• Transactions of the Korean Society of Mechanical Engineers B
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• v.32 no.8
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• pp.629-635
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• 2008

Recently, microturbines have received attention as a small-scale distributed power generator. Since the exhaust gas carries all of the heat release, the microturbine CHP (combined heat and power) system is relatively compact and easy to maintain. Generating hot water or steam is usual method of heat recovery from the microturbine. In this work, a heat recovery unit producing hot water was installed at the exhaust side of a 30 kW class microturbine and its performance characteristics following microturbine power variation was investigated. Heat recovery performance has been compared for different operating conditions such as constant hot water temperature and constant water flow rate. In particular, the influence of water flow rate and hot water temperature on the recovered heat was analyzed.

• Fisheries and Aquatic Sciences
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• v.12 no.4
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• pp.331-338
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• 2009

This study presents physiological rates of respiration and excretion, clearance rate, and assimilation efficiency of the ark shell Scapharca broughtonii, determined during 2007 from specimens collected in Gamak Bay on the south coast of Korea. Physiological parameters were measured monthly under static, laboratory controlled conditions with ambient conditions, and measurements were performed seasonally in order to estimate scope for growth and its probable sources of variation. Temperature directly influenced respiration and excretion. Clearance rates showed a tendency to be low during May-August, which is a period of gametogenesis. Assimilation efficiency was not significantly different seasonally and was independent of the concentration of chlorophyll a. The scope for growth was negative during high-temperature months (July-August), reflecting the high temperature and low clearance rate, and had its highest positive values during spring and autumn. The energy budget or growth potential of bivalves has been applied to other economically important species. Data on the physiological parameters and scope for growth of S. broughtonii obtained in this study will be used to assess the carrying capacity for ark shell cultivation.

• Journal of ILASS-Korea
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• v.26 no.1
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• pp.1-8
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• 2021

Droplet evaporation has been known as a common phenomenon in daily life, and it has been widely used for many applications. In particular, the influence of the different heated substrates on evaporation flux and flow characteristics is essential in understanding heat and mass transfer of evaporating droplets. This study aims to simulate the droplet evaporation process by considering variation of thermal property depending on the substrates and the surface temperature. The commercial program of ANSYS Fluent (V.17.2) is used for simulating the conjugated heat transfer in the solid-liquid-vapor domains. Moreover, we adopt the diffusion-limited model to predict the evaporation flux on the different heated substrates. It is found that the evaporation rate significantly changes with the increase in substrate temperature. The evaporation rate substantially varies with different substrates because of variation of thermal property. Also, the droplet evaporates more rapidly as the surface temperature increases owing to an increase in saturation vapor pressure as well as the free convection effect caused by the density gradient.

• Tribology and Lubricants
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• v.39 no.4
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• pp.123-132
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• 2023

In this study, the expansion, stress, and operating clearance of bearing elements during operation are observed using the inner/outer ring temperature test data of a 3.0×10⁶ DN-class roller bearing. The operating clearance characteristics of inner-/outer-ring cooling (IORC) bearings are compared to those of inner-ring cooling (IRC) bearings. For IRC bearings, the thermal expansion of the outer ring is the most important factor in clearance variation. As a result, the operating clearance is less than the initial clearance of 61 ㎛, and the operating clearance decreases to 0.5 ㎛ at 25,500 rpm. Conversely, the temperature of the outer ring of IORC bearings is lower than that of IRC bearings, so the operating clearance is kept smaller. When the coolant flow rate to the outer ring is approximately 1.5 to 2.0 L/min, the temperature difference between the inner and outer rings is minimized and the operating clearance is maintained at a significantly lower level than IRC bearings. Small operating clearances are expected to be effective in reducing cage slip and skid damage in roller bearings. The results and analysis procedures of this study can be utilized to design of bearing clearance, lubricant flow rate, and assembled interference in the early design stage of aerospace roller bearings.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.7 no.4
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• pp.578-588
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• 1997

Poly-$Si_{1-x}Ge_x$ films on oxidized Si wafer were prepared by rapid thermal chemical vapor deposition using the $SiH_4$ and $GeH_4$ gaseous mixture at various deposition conditions. The deposition temperature, $SiH_4\;: GeH_4$ flow ratio and pressure were varied from 400 to $600^{\circ}C$, 1 : 0.1-2 : 1 and 1 to 50 torr, respectively. In this work, we have investigated the change of Ge composition of poly-$Si_{1-x}Ge_x$ films deposited with the variation of deposition parameters and the effect of Ge composition on the deposition rate. From the experimental results, it was observed that the deposition rate increased with increasing deposition temperature and Ge composition. On the other hand, the Ge composition decreased with increasing temperature. As the deposition pressure increased, the deposition rate and Ge composition were increased linearly to 10 torr but increased slowly above it, which has been attributed to the slower rate of surface reaction than mass transfer.

• Journal of Korean Society on Water Environment
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• v.20 no.1
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• pp.24-31
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• 2004

This study was initiated to evaluate the efficiencies of DEPHANOX and Modified-DEPHANOX, which were devoloped to enhance nitrogen removal efficiency in municipal wastewater treatment. In the results, removal efficiency of organic matters was not affected much by increased loading rate of organic matters which is contained in influent. The nitrogen removal efficiencies according to the loading rate of influent TN was decreased drastically in conditions of over $0.2kg/m^3{\cdot}day$, which is T-N loading rate, and the DEPHANOX process was affected more sensitively than the M-DEPHANOX was. When the temperature was altered from $25^{\circ}C$ to $16^{\circ}C$ at HRT 6hrs, the removal efficiency of ammonia nitrogen was still over 90% and it was concluded that both DEPHANOX and M-DEPHANOX were strong enough to endure temperature variation. Moreover, both processes showed over 90% in ammonia removal efficiencies in over HRT 5hrs, so it was concluded that they were strong in HRT variation. M-DEPHANOX process showed a higher value than DEPHANOX did in T-N removal efficiency to the extent of 4~21 %, which resulted from differency of denitrification rates and the biosorption efficiency of organic matter in both processes. In the condition of HRT less than 4hrs, concentrations of ammonia nitrogen contained in effluents and nitrification reactors, might be sensitively affected by biosorption efficiency of organic matters in first separation tank. In the effect of effluent nitrate concentration in phosphorus removal, the more effluent nitrate concentration was decreased, the more phosphorus removal efficiency was increased. This result is related to the decrease of concentration of effluent nitrate which resulted from nitrification inhibition by decreased HRT.

• Journal of Environmental Health Sciences
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• v.4 no.1
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• pp.23-25
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• 1977

Transaminase has been a popular methods in the clinical laboratory for the diagnosis of particular diseases. The methods we are familiar with should be considered further on the serum states provided on the test to be done. (serum freshness, temperature and duration preserved) I have studied transaminase activities of the serum preserved under frozen (-10$\circ$C), refrigerated (4$\circ$C) and room temperature conditions. At a given interval those activities of serum are measured and then the results are compared with the optical density and calculated for the standard deviation and percent variation (Table 1. & Fig. 1.) G.O.T. activity is maintained decreased at a relatively constant rate from 2nd day to 14th day preservation under frozen and refrigerated but its activity variation at 25$\circ$C are far greater than the above conditions throughout the test periods. Elevated G.P.T. level of serum compared with G.O.T. are remained at any temperature and duration. Unless the determination of amino acid level study can not ruled out clearly.

• Tribology and Lubricants
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• v.13 no.4
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• pp.26-32
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• 1997

The heat generation of the angular contact and the deep groove ball bearing is studied experimentally and numerically. The temperature variation of the inner and outer races and the temperature increase distribution are measured for the shaft rotational speeds, preloads, viscosities of the lubricant and lubrication methods. The measured temperature distributions are used as the input data of the numerical simulation to estimate the heat generation rate at the bearing. The temperatures of the inner and outer race increase more rapidly and approach faster to their steady values as the rotational speed increases. The optimal viscosity of the oil to minimize the heat generation is 8~10 cSt at 4$0^{\circ}C$ when the oil-air lubrication method is adopted. The heat generation of the bearing increases with the rotational speed and depends more on the lubrication method than on the preload variation.

• The Transactions of the Korean Institute of Electrical Engineers
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• v.35 no.2
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• pp.67-76
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• 1986

It is observed that an appreciable short-circuit current (Is) flows by the time variation of temperature without applying external field in M1(metal)-P(polymer)-M2(metal)system. In M1-P-M2(A1) system, Is flows in the direction from the electrode(A1) having a lower workfunction to the counter electrode(M1) during heating and its magnitude increases as the thickness of polymer is decreased and as the heating rate is raised. The sign of Is is reversed in lower temperature region (under glass transition temperature) when the direction of temerature variation is changed during heating and cooling. From these experimental results, we can sugest that Is flows in the external short-circuit during the space charge distribution formed around both interfacial surfaces (M1-P and P-M2) is continuously maintained in the non-equilibrium state but not in equilibrium state.

• Journal of Environmental Science International
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• v.13 no.12
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• pp.1059-1065
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• 2004

Bio sparging experiments were conducted in a laboratory column to investigate the potential removal of diesel contaminated groundwater. The objectives in this study were (a) to determine the extent of diesel degradation in laboratory columns under supplement of nutrient; (b) to determine the effect of variation of air flow in the removal of diesel and (c) to evaluate the potential enhancement of diesel degradation as a function of temperature. Our results showed that the nutrient supplement and higher air flow greatly enhanced diesel degradation. However, the variation of water temperature examined slightly increased degradation rate of diesel fuel.