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MacroFlow: Electronics Cooling

A Software Tool for Rapid Flow and Thermal Design of Electronics Cooling, Semiconductor Processing, and General Flow Systems

  • A Liquid-Cooled Avionic System  » Click to zoom ->

    A Liquid-Cooled Avionic System

  • Component Pallet  » Click to zoom ->

    Component Pallet

  • The Enhanced Design Cycle  » Click to zoom ->

    The Enhanced Design Cycle

MacroFlow is very well suited for rapid flow and thermal design of a variety of air- and liquid-cooled systems in Computer, Telecom, Defense, and Power electronics applications. The component library in MacroFlow includes many electronics-cooling components such as Fan and Pump, Heat sink, Cold Plate, and Heat Exchanger, Air Filter, Screen, and Quick Disconnect. Since MacroFlow-based analysis is very simple and fast, its use allows determination of a good system design early in the design cycle.

Flow and thermal characteristics of the components can be defined by specifying their geometry for utilizing built-in correlations or through direct specification in suitable functional forms. In addition, characteristics of off-the-shelf products offered by leading vendors can be chosen from the embedded libraries for Heat Exchangers and Cold Plates from Lytron, Quick Disconnects from Aeroquip, Fans from Dynamic Air Engineering, Comair-Rotron and JMC Products, and Air Filters from Universal Air Filter.   


The features and capabilities of MacroFlow include:

  • Analysis of steady and transient systems
  • Intuitive graphical user interface
  • A built-in library of components
  • Customizable flow and thermal characteristics of any component
  • Powerful solution algorithm for fast and robust solution of complex models
  • Comprehensive post-processing through plots tables, animations, and more
  • Exporting of pictures in various graphical formats and of tables into spreadsheets for further processing, report writing, and presentations

Integrated Design Environment

MacroFlow’s integrated computing environment for thermal design of electronics systems reflects the way industrial design is conducted. You save time, get designs into prototype stage faster, identify problem areas sooner, and evaluate numerous design alternatives. The MacroFlow modeling architecture builds your system thermal/flow model with:

  • A flexible Graphical User Interface to construct flow networks representing the system layout.
  • A built-in, engineering library of common electronic packaging components. The flow and heat transfer characteristics of the components are taken from handbooks and vendor data; they can also be user-defined.
  • A robust and efficient solver to calculate flow, pressure, and temperature at every critical point in the electronics system package
  • An integrated, post-processing data and visualization suite for examination of results and their communication to team members.
  • Built-in engineering utilities for fast modeling including units conversion, calculated variables, and component libraries for common electronic packaging elements.

Extensive Library of Components

The component library in MacroFlow contains extensive flow and thermal characteristics of components most commonly encountered in electronics cooling systems and flow delivery systems in semiconductor processing. The characteristics are in the form of accurate pressure drop and thermal resistance correlations that are compiled from various handbooks and vendor-supplied data of off-the-shelf components.

Flow Path Elements

  • Nozzles, intake screens, and exhausts with selectable geometries
  • Straight and screened inlet and exhaust
  • Ducts and zero resistance flow paths
  • Abrupt or gradual area changes, elbows, orifices, valves
  • Junction components including tee, wye, and cross

Electronic Packaging Components

  • Fans and blowers with a customizable database that already includes products from Dynamic Air Engineering, Comair Rotron, and JMC Products
  • Heat Sinks
  • Fan heat sinks for analysis of pressure drop and cooling in fan-cooled impingement heat sinks
  • Card Passages
  • Air filters with a customizable database that includes characteristics of air filters made by Universal Air Filter
  • Plenums and tanks
  • Heat Exchangers with a customizable database that includes characteristics of products offered by Lytron
  • Cold Plates with a customizable database that includes products offered by Lytron
  • Quick Disconnect (QD) component that accounts for directionality of the flow on pressure drop in QDs and includes characteristics of QDs offered by Aeroquip
  • Flow Map component that allows specification of the characteristics of cooling units (LRUs) in terms of the variation of pressure drop with flow rate and temperature.
  • Power Supplies
  • Generalized heat exchanger model
  • Generic Resistance element for specifying user defined characteristics

All thermal and flow information corresponding to a component is user accessible for customization, naming, and storage in a user-defined database. Further, performance curves for nonlinear, or time-dependent data can be added using polynomial, or piecewise-linear data form.

Comprehensive Heat Transfer Capability

MacroFlow enables accurate prediction of the system temperature distributions in one unified architecture. Calculated variables include the bulk fluid temperature in all flow paths, the average surface temperature of every component, and heat loss/gain. Additionally, a variety of thermal boundary conditions can be modeled such as:

  • Specified heat dissipation or heat flux
  • Environmental heat loss at a specified temperature due to natural or forced convection in combination with radiation
  • Incident external radiation such as the solar flux
  • The thermal resistance considered includes the internal, wall, and external resistances in presence of heat loss to the surroundings. The internal and external heat transfer coefficients can be calculated from empirical or user- defined correlations for forced and natural convection.

Powerful Solution Methodology

MacroFlow uses the technique of Flow Network Modeling (FNM). In this technique, a flow system is represented as a network of components and flow paths. Then, the specific network characteristics are defined by the user, through tab-dialog input. These component characteristics include volumes, flow resistances, heat transfer coefficients, and any other required properties, all of which can vary with time.

The FNM methodology is fast because it does not attempt to calculate the detailed variation within a component but it utilizes overall component characteristics. This results in a small number of equations that describe the flow and heat transfer over the entire system which can be solved in a rapid manner. Further, since the component characteristics are empirically determined, the predicted behavior of the system is very accurate.

Conservation of mass, momentum, and energy are enforced over the various components and connections. A pressure-correction based solution method is developed for the analysis of the discretization equations that describe conservation of mass, momentum, and energy over an unstructured network. A direct solution method with Newton-Raphson linearization is used for their solution. The resulting solution method is very fast (solution in less than a minute) and robust.  

Extensive Capabilities for Examination of Results

Results of analysis of a network model can be examined in a variety of ways as described below:

  • Plots – Predicted variations of various physical quantities can be plotted as Bar Charts or Line Graphs. The appearance of the plots can be customized by specifying the plot color, axis titles, axis range, and font/orientation/format of the captions.
  • Tables – Numerical values of predicted quantities can be listed in tabular format in any user-specifiable units.
  • On-Screen Display of Results – Specific physical quantities of interest can be listed directly on the screen for chosen components to enable convenient examination of the system performance.
  • Animation – The flow of the fluid through the system can be visualized as an animation of colored balls through the network model. Flow animation provides quantitative information because the speed of the dots is proportional to the local flow rate or velocity and the dots are colored according to the local temperature or pressure.
  • Export of Plots and Tables – Both the plots and the workspace can be exported as pictures of a suitable format (bmp, gig, jpg, png, tif) to a user-specifiable file for inclusion in reports and presentations. Similarly, tables can be exported as files of csv format for reading into Excel spreadsheets for further processing of data.

In order to facilitate easy creation of the list of components for which results are to be examined using on-screen display, user can visually select the components by first highlighting them on the network before creating plots, tables, or on-screen display of results. The list of components can, of course, be further modified within the individual dialogs. This capability virtually eliminates the need for selecting components by their names, which can be cumbersome for large networks.

Application for Thermal Design

MacroFlow is ideally suited for system-level thermal design during the Conceptual Design stage. Its object-oriented nature enables quick construction of flow networks of cooling systems and the powerful solution method enables rapid analysis. Thus, many different system layouts, “what if” studies, and contingencies such as fan failure can be evaluated very quickly for arriving at few good system-level design early in the design cycle. MacroFlow is a productivity tool. Its use results in significantly shorter design cycles, better product quality, and reduces the time to market.

Construction of Flow Networks for Electronics Systems

Practical electronics cooling systems can be represented as a network of components such as ducts, heat sinks, screens, filters, passages within card arrays, fans, bends, and tee junctions. Interconnections of these components correspond to the paths followed by the coolant as it passes through the system. Flow and thermal characteristics of individual components are obtained from handbooks, laboratory testing, and vender data. The emphasis of FNM is the analysis of the interaction among the components for determining the system performance. Therefore, prediction of the details of flow and heat transfer within a component is not attempted.

Types of Cooling Systems Designed Using MacroFlow

MacroFlow is applicable to the design and analysis of system level cooling for electronics used in: computers, data processing, telecommunications, military and commercial avionics, automotive and transportation equipment, consumer goods, and medical applications. MacroFlow can be applied to open or closed systems, air or liquid cooling, and forced or natural convection for:

  • PC enclosures
  • Liquid cooled supercomputers
  • Workstations
  • Telecommunications cabinets
  • High-end servers
  • Avionics cooling
  • Projection equipment
  • VME based microcomputers
  • Mainframes
  • Electronic navigation systems
  • Consumer electronics
  • Space and satellite electronics

Benefits and Limitations of MacroFlow

FNM offers a simple, quick, and accurate method for flow and thermal performance of electronics systems. Some of the benefits it offers for system-level thermal design are described below.

  • Evaluation of Competing Designs – The strength of FNM is the analysis of system-wide interaction of individual components. Thus, thermal performance of competing physical layouts of the system can be evaluated very quickly and accurately through FNM analysis of corresponding flow networks involving different interconnections of the same set of system components.
  • New Concepts for Design Improvements – FNM analysis of a system provides a clear overview of the flow and temperature distribution in the system. This is very useful not only in identifying the problem areas in the system but also in generating ideas for design improvements (e.g. incorporation of flow balancing elements, addition of backup fans). Further, benefits of these improvements can also be quickly evaluated.
  • "What If" Studies – FNM analysis is ideally suited for determining the magnitude of the impact on system performance under "what if" and contingency scenarios (e.g. fan failure and rise in ambient temperature).
  • Complementary Use with CFD – FNM and CFD complement and enhance each other. Thus, CFD can be used for accurate determination of characteristics of nonstandard components (e.g. complex heat sinks) for use in FNM analysis. Similarly, results of the FNM analysis of an entire system can be used to provide boundary conditions for a detailed analysis of part of a system (e.g. card array) using CFD. FNM also enables focused use of CFD for the analysis of the most feasible system layouts.

The user should also be aware of the following limitations of this approach and use CFD where applicable:

  • Component Temperatures – FNM cannot predict the temperatures at the component level. A detailed board-level thermal network or CFD analysis is necessary for this purpose.
  • Flow Resistances – The accuracy of FNM results depends upon the validity of the flow resistance correlations employed.
  • Network Representation – Flow network representations may not be accurate or even possible for systems in which the flow paths are not well defined. An example of such a system would be an externally cooled sealed cabinet that has large open spaces inside it. A network representation for the buoyancy driven flow inside such a system would be difficult to construct. Therefore, FNM analysis cannot be used when the flow system cannot be represented as a network of identifiable flow paths.

The Enhanced Design Cycle

An enhanced design cycle that incorporates FNM in the early design stage, is shown in the flow chart below. Use of FNM for Conceptual System Design significantly reduces the effort that is otherwise required for system-level thermal analysis. CFD can then be used in a focused manner for detailed analysis of flow distribution and component temperatures in critical parts of a system or in specific competing system designs. The proposed design cycle significantly shortens the time required for arriving at the final design and improves the quality of the product by enabling the thermal engineer to explore more design options. Thus, use of FNM improves the productivity in the thermal design process and results in an optimum design cycle.