• Transactions of the Korean Society of Mechanical Engineers B
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• v.37 no.8
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• pp.781-788
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• 2013

Predicting the engine component temperature is a basic step to conduct structural safety evaluation in medium-speed diesel engine design. Recent trends such as increasing power density and performance necessitate more effective thermal management of the engine for achieving the desired durability and reliability. In addition, the local temperatures of several engine components must be maintained in the proper range to avoid problems such as low- or high-temperature corrosion. Therefore, it is very important to predict the temperature distribution of each engine part accurately in the design stage. In this study, the temperature of an engine component is calculated by using steady-state conjugate heat transfer analysis. A proper approach to determine the thermal load distribution on the thermal boundary area is suggested by using 1D engine system analysis, 3D transient CFD results, and previous experimental data from another developed engine model. A Hyundai HiMSEN engine having 250-mm bore size was chosen to validate the analysis procedure. The predicted results showed a reasonable agreement with experimental results.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.19 no.3
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• pp.69-74
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• 2018

Large industrial motors require a large area because of the high risk of shutdown accidents and large industrial accidents due to the lowering of the dielectric strength of the armature windings and overheating problems. Therefore, there is a demand for a large-capacity motor that has small size, light weight, and excellent dielectric strength compared with conventional motors. Superconducting motors have advantages of high efficiency and output power, low size, low weight, and improved stability. This results from greatly increasing the magnetic field generation by using superconductive field coils in rotating machines such as generators and motors. It is very important to design and analyze the cooling system to lower the critical temperature of the wires to achieve superconducting performance. In this study, a field loss analysis and low-temperature heat transfer analysis of the cooling system were performed through the conceptual design of a 100-HP high-temperature superconducting synchronous motor. The field loss analysis shows that a uniform pore magnetic flux density appears when high-temperature superconducting wire is used. The low-temperature heat transfer analysis for gaseous neon and liquid neon showed that a flow rate of 1 kg/min of liquid neon is suitable for maintaining low-temperature stability of the high-temperature superconducting wire.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.35 no.2
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• pp.145-152
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• 2011

The performance of flat-tube radiators with louvered fins was numerically investigated for different tube insertion lengths. The results of numerical analysis using CFX-11 were compared with experimental results. In this study, three types of flat-tube radiators with louvered fins were considered. An experiment was conducted to validate the numerical results. Flow rate ratio (FR) and Stotal were introduced to understand the uniformity of flow distribution easily. The results of numerical analysis revealed that the heat transfer rate and pressure drop increased as the mass flow rate increased. Further, the results showed that the heat transfer rate of sample 3 with h/D = 0.5 was higher than that of the other samples. The pressure drop increased as the insertion length toward the header part increased, and the pressure drop in the case of sample 3 appeared to be the highest. The factor Stotal showed that the uniformity of the flow distribution in the case of sample 1 with h/D = 0 was higher than that in the case of the other samples.

• Journal of Animal Environmental Science
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• v.9 no.2
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• pp.69-78
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• 2003

In this study, the energy conversion equipment from the radiation energy to mechanical energy by using n­pentane as the operating fluid was constructed and the performance to pump the water was tested for the utilization of solar powered water pump. The equipment was designed optimally, after the theoretical analyses of the water pumping head and water quantity per cycle were done. The pentane vapour temperature in the condenser and the temperature of the outlet water from the condenser became lowered and the heat transfer rate became higher with decreasing the water inlet level to the condenser. The temperature difference between the condenser and the water tank was significant. Therefore, the distance between the water tank and condenser was recommended to be shorten and the diameter of their connecting pipe was recommended to be narrow in order to reduce the resistance of the fluid passage and improve the heat transfer rate. The amount of water pumped was 1.6­2.4 liters. Mass flow rate of the cooling water became lowered when the cooling water pipe was prolonged from the condenser to improve the heat transfer rate.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.30 no.12 s.255
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• pp.1164-1172
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• 2006

Measurements of the local heat transfer coefficients on hemispherical convex and concave surfaces with a turbulent impinging jet were made. The Reynolds number used was 11000, 23000, 50000 and the nozzle- to- surface distance was L/d=2, 4, 6, 8, and 10 and the jet angle was a = $0^{\circ}$, $15^{\circ}$, $30^{\circ}$ and $40^{\circ}$. In case of concave surface, the Nusselt number at the stagnation point decreases as the jet angle increases and has the maximum value for L/d=6. The X-axis Nusselt number distributions exhibit secondary maxima at $0^{\circ}$ $\leq$ a $\leq$ $15^{\circ}$, L/d $\leq$ 4 for X/d<0(upstream) and at $0^{\circ}$ $\leq$ a $\leq$ $40^{\circ}$, L/d $\leq$ 4 and at $30^{\circ}$ $\leq$ a $\leq$ $40^{\circ}$, 4 < L/d $\leq$ 6 for X/d<0(downstream). The secondary maximum occurs at long distance from the stagnation point as the jet angle increases or the nozzle-to-surface distance decreases. In case of convex, correlations of the stagnation point Nusselt number according to Reynolds number, jet-to-surface distance ratio and dimensionless surface angle are presented. In the stagnation point, in term of Ren, n ranges from 0.43 in case of 2 $\leq$ L/d $\leq$ 6 to 0.45 in case of 6 < L/d $\leq$ 10, there agrees roughly appears to be laminar boundary layer result. The maximum Nusselt number, in this experiment, occurred in the direction of upstream. The displacement of the maximum Nusselt number from the stagnation point increases with increasing surface angle or decreasing nozzle-to-surface distance. On this condition about surface curvature D/d=10, the maximum displacement is about 0.7 times of the jet nozzle diameter. The ratio of the maximum Nusselt number to the stagnation Nusselt number increases as the jet angle increases.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.38 no.3
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• pp.243-254
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• 2014

It is essential to predict the coil temperature under over load and over speed conditions for reliability in high speed low torque surface mounted PM synchronous motors(SPM). In the present study, the losses and coil temperature are measured under rated condition and calculated under over speed and over load conditions in the three different motors with 35PN440, 25PN250 and 15HTH1000. The heat transfer modeling has been performed based on acquired losses and temperature. The difference of coil temperature between heat transfer modeling and experiment is less than 6.4% under no load, over speed and over load conditions. Subsequently, the coil temperature of the motor with 15HTH1000 is 84.4% of the coil temperature of the motor with 35PN440 when speed is 0.9 and load is 3.0. The output of motor with 15HTH1000 is 85.2% greater than the output of the motor with 35PN440 when the dimensionless coil temperature is 1.0.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.40 no.11
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• pp.755-759
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• 2016

The use of heat pipes in the electronic telecommunication field is increasing. Among the various types of heat pipes, the thin flat heat pipe has relatively high applicability compared with the circular heat pipe in the electronic packaging application. The thin flat heat pipe based on extrusion fabrication has a simple capillary wick structure consisting of rectangular cross sectional grooves on the inner wall of the pipe. Although the groove serves as a simple capillary wick, and many such grooves are provided on the inner wall, it is difficult for the grooves to realize a sufficiently high capillary force. In the present study, a thin flat heat pipe with a wire bundle was developed to overcome the drawback of poor capillary force in the thin flat heat pipe with grooves, and was evaluated by conducting tests. In the performance test, the thin flat heat pipe with the wire bundle showed a lower thermal resistance of approximately 3.4 times, and a higher heat transfer rate of approximately 3.8 times with respect to the thin flat heat pipe with grooves as the capillary wick respectively. The possibility of using the wire bundle as a capillary wick in the heat pipe was validated in the present study; further study for commercializing this concept will be taken up in the future.

• Journal of Energy Engineering
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• v.22 no.4
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• pp.399-405
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• 2013

The gas motion inside the engine cylinder plays a very important role in determining the thermal efficiency of an internal combustion engine. A precise information of in-cylinder three dimensional complex gas motion is crucial in optimizing engine design. Homogeneous charge compression ignition (HCCI) engine is a combustion concept, which is a hybrid between Otto and Diesel engine. The turbulent diffusion leads to increased rates of momentum, heat and mass transfer. The in-cylinder turbulence flow was found to affect the present HCCI combustion mainly through its influence on the wall heat transfer. This study investigates the effect of piston geometry shape on the turbulent flow characteristics of in-cylinder from the numerical analysis using the LES model and the results obtained can offer guidelines of the combustion geometries for better combustion process and engine performance.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.41 no.11
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• pp.874-882
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• 2013

Kerosene(Jet A-1), one of the propellants for each stage's engine of the Korea Space Launch Vehicle-II(KSLV-II), functions as coolant at the same time as it flows inside the cooling jacket of the combustion chambers and is injected through the film cooling holes. A physical surrogate mixture model to reproduce the thermophysical characteristics of Jet A-1 has been selected and the thermodynamic/transport properties of the model fuel under high pressure including supercritical conditions have been estimated using SUPERTRAPP(NIST SRD4). Comparisons with the measured properties suggest that proposed database can be used to extract properties of Jet A-1 for conjugate heat transfer analysis of liquid propellant rocket engine thrust chambers. Predicted combustion/cooling performance of regeneratively cooled thrust chambers shall be validated through comparisons with upcoming firing test results.

• Journal of Hydrogen and New Energy
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• v.24 no.4
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• pp.295-301
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• 2013

Long-term global energy-demand growth is expected to increase driven by strong energy-demand growth from developing countries. Fusion power offers the prospect of an almost inexhaustible source of energy for future generations, even though it also presents so far insurmountable scientific and engineering challenges. One of the challenges is safe handling of hydrogen isotopes. Metal hydrides such as depleted uranium hydride or ZrCo hydride are used as a storage medium for hydrogen isotopes reversibly. The metal hydrides bind with hydrogen very strongly. In this paper, we carried out a modeling and simulation work for absorption/desorption of hydrogen by ZrCo in a horizontal annulus cylinder bed. A comprehensive mathematical description of a metal hydride hydrogen storage vessel was developed. This model was calibrated against experimental data obtained from our experimental system containing ZrCo metal hydride. The model was capable of predicting the performance of the bed for not only both the storage and delivery processes but also heat transfer operations. This model should thus be very useful for the design and development of the next generation of metal hydride hydrogen isotope storage systems.