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Nucleate pool boiling of R134a on cold sprayed Cu–CNT–SiC and Cu–CNT–AlN composite coatings
Pialago, Edward Joshua T.,Kwon, Oh Kyung,Jin, Jae Sik,Park, Chan Woo Elsevier 2016 Applied Thermal Engineering Vol.103 No.-
<P><B>Abstract</B></P> <P>Ternary copper–carbon nanotube–silicon carbide (Cu–CNT–SiC) and copper–carbon nanotube–aluminum nitride (Cu–CNT–AlN) composite coatings, which were fabricated by mechanical alloying and cold gas dynamic spraying, were used as heating surfaces for boiling heat transfer enhancement. The surfaces of these composite coatings had randomly distributed micro- and nano-sized cavities, which served as active sites for bubble nucleation. Nucleate boiling heat transfer tests on the composite coatings were investigated in a pool of saturated R134a refrigerant at 4.8±0.04°C. Boiling inception on the Cu–CNT–SiC and Cu–CNT–AlN coatings started at heat flux values of about 10–20kW/m<SUP>2</SUP> and at wall superheats that were about 4°C lower than that of the plain Cu plate. The Cu–CNT coating had maximum boiling heat transfer enhancement ratio <I>E</I> <SUB>h,max</SUB> of 1.48 as compared to the plain Cu plate. With the addition of SiC and AlN particles into the composition of the Cu–5CNT composite, the enhancement was augmented further. The coating with 20vol.% AlN exhibited the highest enhancement with an <I>E</I> <SUB>h,max</SUB> of 2.83. This was followed by the coating with 10vol.% SiC with an <I>E</I> <SUB>h,max</SUB> equal to 2.52. Although the Cu–CNT–ceramic coatings had high <I>E</I> <SUB>h,max</SUB>, the <I>E</I> <SUB>h</SUB> decreased at high heat fluxes. The maximum enhancement by achieved by each of the composite coatings was observed at heat fluxes within 100–200kW/m<SUP>2</SUP>.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Cu–CNT–SiC and Cu–CNT–AlN coatings were fabricated by mechanical alloying and cold spraying. </LI> <LI> The coatings were used as heating surfaces for the enhancement of nucleate boiling of R134a. </LI> <LI> The ternary composite coatings showed boiling enhancement ratios of up to 2.83. </LI> <LI> The (Cu–5CNT)–20AlN composite coating exhibited the highest boiling enhancement. </LI> <LI> Maximum enhancement by each composite coating was observed at heat fluxes within 100–200kW/m<SUP>2</SUP>. </LI> </UL> </P>
Pialago, Edward Joshua T.,Kwon, Oh Kyung,Kim, Min-Soo,Park, Chan Woo Elsevier 2015 JOURNAL OF ALLOYS AND COMPOUNDS Vol.650 No.-
<P><B>Abstract</B></P> <P>Ternary copper (Cu)–carbon nanotube (CNT)–aluminum nitride (AlN) composite coatings were consolidated by the cold gas dynamic spray (CGDS) deposition of mechanically alloyed (MA) powders. The MA powder and CGDS coating samples were characterized by weight and size measurements, optical microscopy, scanning electron microscopy, energy-dispersive X-ray spectroscopy (EDX), and X-ray diffraction (XRD). The porosity and roughness of the coatings were examined by porosimetry and profilometry, respectively. Also, the wettability of the coatings in saturated liquid R134a refrigerant was investigated. The EDX analysis depicted the non-homogeneous dispersion of the AlN as well as the CNT. The XRD results revealed that the composite powders and coatings had undergone microstraining and grain size reduction due to deformation. Metallographic examination showed that the coating internal microstructures had lamellar and compacted features, which evidenced the severe deformation that resulted from the impact during particle deposition. Although the coatings had externally porous surfaces, they had dense and non-porous internal microstructures. Moreover, smaller pores were located inside the larger pores or craters on the surfaces. The addition of 10 vol.% and 20 vol.% AlN into the Cu–5CNT mixture produced ternary Cu–CNT–AlN composite coatings with fine pores that were directly open to the surfaces. Lastly, the coatings with AlN were more wettable in liquid R134a than the plain Cu plate and pure Cu and Cu–5CNT coatings.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Cu–CNT–AlN coatings were fabricated by mechanical alloying and cold spraying. </LI> <LI> The dispersion of fillers in the Cu–CNT–AlN coatings was not homogeneous. </LI> <LI> The Cu–CNT–AlN coatings were less rough and less porous than the other coatings. </LI> <LI> The Cu–CNT–AlN coatings had smaller surface pores than the other coatings. </LI> <LI> The Cu–CNT–AlN coatings were more wettable in liquid R134a than the other coatings. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>
피알라고 애드워드(Edward Joshua Pialago),정희여(Heeyeo Jung),유다영(Dayoung Yu),배성만(Seongman Bae),박찬우(Chan-Woo Park) 대한기계학회 2010 대한기계학회 춘추학술대회 Vol.2010 No.11
In the present study, the mechanical alloying of carbon nanotubes (CNTs) and copper powder by ball milling is being investigated. Results show that the physical characteristics such as the dispersion of CNTs and the presence or absence of the agglomeration of particles are depended on the milling time and CNT content of the powder mixture. Depending on the end application of the CNT-Cu powder composite, the desired composite can be fabricated by controlling the milling parameters such as mixture composition, milling time as well as temperature.
Kim, Dae-Hae,Pialago, Edward Joshua T.,Shin, Jai-Yoon,Kwon, Oh Kyung,Kim, Min-Soo,Park, Chan Woo Elsevier 2017 Applied thermal engineering Vol.123 No.-
<P><B>Abstract</B></P> <P>In this study, turbulence generators with rectangular geometry were designed to be fixed inside the tube of an oil cooler for the hydraulic steering of automobiles and their performance characteristics in the heat exchanger were investigated. The heat transfer rates, heat transfer coefficients, the coefficient of the pressure drop values, and friction factors were measured in accordance to the flow rates and inlet temperature of the oil. The resulting Nusselt numbers (Nu) increased when the angle of the turbulence generator wings was increased up to 45–65° but decreased when the angle was increased further up to 75°. On the hand, the friction factor (<I>f</I>) continued to increase as the angle configuration was increased. The highest value of the thermal performance enhancement factor (TEF), which was 6.46, was obtained from the turbulence generator angle of 45°, which could be considered as the optimum angle configuration. Lastly, the empirical correlations that were developed for the Nu and the <I>f</I> had good agreement with the experimental values and both had conservative error range of ±20%.</P>
Kristian Arvin Ada,Edward Joshua Pialago,Xiru Zheng,Chan Woo Park 대한기계학회 2012 대한기계학회 춘추학술대회 Vol.2012 No.11
The heat transfer performance effects of Fe/CNT composite coating of the inside pipe surface of a carbon steel tube was investigated. The effects were compared with pure carbon steel to identify whether an enhancement occurred or not. The powder composite used in this experiment was created through ball milling at 900 rpm in 4 hours using an attrition ball mill. After creating the powder it is sprayed on the inside pipe surface of a carbon steel tube through electrostatic spraying then sintered at 600 ℃ for 8 hrs. The CNT used in this work is a multi-walled carbon nanotube. The CNT and Fe powder are used as received and did not undergo any chemical processes. The composite coating consists of iron as the base powder and different volume percent of CNT’s namely 5, 10, 15, 20 and 30 vol. % respectively. Another type of tube used also is the plain carbon steel as a standard reference and basis for analysis and interpretation of the results. The heat transfer performance was obtained and compared with each other. Based on the result the CNT composite coating having a 20 vol. % CNT gives the highest heat transfer performance. Too much CNT or a composition of 30 vol. % in the composite affects the heat transfer performance of the pipe making it less effective due to the powder being too small and the coagulation of the powders during powder making and sintering process. Surface characterization is done by FESEM imaging and EDX to identify whether a presence of CNT is observed in the composite coating. The pore size density is also analyzed through the use of pore size analyzer. Raman spectroscopy is used to identify structure change of the coating materials. The surface roughness was acquired by the use of Mitutoyo Surftest SJ-400 which immediately gives a direct average of the surface roughness being measured.