Showing papers on "Critical heat flux published in 2021"
TL;DR: In this article, the authors present the advancements of enhanced microchannels from the fabrication perspective, which is critical for the application and commercialization of the enhanced microchannel heat sinks in high heat flux dissipations.
101 citations
TL;DR: In this article, the boiling heat transfer coefficient (BHTC) of graphene oxide-water nano-suspension (NS) was quantified in the boiling water transfer regime.
49 citations
TL;DR: In this article, the role of surface engineering in enhanced pool boiling of highly wetting dielectric liquids is reviewed and discussed for both saturated and sub-cooled testing conditions, and the promising engineered surfaces in terms of improved boiling performance (higher heat transfer coefficient (HTC), critical heat flux (CHF), and temperature excursion) are highlighted.
47 citations
TL;DR: A comprehensive review of historical efforts in measuring the contact angles of water over a wide temperature range on a variety of solids, not limited to metallic surfaces is presented and a theoretical understanding of the temperature dependence is given based on surface thermodynamic analysis.
44 citations
TL;DR: In this paper, a review of nanotechnology-based methods on boiling enhancement including nanoscale modified surfaces and nanofluids is summarized, and different coupled methods, including (a) hybrid nano-fluids; (b) combined methods of using both nanoflide and surface modification; (c) bi-feature surfaces with multi-wettability (biphilic), multi-material, or multi-scale coating for surface modification, are discussed.
37 citations
TL;DR: In this paper, the authors present a systematized review of articles addressing jet impingement boiling, which includes research spanning over five decades and jets of various fluids, operating conditions, and geometrical configurations.
33 citations
TL;DR: In this paper, a comprehensive review of published articles addressing nanoscale techniques for both pool boiling and flow boiling enhancement is provided, with particular focus on reliability concerns stemming from any time-dependent variations in boiling performance.
32 citations
TL;DR: In this article, the authors proposed a new high aspect ratio groove-wall microchannel (height=200mm, width=80μm, length=10mm, AR=2.5), which features a series of rectangular grooves etched on the plain side walls.
31 citations
30 citations
TL;DR: In this paper, a thorough review and investigation of published articles describing the various surface modification method (nanomaterial coating, nano/micro porous coating, nanomaterial structured surface) for pool boiling and flow boiling heat transfer enhancement as well as the effect of surface modification on wettability, porosity, surface roughness, nucleation sites are studied.
28 citations
TL;DR: In this article, the authors used high-magnification in-liquid endoscopy to directly probe bubble behavior during boiling and found that two distinct three-phase contact lines underneath growing bubbles on structured surfaces, resulting in retention of a thin liquid film within the structures between the two contact lines due to their disparate advancing velocities.
Abstract: Enhancing critical heat flux (CHF) during boiling with structured surfaces has received much attention because of its important implications for two-phase flow. The role of surface structures on bubble evolution and CHF enhancement remains unclear because of the lack of direct visualization of the liquid- and solid-vapor interfaces. Here, we use high-magnification in-liquid endoscopy to directly probe bubble behavior during boiling. We report the previously unidentified coexistence of two distinct three-phase contact lines underneath growing bubbles on structured surfaces, resulting in retention of a thin liquid film within the structures between the two contact lines due to their disparate advancing velocities. This finding sheds light on a previously unidentified mechanism governing bubble evolution on structured surfaces, which has notable implications for a variety of real systems using bubble formation, such as thermal management, microfluidics, and electrochemical reactors.
TL;DR: In this paper, a constructal design of high heat flux two-stacked horizontal microchannel heat sinks is presented for cooling of electronic devices using ANSYS Computational Fluid Dynamics (CFD) code for subcooled nucleate boiling.
TL;DR: In this article, the influence of heterogeneous wettability-patterned surfaces with varying interspacing on flow boiling heat transfer characteristics was investigated by analyzing the relationship between bubble lift forces and the various hydrophobic patterned shapes in a horizontal flow channel.
TL;DR: In this article, the authors decouple the contributions of the intrinsic surface wettability from the hierarchical (dual-layer) structure on the boiling enhancement by growing nanograss as the substructure and the micro flowers with different cover density as the superstructure.
TL;DR: In this paper, the authors investigated microtube structures, where a cavity is defined at the center of a pillar, as structural building blocks to enhance the critical heat flux (CHF) and the heat transfer coefficient (HTC) simultaneously in a controllable manner.
Abstract: Boiling is an essential process in numerous applications including power plants, thermal management, water purification, and steam generation. Previous studies have shown that surfaces with microcavities or biphilic wettability can enhance the efficiency of boiling heat transfer, that is, the heat transfer coefficient (HTC). Surfaces with permeable structures such as micropillar arrays, in contrast, have shown significant enhancement of the critical heat flux (CHF). In this work, we investigated microtube structures, where a cavity is defined at the center of a pillar, as structural building blocks to enhance HTC and CHF simultaneously in a controllable manner. We demonstrated simultaneous CHF and HTC enhancements of up to 62 and 244%, respectively, compared to those of a smooth surface. The experimental data along with high-speed images elucidate the mechanism for simultaneous enhancement where bubble nucleation occurs in the microtube cavities for increased HTC and microlayer evaporation occurs around microtube sidewalls for increased CHF. Furthermore, we combined micropillars and microtubes to create surfaces that further increased CHF by achieving a path to separate nucleating bubbles and rewetting liquids. This work provides guidelines for the systematic surface design for boiling heat transfer enhancement and has important implications for understanding boiling heat transfer mechanisms.
TL;DR: In this article, a porous surface covered by microcavities (MCPS) was developed, which was fabricated by the three-step method of a powder sintering technique followed by chemical modification methods to realize simultaneous enhancement of critical heat flux (CHF) and heat transfer coefficient (HTC) for boiling heat transfer processes.
TL;DR: In this paper, the influence of surface wettability on pool boiling heat transfer on metal foam covers was analyzed, and a new correlation was developed with an average deviation of 14.1%.
TL;DR: In this article, an experimental investigation of key parameters influencing CHF for confined round single jets and jet arrays impinging normally onto square heated surfaces is performed using R-134a, a fluid widely used for thermal management of electronic and power devices, especially in aerospace applications.
TL;DR: In this article, the authors used MWCNT-based nanofluids as a cooling fluid and compared its performance with the water, and reported the bubble dynamics data, including the departure diameter, departure frequency, bubble growth time and bubble wait time.
TL;DR: In this article, the authors investigated the effect of high aspect ratio microchannels with micro connection slots on the performance of flow boiling and demonstrated that the microchannel heat sink with tens of micro-slots can be an effective approach for suppressing flow boiling instability and enhancing flow boiling heat transfer performance.
TL;DR: In this article, composite porous structures were manufactured with selective laser melting (SLM) technique from aluminum alloy (AlSi10Mg) powder, and the heat transfer characteristics of a composite porous structure with composite pores (0.6mm small pores and 2mm large pores) for pool boiling under atmospheric pressure were investigated.
24 Mar 2021
TL;DR: In this paper, a convolutional neural network was used to predict the boiling crisis for mitigating thermal runaway-induced accidents in boiling-based systems and achieved a validation accuracy of 99.92% against the ground truth.
Abstract: Summary Advance prediction of boiling crisis is critical to the safety and economy of many thermal systems. Here, we perform steady-state near-saturated boiling experiments on a plain copper surface and acquire the acoustic emissions (AEs) in natural convection, nucleate, and transition boiling regimes. We use the corresponding AE spectrograms to train a convolutional neural network, which shows a validation accuracy of 99.92% against the ground truth. We next evaluate the trained network on experiments with water and aqueous solutions of ionic liquid and surfactant on plain and nanostructured copper surfaces with time-varying heat inputs. Despite the variations in boiling surfaces, working fluids, and the heating strategy between the training and the evaluation datasets, the network accurately predicts the respective boiling regimes. Finally, we use the insights to perform advance prediction of boiling crisis for mitigating thermal runaway-induced accidents in boiling-based systems.
TL;DR: In this paper, the authors investigate the effect of electric fields on spray cooling and show that droplet size decreases and spray velocity increases with increasing applied voltage, and droplet formation and subsequent impinging behavior are gradually dominated by electric forces.
TL;DR: In this article, the authors proposed a gradient wick channel topology to delay the capillary limit and enhance the two-phase flow boiling heat transfer coefficient (HTC) and delay critical heat flux.
TL;DR: In this article, the authors present a detailed assessment of pool boiling heat transfer enhancement, relating this to Part I [1], which presented a critical assessment of fundamental concepts of heterogeneous nucleation.
Abstract: Heat transfer enhancement by surface modification has been extensively studied in the last twenty years. However, there remains a large discrepancy among researchers on the performance of enhanced surfaces even for the same fluid and surface preparation technique. The reasons of this discrepancy are not understood and are not discussed in past papers, including paper reviews. Part II of this two-part paper aims to present a detailed assessment of pool boiling heat transfer enhancement, relating this to Part I [1], which presented a critical assessment of fundamental concepts of heterogeneous nucleation. Current challenges in evaluating the performance of enhanced surfaces is first discussed. The performance of smooth and roughened surfaces is then discussed and the effect of fluid type is explained. Pool boiling data of two fluids, namely water and FC-72, on two enhanced substrate materials, i.e. copper and silicon were digitized and assessed in order to elucidate the reason for the discrepancy in published works and present future recommendations for heat transfer enhancement. The heat transfer enhancement mechanisms adopted by researchers were presented and critically discussed and compared. The paper contributes to the understanding of the effect of fluid-surface combinations and suggest guidelines for researchers to consider when evaluating the performance of enhanced surfaces. This will help the research community and industry to conclude on the best surface structure and surface manufacturing technique matching particular fluid of interest.
TL;DR: In this article, the authors studied the effects of incorporating pillars on the nucleation site interaction and nucleate boiling heat transfer on a hybrid rough surface, a surface with multiple cavities and a pillar on sides of each cavity, using a two-dimensional pseudopotential phase-change lattice Boltzmann method.
TL;DR: In this article, the effects of the groove-wall microchannel aspect ratio, groove spacing ratio, and groove depth on the flow boiling performance were investigated for deionized water working fluid with mass fluxes of 446-963 kg/m2·s.
TL;DR: In this paper, a three-dimensional analysis of surface potential energy is used to address its relationship to surface wettability and nanoscale pool boiling characteristics of liquid molecules, which reveals that the increase in surface wetability can improve the heat transfer coefficient and critical heat flux under high superheat conditions in both nano- and macroscale systems.
TL;DR: In this article, a neural network model was developed to predict the margin to the boiling crisis from high-resolution infrared measurements of the bubble dynamics on surfaces with different morphologies and wettability.
Abstract: We develop a neural network model capable of predicting the margin to the boiling crisis (i.e., the departure from nucleate boiling ratio, DNBR) from high-resolution infrared measurements of the bubble dynamics on surfaces with different morphologies and wettability (or wickability). We use a feature ranking algorithm, i.e., minimum redundancy maximum relevance, to elucidate the importance of fundamental boiling parameters, i.e., nucleation site density, bubble departure frequency, growth time, and footprint radius, in predicting the boiling crisis. We conclude that these parameters are all necessary and equally important. This result has profound implications, as it undermines the general validity of many observations and mechanistic models that attempt to predict the critical heat flux (CHF) by describing how a single boiling parameter changes with the heat flux or from one surface to another. Notably, the neural network model can predict the DNBR on CHF-enhancing surfaces of different wickability without using any input information related to the surface properties. This result suggests that, at least on the considered surfaces, surface wickability enhances the CHF by modifying the bubble dynamics, i.e., the aforesaid boiling parameters, rather than acting as an additional heat removal mechanism.
TL;DR: In this paper, the authors discuss recent research progress on structured surface-enhanced flow boiling and focus on the challenges remaining, including the need for better understanding of the mechanisms governing surface-structureenhanced Flow Boiling and their effect on heat transfer coefficient, critical heat flux, pressure drop, and flow stability.
Abstract: High-vapor-quality flow boiling on structured surfaces has the potential to enhance heat transfer performance and reduce temperature/pressure instability compared to conventional lower quality flow boiling on smooth surfaces. In this article, we discuss recent research progress on structured surface-enhanced flow boiling. We discuss lessons learned and focus on the challenges remaining. Although some degree of mechanistic understanding of the effect of surface structures on the flow boiling process has been gained, many important challenges remain to enable real utilization. Primarily, a need exists for a greater fundamental understanding of the processes if design tools are to be developed capable of guiding engineers to select and implement enhancements. The challenges discussed stem from a community-wide workshop focusing on high-exit-quality flow boiling, held in June 2020. Four key challenges were identified: 1) the need for better understanding of the mechanisms governing surface-structure-enhanced flow boiling and their effect on heat transfer coefficient, critical heat flux, pressure drop, and flow stability; 2) the need for rigorous quantification of surface durability and manufacturing scalability; 3) the need to understand effects of using working fluids other than water including refrigerants, supercritical fluids, and other dielectric fluids; and 4) the need to establish thermal resistance limits dependent on liquid film thickness. We end this article by providing conclusions detailing where we believe that the community should direct both fundamental and applied efforts in order to solve the identified challenges, which limits the implementation of high-vapor-quality flow boiling on surface structures.