Pool Boiling Heat Transfer Characteristics Research Articles

Analysis of pool boiling heat transfer characteristics on copper-based structured surfaces modified with superhydrophilic, hydrophobic, superhydrophobic and hybrid biphilic properties

This study involves the fabrication and characterization of original, hydrophobic, superhydrophilic, superhydrophobic and hybrid biphilic pattern coupled with the flat and pillar-structured surfaces. The boiling performance of the seven wettability structured surfaces is experimentally and numerically investigated, aiming at analyzing the boiling mechanism of wetting pattern coupled with structures. The findings indicate that coupling superhydrophobicity pillar structure surface (SHO-PS) result in an excellent boiling performance, the superhydrophilicity have difficulty in improving the heat transfer coefficient and critical heat flux. Analysis of the bubble dynamics behaviors reveals a strong positive correlation between the bubble nucleation sites and bubble departure diameter, except for hydrophobic flat structured surface (HO-FS) and superhydrophobicity pillar structured surface (SHO-PS), which exhibit the negative correlation. The bubble departure frequency shows a linear correlation with the contact angle of all the modified surfaces. In the simulation, it is observed that the similar bubble dynamic behaviors in experiment.

Experimental study on heat transfer characteristics of R245fa pool boiling outside horizontal tubes

Full-liquid evaporator is an important part of the Organic Rankine Cycle (ORC). It is of great guiding significance to study the pool boiling heat transfer characteristics (high-temperature level) of the evaporator heat exchange tube for evaporator design. The pool boiling heat transfer characteristics (high-temperature level) of working fluid R245fa outside smooth tube and fish-scale tube are analyzed. The outcomes exhibit that the overall Heat Transfer Coefficient (HTC) of the smooth tube is 1.9–3.9 kW m−2 K−1, and the fish-scale tube is 3.8–4.3 kW m−2 K−1 when the saturation temperature of organic working medium R245fa is 80.5 °C. The HTC outside the fish scale tube is 1.45–3.13 instances that of the smooth tube. The external HTC of the smooth tube and fish-scale tube increases with the increase of heat flux, but the strengthening rate decreases. After the outer wall of the heat exchange tube used in the ORC evaporator is strengthened, the water velocity in the tube increases, which can not only strengthen the heat exchange in the tube but also play an anti-scaling effect.

Enhanced pool boiling heat transfer characteristics on microstructured copper surfaces coated with hybrid nanofluid

Enhanced pool boiling heat transfer characteristics on microstructured copper surfaces coated with hybrid nanofluid

Corrosive effect on saturated pool boiling heat transfer characteristics of metallic surfaces with hierarchical micro/nano structures

Surface modification is of critical interest to enhance boiling heat transfer in terms of heat transfer coefficient or critical heat flux (CHF), which is significantly affected by distinct surface morphology and wettability and it can improve the efficiency and safety of equipment. Furthermore, actual service environment may cause severe corrosion to the processed structured surfaces while its consequence on boiling heat transfer is still obscure. In this article, comprehensive researches are conducted to unravel corrosive effect on metallic samples made of stainless steel (SS) and Inconel materials with microstructures. Different constructions (i.e., microgroove, microcavity and micropillar array) and characteristic dimensions (∼20, 50 μm) of microstructure, various duration time (up to 300 days) and pH values (∼7.0–8.5) of corrosive environment are compared thoroughly. Conclusions can be drawn that not all microstructures can enhance pool boiling heat transfer characteristics, especially in terms of CHF values. More importantly, CHF value of SS microgroove sample firstly increases from 60.94 to 94.09 W·cm−2 in 50 days, then decreases to 47.77 W·cm−2 in 300 days, which can be attributed to competition result between formation of hierarchical micro/nano structure with enhancing wicking capability and chemistry condition with increasing contact angle. In addition, distinct bubble dynamics during pool boiling is also analyzed. The insights obtained from this article can be used to guide surface modification method and to reveal evolvement rule of engineered metallic surface in highly corrosive and harsh boiling heating transfer environment.

POOL BOILING HEAT TRANSFER CHARACTERISTICS OF POROUS NICKEL MICROSTRUCTURE SURFACES

Pool boiling is an effective heat dissipation approach in electronic cooling, battery thermal management, etc. This study used the electrochemical deposition method to fabricate one smooth nickel specimen (named Ni-smooth) and three specimens with a porous nickel-stacked structure. The three porous specimens were created with deposition current densities of 0.5 A·cm<sup>-2</sup> (named Ni-0.5), 2.0 A·cm<sup>-2</sup> (names Ni-2.0), and 5.0 A·cm<sup>-2</sup> (named Ni-5.0), respectively. The four samples underwent microstructural characterization via scanning electron microscopy. The increasing current density led to the porous nickel surface exhibiting a more distinct pore structure, and the nickel sphere grains became more refined, developing a loose "mound-like" structure. A marked increase in the nickel film thickness was also observed. Through visual experiments, we evaluated their wettability, and through pool-boiling experiments, we tested their boiling heat-transfer properties. Our findings suggest that samples incorporating a porous nickel structure consistently outperform unmodified samples regarding heat-transfer efficiency. Specifically, sample Ni-0.5A demonstrated the most optimal boiling heat-transfer performance, evidenced by a 32.2% reduction in temperature at the onset of boiling, a 19.9% increase in critical heat flux density, and a 78.6% larger maximum heat-transfer coefficient compared to the smooth nickel sample. These marked improvements are intrinsically linked to the specific characteristics of the porous nickel structure. The higher performance of samples Ni-0.5 can be attributed to the presence of additional nucleation sites within the porous structure and the formation of smaller micro-crystalline dendritic constructs due to the specific current density applied during electrodeposition. Understanding this relationship between surface characteristics and electrodeposition is essential in maximizing heat-transfer efficiency.

PRESSURE EFFECT ON POOL BOILING HEAT TRANSFER CHARACTERISTICS OF HIGH-VOLATILE LIQUIDS WITH STRUCTURED SURFACE

The study of enhancement of the heat transfer during boiling and an increase of the critical heat fluxes (CHF) have a great importance in design of the modern and cost-effective heat transfer devices for thermal management of microelectronics, cryogenics and refrigeration, and the power electrical engineering industry. In this work we present the results of the experimental studies of the heat transfer and CHF during the pool boiling of refrigerants R113, RC318, and dielectric liquid HFE-7100 on a structured surface under saturation conditions in the range of reduced pressures 0.03-0.36. The effect the heat flux and pressure on the boiling heat transfer coefficient was studied. It is shown that the correlation of Yagov predicts with an accuracy of ± 35% the CHF for pool boiling of highly volatile liquids on structured surfaces in a wide range of reduced pressure.

Enhanced nucleate pool boiling heat transfer on CNTs-Cu nanoparticles-coated surfaces: Effects of sintering temperature and CNTs composition on pool boiling behavior

The present study involves the experimental investigation of pool boiling heat transfer characteristics on CNTs-Cu nanoparticles-coated heating surfaces. The advantages of coating the mixture of infinitesimal CNTs with Cu particles on the copper surface are to generate the active nucleation site density by porous structures and enhance the thermal conductivity of the heating surfaces. To explore the effects of sintering temperatures and CNTs composition on pool boiling behavior, we fabricated the boiling test sections under the sintering temperatures of 700, 750, and 800 °C for four different CNTs compositions of 0.0CNTs-100Cu, 0.2CNTs-99.8Cu, 0.3CNTs-99.7Cu, and 0.5CNTs-99.5Cu in wt.%. We first analyzed the surface morphologies, that is, the average pore size, porosity, and pore density, to characterize each tested sample. Pool boiling experiments were later conducted under atmospheric pressure using water to obtain the pool boiling curves and bubble dynamics for different sintering temperatures and CNTs composition. Based on the experimental analysis, nucleate boiling heat transfer enhancement was interpreted in relation to the sintering temperature with surface morphologies and CNTs composition in relation to improved pore density. Compared to the bare copper surface, the achieved maximum enhancement for boiling heat transfer coefficient and critical heat flux were 3.86 and 1.49, respectively, when a 0.5CNTs-Cu-coated surface sintered at 800 °C was applied.

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.

Augmentation of pool boiling heat transfer on tube bundles using metal foam

Pool boiling on a tube bundle is one of the most important heat transfer modes in several industrial applications, including steam generators, shell and tube heat exchangers for waste heat recovery, and desalination. Although several enhanced tubes (e.g., external micro-finned tubes) have been extensively studied and commercialized, the studies that pertain to the metal foam enhanced tube bundles are limited in the open literature. The objective of the present study is to perform an experimental study to analyze the pool boiling heat transfer characteristics of a metal foam tube bundle and compare its performance with that of a tube bundle with no enhancement. The performance of the metal foam tube bundles with different porosities (81%, 75%, and 62%) is compared against the conventional bare tube bundle. The results showed that the heat transfer coefficients of the metal foam tube bundles are 100–212% higher than those of the bare tube bundle. Among the different porosities, metal foam with 75% porosity showed a higher heat transfer coefficient. Furthermore, the wall temperature of the metal foam tubes is nearly 5–14⁰C lower than that of the bare tubes. When compared with a tube pitch of 25.4 mm, a tube pitch of 19.05 mm showed a maximum of 9% and 14% enhancement in bare and metal foam tube bundles, respectively.

Experimental investigation and correlation analysis of pool boiling heat transfer on the array surfaces with micro-fins using FC-72 for the electronic thermal management

Pool boiling heat transfer characteristics were investigated on the both homogeneous and fractal array micro-pin-finned surfaces using FC-72 as working fluid. Two distinct fractal geometry pattern surfaces (Array4 and Array9) were designed to further explore their boiling heat transfer performance. The effect of different subcoolings (0 K, 15 K and 25 K) has also been analyzed combining fractal array surfaces. Bubble dynamics were captured using a high-speed camera. The results present the the array micro-pin-finned surfaces with less heat transfer area ratio can achieve similar or even higher CHF compared to the uniform micro-pin-finned surface (PF0.3–0.2–2), especially for subcooled boiling (ΔTsub = 25 K). Notably, bubbles nucleate and grow prior to reaching the micro-pin-finned unit region. This phenomenon is evident in visual images, indicating that the fractal array effectively impedes bubble coalescence, particularly during subcooled boiling. Besides, this fractal array surface can provide liquid supply channels and prevent dry-out. The mechanism behind the heat transfer enhancement and CHF triggering is elucidated based on liquid replenishment and bubble coalescence behaviors. A CHF prediction model was established considering the effect of liquid subcooling, rectangular array distribution, and micro-fins feature size. And the prediction results from this model show well agreement with experimental values and data points from literature, with mean absolute deviation being less than ± 15 %.

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.

Experimental study on boiling heat transfer of γ-Fe2O3 nanofluids on a downward heated surface

Abstract This investigation reports on the experimental outcomes of the pool boiling heat transfer characteristics, specifically on the downward heated surface, concerning reverse osmosis water and γ-Fe2O3 nanofluids. To conduct the pool boiling experiments, γ-Fe2O3 nanofluids were prepared with variable concentrations ranging from 2 mg/L to 10 mg/L. Analysis of the experimental data revealed that a concentration of 5 mg/L yielded the greatest enhancement effect on critical heat flux (CHF), with an increase of 13.5 %. However, the results also indicated that excessively high concentrations of nanofluid had a negative impact on CHF enhancement. The impact of nanofluids on heat transfer performance was investigated by analyzing the observed bubble behavior during the boiling process, measuring the drop angle and surface roughness post-experiment, and characterizing the heated surface morphology via scanning electron microscopy (SEM). Through these methods, the underlying mechanism behind the impact of nanofluids on heat transfer performance was identified and analyzed.

Experimental determination of the role of roughness and wettability on pool-boiling heat transfer of refrigerant

In order to investigate pool boiling heat transfer characteristics of refrigerants on different surfaces, an experimental rig is established and verified in this study. The pool boiling heat transfer experiment is conducted with R134a at three saturation temperatures. Six surfaces with Ra roughness ranging from 0.133 to 5.742 μm and two types of wettability are tested in the study. The heat flux varies from 40 to 280 kW/m2. Experimental results indicate that higher roughness is favorable to boiling heat transfer. Shieldex coating on copper surfaces can deteriorate heat transfer by 20% approximately. Visualization analysis was carried out with a high-speed camera to study bubble behavior. A new-found mode of bubble departing was observed at lower heat flux. Besides, the data were correlated in the form of Rohsenow correlation, and comparison and supplement are concluded based on data obtained in this study.

Electrowetting-assisted pool boiling heat transfer characteristics under low gravity conditions

In pool boiling under low gravity conditions, the vapor bubbles remain attached to the heating surface, which deteriorates the heat transfer rate. The present work demonstrates the integration of the electrowetting (EW) technique to resolve the bubble departure problem in pool boiling at low gravity conditions. A phase-field-based numerical method with a dynamic contact angle model has been implemented in COMSOL Multiphysics (V5.3) to investigate the problem. The bubble dynamics in the electrowetting integrated pool boiling for low gravity conditions are analyzed at various frequencies for different voltage waveforms, i.e., square, sinusoidal, and triangle. The EW technique increases the departure frequency of the bubble and the heat transfer rate compared to the conventional pool boiling. The sinusoidal voltage waveform shows the best performance among different voltage waveforms, producing 119.3% higher bubble departure frequency and 74.3% heat transfer enhancement than the conventional pool boiling.

Pool Boiling Heat Transfer Characteristics of New and Recycled Alumina Nanofluids

This paper reports an experimental investigation of the heat transfer features of new and recycled Alumina (Al2O3) nanofluids (NFs) in the pool boiling (PB) system. The mixture of ethylene glycol (EG) and distilled water (DW) is selected as the base fluid (BF), and NFs samples of two low concentrations (0.01 and 0.05 vol.%) of Al2O3 nanoparticles were prepared. Furthermore, the characteristics of the prepared NFs are evaluated to investigate the heat transfer performance as well as the reusability of the NFs for long-term applications and recycling consideration. Although there have been a large number of boiling studies with NFs, the current study is the first of its kind that addresses the mentioned operation conditions of recycling NF samples. The results are compared with the relevant BF in terms of properties, critical heat flux (CHF), burnout heat flux (BHF), and the convection coefficient of the Al2O3 NFs in the PB system. The results showed good enhancements in both CHF and BHF of these NFs yielding up to 60% and 54% for BHF at 0.05 vol.%, respectively. The reusage of the previously used (recycled) Al2O3 NF showed a considerable increase in heat transfer performance compared to base fluids but slightly lower than the newly prepared one. The results of the reused nanofluids demonstrate the great prospects of their recyclability in heat transfer systems and processes such as in pool boiling.

Pool boiling heat transfer characteristics of a stepped microchannel structured heating surface

Structured heating surfaces modify the bubble ebullition cycle in pool boiling, thereby enhancing heat transfer. The present work explores an innovative structured heating surface for heat transfer enhancement in pool boiling. Two types of microstructured, i.e., stepped microchannels (SMC) and stepped-segmented microchannels (SSMC) surfaces, have been fabricated on a heating surface, and their heat transfer characteristics are experimentally investigated. Saturated pool boiling experiments are performed with deionized water at atmospheric pressure, and the performance of both the structured surfaces is compared with a plain copper heating surface. All three heating surfaces are fabricated using a wire-EDM process with the same footprint area of 10 × 10 mm2. The SSMC structured surface exhibits the maximum heat transfer coefficient (HTC) and results in 296% heat transfer enhancement compared to the plain copper surface. The surface also makes a 224% enhancement in the critical heat flux (CHF) compared to the plain copper surface. Compared to the plain copper surface, the SMC structured surface shows an enhancement of 200% in HTC and 162% in CHF. For the same operating conditions, the SSMC structured surface shows better pool boiling heat transfer characteristics than the similar structured surfaces reported in the literature. More nucleation sites, better bubble evolution along the expanding cross-section stepped channel, and efficient rewetting of the heating surface contribute to the excellent thermal performance of the SSMC structured surface.

Pool boiling heat transfer characteristics of R-1233zd(E) on smooth tube subject to POEC-220 lubricant oil

Pool boiling heat transfer characteristics of low pressure and low GWP refrigerant R-1233zd(E) alternative to R-123 and R-245fa on a smooth copper tube are investigated with the influence of POE (polyolester)-lubricant oil POEC-220 (220 cSt). The experiments were conducted at a saturation temperature of 10°C, and 26.7°C in 10−90 kWm−2 heat flux range. The mass concentration of POEC-220 oil varied from 1−10%. The obtained results exhibit that the addition of POE lubricant to the pure low-pressure refrigerant R-1233zd(E) degraded the heat transfer performance. The average degradation of heat transfer coefficients (HTCs) for mass concentration of oil 1%, 3%, 5%, and 10% are 9.40%, 7.16%, 15.31%, and 42.87% respectively when compared to that of pure refrigerant. It is found that the nucleation sites are especially reduced at the bottom part of the test tube. Yet, either Augmentation or reduction of HTC with the presence of lubricant oil is mainly attributed to the absolute pressure (low/medium/high) of the working refrigerant/fluid/system/evaporator, the mass concentration of oil, boiling surface, and applied heat flux. However, augmentation in the HTC with less oil addition (e.g., less than 5%) can be seen for absolute pressures between 150 and 700 kPa.

Experimental study on pool boiling heat transfer characteristics of TiO2 nanofluids on a downward-facing surface

Boiling heat transfer is an effective method for equipment to dissipate heat, which has been widely used in power industry and electronic products, but it is limited as its CHF value. It is well known that the CHF value can be enhanced by adding nanoparticles in order to reach higher heat flux requirements of nuclear power plants, electric vehicles and other high-power equipment. This experiment discussed the effect of different concentrations of TiO2 nanofluid on downward-facing boiling heat transfer, the concentrations were 0.0001 wt%, 0.0005 wt%, 0.001 wt%, 0.005 wt% and 0.01 wt%. The law of bubble behaviors throughout the boiling process was also observed. It was found that TiO2 nanofluid has an enhanced effect on CHF, the enhancement effect of nanofluid on CHF changes with the change of concentration and the maximum enhancement can be about 33%. The change of contact angles and roughness of the heating surface was detected, combined with the SEM image, it could be concluded that the deposition of TiO2 nanoparticles which changes the structure of the heating surface is the main reason why the nanofluid enhances heat transfer.

Experimental study on saturation pool boiling heat transfer characteristics of R245fa on the surface covered by sintered copper powder

In this paper, the mechanism of pool boiling heat transfer enhancement on the surface covered with sintered copper powder porous layer has been investigated. The refrigerant R245fa with great application prospect in electronic cooling field was selected as the test fluid. According to the results, the boiling heat transfer performance of R245fa could be effectively enhanced by attaching the sintered copper powder porous layer to the plain copper surface. Even when the wall superheat was as low as 2.2 °C, the sintered copper powder surface with the particle size of 110 μm and thickness of 0.6 mm could still be efficiently triggered to boiling. The heat transfer coefficient and CHF were significantly improved up to 247.71% and 255.15% compared with that of plain copper surface, respectively. However, with the thickness of porous layer increased from 0.6 mm to 0.9 mm, the maximum heat transfer coefficient for the enhanced surface with particle size of 30 μm went up to 136.01%, while the CHF value decreased by 92.52%. For 65 μm and 110 μm surfaces, the change of porous layer thickness had little effect on the heat transfer coefficient in the initial boiling stage, but presented the contrary influence trend at high heat flux conditions.

Heat transfer characteristics of R‐454B and R‐454B/POE‐oil mixture on smooth and GEWA tube: Alternative to R‐410A

To clarify the compatibility of low GWP refrigerant R-454B alternative to high GWP refrigerant R-410A, the pool boiling heat transfer characteristics is presented subject to lubricant oil POEA-68. The tests were conducted on a smooth and highly structured GEWA-B5H tube at different saturated temperatures of 10, 0, and, −6 °C in 10 to 90 kW/m2 heat flux range. Results show that on both tubes the average heat transfer coefficient (HTC) of pure R-454B at all the saturation temperatures and heat flux is 26 to 34% lower than the pure R-410A. The heat transfer capacity of the GEWA-B5H tube is 2.5 to 5.5 times higher than compared to the smooth copper tube at the same saturation temperature and heat flux for both refrigerant R-454B and R-410A. Yet to elucidate the compatibility of POE oil with R-454B, the low viscosity oil POEA-68 is added by a mass fraction (ω%) of 1% to 10% and 0.25% to 5% for the smooth and GEWA-B5H tube, respectively. The mixing of oil alters the HTC, augmentation or deterioration in HTC compared to pure refrigerant is dependent on the liquid pressure (evaporator pressure), heat flux, boiling surface, and mass fraction of oil.