ro = 0.05
Ri = 0.5*Ro
and then define the
conductor indirectly:
1,1,2,2*pi*con*Len/ln(Ro/RI)
Notice the use of
parentheses, of builtin constants like "pi," and of builtin functions like
natural logarithms "ln( )." While the ability to use arbitrarily complex
expressions is a significant improvement, the real power of registers and
expressions is that they can be used throughout the input file in almost any
location where SINDA/FLUINT requires a data value. This means that a key
dimension (perhaps "Ro" in the above example) can be changed in one location
(the Header Register Data block), and the effects will propagate consistently
throughout the input file according to the relationships the user has
predefined. As illustrated above, registers can themselves be defined by complex
expressions that perhaps even contain references to other registers.
Registers and expressions
not only greatly improve the selfdocumentation of the model, they facilitate
long term model maintenance and the generation of parametric analyses. In the
next version, the ability to perform parametric analyses will be taken a major
step further with the advent of dynamic registers that can change during the
solution, effecting widespread changes to the model with minimal user commands.
Condensible/Volatile
Mixtures
Working fluids mixtures,
previously limited to nonvolatile liquids and/or noncondensible gases, can now
include a species that can either change phase or that is a real (imperfect)
gas. This significant enhancement covers important applications such as
psychrometrics (air/water mixtures) in heating, ventilation, and air
conditioning (HVAC) systems, air/fuel systems with volatile fuels, pressurized
liquid propellant and fire retardant delivery systems, as well as noncondensible
gas and oil contamination in steam systems, twophase coolant loops, and vapor
compression cycles. When a substance condenses in the presence of noncondensible
gases (e.g., a condensing heat exchanger) the effects of the diffusion barrier
formation are automatically included along with other thermodynamic effects. In
future versions, the dissolution and evolution of noncondensibles in liquid will
be available in prepackaged form, as will complete nonequilibrium twophase duct
flow simulations.
Other Enhancements
Among the miscellaneous
improvements made to SINDA/FLUINT is a new option for calling VARIABLES 1 within
each FWDBCK time step iteration. This option not only provides higher fidelity
for temperaturedependent variations and logic, it makes most logic written for
steadystate analyses more reusable in transients.
Other improvements include a
variable node solution order that reduces steadystate run times, and additional
fluid property definitions (e.g., molecular weights, diffusion coefficients). 