Introduction to Computational Fluid Dynamics Lecture 3: System-level CFD analysis: MacroflowRemarksOutlineTypical Challenges in the Design of Complex Flow SystemsModeling Options for System DesignReal System – Exhaust System of a Dump TruckWhat is Flow Network Modeling?A Network for a Piping SystemFNM of Complex Flow SystemsAdvantages of the FNM TechniqueLimitations of FNMComplementary Nature of FNM and CFDTime Required to Analyze a Typical SystemThermal Design Process Conventional and EnhancedModified Bernoulli’s EquationFlow ResistanceSlide 17Flow Resistance of a DuctFlow Through an Area ChangeFlow Induced by FansSystem Operating PointOverall Thermal ResistanceHeat Transfer in FNMHeat Transfer in FNM (continued)FNM for System DesignMacroFlowTM A Flow Network Modeling Tool for the Design of Flow SystemsCapabilities of MacroFlowDemonstration of MacroFlowFlow through an “S” ManifoldSlide 30Flow through a “U” ManifoldSlide 32Exhaust System of a Dump Truck – Physical SystemExhaust System – The Design ProblemExhaust System – Flow Network ModelExhaust System – Design CycleLiquid Cooling System for Automatic Test EquipmentATE System – The Design ProblemLiquid Cooling System – Characteristics of One LCMPowerPoint PresentationLiquid Cooling System – Distribution of Flow rates in One Branch of the ManifoldEngineering Applications of MacroFlow01/14/191ME 5337/7337Notes-2005-003Introduction to Computational Fluid DynamicsLecture 3: System-level CFD analysis: Macroflow01/14/192ME 5337/7337Notes-2005-003RemarksAll the slides presented in this lecture were provided by Kanchan Kelkar, Principal engineer, Innovative researchThis material is copyrighted by Innovative Research, Inc.01/14/193ME 5337/7337Notes-2005-003OutlineOverview of the Design Process and the Role of FNMTheory of FNMDemonstration of MacroFlowValidation of FNM ResultsApplications and Case studiesCopyright: Innovative Research01/14/194ME 5337/7337Notes-2005-003Typical Challenges in the Design of Complex Flow SystemsBlower/Pump SizingFlow BalancingFilter DegradationBypass EffectManifold MaldistributionValve SelectionMinimizing Pressure LossTube Sizingetc.Copyright: Innovative Research01/14/195ME 5337/7337Notes-2005-003Modeling Options for System DesignHand Calculations (HC)Tedious and very limitedSpreadsheets (SS)System-specific, inflexible, and time intensiveFlow Network Modeling (FNM)Simple, fast, and accurateComputational Fluid Dynamics (CFD)Time intensive for model definition, solution, and postprocessingSuitable for component analysis, not suitable for system-level designCopyright: Innovative Research01/14/196ME 5337/7337Notes-2005-003Real System – Exhaust System of a Dump Truck Flow Network Modeling is the only feasible techniqueCopyright: Innovative Research01/14/197ME 5337/7337Notes-2005-003What is Flow Network Modeling?Flow systems are like electrical circuits.Just as a voltage drop drives a current, a pressure drop creates fluid flow.The flow distribution through different flow paths depends upon their flow resistances.A flow system can be represented as a network of flow resistances. This approach is called Flow Network Modeling (FNM).Copyright: Innovative Research01/14/198ME 5337/7337Notes-2005-003A Network for a Piping SystemCopyright: Innovative Research01/14/199ME 5337/7337Notes-2005-003FNM of Complex Flow SystemsA network model of the flow system is constructed by identifying flow paths through filters, screens, bends, tees, blowers/pumps, valves, orifices, etc.The flow resistance relationships can be obtained from handbooks, vendor specs, in-house testing, or CFD analysis.The flow rates, pressures, and temperatures throughout the system are calculated by solving mass, momentum, and energy equations.Copyright: Innovative Research01/14/1910ME 5337/7337Notes-2005-003Advantages of the FNM TechniqueFNM is simple, fast, and accurateSimple because it is modular and object-oriented Fast because it uses overall characteristicsAccurate because characteristics are empirically determinedCopyright: Innovative Research01/14/1911ME 5337/7337Notes-2005-003Limitations of FNMThe flow system must be described in terms of identifiable flow paths with definable resistance characteristics. FNM provides gross (rather than detailed) predictions:FNM solution does not give local velocity vectors, flow separation, reattachment, etc.Detailed temperature distributions, local heat fluxes, etc. are not calculated.Accurate resistance correlations are needed for reliable prediction. Copyright: Innovative Research01/14/1912ME 5337/7337Notes-2005-003Complementary Nature of FNM and CFDFNM allows focused and efficient use of CFDExamine hundreds of design alternatives by FNM (Conceptual Design) and select a few promising designs for CFD analysis (Detailed Design).Use FNM for an entire system and provide boundary conditions for the CFD analysis of a subsystem.Use of CFD at the component level for determining the flow resistances enhances the accuracy of the to the FNM technique.Complementary use of System Analysis and CFD results inA comprehensive set of tools for complex flow systems.Shorter design cycleCopyright: Innovative Research01/14/1913ME 5337/7337Notes-2005-003Time Required to Analyze a Typical SystemSetup Time Run TimeFNM 1 Hour 10 SecondsBy using FNM, you save a substantial amount of design engineer’s timeCopyright: Innovative Research01/14/1914ME 5337/7337Notes-2005-003Thermal Design Process Conventional and EnhancedConventionalTest-BasedEnhancedFNM-BasedHCTestingFNM CFD TestingFNM TestingCopyright: Innovative Research01/14/1915ME 5337/7337Notes-2005-003Modified Bernoulli’s EquationFor constant density and no gravity head:p1 + V12/2 = p2 + V22/2 + LossesThe losses are due to viscous forces, flow separation, expansion/contraction, bends, etc.Losses = K(V2/2) where K is the loss coefficient.Thus, P = P1 - P2 = K(V2/2)12Copyright: Innovative Research01/14/1916ME 5337/7337Notes-2005-003Flow ResistanceP = P1 - P2 = K(V2/2)Q = VA  P = K( Q2) / (2A2)Flow resistance:P /Q = (K Q) / (2A2) (nonlinear)The values of K are available for screens, orifices, bends, expansion/contraction, T-junctions, etc.For electronics cooling, the K values are needed for card arrays, heat sinks, power supplies, etc.Copyright: Innovative