Thermochromic liquid crystals have been exploited in novelties and in high-technology applications alike since the earliest years of liquid crystal technology. They have also played a central role in the elucidation of the structures of liquid crystal phases and their inter-relationship, the optics of mesophases, the nature of phase transitions and their static and dynamic continuum theory. Despite this long history, many of the materials and applications have been continually exploited for several decades, indicating an early achievement of maturity in this area of liquid crystal technology. This article briefly reviews the main materials, applications and devices, and attempts to place them in the context of related developments in liquid crystal science.

Thermochromic liquid crystals

In this study, forced cooling of heat sinks mounted on CPUs was investigated. Heat sink effectiveness, effect of turbulence models, effect of radiation heat transfer and different heat sink geometries were numerically analyzed by commercially available computational fluid dynamics softwares Icepak and Fluent. The numerical results were compared with the experimental data and they were in good agreement. Conjugate heat transfer is simulated for all the electronic cards and packages by solving Navier-Stokes equations. Grid independent, well converged and well posed models were run and the results were compared. The best heat sink geometry is selected and it is modified in order to have lower maximum temperature distribution in the heat sink. This paper was also originally published as part of the Proceedings of the ASME 2005 Pacific Rim Technical Conference and Exhibition on Integration and Packaging of MEMS, NEMS, and Electronic Systems.Copyright © 2005 by ASME

CFD Analyses of Heat Sinks for CPU Cooling With Fluent

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Thermal analysis of cpu with variable baseplate heat-sink using cfd

Electronics cooling assemblies are provided which include an air-cooled heat sink, an auxiliary air-moving device, and an airflow-blocking mechanism. The heat sink couples to one or more heat-generating electronic components, and dissipates heat from the electronic component(s) to a cooling airflow passing across the heat sink. The auxiliary air-moving device provides, when active, an increased flow rate of the cooling airflow across the heat sink. The airflow-blocking mechanism toggles between a passive airflow position and an active airflow position. In the passive airflow position, the airflow-blocking mechanism allows the cooling airflow to exhaust from the heat sink without passing through the air-moving device, and in the active airflow position, the airflow-blocking mechanism allows the cooling airflow to exhaust from the auxiliary air-moving device.

Electronics cooling assembly with multi-position, airflow-blocking mechanism

Based on the structure parameter and operating principle of the cooling system of traction converter for CRH3 high-speed electric multiple units (EMUs), a finite element model of air heat exchanger is built. Then the simulation including temperature field and fluid field is done. In order to verify the ability of the cooling system, a thermal capacity test rig for the traction converter is built. With the test rig, the temperature rise of traction converter and supply air volume of cooling system are measured in Wu-Guang high speed railway. The results show that when the high speed EMUs running in high speed, the supply air volume of cooling system will decrease, and the cooling system of traction converter for CRH3 EMUs can meet the requirement when the train continuous running in 330km/h. The simulated results are verified by the test results. The test and investigation on the thermal capacity of traction converter for high speed EMUs are firstly developed in China which makes a contribution to the design of the new generation high speed EMUs.

Research on the thermal capacity of the traction converter of CRH3 electric multiple units

All electronics generate heat. No device operates at 100% efficiency. The energy lost within a circuit dissipates as heat. That heat is the difference between the input and output power. The author suggests that the design for cooling is too often delayed in a project until too late. The resulting fixes or solutions are usually far from optimal, and they typically delay completion of the instrument. In this column, he discusses some of the concepts involved in cooling equipment. At the end of the column, he presents several case studies for cooling instruments.

K. Fowler

Papers

Heat transfer and cooling