• Journal of Sensor Science and Technology
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• v.18 no.2
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• pp.103-109
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• 2009

Thermal time constant measurement system was designed and fabricated to measure the thermal time constant, which shows a dynamic property of the thermocouple. Type K thermocouple samples were fabricated with variable shape each other and the thermal time constants of thermocouples were measured using the home-made thermal time constant measurement system. Thermal time constants of 12 type K thermocouple samples were distributed from 0.03 s to 8.2 s. It showed experimentally that the thermal time constant of thermocouple was increased linearly for the increase of the sheath diameter of thermocouple.

• The Transactions of the Korean Institute of Electrical Engineers C
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• v.50 no.11
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• pp.539-543
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• 2001

ln this paper, the $Sr_{l-x}Ca_xTiO_3(0\leqx\leq0.2)-based$ grain boundary layer ceramics were fabricated to measure dielectric properties with the sintering temperature and the thermal treatment time. The sintering temperature and time were $1420~15206{\circ}C$, 4hours, and the thermal treatment temperature and time of the specimen were $l150^{\circ}C$, 1, 2, 3hours, respectively. The structural and the dielectric properties were investigated by SEM, X-ray, HP4194A and K6517. The average grain size was increased with increasing the sintering temperature, but it decreased up to 15mo1% with increasing content of Ca. X-ray diffraction analysis results showed that all specimens were the cubic structure, and the main peaks were moved to right and the lattice constant were decreased with increasing content of Ca. The appropriate thermal treatment time and temperature of CuO to obtain dielectric properties of $\varepsilon_r>50000,\; tan \delta<0.05\; and \;\DeltaC<\pm10%$ were 2hrs and $l150^{\circ}C$, respectively.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
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• 2004.04a
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• pp.416-423
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• 2004

This paper presents the thermal characteristic analysis of a high-speed horizontal machining center with spindle speed of 50,000rpm and feedrate of 120m/fin. The spindle system is designed based on the built-in motor, angular contact ceramic ball bearings, oil-air lubrication and oil-jacket cooling method. The X-axis and Y-axis feeding systems are composed of the linear motors and linear motion guides, and the Z-axis feeding system is composed of the servo-motor, ball screw and linear motion guides. The thermal characteristics such as the temperature distribution, temperature rise, thermal deformation and step response, are estimated based on the finite element model of machining center and the heat generation rates of heat sources related to the machine operation conditions. Especially, the thermal time constant assessed from the step response function is introduced as an index of thermal response characteristics.

• Transactions of the Korean Society of Machine Tool Engineers
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• v.13 no.5
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• pp.30-37
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• 2004

This paper presents the thermal characteristic analysis of a high-speed horizontal machining center with spindle speed of 50,000rpm and feedrate of 120m／min. The spindle system is designed based on the built-in motor, angular contact ceramic ball bearings, oil-air lubrication and oil-jacket cooling method. The X-axis and Y-axis feeding systems are composed of the linear motors and linear motion guides, and the Z-axis feeding system is composed of the servo-motor, ball screw and linear motion guides. The thermal characteristics such as the temperature distribution, temperature rise, thermal deformation and step response, are estimated based on the finite element model of machining center and the heat generation rates of heat sources related to the machine operation conditions. Especially, the thermal time constant assessed from the step response function is introduced as an index of thermal response characteristics.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.56 no.7
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• pp.1261-1267
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• 2007

Although LEDs have been used in various applications with improving the brightness and luminous efficacy, the electrical and optical characteristics of high power LED varies at different temperature and starting time. In this paper, optimal heat sink and apparatus design were conducted using IR camera and ICEPAK on the LED bulb consisting with fourteen LED array. The temperatures of heat sink and LED device of the designed LED bulb without cooling pan were $74^{\circ}C\;and\;96.8^{\circ}C$, respectively, showing in good themal characteristics. For high efficiency driving circuit of LED array adopted optimal heat sink design, driving circuits of constant voltage and current circuits were suggested and fabricated. As a result the efficacy of all driving circuits showed more than 20 lm/W. Also, the constant current circuits are suitable for signal lamp, hallway lamp, and flash lamp having short operating time(about 30 min). On the other hand, a reading light and indoor lamp having long operating time can be controlled by constant voltage circuit.

• Transactions of the Korean Society of Mechanical Engineers
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• v.14 no.1
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• pp.130-137
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• 1990

Thermal shock stress intensity factor for an edge-cracked plate subjected to thermal shock is obtained from Bueckner's weight function method. It is shown that thermal shock stress intensity factor has maximum values with variation of time and crack length and that there is most dangerous crack length. By comparing thermal shock stress intensity factor with fracture toughness, the fracture time and critical temperature difference due to thermal shock are determined theoretically. Under constant thermal shock temperature difference, and increase of crack length is shown to increase fracture time. The theoretical fracture time is compared with experimental value measured by acoustic emission method with soda lime glass.

• Journal of computational fluids engineering
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• v.19 no.4
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• pp.1-7
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• 2014

A numerical study of transient conjugate heat transfer on micro heater in a micro-channel substrate under a sinusoidal heat load was conducted. It was found that the time constant is not affected by the maximum heating magnitude of the sinusoidal heat load. However, the time constant increases with low duration of the sinusoidal heating period and low Reynolds number. Moreover, there is a threshold where a heater temperature do not reach to time constant at low thermal diffusivity, low flow rate, and low pulse duration of the sinusoidal heating. The time constant should be considered for transient convective heat transfer under transient sinusoidal heat load in a micro heat sink.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.21 no.12
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• pp.695-702
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• 2009

Dynamic behavior of Libr-water absorption system using low-temperature hot water was investigated numerically. Thermal-hydraulic model of single-effect/double-lift 100 RT chiller was developed by applying transient conservation equations of total mass, Libr mass, energy and momentum to each component. Transient variations of system properties and transport variables were analysed during start-up operation. Numerical analysis were performed to quantify the effects of bulk concentration and part-load operation on the system performance in terms of cooling capacity, coefficient of performance, and time constant of system. For an absorption chiller considered in the present study, optimum bulk concentration was found to exist, which resulted in the minimum time constant with stable cooling capacity. COP and time constant increased as the load decreased down to 40%, below which the time constant increased abruptly and COP decreased as the load decreased further.

• Journal of the korean Society of Automotive Engineers
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• v.12 no.4
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• pp.75-82
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• 1990

To study on the behavior of the early stage of the spark kernel at constant pressure condition, the expressions of the thermal properties such as compressibility factor, thermal conductivity, and electrical conductivity of the high temperature air were newly suggested. The newly suggested simple expressions of the thermal properties of the high temperature air showed good results. Under the assumption of constant pressure, one dimensional numerical analysis was executed by varying surrounding conditions and discharging current of electrical spark. Numerical results show tat high surrounding pressure suppresses the growth of the spark kernel but supplies much electrical energy into the air, on the other hand high surrounding temperature increases the growth of the spark kernel but supplies less electrical energy. Also the result shows that , in case of direct current discharge, deposited electrical energy is able to be expressed in linear function of time approximately.

• Proceedings of the IEEK Conference
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• 2004.08c
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• pp.872-875
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• 2004

In this paper, thermal response analysis of a temperature controlled three-axis accelerometer for high temperature environments with integrated micro-heaters and temperature sensors is investigated with finite element method (FEM) program, ANSYS and infrared thermal measurement systems. And availability to application fields from a viewpoint about short thermal response time is discussed. In this paper, the time of three-axis accelerometer for high temperatures becoming $300^{\circ}C$ by integrated micro-heaters and temperature sensors to reduce thermal drift characteristics was analyzed as a thermal response time of this device. The simulated thermal response time (time until SOI piezoresistors actually becomes $300^{\circ}C$) of three-axis accelerometer for high temperatures with ANSYS is about 0.6s, and measured result with infrared temperature measurement systems is about 0.64s. Experimental results using infrared thermal measurement systems agreed well with these theoretical results.