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Cooling Methods for Electronic Equipment Guide Manual

Electrical, Instrumentation, Electronic Design and Engineering
Heat Transfer Engineering and Design

Guide Manual of Cooling Methods for Electronic Equipment
Bureau of Ships Navy Department
224 Pages

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Open: Guide Manual of Cooling Methods for Electronic Equipment

Introduction

The military requirements for electronic equipment have been steadily increasing. This trend in demand for equipment having improved performance, decreased size, greater reliability and complexity of function is continuing. For example, a typical destroyer in 1937 incorporated a total of approximately 60 active vacuum tubes maintained by a single technician. By 1944 a destroyer utilized 850 tubes. In 1952 this total had increased to 3200 tubes, serviced by l1 technicians. The trend to increased complexity will not change in the foreseeable future. As a result, electronic design problems are multiplying in severity. Production mechanization and electronic cooling programs are among the current endeavors to obtain satisfactory economy and reliability. It is necessary that these and associated problems be resolved in order to achieve acceptable electronic devices.

Reliability is of paramount importance. Reliability has been defined as the ratio of the time the equipment is in usable operating condition to the total time the equipment is required for use. In general, the reliability of current electronic equipment is poor. In fact, it has been concluded that it would be economical to pay more than twice the present cost for military electronic equipment if reliability could be improved to 50 per cent.

Miniaturization has led to ever increasing heat concentrations with the necessity for adequate heat transfer within equipment. Effective heat removal is of prime importance in obtaining satisfactory life, reliability and electronic performance. If the temperatures of electronic parts exceed certain values, malfunctioning and failures follow. Thus, the science of heat transfer must be employed in electronic design.

TOC

I. PROMULCATING LETTER
II. INTRODUCTION 2
III. BASIC DESIGN CONCEPTS
A. FUNDAMENTAL PRINCIPLES OF HEAT REMOVAL 5
B. APPROACHES TO THE THERMAL DESIGN OF ELECTRONIC EQUIPMINT 7
C. METHODS OF THERMALLY RATING Electronic EQUIPMENT AND PARTS 7
IV. INTRODUCTION TO HEAT TRANSFER
A. GENERAL 9
B. CONDUCTION 9
C. CONVECTION 10
D. EVAPORATION AND CONDENSATION 1l
E. RADIATION l.1
F. COMBINED MODES OF HEAT TRANSFER 23
G. RESISTANCE CONCEPT FOR HEAT FLOW THROUGH A WALL 13
H. THE ULTIMATE SINK 15
J. RELATIVE MAGNITUDES OF HEAT TRANSFER PROCESSES 15
V. NATURAL METHCDS OF HEAT REMOVAL
A. GENERAL 17
B. THEORY 17
1. Heat Transfer by Metallic Conduction 17
2. Free Convection in Gases 28
3. Radiation 34
4. Radiation and Gaseous Conduction 39
C. NATURAL METhaJ6 of COOLING electronic parts
.. General 41
2. Vacuum Tubes 41
a. Hot Spot Locations 41
b. Shields for Removing Heat from Tube Envelopes 41
(1) General 41
(2) Miniature Tube Shields 43
(3) Subminiature Tube Shields 47
c. Unshielded Tubes 61
3. Resistors 61
h. Iron Core Inductors 63
D. NATURAL METHODS OF COOLING ASSEMBLIES 63
1. Metallic Conduction Cooling 63
2. Plastic Embedment 69
E. THE PLACEMENT OF PARTS WITHIN SUBASSEMBLIES 70
F. NATURAL METHODS OF COOLING ELECTRONIC EQUIPMENT CASES 70
VI. FORCED AIR COOLING
A. GENERAL THEORY 74
B. FORCED AIR COOLING DESIGN 81
C. PRESSURE DROP AND COOLING POWER REQUI&EMENTS 84
D. FANS AND BLOWERS 86
E. COLD PLATE HEAT EXCHANGERS 89
VII. LIQUID COOLING
A. CENERAL 93
B. THEORY 94
C. DIRCT LIQUID IMMERSION 101
1. General 101
2. Design Considerations 103
D. DIRECT LIQUID IMMERSION WITH AGITATION 108
E. DIRECT FORCED LIQUID COOLING 108
1. General 108
2. Typical System 108
3. Direct Spray Cooling ill
4. Detailed Design Considerations 113
F. INDIRECT FORCED LIQUID COOLING SYSTEMS 116
1. General 116
2. Liquid Cooled Cold Plates 117
3. Improvement of Existing Equipment by Liquid Cooling 117
4. New Equipment 117
G. COMPOSITE LIQUID COOLING SYSTEMS 120
H. CHARACTERISTICS OF COOLANTS 120
VIII. VAPORIZATION COOLING
A. GENERAL 121
B. NOTES ON VAPORIZATION COOLING AND BOILING 122
C. DIRECT VAPORIZATION COOLING SYSTEMS 123
1. Liquid Potting 123
2. Expendable Direct Vaporization Cooling 125
3. Direct Spray Systems 128
D. INDIRECT VAPORIZATION COOLING 128
1. General 128
2. Examples of Indirect Vaporization Cooling Systems 130
E. DESIGN NOTES 133
F. NOTES ON PROPERTIES OF VAPORIZATION COOLANTS 134
1. Freons 134
2. Perfluorocarbons 134
3. Fluorochemicals 136
4. Other Coolants 137
IX. THE SELECTION OF OPTIMUM COOLING METHODS
A. GENERAL 138
B. HEAT TRANSFER WITHIN A UNIT 138
C. HEAT TRANSFER TO THE ULTIMATE SINK 142
D. DESIGN EXAMPLE OF THE SELECTION CF OPTIMUM COOLING METHODS 143
X. THE TEMFERATURE LIMITS AND RATINGS OF ELECTRONIC EQUIPMENT
AND PARTS
A. GENERAL 145
B. THE THERMAL LIMITATIONS OF VACUUM TUHES 145
1. General 145
2. Heat Transfer Within Vacuum Tubes 146
3. Limiting Factors 147
4. Vacuum Tube Ratings 149
C. THE THERMAL LIMITATIONS OF SENICONDUCTOR DEVICES 151
D. THE THERMAL LIMITATIONS OF MAGNETIC CORE DEVICES 156
E. THE THERMAL LIMITATIONS OF RESISTORS 159
1. General 159
2. Fixed Resistors 159
3. Variable Resistors 160
F. THE THERMAL LIMITATIONS OF CAPACITORS 161
1. General 161
2. Fixed Capacitors 161
3. Variable Capacitors 162
XI. Recommendations FOR DETERMINING AND IMPROVING THE THERMAL
PERFORMANCE OF ELECTRONIC EQUIPMENT
A. THE THERMAL ANALYSIS OF ELECTRONIC EQUIPMENT 163
B. IMPROVING THE THERMAL PERFORWANCE OF EXISTING ELECTRONIC 163
EQUIPMENT
C. THE DESIGN OF EFFICIENT ELECTRONIC CIRCUITS 165
XII. APPENDIX
A. SYMBOLS AND NOMENCLATURE 169
B. LIST OF ASSOCIATED REPORTS 172
C. TABLES AND CHARS 173
D. BIBLIOGRAPHY 195