Unremitting endeavors have been devoted by numerous researchers to ameliorate thermal performance of pool boiling by reducing the superheat temperature value using various approaches. This study aims ...to experimentally investigate the pool boiling thermal performance of Al2O3 and CeO2 hybrid nanoparticles with 50:50 mixing ratio based deionizedc1 water at atmospheric pressure condition. The pool boiling curves, pool boiling heat transfer coefficient PBHTC enhancement ratio with different dilute volumetric concentrations ranging (0.01–0.1% Vol.) from horizontal typical copper tube were examined. Results demonstrated that the enhancement ratio for hybrid nanofluid was improved compared to DI water, and the higher enhancement ratio was 1.37 for volume concentration of 0.05% Vol at low heat flux. Finally, this type of hybrid nanofluids could remove high heat flux at a small temperature difference, especially with this type of heater geometry, initial surface roughness, nanoparticles type, size, and the volumetric concentration.
•Performance of pool boiling heat transfer of new hybrid nanofluids was experimentally studied.•Temperatures distribution along heating surface for DI water and nanofluid at different heat fluxes were discussed.•The higher PBHTC enhancement percentage was 37% for hybrid nanofluids at volume fraction 0.05% Vol. and moderate heat flux.•Heater geometry has an important effect on PBHTC of nanofluids.•Introduction.
•A high-fidelity approach has been developed to predict the nucleate boiling date of roughened surfaces.•This model includes most influential surface features, testing conditions, and liquid ...thermophysical properties.•This method estimates the HTC with a coefficient of determination = 0.994 and mean absolute error = 0.65.•This method is effective for variety of roughened surfaces subject to different working fluids and testing conditions.
The existing nucleate pool boiling correlations have theoretical footings and their usefulness is restricted by the failure to effectively account for the surface effect. To tackle this problem, a high-fidelity approach based on deep learning has been developed to predict the nucleate boiling surfaces subject to various surface roughness. The proposed model accounts for the effect of surface roughness, roughness fabrication method, surface material, surface inclination, saturation temperature, and pressure on the pool boiling performance of dielectric liquids, water, and refrigerants. The proposed method can accurately predict the boiling heat transfer performance of roughened surfaces by including the most influential surface characteristics, testing conditions, and liquid thermophysical properties into the architecture of the developed model. Correlation matrix identifies that heat flux, surface inclination, surface roughness, thermal conductivity of surface material, liquid saturation temperature, and pressure are the prime factors to affect the nucleate boiling heat transfer coefficient. Different neural networks (DNNs) are built and tested in order to find an optimal model based on an experimental dataset of 13000 data points. The final selected model can estimate the investigated parameter with a coefficient of determination (R2) = 0.994 and mean absolute error (MAE) = 0.65. The suggested method can be utilized to predict the boiling heat transfer performance of a variety of roughened surfaces subject to different working fluids and testing conditions.
•A simplified 2D model of pool boiling in metal foams is constructed.•Forced convection promotes bubble departure at the bottom of metal foams.•Forced convection maintains a stable pressure drop and ...promotes fluid supply.•The heat transfer mechanism of pool boiling with forced convection is revealed.
Forced convection boiling in metal foams may have a higher heat transfer performance than natural convection boiling, and the enhanced heat transfer mechanism should be revealed. In this study, the pool boiling of methanol in metal foams (thickness, 2 mm; pore density, 30 PPI; porosity, 95 %) under forced convection conditions is simulated using the Couple Level Set and Volume of Fluid (CLSVOF) model coupled with the user defined function (UDF) of phase change model. The numerical model is used to analyze the effects of forced convection on pool boiling through the simulation of bubble behaviors, temperature and pressure fields. Moreover, experiments are conducted on the pool boiling with forced convection at flow rates of 30, 40, and 50 mL min−1, and the numerical results are validated with experimental results. The results demonstrate that the flushing rate of the bottom bubble increases by 1.5 times, resulting in a 23 % increase in the maximum heat transfer coefficient (HTC). It is worth noting that an increase in forced convection flow rate does not introduce significant pressure drop increases (1–4 Pa) and fluctuations (10–70 Pa). The numerical analysis and experimental validation have shown that forced convection during pool boiling can maintain stable pressure drop and promote working fluid supply and bubble departure for enhancing heat transfer. This study provides an understanding of pool boiling with forced convection and serves as a valuable reference for designing efficient heat exchange systems with stable pressure drop.
Pool boiling with forced convection is safe and stable and gives enhanced boiling heat transfer by improved bottom bubble flushing and working fluid supply. Display omitted
•3D numerical model of pool boiling outside T-fin tubes has been established.•The accuracy of the adopted CFD model has been validated.•Discussed the effect of fin density on pool boiling outside of ...T-fin tubes.•Proposed ideas for optimizing the structure of T-fin tubes.•Studied the mechanism of heat transfer and flow outside high-performance tubes.
Experiments and numerical analyses of saturated pool boiling have been carried out on the outer surfaces of horizontal smooth tubes and T-fin tubes. Using a computational model that closely matches the experimental results, the study examined the dynamics of the bubbles as well as the boiling heat transfer coefficients in both the circumferential and axial orientations of the T-fin tubes. For the first time, comprehensive information on the process of high-performance external tube boiling has been made available. The findings demonstrate that an increase in fin density on the surface of the T-fin tubes leads to an abundance of bubble nuclei, with the escaping bubbles exhibiting both increased size and accelerated velocity. Due to the distinctive configuration of the T-fin tube, the local heat flow is lowest at the root fin and highest at the fin tip, indicating that heat transfer is inhibited in the narrow cavity between the two lateral fins. The optimal fin density, which corresponds to the maximum overall heat transfer coefficient has been identified. This states that the enhanced heat transfer mechanism within the T-fin tube is a symbiotic effect of both the increase in heat transfer area and the subsequent degradation of heat transfer fostered by the bubbling of the tube.
•Object of analysis: minichannels 5.5, 6.0 and 10 mm deep and 0.5 1.2 mm wide.•Boiling curves for ethanol, FC-72 and Novec-649.•Visualization studies: growing bubble diameter changes and bubble ...departure diameter.•Determining the bubble departure diameter with static and dynamic methods.
Pool boiling heat transfer experiments were conducted with ethanol, Novec-649 and FC-72 at atmospheric pressure on surfaces with deep minichannels. The minichannels 5.5, 6.0 and 10 mm deep and 0.5–1.2 mm wide were uniformly spaced with a pitch of 2.0 mm on the base surfaces. Heat transfer coefficients obtained with ethanol were similar for all surfaces tested. Novec-649 and FC-72 produced the highest coefficients at heat fluxes above 100 kW/m2 in 1 mm wide minichannels. All the working fluids provided a significant increase in the maximum (critical) heat flux. The images were recorded using high speed imaging techniques across the entire surface of the samples. Boiling visualization aimed to study vapor bubble diameter changes during the growth period and measure the bubble departure diameter.
The bubble diameter at departure was also determined analytically according to force balance static and dynamic variants. The dynamic variant provided a high consistency between the theoretical and experimental data for bubble departure diameter with FC-72 and Novec-649.
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. In conclusion, 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.
•Using oxide nanoparticles of cobalt in deionized water to heat transfer analysis of boiling process in a nucleate regime on a copper surface.•Improvement of the heat transfer coefficient of pool ...boiling under a magnetic field for low volume fractions.•Maximum heat transfer of cobalt oxide-deionized water is 58% compared to the deionized water.•This nanofluid can be applied to increase the heat transfer rate at low concentrations.
In this paper, the analysis of the boiling process is studied in a nucleate regime on a copper surface through using oxide nanoparticles of cobalt (Co3O4) in deionized water at volume fractions of 0.005, 0.01, 0.05, 0.1, and 0.2% by means of a nucleate boiling device. The nanoparticles’ average size is about 45 nm for cobalt oxide. As the nanofluid concentration increases, the deposition and the boiling surface heat resistance increases, the nucleation points and coefficient of the boiling heat transfer decrease due to deposition. Despite the magnetic field positive effect on dilute liquids, sediment has a more negative effect than the magnetic field on concentrated nanofluids. The results reveal the improvement of the heat transfer coefficient of pool boiling under a magnetic field for low volume fractions. Maximum heat transfer of Co3O4/ DI-water is 58% compared to the DI-water observed at the concentration of 0.005%. This nanofluid can be applied to increase the heat transfer rate at low concentrations.
•CHF enhancement techniques by the various surface modifications are reviewed.•The key factors for significant CHF enhancement and the mechanisms are discussed.•The recommendations are made for ...future studies to enhance the CHF of a saturated pool boiling.
Numerous surface modifications were proposed to enhance the critical heat flux (CHF) in a saturated pool boiling. CHF enhancement is a result of the effects of extended surface area, nucleation site density, wettability, capillary wicking, and wavelength decrease based on the modified Zuber hydrodynamic stability model. A number of combined techniques for CHF enhancement have been proposed. The objective of this paper is to review the CHF enhancement techniques by the various surface modifications and to introduce the enhancement mechanism. Moreover, recommendations are made for future studies to enhance the CHF of a saturated pool boiling.
•This review explores passive enhancement of pool boiling using surface modification.•Examined are macrosacle, microscale, nanoscale and multiscale (hybrid-scale) techniques.•Addressed are ...performance goals of inhibiting incidence hysteresis and increasing both nucleate boiling heat transfer coefficient and CHF.•Shown is that micro and nano surface features are susceptible to blockage and changes in performance over time.
This paper provides a comprehensive review of published articles addressing passive enhancement of pool boiling using surface modification techniques. They include macroscale, microscale, and nanoscale surfaces, as well as multiscale (hybrid-scale), and hybrid-wettability techniques. Different enhancement methods are assessed in terms of underlying fluid routing mechanisms and ability to achieve three distinct heat transfer goals: eliminating incipient boiling hysteresis, increasing nucleate boiling heat transfer coefficient, and ameliorating critical heat flux (CHF), especially for inert dielectric coolants that are both highly wetting and possess relatively poor thermophysical properties. While different enhancement scales are shown to provide different degrees of success in achieving the three goals, it is shown that both microscale and nanoscale surface features are susceptible to blockage, resulting in deterioration of the enhancement over time. This review also points to scarcity of sufficiently sized databases for a given enhancement scheme in terms of fluid type, surface material, size, and orientation, enhancement shape, pattern, and scale, and operating pressure. This renders available findings less-than-adequate tools for design of practical cooling systems.
•Three-dimensional pseudo potential lattice Boltzmann model is built up to study boiling on two-tier hierarchical structured surface.•Mechanism of accelerated bubble departure on hierarchical ...surfaces with upward-orientation secondary pillar is revealed.•Lateral-orientation secondary structures can deteriorate heat transfer and bring larger flow resistance.•Hierarchical structured surface with upward-orientation secondary pillars achieves best boiling performance at high wall temperature.
In this paper, pool boiling on two-tier hierarchical structured surface is investigated with three-dimensional LB method. Two-tier pillar structures with different scales are designed, termed as primary and secondary pillar, respectively. On the hierarchical surface with upward-orientation secondary pillars, the bubble departure is promoted. And, the heat transfer can be improved by increasing the primary pillar spacing and enhancing surface wettability. Increasing the height of secondary pillar is favorable for enhancing capillary wicking, but can also bring greater flow resistance. On the hierarchical surface with lateral-orientation secondary pillars, the heat transfer is limited by the large flow resistance. With the enlargement of primary pillar spacing, the impact brought by flow resistance is moderated, and the heat flux can be enhanced. Finally, the boiling performance regarding the effect of wall temperature is concerned, where the structured surface with upward-orientation secondary pillars show the better boiling performance than other structured surfaces.
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