Pool Boiling Heat Transfer Enhancement of Water Using Brazed Copper Microporous Coatings

2016 ◽  
Vol 138 (7) ◽  
Author(s):  
Seongchul Jun ◽  
Hyoseong Wi ◽  
Ajay Gurung ◽  
Miguel Amaya ◽  
Seung M. You
Keyword(s):  
Heat Transfer ◽  
Coating Thickness ◽  
Boiling Heat Transfer ◽  
Average Particle Size ◽  
Nucleate Boiling ◽  
Copper Surface ◽  
Heat Fluxes ◽  
Porous Coating ◽  
Average Particle ◽  
Thermally Conductive

A novel, high-temperature, thermally conductive, microporous coating (HTCMC) is developed by brazing copper particles onto a copper surface. This coating is more durable than many previous microporous coatings and also effectively creates re-entrant cavities by varying brazing conditions. A parametric study of coating thicknesses of 49–283 μm with an average particle size of ∼25 μm was conducted using the HTCMC coating to understand nucleate boiling heat transfer (NBHT) enhancement on porous surfaces. It was found that there are three porous coating regimes according to their thicknesses. The first regime is “microporous” in which both NBHT and critical heat flux (CHF) enhancements gradually grow as the coating thickness increases. The second regime is “microporous-to-porous transition” where NBHT is further enhanced at lower heat fluxes but decreases at higher heat fluxes for increasing thickness. CHF in this regime continues to increase as the coating thickness increases. The last regime is named “porous,” and both NBHT and CHF decrease as the coating thickness increases beyond that of the other two regimes. The maximum NBHT coefficient observed was ∼350,000 W/m2K at 96 μm thickness (microporous regime) and the maximum CHF observed was ∼2.1 MW/m2 at ∼225 μm thickness (porous regime).

Pool Boiling Heat Transfer Enhancement of Water Using Brazed Copper Microporous Coatings

2015 ◽  
Author(s):  
Seongchul Jun ◽  
Hyoseong Wi ◽  
Ajay Gurung ◽  
Miguel Amaya ◽  
Seung M. You
Keyword(s):  
Heat Transfer ◽  
Coating Thickness ◽  
Boiling Heat Transfer ◽  
Average Particle Size ◽  
Nucleate Boiling ◽  
Copper Surface ◽  
Heat Fluxes ◽  
Porous Coating ◽  
Average Particle ◽  
Nucleate Boiling Heat Transfer

A novel, high-temperature, thermally-conductive, microporous coating (HTCMC) is developed by brazing copper particles onto a copper surface. This coating is more durable than many previous microporous coatings and also effectively creates reentrant cavities by optimizing brazing conditions. A parametric study of coating thicknesses of 49–283 μm with an average particle size of ∼25 μm was conducted using the HTCMC coating to understand nucleate boiling heat transfer (NBHT) enhancement on porous surfaces. It was found that there are three porous coating regimes according to their thicknesses. The first regime is “microporous” in which both NBHT and critical heat flux (CHF) enhancements gradually grow as the coating thickness increases. The second regime is “microporous-to-porous transition” where NBHT is further enhanced at lower heat fluxes but decreases at higher heat fluxes for increasing thickness. CHF in this regime continues to increase as the coating thickness increases. The last regime is named as “porous”, and both NBHT and CHF decrease as the coating thickness increases further than that of the other two regimes. The maximum nucleate boiling heat transfer coefficient observed was ∼350,000 W/m2K at 96 μm thickness (“microporous” regime) and the maximum CHF observed was ∼2.1 MW/m2 at ∼225 μm thickness (“porous” regime).

Nucleate Boiling Comparison between Teflon-Coated Plain Copper and Cu-HTCMC in Water

2018 ◽  
Vol 140 (8) ◽  
Author(s):  
Seongchul Jun ◽  
Jin Sub Kim ◽  
Jungho Lee ◽  
Seung M. You
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Boiling Heat Transfer ◽  
Average Particle Size ◽  
Nucleate Boiling ◽  
Heat Fluxes ◽  
Average Particle ◽  
Thermally Conductive ◽  
Bubble Sizes ◽  
Coated Surfaces

The hydrophobic, Teflon-coated surfaces on plain copper and Cu-HTCMC (High temperature Thermally Conductive Microporous Coating) compared on pool boiling heat transfer of water. The HTCMC was created by sintering of copper powders with the average particle size of 67 µm and about 300 µm coating thickness that showed a good boiling heat transfer and the CHF enhancement from the previous study at saturation of water [1]. The Teflon-coated surfaces were created by coating of Amorphous Fluoroplastic (AF) 2400 resin on both plain copper and Cu-HTCMC. The static angles of both surfaces showed hydrophobic as about 120-130°. The departure bubble sizes created by merged bubbles of both surfaces are comparable as about 7 mm at 5 kW/m2 and the sizes are increased as heat flux increases. However, unlike to the plain surface, the smaller bubbles on Cu-HTCMC are not observed at the heat flux of 5 kW/m2 because the number of nucleation sites created in the porous structure are huge smaller bubbles are merged as soon as they grow from pores. As heat flux reaches the surfaces are covered by vapor film and reached the critical heat flux (CHF) at much lower heat fluxes compared to hydrophilic surfaces but the CHF values of Teflon-coated Cu-HTCMC is 640 kW/m2 and the value is more than tenfold higher than that of Teflon-coated plain copper.

scholarly journals Effect of Subcooling on Pool Boiling of Water from Sintered Copper Microporous Coating at Different Orientations

2018 ◽  
Vol 2018 ◽  
pp. 1-9 ◽  
Author(s):  
Seongchul Jun ◽  
Jinsub Kim ◽  
Seung M. You ◽  
Hwan Yeol Kim
Keyword(s):  
Heat Transfer ◽  
Boiling Heat Transfer ◽  
Pool Boiling ◽  
Average Particle Size ◽  
Nucleate Boiling ◽  
Copper Surface ◽  
Average Particle ◽  
Pool Boiling Heat Transfer ◽  
Microporous Coating ◽  
Plain Surface

The subcooling effect on pool boiling heat transfer using a copper microporous coating was experimentally studied in water for subcoolings of 10 K, 20 K, and 30 K at atmospheric pressure and compared to that of a plain copper surface. A high-temperature thermally conductive microporous coating (HTCMC) was made by sintering copper powder with an average particle size of 67 μm onto a 1 cm × 1 cm plain copper surface with a coating thickness of ~300 μm. The HTCMC surface showed a two times higher critical heat flux (CHF), ~2,000 kW/m2, and up to seven times higher nucleate boiling heat transfer (NBHT) coefficient, ~350 kW/m2K, when compared with a plain copper surface at saturation. The results of the subcooling effect on pool boiling showed that the NBHT of both the HTCMC and the plain copper surface did not change much with subcooling. On the other hand, the CHF increased linearly with the degree of subcooling for both the HTCMC and the plain copper surface. The increase in the CHF was measured to be ~60 kW/m2for every degree of subcooling for both the HTCMC and the plain surface, so that the difference of the CHF between the HTCMC and the plain copper surface was maintained at ~1,000 kW/m2throughout the tested subcooling range. The CHFs for the HTCMC and the plain copper surface at 30 K subcooling were 3,820 kW/m2and 2,820 kW/m2, respectively. The experimental results were compared with existing CHF correlations and appeared to match well with Zuber’s formula for the plain surface. The combined effect of subcooling and orientation of the HTCMC on pool boiling heat transfer was studied as well.

Pool Boiling Heat Transfer with Nanotube Arrays Surface on Titanium

2012 ◽  
Vol 550-553 ◽  
pp. 2913-2916 ◽  
Author(s):  
Jin Liang Tao ◽  
Xin Liang Wang ◽  
Pei Hua Shi ◽  
Xiao Ping Shi
Keyword(s):  
Heat Transfer ◽  
Boiling Heat Transfer ◽  
Heat Transfer Performance ◽  
Pool Boiling ◽  
Nucleate Boiling ◽  
Test Fluid ◽  
Porous Coating ◽  
Pool Boiling Heat Transfer ◽  
Nucleate Boiling Heat Transfer ◽  
Boiling Heat Transfer Coefficient

In this paper, a new porous coating was formed directly on the surface of titanium metal via anodic oxidation. And by the SEM, the morphology of the coating, which is composed of well-ordered perpendicular nanotubes, was characterized. Moreover, taking deionized water as the test fluid, a visualization study of the coating on its pool boiling heat transfer performance was made. The results demonstrated that compared with the smooth surface, the nucleate boiling heat transfer coefficient can increase 3 times while the nucleate boiling super heat was reduced 30%.

Nucleate Boiling Heat Transfer of Binary Mixtures at Low to Moderate Heat Fluxes

1999 ◽  
Vol 121 (2) ◽  
pp. 365-375 ◽  
Author(s):  
R. J. Benjamin ◽  
A. R. Balakrishnan
Keyword(s):  
Heat Transfer ◽  
Stainless Steel ◽  
Binary Mixtures ◽  
Boiling Heat Transfer ◽  
Heating Surface ◽  
Nucleate Boiling ◽  
Steel Tube ◽  
Heat Fluxes ◽  
Stainless Steel Tube ◽  
Turbulent Natural Convection

A model for nucleate pool boiling heat transfer of binary mixtures has been proposed based on an additive mechanism. The contributing modes of heat transfer are (i) the heat transferred by microlayer evaporation, (ii) the heat transferred by transient conduction during the reformation of the thermal boundary layer, and (iii) the heat transferred by turbulent natural convection. The model takes into account the microroughness of the heating surface which has been defined quantitatively. The model compares satisfactorily with data obtained in the present study and in the literature. These data were obtained on a variety of heating surfaces such as a vertical platinum wire, a horizontal stainless steel tube and flat horizontal aluminium, and stainless steel surfaces (with various surface finishes) thereby demonstrating the validity of the model.

Oil Effects on In-Tube Evaporation of CO2 by Altering Flow Regime and Properties

2013 ◽  
Author(s):  
Pega Hrnjak ◽  
Seongho Kim
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Boiling Heat Transfer ◽  
Flow Boiling ◽  
Nucleate Boiling ◽  
Heat Fluxes ◽  
Circulation Rate ◽  
Convective Boiling ◽  
Mass Fluxes

Flow boiling heat transfer characteristics of CO2 with and without oil were investigated experimentally in horizontal smooth and enhanced tubes with an inner diameter of 11.2 mm. The visualization of flow pattern provides a detailed attributes of the nucleate and the convective boiling heat transfer. In order to investigate the effect of the miscible oil on the heat transfer of CO2, POE (polyolester) RENSIO C85E oil is added to give an oil circulation rate (OCR) between 0.5% and 2%. Results are compared with those of pure CO2. The experimental conditions include evaporation temperatures of −15 °C, mass fluxes from 40 to 200 kg/m2 s, heat fluxes from 0.5 to 10 kW/m2, and vapor qualities from 0.1 to 0.8. Oil generally deteriorates the heat transfer coefficient of pure CO2. The reduction in heat transfer coefficient is most apparent at low vapor qualities, 0.1 to 0.4, and at low mass fluxes, 100 and 200 kg/m2. It is caused by the suppression of nucleate boiling due to increased surface tension. At conditions where the convective boiling contribution is dominant, vapor qualities above 0.5, oil increases heat transfer coefficients. Through visualization, it is shown that the wetted area on the perimeter of inner tube is enhanced due to formation of foaming in the smooth tube. However, such enhancement of heat transfer due to forming is negligible in the enhanced tube, because the enhanced factor due to micro-finned structures is dominant.

Subcooled Boiling Heat Transfer in a Short Vertical SUS304-Tube at High Liquid Reynolds Number

2009 ◽  
Author(s):  
Koichi Hata ◽  
Suguru Masuzaki
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Boiling Heat Transfer ◽  
Flow Boiling ◽  
Nucleate Boiling ◽  
Test Tube ◽  
Heat Fluxes ◽  
Subcooled Boiling ◽  
Transfer Coefficients ◽  
Spontaneous Nucleation

The subcooled boiling heat transfer and the steady state critical heat fluxes (CHFs) in a short vertical SUS304-tube for the flow velocities (u = 17.28 to 40.20 m/s), the inlet liquid temperatures (Tin = 293.30 to 362.49 K), the inlet pressures (Pin = 842.90 to 1467.93 kPa) and the exponentially increasing heat input (Q = Q0 exp(t/τ), τ = 10 s) were systematically measured by the experimental water loop comprised of a multistage canned-type circulation pump with high pump head. The SUS304 test tubes of inner diameters (d = 3 and 6 mm), heated lengths (L = 33 and 59.5 mm), effective lengths (Leff = 23.3 and 49.1 mm), L/d (= 11 and 9.92), Leff/d (= 7.77 and 8.18), and wall thickness (δ = 0.5 mm) with average surface roughness (Ra = 3.18 μm) are used in this work. The inner surface temperature and the heat flux from non-boiling to CHF were clarified. The subcooled boiling heat transfer for SUS304 test tube was compared with our Platinum test tube data and the values calculated by other workers’ correlations for the subcooled boiling heat transfer. The influence of flow velocity on the subcooled boiling heat transfer and the CHF is investigated into details and the widely and precisely predictable correlation of the subcooled boiling heat transfer for turbulent flow of water in a short vertical SUS304-tube is given based on the experimental data. The correlation can describe the subcooled boiling heat transfer coefficients obtained in this work within 15% difference. Nucleate boiling surface superheats for the SUS304 test tube become very high. Those at the high liquid Reynolds number are close to the lower limit of Heterogeneous Spontaneous Nucleation Temperature. The dominant mechanisms of the flow boiling CHF in a short vertical SUS304-tube are discussed.

scholarly journals Bubble dynamics and mechanistic boiling heat transfer prediction on a scored copper surface

2021 ◽  
Vol 2116 (1) ◽  
pp. 012009
Author(s):  
Zhen Cao ◽  
Zan Wu ◽  
Bengt Sundén
Keyword(s):  
Heat Transfer ◽  
Boiling Heat Transfer ◽  
Bubble Dynamics ◽  
Mechanistic Model ◽  
Transient Heat Conduction ◽  
Nucleation Site ◽  
Copper Surface ◽  
Heat Fluxes ◽  
Transfer Model ◽  
Microlayer Evaporation

Abstract In this study, pool boiling heat transfer of de-ionized water was experimentally studied on a scored copper surface at a heat-flux range of 0 - 60 W/cm2. Bubble dynamics in an isolated bubble region were carefully investigated, including bubble departure diameters, bubble departure frequencies, and active nucleation site densities. The bubble dynamics were compared with available models, indicating the suitable models regarding the present experimental results. Then, based on the bubble dynamics, a mechanistic heat transfer model, developed in our previous studies, was employed to predict the present boiling curve. In the mechanistic model, heat fluxes from natural convection, transient heat conduction, and microlayer evaporation were incorporated.

Pool Boiling Heat Transfer of Alumina-Water, Zinc Oxide-Water and Alumina-Water+Ethylene Glycol Nanofluids

2005 ◽  
Author(s):  
Gilbert Moreno ◽  
Steven J. Oldenburg ◽  
Seung M. You ◽  
Joo H. Kim
Keyword(s):  
Heat Transfer ◽  
Zinc Oxide ◽  
Ethylene Glycol ◽  
Aluminum Oxide ◽  
Boiling Heat Transfer ◽  
Pool Boiling ◽  
Nucleate Boiling ◽  
Average Particle ◽  
Al2o3 Nanoparticles ◽  
Significant Difference

This investigation conducts pool boiling experiments under saturated conditions (Tsat = 60 °C) using nanofluids as the coolants. Three different nanofluids were tested including zinc oxide (ZnO)-water, aluminum oxide (Al2O3)-water and aluminum oxide (Al2O3)-water+ethylene glycol (ethylene glycol solution). At saturation (Tsat = 60°C), the pool boiling performance of the two pure water based nanofluids were similar. The maximum CHF enhancement as compared to the predicted Zuber’s [1] CHF evaluated at an equivalent saturation temperature is ∼180% for Al2O3-water nanofluids and ∼240% for ZnO-water nanofluids. In both cases, no degradation in the boiling heat transfer rate was observed for lower nanoparticle concentrations. However, higher nanoparticle concentrations demonstrate nucleate boiling heat transfer degradation at high heat fluxes. The dispersion of Al2O3 nanoparticles in various ethylene glycol solutions is also found to enhance CHF by as much as ∼130%. A significant difference in the diameter of individual grains/particles (27 ± 16.3 nm) and the volume weighted average diameter of particles in solution (155 ± 80 nm) indicates that the Al2O3-water nanofluids consist primarily of nanoparticle agglomerates. Gravimetric fractionation of the nanofluid produced nanofluids with particle/particle aggregate average diameters that ranged from 69–346 nm. Over the size range tested, there was no significant CHF dependence on the average particle diameter.

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