https://docs.lib.purdue.edu/cgi/viewcontent.cgi?article=1023&context=coolingpubs

Characteristics of an evaporating thin film in a microchannel

https://docs.lib.purdue.edu/cgi/viewcontent.cgi?article=1142&context=coolingpubs

A microscale model for thin-film evaporation in capillary wick structures

Review of two-phase flow and flow boiling of mixtures in small and mini channels

The topology and geometry of microstructures play a crucial role in determining their heat transfer performance in passive cooling devices such as heat pipes. It is therefore important to characterize microstructures based on their wicking performance, the thermal conduction resistance of the liquid filling the microstructure, and the thin-film characteristics of the liquid meniscus. In the present study, the free-surface shapes of the static liquid meniscus in common microstructures are modeled using SURFACE EVOLVER for zero Bond number. Four well-defined topologies, viz., surfaces with parallel rectangular ribs, horizontal parallel cylinders, vertically aligned cylinders, and spheres (the latter two in both square and hexagonal packing arrangements), are considered. Nondimensional capillary pressure, average distance of the liquid free-surface from solid walls (a measure of the conduction resistance of the liquid), total exposed area, and thin-film area are computed. These performance parameters are presented as functions of the nondimensional geometrical parameters characterizing the microstructures, the volume of the liquid filling the structure, and the contact angle between the liquid and solid. Based on these performance parameters, hexagonally-packed spheres on a surface are identified to be the most efficient microstructure geometry for wicking and thin-film evaporation. The solid-liquid contact angle and the nondimensional liquid volume that yield the best performance are also identified. The optimum liquid level in the wick pore that yields the highest capillary pressure and heat transfer is obtained by analyzing the variation in capillary pressure and heat transfer with liquid level and using an effective thermal resistance model for the wick. DOI: 10.1115/1.3160538

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Analysis of the Wicking and Thin-Film Evaporation Characteristics of Microstructures

Boiling heat transfer in a hydrofoil-based micro pin fin heat sink

An analytical model is presented that can be used to predict the heat-transfer characteristics of film evaporation on a microgroove surface. The model assumes that the liquid flow along a "V"-shaped groove channel is driven primarily by the capillary pressure difference due to the receding of the meniscus toward the apex of the groove, and the flow up the groove side wall is driven by the disjoining pressure difference. It also assumes that conduction across the thin liquid film is the dominant mechanism of heat transfer. A correlation between the Nusselt number and a nondimensional parameter ¥ is developed from this model which relates the heat transfer for the microgroove surface to the fluid properties, groove geometry, and the constants for the disjoining pressure relation. The results of a limited experimental study of the heat transfer during vaporization of a liquid coolant on a microgroove surface are also reported. Film-evaporation transfer coefficients inferred from these experiments are found to correlate fairly well in terms of Nusselt number and ¥ parameter format developed in the model. The results of this study suggest that disjoining pressure differences may play a central role in evaporation processes in microgroove channels.

Film evaporation from a micro-grooved surface―an approximate heat transfer model and its comparison with experimental data

Boiling data and the critical heat flux conditions are reported for both channel flow and jet impingement flow using varying concentrations of R-ll in R-113. An array of 10 flush-mounted heated elements on one wall of a vertical passage was cooled by subcooled boiling. Data indicate that for channel flow boiling, the addition of R-ll to R-113 does not produce a significant change in the critical heat flux condition. For channel flow boiling, the data indicate that addition of a small amount of a less volatile component slightly increased the critical heat flux, whereas, the addition of a small amount of a more volatile component decreased it. The critical heat flux data for channel flow were also found to agree well with critical heat flux correlations for pure fluids if the mole-weighted mean properties of the mixture were used to compute the critical heat flux from the pure fluid correlation. However, for jet impingement flow with binary mixtures, deviations existed between measured data and pure fluid correlation predictions using mole-weighted mean properties of the mixture. The significance of the findings of this study with regard to the use of binary mixtures of dielectric fluids for immersion cooling of electronic components is discussed in this article.

V. P. Carey

Papers

Film evaporation from a micro-grooved surface―an approximate heat transfer model and its comparison with experimental data

Subcooled convective boiling of binary mixtures over an array of heated elements