In this paper, we quantified the heat transfer coefficient (HTC) of Fe3O4 aqueous nano-suspension at various mass concentrations of 0.05% 0.2%. The potential role of operating parameters including ...heat flux perpendicular to the surface (HF), concentration of the nanoparticle (NP), strength of magnetic field (MF), zeta potential and concentration of a specific surfactant on HTC, critical heat flux (CHF) and transient fouling resistance of the surface was identified. Results showed that MF can lower the fouling resistance providing that the nano-suspension is stable. It was shown that in this case, the HTC value was also promoted. However, the enhancement of HTC strongly depended on the zeta potential value. Likewise, by increasing the NP concentration, the CHF value was augmented, while the HTC was promoted u to wt. % = 0.15 and then decreased at wt. % = 0.2. This behavior was attributed to the existence of a thermal resistance on the surface. Notably, the bubble formation on the surface was intensified due to the MF, which was attributed to the formation of irregularities and micro-cavities due to the deposition of the NPs.
•The pool boiling heat transfer to Fe3O4/water nanofluid was conducted.•Critical heat flux and heat transfer coefficient were quantified in pool boiling.•Influence of magnetic field on boiling thermal performance was analyzed.•Bubble formation under the magnetic field was visualized.
Pool boiling with high energy conversion efficiency is critical to steam generation, electronics cooling, water purification, and other energy applications. Great efforts have been taken to the ...design and fabrication of high-performance pool boiling systems to meet the requirements of high heat flux applications. Three-dimensional complex structures (3D-CS) that can suppress wall superheat at the onset of nucleate boiling, enhance the heat transfer coefficient and critical heat flux are taken as an effective means to enhance the pool boiling performances. Relatively recent advances in the fabrication of 3D-CS have led to exciting enhancements in pool boiling performances and a better understanding of the underlying science. The superiority of 3D-CS in pool boiling heat transfer is mainly attributed to the larger heat transfer area, more nucleation sites, better bubble dynamics, and faster liquid rewetting rate, etc. In this review, the structural characteristics and pool boiling enhancement of 3D-CS are reviewed from the perspective of fabrication methods. Traditional machining methods, special machining methods, and other machining methods used for fabricating 3D-CS are introduced and their advantages and disadvantages are summarized. Emphasis is on the influence of fabrication methods on pool boiling enhancement of 3D-CS, which is beneficial to the application and commercialization of pool boiling systems. Moreover, some challenges and research recommendations of 3D-CS are presented for future studies.
•A review on pool boiling enhancement of three-dimensional complex structures (3D-CS) is presented.•The structural characteristics of 3D-CS are reviewed from the perspective of fabrication methods.•Almost all the fabrication methods used to fabricate 3D-CS are summarized.•The influence of fabrication methods on pool boiling enhancement of 3D-CS is discussed.
With recent advances in micro- and nanofabrication, superhydrophilic and superhydrophobic surfaces have been developed. The statics and dynamics of fluids on these surfaces have been well ...characterized. However, few investigations have been made into the potential of these surfaces to control and enhance other transport phenomena. In this article, we characterize pool boiling on surfaces with wettabilities varied from superhydrophobic to superhydrophilic, and provide nucleation measurements. The most interesting result of our measurements is that the largest heat transfer coefficients are reached not on surfaces with spatially uniform wettability, but on biphilic surfaces, which juxtapose hydrophilic and hydrophobic regions. We develop an analytical model that describes how biphilic surfaces effectively manage the vapor and liquid transport, delaying critical heat flux and maximizing the heat transfer coefficient. Finally, we manufacture and test the first superbiphilic surfaces (juxtaposing superhydrophobic and superhydrophilic regions), which show exceptional performance in pool boiling, combining high critical heat fluxes over 100W/cm2 with very high heat transfer coefficients, over 100kW/m2K.
Functionalized interfaces enhancing phase-change processes have immense applicability in thermal management. Here, a methodology for fabrication of surfaces enabling extreme boiling heat transfer ...performance is demonstrated, combining direct nanosecond laser texturing and chemical vapor deposition of a hydrophobic fluorinated silane. Multiple strategies of laser texturing are explored on aluminum with subsequent nanoscale hydrophobization. Both superhydrophilic and superhydrophobic surfaces with laser-engineered microcavities exhibit significant enhancement of the pool boiling heat transfer. Surfaces with superhydrophobic microcavities allow for enhancements of a heat transfer coefficient of over 500%. Larger microcavities with a mean diameter of 4.2 μm, achieved using equidistant laser scanning separation, induce an early transition into the favorable nucleate boiling regime, while smaller microcavities with a mean diameter of 2.8 μm, achieved using variable separation, provide superior performance at high heat fluxes. The enhanced boiling performance confirms that the Wenzel wetting regime is possible during boiling on apparently superhydrophobic surfaces. A notable critical heat flux enhancement is demonstrated on superhydrophobic surfaces with an engineered microstructure showing definitively the importance and concomitant effect of both the surface wettability and topography for enhanced boiling. The fast, low-cost, and repeatable fabrication process has great potential for advanced thermal management applications.
Multiwalled carbon nanotubes (MWCNTs) exhibit outstanding physical properties, including high thermal conductivity, excellent mechanical strength, and low electrical resistivity, which make them ...suitable candidates for a variety of applications. The work presented in this paper focuses on the pool boiling performance of refrigerant R-134a on microporous Cu-MWCNT composite surface layers. A two-stage electrodeposition technique was used to fabricate Cu-MWCNT composite coatings. In order to achieve variation in the surface properties of the Cu-MWCNT composite surface layer, electrodeposition was carried out at various bath temperatures (25 °C, 30 °C, 35 °C, and 40 °C). All surfaces coated with the Cu-MWCNT composite demonstrated superior boiling performance compared to the uncoated surface. Heat transfer coefficient (HTC) values for Cu-MWCNT composite surface layers, prepared at bath temperatures of 25 °C, 30 °C, 35 °C, and 40 °C, exhibited improvements of up to 1.75, 1.88, 2.06, and 2.22, respectively, in comparison to the plain Cu surface.
•Study explores pool boiling of HFE-7100 on copper surfaces.•Heat transfer coefficient improves with increasing roughness.•An optimal hole diameter and pitch for artificial nucleation sites gives ...best heat transfer.•Combination of roughness and hole pattern further improves the heat transfer.
This study explores pool boiling of HFE-7100 on copper surfaces. The key objective of this study was to examine the effects that surface modifications have on nucleate boiling performance. The surface enhancements studied are roughness, artificial nucleation sites, and a combination of both. Observing roughness between 0.480 μm to 7.564 μm shows that the heat transfer coefficient improves with increasing roughness. Observing hole diameters from 1 mm to 3 mm and hole pitch, or spacing to diameter ratio, from 1.75 to 3.5; a configuration with a hole diameter of 1 mm and pitch of 2.5 provides the best improvement to heat transfer coefficient compared to a bare surface with a roughness of 0.480 μm, while the configuration with a hole diameter of 1 mm and pitch of 3.5 provides worse heat transfer coefficient compared to a bare surface with a roughness of 0.480 μm. Applying a roughness to a hole pattern also improves the heat transfer coefficient with increasing roughness compared to both a bare surface with a roughness of 0.480 μm, as well as to the hole pattern alone. The majority of the surface enhancement modes yield overall improvements in heat transfer coefficient. The introduction of surface enhancement decreases critical heat flux across all samples.
•The CHF of coupled rectangular copper column surfaces is exceeding four times that of smooth surfaces.•Coupled micro-pin-finned surfaces could effectively manipulate bubble distribution and obtain a ...higher CHF.•The CHF of coupled surfaces increases by 19.32% and 313.06% compared with the PF and SS surface.•Bubbles are created in hydrophilic areas, and routes between copper columns supply liquid and hinder bubble coalescence.•The vapor column spacing coefficient and lattice width coefficient are presented to analyze the boiling heat transfer characteristics.
The performance of identical hydrophilic-hydrophobic coupled micro-pin-finned surfaces was evaluated using FC-72 as the working fluid in pool boiling experiments. Three hydrophilic and hydrophobic coupled rectangular copper column surfaces (HH4, HH9, and HH16) were constructed to analyze their boiling heat transfer properties. By integrating the micro-pin-finned surface (PF) and the smooth surface (SS), the impact of various subcoolings (0 K, 15 K, and 25 K) on the critical heat flux (CHF) was explored. Surface HH16 showed the greatest sensitivity to subcooling effects on CHF, followed by HH9 and HH4, respectively. For HH9, the CHF at ΔTsub = 0 K, 15 K, and 25 K, reached 69.6 W·cm−2, 84.2 W·cm−2, and 93.7 W·cm−2, respectively. In comparison to other surfaces (PF, HH4, HH16), the CHF of HH9 climbs by 19.32 %, 8.75 %, and 10.8 % at saturated boiling, respectively. A high-quality camera captured bubble dynamics during the experiments. The results reveal that the hydrophilic and hydrophobic coupled micro-pin-finned copper surface has a greater critical heat flux (CHF) than the standard rectangular micro-pin-finned surface, although heat transfer performance (HTC) drops marginally (both saturated and subcooled boiling). Visual monitoring demonstrates that these coupled surfaces effectively prevent bubble coalescence during subcooled boiling. Additionally, this novel surface design may serve as an effective strategy to reduce drying and delay the onset of boiling crises. The CHF improvement of the HH9 on SS surface was 313.06 %, significantly higher than the 246.17 % of PF on SS, marking a performance increase of 66.89 %. The influence mechanism of the Lattice width coefficient and the Vapor column spacing coefficient on CHF were analyzed. Fluid replenishment and bubble formation behavior were applied to clarify the strengthened heat transfer and CHF triggering mechanism on the surface of the hydrophilic and hydrophobic coupled rectangular micro-pin-finned copper column surface.
Evaluating boiling heat transfer enhancement depends on reliable reference values in the form of boiling curves and critical heat flux (CHF) values. Typically, the evaluation is performed in pool ...boiling conditions with water at atmospheric pressure. Literature includes a wide scatter in reference values, prompting this study to comprehensively evaluate boiling performance and CHF on reference surfaces to investigate the scatter's origin and set a definitive reference value. The study recorded 125 boiling curves and CHF values on nominally identical bare copper surfaces, establishing an average boiling curve and mean CHF value. Despite consistent experimental conditions, the recorded CHF values displayed significant variability with a mean CHF of 1112 ± 102 kW m−2 and a scatter from 902 kW m−2 (−19 % of average CHF) to 1339 kW m−2 (+25 % of average CHF). Using Rohsenow's correlation on the average boiling curve, a Csf factor of 0.0151 was obtained. The acquired CHF data is proposed to serve as a foundational benchmark for future research in enhancing pool boiling heat transfer.
Display omitted
•Measurement of 125 boiling curves on nominally identical copper samples.•Average CHF determined as 1112 kW m−2 ± 102 kW/m−2.•Determination of the average boiling curve for water boiling on bare copper.•Fitting of Rohsenow's correlation, yielding average Csf = 0.0151.•Compilation of a CHF database as a foundational benchmark for future studies.
In this study, a stable hydrophilic thin layer resembling SiOx is formed on the copper surface by combining plasma polymerization using hexamethyldisiloxane (HMDSO) and Ar plasma activation. The ...effect of coating on the Heat Transfer Coefficient (HTC) and Critical Heat Flux (CHF) at two different subcooling temperatures is investigated through pool boiling experiments. It is found that the HTC and CHF of the modified surface improved by 42 % and 97 %, respectively. The chemical composition of the coating, as well as changes in surface roughness, wettability, and porosity, are studied using the Scanning Electron Microscope (SEM), Energy Dispersive X-ray spectrometer (EDX), Fourier Transform Infrared (FT-IR) spectroscopy, and contact angle measurement. The boiling/cooling experiments for the plasma-coated surface show good stability, demonstrating that the surface characteristics remain stable even after three boiling/cooling cycles.
Many methods for enhancing nucleate pool boiling have been proposed to improve the two-phase heat transfer performance in recent years. This article offers a comprehensive comment from published ...literature in terms of the surface modification of reinforcing heat transfer. Two types of surface modification regarding enhancement of boiling heat transfer coefficient and critical heat flux are categorized for the first time in this paper. The first and most widespread way is artificially changing the characteristics of the surface in advance to improve boiling performance, such as structured surface and surface coating with nanoparticles, namely, the “passive” technology. Oppositely, the “active” one on boiling enhancement seems to have more potential for development and it is favored by some researchers. In brief, the transformation of geometrical shape or characteristics such as wettability spontaneously occurs during boiling, the critical heat flux would thus be delayed. The heat transfer performance, as a result, would be significantly ameliorated. This kind of “smart surface” is usually made up of specific shape memory alloy, polymers, metallic oxides, etc. The mechanisms of boiling enhancement regarding modified surfaces are also reviewed, the capillary wicking, for instance, plays vital role in it. Moreover, various surfaces are presented with emphasis on their advantages/disadvantages. Through the analysis and comparison of the two kinds of modified surfaces, this review also points out some challenges existing in the current studies concerning this topic, such as numerical study, which are worth solving or optimizing to efficiently and economically improve the boiling heat transfer in future.
•Pool boiling enhancement by the modified passive and active surface are reviewed.•The critical factors for boiling enhancement and mechanisms are analyzed.•Smart surfaces have promising applications although related study is rare.•Opportunity and challenge coexist for pool boiling enhancement techniques.
PDF
