The heat transfer characteristics of double-pipe spiral heat exchanger using aluminum oxide nano-fluid were investigated by three different sizes of curvature size, experimentally. Five concentration of nano-fluid as working fluid were made and tested to analyze the heat transfer characteristics. As results, the heat transfer performance was improved at 0.25% of nano-fluid due to high thermal conductivity, however, as the concentration of nanofluid increased (~2.0%), the heat transfer performance deteriorated due to the increase in thermal resistance caused by the sedimentation of particles in the flow path. In addition, the nano-fluid has a higher pressure drop than water due to its high density and viscosity. The optimal range for heat transfer enhancement of nano-fluid was found to be less than 4.0 LPM in flow rate and 0.25% of nano-fluid concentration in this study.

초음속 혹은 극초음속 미사일의 레이돔은 공력 가열로 인해 과도한 열유속에 노출된다. 또한 미사일은 발사 후 속도와 고도가 변화 하면서 이에 따라 레이돔에 가해지는 열유속이 변화한다. 이러한 열부하에 의해 레이돔의 온도가 소재의 허용 온도를 초과하면, 레이 돔은 레이더를 보호하는 기능을 상실하게 된다. 따라서 비행 시나리오에 따른 레이돔의 열전달 특성을 고려하여 레이돔을 설계해야 한다. 본 연구에서는 준-비정상 기법을 적용하여 가상의 비행 시나리오에서의 레이돔의 열전달 특성을 분석하고 준-비정상 기법의 정 확도와 효율성을 평가하였다. 준-비정상 기법을 적용하여 시간에 따른 레이돔 외벽의 열유속과 온도 분포를 도출하였으며, 15초 이후 레이돔 외벽의 온도가 소재의 허용 온도 이상으로 가열되는 부분이 있는 것을 확인하였다. 또한 준-비정상 기법을 통해 도출된 결과 와 비정상 해석 결과를 비교하여 레이돔 평균 온도 측면에서 15% 이내의 오차로 예측할 수 있고 해석 소요 시간은 75%가 단축되는 것 을 확인하여 준-비정상 기법의 효율성을 입증하였다.

The hydrogen valve used in this study is intended to be applied to a automobile, and since there is a limit to the length of the stem, it is necessary to review the optimized stem, and for this, it is required to investigate the heat transfer characteristics of the hydrogen shut-off valve. For this, the temperature of the entire shut-off valve and especially the plunger and O-ring, which are key components in the solenoid valve driving the hydrogen shut-off valve, was calculated using the ANSYS-CFX flow analysis program. From the analysis results, the length of the stem capable of maintaining the design temperature of -40℃ or higher should be at least 139 mm, and it is judged that it should be 140 mm or more considering safety. When determining the stem length of the hydrogen blocking valve for automobiles, constraints on installation in automobiles should be considered.

Research has been conducted on acoustic metamaterials that control the transmission characteristics of reflected and refracted waves using phase delay by resonators. Using one-dimensional theory, the phase delay equations for the 1/4 wavelength and Helmholtz resonator are presented. These one-dimensional analysis results are compared with the results predicted by three-dimensional FEM. The advantages and disadvantages of 1/4 wavelength and Helmholtz resonator were confirmed in implementing phase delay. An acoustic metamaterial with a refraction angle of 30° was manufactured using multiple tubes and then the sound pressure distribution was measured. A relatively large sound pressure was measured at the target position of 30°, which was compared with the 3D FEM analysis results. Simulations confirmed that a phase delay range closer to 2π was more effective in refraction, but varying the number of resonators was found to have minimal impact on which additional research is needed for generalization.

The heat transfer characteristics of double-pipe spiral heat exchanger were investigated by various curvature sizes, experimentally. The three different sizes of heat exchanger were made and tested with water as a working fluid to analyze the heat transfer characteristics. The heat transfer rates, overall heat transfer coefficient and pressure drop were analyzed with various heat exchanger sizes (i.e., curvature ratios). As result, the heat transfer rate increased with increasing the size of the heat exchanger as the flow rate increased due to increasing the area size of heat transfer. However, the overall heat transfer coefficient and pressure drop increased with decreasing the heat exchanger size (i.e., increased curvature ratio) due to the enhanced centrifugal force and inertia.

In crustaceans, molting is regulated by interactions between ecdysteroid and juvenile hormone (JH) signaling pathway-related genes. Unlike the ecdysteroid signaling pathway, little information on the role of JH signaling pathway-related genes in molting is available in zooplanktonic crustaceans. In this study, three genes (juvenile hormone acid O-methyltransferase (JHAMT ), methoprene-tolerant (Met ), and juvenile hormone epoxide hydrolase (JHEH )) which are involved in the synthesis, receptor-binding, and degradation of JH were identified using sequence and phylogenetic analysis in the brackish water flea, Diaphanosoma celebensis. Transcriptional changes in these genes during the molting cycle in D. celebensis were analyzed. Sequence and phylogenetic analysis revealed that these putative proteins may be functionally conserved along with those of insects and other crustaceans. In addition, the expression of the three genes was correlated with the molting cycle of D. celebensis, indicating that these genes may be involved in the synthesis and degradation of JH, resulting in normal molting. This study will provide information for a better understanding of the role of JH signaling pathwayrelated genes during the molting process in Cladocera.

Asphalt concrete(Ascon) is used to repair potholes and cracks. Special truck-mounted cargo boxes transport 200℃ asphalt concrete to repair potholes and cracks. However, long working and transportation hours to repair wide roads decrease the temperature of the asphalt concrete inside the cargo boxes. If the asphalt concrete temperature drops below 170℃, the adhesion with roads that need repair decreases. Therefore, the temperature of the asphalt concrete needs to be maintained for a long time. Conventional asphalt concrete cargo boxes are mostly burner-type models using hot air to prevent the temperature of the asphalt concrete from dropping. However, there are significant temperature differences between the asphalt concrete near and far away from the hot air, so the temperature decreases over time and leads to the disposal of large amounts of asphalt concrete. This causes waste of resources and environmental pollution. Therefore, this study proposed a heat dissipation cut-off type cargo box model to solve this problem and demonstrated its performance over conventional burner-type models through tests and analysis.

Solar energy is being constantly studied since it can reduce green house gas by adapting cooling and heating system of domestic architecture as a clean energy source. This study confirmed the reliability of experimental apparatus with temperature measurement of each components by developing cooling and heating system which is combined with artificial solar thermal energy using halogen lamp and refrigerator, examined the heat transfer characteristics according to room internal temperature and lamp distance with the materials of emissive plate (acrylic, copper and stainless). As a result of it, We found that the room internal temperature 18℃ was finer than 21℃ and 24℃ in case of heat transfer rate according to each components. Also, copper in the material change of emissive plate was showed finer heat transfer effects than stainless because of high thermal absorptivity when lamp distance was short.

The effect of flow direction on heat transfer in water cooling channel of lithium-ion battery is numerically investigated. Battery Design StudioⓇ software is used for modeling electro-chemical heat generation in the battery and the conjugated heat transfer is analyzed with the commercial package STAR-CCM+. The result shows that the maximum temperature and temperature difference of battery with Type 1 are the lowest because the heat transfer in the entrance region near the electrode is enhanced. As the inlet velocity is increased, the maximum temperature and temperature difference of battery decreases but the pressure loss increases. The pressure loss in Type 2 channel is the lowest due to the shortest channel length, while the pressure loss with Type 3 or 4 channel is the highest because of the longest channel length. Considering heat transfer performance and pressure loss, Type 1 is the best cooling channel.

For form stability of membrane structures, membrane material is required to be in tension. Therefore, in planning and maintenance management, the engineer should consider enough about introduction of stress during construction and re-introduction of stress after completion. Clamping part is an important portion with the function for introducing tension into membrane materials, and the function to transmit stress to boundary structures, such as steel frames. Then, the purpose of this research is to clarify stress condition and stress transfer mechanism including clamping part of membrane structures, and to grasp the changing tendency of membrane structures with the passage of time. In this research, following previous one, we perform well-balanced evaluation by conducting tensile fractured tests of clamping part's specimens, and by measuring individually the amount of displacement of not only overall specimen's length but membrane material and clamping part. Thereby, we consider the influence the difference in the hardness of edge rope and the difference in the direction of thread affect modification and fracture load.

In this paper, the heat transfer performance of nanofluids is predicted by numerical analysis methods. The nanoparticles used in this study is SiO2, with concentrations of 1, 2, 3vol.%, and the base fluid is water. Reynolds number of nanofluids ranges from 10,000 to 50,000. A numerical study on the heat transfer characteristics of nanofluid was conducted using a single-phase model. The temperature of the fluid entering from the inlet of the tube is 293.15K. A constant heat flux of 31,650W/m2 was applied at the wall, and the thickness of the wall was ignored. Heat transfer coefficients, thermal conductivity and Nusselt number were selected as indicators for comparing heat transfer performance of nanofluids. As the nanofluid concentration increases, the temperature and velocity distribution by the cross section of the coil tube and straight tube increased. As the Reynolds number increases, temperature difference between inner direction and outer direction reduced in coil tube. For straight tube, the temperature difference between the wall and the center of the tube also decreased.

The purpose of this study is to analyze the temperature and heat resistance distribution, which is a criterion for evaluating the cooling performance, by using computer simulation of the cooling system combined with the CPU of the individual highest heat generation section, and use it as important data for the heat sink design. Using a single material of Al 6063-T5, which is an integral part of the desktop, fan and heat sink, fins and base, the analysis was carried out with various fin numbers, thicknesses, pitches and shapes of heat sinks. Ambient temperature, 25°C, heat source, 130W and cooling fan speed, 2500 rpm (50CFM) were used as boundary conditions, and heat transfer characteristics regarding temperature distribution and heat resistance were investigated using ANSYS Icepak. As a result, it has been found that as the number of fins of heat sink increases, the heat dissipation area increases to decrease heat resistance, and as the distance between each fin decreases, the ventilation resistance increases to decrease the flow intensity of the cooling air in contact with the heat dissipation area. The sunburst array also exhibits better heat transfer characteristics by obtaining a lower distribution of heat resistance with a cooling effect of about 10°C than the one-way basic array.