Monoporous micropillar wick structures, I-Mass transport characteristics

Ravi, Saitej; Horner, David A.; Moghaddam, Saeed

doi:10.1016/j.applthermaleng.2014.04.057

Cited by 32 publications

(25 citation statements)

References 17 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…In addition, a thicker liquid allows a higher liquid mass flow rate, which contributes to a higher q dry-out . This trend agrees with previous modeling based on the Darcy's equation and experimental observations 14,15 . However, increasing the height of the pillars increases the superheat at the solid surface.…”

Section: Resultssupporting

confidence: 93%

Prediction and Characterization of Dry-out Heat Flux in Micropillar Wick Structures

Zhu

Antao

et al. 2016

Langmuir

View full text Add to dashboard Cite

Thin-film evaporation in wick structures for cooling high-performance electronic devices is attractive because it harnesses the latent heat of vaporization and does not require external pumping. However, optimizing the wick structures to increase the dry-out heat flux is challenging due to the complexities in modeling the liquid-vapor interface and the flow through the wick structures. In this work, we developed a model for thin-film evaporation from micropillar array wick structures and validated the model with experiments. The model numerically simulates liquid velocity, pressure, and meniscus curvature along the wicking direction by conservation of mass, momentum, and energy based on a finite volume approach. Specifically, the three-dimensional meniscus shape, which varies along the wicking direction with the local liquid pressure, is accurately captured by a force balance using the Young-Laplace equation. The dry-out condition is determined when the minimum contact angle on the pillar surface reaches the receding contact angle as the applied heat flux increases. With this model, we predict the dry-out heat flux on various micropillar structure geometries (diameter, pitch, and height) in the length scale range of 1-100 μm and discuss the optimal geometries to maximize the dry-out heat flux. We also performed detailed experiments to validate the model predictions, which show good agreement. This work provides insights into the role of surface structures in thin-film evaporation and offers important design guidelines for enhanced thermal management of high-performance electronic devices.

show abstract

Section: Resultssupporting

confidence: 93%

Prediction and Characterization of Dry-out Heat Flux in Micropillar Wick Structures

Zhu

Antao

et al. 2016

Langmuir

View full text Add to dashboard Cite

show abstract

“…In this study, the ability of a surface to wick a liquid is simply defined as the product of its permeability and capillarity ( K wick P c ) to avoid any assumption. This value for different surface structures is calculated using two models that were experimentally verified in prior studies 47 – 50 (see section S2 in the Supplementary section for more details).…”

Section: Experimental Studiesmentioning

confidence: 99%

A New Paradigm for Understanding and Enhancing the Critical Heat Flux (CHF) Limit

Fazeli

Moghaddam

2017

Sci Rep

Self Cite

View full text Add to dashboard Cite

Nearly a century of research on enhancing critical heat flux (CHF) has focused on altering the boiling surface properties such as its nucleation site density, wettability, wickability and heat transfer area. But, a mechanism to manipulate dynamics of the vapor and liquid interactions above the boiling surface as a means of enhancing CHF has not been proposed. Here, a new approach is implemented to limit the vapor phase lateral expansion over the heat transfer surface and actively control the surface wetted area fraction, known to decline monotonically with increasing heat flux. This new degree of freedom has enabled reaching unprecedented CHF levels and revealed new details about the physics of CHF. The impact of wickability, effective heat transfer area, and liquid pressure on CHF is precisely quantified. Test results show that, when rewetting is facilitated, the CHF increases linearly with the effective surface heat transfer area. A maximum CHF of 1.8 kW/cm 2 was achieved on a copper structure with the highest surface area among all tested surfaces. A model developed based on the experimental data suggests that the thermal conductivity of the surface structures ultimately limits the CHF; and a maximum CHF of 7-8 kW/cm 2 may be achieved using diamond surface structures.Boiling is a ubiquitous mechanism of heat transfer with numerous applications ranging from small-scale HVAC and refrigeration systems used in most buildings to large boilers in energy and process industries. Due to its unique performance characteristics, boiling has been implemented in extremely demanding applications such as fusion reactors 1-3 . The ebullition process in boiling triggers a set of heat and mass transfer events that can generate extremely high local cooling rates [4][5][6] . As such, in response to demands for removing heat from confined spaces in modem applications [7][8][9][10]

show abstract

“…Devices with ordered macropores have been employed for separation, reaction, and heat transfer. [38][39][40][41] Materials containing ordered mesopores have been applied in sensing, [42][43][44] drug release, [45][46][47][48][49] separation, [50][51][52][53][54][55][56] and catalysis. [57][58][59][60][61] 2D ordered structures like pillar arrays, bundles of fibers, and capillary bundles are, in general, arrangements in which one phase (solid or void) can be considered as formed by non-overlapping cylinders.…”

Section: Exemplary Structures Of Porous Materials 21 Ordered Structuresmentioning

confidence: 99%

“…Due to the flexibility of the lithographic preparation process arrays with a pillar diameter of a few hundred nanometers have been realised 41 as well as pillars with a size of tens of micrometers. 39 Also the degree of order can be systematically adjusted from a crystal-like to a stochastic arrangement. 62 Similarly, aligned fibers covering a wide range of materials can be prepared by electrospinning, 63,64 resulting in arrays of uniaxially aligned fibers with diameters of typically several hundred nanometers.…”

Section: Exemplary Structures Of Porous Materials 21 Ordered Structuresmentioning

confidence: 99%

Characterization of microscopic disorder in reconstructed porous materials and assessment of mass transport-relevant structural descriptors

2016

View full text Add to dashboard Cite

The targeted optimization of the functional properties of porous materials includes the understanding of their transport properties and thus requires knowledge about the relationship between material synthesis, resulting in three-dimensional material morphology, and relevant transport properties. In this Perspective, we present our views and results on the characterization of microscopic disorder in functional porous materials, which are widely used today as fixed beds in adsorption, separation, and catalysis. This allows us to identify structural parameters that impact their mass transport properties and eventually their overall performance in technological operations. We address this complex topic at the following levels: (i) computer-generation of disordered packings allows the systematic investigation of the bed porosity (packing density) and degree of packing heterogeneity. These studies are complemented by the physical reconstruction of real packed and monolithic beds, which resolves the salient features of the packing process and monolith synthesis that are under the control of the experimentalist. (ii) Once reconstructed packed-bed and monolith morphologies are available, they are analysed by statistical methods to derive structural descriptors for their mass transport properties. Spatial tessellation schemes and chord length distributions are shown to be suitable for that purpose. They lead us to sensitive correlations of the degree of pore-environment heterogeneity and packing-scale disorder with the dynamics of (random) diffusion and (flow-field dependent) hydrodynamic dispersion, respectively. (iii) Direct or pore-scale numerical simulations are implemented on a highperformance computing platform to quantify the relevant transport properties of the materials. This complementary approach highlights the morphological descriptors of mass transport efficiency. They are validated by the simulations and in the future could direct the rational design of materials from their synthesis to targeted applications based on physical reconstruction.

show abstract

Monoporous micropillar wick structures, I-Mass transport characteristics

Cited by 32 publications

References 17 publications

Prediction and Characterization of Dry-out Heat Flux in Micropillar Wick Structures

Prediction and Characterization of Dry-out Heat Flux in Micropillar Wick Structures

A New Paradigm for Understanding and Enhancing the Critical Heat Flux (CHF) Limit

Characterization of microscopic disorder in reconstructed porous materials and assessment of mass transport-relevant structural descriptors

Contact Info

Product

Resources

About