Transient Characteristics of Pool Boiling Heat Transfer in Nanofluids

2012 ◽  
Vol 134 (5) ◽  
Author(s):  
Sang M. Kwark ◽  
Ratan Kumar ◽  
Gilberto Moreno ◽  
Seung M. You
Keyword(s):  
Heat Transfer ◽  
Boiling Heat Transfer ◽  
Base Fluid ◽  
Pool Boiling ◽  
Thermal Characteristics ◽  
Boiling Curve ◽  
Heater Surface ◽  
Cooling Fluid ◽  
Transient Characteristics ◽  
Conductivity Enhancement

This study shows the transient characteristics of the pool boiling curves using nanofluid as the boiling fluid. This time-dependency is in sharp contrast to a unique steady-state pool boiling curve that is typically obtained for a pure fluid. Past nanofluids research has provided interesting information about the thermal characteristics for this potentially promising cooling fluid. Results from these studies have shown some extraordinary critical heat flux (CHF) values and thermal conductivity enhancement that is yet to be explained by existing theories and correlations. The nature of the pool boiling curve for a nanofluid is dependent on the nanoparticle concentration in the base fluid. Higher concentration nanofluids show a perceptible degradation in the boiling heat transfer (BHT) coefficient but have exhibited an enhanced CHF value (up to ∼80%) when compared to the CHF value of the base fluid (water). Another key observation has been in the significant deposition of nanoparticles on the heater surface. This fouling of the heater surface by nanoparticles is widely viewed as a main contributor that modifies the pool boiling curve of the base liquid. The deposition of the nanoparticles on the heater surface is dynamic and this in turn makes the nanofluid pool boiling curve exhibit transient characteristics.

Transient Characteristics of Pool Boiling Heat Transfer in Nanofluids

2009 ◽  
Author(s):  
Sang M. Kwark ◽  
Ratan Kumar ◽  
Gilberto Moreno ◽  
Seung M. You
Keyword(s):  
Heat Transfer ◽  
Boiling Heat Transfer ◽  
Base Fluid ◽  
Pool Boiling ◽  
Thermal Characteristics ◽  
Boiling Curve ◽  
Heater Surface ◽  
Transient Characteristics ◽  
Conductivity Enhancement ◽  
Boiling Heat Transfer Coefficient

This study shows the transient characteristics of the pool boiling curves using nanofluid as the boiling fluid. This time-dependency is in sharp contrast to a unique steady-state pool boiling curve that is typically obtained for a pure fluid. Past researches on nanofluids have provided several interesting information about the thermal characteristics for this potentially promising cooling fluid. Results from these studies have shown some extraordinary critical heat flux (CHF) values and thermal conductivity enhancement that is yet to be explained by existing theories and correlations. The nature of the pool boiling curve for a nanofluid is dependent on the nanoparticle concentration in the base fluid. Higher concentration nanofluids show a perceptible degradation in the boiling heat transfer coefficient but have exhibited an enhanced CHF value (up to ∼80%) when compared to the CHF value of the base fluid (water). Another key observation has been in the significant deposition of nanoparticles on the heater surface. This fouling of the heater surface by nanoparticles is widely viewed as a main contributor that modifies the pool boiling curve of the base liquid. The deposition of the nanoparticles on the heater surface is dynamic and this in turn makes the nanofluid pool boiling curve exhibit transient characteristics.

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.

Characterization and Pool Boiling Heat Transfer Studies of Nanofluids

2009 ◽  
Vol 131 (8) ◽  
Author(s):  
R. Kathiravan ◽  
Ravi Kumar ◽  
Akhilesh Gupta ◽  
Ramesh Chandra
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Copper Nanoparticles ◽  
Boiling Heat Transfer ◽  
Base Fluid ◽  
Pool Boiling ◽  
Outer Diameter ◽  
Distilled Water ◽  
Pool Boiling Heat Transfer

Copper nanoparticles with an average size of 10 nm are prepared by the sputtering method and are characterized using different techniques, viz., X-ray diffraction spectrum, atomic force microscopy, and transmission electron microscopy. The pool boiling heat transfer characteristics of 0.25%, 0.5%, and 1.0% by weight concentrations of copper nanoparticles dispersed in distilled water and in distilled water with 9.0 wt % of sodium dodecyl sulfate (SDS) are studied. Also the data for the boiling of pure distilled water and water with SDS are acquired. The above data are obtained using commercial seamless stainless steel tube heater with an outer diameter of 9.0 mm and an average surface roughness of 1.09 μm. The experimental results concluded that (i) critical heat flux (CHF) obtained in water with surfactant nanofluids gives nearly one-third of the CHF obtained by copper-water nanofluids, (ii) pool boiling heat transfer coefficient decreases with the increase in the concentration of nanoparticles in water base fluids, and (iii) heat transfer coefficient increases with the addition of 9.0% surfactant in water. Further addition of nanoparticles in this mixture reduces the heat transfer coefficient. (iv) CHF increases nearly 50% with an increase in concentration of nanoparticles in the water as base fluid and nearly 60% in the water with surfactant as base fluid.

A New Perspective on Heat Transfer Mechanisms and Sonic Limit in Pool Boiling

2019 ◽  
Vol 141 (5) ◽  
Author(s):  
Satish G. Kandlikar
Keyword(s):  
Heat Transfer ◽  
Boiling Heat Transfer ◽  
Pool Boiling ◽  
Superheated Liquid ◽  
Heater Surface ◽  
Liquid Stream ◽  
Maximum Heat ◽  
Pool Boiling Heat Transfer ◽  
Maximum Heat Transfer ◽  
Secondary Evaporation

Pool boiling is postulated as a single-phase heat transfer process with nucleating bubbles providing a liquid pumping mechanism over the heater surface. This results in three fluid streams at the heater surface—outgoing vapor and liquid streams, and an incoming liquid stream. Heat transfer during periodic replacement of the liquid in the influence region around a nucleating bubble is well described by transient conduction (TC) and microconvection (MiC) mechanisms. Beyond this region, free convection (FC) or macroconvection (MaC) contributes to heating of the liquid. A bubble growing on the heater surface derives its latent heat from the surrounding superheated liquid and from the microlayer providing a direct heat conduction path. Secondary evaporation occurs in the bubbles rising in the bulk after departure, and at the free surface. This secondary evaporation does not directly contribute to the heat transfer at the heater surface but provides a means of dissipating liquid superheat. A sonic limit-based model is then presented for estimating the theoretical upper limit for pool boiling heat transfer by considering the three fluid streams to approach their respective sonic velocities. Maximum heat transfer rates are also estimated using this model with two realistic velocities of 1 and 5 m/s for the individual streams and are found to be in general agreement with available experimental results. It is postulated that small bubbles departing at high velocity along with high liquid stream velocities are beneficial for heat transfer. Based on these concepts, future research directions for enhancing pool boiling heat transfer are presented.

scholarly journals Pool Boiling Amelioration by Aqueous Dispersion of Silica Nanoparticles

Nanomaterials ◽  
2021 ◽  
Vol 11 (8) ◽  
pp. 2138
Author(s):  
Sayantan Mukherjee ◽  
Naser Ali ◽  
Nawaf F. Aljuwayhel ◽  
Purna C. Mishra ◽  
Swarnendu Sen ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Contact Angle ◽  
Boiling Heat Transfer ◽  
Base Fluid ◽  
Bubble Diameter ◽  
Pool Boiling ◽  
Nucleate Boiling ◽  
Surface Wettability ◽  
Bulk Fluid ◽  
Pool Boiling Heat Transfer

Non-metallic oxide nanofluids have recently attracted interest in pool boiling heat transfer (PBHT) studies. Research work on carbon and silica-based nanofluids is now being reported frequently by scholars. The majority of these research studies showed improvement in PBHT performance. The present study reports an investigation on the PBHT characteristics and performance of water-based silica nanofluids in the nucleate boiling region. Sonication-aided stable silica nanofluids with 0.0001, 0.001, 0.01, and 0.1 particle concentrations were prepared. The stability of nanofluids was detected and confirmed via visible light absorbance and zeta potential analyses. The PBHT performance of nanofluids was examined in a customized boiling pool with a flat heating surface. The boiling characteristics, pool boiling heat transfer coefficient (PBHTC), and critical heat flux (CHF) were analyzed. The effects of surface wettability, contact angle, and surface roughness on heat transfer performance were investigated. Bubble diameter and bubble departure frequency were estimated using experimental results. PBHTC and CHF of water have shown an increase due to the nanoparticle inclusion, where they have reached a maximum improvement of ≈1.33 times over that of the base fluid. The surface wettability of nanofluids was also enhanced due to a decrease in boiling surface contact angle from 74.1° to 48.5°. The roughness of the boiling surface was reduced up to 1.5 times compared to the base fluid, which was due to the nanoparticle deposition on the boiling surface. Such deposition reduces the active nucleation sites and increases the thermal resistance between the boiling surface and bulk fluid layer. The presence of the dispersed nanoparticles caused a lower bubble departure frequency by 2.17% and an increase in bubble diameter by 4.48%, which vigorously affects the pool boiling performance.

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