https://docs.lib.purdue.edu/cgi/viewcontent.cgi?article=1116&context=coolingpubs

A composite heat transfer correlation for saturated flow boiling in small channels

A review of small heat pipes for electronics

We report on a thermal imaging technique based on fluorescence polarization anisotropy measurements, which enables mapping the local temperature near nanometer-sized heat sources with 300 nm spatial resolution and a typical accuracy of 0.1 degrees C. The principle is demonstrated by mapping the temperature landscape around plasmonic nano-structures heated by near-infrared light. By assessing directly the molecules' Brownian dynamics, it is shown that fluorescence polarization anisotropy is a robust and reliable method which overcomes the limitations of previous thermal imaging techniques. It opens new perspectives in medicine, nanoelectronics and nanofluidics where a control of temperature of a few degrees at the nanoscale is required.

Temperature mapping near plasmonic nanostructures using fluorescence polarization anisotropy.

A review of the capabilities of high heat flux removal by porous materials, microchannels and spray cooling techniques

https://docs.lib.purdue.edu/cgi/viewcontent.cgi?article=1090&context=coolingpubs

Refrigerant flow boiling heat transfer in parallel microchannels as a function of local vapor quality

A detailed analysis of microchannel/microgap heat transfer data for two-phase flow of refrigerants and dielectric liquids, gathered from the open literature and sorted by the Taitel and Dukler flow regime mapping methodology, is performed. Annular flow is found to be the dominant regime for this thermal transport configuration and to grow in importance with decreasing channel diameter. A characteristic M-shaped heat transfer coefficient variation with quality (or superficial velocity) for the flow of refrigerants and dielectric liquids in miniature channels is identified. The inflection points in this M-shaped curve are seen to equate approximately with flow regime transitions, including a first maximum at the transition from Bubble to Intermittent flow and a second maximum at moderate qualities in Annular flow, just before local dryout begins. The predictive accuracy of five classical two-phase heat transfer correlations for miniature channel flow is examined. Selecting the best fitting of the classical ...

Modeling and Prediction of Two-Phase Microgap Channel Heat Transfer Characteristics

Driven by the continuing Moore’s Law evolution in chip technology, power dissipation of nanoelectronics chips could exceed 300W, with heat fluxes above 150W/cm2, within the next few years, along with localized, sub-millimeter zones with heat fluxes in excess of 1kW/cm2. New and novel cooling techniques, with the ability to selectively cool sub-millimeter “sun spots” while providing effective global cooling for high heat flux chips are needed. Several promising approaches, including the application of miniaturized silicon and BiTe thermoelectric coolers and direct cooling with dielectric liquids through thin film evaporation, will be described.

Thermal management of high heat flux nanoelectronic chips

Rapidly increasing light emitting diode (LED) heat fluxes necessitate the development of aggressive thermal management techniques that can intercept the dissipated heat directly in the submount. Microgap coolers, which eliminate solid-solid thermal interface resistance and provide direct contact between chemically inert, dielectric fluids and the back surface of an active electronic component, offer a most promising approach for cooling high-power LEDs. This paper focuses on the two-phase thermofluid characteristics of a dielectric liquid, FC-72, flowing in an asymmetrically heated chip-scale microgap channel, 10 mm wide × 37 mm long, with channel heights varying from 110 μm to 500 μm and channel wall heat fluxes of 200 kW/m2. The experimental two-phase, area-averaged heat transfer coefficients of FC-72 reached 10 kW/m2·K, significantly higher than the single-phase FC-72 values, thus providing cooling capability in the range associated with water under forced convection. Data obtained for single-phase water yielded very good agreement with predictions for the convective heat transfer coefficients and served to validate the accuracy of the experimental apparatus and measurement technique. It is shown that this two-phase cooling approach could be used to dissipate in excess of 600 kW/m2 in the submount of high-power LEDs.

Direct Submount Cooling of High-Power LEDs

Characterization and prediction of two-phase flow regimes in miniature tubes

A comprehensive literature review and analysis of recent microchannel/microgap heat transfer data for two-phase flow of refrigerants and dielectric liquids is presented. The flow regime progression in such a microgap channel is shown to be predicted by the traditional flow regime maps. Moreover, Annular flow is shown to be the dominant regime for this thermal transport configuration and to grow in importance as the channel diameter decreases. The results of heat transfer studies of single miniature channels, as well as the analysis and inverse calculation of IR images of a heated microgap channel wall, are used to identify the existence of a characteristic M-shaped heat transfer coefficient variation with quality (or superficial velocity), with inflection points corresponding to transitions in the two-phase cooling modalities. For the high-quality, Annular flow conditions, the venerable Chen correlation is shown to yield predictive agreement for microgap channels that is comparable to that attained for macrochannels and to provide a mechanistic context for the thermal transport rates attained in microgap channels. Results obtained from infrared imaging, revealing previously undetected, large surface temperature variations in Annular flow, are also reviewed and related to the termination of the favorable thin-film evaporation mode in such channels.

Emil Rahim

Papers

Modeling and Prediction of Two-Phase Microgap Channel Heat Transfer Characteristics

Thermal management of high heat flux nanoelectronic chips

Direct Submount Cooling of High-Power LEDs

Characterization and prediction of two-phase flow regimes in miniature tubes

Two-Phase Thermal Transport in Microgap Channels—Theory, Experimental Results, and Predictive Relations