Effect of Heat Flux on Pool Boiling Heat Transfer Enhancement (Numerical Investigation Approach)

2020 ◽  
Author(s):  
T. S. Mogaji ◽  
O. A. Sogbesan ◽  
Tien-Chien Jen
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Heat Transfer Enhancement ◽  
Numerical Investigation ◽  
Boiling Heat Transfer ◽  
Pool Boiling ◽  
Nucleate Boiling ◽  
Transfer Enhancement

Abstract This study presents numerical investigation results of heat flux effect on pool boiling heat transfer enhancement during nucleate boiling heat transfer of water. The simulation was performed for five different heated surfaces such as: brass, copper, mild steel, stainless steel and aluminum using ANSYS simulation software at 1 atmospheric pressure. The samples were heated in a domain developed for bubble growth during nucleate boiling process under the same operational condition of applied heat flux ranged from 100 to 1000 kW/m2 and their corresponding heat transfer coefficient was obtained numerically. Obtained experimental data of other authors from the open literature result is in close agreement with the simulated data, thus confirming the validity of the CFD simulation method used in this study. It is found that heat transfer coefficient increases with increasing heat flux. The results revealed that in comparison to other materials tested, better heat transfer performance up to 38.5% and 7.11% is observed for aluminum and brass at lower superheated temperature difference conditions of 6.96K and 14.01K respectively. This behavior indicates better bubble development and detachment capability of these heating surface materials and could be used in improving the performance of thermal devices toward producing compact and miniaturized equipment.

scholarly journals Quantitative Evaluation of the Dependence of Pool Boiling Heat Transfer Enhancement on Sintered Particle Coating Characteristics

2016 ◽  
Vol 139 (2) ◽  
Author(s):  
Suchismita Sarangi ◽  
Justin A. Weibel ◽  
Suresh V. Garimella
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Boiling Heat Transfer ◽  
Pool Boiling ◽  
Transfer Enhancement ◽  
Pool Boiling Heat Transfer ◽  
Boiling Heat Transfer Coefficient ◽  
Coating Characteristics

Immersion cooling strategies often employ surface enhancements to improve the pool boiling heat transfer performance. Sintered particle/powder coatings have been commonly used on smooth surfaces to reduce the wall superheat and increase the critical heat flux (CHF). However, there is no unified understanding of the role of coating characteristics on pool boiling heat transfer enhancement. The morphology and size of the particles affect the pore geometry, permeability, thermal conductivity, and other characteristics of the sintered coating. In turn, these characteristics impact the heat transfer coefficient and CHF during boiling. In this study, pool boiling of FC-72 is experimentally investigated using copper surfaces coated with a layer of sintered copper particles of irregular and spherical morphologies for a range of porosities (∼40–80%). Particles of the same effective diameter (90–106 μm) are sintered to yield identical coating thicknesses (∼4 particle diameters). The porous structure formed by sintering is characterized using microcomputed tomography (μ-CT) scanning to study the geometric and effective thermophysical properties of the coatings. The boiling performance of the porous coatings is analyzed. Coating characteristics that influence the boiling heat transfer coefficient and CHF are identified and their relative strength of dependence analyzed using regression analysis. Irregular particles yield higher heat transfer coefficients compared to spherical particles at similar porosity. The coating porosity, pore diameter, unit necking area, unit interfacial area, effective thermal conductivity, and effective permeability are observed to be the most critical coating properties affecting the boiling heat transfer coefficient and CHF.

Mechanism of Nucleate Boiling Heat Transfer Enhancement From Microporous Surfaces in Saturated FC-72

2002 ◽  
Vol 124 (3) ◽  
pp. 500-506 ◽  
Author(s):  
J. H. Kim ◽  
K. N. Rainey ◽  
S. M. You ◽  
J. Y. Pak
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Transfer Enhancement ◽  
Latent Heat ◽  
Boiling Heat Transfer ◽  
Nucleate Boiling ◽  
Direct Result ◽  
Vapor Flow ◽  
High Heat Flux ◽  
Transfer Enhancement

The present study is an experimental investigation of the nucleate pool boiling heat transfer enhancement mechanism of microporous surfaces immersed in saturated FC-72. Measurements of bubble size, frequency, and vapor flow rate from a plain and microporous coated 390 μm diameter platinum wire using the consecutive-photo method were taken to determine the effects of the coating on the convective and latent heat transfer mechanisms. Results of the study showed that the microporous coating augments nucleate boiling performance through increased latent heat transfer in the low heat flux region and through increased convection heat transfer in the high heat flux region. The critical heat flux for the microporous coated surface is significantly enhanced over the plain surface due to decreased latent heat transfer (decreased vapor generation rate) and/or increased hydrodynamic stability from increased vapor inertia; both of which are a direct result of increased nucleation site density.

Effects of Heater Material and Surface Orientation on Heat Transfer Coefficient and Critical Heat Flux of Nucleate Boiling

2017 ◽  
Author(s):  
Yong Mei ◽  
Yechen Zhu ◽  
Botao Zhang ◽  
Shengjie Gong ◽  
Hanyang Gu
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Boiling Heat Transfer ◽  
Orientation Angle ◽  
Nucleate Boiling ◽  
Copper Surface ◽  
Surface Orientation ◽  
Reactor Vessel

External reactor vessel cooling (ERVC) is the key technology for In-Vessel Retention (IVR) to ensure the safety of a nuclear power plant (NPP) under severe accident conditions. The thermal margin of nucleate boiling heat transfer on the reactor pressure vessel (RPV) lower head is important for ERVC and of wide concern to researchers. In such boiling heat transfer processes, the reactor vessel wall inclination effect on the heat transfer coefficient (HTC) and critical heat flux (CHF) should be considered. In this study, experiments were performed to investigate the effects of heater material and surface orientation on the HTC and CHF of nucleate boiling. Copper and stainless steel (SS) surfaces were used to perform boiling tests under atmosphere pressure. The orientation angle of both boiling surfaces were varied between 0° (upward) and 180° (downward). The experimental results show that the surface orientation effects on the HTC is slight for both the copper surface and the SS surface. In addition, the relationship of measured CHF values with the inclination angles was obtained and it shows that the CHF value changes little as the inclination angle increases from 0° to 120° but it decreases rapidly as the orientation angle increases towards 180° for both boiling surfaces. The material effect on CHF is also observed and the copper surface has higher CHF value than the SS surface. Based on the experimental data, a correlation for CHF prediction is developed which includes both the surface orientation effect and the heater material effect.

Effect of Particle Morphology on Pool Boiling From Surfaces Coated With Sintered Particles

2015 ◽  
Author(s):  
Suchismita Sarangi ◽  
Justin A. Weibel ◽  
Suresh V. Garimella
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Critical Heat Flux ◽  
Boiling Heat Transfer ◽  
Heat Transfer Performance ◽  
Pool Boiling ◽  
Particle Morphology ◽  
Wall Superheat

Immersion cooling strategies often employ surface enhancements to improve the pool boiling heat transfer performance. Sintered particle/powder coatings with different constituent particle sizes and total layer thicknesses have been commonly used on smooth surfaces to reduce the wall superheat and increase the critical heat flux during pool boiling. However, the role of the particle morphology on pool boiling has not been explicitly investigated. Since the morphology of the particles affects the pore shape, permeability, surface roughness, effective conductivity and diffusivity of the sintered coating, it will impact the heat transfer coefficient and critical heat flux during boiling. In this study, pool boiling of FC-72 is experimentally investigated using copper surfaces coated with a layer of sintered copper particles of irregular, dendritic and spherical morphologies. In order to isolate the effect of particle morphology, particles with the same effective diameter (90–106 μm) are sintered under controlled conditions that yield the same porosity (∼60%) and coating thickness (∼6 particle diameters) for all samples tested. The effects of particle morphology on the incipient wall superheat, nucleate boiling heat transfer coefficient, and critical heat flux are analyzed. The morphology of the pore structure in the coating formed by sintering is observed with SEM images; bubble nucleation and departure characteristics affecting the heat transfer performance of the coatings are qualitatively assessed with the aid of high-speed flow visualizations to corroborate the trends observed in the boiling curves. The irregular particles are observed to show the highest heat transfer coefficient, followed by dendritic and then spherical particles. The critical heat flux is found to be independent of the particle morphology.

scholarly journals Development of a new correlation for estimating pool boiling heat transfer coefficient of MEG/DEG/water ternary mixture

2012 ◽  
Vol 18 (1) ◽  
pp. 11-18 ◽  
Author(s):  
M.M. Sarafraz ◽  
S.A. Alavi-Fazel ◽  
Y. Hasanzadeh ◽  
A. Arabshamsabadi ◽  
S. Bahram
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Boiling Heat Transfer ◽  
Pool Boiling ◽  
Ternary Mixtures ◽  
Average Error ◽  
Pool Boiling Heat Transfer ◽  
Boiling Heat Transfer Coefficient

Pool boiling heat transfer coefficient of monoethylene glycol (MEG), diethylene glycol (DEG) and water ternary mixtures has been experimentally measured up to heat flux 114 kW/m2 at various volumetric concentrations of MEG and DEG. As expected, heat transfer coefficient was strongly taken as a direct function of heat flux. Existing well-known correlations are shown to be unable to predict the acceptable values for the tested ternary mixtures, particularly at different concentrations of MEG and DEG. Furthermore, a new modified correlation is developed on the basis of the Stephan - Preu?er correlation that predicts the values of heat transfer coefficients with absolute average error of about 7% that is reasonable and acceptable values in compare to other existing correlations.

The effect of surfactant concentrations and surface material on heat transfer coefficient in nucleate boiling regime

Kerntechnik ◽  
2021 ◽  
Vol 86 (5) ◽  
pp. 365-374
Author(s):  
A. M. Refaey ◽  
S. Elnaggar ◽  
S. H. Abdel-Latif ◽  
A. Hamza
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Boiling Heat Transfer ◽  
Two Phase Flow ◽  
Surfactant Solution ◽  
Nucleate Boiling ◽  
Phase Flow ◽  
Two Phase

Abstract The nucleate boiling regime and two-phase flow are greater importance to the safety analysis of nuclear reactors. In this study, the boiling heat transfer in nuclear reactor is numerical investigated. The computational fluid dynamics (CFD) code, ANSYS Fluent 17.2 is used and the boiling model is employed. The numerical predictions obtained are compared with the experimental data reported by A. Hamza et al. [9]. An experimental test rig is designed and constructed to investigate the effect of cooling water chemistry control and the material of heater surface. CFD software, allows the detailed analysis of the two-phase flow and heat transfer. In this paper, we evaluate the accuracy of the boiling model implemented in the ANSYS Fluent code. This model is based on the heat flux partitioning approach and accommodates the heat flux due to single-phase convection, quenching and evaporation. The validation carried out of surfactant fluid/vapor two-phase flow inside the 2-D cylindrical boiling vessel. A heated horizontal pipe with stainless steel, Aluminum, and Zircalloy surface materials are used to numerically predict the field temperature and void fraction. Different surfactant concentrations ranging from 0, (pure water) to 1500 ppm, and heat fluxes ranging from 31 to 110 kW/m2 are used. The results of the predicted model depict that the addition of SDS Surfactant and increasing the heat flux improves the coefficient of boiling heat transfer for a given concentration. Also, it was found that the increasing of the concentration of aqueous surfactant solution increases the pool boiling heat transfer coefficient. The aqueous surfactant solution SDS improved the heat transfer coefficient of Aluminum, Zircalloy and stainless steel surface materials by 135%.138% and 120% respectively. The results of the numerical model are nearly in agreement with that measured in experimental.

Effect of Inclination on Pool Boiling of FC-72 Dielectric Liquid on Porous Graphite

2005 ◽  
Author(s):  
Jack L. Parker ◽  
Mohamed S. El-Genk
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Inclination Angle ◽  
Boiling Heat Transfer ◽  
Pool Boiling ◽  
Nucleate Boiling ◽  
Porous Graphite ◽  
Nucleate Boiling Heat Transfer ◽  
Boiling Heat Transfer Coefficient

Saturation pool boiling experiments of FC-72 liquid on a flat, porous graphite and smooth copper surfaces measuring 10 × 10 mm investigated the effect of surface orientation on nucleate boiling and Critical Heat Flux (CHF). The inclination angle of the surface increased from 0° (upward-facing) to 60°, 90°, 120°, 150°, and 180° (downward facing). Results demonstrated significant increases in the nucleate boiling heat transfer coefficient and CHF on porous graphite, compared to those on copper. At low surface superheats, increasing the inclination angle increases the nucleate boiling heat transfer coefficient, which decreases with increased inclination angle at high surface superheats. These results and the measured decreases of CHF with increased inclination angle are consistent with those reported earlier by other investigators for dielectric and non-dielectric liquids. On smooth surfaces and micro-porous coatings, the reported fractional decreases in CHF with increased inclination angle are almost identical, but markedly larger than those measured in this work on porous graphite. On these surfaces the reported CHF in the downward-facing position (180° inclination) is ∼10–20% of that in the upward-facing position (0° inclination), compared to ∼53.3% on porous graphite. The CHF values of FC-72 liquid on porous graphite, which also decreased with increased inclination angle, are correlated using the general form suggested by Kutatelatze (1961) to within ± 5% of the experimental data.

Nucleate Boiling Characteristics of R-113 in a Small Tube Bundle

1992 ◽  
Vol 114 (2) ◽  
pp. 425-433 ◽  
Author(s):  
P. J. Marto ◽  
C. L. Anderson
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Boiling Heat Transfer ◽  
Tube Bundle ◽  
Nucleate Boiling ◽  
Heat Fluxes ◽  
Average Heat Transfer Coefficient ◽  
Average Heat

Heat transfer measurements were made during nucleate boiling of R-113 from a bundle of 15 electrically heated, smooth copper tubes arranged in an equilateral triangular pitch. The bundle was designed to simulate a portion of a refrigeration system flooded-tube evaporator. The outside diameter of the tubes was 15.9 mm, and the tube pitch was 19.1 mm. Five of the tubes that were oriented in a vertical array on the centerline of the bundle were each instrumented with six wall thermocouples to obtain an average wall temperature and a resultant average heat transfer coefficient. All tests were performed at atmospheric pressure. The majority of the data were obtained with increasing heat flux to study the onset of nucleate boiling and the influence of surface “history” upon boiling heat transfer. Data taken during increasing heat flux showed that incipient boiling was dependent upon the number of tubes in operation. The operation of lower tubes in the bundle decreased the incipient boiling heat flux and wall superheat of the upper tubes, and generally increased the boiling heat transfer coefficients of the upper tubes at low heat fluxes where natural convection effects are important. The boiling data confirmed that the average heat transfer coefficient for a smooth-tube bundle is larger than obtained for a single tube.

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