Thermophysical Properties and Pool Boiling Characteristics of Water-in-Polyalphaolefin Nanoemulsion Fluids

2013 ◽  
Vol 135 (9) ◽  
Author(s):  
Jiajun Xu ◽  
Bao Yang ◽  
Boualem Hammouda
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Thermophysical Properties ◽  
Self Assembly ◽  
Boiling Heat Transfer ◽  
Small Angle Neutron Scattering ◽  
Room Temperature ◽  
Pool Boiling ◽  
Water Concentration ◽  
Interesting Phenomenon

In this work, thermophysical properties, microstructure, and pool boiling characteristics of water-in-polyalphaolefin (PAO) nanoemulsion fluids have been measured in the water concentration range of 0–10.3 vol. %, in order to gain basic data for nanoemulsion boiling. Water-in-PAO nanoemulsion fluids are formed via self-assembly with surfactant: sodium sullfosuccinate (AOT). Thermal conductivity of these fluids is found to increase monotonically with water concentration, as expected from the Maxwell equation. Unlike thermal conductivity, their dynamic viscosity first increases with water concentration, reaches a maximum at 5.3 vol. %, and then decreases. The observed maximum viscosity could be attributed to the attractive forces among water droplets. The microstructures of the water-in-PAO nanoemulsion fluids are measured via the small-angle neutron scattering (SANS) technique, which shows a transition from sphere to elongated cylinder when the water concentration increases above 5.3 vol. %. The pool boiling heat transfer of these water-in-PAO nanoemulsion fluids is measured on a horizontal Pt wire at room temperature (25 °C, subcooled condition). One interesting phenomenon observed is that the pool boiling follows two different curves randomly when the water concentration is in the range of 5.3 vol. % to 7.8 vol. %.

Thermophysical Properties and Pool Boiling Characteristics of Water in Polyalphaolefin Nanoemulsion Fluids

2012 ◽  
Author(s):  
Jiajun Xu ◽  
Bao Yang
Keyword(s):  
Thermal Conductivity ◽  
Thermophysical Properties ◽  
Dynamic Viscosity ◽  
Self Assembly ◽  
Pool Boiling ◽  
Water Concentration ◽  
Interesting Phenomenon ◽  
Conductivity Increase ◽  
Thermal Conductivity Increase ◽  
Measured Thermal Conductivity

In this work, thermophysical properties and pool boiling characteristics of water-in-polyalphaolefin (PAO) nanoemulsion fluids and their dependence on water concentration have been investigated experimentally. Water-in-PAO nanoemulsion fluids are formed via self-assembly with surfactant sodium sullfosuccinate (AOT). Thermal conductivity of the fluids is found to increase with water concentration, as expected from the Maxwell equation. However, the measured thermal conductivity increase is very moderate, e.g., a 16% increase for 8.6Vol. %. Unlike thermal conductivity, the dynamic viscosity of these nanoemulsion fluids first increases with water concentration, reaches a maximum, and then decreases. This trend could be attributed to the attractive forces among water droplets. The boiling behavior of these nanoemulsion fluids has been altered due to water nanodroplets. Adding water nanodroplets can lower the nanoemulsion’s boiling point compared to the pure PAO. Another interesting phenomenon observed is that pool boiling of nanoemulsion fluids randomly follows two different curves when the water concentration is in the range of 5.3 Vol. % to 7.8 Vol. %. The mechanism underlying this phenomenon is not understood yet, but it may be related to the evolution of microstructures in the water-in-PAO nanoemulsion fluids.

Pool Boiling Characteristics of Metallic Nanofluids

2011 ◽  
Vol 133 (11) ◽  
Author(s):  
K. Hari Krishna ◽  
Harish Ganapathy ◽  
G. Sateesh ◽  
Sarit K. Das
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Boiling Heat Transfer ◽  
Volume Fraction ◽  
Pool Boiling ◽  
Heat Fluxes ◽  
Solid Particles ◽  
Heater Surface ◽  
Heat Transfer Characteristics ◽  
Transfer Characteristics

Nanofluids, solid-liquid suspensions with solid particles of size of the order of few nanometers, have created interest in many researchers because of their enhancement in thermal conductivity and convective heat transfer characteristics. Many studies have been done on the pool boiling characteristics of nanofluids, most of which have been with nanofluids containing oxide nanoparticles owing to the ease in their preparation. Deterioration in boiling heat transfer was observed in some studies. Metallic nanofluids having metal nanoparticles, which are known for their good heat transfer characteristics in bulk regime, reported drastic enhancement in thermal conductivity. The present paper investigates into the pool boiling characteristics of metallic nanofluids, in particular of Cu-H2O nanofluids, on flat copper heater surface. The results indicate that at comparatively low heat fluxes, there is deterioration in boiling heat transfer with very low particle volume fraction of 0.01%, and it increases with volume fraction and shows enhancement with 0.1%. However, the behavior is the other way around at high heat fluxes. The enhancement at low heat fluxes is due to the fact that the effect of formation of thin sorption layer of nanoparticles on heater surface, which causes deterioration by trapping the nucleation sites, is overshadowed by the increase in microlayer evaporation, which is due to enhancement in thermal conductivity. Same trend has been observed with variation in the surface roughness of the heater as well.

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.

scholarly journals Determining the Factors Affecting the Boiling Heat Transfer Coefficient of Sintered Coated Porous Surfaces

2021 ◽  
Vol 13 (22) ◽  
pp. 12631
Author(s):  
Uzair Sajjad ◽  
Imtiyaz Hussain ◽  
Muhammad Sultan ◽  
Sadaf Mehdi ◽  
Chi-Chuan Wang ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Thermophysical Properties ◽  
Boiling Heat Transfer ◽  
Pool Boiling ◽  
Morphological Features ◽  
Porous Surfaces ◽  
Boiling Heat Transfer Coefficient ◽  
Influential Parameters

The boiling heat transfer performance of porous surfaces greatly depends on the morphological parameters, liquid thermophysical properties, and pool boiling conditions. Hence, to develop a predictive model valid for diverse working fluids, it is necessary to incorporate the effects of the most influential parameters into the architecture of the model. In this regard, two Bayesian optimization algorithms including Gaussian process regression (GPR) and gradient boosting regression trees (GBRT) are used for tuning the hyper-parameters (number of input and dense nodes, number of dense layers, activation function, batch size, Adam decay, and learning rate) of the deep neural network. The optimized model is then employed to perform sensitivity analysis for finding the most influential parameters in the boiling heat transfer assessment of sintered coated porous surfaces on copper substrate subjected to a variety of high- and low-wetting working fluids, including water, dielectric fluids, and refrigerants, under saturated pool boiling conditions and different surface inclination angles of the heater surface. The model with all the surface morphological features, liquid thermophysical properties, and pool boiling testing parameters demonstrates the highest correlation coefficient, R2 = 0.985, for HTC prediction. The superheated wall is noted to have the maximum effect on the predictive accuracy of the boiling heat transfer coefficient. For example, if the wall superheat is dropped from the modeling parameters, the lowest prediction of R2 (0.893) is achieved. The surface morphological features show relatively less influence compared to the liquid thermophysical properties. The proposed methodology is effective in determining the highly influencing surface and liquid parameters for the boiling heat transfer assessment of porous surfaces.

Nucleate Boiling on Biotemplated Nanostructured Surfaces

2012 ◽  
Author(s):  
Md. Mahamudur Rahman ◽  
Stephen M. King ◽  
Emre Olceroglu ◽  
Matthew McCarthy
Keyword(s):  
Heat Transfer ◽  
Self Assembly ◽  
Boiling Heat Transfer ◽  
Pool Boiling ◽  
Nucleate Boiling ◽  
Pool Boiling Heat Transfer ◽  
Nanostructured Surfaces ◽  
Transfer Capability ◽  
Good Agreement

The fabrication and characterization of biotemplated nanostructured surfaces for enhanced pool boiling heat transfer is reported. By introducing micro/nano-porosity and surface roughness at the liquid-vapor interface, significant enhancement in surface heat transfer capability can be achieved during nucleate boiling. This work uses the self-assembly and mineralization of the Tobacco mosaic virus (TMV) to create superhydrophilic (∼9°), superhydrophobic (∼163°), and mixed hydrophilic-hydrophobic (∼70°) surfaces to investigate the effects of surface wettability and heterogeneity on boiling heat transfer performance. Pool boiling results showing CHF and HTC values for nickel-coated TMV, Teflon-coated TMV, mixed nickel + Teflon coated TMV, flat silicon, and flat Teflon are reported. The mixed surfaces demonstrate a CHF enhancement of ∼ 70% compared to flat silicon and ∼140% compared to flat Teflon. The results are in good agreement with the literature and will guide the design of optimized surfaces for further enhancement. This work demonstrates the feasibility of enhancing pool boiling heat transfer using TMV based nanostructured coatings.

Boiling Heat Transfer in a Shallow Fluidized Particulate Bed

1987 ◽  
Vol 109 (1) ◽  
pp. 196-203 ◽  
Author(s):  
Y. K. Chuah ◽  
V. P. Carey
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Heat Flux ◽  
Boiling Heat Transfer ◽  
Pool Boiling ◽  
Thin Layers ◽  
Surface Nucleation ◽  
Particle Layer ◽  
Wall Superheat ◽  
Flux Level

Experimental data are presented which indicate the effects of a thin layer of unconfined particles on saturated pool boiling heat transfer from a horizontal surface. Results are presented for two different types of particles: (1) 0.275 and 0.475-mm-dia glass spheres which have low density and thermal conductivity, and (2) 0.100 and 0.200-mm-dia copper spheres which have high density and thermal conductivity. These two particle types are the extremes of particles found as corrosion products or contaminants in boiling systems. To ensure that the surface nucleation characteristics were well defined, polished chrome surfaces with a finite number of artificial nucleation sites were used. Experimental results are reported for heat fluxes between 20 kW/m2 and 100kW/m2 using water at 1 atm as a coolant. For both particle types, vapor was observed to move upward through chimneys in the particle layer, tending to fluidize the layer. Compared with ordinary pool boiling at the same surface heat flux level, the experiments indicate that addition of light, low-conductivity particles significantly increases the wall superheat, whereas addition of heavier, high-conductivity particles decreases wall superheat. Heat transfer coefficients measured in the experiments with a layer of copper particles were found to be as much as a factor of two larger than those measured for ordinary pool boiling at the same heat flux level. The results further indicate that at least for thin layers, the boiling curve is insensitive to layer thickness. These results are shown to be consistent with the expected effects of the particles on nucleation, fluid motion, and effective conductivity in the pool at or near the surface. The effect of surface nucleation site density on heat transfer with a particle layer present is also discussed.

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