Effects of Varying Geometrical Parameters on Boiling From Microfabricated Enhanced Structures
01 Feb 2003-Journal of Heat Transfer-transactions of The Asme (American Society of Mechanical Engineers)-Vol. 125, Iss: 1, pp 103-109
TL;DR: In this article, the effect of varying the pore size, pitch and height on the boiling performance was studied, with fluorocarbon FC-72 as the working fluid, and the authors found that a larger pore and smaller pitch resulted in higher heat dissipation at all heat fluxes.
Abstract: The current study involves two-phase cooling from enhanced structures whose dimensions have been changed systematically using microfabrication techniques. The aim is to optimise the dimensions to maximize the heat transfer. The entranced structure used in this study consists of a stacked network of interconnecting channels making it highly porous. The effect of varying the pore size, pitch and height on the boiling performance was studied, with fluorocarbon FC-72 as the working fluid. While most of the previous studies on the mechanism of enhanced nucleate boiling have focused on a small range of wall superheats (0-4 K), the present study covers a wider range (as high as 30 K) A larger pore and smaller pitch resulted in higher heat dissipation at all heat fluxes. The effect of stacking multiple layers showed a proportional increase in heat dissipation (with additional layers) in a certain range of wall superheat values only. In the wall superheat range 8-13 K, no appreciable difference was observed between a single layer structure and a three layer structure. A fin effect combined with change in the boiling phenomenon within the sub-surface layers is proposed to explain this effect.
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TL;DR: In this paper, a comprehensive review of published articles addressing passive enhancement of pool boiling using surface modification techniques is provided, including macroscale, microscale, and nanoscale surfaces, as well as multiscale (hybrid-scale), and hybrid-wettability techniques.
343 citations
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TL;DR: In this article, the authors evaluate the pool boiling performance of structured surface features etched on a silicon chip and find that surface modifications to silicon chips can improve the heat transfer coefficient by a factor up to 3.4 times the performance of a plain chip.
Abstract: Pool boiling is of interest in high heat flux applications because of its potential for removing large amount of heat resulting from the latent heat of evaporation and little pressure drop penalty for circulating coolant through the system. However, the heat transfer performance of pool boiling systems is not adequate to match the cooling ability provided by enhanced microchannels operating under single-phase conditions. The objective of this work is to evaluate the pool boiling performance of structured surface features etched on a silicon chip. The performance is normalized with respect to a plain chip. This investigation also focuses on the bubble dynamics on plain and structured microchannel surfaces under various heat fluxes in an effort to understand the underlying heat transfer mechanism. It was determined that surface modifications to silicon chips can improve the heat transfer coefficient by a factor up to 3.4 times the performance of a plain chip. Surfaces with microchannels have shown to be efficient for boiling heat transfer by allowing liquid to flow through the open channels and wet the heat transfer surface while vapor is generated. This work is expected to lead to improved enhancement features for extending the pool boiling option to meet the high heat flux removal demands in electronic cooling applications.
139 citations
TL;DR: This survey, although extensive cannot include every paper; some selection is necessary, is intended to encompass the English language heat transfer papers published in 2003, including some translations of foreign language papers.
106 citations
Cites methods from "Effects of Varying Geometrical Para..."
...Boiling from microfabricated structures is documented to support optimization of the dimensions for maximizing heat transfer [814]....
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TL;DR: In this article, the authors evaluated two-phase heat exchangers for single-phase flows and showed that they can achieve state-of-the-art performance in terms of heat transfer.
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TL;DR: The porous surface structure was manufactured with precision for the experimental study of nucleate boiling heat transfer in R-11 and the data of bubble formation were obtained with a variety of geometrical and operational parameters; the pore diameters were of 50, 100, 150, 150..mu..m, there was a combination of pores of different sizes; and the system pressures were of 0.04, 0.1,0.23 MPa as mentioned in this paper.
Abstract: The porous surface structure was manufactured with precision for the experimental study of nucleate boiling heat transfer in R-11. Boiling curves and the data of bubble formation were obtained with a variety of geometrical and operational parameters; the pore diameters were of 50, 100, 150 ..mu..m, there was a combination of pores of different sizes; and the system pressures were of 0.04, 0.1, 0.23 MPa. The boiling curves exhibit certain trends effected by the diameter and population density of pores. A combination of high system pressure and pore sizes of 100 or 150 ..mu..m dia enables boiling to persist even when the wall superheat is reduced to an extremely low level of 0.1 K. A noteworthy feature of porous surface boiling is that intense bubble formation does not necessarily yield a high heat-transfer performance. Examination of the data indicates that liquid suction and evaporation inside the cavities are a proable mechanism of boiling with small temperature differences.
114 citations
102 citations