• Solar Energy
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• v.15 no.3
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• pp.91-103
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• 1995

Non-gray radiation with convection in the entrance region of a smooth tube is numerically investigated. The fluid is a mixture of carbon dioxide, water vapor, and nitrogen to simulate combustion products of propane. The flow is assumed to be laminar and hydrodynamically and thermally developing. The P-1 approximation is used to simplify the radiative transfer equation and the exponential wide band model is adapted to model the spectral absorption coefficients of non-gray gas mixture. The bulk mean temperature and Nusselt number variation along the tube axis are shown for several inlet and wall temperature pairs to show the effect of temperature on the heat transfer characteristics. Nusselt numbers for simultaneously developing flow are compared to those for thermally developing flow. In addition, the effect of the mole fraction of the non-gray gases on convective and radiative Nusselt numbers is investigated.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.8 no.3
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• pp.375-385
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• 1996

Turbulent flow and heat transfer characteristics around staggered tube banks were studied using the 3-D Navier-Stokes equations and energy equation governing a steady incompressible flow, which were reformulated in a non-orthogonal coordinate system with cartesian velocity components and discretized by the finite volume method with a non-staggered variable arrangement. The predicted turbulent kinetic energy using RNG $k-{\varepsilon}$ model was lower than that of standard $k-{\varepsilon}$ model but showed same result for mean flow field quantities. The prediction of the skin friction coefficient using RNG $k-{\varepsilon}$ model showed better trend with experimental data than standard $k-{\varepsilon}$ model result. The inclined flow showed higher velocity and skin friction coefficient than transverse flow because of extra strain rate ($\frac{{\partial}w}{{\partial}y}$). Also, this was why the inclined flow showed higher local heat transfer coefficient than the transverse flow.

• Journal of the Korean Institute of Gas
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• v.11 no.4
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• pp.35-40
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• 2007

In this paper, evaporation heat transfer characteristics of propane and iso-butane in micro-fin tubes were investigated experimentally. Test section has a micro-fin tube with outside diameter of 12.70 mm, and 75 fins with a fin heights of 0.25 mm. The experimental results summarize as the followings: The average evaporation heat transfer coefficients of He's refrigerants is higher than those of HCFC22, and appeared in the order of iso-butane, propane with respect to the approaching of the high mass flux. The evaporation heat transfer coefficient of micro fin tube is about $10{\sim}80%$ higher than those of smooth tube. This results from the study can be used in the case of designing heat transfer exchanger using hydrocarbons as the refrigerant for the air-conditioning systems.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.1 no.3
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• pp.244-251
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• 1989

A numerical study has been performed on the natural convection heat transfer from a conducting tube with two axial fins to a surrounding cylinder. As increasing dimensionless fin length ($L_F$), the center of flow moves to the bottom of annulus and the recirculating flow rate is decreased. The maximum local Nusselt number of conducting tube appears at ${\theta}=180^{\circ}$ for $L_F=0.0$, but at ${\theta}=130^{\circ}$ for $L_F{\geq}0.3$ and that of outer cylinder appears at ${\theta}=13^{\circ}$ for $L_F{\leq}0.6$ but at ${\theta}=33^{\circ}$ for $L_F=1.0$. The fin temperature is decreased by increasing radial distance and the temperature distribution of the downward fin is generally less than that of the upward fin. By increasing fin length, the local Nusselt number of the upward fin appears negative values for $L_F=1.0$, but appears positive values for $L_F<0.8$, and that of the downward fin appears positive values.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.20 no.6
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• pp.82-91
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• 2021

We compared the heat transfer characteristics of the parallel and the counterflow flow in the concentric double tube of the Al₂O₃/water nanofluids using numerical methods. The high- and low-temperature fluids flow through the inner circular tube and the annular tube, respectively. The heat transfer characteristics according to the flow direction were compared by changing the volume flow rate and the volume concentration of the nanoparticles. The results showed that the heat transfer rate and overall heat transfer coefficient improved compared to those of basic fluid with increasing the volume and flow rate of nanoparticles. When the inflow rate was small, the heat transfer performance of the counterflow was about 22% better than the parallel flow. As the inflow rate was increased, the parallel flow and the counterflow had similar heat transfer rates. In addition, the effectiveness of the counterflow increased from 10% to 22% rather than the parallel flow. However, we verified that the increment in the friction factor of the counterflow is not large compared to the increment in the heat transfer rate.

• The Journal of the Acoustical Society of Korea
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• v.29 no.7
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• pp.439-447
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• 2010

In this paper, the resonant characteristic of a Tonpilz transducer with a fixed tail mass has been researched and the feasibility to utilize the transducer in that resonant frequency has been analyzed. The additional resonance is occurred by adhering an elastic tube to the tail mass of a conventional Tonpilz transducer and fixing the other end of the tube. The characteristic of this low resonant mode is analyzed by means of the finite element method, then it is shown that this mode is affected by the variation of the stiffness of the tube as well as the mass of the head mass and tail mass. Based on the analysis results, the Tonpilz transducer is designed to meet specific performance conditions.

• The Korean Journal of Zoology
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• v.26 no.2
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• pp.95-106
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• 1983

Selections for rapid and slow walking behavior were carried out with the populations, drived from Oregon-R and lethal free strain of Drosophila melanogaster. The behavior was measured by means of connected test-tube apparatus. The populations responded effectively to the artificial selection, and it reached the selection plateau after 7 generations. The realized heritability for the first 10 generations was estimated to be about $9\\sim14%$ for the rapid walking behavior, and those for slow walking behavior was about $11\\sim16%$. The results of hybridization analysis between selected populations at generations 8 and 10 indicated that some polygenes showing a slow walking behavior were partially dominant over polygenes controlled rapid trait. The populations selected for rapid and slow walking behavior were relaxed after 10 generations of selection. The response to natural selection of rapid population was completely returned to their neutral states after only 5 generations. Such phenomena would be explained by the genetic homeostasis resulted from an action of natural selection. However, the slow population did not make any difference from walking scores of their original artificial selection. It seems reasonable to assume that the slow walking behavior was possibly controlled by a major gene.

• Journal of the Korean Society of Radiology
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• v.15 no.7
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• pp.1007-1013
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• 2021

A Study that Cronbach Alpha values were Significantly higher at 0.813 in the Composite AP axial Radiography Signal to Noise Ratio(SNR) for Evaluating uniform Density and Advanced Images of the Entire Foot without overlap with the legs. The Subjective Evaluation ROC also scored a high score of 18 on Foot Calcaneus bone 10° from the Foot Metatarsal bone, and 18 on the Examination by tilting the Sharpness X-ray Tube 20° from the Foot Calcaneus bone. Results show uniform Density and images at 10° rearward of Foot Metatarsal bone and 20° forward of Foot Calcaneus bone during the Composite AP axial Radiography X-ray Examination of Infants.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2009.05a
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• pp.177-180
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• 2009

A Possibility of combustion instability on longitudinal mode has a high level at large scale of L/D. Solid propellant has a metal particle and a grain of control to pressure oscillation. Solid rocket motor in slotted-tube grain controls pressure oscillation of longitudinal mode. If slot length is shot, pressure oscillation of longitudinal mode is amplified by cylinder part after middle phase of total burn time. A study has analyzed pressure oscillation of longitudinal mode at spectrum and acoustic modal analysis at pressure of result on static firing test.

• Journal of the Korea institute for structural maintenance and inspection
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• v.27 no.2
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• pp.25-32
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• 2023

In this study, a double wall system is introduced, which was invented to simplify the complicated manufacturing process of the existing precast concrete (PC) double wall systems and to remove defects such as laitance that may occur during the production of concrete panels. An experimental study was conducted to investigate the tensile resisting capacity of the steel tube which is embedded in the precast concrete panel to keep the spacing between PC panels and to prevent damage of the PC panels during transportation and casting concrete onsite. The experiment was planned to determine the detail of effective steel tube connection considering the steel plate treatment method according to the formation of the opening, the presence of embedded concrete, and the reinforcement welding for additional dowel action as key variables. As a result, the ultimate tensile strength increased by 20-30% compared to the control specimen (ST) except for the steel tube specimen (ST_CP) which has steel plates bent inward at the end part of the steel tube. Since the specimen (ST_CON) filled with concrete inside the control specimen has no additional process and cost for the steel tube connections compared to the control specimen during the production of the developed double wall system, it is determined to be the appropriate detail of steel tube connection.