• Journal of Advanced Marine Engineering and Technology
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• v.40 no.3
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• pp.152-156
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• 2016

Wastewater heat recovery heat pump systems use heated wastewater from public baths or factories as the heat pump's heat source. Generally, this system uses a bare tube evaporator. In the heat transfer process from wastewater to refrigerant, thermal resistance is caused primarily by fouling deposits on the outside surface of tube. Fouling directly increases thermal resistance and decreases heat pump efficiency. Thus, it is desirable to eliminate fouling. In this study, we fabricated a fouling mitigation device using a bubbling fluidized bed with cleaning sponge balls in the wastewater bath. Experimental conditions were as follows: $20^{\circ}C$ cold-water temperature, $40^{\circ}C$ wastewater temperature, 100 L/h cold water flow rate, and $0.161m^2$ heat exchanger surface area. Experimental results showed that the thermal resistance of fouling decreased by 56% with the fluidized bed alone and by 86% with both the fluidized bed and cleaning sponge balls.

• Transactions of the KSME C: Technology and Education
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• v.3 no.4
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• pp.265-271
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• 2015

The bonding process should be achieved in vacuum environment to avoid air bubble. In this study, we studied about pressure uniformity that became an issue in thermo compression bonding usually. Uniform press is realized by the method that use air spring and metal form spring. The concept of uniform press using air spring is removed except pressing direction in the press processing so angle between the vector of pressure surface and the pressure axis is parallel automatically. Air spring compensate the errors of machining and assembly. Metal form compensate the thermal deformation and flatness error.

• Journal of the Korea Institute of Building Construction
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• v.17 no.6
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• pp.507-515
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• 2017

This study is to develop a high quality lightweight foamed concrete that can be applied in the field using EXFG by cracking reducing agent combined with FGD and ALS. First, to increase the volume of foam, the flow and density of the mixture was increased and decreased, respectively. At this time, the effect of substitution ratio of EXFG on fluidity was negligible. The fraction of foam was the highest at EXFG 1%, and the settlement was found to be prevented by the expansion reaction at EXFG 1%. At this time, the ratio of foam was 65%. In the compressive strength, the strengths were similar or decreased when the substitution ratio of EXFG was more than 1%. The apparent density satisfied the KS 0.5 type at the bubble contents was 65%. In case of EXFG substitution, dry shrinkage was decreased by about 10%. As the substitution ratio of EXFG increased, the thermal conductivity increased proportionally.

• Journal of the Korean Solar Energy Society
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• v.29 no.5
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• pp.35-44
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• 2009

In this study, boiling heat transfer coefficients(HTCs) and critical heat flux(CHF) are measured on a smooth square flat copper heater in a pool of pure water with and without carbon nano tubes(CNTs) dispersed at $60^{\circ}C$. Tested aqueous nanofluids are prepared using multi-walled CNTs whose volume concentrations are 0.0001, 0.001, 0.01, and 0.05%. For dispersion of CNTs, polyvinyl pyrrolidone(PVP) is used in distilled water. Pool boiling HTCs are taken from $10kW/m^2$ to critical heat flux for all nanofluids. Test results show that the pool boiling HTCs of the nanofluids are lower than those of pure water in entire nucleate boiling regime. On the other hand, critical heat flux is enhanced greatly showing up to 200% increase at volume concentration of 0.001% CNTs as compared to that of pure water. This is related to the change of surface characteristics by the deposition of CNTs. This deposition makes a thin CNT layer on the surface and the active nucleation sites of heat transfer surface are decreased due to this layer. The thin layer acts as the thermal resistance and also decreases the bubble generation rate resulting in a decrease in pool boiling HTCs. The same layer, however, maintains the nucleate boiling even at very high heat fluxes and reduces the formation of large vapor canopy at near CHF resulting in a significant increase in CHF.

• Journal of Energy Engineering
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• v.2 no.2
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• pp.179-186
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• 1993

Heat pipes. applied to a flat plate solar collector, have a long and slender configuration with relatively low heat flux in the evaporator section. Such a heat pipe has a tendency to build-up a liquid pool at the lower part of the evaporator section. and at this pool occurs such complicated phenomena of evaporation and fluid dynamics as superheat, sudden generation of bubble, its likely explosive growth process and flooding, etc. In the present study. we tried to solve these problems by means of adjusting two principal design parameters, the liquid inventory and the installation region of the wick, using 4 heat pipes and 3 thermospheres. The corresponding results can be summarized as follows$\^$1)/. The effective thermal conductances of the heat pipe was greatly improved by eliminating the wick in the adiabatic and condenser sections$\^$2)/. The liquid inventory should be increased by about 40% larger than what is saturated the wick$\^$3)/. In the evaporator section the wick has a favorable effect to reduce both unstable operation by intermittent occurrence of nucleate boiling and response time at the initial start-up process.

• Composites Research
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• v.28 no.2
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• pp.70-74
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• 2015

In this paper, carbon nanotubes (CNTs) and micro glass bubbles (GBs) have been incorporated into a polyamide6 (PA6) matrix to impart thermoelectric properties. The spaces created in the matrix by GBs allows the formation of "segregated" CNT network. The tightly bound CNT network, if controlled properly, can serve as a conductive path for electron transport, while prohibiting phonon transport, which would provide an ideal configuration for thermoelectric applications. The CNTs and GBs were dispersed in a nylon-formic acid solution using horn sonication followed by coagulation in deionized water, and nanocomposite panels were fabricated using a hot press. The performance of nanocomposite panels was evaluated from thermal and electrical conductivities and Seebeck coefficient, and a thermoelectric figure of merit as high as 0.016 was achieved.

• Nuclear Engineering and Technology
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• v.48 no.4
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• pp.847-858
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• 2016

An overview is given on the work of the Laboratory of Nuclear Energy Systems at ETH, Zurich (ETHZ) and of the Laboratory of Thermal Hydraulics at Paul Scherrer Institute (PSI), Switzerland on tight-lattice bundles. Two-phase flow in subchannels of a tight triangular lattice was studied experimentally and by computational fluid dynamics simulations. Two adiabatic facilities were used: (1) a vertical channel modeling a pair of neighboring sub-channels; and (2) an arrangement of four subchannels with one subchannel in the center. The first geometry was equipped with two electrical film sensors placed on opposing rod surfaces forming the subchannel gap. They recorded 2D liquid film thickness distributions on a domain of $16{\times}64$ measuring points each, with a time resolution of 10 kHz. In the bubbly and slug flow regime, information on the bubble size, shape, and velocity and the residual liquid film thickness underneath the bubbles were obtained. The second channel was investigated using cold neutron tomography, which allowed the measurement of average liquid film profiles showing the effect of spacer grids with vanes. The results were reproduced by large eddy simulation + volume of fluid. In the outlook, a novel nonadiabatic subchannel experiment is introduced that can be driven to steady-state dryout. A refrigerant is heated by a heavy water circuit, which allows the application of cold neutron tomography.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.24 no.9
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• pp.685-692
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• 2012

In this work, nucleate pool boiling heat transfer coefficients(HTCs) of 5 refrigerants of different vapor pressure are measured on horizontal Thermoexcel-E square surface of 9.53 mm length. Tested refrigerants are R32, R22, R134a, R152a and R245fa. HTCs are taken from 10 $kW/m^2$ to critical heat fluxes for all refrigerant at $7^{\circ}C$. Wall and fluid temperatures are measured directly by thermocouples located underneath the test surface and in the liquid pool. Test results show that critical heat fluxes(CHFs) of Thermoexcel-E enhanced surface are greatly improved as compared to that of a plain surface in all tested refrigerants. CHFs of all refrigerants on the Thermoexcel-E surface are increased up to 100% as compared to that of the plain surface. The improvement of Thermoexcel-E surface in CHF, however, is lower than that of the low fin surface. HTCs on Thermoexcel-E surface increase with heat flux. But after certain heat flux, HTCs began to decrease due to the difficulty in bubble removal caused by the inherent complex nature of this surface. Therefore, at heat fluxes close to the critical one, sudden decrease in HTCs needs to be considered in thermal design with Thermoexcel-E surface.

• Nuclear Engineering and Technology
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• v.35 no.4
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• pp.356-368
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• 2003

Material properties such as coolant specific heat, film heat transfer coefficient, cladding thermal conductivity, surface diffusion coefficient of the multi-bubble are improved in MACSIS-Mod1. The axial power and flux profile module was also incorporated with irradiation history. The performance and feasibility of the updated driver fuel pin have been analyzed for nominal parameters based on the conceptual design for the KALIMER breakeven core by MACSIS-MOD1 code. The fuel slug centerline temperature takes the maximum at 700mm from the bottom of the slug in spite of the nearly symmetric axial power distribution. The cladding mid-wall and coolant temperatures take the maximum at the top of the pin. Temperature of the fuel slug surface over the entire irradiation life is much lower than the fuel-clad eutectic reaction temperature. The fission gas release of the driver fuel pin at the end of life is predicted to be $68.61\%$ and plenum pressure is too low to cause cladding yielding. The probability that the fuel pin would fail is estimated to be much less than that allowed in the design criteria. The maximum radial deformation of the fuel pin is $1.93\%$, satisfying the preliminary design criterion ($3\%$) for fuel pin deformation. Therefore the conceptual design parameters of the driver fuel pin for the KALIMER breakeven core are expected to satisfy the preliminary criteria on temperature, fluence limit, deformation limit etc.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.29 no.1 s.232
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• pp.67-73
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• 2005

The paper presents a single-heater microfluid injector, whose ejected droplet volume is adjusted by digital current path control for a single microheater. The previous droplet volume adjustable methods have used the digital current control for multiple heaters or the analog current control for a single heater, while the present method uses the digital current control for a single microheater. Two different microinjectors, having a rectangular heater and a circular hearter, are designed and fabricated in the chip area of $7.64\;mm{\times}5.26\;mm$. The fabricated microinjectors have been tested and characterized for the number, size, shape and lifetime of the generated bubbles as well as for the volume and velocity of the ejected droplets. The input power for the rectangular heater and the circular heater has been varied in the ranges of $8.7{\sim}24.9{\mu}W\;and\;8.1{\sim}43.8{\mu}W$, respectively. The projected area of the generated bubble has been changed in the ranges of $440{\sim}l,3600{\mu}m^2\;and\;800{\sim}3,300{\mu}m^2$ for the rectangular heater and the circular heater, respectively. The microinjector with the rectangular heater ejects three discrete levels of the droplet in the volume range of $9.4{\sim}20.7pl$ with the velocity range of $0.8{\sim}1.7m/s$, while the microinjector with the circular heater achieves five discrete levels of the droplet in the volume range of $7.4{\sim}27.4pl$ with the velocity range of $0.5{\sim}2.8m/s$.