• Proceedings of the Korean Society of Precision Engineering Conference
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• 2002.10a
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• pp.980-984
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• 2002

This paper has studied thermal characteristics of machine tool to develope high speed spindle and optimum design condidering the thermal deformation. Comparing the test data of temperature measurement and structural analysis data using FEM, we verified the test validity and predicted thermal deformation, influence of spindle generation of heat, and established cooling system to prevent the thermal deformation. 1) The temperature rise of spindle system depends on increasing number of rotation and shows sudden doubling increment of number of rotation over 7,000rpm. 2) Oil jacket cooling can be effective cooling method below 8,000rpm but, over 8,000rpm, it shows the decrement of cooling effect. 3) Comparing FEM analysis results and revolution test results, we can confirm approximate temperature change consequently, it is possible to simulate temperature rise and thermal distribution on the inside of spindle system. 4) We can confirm that simulated approach by FEM analysis can be effective method in thermal-appropriate design.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
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• 2002.10a
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• pp.498-503
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• 2002

This paper has studied thermal characteristics of machine tool to develope high speed spindle and optimum design considering the thermal deformation. Comparing the test data of temperature measurement and structural analysis data using FEM, we verified the test validity and predicted thermal deformation, influence of spindle generation of heat, and established cooling system to prevent the thermal deformation. 1) The temperature rise of spindle system depends on increasing number of rotation and shows sudden doubling increment of number of rotation over 7,000rpm. 2) Oil jacket cooling can be effective cooling method below 8,000rpm but, over 8,000rpm, it shows the decrement of cooling effect. 3) Comparing FEM analysis results and revolution test results, we can confirmn approximate temperature change consequently, it is possible to simulate temperature rise and thermal distribution on the inside of spindle system. 4) We can confirm that simulated approach by FEM analysis can be effective mettled in thermal-appropriate design.

• Journal of the Korean Society of Propulsion Engineers
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• v.23 no.2
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• pp.27-37
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• 2019

The shell and tube heat exchangers installed in the propulsion system test complex (PSTC) at the Naro Space Center heats cryogenic helium to 500 K with a heat transfer oil. As the experimental helium outlet temperature was lower than expected (less than 100 K), the boundary layer effect of the heat transfer oil is predicted to be the cause of the performance deterioration. A computational fluid dynamics (CFD) analysis was performed to verify where the boundary layer effect exists; however, the boundary layer effect has no significant impact on the performance of the heat exchanger. An alternative method to improve the performance of the heat exchanger by changing the heat transfer oil has been discussed in this paper. The low viscosity and high thermal conductivity at high temperature (~500 K) of heat transfer oil at the shell-side are required to improve the thermal performance of the heat exchanger. The experimental performance of the heat exchanger, used to exchange heat between the cryogenic helium and hot heat transfer oil at the PSTC are summarized in this paper.

• Proceedings of the KSR Conference
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• 2008.11b
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• pp.1799-1802
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• 2008

More than 7 million people use the Seoul metropolitan subway network daily. This number tends to increase due to the increase of oil price. Indoor air quality of electrical multiple unit (EMU) is strongly affected by outdoor air quality, however, indoor thermal comfort is subjected to heating, ventilating, and air conditioning (HVAC) system of EMU. In general, air temperature, humidity, air velocity, surface temperature, and illumination are key parameters affecting thermal comfort of passenger. It is known that the well-designed HVAC system should improve the thermal comfort of passengers and should increase the energy efficiency of HVAC system also. In this study, we analyzed the thermal comfort of advanced EMU developed by Korea Railroad Research Institute by using the computational fluid dynamics (CFD) in order to find the optimum HVAC system which can improve thermal comfort of passengers with a minimal energy use.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
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• 2002.04a
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• pp.221-226
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• 2002

This paper presents the thermal characteristics analysis of a high-speed HMC(horizontal machining center) with spindle speed of 30,000rpm and fried rate of 40m/min. The spindle speed is achieved by introducing angular contact ball bearings, oil-jet lubrication method, oil jacket cooling method, and so on. The spindle system is a motor-separated type composed of the main spindle and sub-spindle which are mechanically connected by the flexible coupling. The spindles are supported by two front and rear bearings, and the built-in motor is located between the front to and rear bearings of the sub-spindle. The thermal analysis model of HMC is constructed by the finite element method, and the thermal characteristics in the design stage are estimated based on temperature distribution and heat flow under the various testing conditions related to spindle speed and feed rate.

• Journal of the Korean Society for Precision Engineering
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• v.13 no.7
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• pp.140-147
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• 1996

Machining accuracy of machine tools spindles using the hydrostatic bearing, largely depends on the static stiffness and the thermal deformation of the spindle unit. In this paper, the modelling and static, thermal analysis of the hydrostatic spindles were performed for the relationship between the design variables like the bearing span, overhang, bearing stiffness and static stiffness at spindle. The goal of optimization is the mazimum, static stiffness at spindle nose with lower temperature rise in hydrostatic bearing. Temperature rise of hydrostatic bearing is minimized with the variables of spindle diameter and oil supply pressure. Finally, validity of the proposed algorithm is verified by improving the static, thermal performance of the existing hydrostatic spindles.

• Elastomers and Composites
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• v.55 no.1
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• pp.59-66
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• 2020

Herein, we investigated the thermal conductivity and thermal stability of natural rubber composite systems containing hybrid fillers of boron nitride (BN) and aluminum nitride (AlN). In the hybrid system, the bimodal distribution of polygonal AlN and planar BN particles provided excellent filler-packing efficiency and desired energy path for phonon transfer, resulting in high thermal conductivity of 1.29 W/mK, which could not be achieved by single filler composites. Further, polyethylene glycol (PEG) was compounded with a commonly used naphthenic oil, which substantially increased thermal conductivity to 3.51 W/mK with an excellent thermal stability due to facilitated energy transfer across the filler-filler interface. The resulting PEG-incorporated hybrid composite showed a high thermal degradation temperature (T₂) of 290℃, a low coefficient of thermal expansion of 26.4 ppm/℃, and a low thermal distortion parameter of 7.53 m/K, which is well over the naphthenic oil compound. Finally, using the Fourier's law of conduction, we suggested a modeling methodology to evaluate the cooling performance in thermal management system.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.35 no.2
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• pp.113-120
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• 2011

A technique for measuring the thermal diffusivity of nanofluids is proposed in this study. In theory, it has been well known that the transient hot-wire method can be used to measure the thermal conductivity and diffusivity of fluids simultaneously. However, when traditional methods were employed, the accuracy of the calculated thermal conductivity was considerably higher than that of diffusivity. The proposed method has two advantages for practical use: it only needs a simple data-conversion process for calculating the diffusivity, and it can skip the tedious calibration process involved in the case of a wire sensor. A validation experiment for the new system has been performed with the basic fluids, and the comparison experiment to compare the change in diffusivity of the base oil and the change in diffusivity of the nano oil has been carried out. It is expected that the present system will provide numerous methods for investigating the variation in the thermal properties other than thermal conductivity.

• Tribology and Lubricants
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• v.34 no.2
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• pp.43-48
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• 2018

This paper presents the thermohydrodynamic analysis of tilting journal pad bearings supporting a power turbine rotor applied to a 250 kW super-critical $CO_2$ cycle. In the analysis, the generalized Reynolds equation and 3D energy equation are solved to predict oil film temperature and the 3D heat conduction equation is solved for pad temperature. The power turbine rotor is supported by two tilting pad bearings consisting of five pads with an oil supply block between the pads. Copper backing pads with higher thermal conductivity compared to steel backing pads are adopted to improve thermal management. The predicted maximum pad temperature is around $55^{\circ}C$ which is approximately $15^{\circ}C$ higher than oil supply temperature. In addition, the predicted minimum film thickness is 50 mm at a rotating speed of 5,000 rpm. These results indicate that there is no issue in the thermal behavior of the bearing. An operation test is performed with a power turbine module consisting of a power turbine, a reduction gear and a generator. Thermocouples are installed at the 75% position from the leading edge of the pad to monitor pad temperature. The power turbine uses compressed air at a temperature of $250^{\circ}C$ in its operation. The steady state pad temperatures measured in the test show good agreement with the predicted temperatures.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.38 no.11
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• pp.915-924
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• 2014

In an aero gas-turbine engine, a surface air-oil heat exchanger (SAOHE) is used to cool the oil system for the gearboxes and electric generators. The SAOHE is installed inside the fan casing of the engine in order to dissipate the heat from the oil system into the bypass duct stream. The purpose of this study was to develop an effective numerical method for designing an SAOHE for an aero gas-turbine engine. A two-dimensional model using a porous medium was developed to evaluate the aero-thermal performance of the fins of the heat exchanger, and a one-dimensional flow and thermal network program was developed to save time and cost in the evaluation of the heat exchanger performance. Using this network program, the pressure drop and heat transfer performance of the heat exchanger were predicted, and the results were compared with two-dimensional computational fluid dynamics results and experiment data for validation.