A Unified Three Dimensional Numerical Simulation of the Pool Boiling Curve

2017 ◽  
Author(s):  
Deepak Garg ◽  
Vijay K. Dhir
Keyword(s):  
Heat Flux ◽  
Contact Angle ◽  
Numerical Model ◽  
Critical Heat Flux ◽  
Void Fraction ◽  
Pool Boiling ◽  
Three Dimensional ◽  
Boiling Curve ◽  
Wall Superheat ◽  
Experimental Values

Three dimensional numerical simulations for pool boiling of saturated water at atmospheric pressure conditions are performed on a horizontal surface using finite difference method under the framework of parallel computing. Since heat conduction in the solid phase is not considered, in order to simulate realistic heating surface, dependence of bubble nucleation frequency and nucleation site density on wall superheat and contact angle are obtained from the correlations reported in the literature. Steady state boiling curve for all the three regimes viz. nucleate, transition and film boiling has been obtained with a unified numerical model by incrementing the wall superheat for a static contact angle of 38°. Evaporative heat flux from the microlayer is separately accounted for in the present study by sub grid modeling. Both the phases are considered as incompressible while the interface separating the phases is solved using level set method. The governing equations of mass, momentum and energy for both the liquid and the vapor phase are solved coupled with the jump conditions at the interface employing ghost fluid and cut cell method. Diffusion terms are treated implicitly while convection terms are treated using second order ENO scheme. Spatial and temporal averaged wall heat flux and wall void fraction are plotted and compared against correlations and experimental values previously reported. The nucleate boiling heat flux obtained from the present numerical model is under predicted in comparison to the Stephan and Abdelsalam correlation. Comparison of the computed wall void fraction against experimental values is done for the transition boiling region. At critical heat flux formation of long vapor column was seen while intermittent liquid surface contacts were seen in the transition boiling regime. The computed critical heat flux value is lower than that obtained from the correlation of Maracy and Winterton.

A Unified Three-Dimensional Numerical Model for Boiling Curve in a Temperature Controlled Mode1

2018 ◽  
Vol 141 (1) ◽  
Author(s):  
Deepak Garg ◽  
V. K. Dhir
Keyword(s):  
Heat Flux ◽  
Numerical Model ◽  
Void Fraction ◽  
Three Dimensional ◽  
Nucleation Site ◽  
Boiling Curve ◽  
Increase With Increase ◽  
Wall Superheat ◽  
Uniform Wall ◽  
Temperature Controlled

In the present study, level set method is used to simulate the entire boiling curve in a temperature-controlled mode spanning all the three regimes viz., nucleate, transition, and film boiling with a unified numerical model supplemented with correlations specifying nucleation site density and waiting time between successive nucleations. In order to improve the performance of the code, parallel computing has also been implemented. Vapor evolution process along with temporal- and spatial-averaged wall heat flux and wall void fraction are computed for a uniform wall superheat case. Wall void fraction is found to increase with increase in wall superheat nonlinearly as different regimes of boiling were traversed. Energy partitioning from wall into liquid, interface, and microlayer has also been examined where it is found that as the wall void fraction increases, the percent energy going into liquid decreases while the microlayer contribution peaks around critical heat flux (CHF). Numerical simulations are carried out in 3D with water as test liquid and contact angle of 38 deg.

Boiling Heat Transfer and Critical Heat Flux Enhancement of Upward- and Downward-Facing Heater in Nanofluids

2013 ◽  
Vol 135 (7) ◽  
Author(s):  
Muhamad Zuhairi Sulaiman ◽  
Masahiro Takamura ◽  
Kazuki Nakahashi ◽  
Tomio Okawa
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Critical Heat Flux ◽  
Boiling Heat Transfer ◽  
Pool Boiling ◽  
Nucleate Boiling ◽  
Flux Enhancement ◽  
Optimum Configuration ◽  
Wall Superheat ◽  
Nucleate Boiling Heat Transfer

Boiling heat transfer (BHT) and critical heat flux (CHF) performance were experimentally studied for saturated pool boiling of water-based nanofluids. In present experimental works, copper heaters of 20 mm diameter with titanium-oxide (TiO2) nanocoated surface were produced in pool boiling of nanofluid. Experiments were performed in both upward and downward facing nanofluid coated heater surface. TiO2 nanoparticle was used with concentration ranging from 0.004 until 0.4 kg/m3 and boiling time of tb = 1, 3, 10, 20, 40, and 60 mins. Distilled water was used to observed BHT and CHF performance of different nanofluids boiling time and concentration configurations. Nucleate boiling heat transfer observed to deteriorate in upward facing heater, however; in contrast effect of enhancement for downward. Maximum enhancements of CHF for upward- and downward-facing heater are 2.1 and 1.9 times, respectively. Reduction of mean contact angle demonstrate enhancement on the critical heat flux for both upward-facing and downward-facing heater configuration. However, nucleate boiling heat transfer shows inconsistency in similar concentration with sequence of boiling time. For both downward- and upward-facing nanocoated heater's BHT and CHF, the optimum configuration denotes by C = 400 kg/m3 with tb = 1 min which shows the best increment of boiling curve trend with lowest wall superheat ΔT = 25 K and critical heat flux enhancement of 2.02 times.

Observations of the Critical Heat Flux Process During Pool Boiling of FC-72

2014 ◽  
Vol 136 (4) ◽  
Author(s):  
J. Jung ◽  
S. J. Kim ◽  
J. Kim
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Critical Heat Flux ◽  
Pool Boiling ◽  
High Heat ◽  
Line Length ◽  
Boiling Curve ◽  
High Heat Flux ◽  
Transfer Coefficients ◽  
Ir Camera

Experimental work was undertaken to investigate the process by which pool-boiling critical heat flux (CHF) occurs using an IR camera to measure the local temperature and heat transfer coefficients on a heated silicon surface. The wetted area fraction (WF), the contact line length density (CLD), the frequency between dryout events, the lifetime of the dry patches, the speed of the advancing and receding contact lines, the dry patch size distribution on the surface, and the heat transfer from the liquid-covered areas were measured throughout the boiling curve. Quantitative analysis of this data at high heat flux and transition through CHF revealed that the boiling curve can simply be obtained by weighting the heat flux from the liquid-covered areas by WF. CHF mechanisms proposed in the literature were evaluated against the observations.

Investigation of Pool Boiling Critical Heat Flux Enhancement on a Modified Surface Through the Dynamic Wetting of Water Droplets

2012 ◽  
Vol 134 (7) ◽  
Author(s):  
Ho Seon Ahn ◽  
Joonwon Kim ◽  
Moo Hwan Kim
Keyword(s):  
Surface Tension ◽  
Heat Flux ◽  
Contact Angle ◽  
Critical Heat Flux ◽  
Pool Boiling ◽  
Water Layer ◽  
Contact Angles ◽  
Water Droplets ◽  
Dynamic Wetting ◽  
Modified Surface

Dynamic wetting behaviors of water droplet on the modified surface were investigated experimentally. Dynamic contact angles were measured as a characterization method to explain the extraordinary pool boiling critical heat flux (CHF) enhancement on the zirconium surface by anodic oxidation modification. The sample surface is rectangular zirconium alloy plates (20 × 25 × 0.7 mm), and 12 μl of deionized water droplets were fallen from 40 mm of height over the surface. Dynamic wetting movement of water on the surface showed different characteristics depending on static contact angle (49.3 deg–0 deg) and surface temperature (120 °C–280 °C). Compared with bare surface, wettable and spreading surface had no-receding contact angle jump and seemed stable evaporating meniscus of liquid droplet in dynamic wetting condition on hot surface. This phenomenon could be explained by the interaction between the evaporation recoil and the surface tension forces. The surface tension force increased by micro/nanostructure of the modified zirconium surface suppresses the vapor recoil force by evaporation which makes the water layer unstable on the heated surface. Thus, such increased surface force could sustain the water layer stable in pool boiling CHF condition so that the extraordinary CHF enhancement could be possible.

On the Mechanism of Pool Boiling Critical Heat Flux Enhancement in Nanofluids

2010 ◽  
Vol 132 (6) ◽  
Author(s):  
Hyungdae Kim ◽  
Ho Seon Ahn ◽  
Moo Hwan Kim
Keyword(s):  
Heat Flux ◽  
Critical Heat Flux ◽  
Heated Surface ◽  
Pure Water ◽  
Pool Boiling ◽  
Nucleate Boiling ◽  
Titania Nanoparticles ◽  
Nanoparticle Layer ◽  
Wall Superheat ◽  
Dry Spot

The pool boiling characteristics of water-based nanofluids with alumina and titania nanoparticles of 0.01 vol % were investigated on a thermally heated disk heater at saturated temperature and atmospheric pressure. The results confirmed the findings of previous studies that nanofluids can significantly enhance the critical heat flux (CHF), resulting in a large increase in the wall superheat. It was found that some nanoparticles deposit on the heater surface during nucleate boiling, and the surface modification due to the deposition results in the same magnitude of CHF enhancement in pure water as for nanofluids. Subsequent to the boiling experiments, the interfacial properties of the heater surfaces were examined using dynamic wetting of an evaporating water droplet. As the surface temperature increased, the evaporating meniscus on the clean surface suddenly receded toward the liquid due to the evaporation recoil force on the liquid-vapor interface, but the nanoparticle-fouled surface exhibited stable wetting of the liquid meniscus even at a remarkably higher wall superheat. The heat flux gain attainable due to the improved wetting of the evaporating meniscus on the fouled surface showed good agreement with the CHF enhancement during nanofluid boiling. It is supposed that the nanoparticle layer increases the stability of the evaporating microlayer underneath a bubble growing on a heated surface and thus the irreversible growth of a hot/dry spot is inhibited even at a high wall superheat, resulting in the CHF enhancement observed when boiling nanofluids.

Pool Boiling Critical Heat Flux Enhancement Using Three-Dimensional Porous Structures

2018 ◽  
Vol 2018 (0) ◽  
pp. 0192
Author(s):  
Tomotaka Ueki ◽  
Kyoshiro Kawano ◽  
Tomohide Yabuki ◽  
Koji Miyazaki ◽  
Massoud Kaviany
Keyword(s):  
Heat Flux ◽  
Critical Heat Flux ◽  
Pool Boiling ◽  
Three Dimensional ◽  
Porous Structures ◽  
Flux Enhancement

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.

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