Showing papers by "Avram Bar-Cohen published in 1986"

High heat from a small package

Abstract: Circuitry contained in a single 100-chip IBM Thermal Conduction Module (TCM) would occupy a space as large as the Empire State Building if it were built with the vacuum-tube technology of the 1950's. The amount of power needed to energize the vacuum tubes would be enormous compared to the 580 W dissipated in a TCM in today's IBM 3090 computer. One might suppose, therefore, that thermal management in computers would be relatively simpler than in the past. But with each new system that is introduced, engineers are faced with greater challenges in the cooling of microelectronic packages. A case in point is the recently announced Fujitsu system that will have 336 chips mounted on both sides of a printed circuit board of 54 x 49 cm. Each chip dissipates approximately 10 W, and the whole board is believed to dissipate more than 3 kW. Computers are becoming increasingly harder to cool, in part because microelectronic devices are becoming functionally denser. The printed features on Very Large Scale Integration (VLSI) devices are shrinking to less than a micron in size, and a minimum size of 1000 Angstroms is not far in the future. With this miniaturization, the scale of circuit integrationmore » has increased from one transistor per circuit in 1958 and fewer than 100 components (transistors, diodes, resistors, or capacitors) per chip in the early 1960's, to approximately 100,000 in 1980. In 1982, chip-gate density jumped to 450,000 components in the Hewlett-Packard 32-bit CPU chip and to 460,000 in Texas Instruments' static RAM chip. This five-orders-of-magnitude increase in circuit integration in the past 25 years is also the result of successive revolutions in device technology, from transitor/transistor logic (TTL), JTOS emitter-coupled logic (ECL), to negative metal-oxide semiconductors (NMOS), and most recently, to complementary metal-oxide semiconductors (CMOS).« less

Wall superheat excursions in the boiling incipience of dielectric fluids.

Abstract: Many of the candidate fluids for immersion cooling of microelectronic components possess both low surface tension and high gas solubility. As a consequence, ebullient heat transfer with such fluids is accompanied by nucleation anomalies and a frequently observed wall temperature overshoot. The difficulty in preventing this thermal excursion and in predicting its magnitude constrains the development of immersion cooling systems. This paper begins with a brief review of the mechanisms that may be responsible for delayed nucleation and examines the limited literature on incipience superheat excursions.

Future Opportunities and Challenges in Heat Transfer— An Industrial Perspective

Abstract: The competition-induced transformation of the industrial environment, currently under way, is placing new demands on the engineering profession. The consequent opportunities and challenges facing the thermal community in the United States during the next decade are explored. It is suggested that the thermal community can take the lead in reversing the growing alienation of academic research from industrial needs by redefining its research agenda, by altering the format of technical meetings, by broadening and deepening training in heat transfer, and by supporting the establishment of ‘product family’ institutes at leading U.S. universities