Showing papers on "Critical heat flux published in 2022"
37 citations
TL;DR: In this paper, the authors studied the wall heat flux partitioning during the pool boiling of water on thin metallic surfaces and showed that the mechanisms of heat transfer on substrates of small thermal capacity are very different compared to substrates with large thermal capacity.
22 citations
TL;DR: In this article , the saturated pool boiling heat transfer performance on the surface of T-shaped micro-fins was investigated with deionized water as working medium, which showed that the merging of bubbles on the outside of the channel surface could strengthen the vertical and horizontal replenishment of the liquid to dry spot in the channel, thereby delaying the occurrence of critical heat flux.
20 citations
TL;DR: In this paper , a three-tier hierarchical structure is proposed to enhance the critical heat flux (CHF) by defining nucleation sites with microcavities interspersed within hemi-wicking structures.
Abstract: Boiling is an effective energy‐transfer process with substantial utility in energy applications. Boiling performance is described mainly by the heat‐transfer coefficient (HTC) and critical heat flux (CHF). Recent efforts for the simultaneous enhancement of HTC and CHF have been limited by an intrinsic trade‐off between them—HTC enhancement requires high nucleation‐site density, which can increase bubble coalescence resulting in limited CHF enhancement. In this work, this trade‐off is overcome by designing three‐tier hierarchical structures. The bubble coalescence is minimized to enhance the CHF by defining nucleation sites with microcavities interspersed within hemi‐wicking structures. Meanwhile, the reduced nucleation‐site density is compensated for by incorporating nanostructures that promote evaporation for HTC enhancement. The hierarchical structures demonstrate the simultaneous enhancement of HTC and CHF up to 389% and 138%, respectively, compared to a smooth surface. This extreme boiling performance can lead to significant energy savings in a variety of boiling applications.
19 citations
TL;DR: In this article , a comprehensive summarization in using hybrid or hierarchical structures with the adhesion of smart materials for enhancing the heat transfer coefficient (HTC) and critical heat flux (CHF) simultaneously in boiling phenomenon is presented.
Abstract: The study concerns a comprehensive summarization in using hybrid or hierarchical structures with the adhesion of smart materials for enhancing the heat transfer coefficient (HTC) and critical heat flux (CHF) simultaneously in boiling phenomenon. A review of approaches for surface modifications to enhance the pool boiling heat transfer was conducted firstly. Specifically, these include modifications by fabrication of micro/nano structures, addition of micro/nano coatings or porous surfaces, or the combination of the above, which artificially optimize the wettability of the heated surface in advance of the boiling process. As a result, the design of hybrid surfaces can be optimized. Subsequently, great effort was put in introducing the recent development of smart surfaces fabricated by typical methods. The appliance of the smart materials can actively change the wettability characteristics of surfaces during the boiling process. On these basis, the potentials of the promising surface combining micro-nano scaled and wettability hybrid structures with smart materials was discussed. These include the evaluation of the maximum HTC and CHF that could be achieved, the advanced techniques for manufacturing the enhanced surfaces, and the extended applications in diverse fields for the achievement of super high heat flux transportation based on the combined smart surfaces. However, several vital challenges associated with smart surfaces need to be addressed. For example, the rigorous thermal conditions for the wettability transformation on metal oxide films, the weak mechanical property of switchable polymers, the cost and recovery ratio of shape memory alloys (SMAs), and the mismatch of temperature range for the wettability transition in the boiling process, etc. Nevertheless, suggestions have been given in this review to provide solutions in perspective of structure machining, materials selections and fabrication methods. Smart surfaces inspired from the natural environment can act as a crucial role in low carbon energy and environment applications. These include the anti-fogging, anti-icing, oil/water separation, drag-reduction and anti-corrosion for environment protecting, and power generation, anti-conditioning, thermal management, solar cells and nanogenerators for energy-saving purposes.
17 citations
TL;DR: In this paper , the effect of the distribution of nanostructures on the pool boiling heat transfer performance of micro-nano composited surfaces in FC-72 was investigated.
17 citations
TL;DR: In this article, the authors presented a mechanistic and predictive theory for the boiling crisis, combining the thermo-fluidic interaction between bubbles and the stochastic interaction of nucleation sites.
16 citations
TL;DR: In this article , the authors studied the wall heat flux partitioning during the pool boiling of water on thin metallic surfaces and showed that the mechanisms of heat transfer on substrates of small thermal capacity are very different compared to substrates with large thermal capacity.
16 citations
TL;DR: In this paper, a new type of GNP-Fe3O4 hybrid nanoparticles is prepared, and the crystal structure test proves that it has high purity, contains a variety of hydrophilic functional groups, and has a strong binding force between elements.
16 citations
TL;DR: In this article , a set of mathematic models suitable for flow boiling simulation and CHF prediction in rod bundle channels of PWR, including Eulerian two-phase model combined with wall boiling model, were established using CFD method.
15 citations
TL;DR: In this paper , the authors investigated the flow boiling performance of non-closed droplet micro pin-fin arrays and bubbles behaviors in three different regions around micro pins-fins, where deionized water was selected as coolant, circulating under heat flux in the range of 2.51-144.64 W/cm2.
TL;DR: In this paper , a review of the recent developments in the utilization of boiling phenomena in nanofluid as a coolant in the Hyper Vapotron (HV) is presented.
Abstract: Plasma-facing components (PFCs) are used as the barrier to the beam of high heat flux generated due to nuclear fusion. Therefore, efficient cooling of PFCs is required for safety and smooth operation of a fusion reactor. The Hyper Vapotron (HV) is generally used as the heat exchanger to cool down the PFCs during operation. These heat exchangers use pool and flow boiling mechanisms, and hence, their ability is inherently constrained by critical heat flux (CHF). The boiling of nanofluid is very promising as the working fluid in the HV. The efficiency of the HV increases due to the increase in CHF by applying nanofluids. However, the feasibility of nanofluid cooling in fusion reactors needs proper understanding. This paper reviews the recent developments in the utilization of boiling phenomena in nanofluid as a coolant in the HV. Experiments, theoretical studies, significant achievements, and challenges are analyzed and discussed. Finally, important points are indicated for future research.
TL;DR: In this article , the heat transfer characteristics of a one-side heated hypervapotron cooling channel under subcooled flow conditions were analyzed and the effects of system parameters such as the system pressure, sub-cooling, and mass flow rate on heat transfer were analyzed, and prediction performance of existing heat transfer correlations developed for application to the three flow regimes was evaluated.
TL;DR: In this paper , silicon microchannels with microporous decorated sidewalls were applied to enhance water flow boiling heat transfer, especially the critical heat flux (CHF), and an improvement of 228% in effective heat transfer coefficient was achieved in the early nucleate boiling regime at the mass flux of 113 kg/cm2 compared with the plain-wall micro channels owing to the increased nucleation site density on the porous walls.
TL;DR: In this paper, a review of published articles on the thermal performance enhancements of a vapor chamber, which is one of the most-studied two-phase liquid-vapor-based cooling system for high heat-flux-dissipating systems in the last few decades, is presented.
TL;DR: In this article, the authors investigated the pool boiling heat transfer and bubble dynamics over V-shaped open microchannels prepared on copper by ultrafast laser micromachining and found that the critical heat flux and heat transfer coefficient increase with the increase of depth-to-width ratio.
TL;DR: In this article , the effects of solid-liquid interactions on nucleate boiling over super-hydrophilic surfaces are quantitatively illustrated, and an optimal interaction energy coefficient (α = 1.5) for achieving maximal boiling enhancement is obtained.
TL;DR: In this article, porous coatings in microchannels were used to enhance flow boiling heat transfer in HFE-7200 with a plain, micro-milled copper microchannel heat sink at similar operating conditions.
TL;DR: In this article , the authors investigated the pool boiling heat transfer and bubble dynamics over V-shaped open microchannels prepared on copper by ultrafast laser micromachining and found that the critical heat flux and heat transfer coefficient increase with the increase of depth-to-width ratio.
TL;DR: In this article , a two-phase heat spreader with a liquid-vapor phase change was demonstrated to have a heat removal capability of 552 W/cm2 from an area of 25 mm2 with a temperature increase of less than 8 K, corresponding to a heat transfer coefficient of 732.5 kW/m2·K.
Abstract: Many of the advanced technologies, e.g., microprocessors, laser and radar, and power transmitters and amplifiers, are becoming increasingly dependent on the ability to dissipate the enormous amount of waste heat in extremely small areas. Two-phase heat spreaders utilizing the liquid-vapor phase change are appealing due to the high performance and potentially low cost. However, thin film evaporation is limited by the capillary dry-out of wicking structures. We demonstrate here an ultra-high thermal conductance and high flux heat spreader enabled by a capillary-driven liquid film boiling process on a hierarchical mesh wicking structure. By manipulating liquid wicking flow and vapor bubble escape, liquid film boiling is demonstrated to have a heat removal capability of 552 W/cm2 from an area of 25 mm2 with a temperature increase of less than 8 K, corresponding to a heat transfer coefficient of 732.5 kW/m2·K. The effective thermal conductivity of the 1-mm-thick two-phase heat spreader is larger than 104 W/m·K.
TL;DR: In this article , porous coatings in microchannels were used to enhance flow boiling heat transfer in HFE-7200 with a plain, micro-milled copper microchannel heat sink at similar operating conditions.
TL;DR: In this article , the coupling effect of a uniform electric field and the microstructured surfaces on pool boiling in FC-72 at the liquid subcoolings (Δ T sub ) of 5 K, 15 K, 25 K, and 35 K was studied.
TL;DR: In this paper, the coupling effect of a uniform electric field and the microstructured surfaces on pool boiling in FC-72 at the liquid subcoolings (ΔTsub) of 5 k, 15 k, 25 k, and 35 k was studied.
TL;DR: In this paper , the influence of the operating parameters in terms of mass flux, heat flux and saturation pressure on the flow boiling heat transfer coefficient is investigated and discussed, and the assessment of predictive methods is carried out for experimental data not belonging to stratified flow and post-dry-out heat transfer, that could not be predicted by conventional flow pattern maps.
TL;DR: In this article , the authors used dimensional analysis based on Python code to develop new ONB correlations that reflect the influence of system parameters, with the results indicating that the flow rate and degree of subcooling are proportional to the ONB heat flux because increasing these factors improves the forced convection heat transfer and increases the condensation rate.
Abstract: Abstract The onset of nucleate boiling (ONB) is the point at which the heat transfer mechanism in fluids changes and is one of the thermo-hydraulic factors that must be considered when establishing a cooling system operation strategy. Because the high heat flux of several MW m −2 , which is loaded within a tokamak, is applied under a one-side heating condition, it is necessary to determine a correlative relation that can predict ONB under special heating conditions. In this study, the ONB of a one-side-heated screw tube was experimentally analyzed via a subcooled flow boiling experiment. The helical nut structure of the screw tube flow path wall allows for improved heat transfer performance relative to plain tubes, providing a screw tube with a 53.98% higher ONB than a plain tube. The effects of the system parameters on the ONB heat flux were analyzed based on the changes in the heat transfer mechanism, with the results indicating that the flow rate and degree of subcooling are proportional to the ONB heat flux because increasing these factors improves the forced convection heat transfer and increases the condensation rate, respectively. However, it was observed that the liquid surface tension and latent heat decrease as the pressure increases, leading to a decrease in the ONB heat flux. An evaluation of the predictive performance of existing ONB correlations revealed that most have high error rates because they were developed based on ONB experiments on micro-channels or plain tubes and not under one-side high heat load conditions. To address this, we used dimensional analysis based on Python code to develop new ONB correlations that reflect the influence of system parameters.
TL;DR: In this article , the authors investigated critical heat flux (CHF) for sub-cooled flow boiling of n-Perfluorohexane based on results of pre-launch Earth-gravity Mission Sequence Tests (MSTs) of the Flow Boiling and Condensation Experiment (FBCE), which was launched to the International Space Station (ISS) in August 2021.
TL;DR: In this paper , an experimental investigation of flow boiling in a horizontal narrow microchannel with hydraulic diameter of Dh = 952 μm was conducted, and the boiling curves, heat transfer coefficients, bubble behaviors and heat transfer enhancement mechanism were discussed with the variation of heat flux, mass flux and inlet temperature.
TL;DR: In this article , a parametric analysis on the two-phase local heat transfer coefficients was conducted for channel mass fluxes from 415 kg/m2s to 1153 kg/ m2s and saturation temperatures of 30.5 ∘C and 40.5∘C.
TL;DR: In this paper , a combination of chemical etching and heat treatment processes is employed to make the bare copper surface hydrophobic in nature, with the modification of wettability, a different micro-structured feature is developed on the surface.
TL;DR: In this paper , a new wick comprised of silicon micro-pinfin arrays is explored to significantly enhance the flow boiling heat transfer performance, and the overall heat transfer coefficient is substantially increased up to 75%.