online_ch_cooling_elect_equipment

online_ch_cooling_elect_equipment - 15-R3606 8:39 AM Page...

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COOLING OF ELECTRONIC EQUIPMENT E lectronic equipment has made its way into practically every aspect of modern life, from toys and appliances to high-power computers. The re- liability of the electronics of a system is a major factor in the overall re- liability of the system. Electronic components depend on the passage of electric current to perform their duties, and they become potential sites for ex- cessive heating, since the current flow through a resistance is accompanied by heat generation. Continued miniaturization of electronic systems has resulted in a dramatic increase in the amount of heat generated per unit volume, com- parable in magnitude to those encountered at nuclear reactors and the surface of the sun. Unless properly designed and controlled, high rates of heat gener- ation result in high operating temperatures for electronic equipment, which jeopardizes its safety and reliability. The failure rate of electronic equipment increases exponentially with temperature. Also, the high thermal stresses in the solder joints of electronic components mounted on circuit boards resulting from temperature variations are major causes of failure. Therefore, thermal control has become increas- ingly important in the design and operation of electronic equipment. In this chapter, we discuss several cooling techniques commonly used in electronic equipment such as conduction cooling, natural convection and radiation cooling, forced-air cooling, liquid cooling, and immersion cooling. This chapter is intended to familiarize the reader with these techniques and put them into perspective. The reader interested in an in-depth coverage of any of these topics can consult numerous other sources available, such as those listed in the references. 1 ONLINE CHAPTER 2 CONTENTS 1 Introduction and History 2 2 Manufacturing of Electronic Equipment 3 3 Cooling Load of Electronic Equipment 9 4 Thermal Environment 10 5 Electronics Cooling in Different Applications 11 6 Conduction Cooling 13 7 Air Cooling: Natural Convection and Radiation 28 8 Air Cooling: Forced Convection 36 9 Liquid Cooling 49 10 Immersion Cooling 52 Summary 57 References and Suggested Reading 58 Problems 58
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1 INTRODUCTION AND HISTORY The field of electronics deals with the construction and utilization of devices that involve current flow through a vacuum, a gas, or a semiconductor. This exciting field of science and engineering dates back to 1883, when Thomas Edison invented the vacuum diode. The vacuum tube served as the foun- dation of the electronics industry until the 1950s, and played a central role in the development of radio, TV, radar, and the digital computer. Of the several computers developed in this era, the largest and best known is the ENIAC (Electronic Numerical Integrator and Computer), which was built at the Uni- versity of Pennsylvania in 1946. It had over 18,000 vacuum tubes and occu- pied a room 7 m 14 m in size. It consumed a large amount of power, and its reliability was poor because of the high failure rate of the vacuum tubes.
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