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The technique of Flow Network Modeling (FNM) as incorporated in MacroFlow has been used to design a cooling system
for a variety of electronic devices. Technical publications that describe both the technique and its practical application are listed below:
Improving Productivity in Electronic Packaging with Flow Network Modeling
Thermal Design Methodology for Electronic Systems
Analysis and Design of liquid-Cooling systems using Flow Network Modeling (FNM)
A Flow Network Analysis of a Liquid Cooling System that Incorporates Microchannel Heat Sinks
Design and Verification of a Partial Recirculation Scheme for a Telecom Shelf
Flow Network Modeling: A Case Study in Expedient System Prototyping
Thermal Design of a Base Transceiver Station Using Flow Network Modeling
Use of Flow Network Modeling (FNM) for the Design of an Air-Cooled Server
Analysis of the Effect of Flow Bypass on the Performance of Heat Sinks Using Flow Network Modeling (FNM)
Use of Flow Network Modeling (FNM) for the Design of a Burn-in Oven
Use of Flow network Modeling for the Design of an Intricate Cooling manifold
Rapid Scale-Up Design of a Forced Convection, Radio Frequency Absorption Cooling Using Flow Network
Modeling and Computational Fluid Dynamics
Use of Flow Network Modeling (FNM) for Enhancing the Design Process of Electronic Cooling Systems
Thermal Analysis of an Electronics Enclosure: Coupling Flow Network Modeling (FNM) and Computational
Fluid Dynamics (CFD)
Analysis of Flow Distribution in a Power Supply Using Flow Network Modeling (FNM)
Improving Productivity in Electronic Packaging with Flow Network Modeling (.pdf)
This study introduces the concept of Flow Network Modeling (FNM) and its application in the design of electronics cooling systems. FNM enhances the productivity of the thermal designer by
fulfilling the need for a technique between spreadsheets and CFD for system-level design. A generalized FNM methodology has been described that involves network representation of a flow system by
tracing the paths followed by the cooling streams. Each flow path and component in the network is assigned flow and heat transfer characteristics. Then, the mass, momentum, and energy equations are
solved to determine system-wide distribution of the flow rate and local bulk temperature of the coolant. Although the use of the FNM approach has been illustrated for the design of an air cooled
computer system, a liquid cooled system would be analyzed similarly.
The FNM approach offers the following benefits in the design of electronics cooling systems:
- Rapid and accurate evaluation of competing system configurations during the conceptual design stage.
- Developing ideas for design improvements and analysis of “what if” scenarios.
- Focused, selective, and efficient use of CFD analysis for later detailed design.
Reference: Belady C., Kelkar K.M., and Patankar S.V., “Improving Productivity in Electronics Packaging with Flow Network Modeling (FNM)”, Electronics Cooling, volume 5, no. 1,
January 1999.
Thermal Design Methodology for Electronics Systems (.pdf)
This paper presents the thermal design methodology used to design a multi-processor server – RP8400. The proposed methodology combines well-known analytical and experimental thermal design tools
and heat transfer correlations. Flow Network Modeling (FNM) and Computational Fluid Dynamics (CFD) techniques, and experimental measurements. The key benefits of this methodology are its emphasis
on the use of varied design tools, each applied at its optimal point in the product design cycle. Thus, analysis time is greatly reduced, with acceptable sacrifice to accuracy and detail, during
the earliest stages of the design when the design concept is fluid, new ideas abound, and speed is paramount. Detailed analyses, providing a greater degree of accuracy, are performed in the later
stages of the development cycle when the designs are firm, changes are fewer, and optimization/validation is the goal. In this manner, thermal risk is systematically reduced throughout the product
design cycle. This study first gives an overview of the thermal design methodology. Direct application of the methodology to the design of an enterprise server, the RP8400, is then discussed with a
comparison of the numerical modeling and empirical measurements. The methodology is shown to provide adequate results for the thermal design of large systems possessing complex three-dimensional
flow patterns. The key advantages of the methodology include a low risk design which meets project schedules and use of optimum combination of design tools to increase productivity and reduce
design time.
Analysis and Design of liquid-Cooling systems using Flow Network Modeling (FNM) (.pdf)
Liquid cooling is used for thermal management of electronics in defense, power, medical, and computer applications due to the increasing power density and the desire for compact
packaging. The objectives in the design of these systems are to create a sufficient amount of total flow and to appropriately distribute the flow to individual cold plates so as to maintain the
electronic component temperatures at the desired level. The technique of Flow Network Modeling (FNM) is ideally suited for the analysis of flow distribution and heat transfer in liquid-cooling
systems. This article describes the technical basis of the FNM technique and illustrates its application in the design of a distributed-flow cold plate and of a complete water-cooled system. Design
iterations for the distributed cold plate involve changing the size of the header tube so as to achieve a uniform flow distribution in the crossflow passages within the cold plate. The water-cooled
system involves a manifold layout with individual branches containing cold plates of varying capacity for removing heat loads that differ by an order of magnitude. Use of an inverse design method
is illustrated for achieving the desired flow distribution within the manifold and the design procedure for sizing the heat exchanger, pump, and the main orifice are also described. The study
demonstrates the utility of the FNM technique for rapid and accurate evaluation of different design options and the ensuing productivity benefits in the design of liquid cooling systems.
A Flow Network Analysis of a Liquid Cooling System that Incorporates Microchannel Heat Sinks (.pdf)
The objective of this study is to show the applicability of Flow Network Modeling (FNM) in analyzing liquid cooling systems that incorporate microchannel heat sinks. The study is divided in two
parts. In the first part, an analytical model of a microchannel heat sink is proposed and its validity is established by comparison with a detailed CFD analysis. In the second part of the study, a
liquid cooled system that accommodates three microchannel heat sinks is analyzed using Flow Network Modeling (FNM). In the FNM method, the pressure drop and heat transfer coefficient of the
components in the system are calculated using analytical or empirical correlations. The goal of the analysis is to balance the liquid flow passing through each heat sink so that the case
temperatures of the individual chips remain below the recommended value. Use of the FNM technique enables rapid selection of the tubes and orifices for achieving the desired overall flow and the
flow distribution.
Design and Verification of a Partial Recirculation Scheme for a Telecom Shelf (.pdf)
Flow Network Models are used to design an innovative cooling system for a high power telecoms shelf which uses the partial recirculation of air to increase air velocities over the circuit cards.
The study first outlines the design of the recirculation cooling system and the associated design objectives. This is followed by a description of the Flow Network Model used for the analysis of
the cooling system. The study also involved systematic measurement of the average slot velocities for the initial design. Predictions for the bulk flow from the network model were in good agreement
with the measurements. The differences between the measurements and predictions for the recirculating bulk flow were a result of the much higher than anticipated density of the power cables routed
across the recirculation duct.
Flow Network Modeling: A Case Study in Expedient System Prototyping (.pdf)
A number of analysis techniques and the corresponding tools are available to the thermal engineer for comprehensive design of electronics systems. This study presents the use of the Flow Network
Modeling (FNM) technique as originally proposed by G. Ellison to perform first order thermal analysis on a next-generation mid-range computer design. This method is used to predict the pressure
drops and fan-performance in the complex computer system prior to building the hardware, performing sub-system flow measurements, or complementing CFD analyses. In the particular application, use
of FNM allowed a small design team to sufficiently validate the system layout early in the product design cycle, enabling continued sub-system layout, detailed design, and prototype production
within the constraints of the project’s aggressive schedule. Results of the Elisson-based hand calculations are compared with a commercially available FNM software package MacroFlow and with data
taken from a system prototype. Comparison shows that the results agree well, validating the use of FNM as an aid in developing thermally feasible computer designs.
Minichiello, A., “Flow Network Modeling: A Case Study in Expedient System Prototyping,” Proceedings; Itherm 2000: Seventh Intersociety Conference on Thermal and
Thermomechanical Phenomena in Electronic Systems, Las Vegas, Nevada, May 2000, pp. 70-77.
Thermal Design of a Base Transceiver Station Using Flow Network Modeling (FNM) (.pdf)
The objective of this study was to perform thermal analysis for the design of a Base Transceiver Station (BTS) outdoor frame, which consists of a PCB rack, an ATM switch unit, a RF amplifier unit,
two RF filters, and a rectifier. The electronic components are completely isolated from the outside ambient air. The primary objective of the analysis was to package all these units into a compact
portable cabinet with effective cooling strategies for outdoor environmental conditions. The FNM technique was used for the thermal analysis from Conceptual Design through the Final Design. At the
Conceptual Design phase, flow network models were built to examine different packaging concepts and to generate new design proposals by identifying the problem areas of the examined design
concepts. A highly integrated heat exchanger/BTS frame design concept was developed after iterations of this process. At the detailed design stage, FNM analysis was used for the placement of units,
for necessary air baffling and flow balancing, and for the design of the heat exchanger. The results of the FNM analysis were also used to provide boundary conditions for detailed unit-level
analysis using the CFD technique. The use of FNM benefits the design process due to its ability to provide quick system-level modeling and problem solving. A CFD analysis of the BTS frame requires
tremendous modeling effort and computational time and is neither feasible nor necessary at the early design stage. Use of FNM shortened the design process significantly.
Zhu N.Q., Plaza D., and Maitz C.R., “Thermal Design of a Base Transceiver Station Using MacroFlow,” Proceedings: HD International, The International Conference and Exhibition
on High Density Interconnect and Systems Packaging, Denver, Colorado, April 2000, pp. 414-419.
Use of Flow Network Modeling (FNM) for the Design of an Air-Cooled Server (.pdf)
This study involves the application of FNM for the design of an air-cooled server. MacroFlow is used to investigate the flow distribution in different system layouts, generate ideas for
performance improvements based on predicted system-wide flow distribution, and evaluate these modifications on the air-flow performance of the system. Use of FNM is shown to significantly reduce
the time required for a comparative performance evaluation of different system configurations. Such rapid analysis enabled development of a good system design during the Conceptual Design Stage,
before the design proceeded to a stage where changes are very costly to implement. An enhanced design cycle is outlined that uses FNM analysis during the early design stage for shortening the
overall design process, enhancing the quality of the final design, and improving the productivity of the thermal design engineer in a significant manner.
Reference: Steinbrecher R., Radmehr A, Kelkar K.M., and Patankar S.V., "Use of Flow Network Modeling (FNM) for the Design of Air-Cooled Servers", Proceedings, the
Pacific Rim/ASME International Intersociety Electronic and Photonic Packaging Conference (InterPack), vol.2, 1999, pp. 1999-2008.
Analysis of the Effect of Flow Bypass on the Performance of Heat Sinks Using Flow Network Modeling (FNM) (.pdf)
Heat sinks are used in electronics cooling systems to provide extra area for transfer of the heat dissipated by semiconductor devices. However, in presence of clearance regions around the heat
sink, flow that would otherwise go through the heat sink bypasses it. The present study uses the technique of Flow Network Modeling (FNM) to analyze the effect of flow bypass on the heat transfer
performance of a plate fin heat sink. The physical situation analyzed corresponds to a typical wind tunnel test cell used for the characterization of the heat sink performance. Results of network
analysis predict that increasing the bypass region has a strong effect on decreasing the flow rate through the heat sink. Therefore, the effectiveness of the heat sink is reduced when large
clearance regions are present around it. The network analysis is shown to be very easy, quick, and accurate. It can be used for analyzing the placement of heat sinks in practical cooling systems.
Reference: Radmehr A, Kelkar K.M., Kelly P.J., Patankar S.V., and Kang S.S., "Analysis of the Effect of Bypass on the Performance of Heat Sinks Using Flow Network Modeling
(FNM)", Proceedings, the 15th Annual IEEE Semiconductor Thermal Measurement and Management Symposium (SemiTherm), 1999, pp. 42-47.
Use of Flow Network Modeling (FNM) for the Design of a Burn-in Oven (.pdf)
Electronic components undergo burn-in inside a forced convection oven as a part of the production cycle. The purpose of the burn-in oven is to accelerate mechanisms of quality failures and screen
for infant mortality over a specified production lot of electronic components. For system-level design of a burn-in oven, the Flow Network Modeling technique allows rapid and accurate investigation
of the flow distribution for different arrangements of the burn-in boards within the zones and alternate placements of the components on the boards. This case study illustrates how FNM is useful in
significantly shortening the overall design process, reducing the risk of design changes later in the design cycle, and improving the productivity of the thermal and process design engineers.
Reference: Dishongh T., Kelly P.J., Kelkar K.M., and Patankar S.V., "System-Level Design for Electronics Packaging and Production: A Case Study using FNM for the Design of a
Burn-In-Oven", Advanced Packaging, June-July, 1999, pp. 62-66.
Use of Flow Network Modeling for the Design of an Intricate Cooling Manifold (.pdf)
One of the Automatic Test Equipment (ATE) designed at Teradyne utilizes a water-based cooling system in an intricate manifold that serves as the base for mounting numerous liquid cooling modules
spaced between circuit boards. Efficient circulation of water through this manifold is critical for the proper operation of the liquid cooling modules. This study uses the technique of Flow Network
Modeling (FNM) for a comparative study of the flow distribution in a variety of cooling manifold designs. Each manifold is modeled using a network of flow components such as tubes, orifices,
valves, tee-junctions, and area contractions/expansions. In the optimal design, pressure differentials between elements in the system should be at a minimum and the all modules should have the same
flow rate through it. However, due to the complexity of the manifold, the flow distribution is governed by many system parameters and achieving the desired flow balance is not easy. FNM technique
allowed rapid and accurate comparison of the relative performance of different designs and suggested design improvements. Thus, use of the FNM technique improved the efficiency of the manifold
design process by reducing prototype design time, and design and experimental testing costs.
Reference: Verma N, "use of Flow Network Modeling for the Design of an Intricate Cooling Manifold,” Proceedings, The International Conference & Exhibition on High
Density Interconnect and System Packaging, Denver, Colorado, April 2000, pp. 408-413.
Rapid Scale-Up Design of a Forced Convection, Radio Frequency Absorption Cooling Using Flow Network Modeling and Computational Fluid Dynamics (.pdf)
This study was performed to evaluate the scalability of an existing air-cooled, radio frequency (RF) absorption load design using system-level investigations with Flow Network Modeling (FNM) and
detailed results from Computational Fluid Dynamics (CFD). The novelty of this study lies in the coupled application of FNM and CFD techniques to a high-power, digital broadcast load consisting of a
validated RF absorption structure, existing air moving devices, and a tested system design which were scaled to develop a cooling chassis capable of increased RF power levels. Since design targets
were well defined for the existing system, it was possible to use the FNM technique for rapid progression to the new, higher power design in the conceptual stage by evaluating sensitivities to
cross-sectional area, free area ratio, air moving devices, and power levels. The FNM results were then used as a form baseline for detailed CFD analysis to substantially reduce the number of
time-consuming CFD iterations. This greatly shortened the design cycle and resulted in unprecedented time to market. The study describes design considerations of air-cooled loads and the
application of the FNM technique to their design. FNM and CFD estimates of the volumetric flow rates, average velocities, component pressure drops, and global temperatures of the absorbing media
are presented and compared with experimental data.
Use of Flow Network Modeling (FNM) for Enhancing the Design Process of Electronic Cooling Systems (.pdf)
The FNM methodology has been applied for the prediction of flow distribution in an air-cooled cabinet, in which air is blown by a fan through a manifold entrance into passages of a card array.
MacroFlow-based analysis accurately predicts the maldistribution of the flow through various card passages. Effect of a design modification involving gradual reduction of the area at the bottom of
the cards through a tapered wall is also analyzed to determine the extent of the taper required. This example illustrates the simplicity, speed, and utility of FNM technique for system-level
thermal design.
Reference: Kelkar K.M., Radmehr A., Kelly P.J., Patankar S.V., and Belady C., "Use of Flow Network Modeling (FNM) for Enhancing the Design Process of Electronic Cooling
Systems", Proceedings, International Systems Packaging Symposium, San Diego, January 1999, pp. 58-63.
Thermal Analysis of an Electronics Enclosure: Coupling Flow network Modeling (FNM) and Computational Fluid Dynamics (CFD) (.pdf)
The novelty of this study lies in the complementary use of the technique Flow Network Modeling (FNM) and Computational Fluid Dynamics (CFD) for quick and accurate analysis of a cabinet used for a
high-speed internet subscriber device. The enclosure consists of thirteen PCBs and two axial fans. The detailed flow distribution between the passage formed by adjacent PCBs is analyzed using CFD
to determine the impedance characteristics. A flow network model of the entire system is then constructed with individual card passages represented by the CFD-based impedance. Other standard
components are characterized using the correlations available in handbooks as available in the commercial package MacroFlowTM. The network analysis of the entire system accounts for the
interaction of the fan curve and flow impedances to predict the flow distribution in individual passages. This is, in turn, used as boundary conditions in the CFD analysis to obtain the thermal map
of individual cards. Predicted distribution of the flow rates agrees well (within 10%) with the experimental measurements.
Reference: Kowalski T., and Radmehr A., “Thermal Analysis of an Electronics Enclosure: Coupling Flow Network Modeling (FNM) and Computational Fluid Dynamics (CFD),”
Proceedings, Sixteenth Annual IEEE Semiconductor Thermal Measurement and Management Symposium; San Jose, CA, March 2000, pp. 60-67.
Analysis of Flow Distribution in a Power Supply Using Flow Network Modeling (FNM) (.pdf)
This study presents an analysis of flow distribution in a new-generation power supply used in telecommunication applications. The power supply involves several boards arranged in a rack, with each
board containing several magnetic components, EMI screens, and heat sinks and fans. The novelty of this study lies in the use of a two-level flow network approach to achieve modularity and gain
further efficiencies in the use of the FNM technique. A network model of a passage formed by two successive boards is first constructed to determine the characteristics that determine the flow in
and out of each power supply. A network model of the entire system is constructed by arranging the compact models for each passage in a manifold arrangement corresponding to the physical
arrangement in the rack. Analysis is then carried out for three placements of the cabinets, namely isolated cabinets, two cabinets side-by-side, and three or more cabinets side-by-side. Results
show that for a single cabinet, the flow is uniformly distributed among the passages because of the presence of side vents. However, with multiple cabinets placed side-by-side, the forward flow
streams from individual passages are forced to merge in the header at the back of the cabinet. The resulting combining manifold gives rise to a maldistribution of flow among passages with lower
flow rates in the bottom passages. The two-level network modeling approach is well suited for a top-down design and packaging of large-scale electronics systems for achieving the desired thermal
performance.
Reafi-Ahmed G., Radmehr G., and Kelkar K.M.,”Analysis of Flow Distribution in a Power Supply Using Flow Network Modeling,” Proceedings; Itherm 2000: Seventh Intersociety
Conference on Thermal and Thermomechanical Phenomena in Electronic Systems, Las Vegas, Nevada, May 2000, pp. 90-98.
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