Pool Boiling Heat Transfer Performance Research Articles

Effect of micro-/nano-porous thin film surfaces prepared by a hybrid method of etching and electrochemical deposition on pool boiling heat transfer performance

Surfaces created using efficient and inexpensive methods are highly demanded in industrial applications of extremely high temperatures. In this study, Composite Nano-particle Coated Over CuO Filmed (CNCCF) surface is prepared through two processes, first through chemical etching to produce a thin film of CuO over bare Cu surface, and secondly deposition of Ni-Al2O3 composite nano-particle over CuO thin filmed copper surface by electrochemical deposition process. The completed CNCCF surface exhibits favorable characteristics for improved boiling heat transmission, such as wettability, roughness, porosity, etc. An experiment on pool boiling is conducted on the CNCCF and bare Cu surface. DI water at atmospheric pressure is used as the boiling fluid. Findings show that the CNCCF surface exhibits enhanced Critical Heat Flux (CHF) and Boiling heat Transfer Coefficient (BHTC) than bare Cu surface. The increased porosity, roughness, and other properties of the CNCCF surface are the cause of this improvement in CHF and BHTC. A high-speed camera is also used to monitor and analyze bubble behavior during boiling on all surfaces, including the Bare Cu. Further evidence for the enhancement of boiling heat transfer on the CNCCF surface comes from the nucleation site density, departure diameter, and frequency characteristics of bubbles.

Hierarchical sintered porous surfaces with enhanced pool boiling heat transfer performance for high-power cooling applications

Porous surfaces fabricated by sintering maintain good pool boiling heat transfer performances and have the advantages of high processing efficiency and low cost. Hierarchical sintered porous structures (HS) composed of copper mesh and porous column array are fabricated by a sintering process. Chemical oxidation and high-temperature reduction are used to deposit micro/nano coating on HS (NHS). The porous column array induces the capillary value effect and enhances the capillary performances of HS and NHS. The micro/nano coating provides more nucleation sites and further enhances the capillary velocity. The faster capillary velocity and higher volumetric flow rate of HS and NHS result in much higher critical heat flux (CHF) than sintered mesh surfaces (MS). The CHF of NHS reaches 2422.9 kW/m2, which is 43.7 % and 21 % higher than that of MS and HS, respectively. A good linear relationship between the volumetric flow rate and the CHF is observed. Besides, the porous structures greatly enhance the heat transfer coefficient (HTC). The micro/nano coating of NHS has a more obvious enhancement effect on HTC at low heat fluxes. The pool boiling heat transfer performance of HS and NHS is comparable to or even better than those in literature and has the feasibility of application in high-power cooling scenarios.

Pool boiling heat transfer performance of low-GWP refrigerant R-513A on smooth tube

Pool boiling heat transfer performance of low-GWP refrigerant R-513A on smooth tube

Experimental Investigation on Pool Boiling Heat Transfer Performance of Superhydrophilic, Hydrophilic and Hydrophobic Surface

Experimental Investigation on Pool Boiling Heat Transfer Performance of Superhydrophilic, Hydrophilic and Hydrophobic Surface

Pool boiling heat transfer performance of micro-embossing molds for the fabrication of polymer wicks

As flexible heat dissipation devices are urgently needed for flexible electronics, polymers with the advantages of good flexibility, insulation, and low density have attracted wide attention. It would be interesting to fabricate thermal functional structures on polymers to overcome their low thermal conductivity. This study aims to design and fabricate a micro-embossing mold to process polymer three-dimensional microgroove wicks (3D-MWs), which are applied in flexible heat pipes and achieve high thermal conductivity. Three kinds of tungsten steel molds were processed by using two wire electrical discharge machining processes (WEDM), two electrical discharge shaping machining processes (EDSM), and a combination of WEDM and EDSM. The 3D-MWs of the tungsten steel mold were reprinted onto the polymer films by a two-step embossing process. To investigate the effects of microstructures on boiling heat transfer performances, tungsten steel molds fabricated by different methods were tested to reflect the heat dissipation potential of the polymer 3D-MWs. The results showed that the 3D-MWs fabricated by the combination of WEDM and EDSM exhibit good boiling heat transfer performance and high processing efficiency, with a critical heat flux of 1040.1 kW/m2 and a maximum heat transfer coefficient of 38.4 kW/m2·°C. These values are 46% and 611% higher than those of the smooth tungsten steel surface, respectively, making it a superior choice for micro-embossing molds.

Study of orientation effects to pool boiling heat transfer performance from the circular pin fins structure

Increasingly sophisticated technological advances generate heat that needs to be managed properly to ensure the optimality of the operation of these components. One solution offered is the pool boiling cooling method, which has a high heat transfer coefficient. This research aims to study how the orientation angle of the boiling pool affects the heat transfer coefficient. This approach aims to improve cooling effectiveness, especially in the context of moving systems, where the influence of orientation angle is an important factor. In the research related to pool boiling, various orientation angles from 0° to 20° were used on aluminum-based fins in the form of inline pin fins. These fins have a circular shape with a size of 30 mm × 30 mm. The working fluid used in this study is HFE-7100, which has dielectric properties. This study was conducted with heat levels ranging from 10 to 50 W before reaching the Critical Heat Flux (CHF) value. The results show that the orientation angle has a significant impact on the heat transfer coefficient as well as the dynamics of bubble formation. The results also indicate that the greater the orientation angle, the smaller the area of spread and bubble growth that occurs. This decrease in bubble growth area results in an increase in surface temperature. With the circular pin fins test specimen, an increase in surface temperature was found in this study, when the angle θ = 10° amounted to 1.08℃, for the angle θ = 20° amounted to 2.37℃ under the condition of q'' = 55.56 kW/m2. While the highest average value of heat transfer coefficient occurs at angle θ = 0°, the value reaches 3.91 kW/m2∙K and decreases at angle θ = 10° by 3.79%, for angle θ = 20° by 6.56%

Saturated Boiling Enhancement of Novec-7100 on Microgrooved Surfaces with Groove-Induced Anisotropic Properties

The effects of the anisotropic properties (wettability and roughness) of microgrooved surfaces on heat transfer were experimentally investigated during pool boiling using Novec-7100 as a working fluid. The idea for introducing the concept of anisotropic wettability in boiling experiments draws inspiration from biphilic surfaces. The investigation is also motivated by two-phase immersion cooling, which involves phase-change heat transfer, using a dielectric liquid as a working fluid. Very few studies have focused on the effects of surfaces with anisotropic properties on boiling performance. Thus, this study aims to examine the pool-boiling heat transfer performance on surfaces with microgroove-induced anisotropic properties under the saturation condition. A femtosecond-laser texturing method was employed to create microgrooved surfaces with different groove spacings. The results indicated that anisotropic properties affected the heat transfer coefficient and critical heat flux. Relative to the plain surface, microgrooved surfaces enhanced the heat transfer performance due to the increased number of bubble nucleation sites and higher bubble detachment frequency. An analysis of bubble dynamics under different surface conditions was conducted with the assistance of high-speed images. The microgrooved surface with a groove spacing of 100 μm maximally increased the BHTC by 37% compared with that of the plain surface. Finally, the CHF results derived from experiments were compared with related empirical correlations. Good agreement was achieved between the results and the prediction correlation.

Experimental investigation of nucleate pool boiling heat transfer characteristics on modified copper surface via laser-structured microstructures

This study aims to evaluate the performance of pool boiling heat transfer on a structured surface subjected to constant heat flux. A nanosecond laser ablation was used to create different surface profiles on copper samples. Specifically, a series of step-like microstructured surfaces with varying secondary groove widths were fabricated to investigate their effect on pool boiling heat transfer performance of distilled water. The results indicated a significant enhancement in heat transfer performance for the laser-structured surfaces compared to the smooth surface at low heat flux. This improvement was attributed to the increased surface area, nucleation frequency, and nucleation site density. However, at higher heat flux, the surface with a smaller secondary groove width (LS 2) exhibited a decline in heat transfer performance, which was likely due to larger bubble escaping resistance. In contrast, the surface with a larger secondary groove width (LS 1) demonstrated the best heat transfer performance. The current work would help in finding an optimum surface structuring design for gaining higher boiling heat transfer performance which benefits industries dealing with thermal management processes.

Effect of dense packed micro-/nano-porous thin film surfaces developed by a combined method of etching, electrochemical deposition and sintering on pool boiling heat transfer performance

Effect of dense packed micro-/nano-porous thin film surfaces developed by a combined method of etching, electrochemical deposition and sintering on pool boiling heat transfer performance

Pool Boiling Heat Transfer Characteristics of SiO2 and BN Nanoparticles Dispersed Mono and Hybrid Nanofluids.

This study reports an experimental investigation of pool boiling (PB) heat transfer performance of hybrid (two types of particles) and mono (single-particle) nanofluids consisting of Boron nitride (BN) and Silicon dioxide (SiO2) nanoparticles (NPs). While hybrid nanofluids (HNFs) were prepared in a total particle concentration of 0.05 vol.% with four different percentages of these two types of NPs (are 0.01/0.04, 0.02/ 0.03, 0.03/0.02, and 0.04/0.01 (BN vol.%/SiO2 vol.%)), two mono nanofluids (MNFs) of BN and SiO2 nanoparticles were prepared at the same total concentration of 0.05 vol.% for each NP type. Both nanofluids (NFs) were prepared in the base fluid (BF), which is the mixture of 15 vol.% of ethylene glycol (EG) and 85 vol.% of distilled water (DW). Then, the boiling heat transfer performance of these MNFs and HNFs was assessed by experimentation in a pool boiling test rig. The obtained results demonstrated good improvements in critical heat flux (CHF) and burnout heat flux (BHF) of both types of NFs. The CHF increased by up to 80% for BN-based MNF and up to 69% for HNF at 0.04 vol.% BN, which is the maximum percentage of BN into HNF, while the lowest improvement in CHF was 48% for the SiO2-based MNF compared to the BF. Similarly, the BHF was found to increase with the increasing in the loading of BN nanoparticles and a maximum enhancement of BHF of 103% for BN-based MNF was observed. These HNFs and MNFs exhibited significantly improved pool boiling heat transfer performance compared to this BF, and it became lower by increasing the percentage of SiO2 NPs in the HNFs.

Enhancement of the critical heat flux for downward-facing saturated pool boiling on the reticular hollow shell structure surfaces

In-vessel retention (IVR) technology was currently an effective strategy for retaining molten materials in the reactor pressure vessel (RPV) when the nuclear power plants occurred severe accident, further ensuring the integrity of RPV. The effectiveness of IVR depended on the critical heat flux (CHF) of external reactor vessel cooling (ERVC). A novel type of reticular hollow shell structure (RHS) was designed to meet this need. Five RHS surfaces were designed and the pool boiling heat transfer performance were investigated in saturated deionized water, the experimental inclination angles were 5°, 30°, 45°, 60° and 90°. The boiling heat transfer coefficient (BHTC) and CHF were measured by steady-state heating and transient quenching methods. The experiment results showed that the CHF increased with the increase of inclination angles, and the CHF of all RHS surfaces were significantly enhanced compared with the plain surface. The maximum CHF value and the maximum CHF enhancement exhibited on surface 4, with a maximum CHF of 2992.2 kW/m2.When the inclination angle was 30°, the maximum CHF could reach 2338.6 kW/m2, which was 160.3% enhancement over the plain surface. Surface 1 and surface 3 had better BHTCs, and the maximum values were 178.3 kW/(m2·K) and 126.8 kW/(m2·K), respectively, which were much better than other structured surfaces. The RHS could form a gas–liquid conversion system, which was composed of cavities and alternating channels to increase the surface nucleation sitesand accelerate the circulation of cooling water, thus obtained the high CHF and high BHTC characteristics. RHS provided a large enough CHF margin to ensure that the RPV was continuously cooled and its integrity was maintained. Finally, the behavior of bubbles generation, coalescence, sliding and detachment in reticular hollow shell structure were systematically analyzed.

Effect of Novel Cu@ZnO Hybrid Nanofluids on Pool Boiling Heat Transfer Performance

Effect of Novel Cu@ZnO Hybrid Nanofluids on Pool Boiling Heat Transfer Performance

Pool boiling experimental investigation on in-situ hierarchical Cu(OH)2 nanograss

This study fabricated the in-situ Cu(OH)2 hierarchical nanograss surface (HNS) via immersion method for simultaneous enhancement of the critical heat flux (CHF) and heat transfer coefficient (HTC) in diverse experimental conditions. Nanograss stripes were patterned, and then in-situ grown on the copper substrate through the chemical modification. The effect of the Cu(OH)2 HNS on the pool boiling heat transfer performance was systematically examined. Furthermore, the optimized HNS which can exhibit the highest CHF and HTC was identified based on comparative experiments. It is found that the numerous nanoscale cavities existing in the HNS can act as the active nucleation sites for facilitating the boiling process. Experimental results reveal that the HNS can reduce the independent bubble departure diameter, increase the bubble departure frequency and significantly delay the bubble mergence due to much improved capillary pumping and replenishment of cooling liquid. According to the experiments, the CHF on the optimized HNS sample, were improved by 97.8% compared with the smooth surface and the HTC is enhanced to 2.4 W/cm2K, which is equivalent to an augmentation of 25.7% compared to that on smooth surface. Meanwhile, the HNS can improve the heat transfer uniformity and stability with temporal temperature variations less than 1 K at CHF, which is pivotal to the efficient thermal management of miniaturized devices.

Synergistic effect of mixed wettability of micro-nano porous surface on boiling heat transfer enhancement

In this work, a simple immersion technique was created to further enhance the pool boiling heat transfer performance of micro-nano copper foam by modifying its mixed wettability. The SEM images exhibit that the entirely-covered micro/nanostructures can be observed on the super-hydrophilic copper foam, while the hydrophilic-hydrophobic copper foam is covered with nanograss partially. The experiments indicated that the hydrophilic-hydrophobic copper foam showed the best heat transfer coefficient of the all sample surfaces at a high heat flux (>40 W/cm2), which can be as high as 4.15 W/cm2·K. Meanwhile, the critical heat flux (CHF) was measured as 108.32 W/cm2, which was 157.3% higher than that on the smooth surface, and 57%, 33.2% and 37.4% higher than that of untreated, super-hydrophilic, super-hydrophobic copper foams, respectively. Interestingly, due to the unique modification of the surface, the onset of boiling (ONB) on the sample was much reduced from 9 K to 0.5 K. These improvements are due to the increasing nucleation density, the reduced bubble departure diameter and the much shortened bubble period compared to other comparative samples. It is speculated that enhancement of the boiling heat transfer is attributed to the synergistic effect of improved bubble nucleation, the vapor escape, and the liquid replenishment on the designed sample with a mix wettability.

Effect of graphene oxide coating on bubble dynamics and nucleate pool boiling heat transfer

Materials coating has been proved to be an effective mean to increase the number of active nucleating sites, and therefore generate more vapor bubbles and lead to better poolboiling heat transfer performance. In this work, graphene oxide (GO) is coated on a boiling surface by self-assembly method, to enhance critical heat flux (CHF). The pool boiling is carried out on a smooth copper surface to study the effect of GO coating using distilled water as the working fluid along with bubble dynamic visualization. GO coating facilitates bubble nucleation by providing numerous microscale cavities. The visualization investigation of bubble dynamic behavior shows that the CO-coated surface exhibits a higher bubble departure frequency, a smaller bubble departure diameter and smaller bubble diameters in the pool, indicating greatly enhanced heat transfer effects. Meanwhile, the GO-coated surface exhibited a smaller contact angle than the copper surface, revealing that surface becomes more hydrophilic after GO coating. Consequently, GO-coated surface with a coating time of 4 h provides a CHF of 224.3 W/cm2 and a heat transfer coefficient (HTC) of 8.79 W/(cm2·K), representing an improvement of 94.0% in CHF and 83.5% in HTC compared to smooth copper surface.

Electric field inspired alternating surface wettability for enhancing pool boiling heat transfer performance: A lattice Boltzmann method study

Electric field and surfactants have been proven to potentially alter surface wettability on demand. In this work, alternating wettability inspired by an electric field has been used to enhance boiling heat transfer performance in terms of critical heat flux (CHF) over a rough surface by using two-dimensional lattice Boltzmann simulations. In alternating wettability, the surface wettability changes with time between hydrophobic and hydrophilic. The effects of the parameters, including alternating wettability time-period and wettability contrast on the boiling process have been revealed. The simulation results show that for the alternating wettability: when surface is hydrophobic bubble expansion is faster, and then wettability transition to hydrophilic quickly retracts three-phase contact line leading to faster bubble shrinking as compared to constantly hydrophobic and constantly hydrophilic surfaces. Furthermore, the rapid shrinking of the bubble tends to disintegrate vapor film on the surface at high wall superheats, resulting in a 53% enhancement in CHF compared to a constantly hydrophilic surface. The bubble departure takes much longer time for too small/large time-periods of alternating wettability. The CHF increases with time-period, becomes maximum at a certain value and then reduces. The CHF also increases with wettability contrast, becomes largest for hydrophilic and hydrophobic contact angles 55o and 107o, respectively, and decreases with further increase in wettability contrast due to high potential for vapor film formation.

Effect of thermal contact resistance on the CHF and HTC for pool boiling heat transfer

In recent years, there has been increasing interest in the demand for heat dissipation of electronic devices. Constructing micro/nanostructures and using nanofluid for the pool boiling heat transfer have proved to be a notoriously effective method to increase the critical heat flux (CHF) as well as the heat transfer coefficient (HTC). When the tested samples with micro/nanostructures are soldered to the upper of the heated copper block, the CHF boiling curves of the tested samples always shift right, which may be caused by the thermal contact resistance (TCR) from the soldering interface. However, it is rarely for the research to be reported the effect of the thermal contact resistance on the pool boiling heat transfer performance. This paper highlights the effect of the TCR on the CHF and HTC for pool boiling heat transfer by comparing the boiling curve of the non-soldering, the soldering, and the Rohsenow curve. The relationship between the difference in temperature with increased heat flux is established by measuring the TCR of the soldering interface, and the relationship at the different soldering interface morphology has been explored. The results show that the CHF boiling curve with soldering shift right 106–144 % than that of the non-soldering, and the HTC decreases by 45.6–63.5 %. The shifted boiling curve could be corrected by the relationship between the TCR with increased heat flux. However, the boiling curve cannot be corrected by the relationship when the soldering interface has voids. This work demonstrates that the deviation between the boiling curve of soldering with the boiling curve of non-soldering is universal for engineering applications by comparing similar studies. Regardless of whether soldering is used in pool boiling heat transfer experiments, the Rohsenow curve is still an important reference, but the effect of TCR must be considered in the pool boiling curve of soldering.

Synergistic effect of coating copper foam with carbon nanotubes on pool boiling heat transfer performance

Pool boiling heat transfer is a commonly used method for efficient phase change heat transfer. This paper studied the synergistic enhancement of heat transfer performance of pool boiling in deionized water by introducing an MWCNT (multi-walled nanotube) coating on a foam copper frame, and the influence of MWCNT content was explored. The results showed that the MWCNT coating strengthened the critical heat flux (CHF) and heat transfer coefficient (HTC) compared to a polished Cu surface. When 2.4 mg of MWCNTs were deposited, the maximum CHF was reached (785.2 kW·m−2), 3.41 times that of the polished Cu surface; and when 2.8 mg were deposited, the maximum HTC was reached (33.41 kW·m−2· k−1), 2.50 times that of the polished Cu surface. The results show that this heat transfer surface improves the performance of pool boiling heat transfer. A high-speed camera was used to record the bubble state during the boiling process of the pool. A simulation of the physical model in ANSYS Workbench returned the same results as the experiments.

Pool boiling heat transfer enhancement on the hybrid surfaces coupling capillary wick and minichannels

Pool boiling heat transfer can fully utilize the latent heat of the vaporization, to meet the heat dissipation needs of high-power electronic components. In this study, several enhanced hybrid surfaces were designed and processed by sintering spherical copper powder on the minichannels in different ways. The coupled effects of various parameters of capillary wick and minichannels were considered to enhance the pool boiling heat transfer performance of these hybrid surfaces using HFE-7100 as the working fluid. The bubble dynamic behaviors were captured and analyzed by the high-speed camera. The results indicate that the ring groove around the minichannels and the capillary wick have a significant impact on the boiling heat transfer of these hybrid surfaces. This is because the capillary wick provide a large number of nucleation sites and large specific surface area, which can greatly reduce the contact thermal resistance between the capillary wick and the minichannels. At ΔTsub = 30 K, the critical heat flux (CHF) of hybrid surfaces coupling capillary wick and minichannels is up to 147.4 W/cm2, and its maximum heat transfer coefficient (HTC) is 2.69 W/(cm2·K). Compared with minichannels without capillary wick covered, the CHF and HTC are increase by 86.8% and 192.0%, respectively. Furthermore, a correlation for predicting CHF on these hybrid surfaces covered capillary-wick is proposed. Dimensionless parameters such as the subcooled Jakob coefficient (Jasub), the outer surface area enhancement ratio (AER), the particle distribution coefficient (PDC) and the ratio of inner to outer surface area of capillary wick (IOR) are defined to estimate the effect of different factors on the CHF.

Pool Boiling Heat Transfer Performance of R-134a on Microporous Al Surfaces Electrodeposited from AlCl3/Urea Ionic Liquid

Pool Boiling Heat Transfer Performance of R-134a on Microporous Al Surfaces Electrodeposited from AlCl3/Urea Ionic Liquid