• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.12 no.5
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• pp.457-465
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• 2000

An experiment was carried out to evaluate the thermal performance of the wire-coil inserts method. Tested were the smooth tubes with the wire-nil inserts of various pitch and helix angle combinations. Test fluids were the 50%-solution of the ethylene glycol and the Hue water. Heat transfer coefficient and friction factors were deduced from the measured values of temperatures, flowrates and pressure drops. A unified dimensionless correlation for the heat transfer coefficients was developed as a function of the pitch to diameter ratio, the Reynolds number and the Prandtl number. An exergy analysis was performed to evaluate an optimal operating condition with the wire-coil inserts.

• Applied Science and Convergence Technology
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• v.24 no.5
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• pp.136-141
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• 2015

We studied the compact anode design to develop 100 kW rotating anode X-ray tube with large focal spot 1.2 mm, small focal spot 0.6 mm and tube voltage 150 kV for large hospital digital radiography using computer thermal simulation. The larger thermal radiation effect in a high vacuum can reduce the temperature of anode so the method to increase the surface area of anode is investigated. The anode has the multi-tier shape at the back side of TZM body of anode and also bigger diameter of anode. The number of multi-tiers was varied from 6 to 15 and the diameter of anode was also varied from ${\Phi}74$ to ${\Phi}82$. From ANSYS transient thermal simulation result, we could obtain $1056.4^{\circ}C$ anode maximum temperature when applying 100 kW input power at 0.1 second on target focal track which is less than $1091^{\circ}C$ of the conventional 75 kW X-ray tube with reduced anode weight by 15.5% than the conventional anode. The compact anode of reduced anode weight is able to improve the unwanted noise when the rotor is rotating at high-speed and also reduce the rotational torque which the cost effective stator-coil is possible. It is believed that the anode with 15 ea multi-tiers using ${\Phi}82$ can satisfy with the specification of the anode heat capacity. From the results of this paper, it has been confirmed that the proposed compact anode can be used as the anode of 100 kW rotating anode X-ray tube for digital radiography.

• Journal of Ocean Engineering and Technology
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• v.24 no.5
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• pp.22-30
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• 2010

The fuel tank of a ship is filled with heavy fuel oil (HFO) that has a very high viscosity. In order to inject the HFO into the engine easily, heating coils are usually installed inside the fuel tank to heat the HFO and lower its viscosity. Currently, several different types of heating coils are used, e.g., fin-type, bare-type, drum-type, and shell-and-tube-type. It is well known that the shell-and-tube-type heating coil has good performance and high efficiency. In this study, experiments were conducted to determine the heat transfer efficiencies of three different shell-and-tube-type heating coils. Heat transfer efficiency was evaluated by using FLUENT 6.3.26 software. Also, structural safety was assessed by using ANSYS.simulation software.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
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• 2003.10a
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• pp.118-124
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• 2003

응축기, 증발기, 전열관에 사용되는 Fin Tube는 열전달효율 향상을 위하여 Fin의 높이 를 증가시키고, Tube의 최소두께를 얇게 가공하는 경향으로 발전하고 있다. 따라서, Fin Tube의 와전류탐상(ECT; Eddy Current Testing)에 의한 결함검출에 더욱 어려움이 예상된다. 본 연구에서는 Fin Tube의 Fin 높이를 3단계로 변화시켜 Tube를 제작하고, Tube에 축 방향결함, 원주방향결함, 원형결함을 각각 Fin Tube의 안쪽에 최소두께의 20%, 40%, 60% 의 동일결함율을 갖는 인공결함 시험편을 제작하였다. 제작한 원형결함시험편에 와전류탐상을 수행하여 Fin 높이에 따른 최적주파수의 변화를 연구하였다. Fin높이가 다른 원형결함 시험편에 1~20KHz 주파수를 적용한 결과 최적주파수는 12KHz로 Fin높이에 크게 영향을 받지 않음을 밝혔다 또한 Fin높이에 따른 최적주파수변화는 크지 않으나 Fin 높이가 높을수록 100%관통결함의 위상각(40')에 근접하여 나타났다. 축방향결함, 원주방향결함, 원형결함을 갖는 시험편에 와전류탐상을 수행한 결과 원형결함을 갖는 시험편의 신호 감도가 축방향결함, 원주방향결함보다 좋게 나타났다.

• Solar Energy
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• v.20 no.4
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• pp.61-67
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• 2000

The purpose of this study is to improve heat transfer by attaching rectangular fins to tube. Experiments were carried out under the following conditions - Aspect ratio$(W_f/R_f)$ is 0.7, 1.2 and 1.8. Temperature conversion between high and low positions of water in the thermal storage appeared because maximum density point of water is about $4^{\circ}C$ and inlet direction of working fluid influenced conductive heat transfer Compared with the unfinned tube(bare tube), the rectangular tube increased the ice thermal storage energy and the ice thermal storage energy was increased as aspect ratio was increased.

• Journal of Biomedical Engineering Research
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• v.16 no.4
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• pp.481-491
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• 1995

Endovaginal and endorectal receiver only surface coils were designed for MR imaging (MRI) and $^1H$ MR spectroscopy (MRS) for the uterine cervix and the prostate. The shape of endovaginal coil wire was rectangular with round corner. Size of the coil wire was empirically determined for 7cm and 4cm along the long and short axis, respectively. The coil wire loop was supported by acryl handle and bent about $150^{\circ}$ at one side of the loop considering the average angle of the cervix to the vagina. We called this as a "spoon-type endovaginal coil". The wire of the endorectal coil was made of the flexible materials so that the wire loop became long elliptic shape by pushing the acryl handle into the plastic tube for the comfort of patients when the coil was inserted into the cervix. Then, the shape was maintained to be circle by popping out handle. Conventional spin echo (SE) and fast spin echo (FSE) sequences were used as 71 and 72 weighted imaging sequences, respectively. Matrix size was 128~$256{\times}256$. FOVs for surface coil and body coil were 14cm and 24cm, respectively. 3D volume localized in vivo $^1H$ MR spectroscopy of the human cervix and prostate was performed using PRESS or STEAM localization method with the following parameters . TR=3 sec, TE=135 msec for PRESS or 30 msec for STEAM, NEX=2, NS=48, Sl=2048, and SW=2500 Hz. Using home-built endovaginal and endorectal coils, excellent T1- and T2-images were obtained to visualize early cervical and prostate tumors. 3D volume localized in vivo IH MRS was useful to differentiate the cancerous tissue from the normal tissue.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.27 no.2
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• pp.69-74
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• 2015

In this work, we studied the shell and helically coiled tube heat exchangers. Shell and coil heat exchangers with different rate of water flow and plate heat exchanger with same capacity were tested for condensing conditions. We proposed design guide using modified Wilson plot method. We compared fouling characteristics between shell and coil heat exchanger and plate heat exchanger, when they were washed and were not washed. The shell and coil heat exchanger showed 120% of higher saturated fouling resistance value and 4% of better heat transfer ratio than the plate heat exchanger.

• Proceedings of the KSMRM Conference
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• 2001.11a
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• pp.151-151
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• 2001

Purpose： 3.0 Tesla whole-body resonator provides a potential to have significant increase in imag quality and resolution in high resolution application such as cardiac, spine and extremit imaging. The aim of this study is to design an optimized 3.0T whole-body coil to produce high sensitivity and quality using slotted tube resonator.

• Transactions of the Korean Society of Mechanical Engineers
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• v.17 no.9
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• pp.2358-2372
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• 1993

In this study, the computer modeling for prediction of the performance of fin-tube heat exchanger using alternative refrigerant, HFC-134a was developed and the computer program for calculating the various properties of HFC-134a and the existing refrigerant CFC-12 and HCFC-22 was made. The heat exchanger modeling is based on a tube-by-tube approach, which is capable of analysis for the complex coil array. Performance of each tube is analyzed separately by considering the cross-flow heat transfer with external airstream and the appropriate heat and mass transfer relationships. A performance comparison according to the different refrigerants is provided using this developed model. As the result of this study, total heat transfer rate of evaporator and condenser using HFC-134a were found higher than that of using CFC-12 for the same operating conditions. When the mass flow rate of HFC-134a was less than CFC-12 about 18. 16%, the cooling capacities of evaporator were found to be the same.

• The korean journal of orthodontics
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• v.26 no.4
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• pp.341-348
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• 1996

The efficiency of maxillary canine retraction by means of sliding mechanics along an 0.016 continuous labial arch and an 0.009 inch in diameter with a lumen of 0.030 inch NiTi closed coil spring was compared with that using the same NiTi closed coil spring and Molar Anchoring Spring(MAS) which was designed by author. MAS was made of .017" X .025" TMA wire and was given 60 degree tip-back bend on the wire close to the molar tube. This study was designed to investigate molar and canine root control during retraction into an extraction site with continuous arch wire system. Two techniques were tested with a continuous arch model embedded in a photoelastic resin. A photoelastic model was employed to visualize the effects of forces applied to canine and molar by two retraction mechanics. With the aid of polarized light, stresses were viewed as colored fringes. The photoelastic overview of the upper right quadrant showed that stress concentrations were observed in its photoelastic model. The obtained results were as follows. 1. Higher concentration of compression can be seen clearly at the distal curvature of the canine and mesial curvature of the molar and premolar when NiTi closed coil spring was applied only, which means severe anchorage loss of the molar and uncontrolled tipping of the canine. 2. The least level compression was presented at the mesial root area of the molar and premolar, and mesial root area of the canine when NiTi closed coil spring and MAS were used simultaneously. Especially mesial alveolar crest region of the canine was shown moderate level of compression that means MAS can be used as a appliance for anchorage control and prevention of canine extrusion and uncontrolled tipping during canine retraction.