SEC et al. v. MRI
`SEC Exhibit 1020.001
`IPR 2023-00199
`
`

`

`Cooling Techniques for
`Electronic Equipment
`
`SEC et al. v. MRI
`SEC Exhibit 1020.002
`IPR 2023-00199
`
`

`

`Cooling Techniques for
`Electronic EquipJ1llent
`
`DA VE S. STEINBERG
`
`Manager, Mechanical Engineering
`Design Analysis Section
`Litton Guidance and Control Systems
`Woodland Hills, California
`
`JOHN WILEY & SONS, New York • Chichester • Brisbane •Toronto • Singapore
`
`A WILEY-INTERSCIENCE PUBLICATION
`
`SEC et al. v. MRI
`SEC Exhibit 1020.003
`IPR 2023-00199
`
`

`

`Copyright© 1980 by John Wiley & Sons, Inc.
`
`All rights reserved. Published simultaneously in Canada.
`
`Reproduction or translation of any part of this work
`beyond that permitted by Sections 107 or 108 of the
`1976 United States Copyright Act without the permission
`of the copyright owner is unlawful. Requests for
`permission or further information should be addressed to
`the Permissions Department, John Wiley & Sons, Inc.
`
`Library of Congress Cataloging in Publication Data:
`Steinberg, Dave S
`1923-
`Cooling techniques for electronic equipment.
`
`"A Wiley-l nterscience publication:·
`Includes index.
`I . Electronic apparatus a nd appliances-Cooling.
`
`I. Title.
`TK7870.25.S73
`ISBN 0-471-04403-2
`
`621.381
`
`80-14141
`
`Printed in the United States of America
`
`10
`
`SEC et al. v. MRI
`SEC Exhibit 1020.004
`IPR 2023-00199
`
`

`

`To My Wife Annette
`And To My Two Daughters Cori and Stacie
`
`SEC et al. v. MRI
`SEC Exhibit 1020.005
`IPR 2023-00199
`
`

`

`Electronic equipment is slowly reaching into almost every phase of modern
`living , from sewing machines and washing machines to mass transportation
`and atomic energy control systems. The reliability of these systems is of
`great importance to our comfort and safety. If a transistor fails in a television
`set, it may only cause a minor inconvenience. However, if an electronic
`control system should malfunction because it has overheated, it may result
`in substantial property damage and possible injury.
`Electronic systems are rapidly shrinking in size, while their complexity
`and capability continue to grow at an amazing rate. As the power has been
`increasing, the volume has been decreasing, resulting in a dramatic increase
`in the heat density. As a result, the temperatures in many electronic systems
`have been rising rapidly, producing a large increase in the number of fail(cid:173)
`ures.
`High failure rates in electronic boxes may also be caused by high thermal
`stresses in the solder joints of electronic components mounted on circuit
`boards. This is usually due to a high thermal expansion coefficient with
`insufficient strain relief in the component lead wire. This area is discussed
`in detail, together with recommendations for mounting components to pre(cid:173)
`vent this type of failure.
`The purpose of this book is to show designers and engineers quick meth(cid:173)
`ods for designing electronic hardware to withstand severe thermal environ(cid:173)
`ments without failing. Techniques are presented that will permit the devel(cid:173)
`opment of many different types of reliable electronic systems without the
`aid of the powerful new high speed digital computers.
`This book was developed from a series of seminars, lectures, and short
`courses for the cooling of electronic equipment, which I have presented at
`the University of Wisconsin-Extension every year since 1975. The book
`was influenced by my industrial experience in the mechanical design, pack(cid:173)
`aging, and testing of many different types of sophisticated electronic com(cid:173)
`ponents and systems during the past 25 years.
`Mathematical modeling techniques using analog resistor networks are
`also included. For those who wish to use high speed digital computers to
`
`vii
`
`SEC et al. v. MRI
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`IPR 2023-00199
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`

`

`viii
`
`Preface
`
`solve thermal problems, these techniques can be used to break up a complex
`system into many individual thermal resistors and nodes.
`In an attempt to keep the book as simple as possible, the derivations of
`equations were minimized. The emphasis is always on the real electronic
`hardware that is used in today's sophisticated electronic systems. Many
`sample problems are presented, to demonstrate practical and cost effective
`methods for designing efficient, reliable cooling systems.
`Although the metric system for weights and measures is widely used in
`Europe, at the present time it is used by only a few American companies.
`However, there appears to be a strong movement toward conversion from
`the present English system to the metric system. This book was therefore
`written with dual units, English and metric, to permit electronic equipment
`designers and engineers to work with either set of units effectively.
`I thank Mr. Joel Newberger for his contributions in the section on induced
`draft cooling, and Mr. Joel Sloan for proofreading several sections of the
`book.
`
`Westlake Village, Califomia
`August 1980
`
`DAVES. STEINBERG
`
`SEC et al. v. MRI
`SEC Exhibit 1020.007
`IPR 2023-00199
`
`

`

`Contents
`
`Preface
`
`Symbols
`
`1 Evaluating the Cooling Requirements
`
`1.1 Heat Sources, 1
`1.2 Heat Transmission, 2
`Steady State Heat Transfer, 4
`1.3
`1.4 Transient Heat Transfer, 5
`1.5
`Electronic Equipment for Airplanes, Missiles, Satellites,
`and Spacecraft, 6
`1.6 Electronic Equipment for Ships and Submarines, 8
`Electronic Equipment for Communication Systems and
`1.7
`Ground Support Systems, 9
`1.8 Minicomputers, Micrbcomputers, and
`Microprocessors, 10
`1.9 Cooling Specifications for Electronics, 11
`1.10 Specifying the Power Dissipation, 12
`1.11 Dimensional Units and Conversion Factors, 14
`
`2 Designing the Electronic Chassis
`
`2.1
`Formed Sheet Metal Electronic Assemblies, 21
`2.2 Dip Brazed Boxes with Integral Cold Plates, 22
`2.3
`Plaster Mold and Investment Castings with Cooling
`Fins, 24
`2.4 Die Cast Housings, 25
`
`vii
`
`xvii
`
`1
`
`21
`
`ix
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`

`

`x
`
`Contents
`
`2.5
`2.6
`2.7
`2.8
`2.9
`2.10
`
`Large S and Castings, 26
`Extruded Sections for Large Cabinets, 26
`Humidity Considerations in Electronic Boxes, 26
`Conformal Coatings, 28
`Sealed Electronic Boxes, 29
`Standard Electronic Box Sizes, 33
`
`3 Conduction Cooling for Chassis and Circuit Boards
`
`35
`
`3.5
`
`3.1 Concentrated Heat Sources, Steady State
`Conduction, 35
`3.2 Mounting Electronic Components on Brackets, 36
`3.3
`Sample Problem-Transistor Mounted on a Bracket , 39
`3.4 Uniformly Distributed Heat Sources, Steady State
`Conduction, 41
`Sample Problem-Cooling Integrated Circuits on a
`PCB , 44
`3.6 Circuit Board with an Aluminum Heat Sink Core, 46
`Sample Problem-Temperature Rise along a PCB Heat
`3.7
`Sink Plate, 46
`·3.s How to A void Warping on PCBs with Metal Heat
`Sinks , 47
`3.9 Chassis with Nonuniform Wall Sections, 48
`3.10 Sample Problem-Heat Flow along Nonuniform
`Bulkhead, 50
`3.11 Two Dimensional Analog Resistor Networks, 53
`3.12 Sample Problem-Two Dimensional Conduction on a
`Power Supply Heat Sink, 54
`3.13 Heat Conduction across Interfaces in Air, 60
`3.14 Sample Problem-Temperature Rise across a Bolted
`Interface, 64
`3.15 Sample Problem-Temperature Rise across a Small Air·
`Gap, 65
`3.16 Heat Conduction across lnterfaces at High Altitudes, 66
`3.17 Outgassing at High Altitudes, 69
`3.18 Circuit Board Edge Guides, 70
`
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`

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`Contents
`
`xi
`
`3.19 Sample Problem-Temperature Rise across a PCB Edge
`Guide , 72
`3.20 Heat Conduction through Sheet Metal Covers, 72
`3.21 Radial Heat Flow , 73
`3.22 · Sample Problem-Temperature Rise through a Cylindrical
`Shell, 74
`-
`
`4 Mounting and Cooling Techniques for Electronic Components
`
`77
`
`4.1 Various Types of Components, 77
`4.2 Mounting Components on PCBs, 78
`4.3
`Sample Problem-Hot Spot Temperature of an Integrated
`Circuit on a Plug-in PCB, 81
`4.4 How to Mount High Power Components, 87
`4.5 • Sample Problem-Mounting High Power Transistors on a
`Heat Sink Plate, 89
`Electrically Isolating High Power Components, 91
`Sample Problem-Mounting a Transistor on a Heat Sink
`Bracket, 92
`Potted Modules, 94
`Sample Problem-Temperature Rise in a Potted
`Module, 95
`4.10 Component Lead Wire Strain Relief, 98
`
`4.8
`4.9
`
`4.6
`4. 7
`
`S Practical Guides for Natural Convection and Radiation Cooling
`
`106
`
`5.1 How Natural Convection Is Developed, 106
`5.2 Natural Convection for Flat Vertical Plates , 109
`5.3 Natural Convection for Flat Horizontal Plates, 109
`5.4 Heat Transferred by Natural Convection, 110
`Sample Problem- Vertical Plate Natural Convection, Ill
`5.5
`5.6 Turbulent Flow with Natural Convection, 113
`5.7
`Sample Problem-Heat Lost from an Electronic Box, 114
`5.8
`Finned Surfaces for Natural Convection Cooling, 117
`5.9 Sample Problem-Cooling Fins on an Electronic Box, 119
`5.10 Natural Convection Analog Resistor Networks, 121
`5.11 Natural Convection Cooling for PCBs, 123
`
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`xii
`
`Contents
`
`5.12
`
`S.13
`5.14
`5.15
`5.16
`5.17
`5.18
`
`5.19
`
`5.20
`5.21
`5.22
`
`5.23
`5.24
`
`5.25
`5.26
`
`5.27
`
`5.28
`
`5.29
`
`Natural Convection Coefficient for Enclosed Air
`Space , 125
`Sample Problem-PCB Adjacent to a Chassis Wall, 126
`High Altitude Effects on Natural Convection, 129
`Sample Problem-PCB Cooling at High Altitudes, 130
`Radiation Cooling of Electronics, 132
`Radiation View Factor, 136
`Sample Problem-Radiation Heat Transfer from a
`Hybrid , 142
`Sample Problem- Junction Temperature of a Dual FET
`Switch, 145
`Radiation Heat Transfer in Space, 147
`Effects of ale on Temperatures in Space, 148
`Sample Problem-Temperatures of an Electronic Box in
`Space, 150
`Simplified Radiation Heat Transfer Equation, 151
`Sample Problem-Radiation Heat Loss from an Electronic
`Box, 152
`Combining Convection and Radiation Heat Transfer, 154
`Sample Problem-Electronic Box in an Airplane Cockpit
`Area, 155
`Equivalent Ambient Temperature for Reliability
`Predictions, 157
`Sample Problem-Equivalent Ambient Temperature of an
`RC07 Resistor, 159
`Increase in Effective Emittance on Extended
`Surfaces, 160
`
`6 Forced Air Cooling for Electronics
`
`164
`
`Forced Cooling Methods, 164
`6.1
`6.2 Cooling Air Flow Direction for Fans, 165
`Static Pressure and Velocity Pressure, 166
`6.3
`Losses Expressed in Terms of Velocity Heads, 170
`6.4
`Sample Problem-Air Flow Loss at a Fan Entrance, 171
`6.S
`Establishing the Flow Impedance Curve for an Electronic
`6.6
`Box, 172
`
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`SEC Exhibit 1020.011
`IPR 2023-00199
`
`

`

`Contents
`
`xiii
`
`Sample Problem-Fan Cooled Electronic Box, 173
`6.7
`6.8 Hollow Core PCBs, 189
`6.9 Cooling Air Fans for Electronic Equipment, 192
`6.10 Air Filters, 194
`6.11 Cutoff Switches, 195
`6.12 Static Pressure Loss Tables and Charts, 195
`6.13 High Altitude Conditions, 196
`6.14 Sample Problem-Fan Cooled Box at 30,000 Feet, 199
`6.15 Other Convection Coefficients, 203
`6.16 Sample Problem-Cooling A T0-5 Transistor, 205
`6.17 Conditioned Cooling Air from an External Source, 207
`6.18 Sample Problem-Generating a Cooling Air Flow
`Curve, 208
`6.19 Static Pressure Losses for Various Altitude
`Conditions, 209
`6.20 Sample Problem-Static Pressure Drop at 65,000
`Feet, 212
`6.21 Total Pressure Drop for Various Altitude Conditions, 218
`6.22 Sample Problem-Total Pressure Loss through an
`Electronic Box, 219
`6.23 Finned Cold Plates and Heat Exchangers, 219
`6.24 Pressure Losses in Multiple Fin Heat Exchangers, 221
`6.25 Fin Efficiency Factor, 223
`6.26 Sample Problem-Hollow Core PCB with a Finned Heat
`Exchanger, 225
`6.27 Undesirable Air Flow Reversals, 239
`
`7 Cooling Minicomputers, Microcomputers, and Microprocessors
`
`242
`
`Introduction, 242
`7.1
`7.2 Minicomputer Systems, 242
`7 .3
`Sample Problem-PCB Mounted above a Minicomputer
`Floppy Disk, 244
`Sample Problem-Fan Cooled Minicomputer, 249
`7.4
`7.5 Microcomputer Systems, 252
`Sample Problem-Cooling a Microcomputer, 253
`7 .6
`
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`

`

`xiv
`
`Contents
`
`7.7 Microprocessor Development, 255
`7.8 Mounting Microprocessors to Resist Vibration
`Fatigue, 256
`7 .9 Microprocessors in Severe Thermal Environments, 257
`7.10 Sample Problem- Cooling a Microprocessor Mounted
`on a PCB , 257
`
`8 Effective Cooling for Large Racks and Cabinets
`
`260
`
`8.6
`
`Induced Draft Cooling for Large Consoles, 260
`8.1
`8.2 Air Flow Losses for Large Cabinets, 261
`8.3
`Flotation Pressure and Pressure Loss, 262
`Sample Problem-Induced Draft Cooling for a Large
`8.4
`Cabinet, 262
`8.5 Natural Cooling for Large Cabinets with Many Flow
`Restrictions, 267
`Sample Problem-Temperature Rise of Cooling Air in a
`Cabinet with an Induced Draft, 268
`8. 7 Warning Note for Induced Draft Systems, 272
`Tall Cabinets with Stacked Card Buckets, 273
`8.8
`8.9
`Sample Problem-Induced Draft' Cooling of a Console with
`Seven Stacked Card Buckets, 274
`8.10 Electronics Packaged within Sealed Enclosures, 278
`8.11 Small Enclosed Modules within Large Consoles, 281
`8.12 Sample Problem-Small PCB Sealed within an RFI
`Enclosure, 283
`8.13 Test Data for Small Enclosed Modules, 290
`8.14 Pressure Losses in Series and Parallel Air Flow
`Ducts, 293
`8.15 Sample Problem-Series and Parallel Air Flow
`Network, 294
`
`9 Transient Cooling for Electronic Systems
`
`300
`
`9.1
`9.2
`
`9.3
`
`Simple Insulated Sys tems, 300
`Sample Problem-Transient Temperature Rise of a
`Transformer, 301
`Thermal Capacitance, 302
`
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`
`

`

`Contents
`
`xv
`
`Time Constant , 303
`9.4
`9.5 Heating Cycle Transient Temperature Rise, 304
`Sample Problem-Transistor on a Heat Sink , 304
`9.6
`Temperature Rise for Different Time Constants, 308
`9.7
`-Sample Problem-Time for Transistor to Reach 95%
`9.8
`of its Stabilized Temperature , 310
`9.9 Cooling Cycle Transient Temperature Change, 310
`9.10 Sample Problem-Transistor and Heat Sink Cooling, 310
`9.11 Transient Analysis for Temperature Cycling Tests , 312
`9.12 Sample Problem-Electronic Chassis in a Temperature
`Cycling Test, 317
`9.13 Sample Problem- Methods for Decreasing Hot Spot
`Temperatures, 322
`9.14 Sample Problem-Transient Analysis of a n Amplifier
`on a PCB , 324
`
`I 0 Special Applications for Tough Cooling Jobs
`
`331
`
`10.1 New Technology-Approach with Caution, 331
`10.2 Heat Pipes, 331
`10.3 Degraded Performance in Heat Pipes, 333
`10.4 Typical Heat Pipe Performance, 334
`10.5 Heat Pipe Applications, 336
`10.6 Direct and Indirect Liquid Cooling, 340
`Forced Liquid Cooling Systems, 341
`10. 7
`10.8
`Pumps for Liquid Cooled Systems, 342
`Storage and Expansion Tank, 343
`10.9
`10.10 Liquid Coolants, 343
`10.11 Simple Liquid Cooling System, 344
`10.12 Mounting Components for Indirect Liquid Cooling, 344
`10.13 Basic Forced Liquid Flow Relations, 347
`10.14 Sample Problem-Transistors on a Water Cooled Cold
`Plate, 351
`
`References
`
`Index
`
`361
`
`365
`
`SEC et al. v. MRI
`SEC Exhibit 1020.014
`IPR 2023-00199
`
`

`

`1
`Evaluating the
`Cooling Require:ments
`
`1.1 HEAT SOURCES
`
`Electronic equipment relies on the flow and control of electrical current to
`perform a fantastic variety of functions, in virtually every major industry
`throughout the world. Whenever electrical current flows through a resistive
`element, heat is generated in that element. An increase in the current or
`resistance produces an increase in the amount of heat that is generated in
`the element. The heat continues to be generated as long as the current
`continues to flow. As the heat builds up, the temperature of the resistive
`element starts to rise, unless the heat can find a flow path that carries it
`away from the element. If the heat flow path is poor, the temperature may
`continue to rise until the resistive element is destroyed and the current
`stops flowing. If the heat flow path is good, the temperature may rise until
`it stabilizes at a point where the heat flowing away from the element is
`equal to the heat generated by the electrical current flowing in the element.
`Heat is generated by the flow of electiical current in electronic component
`parts such as resistors, diodes, integrated circuits (!Cs), hybrids, transistors,
`microprocessors, relays, dual inline packages (DIPs), large scale integrated
`circuits (LSis), and very large scale integrated circuits (VSis).
`Figure l. l shows an electronic chassis that has heat exchangers (cold
`plates) on the top and bottom surfaces which rely on conditioned cooling
`air for controlling temperatures on plug-in circuit boards.
`Electronic components and electronic systems are rapidly shrinking in
`size while their complexity and capability continue to grow at an amazing
`rate. In addition, the power has been increasing while the volume has been
`decreasing. This has produced a dramatic increase in the power density,
`resulting in rapidly rising temperatures and a large increase in the number
`of failures.
`The temperatures must be controlled on every component to ensure a
`reliable electronic system. If the operating temperatures become too high,
`electronic malfunctions may occur. Malfunctions may produce a simple out
`
`1
`
`SEC et al. v. MRI
`SEC Exhibit 1020.015
`IPR 2023-00199
`
`

`

`2
`
`Evaluating the Cooling Requirements
`
`Figure 1.1 The author discussing design details with two associates. (Courtesy Kearfott
`Division, The Singer Co.)
`
`of tolerance condition for a minor temperature increase, or a catastrophic
`failure for a major temperature increase.
`Heat always flows from the hot area to the cool area. Since the electronic
`components are usually the source of the heat, the electronic components
`will usually be the hottest spots in an electronic system. (During transient
`conditions and temperature cycling tests, the electronic components may
`not necessarily be the hottest points in the system.) The basic heat transfer
`problem in electronic systems is, therefore, the removal of internally gen(cid:173)
`erated heat by providing a good heat flow path from the heat sources to an
`ultimate sink, which is often the surrounding ambient air.
`
`1.2 HEAT TRANSMISSION
`
`There are three basic methods by which heat can be transferred: conduction,
`convection, and radiation. The laws relating to these methods of heat trans(cid:173)
`mission are of primary importance in the design and operation of electronic
`equipment.
`
`SEC et al. v. MRI
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`IPR 2023-00199
`
`

`

`1.2 Heat Transmission
`
`3
`
`Conduction is the transfer of kinetic energy from one molecule to another.
`In an opaque solid it is the only method of heat transfer, where heat flows
`from the hot areas to the cooler areas of the solid. Heat conduction also
`occurs in gases and liquids , but the amount of heat transferred is usually
`smaller for the same geometry.
`Convection is the transfer of heat by the mixing action of fluids. When
`the mixing is due entirely to temperature differences within the fluid, re(cid:173)
`sulting in different densities , the action is known as natural convection.
`When the mixing is produced by mechanical means, such as fans and
`pumps, the action is known as forced convection.
`Thermal radiation is the transfer of energy by electromagnetic waves that
`are' produced by bodies because of their temperature. A hot body radiates
`energy in all directions. When this energy strikes another body, the part
`that is absorbed is transformed into heat.
`Most electronic systems make use of all three basic methods of heat
`transfer to some extent, even though one method may dominate the design.
`For example, an electronic box cooled by forced convection might utilize
`a fan to draw air over electronic components mounted on printed circuit
`boards (PCBs), as shown in Figure 1.2.
`The greatest amount of heat is picked up by forced convection as the
`cool!ng air passes over the individual electronic components that are
`mounted on the PCB. However, some of the heat from the electronic
`components is conducted directly to the PCB under the component body,
`and some of the heat is conducted to the back side of the PCB, through the
`components electrical lead wires, as shown in Figure 1.3. Since the cooling
`
`Cooling air
`exhaust
`
`/
`
`Electronic
`chassis
`housing
`
`Front cover and access panel
`
`Figure 1.2 Electronic box cooled with an exhaust fan.
`
`SEC et al. v. MRI
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`IPR 2023-00199
`
`

`

`4
`
`Evaluating the Cooling Requirements
`
`Electronic
`component
`
`Electrical
`lead wire
`
`Figure 1.3 Heat conduction path from component, with heat flow through lead wires, to back
`side of PCB.
`
`Copper run
`
`air passes over both suifaces of the PCB , the conduction of heat to the back
`side of the PCB provides additional surface area for improved cooling.
`In addition, some of the heat is radiated from the hot components to the
`surrounding chassis walls and to the cooler spots on adjacent PCBs. This
`helps to reduce the component hot spot temperatures.
`
`1.3 STEADY STATE HEAT TRANSFER
`
`If an electronic system is turned on and left running for a very long period
`of time, and if the power requirements remain constant during that period,
`the temperatures of the electronic components and their mounting struc(cid:173)
`tures, such as PCBs, will usually become stable. Minor fl uctuations in the
`line voltages, small changes in the physical properties of the individual
`components, and slight variations in the outside ambient conditions may
`have some small effects on the temperatures within the electronic system.
`For all practical purposes, however, the heat gained (or the power dissi(cid:173)
`pated) by the electronic components is equal to the heat lost, so that the
`system has reached thermal equilibrium. The internal heat has found one or
`more thermal paths from the heat source to the ultimate heat sink. Usually,
`all three methods of heat transfer-conduction, convection, and radiation(cid:173)
`are involved. When the thermal eq uilibrium condition has been reached, the
`rate of heat being transferred by each of the three methods remains constant.
`The temperature gradients are now fixed with the heat flowing from the
`hotter parts of the system to the cooler parts of the system, until the heat
`finally reaches the ultimate sink. These characteristics indicate that the
`system has reached the steady state heat transfer condition. Steady state
`conditions may develop in a matter of mi nutes for small components such
`as transistors and diodes. However, for large electronic consoles, it may
`take a full day of operation before steady state heat transfer conditions
`are reached.
`
`SEC et al. v. MRI
`SEC Exhibit 1020.018
`IPR 2023-00199
`
`

`

`J .4 Transient Heat Transfer
`
`5
`
`1.4 TRANSIENT HEAT TRANSFER
`
`When the rate of heat flow changes within an electronic system, it will
`normally produce a temperature change somewhere in that system. Also,
`when there is a temperature change within an electronic system, there will
`normally be a change in the heat flow rate somewhere in the system.
`Changes of these types are defined as transient heat transfer conditions,
`because the thermal equilibrium of the system is unbalanced. Transient heat
`transfer conditions develop, for example, when the power is first turned on
`in an electronic system. As the current flows through the electronic com(cid:173)
`ponents, heat is generated and the temperatures within the components
`begin to rise, resulting in a transient, or changing condition.
`Transient conditions will also occur in an electronic system when it is
`subjected to temperature cycling tests. Consider a s ystem sitting in an
`environmental chamber where the ambient temperature is slowly being
`cycled between - 54 °C ( -65°F) and + 71 °C ( + I 60°F). In this case, the
`outside temperature often increases more rapidly than do the temperatures
`within the electronic box. Heat then flows from the outside of the box
`toward the interi01:, because heat always flows from the hot body to the
`cold body.
`A satellite in orbit around the earth experiences transient heat transfer
`due to the constantly changing angle with respect to the sun and the earth.
`The intensity of the solar radiation may be constant, but the heat absorbed
`will vary along the surface because the angle the sun makes with respect to
`the surface is changing.
`Sometimes it is necessary to use ~n auxiliary cooling device or technique
`for a short period , until the regular cooling system is available to take over
`the job. Consider the case where a missile is carried under the wing of ah
`airplane. An auxiliary cooling cart is available to supply cooling to the
`electronic system within the missile while the airplane engine is being started
`and checked. The missile electronic system is normally c9oled by the ram
`air during the captive flight phase and during the free flight phase after the
`missile is released from the airplane. No cooling air is provided for the
`missile electronics during the taxi and takeoff period, because of the extra
`weight and cost. Instead , the electronics must rely upon the thermal capac(cid:173)
`ity or thermal inertia of the system to absorb the heat without developing
`excessive temperatures during this period. When a number of airplanes are
`lined up, waiting to take off, delays of 30 min may occur. This may cause
`the electronics to overheat. If the weight of the electronic system is in(cid:173)
`creased, it will increase the thermal inertia and permit cooler operation for
`longer periods of time. For higher power systems , howeyer, a very large
`mass may be required to keep the electronics cool for 30 min, so that a
`more sophisticated technique may be required.
`Sometimes it is desirable to use the change of state from a solid to a
`liquid , or from a liquid to a gas, to absorb heat. A large amount of heat can
`
`SEC et al. v. MRI
`SEC Exhibit 1020.019
`IPR 2023-00199
`
`

`

`6
`
`Evaluating the Cooling Requirements
`
`be absorbed under these conditions. It is often possible to use hollow wall
`construction for the electronic chassis, which could be filled with wax that
`melts at a predetermined temperature. The change of state from a solid to
`a liquid may absorb enough heat to permit the electronics to survive a 30
`min period with no cooling air. Once the airplane is flying, the ram air cools
`the wax , which returns to the solid state. If the missile is not fired, the
`melting wax permits the delaying cycle to be repeated over and over again.
`
`1.5 ELECTRONIC EQUIPMENT FOR AIRPLANES, MISSILES,
`SATELLITES, AND SPACECRAFT
`
`Electronic boxes used in airplanes, missiles, satellites, and spacecraft often
`have odd shapes that permit them to make maximum use of the volume
`available in odd-shaped structures. An odd-shaped box may require more
`time to design, because it is usually more difficult to provide the circuit
`cards with an efficient heat flow path, regardless of the cooling method
`used.
`The trend in military and commercial airplanes and helicopters is toward
`a series of several standard sizes for plug-in types of electronic boxes that
`fit in racks. These are called ATR (air transport rack) boxes. They are of
`various widths, which are known as one quarter, one half, three quarters,
`and full width, each with a short and a long length. The electrical interface
`connectors are oft~n at the rear of the box, with quick release fasteners at
`the front [I].*
`Many of the electronic boxes are cooled by forced convection with bleed
`air from the jet engine compressor section. Since this air is at a high
`temperature and pressure, it is throttled (passed through the cooling tur(cid:173)
`bine), cooled, and dried with a water separator before it is used. This air
`often enters the electronic box at the rear, adjacent to the electrical con(cid:173)
`nectors. Rubber gaskets are used around the inlet ports at the air interface
`to provide an effective plug-in connection, which reduces the leakage at the
`cooling air interface.
`Sometimes the conditioned cooling air is not completely dry because of
`excessive moisture in the air from humidity or a rainstorm. Small drops of
`water will often be carried into the electronics section together with the
`cooling air. If this water accumulates on PCBs or their plug-in connectors,
`electrical problems may develop. Therefore, many specifications do not
`permit external cooling air to come into direct contact with electronic
`components or circuits.
`Air cooled heat exchangers, commonly called air cooled cold plates ,
`which are being used more and more in airplanes, provide conditioned air
`for cooling the electronics. These heat exchangers are usually dip brazed
`
`* Numbers in brackets refer to references at the end of the book.
`
`SEC et al. v. MRI
`SEC Exhibit 1020.020
`IPR 2023-00199
`
`

`

`1.5 Electronic Equipment for Airplanes, Missiles, Satellites, and Spacecraft
`
`7
`
`when many thin [0.006 to 0.008 in (0.15 to 0.20 mm)] aluminum plate fins
`are used. Pin fin aluminum castings are becoming very popular because of
`their low cost. There is usually a slight weight increase with pin fins because
`the walls and fins have to be thicker to permit the molten alumi num to flow
`[2, 3].
`Electronic systems for missiles generall y have two cooling conditions to
`consider, captive and free flight. If the missile flight duration is relatively
`short, the electronics can be precooled during the captive phase so that the
`system can function with no additional cooling during the flight phase. The
`electronic support structure would act as the heat sink, soaking up the heat
`as it is generated, to permit the electronic system to fu nction during the
`free flight phase.
`Some missiles, such as the Cruise missiles, have a very long free flight
`phase, so that the cooling system must be capable of cooling the electronics
`for several hours. If ram air is used at speeds near Mach 1, the ram
`temperature rise of the cooling air may exceed 100°F (55°C). Since Cruise
`missiles fly at low altitudes, where the surrounding ambient air temperatures
`can be as high as I 00°F, the cooling air temperatures could reach values of
`200°F (93°C) even before the cooling process begins. Since the maximum
`desirable component mounting surface temperature is about 2 l 2°F ( 100°C),
`the outside ambient air cannot be used directly for cooling.
`Cruise missiles must carry a large supply of fuel for their long flights. The
`fuel is often pumped through liquid cooled cold plates to provide cooling
`for the electronics. Toward the end of the flight mission, when the fuel
`supply runs low, the temperatures may increase. At this point it may be
`necessary to use the thermal inertia in the electronics structure to keep the
`system cool enough to finish its flight.
`Electronic systems for satellites and spacecraft generally rely upon radia(cid:173)
`tion to deep space for all their cooling. Deep space has a temperature of
`absolute zero, -460°F or 0°Rankine (-273°C or 0°Kelvin). Temperatures
`this low can provide excellent cooling if the proper surface finishes are used
`[4].
`Special surface finishes and treatments may be required for satellites and
`spacecraft to prevent them from absorbing large quantities of heat from the
`sun. This heat may be direct solar radiation plus solar radiation reflected
`from the various planets and their moons (reflected radiation is called
`albedo) [4, 5).
`Liquid cooled cold plates are often used to support electronic systems.
`Pumps then circulate the cooling fluid from the cold plates, where the heat
`is picked up, to the space radiators, where the h~at is dumped to space.
`Conduction heat transfer is used extensively for cooling electronic equip(cid:173)
`ment in space environments. In the hard vacuum conditions of outer space,
`flat and smooth surfaces must be utilized with high contact pressures, to
`minimize the temperature rise across each interface. Although air is not
`normally considered to be a good heat conductor, its presence will sharply
`
`I
`
`SEC et al. v. MRI
`SEC Exhibit 1020.021
`IPR 2023-00199
`
`

`

`8
`
`Evaluating the Cooling Requirements
`
`reduce the contact resistance at most interfaces. Thermal greases are some(cid:173)
`times used to reduce the interface resistance in hard vacuum environments,
`by filling the small voids that would otherwise develop when the air is
`evacuated.
`Air cooling can stiJl be provided in a hard vacuum environment if a sealed
`and pressurized box is used. An internal fan can be used to circulate internal
`cooling air through a liquid cooled cold plate, which would carry away the
`heat. The heat from the fan must be added to the total heat load of the
`system. Also, a sealed box will have a large pressure differential across the
`surfa