Heat transfer software and fluid flow software
   





 




FLUINT/FloCAD Comparison With CFD Tools

Nusselt and Reynolds vs. Navier and Stokes

FLUINT is the 1D thermohydraulic (fluid network modeling, or “FNM”) companion to SINDA, which is a thermal network analyzer (applicable to 1D/2D/3D finite element, finite difference, and/or lumped parameter models). FLUINT can be used in standalone fashion, but more often is accessed using the nongeometric SinapsPlus sketchpad interface. With the recent advent of FloCAD, FLUINT solutions are now even easier to apply from within Thermal Desktop’s geometric (CAD-based) modeling environment. The result is a unique combination of 3D thermal/structural modeling plus 1D fluid modeling with which many engineers are unfamiliar compared to the many commercial CFD (computational fluid dynamics) packages available.
Indeed, engineers unfamiliar with the FloCAD approach often ask “How is it different from CFD?” This document seeks to answer that question. It does not seek to advocate universal use of one method over the other. It does, however, seek to demonstrate why correlation-based methods such as FLUINT/FloCAD have important advantages that will persist even as CFD methods continue to improve in the future.

3D Finned Heat Exchanger with 1-D Air Flow

Advantages of the FLUINT/FloCAD Approach

FLUINT/FloCAD uses a fast-to-build, fast-to-solve empirical approach: the exact details of the geometry are avoided by applying heat transfer and pressure drop correlations, such that a one dimensional flow field is adequate. Simply put, the FLUINT/FloCAD approach eliminates the need for extra meshing. This choice has many repercussions:

  • Cost: The purchase price of the FLUINT/FloCAD suite of tools is much less than that of comparable CFD software. In addition, the time required to learn and retain FLUINT/FloCAD is reduced, as is the time required to build and change models.
  • Speed: The solution speed of FLUINT is orders of magnitude faster than that of CFD approaches: meaningful results can be obtained within minutes on a single PC, rather than hours on networked workstations. This means being able to ask “bigger questions” at either higher levels of assembly or what-if and sensitivity studies using parametric modeling and Advanced Design Modules (for optimizing, calibrating to test, statistical design including tolerancing, etc.).
  • Phenomena: Transient analyses are not a problem for the FLUINT/FloCAD approach, and it makes quick work of systems that are poorly suited for 3D CFD methods, including ducted air or coolant flows, heat pipes, and two-phase flow.


FNM Condenser Model

  • Less accuracy? There is a common presumption that CFD methods assume less than correlation-based approaches, and are therefore more accurate. Indeed, correlation-based methods like FLUINT/FloCAD make assumptions such as fully developed flow profiles that are inappropriate in some instances and such discrepancies must be overcome by additional guidance from the user. However, it is less commonly recognized that CFD methods struggle with heat transfer solutions because heat transfer is estimated based upon the flow field estimation: errors in heat transfer coefficients on the order of 20% are not uncommon. Resolutions of this problem include use of even more fine meshes near the walls (causing even less flexibility and slower solution speeds) and, ironically, application of empiricisms.



Parametric Study of Heat Pipe Degradation

 

Advantages of the CFD approach

The main advantage of CFD over FLUINT/FloCAD “FNM” methods is that certain classes of 2D/3D flow problems that are simply not amenable to 1D methods, or at least require too much user involvement (e.g., correcting for entrance length effects or specifying losses influencing flow splits) to exploit 1D flow solution methods and available heat transfer correlations.

Nonetheless, many engineers continue to use both methods for such problems. Essentially, they use a CFD solution to develop a correlation for use in codes such as FLUINT: using CFD runs to define a flow split, a pressure or velocity boundary condition, an effective loss or heat transfer coefficient, etc. Using these as inputs to FLUINT enables modeling of transients, parametric solutions, optimization, calibrations to test data, two-phase flow solutions, etc.

Perhaps the greatest drawback of FLUINT/FloCAD methods is the lack of postprocessed 3D flowfields and streamlines, which certainly have tremendous appeal in presentations and technical papers. Because flow networks are visually more abstract, some engineers have even created CFD graphics for presentations after completing their design work using FLUINT methods.

For More Information

“Novel Simulation Techniques for Design of Air-cooled Electronics”, IPACK2001-15223.

“CAD-based Methods for Thermal Modeling of Coolant Loops and Heat Pipes", presented at ITHERM 2002.




About Us | Products | Services | Support | What's New | Resources
Home | Request a Quote | Site Map | Feedback

Copyright ® 2010 Cullimore & Ring Technologies, Inc. All rights reserved.