• Journal of ILASS-Korea
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• v.19 no.4
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• pp.174-181
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• 2014

This study investigates the effects of nanoparticle size and temperature on the thermal conductivity enhancement of water-based alumina ($Al_2O_3$) nanofluids, using the centrifuging method and relative centrifugal forces of differing magnitude to produce nanofluids of three different particles without involving any dispersants or surfactants. We determined the coupling dependency in thermal conductivity enhancement relative to nanoparticle size and temperature of the alumina nanofluids and also experimentally showed that the effect of temperature on thermal conductivity is strongly dependent on nanoparticle size. Also, our experimental data presented that the effective medium theory models such as the Maxwell model and Hasselman and Johnson model are not sufficient to explain the thermal conductivity of nanofluids since they cannot account for the temperature- and size-dependent nature of water-based alumina nanofluids.

• Korean Journal of Soil Science and Fertilizer
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• v.44 no.5
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• pp.722-726
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• 2011

The management standard on soil conditions in 'Fuji' apple to produce high quality fruit were not yet made. Therefore, this study was carried out to investigate the optimum soil environmental conditions of ten contents on production of high quality fruit in 'Fuji' apple. The soil and fruit characteristics were analyzed at total 60 orchards in major apple producing areas such as Chungju, Moonkyeung, yeongju, andong, yeosan and yeongcheon (10 orchards an area). The soil environmental factors affected fruit weight was highest relative contribution in saturated hydraulic conductivity of 36.5%. The bulk density and soil pH were low as relative contribution. The fruit weight was influenced by soil physical properties more than soil chemical properties. The soil environmental factors affected sugar content were hydraulic conductivity of 28.3% and organic matter content of 18.2%. The cultivation layer depth and soil pH were low as relative contribution. The fruit coloring was highest relative contribution in saturated hydraulic conductivity 55.9%. while soil pH, cation and soil texture were low. Fruit coloring was high influenced over 70% by soil physical properties. Finally, relative contribution on fruit quality related with sugar content, fruit weight, and coloring were high influenced by saturated hydraulic conductivity of 21.% and organic matter content of 18.7% but bulk density and cultivation layer depth were low relative contribution. The fruit growth and saturated hydraulic conductivity in 'Fuji' apple were very closely related. Therefore, orchard soil management to produce high quality fruit was very importance drainage management and organic matter application. We concluded that scientific soil management is possible by qualifiable of soil management factors.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.18 no.6
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• pp.493-500
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• 2006

This paper concerns the measurement of thermal conductivity of grouting materials for ground loop heat exchanger. A thermal conductivity meter, QTM-500 based on modified transient hot wire method was used to measure the thermal conductivity of neat bentonite and mixtures of bentonite and various additives. Relative to the total mixture mass, as the percent additive was increased the mixture thermal conductivity increased. For the bentonite-silica sand mixtures, the higher density of the sand particles resulted in much higher mixture thermal conductivity. The quartzite and silica sands produced the largest increases in mixture thermal conductivity, while common masonry and limestone sands produced lower thermal conductivity increases.

• Korean Journal of Agricultural Science
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• v.23 no.1
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• pp.108-119
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• 1996

Several parameters of hydraulic architecture relating to hydraulic conductance in xylem vessels were investigated in the current-year shoots of six species of deciduous oak trees. The above parameters were also investigated in the sprouts of Quercus mongolica and Q. variabilis, as well as in the seedlings of Q. mongolica and Q. acutissima. The values of specific conductivity, leaf specific conductivity and Hagen-Poiseuille's relative hydraulic conductivity relating to vessel diameter of Q. dentata were the highest in all of the species studied. The above values of most of the species studied were higher in May-June than in September-October because of increasing the vessel embolism by cavitation and so on through the growing season. The estimated values of relative hydraulic conductivity of vessel by Hagen-Poiseuille's empirical equation and the real values of hydraulic conductivity presented positive relationships in most of the species studied. Huber value and leaf specific conductity using leaf area or leaf weight generally exhibited similar patterns each other even if having some exceptions. The hydraulic conductances of sprouting shoots were much better than those of normal growing shoots in Q. rnongolica and Q. variabilis. The specific conductivity and leaf specific conductivity were rapidly decreased by the vessel embolism through cavitating just after cutting the shoots in Q. mongolica and Q. acutissima seedlings. Diurnal changes of the conductivities in the seedlings of Q. mongolica and Q. acutissima presented the possibility of their self-controlling of conductance by active moisture absorption under mild water stress. Specific conductivity and leaf specific conductivity, and so on of Q. acutissima seedlings subjected to periodical moisture stress or not have decreased through the growing season, but the influences of moisture stress to the conductance were not proved definitely because of influencing similarly and simultaneously to the development of xylem and leaf having inverse relation in the influences. The values of conductivities were higher generally in middle or upper parts of stems than root collar in the seedlings.

• Bulletin of the Korean Chemical Society
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• v.26 no.2
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• pp.241-247
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• 2005

A series of proton conductive inorganic-organic hybrid membranes doped with phosphoric acid ($H_3PO_4$) and/or triethylphosphate (PO(OEt)$_3$) have been prepared by sol-gel process with 3-glycidoxypropyltrimethoxysilane (GPTMS), 3-aminopropyltriethoxysilane (APTES) and tetraethoxysilane (TEOS) as precursors. High proton conductivity of 3.0 ${\times}$ $10^{-3}$ S/cm with composition of 50TEOS-30GPTMS-20APTES-50$H_3PO_4$ was obtained at 120 ${^{\circ}C}$ under 50% relative humidity. Thermal stability of membrane was significantly enhanced by the presence of SiO$_2$ framework up to 250 ${^{\circ}C}$. XRD revealed that the gels are amorphous. IR spectra showed a good complexation of $H_3PO_4$ in the matrix. The conductivity under 75% relative humidity was significantly improved by addition of APTES due to the increase in concentration of defected site in hybrid matrix. The effect of PO(OEt)$_3$, humidifying time, and heat-treatment were also investigated. PO(OEt)$_3$ had no improvement on conductivity and conductivity increased with humidifying time, however, decreased with heating temperature.

• Journal of the Korean Society for Heat Treatment
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• v.17 no.5
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• pp.293-298
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• 2004

For the application of heat sink device, the green sheets of powder of W-XCu and Mo-XCu composites were fabricated by tape casting technique. The mixing ratio of powder and binder was 6:4. The green sheet was shrinked up to 10~20% after sintering and the maximum relative density was above 95%. Thermal conductivity and Thermal expansion systematically increased with increasing Cu contents. The maximum thermal conductivity of W-20wt.%Cu was about 206[W/mK].

• Proceedings of the SAREK Conference
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• 2006.06a
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• pp.713-718
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• 2006

This paper concerns the measurement of thermal conductivity of grouting materials for ground loop heat exchanger. A thermal conductivity meter, QTM-500 based on modified transient hot wire method was used to measure the thermal conductivity of neat bentonite and mixtures of bentonite and various additives. Relative to the total mixture mass, as the percent additive was increased the mixture thermal conductivity increased. For the bentonite-silica sand mixtures, the higher density of the sand particles resulted in much higher mixture thermal conductivity.

• Korean Chemical Engineering Research
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• v.54 no.5
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• pp.593-597
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• 2016

The effects of relative humidity, current density and temperature on the ionic conductivity were studied in PEMFC (Proton Exchange Membrane Fuel Cell). Water contents and water flux in the electrolyte membrane largely affected ion conductivity. The water flux was modelled and simulated by only electro-osmotic drag and back-diffusion of water. Ion conductivities were measured at membrane state out of cell and measured at MEA (Membrane and Electrode Assembly) state in condition of operation. The water contents in membrane increase as relative humidity increased in PEMFC, as a results of which ion conductivity increased. Current enhanced electro-osmotic drag and back diffusion and then water contents linearly increased. Enhancement of current density results in ion conductivity. Ion conductivity of about 40% increased as the temperature increased from $50^{\circ}C$ to $80^{\circ}C$.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1995.11a
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• pp.22-24
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• 1995

The electrical conductivity of TiO$_2$doped ZnO was investigated by means of complex impedance measurement and voltage-current source and meaurement unit. The e1ectrical conductivity of TiO$_2$added ZnO was increased with increasing the concentration of TiO$_2$. The calculated relative dielectric constant was decreased with increasing the concentration of TiO$_2$. The increase of electrical conductivity seems to be the effect of TiO$_2$donor doping.

• Magazine of the Korean Society of Agricultural Engineers
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• v.31 no.1
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• pp.96-105
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• 1989

This laboratory study was performed to produce basic data for the estimation of water requirements for desalinization, through analyzing changes of the electrical conductivity and the exchangeable sodium percentage during the desalinization of reclaimed tidelands. Desalinization experiments were carried out by two water management practices, namely, the leaching method by subsurface drainage and the rinsing method by surface drainage, using samples of silt loam soil and silty clay loam soil collected in reclaimed tidelands. The results obtained from this study were summarized as follows : 1. The sample soils used in this study were saline-sodic soils with the high electrical conductivity and the high exchangeable sodium percentage. 2. Changes of the electrical conductivity and the exchangeable sodium percentage with water requirements for desalinization showed a similar tendency in the desalinization experiment by the same water management practice. 3. The regression equation between the relative electrical conductivity(EC/EC) and water requirements for desalinization(Dw/Ds) could be described by Dw/Ds=O. 29x(EC/EC.) -0.982 (Leaching method), Dw/Ds=3. 678X0. 030(EC/EC ) (Rinsing method). 4. The regression equation between the relative exchangeable sodium percentage (ESP/ESP ) and water requirements for desalinization (Dw/Ds) could be expressed in Dw/Ds = 0.039 x (ESP/ESP. ) - 1. 134 (Leaching method), Dw/Ds=7. 197X0. 024(ESP/ESP ) (Rinsing method). 5. It was estimated that water requirements for the adequate desalinization would be Dw/Ds=0.3 (Leaching method) and Dw/Ds=3.0 (Rinsing method)