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1-13 of 13
Jung-Yeul Jung
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Journal Articles
Journal:
Journal of Heat Transfer
Article Type: Photo Gallery
J. Heat Transfer. August 2016, 138(8): 080907.
Paper No: HT-16-1213
Published Online: July 8, 2016
Abstract
The present study experimentally investigates the evaporative characteristics for a nanofluid droplet on heated surface. For experiments, the alumina (Al2O3) nanoparticles having a 50 nm average diameter were distributed in deionized (DI)water. The equilibrium contact angles (ECA) of DI-water on bare (without texturing) and hole-patterned textured (by µ-CNC machine) copper surfaces were 60o and 82o. Also, advancing and receding contact angles were 73.3o and 25.8o for bare surface, and 101.3o and 55.2o for textured surface. Surface temperature was fixed as 100±0.2oC, measured by resistance temperature detector (RTD) sensors with data logger. During the experiments, the ambient temperature was 22oC with the relative humidity of 32%. At the initial stage, the dynamic contact angle (DCA) of 0.01 vol.% nanofluid droplet on the textured surface drastically increased over its own ECA due to the generation of large bubbles inside the droplet. However, the contact angle of 0.1vol.% nanofluid droplet at t = 5 s was smaller than that of 0.01vol.% case because the increase in nanofluid concentration caused the reduction of surface tension. After that, DCA gradually decreased until dried out, and total evaporation time was significantly delayed in the case of textured surface. Moreover,the heat transfer characteristics during evaporation phenomenon was affected by the nanofluid concentration and the contact area with the heated surface.
Journal Articles
Journal:
Journal of Heat Transfer
Article Type: Photo Gallery
J. Heat Transfer. August 2014, 136(8): 080902.
Paper No: HT-14-1200
Published Online: August 1, 2014
Proceedings Papers
Proc. ASME. IHTC14, 2010 14th International Heat Transfer Conference, Volume 6, 625-630, August 8–13, 2010
Paper No: IHTC14-22556
Abstract
Binary nanoemulsions, nano-sized oil-droplet suspensions in binary solution (H 2 O/LiBr), are developed to enhance the heat and mass transfer performance of absorption refrigeration systems. In this study, a novel four-step method is proposed to prepare the stable oil-in-binary solution (O/S) emulsion. To stabilize the nanoemulsions in a strong electrolyte, a polymeric stabilizer (Gum Arabic) is used as a steric stabilizer. The droplet size and the thermal conductivity of binary nanoemulsions are measured by the dynamic light scattering method and the transient hot-wire method, respectively. It is concluded that the ratio of 2:1 (oil:surfactant) is the best condition for distribution stability. It is also found that the measured thermal conductivity of the oil-in-water nanoemulsion enhances up to 6.4% at 0.1 vol% of oil, and the binary nanoemulsion enhances up to 3.6% at 1.0 vol% of oil in 30 wt% H 2 O/LiBr compared with the estimated one from the Maxwell’s model. This result is compared with electric conductivity of LiBr solution and it is found both conductivities have similar trend. It is finally proposed that the thermal conductivity of the binary nanoemulsion could be enhanced by adding nano-sized droplets of n-decane oil, which has a lower thermal conductivity than that of the base fluid.
Proceedings Papers
Proc. ASME. MNHMT2009, ASME 2009 Second International Conference on Micro/Nanoscale Heat and Mass Transfer, Volume 1, 461-466, December 18–21, 2009
Paper No: MNHMT2009-18177
Abstract
Binary nanoemulsions, oil-droplet suspensions in binary solution (H 2 O/LiBr), are developed to enhance the heat and mass transfer performance of absorption refrigeration cycles. This paper studies the formation and stability of n-decane in H 2 O/LiBr nanoemulsions produced by using polyoxyethylene lauryl ether and polyoxyethylene sorbitan monolaurate as surfactant. To stabilize the nanoemulsions in a strong electrolyte, polymeric stabilizer (gum Arabic) is used as a steric stabilizer. The droplet size and the thermal conductivity of binary nanoemulsions are measured by the dynamic light scattering method and the transient hot-wire method, respectively. It is found that the effective thermal conductivity of binary nanoemulsions (1.0 vol % of n-decane in 30 wt % H 2 O/LiBr) enhances up to 3.59% with the average droplet size of 44.3 nm. The stability has more significant effect on the thermal conductivity enhancement than the initial drop size.
Proceedings Papers
Inward Flow of Micro-Particles in an Evaporating Di-Dispersed Colloid Droplet on Hydrophilic Surface
Proc. ASME. ICNMM2009, ASME 2009 7th International Conference on Nanochannels, Microchannels and Minichannels, 1051-1054, June 22–24, 2009
Paper No: ICNMM2009-82293
Abstract
It is well known that the liquid and the nanoparticles in an evaporating colloid droplet on the hydrophilic surface move radially outward for the contact line to maintain its position. However, the motion of micro-/nano-particles in an evaporating di-dispersed colloid droplet has not been reported to date. In this study, an experiment on an evaporating di-dispersed colloid droplet on the hydrophilic surface is carried out. It is found that nano-particles move radially outward and remain at the contact line while micro-particles move inward toward the center of the droplet. Further the mechanism of the micro-particles moving toward the center of the droplet is found to be due to the surface tension force of the liquid.
Proceedings Papers
Proc. ASME. ICNMM2007, ASME 5th International Conference on Nanochannels, Microchannels, and Minichannels, 483-487, June 18–20, 2007
Paper No: ICNMM2007-30018
Abstract
Micro particles or biological cells mixed in water solution was shown to be separated using the combined electrical force due to dielectrophoresis and mechanical one generated in an evaporating droplet. Micro patterned electrodes of Au were fabricated on the silicon dioxide layer and were used for generating dielectrophoresis. Polystyrene particles, red blood cells and E-coli were used for separating objects. Micro particles and biological cells were separated by adjusting the amplitude and frequency of the applied voltage. The mechanical force is enough to transport the particles to the boundary of the droplet, nevertheless it could not detach the particles trapped at the electrode. Based on this work, the micro particles and biological cells can be separated, controlled and sensed without liquid pumping unit.
Proceedings Papers
Proc. ASME. ICMM2003, 1st International Conference on Microchannels and Minichannels, 291-297, April 24–25, 2003
Paper No: ICMM2003-1032
Abstract
Forced convective heat transfer coefficients and friction factor for flow of water and FC-72 in microchannels with a rectangular cross section were measured. An integrated microsystem consisting of five microchannels on one side and a localized heater and seven polysilicon temperature sensors along the selected channels on the other side was fabricated by using a double side polished silicon wafer. For the microchannels tested, the friction factor constant C = f Re Dh obtained are values between 35.7 and 81.9, which are close to the theoretical value of 57.0. The measured Nusselt number in the laminar regime tested could be correlated by a correlation, Nu = A Re Dh 1.37 Pr 1/3 where A is the value between 0.000 454 and 0.000 646.
Proceedings Papers
Proc. ASME. ICMM2004, ASME 2nd International Conference on Microchannels and Minichannels, 961-966, June 17–19, 2004
Paper No: ICMM2004-2437
Abstract
Proteinaceous bubbles of 185 nm in average diameter were synthesized by a sonochemical treatment of bovine serum albumin in aqueous solution and the nanoparticles (TiO 2 ) solution was made by ultrasonic irradiation. To study the macroscopic flow behavior associated with the changes in the state of microparticles, a flow test of these solutions in microchannels was done. Also the size distributions of the proteinaceous bubbles in solution before and after the flow test were measured by a light scattering method. Test results show that the air-filled proteinaceous bubbles in solution adjust their size to reduce the shear stress encountered in the flow through the microchannel. On the other hand, the flow rate of the solution with nanoparticles suspensions becomes smaller than that of deionized water above the flow rate of 6 cm 3 /min in the microchannel with a dimension of 100×150 μm 2 .
Proceedings Papers
Proc. ASME. ICMM2005, ASME 3rd International Conference on Microchannels and Minichannels, Part B cont’d, 349-354, June 13–15, 2005
Paper No: ICMM2005-75015
Abstract
A bubble-powered micropump was fabricated and tested in this study. The micropump consists of a pair of nozzle-diffuser flow controller and a pumping chamber. The two-parallel micro line heaters were fabricated to be embedded in the silicon dioxide layer above a silicon wafer which serves as a base plate for the micropump. The pumping chamber, the pair of nozzle-diffuser unit and microchannels including the liquid inlet and outlet port were fabricated by etching through another silicon wafer. A glass wafer having two holes of inlet and outlet ports of liquid serve as upper plate of the pump. The sequential photographs of bubble nucleation, growth and collapse were visualized by CCD camera. Clearly liquid flow through the nozzle during the period of bubble growth and slight back flow of liquid at the initial period collapsing can be seen. The mass flow rate was found to be dependent on the duty ratio and the operation frequency. The mass flow rate decreases as the duty ratio increases in the micropump with either circular or square pumping chamber.
Proceedings Papers
Proc. ASME. ICNMM2006, ASME 4th International Conference on Nanochannels, Microchannels, and Minichannels, Parts A and B, 313-317, June 19–21, 2006
Paper No: ICNMM2006-96158
Abstract
A capillary pumped loop (CPL) which can be used for cooling electronic devices such as a CPU of a personal computer or note book was developed. An evaporator and a condenser with the same size of 30 mm × 30 mm × 1.55 mm were designed and fabricated using 3 layer of silicon wafer for the CPL. In the evaporator, 525 μm thickness silicon wafer where an array of 40 × 40 cone shaped micro holes were fabricated was inserted above the compensation cavity for liquid transportation instead of porous wick. The same cone shaped microstructure was used in the condenser to create a stable interface between the liquid and the vapor phases. The CPL fabricated was tested under various conditions such as different relative heights, fill ratios and heat fluxes. The operation conditions of CPL were varied depending on relative height and fill ratio. With an allowable temperature of 82 °C on the evaporator surfaces, the CPL can handle a heat flux of about 3.7 W/cm 2 with the air cooled condenser. Steady state operation condition was achieved within 10 minutes.
Proceedings Papers
Proc. ASME. IMECE2002, Heat Transfer, Volume 2, 209-215, November 17–22, 2002
Paper No: IMECE2002-32777
Abstract
Time dependent surface temperatures on a micro heater were measured when a voltage pulse of 25~200 μs was applied to the heater. The dimensions of the micro polysilicon heaters fabricated on a silicon substrate are 50×5×0.523 μm 3 for a micro line heater and 65×65×0.523 μm 3 for a micro square heater. With the minimum voltage needed for bubble growth, the temperature for bubble nucleation on the heater immersed in FC-72 was measured to be 420.7 K for the micro line heater, which is close to the superheat limit of the working fluid. On the other hand a bubble nucleates at temperature of 388 K on the square heater. Bubble nucleation, growth and subsequent collapse process were visualized by a microscope-35 mm camera with a μs flash unit.
Proceedings Papers
Proc. ASME. IMECE2006, Heat Transfer, Volume 3, 327-332, November 5–10, 2006
Paper No: IMECE2006-13851
Abstract
Convective heat transfer coefficient and friction factor of a nanofluid in rectangular microchannel were measured. An integrated microsystem consisting of a single microchannel on one side and two localized heaters and five polysilicon temperature sensors along the channel on the other side were fabricated. Aluminum dioxide (Al 2 O 3 ) nanofluids with various particle volume fractions were used in experiment to investigate the effect of the volume fraction of the nanoparticles to the convective heat transfer and fluid flow in microchannels. The convective heat transfer coefficient of the Al 2 O 3 nanofluid in laminar flow regime was measured to be increased up to 15% compared to the distilled water at a volume fraction of 1.8 volume percent without major friction loss. The Nusselt number measured increases with increasing the Reynolds number in laminar flow regime. A new type of convective heat transfer correlation was proposed to correlate experimental data of heat transfer coefficient for nanofluids in microchannels.
Journal Articles
Journal:
Journal of Heat Transfer
Article Type: Technical Papers
J. Heat Transfer. August 2003, 125(4): 687–692.
Published Online: July 17, 2003
Abstract
Nucleation temperatures on micro line heaters were measured precisely by obtaining the I-R (current-resistance) characteristic curves of the heaters. The bubble nucleation temperature on the heater with 3 μm width is higher than the superheat limit, while the temperature on the heater with broader width of 5 μm is considerably less than the superheat limit. The nucleation temperatures were also estimated by using the molecular cluster model for bubble nucleation on the cavity free surface with effect of contact angle. The bubble nucleation process was observed by microscope/35 mm camera unit with a flash light of μs duration.
