• Nuclear Engineering and Technology
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• v.41 no.7
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• pp.885-892
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• 2009

This manuscript will discuss a numerical method where the six equations of two-phase flow, the solid heat conduction equations, and the two equations that describe neutron diffusion and precursor concentration are solved together in a tightly coupled, nonlinear fashion for a simplified model of a nuclear reactor core. This approach has two important advantages. The first advantage is a higher level of accuracy. Because the equations are solved together in a single nonlinear system, the solution is more accurate than the traditional "operator split" approach where the two-phase flow equations are solved first, the heat conduction is solved second and the neutron diffusion is solved third, limiting the temporal accuracy to $1^{st}$ order because the nonlinear coupling between the physics is handled explicitly. The second advantage of the method described in this manuscript is that the time step control in the fully implicit system can be based on the timescale of the solution rather than a stability-based time step restriction like the material Courant limit required of operator-split methods. In this work, a pilot code was used which employs this tightly coupled, fully implicit method to simulate a reactor core. Results are presented from a simulated control rod movement which show $2^{nd}$ order accuracy in time. Also described in this paper is a simulated rod ejection demonstrating how the fastest timescale of the problem can change between the state variables of neutronics, conduction and two-phase flow during the course of a transient.

• Journal of Power System Engineering
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• v.2 no.3
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• pp.27-33
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• 1998

The room temperature and air conditioning load in the underground space have been investigated numerically by the unsteady heat conduction equation. The model room has 3 m in height and 10 m in width, and it's position in the underground depth are 0.5 m to 5 m. When the room was located around surface, the room temperatures were strongly influenced by the atmosphere. But the underground depth is more than 2 m, the yearly temperature amplitude was small and the temperature phase was delayed. Up to 5 m of the depth, the cooling and heating load was decreased rapidly, but over 10 m of the depth, the air conditioning load was constant.

• Journal of Industrial Technology
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• v.21 no.A
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• pp.41-50
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• 2001

A comparison is made of the temperature distribution and heat loss from a trapezoidal profile fin using two different 3-dimensional methods. These two methods are analytical and finite difference methods. In the finite difference method 78 nodes are used for a fourth of the fin. A trapezoidal profile fin being the height of the fin tip is half of that of the fin base is chosen arbitrarily as the model. One of the results shows that the relative error in the total convection heat loss obtained by using 78 nodes in the finite difference method as compared to the heat conduction through the fin root obtained by analytic method seems to be good (i.e., -3.5%

• The Korean Journal of Physiology
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• v.23 no.1
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• pp.139-149
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• 1989

Although tail flick reflex (TFR) in rats has been used as a classic model of the nociceptive test to evaluate the action of analgesics, there have been few studies on the origin of the latent period of TFR. Present study was performed to elucidate the mechanism of increase in latency of TFR by morphine in anesthetized rats. Tail skin and dorsolateral tail nerve were stimulated electrically and EMG activities were recorded from abductor caudae dorsalis muscle participating in tail flick reflex. In the case of noxious radiant heat stimulation to tail, the tail flick tension was recorded before and after administration of morphine. Then changes in latency and conduction velocity of peripheral nerve were evaluated. The results obtained were as follows: 1) The latencies of TFR evoked by the electrical stimulation of tail skin and dorsolateral tail nerve were all within 40 ms and were elongated by several milliseconds from control after the administration of morphine. Peripheral conduction velocities of tail flick afferent nerve were within the range of 10-25 m/s. 2) The conduction velocity of peripheral nerve was significantly reduced after morphine administration, therefore the afferent time (utilization time+conduction time to spinal cord) was significantly increased. But the time for central delay and efferent time was not affected by morphine. 3) The conduction velocity under room temperature $(20-25^{\circ}C)$ was significantly reduced after morphine while that under vasodilation state $(40{\sim}42^{\circ}C)$ increased, 30 min and 45 min after morphine. The conduction velocity under vasodilation state without treatment of morphine increased continuously 4) The latency in tension response of TFR evoked by electrical stimulation was elongated by several milliseconds from control while the latency evoked by noxious radiant heat was elongated by several seconds compared with that of control. From the above results, it could be concluded that: 1) the increased latency of TFR evoked by electrical stimulation of the tail after morphine administration was due to the reducton in conduction velocity of peripheral nerve, which was the secondry effect of morphine on the peripheral vasomotion and 2) increased latency of TFR evoked by noxious radiant heat was also due to the same effect of morphine and the increase in cutaneous insulation to the noxious heat.

• Solar Energy
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• v.12 no.3
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• pp.60-69
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• 1992

Heat transfer characteristics and heat storage rate for vertical cylinder packed with paraffin as a latent heat storage material were theoretically studied. Conduction and convection mechanism were applied to the solid and liquid phase, respectively, and the results were compared with that of pure conduction model. The effects of heating temperature, initial solid temperature and aspect ratio on rate of storage were also studied. In the initial stage of melting, the natural convection is nearly restricted by the friction at the wall and the phase boundary. But it is generated when about 40% of solid melts and again it shrinks by the hot liquid situated on the upper part of the cylinder. So overall melting rate is higher then that for pure conduction model. The increase in heating temperature and aspect ratio activates the natural convection, so melting rate becomes higher. And the larger the aspect ratio, the greater the difference between upper and lower size of the solid. In the initial stage of melting, the initial temperature of solid paraffin has great effect on the melting rate, but as melting proceeds its effect lessens gradually.

• Nuclear Engineering and Technology
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• v.48 no.3
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• pp.650-659
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• 2016

As a type of accident-tolerant fuel, fully ceramic microencapsulated (FCM) fuel was proposed after the Fukushima accident in Japan. The FCM fuel consists of tristructural isotropic particles randomly dispersed in a silicon carbide (SiC) matrix. For a fuel element with such high heterogeneity, we have proposed a two-temperature homogenized model using the particle transport Monte Carlo method for the heat conduction problem. This model distinguishes between fuel-kernel and SiC matrix temperatures. Moreover, the obtained temperature profiles are more realistic than those of other models. In Part I of the paper, homogenized parameters for the FCM fuel in which tristructural isotropic particles are randomly dispersed in the fine lattice stochastic structure are obtained by (1) matching steady-state analytic solutions of the model with the results of particle transport Monte Carlo method for heat conduction problems, and (2) preserving total enthalpies in fuel kernels and SiC matrix. The homogenized parameters have two desirable properties: (1) they are insensitive to boundary conditions such as coolant bulk temperatures and thickness of cladding, and (2) they are independent of operating power density. By performing the Monte Carlo calculations with the temperature-dependent thermal properties of the constituent materials of the FCM fuel, temperature-dependent homogenized parameters are obtained.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.9 no.2
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• pp.229-238
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• 1997

A third-order simulation model of VM heat pumps has been developed. This model allows consideration of the major losses such as heat conduction losses through regenerators and displacers, pumping losses and wall-to-gas heat transfer losses in working volumes, in addition to the heat exchanger and regenerator losses. The working volume was divided into 12 control volumes and conservation equations of mass and energy were applied to each control volume. Pressure drop was considered in regenerators only. Thermodynamic behavior of working fluid in a VM heat pump was investigated and effects of major losses on the performance of a VM heat pump were shown.

• 제어로봇시스템학회:학술대회논문집
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• 1996.10b
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• pp.1408-1411
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• 1996

In arc welding processes, because of the complexity and nonlinearity of heat transfer phenomena, it is often difficult to design an effective control system based upon an exact mathematic model. In this paper, we simulated the welding process for various welding conditions and positions to investigate the variations of temperature distribution for those cases. Those will be used as a preinformation for developing quality control system for arc welding process.

• Proceedings of the KSME Conference
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• 2007.05b
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• pp.2113-2118
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• 2007

In this study, a mathematical model for a thermal analysis of a flat heat pipe with a grooved wick structure is presented. The effects of the liquid-vapor interfacial shear stress, the contact angle, and the amount of liquid charge have been included in the proposed model. In particular, the axial variations of the wall temperature and the evaporation/condensation rates are considered by solving the one-dimensional conduction and the augmented Young-Laplace equations, respectively. In order to verify the model, the results obtained from the model are compared to existing experimental data.

• Journal of the Korean Society of Industry Convergence
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• v.12 no.4
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• pp.179-186
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• 2009

Electronic components in an enclosure have been investigated to prevent undesired thermal problems. The electronic devices, such as ECUs of automotive engines, are operated under the contaminated environments, so that they rely on the passive cooling without any fluid-driving methods. Therefore the radiation heat dissipation plays more important role than the conduction and convection heat transfer. Hence their combined heat dissipation phenomena have been simulated by a numerical model to reveal the effects of supplied heat flux, emissivity of material, geometry of enclosure, charging gas and pressure. The result showed that the radiation had a significant effect on the heat dissipation of module in an enclosure, and some space above the module should be reserved to prevent its thermal problem. In addition, the higher thermal conductivity and pressure of gas in an enclosure could be necessary to improve the thermal dissipation from the electronic devices.