• Journal of Mechanical Science and Technology
• /
• v.20 no.12
• /
• pp.2209-2217
• /
• 2006

Dynamic flow characteristics of a counter-flow vortex tube is investigated using hot-wire and piezoelectric transducer (PZT) measurements. The experimental study is conducted over a range of cold air outlet ratios (Y=0.3, 0.5, 0.7, and 1.0) and inlet pressure 0.15 MPa. Temperatures are measured at the cold air outlet and along the vortex tube wall. Hot-wire is located at cold outlet and PZT is installed at inner vortex tube by mounting at throttle valve. The cold outlet temperature results show that the swirl flow of vortex tube is not axisymmetric. The hot-wire and PZT results show that there exist two distinct kinds of frequency, low frequency periodic fluctuations and high frequency periodic fluctuations. It is found that the low frequency fluctuation is consistent with the Helmholtz frequency and the high frequency fluctuation is strongly related with precession oscillation.

• Journal of The Korean Astronomical Society
• /
• v.45 no.1
• /
• pp.19-24
• /
• 2012

Microthermal fluctuations are introduced by atmospheric turbulence very near the ground. In order to detect microthermal fluctuations at Fuxian Solar Observatory (FSO), a microthermal instrument has been developed. The microthermal instrument consists of a microthermal sensor, which is based on a Wheatstone bridge circuit and uses fine tungsten filaments as resistance temperature detectors, an associated signal processing unit, and a data collection, & communication subsystem. In this paper, after a brief introduction to surface layer seeing, we discuss the instrumentation behind the microthermal detector we have developed and then present the results obtained. The results of the evaluation indicate that the effect of the turbulent surface boundary layer to astronomical seeing would become sufficiently small when installing a telescope at a height of 16m or higher from the ground at FSO.

• The Bulletin of The Korean Astronomical Society
• /
• v.37 no.2
• /
• pp.118.1-118.1
• /
• 2012

In situ observations from the Wind spacecraft that statistically analyzed the solar wind proton at 1 AU has indicated that the measured proton temperature anisotropies seems to be regulated by the oblique instabilities (the mirror and oblique firehose). This result is in contradiction with the prediction of linear kinetic theory that the ion-cyclotron (for ${\beta}_{\parallel}$ < 2) and parallel firehose (for ${\beta}_{\parallel}$ <10) would dominate over the oblique instabilities. Various kinds of physical mechanisms have been suggested to explain this disagreement between the observations and linear theory. All of the suggestions consider the solar wind as a unoform magnetized plasma. However the real space environment is replete with the intermediate spatio-temporal scale variations associated with various physical quantities, such as the magnetic field intensity and the solar wind density. In this paper we present that the pervasive intermediate-scale temporal variation of the local magnetic field intensity can lead to the modification of the proton temperature anisotropy versus beta inverse correlation for temperature-anisotropy-driven instabilities. By means of quasilinear kinetic theory involving such temporal variation, we construct the simulated solar wind proton data distribution associated the magnetic fluctuations in (${\beta}_{\parallel}$, $T_{\perp}/T_{\parallel}$) space. It is shown that the theoretically simulated proton distribution and a general trend of the enhanced fluctuations bounded by the oblique instabilities are consistent with in situ observations. Furthermore, the measure magnetic compressibility can be accounted for by the magnetic spectral signatures of the unstable modes.

• International Journal of Industrial Entomology and Biomaterials
• /
• v.33 no.2
• /
• pp.50-53
• /
• 2016

The size of head capsule is one of the most important factors for identifying developmental stage. In order to understand the developmental characteristics of the butterfly Atrophaneura alcinous, we examined fluctuations in larval head capsule size under three different temperature conditions (20, 25, and $30^{\circ}C$) and 60% humidity. As a result, larvae developed to the fifth instar at all three temperatures. The head capsule size of larvae tended to be larger at the lowest temperature and smaller at the highest temperature. The development rate showed a regular change, consistent with Dyar's rule regarding head capsule size development. Furthermore, the development of head capsule size was found to correspond to a second degree polynomial regression better than to a linear regression. On the basis of these results, it would appear to be possible to perform an accurate assessment of instar status during the development of A. alcinous.

• The Journal of Engineering Geology
• /
• v.24 no.4
• /
• pp.575-581
• /
• 2014

The reliable measurement of geotechnical properties in cold regions should account for their fluctuations with temperature. The objective of this paper is to introduce a chemical model based on the Arrhenius equation that can predict the properties of materials as their temperature changes. The model can monitor phases and reaction rates as they change with temperature. It has been already applied in the fields of geology, construction, chemistry, materials engineering, and food science. The application of the Arrhenius equation requires a reliable estimate of the activation energy. Therefore, this study also demonstrates several methods for evaluating activation energy in different contexts through summaries and reviews of previous research related to the Arrhenius equation. This paper may be of wide use in obtaining temperature-dependent parameters in geotechnical engineering.

• Current Optics and Photonics
• /
• v.6 no.3
• /
• pp.297-303
• /
• 2022

Multiple fiber Bragg gratings (FBGs) have been proposed and demonstrated for gas-flow measurements in a flow channel, using the temperature-difference method. This sensor consists of two FBG temperature sensors and two coil heaters. Coil heaters are used to heat the FBGs. The flow rate of the gas can be obtained by monitoring the difference in the Bragg-wavelength shifts of the two FBGs, which has features that exclude the effect of temperature fluctuations. In this study, experiments are conducted to measure the wavelength shift based on the flow rate, and to evaluate the gas-flow rate in a gas tube. Experimental results show that the sensor has a linear characteristic over a flow-rate range from 0 to 25 ℓ/min. The measured sensitivity of the sensor is 3.2 pm/(ℓ/min) at a coil current of 120 mA.

• Journal of the Korean Society of Marine Environment & Safety
• /
• v.23 no.5
• /
• pp.497-512
• /
• 2017

Temporal and spatial variations in surface water temperature were studied using data from temperature monitoring buoys deployed at 47 stations around Boryeong from 2011-2012 off the west coast of Korea. Temperature fluctuations are predominant at diurnal and semidiurnal periods for all seasons, and their amplitudes are large in spring and summer but small in autumn. The maximum annual change in air temperature takes place on August 2nd and August 22th for water temperature, which means the phase for air temperature precedes water temperature by 20 days. The diurnal period of water temperature fluctuation is predominant around Daecheon and Muchangpo Harbors, with the semidiurnal period around Wonsan Island, and the shallow water constituent period on the estuary around Daecheon River. On the whole, air and water temperatures fluctuate with wind. Spectral analyses of temperature records show significant peaks at the 0.5, 1 and 15 day marks with 7-10 day periods of predominant fluctuations. Cross-correlation analyses for the temperature fluctuation show that the waters around Boryeong can be classified into four areas: a mixed water zone around the southeast side of Wonsan Island, an off-shore area to the west, an off-shore area to the south and a coastal area along the shore from Song Island to Muchangpo Harbor.

• Nuclear Engineering and Technology
• /
• v.55 no.10
• /
• pp.3874-3897
• /
• 2023

A high-fidelity computational fluid dynamics (CFD) analysis was performed using the Large Eddy Simulation (LES) model for the lower plenum of the High-Temperature Test Facility (HTTF), a ¼ scale test facility of the modular high temperature gas-cooled reactor (MHTGR) managed by Oregon State University. In most next-generation nuclear reactors, thermal stress due to thermal striping is one of the risks to be curiously considered. This is also true for HTGRs, especially since the exhaust helium gas temperature is high. In order to evaluate these risks and performance, organizations in the United States led by the OECD NEA are conducting a thermal hydraulic code benchmark for HTGR, and the test facility used for this benchmark is HTTF. HTTF can perform experiments in both normal and accident situations and provide high-quality experimental data. However, it is difficult to provide sufficient data for benchmarking through experiments, and there is a problem with the reliability of CFD analysis results based on Reynolds-averaged Navier-Stokes to analyze thermal hydraulic behavior without verification. To solve this problem, high-fidelity 3-D CFD analysis was performed using the LES model for HTTF. It was also verified that the LES model can properly simulate this jet mixing phenomenon via a unit cell test that provides experimental information. As a result of CFD analysis, the lower the dependency of the sub-grid scale model, the closer to the actual analysis result. In the case of unit cell test CFD analysis and HTTF CFD analysis, the volume-averaged sub-grid scale model dependency was calculated to be 13.0% and 9.16%, respectively. As a result of HTTF analysis, quantitative data of the fluid inside the HTTF lower plenum was provided in this paper. As a result of qualitative analysis, the temperature was highest at the center of the lower plenum, while the temperature fluctuation was highest near the edge of the lower plenum wall. The power spectral density of temperature was analyzed via fast Fourier transform (FFT) for specific points on the center and side of the lower plenum. FFT results did not reveal specific frequency-dominant temperature fluctuations in the center part. It was confirmed that the temperature power spectral density (PSD) at the top increased from the center to the wake. The vortex was visualized using the well-known scalar Q-criterion, and as a result, the closer to the outlet duct, the greater the influence of the mainstream, so that the inflow jet vortex was dissipated and mixed at the top of the lower plenum. Additionally, FFT analysis was performed on the support structure near the corner of the lower plenum with large temperature fluctuations, and as a result, it was confirmed that the temperature fluctuation of the flow did not have a significant effect near the corner wall. In addition, the vortices generated from the lower plenum to the outlet duct were identified in this paper. It is considered that the quantitative and qualitative results presented in this paper will serve as reference data for the benchmark.

• Proceedings of the Korean Society for Emotion and Sensibility Conference
• /
• 1999.11a
• /
• pp.3-6
• /
• 1999

There are numerous studies on relations between sleep and environmental factors such as noise, illumination and thermal conditions. Sleep is affected by the thermal environment. This study describes influence of thermal environment on skin temperature, sleep patterns and body movements using physiological and psychological measurements. The results are as follows: 1) The fluctuations of room temperature during sleep appeared skin temperature variations. The more room temperature is high, the more skin temperature is high in 22$^{\circ}C$, 26$^{\circ}C$, 30$^{\circ}C$. 2) A significant relation between body movement and skin temperature was found within room temperature. Under room temperature conditions of 22$^{\circ}C$, 26$^{\circ}C$, 30$^{\circ}C$, there were significantly higher rates of body movement in the room temperature(30$^{\circ}C$). 3) Uncomfortable after sleep in thermal environment is mostly under high temperature(30$^{\circ}C$), and they are about fatigue due to not enough sleeping. 4) The degree of indoor thermal temperature with sufficient sleeping is in 22.8 ∼ 27.8$^{\circ}C$.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
• /
• 2000.06a
• /
• pp.166-172
• /
• 2000

Friction characteristics of phenolic resin-based friction composites containing threedifferent relative amounts of graphite and zirconium silicate were investigated by using a pad-on-disk type friction tester. Constant temperature test and constant interval test at three different initial temperatures(100. 200, 300$^{\circ}C$) were performed to examine the effects of friction heat on friction characteristics at elevated temperature. The friction composite(FMO.7) with higher content of ZrSiO$_4$showed unstable friction force at higher temperature and resulted in larger fluctuations of vibration during friction test. The abrasive action of ZrSiO$_4$in friction composite impeded stable transfer film and induced higher friction heat at friction interface. Friction oscillations according to the temperature were associated with the formation of transfer film(i'd body layer) on the friction composite and the counter part.