Numerical Investigation of Shape Effect on Microdroplet Evaporation

2019 ◽  
Vol 141 (4) ◽  
Author(s):  
Li Shan ◽  
Shuai Shuai ◽  
Binjian Ma ◽  
Zichen Du ◽  
Baris Dogruoz ◽  
...  
Keyword(s):  
Mass Transport ◽  
Contact Line ◽  
Evaporation Rate ◽  
High Heat ◽  
Droplet Evaporation ◽  
Vapor Concentration ◽  
Two Phase ◽  
Spherical Droplet ◽  
Two Phase Cooling ◽  
Liquid Vapor

Abstract As electronic devices continue to shrink in size and increase in functionality, effective thermal management has become a critical bottleneck that hinders continued advancement. Two-phase cooling technologies are of growing interest for electronics cooling due to their high heat removal capacity and small thermal resistance (<0.1 k cm2/W). One typical example of a two-phase cooling method is droplet evaporation, which can provide a high heat transfer coefficient with low superheat. While droplet evaporation has been studied extensively and used in many practical cooling applications (e.g.,, spray cooling), the relevant work has been confined to spherical droplets with axisymmetric geometries. A rationally designed evaporation platform that yields asymmetric meniscus droplets can potentially achieve larger meniscus curvatures, which gives rise to higher vapor concentration gradients along the contact line region, and therefore, yields higher evaporation rates. In this study, we develop a numerical model to investigate the evaporation behavior of asymmetrical microdroplets suspended on a porous micropillar structure. The equilibrium profiles and mass transport characteristics of droplets with circular, triangular, and square contact shapes are explored using the volume of fluid (VOF) method. The evaporative mass transport at the liquid–vapor interface is modeled using a simplified Schrage model. The results show highly nonuniform mass transport characteristics for asymmetrical microdroplets, where a higher local evaporation rate is observed near the locations where the meniscus has high curvature. This phenomenon is attributed to a higher local vapor concentration gradient that drives faster vapor diffusion at more curved regions, similar to a lightning rod exhibiting a strong electric field along a highly curved surface. By using contact line confinement to artificially tune the droplet into a more curved geometry, we find that the total evaporation rate from a triangular-based droplet is enhanced by 13% compared to a spherical droplet with the same perimeter and liquid–vapor interfacial area. Such a finding can guide the design and optimization of geometric features to improve evaporation in advanced microcooling devices.

Numerical Investigation of Shape Effect on Microdroplet Evaporation

2018 ◽  
Author(s):  
Shuai Shuai ◽  
Zichen Du ◽  
Binjian Ma ◽  
Li Shan ◽  
Baris Dogruoz ◽  
...  
Keyword(s):  
Mass Transport ◽  
Contact Line ◽  
Evaporation Rate ◽  
Electronics Cooling ◽  
High Heat ◽  
Droplet Evaporation ◽  
Vapor Concentration ◽  
Two Phase ◽  
Two Phase Cooling ◽  
Liquid Vapor

As electronic devices continue to shrink in size and increase in functionality, effective thermal management has become a critical bottleneck that hinders continued advancement. Two-phase cooling technologies are of growing interest for electronics cooling due to their high heat removal capacity and small thermal resistance (< 0.3 K-cm2/W) [1]. One typical example of a two-phase cooling method is droplet evaporation, which can provide a high heat transfer coefficient with low superheat. While droplet evaporation has been studied extensively and used in many practical cooling applications (e.g., spray cooling), the relevant work has been confined to spherical droplets with axisymmetric geometries. A rationally designed evaporation platform that yields asymmetric meniscus droplets can potentially achieve larger meniscus curvatures, which give rise to higher vapor concentration gradients along the contact line region and therefore yield higher evaporation rates. In this study, we develop a numerical model to investigate the evaporation behavior of asymmetrical microdroplets suspended on a porous micropillar structure. The equilibrium profiles and mass transport characteristics of droplets with circular, triangular, and square contact shapes are explored using the Volume of Fluid (VOF) method. The evaporative mass transport at the liquid-vapor interface is modeled using a simplified Schrage model [2]. The results show highly non-uniform mass transport characteristics for asymmetrical microdroplets, where a higher local evaporation rate is observed near the locations where the meniscus has high curvature. This phenomenon is attributed to a higher local vapor concentration gradient that drives faster vapor diffusion at more curved regions, similar to a lightning rod exhibiting a strong electric field along a highly curved surface. By using contact line confinement to artificially tune the droplet into a more curved geometry, we find the total evaporation rate from a triangular-based droplet is enhanced by 13% compared to a spherical droplet with the same perimeter and liquid-vapor interfacial area. Such a finding can guide the design and optimization of geometric features to improve evaporation in high performance electronics cooling systems.

Model Predictive Control of a Pumped Two-Phase Cooling System With Microchannel Heat Exchangers

2018 ◽  
Author(s):  
Oyuna Angatkina ◽  
Andrew Alleyne
Keyword(s):  
Heat Flux ◽  
Model Predictive Control ◽  
Predictive Control ◽  
Heat Exchangers ◽  
Cooling System ◽  
High Heat ◽  
High Heat Flux ◽  
Two Phase ◽  
Cooling Systems ◽  
Two Phase Cooling

Two-phase cooling systems provide a viable technology for high–heat flux rejection in electronic systems. They provide high cooling capacity and uniform surface temperature. However, a major restriction of their application is the critical heat flux condition (CHF). This work presents model predictive control (MPC) design for CHF avoidance in two-phase pump driven cooling systems. The system under study includes multiple microchannel heat exchangers in series. The MPC controller performance is compared to the performance of a baseline PI controller. Simulation results show that while both controllers are able to maintain the two-phase cooling system below CHF, MPC has significant reduction in power consumption compared to the baseline controller.

Experimental evaluation of a compact two-phase cooling system for high heat flux electronic packages

2019 ◽  
Vol 163 ◽  
pp. 114338 ◽  
Author(s):  
Fengze Hou ◽  
Wenbo Wang ◽  
Hengyun Zhang ◽  
Cheng Chen ◽  
Chuan Chen ◽  
...  
Keyword(s):  
Heat Flux ◽  
Experimental Evaluation ◽  
Cooling System ◽  
High Heat ◽  
High Heat Flux ◽  
Electronic Packages ◽  
Two Phase ◽  
Two Phase Cooling

High Heat Flux Two-Phase Cooling in Silicon Multimicrochannels

2008 ◽  
Vol 31 (3) ◽  
pp. 691-701 ◽  
Author(s):  
B. Agostini ◽  
J.R. Thome ◽  
M. Fabbri ◽  
B. Michel
Keyword(s):  
Heat Flux ◽  
High Heat ◽  
High Heat Flux ◽  
Two Phase ◽  
Two Phase Cooling

Three-Dimensional Calculations of Evaporative Flow in Compressor Blade Rows

2008 ◽  
Vol 130 (3) ◽  
Author(s):  
R. C. Payne ◽  
A. J. White
Keyword(s):  
Evaporation Rate ◽  
Three Dimensional ◽  
Droplet Evaporation ◽  
Compressor Blade ◽  
Computational Method ◽  
Water Mixture ◽  
Liquid Droplets ◽  
Two Phase ◽  
Physical Behavior ◽  
Eulerian Method

The present paper describes a three-dimensional computational method developed to solve the flow of a two-phase air-water mixture, including the effects of evaporation for a monodispersion of liquid droplets. The calculations employ a fully Eulerian method for the conservation of droplet number and liquid mass and are applicable to multiple blade rows, both stationary and rotating. The method is first tested to ensure that it computes the correct droplet evaporation rate and the correct physical behavior for evaporation within a 1D duct. Results are then presented for flow within a single compressor stage, i.e., a rotor-stator combination.

Measurement of Liquid Droplet Evaporation Rate under the Conditions of Intense Heating

2014 ◽  
Vol 698 ◽  
pp. 603-608 ◽  
Author(s):  
Evgenija Orlova ◽  
Dmitriy Feoktistov
Keyword(s):  
Contact Angle ◽  
Contact Line ◽  
Evaporation Rate ◽  
Liquid Droplet ◽  
Droplet Evaporation ◽  
Solid Substrate ◽  
Anodized Aluminum ◽  
Specific Evaporation Rate ◽  
Contact Line Pinning ◽  
Contact Diameter

This paper presents an experimental study of the evaporation of a sessile water-sodium chlorides solution drop to open atmosphere on the solid substrate (anodized aluminum) under the varying heat flux. The main parameters defining drop profile, i. e., contact diameter, contact angle, and height of the drop have been obtained. Specific evaporation rate has been calculated. According to the data analysis it was found, that the sessile water-sodium chlorides solution drop with the highest concentration (16.7%) evaporates in the "reverse depinning" mode. So, there is movement of the contact line in the direction of increasing the surface occupied by the drop. The sessile water and water-sodium chlorides solution drop with 4.8% and 9.1% concentration evaporates in the contact line pinning mode. The influence of the initial concentration of the evaporated solution on the contact angle and the specific evaporation rate was found out.

Droplet Evaporation of Cu–Al2O3 Hybrid Nanofluid Over Its Residue and Copper Surfaces: Toward Developing a New Analytical Model

2020 ◽  
Vol 143 (2) ◽  
Author(s):  
Farooq Riaz Siddiqui ◽  
Chi Yan Tso ◽  
Sau Chung Fu ◽  
Huihe Qiu ◽  
Christopher Y. H. Chao
Keyword(s):  
Analytical Model ◽  
Evaporation Rate ◽  
Heat Dissipation ◽  
High Heat ◽  
Droplet Evaporation ◽  
Copper Surface ◽  
Hybrid Nanofluid ◽  
High Heat Flux ◽  
High Heat Transfer ◽  
Critical Residue

Abstract Droplet evaporation-based cooling techniques, such as the spray cooling, give high heat transfer rates by utilizing latent energy and are usually preferred in thermal applications. However, with the significant rise in heat dissipation levels for high heat flux devices, these devices cannot be thermally managed due to the limited cooling capacity of existing thermal fluids. In this paper, we report the evaporation of the Cu–Al2O3 hybrid nanofluid (HNF) droplet on a copper surface as well as its own residue surface, developed from the evaporation of the first Cu–Al2O3 HNF droplet. As the main novelty, we identify the critical residue size and investigate the residue size effect, above and below the critical residue size, on evaporation rate of the succeeding Cu–Al2O3 HNF droplet resting over a residue surface. We also develop a new analytical model to estimate the Cu–Al2O3 HNF droplet evaporation rate and compare our results with other existing models. The results show that the Cu–Al2O3 HNF droplet gives 17% higher evaporation rate than a water droplet on a copper surface. Also, the evaporation rate of the Cu–Al2O3 HNF droplet on a residue surface sharply increases by 106% with increasing residue size up to the critical residue size. However, further increasing the residue size above its critical value has a negligible effect on the droplet evaporation rate. Moreover, the evaporation rate of the Cu–Al2O3 HNF droplet on its residue surface is enhanced up to 104% when compared to a copper surface.

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