• Structural Engineering and Mechanics
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• v.57 no.5
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• pp.809-821
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• 2016

Concentric-tube continuum robots have formed an active field of research in robotics because of their manipulative exquisiteness essential to facilitate delicate surgical procedures. A set of concentric tubes with designed initial curvatures comprises a robot whose workspace can be controlled by relative translations and rotations of the tubes. Kinematic models have been widely used to predict the movement of the robot, but they are incapable of describing its time-dependent hysteretic behaviors accurately particularly when snapping occurs. To overcome this limitation, here we present a finite element modeling approach to investigating the dynamics of concentric-tube continuum robots. In our model, each tube is discretized using MITC shell elements and its transient responses are computed implicitly using the Bathe time integration method. Inter-tube contacts, the key actuation mechanism of this robot, are modeled using the constraint function method with contact damping to capture the hysteresis in robot trajectories. Performance of the proposed method is demonstrated by analyzing three specifications of two-tube robots including the one exhibiting snapping phenomena while the method can be applied to multiple-tube robots as well.

• Korean Chemical Engineering Research
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• v.57 no.1
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• pp.28-41
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• 2019

We carried out performance analysis of Sodium-Water Reaction Pressure Relief System of Prototype Generation-IV Sodium-Cooled Fast Reactor. We analyzed transient-dynamic behavior of fluids inside the steam generator to vent into a sodium dump tank or a water dump tank when tubes in the steam generator were broken to cause a large-water-leak accident. Accordingly, we preliminarily evaluated design requirements of our system. Our results showed that sodium in the shell side of the steam generator and in Intermediate Heat Transport System was completely vented within 50 s and feed water in the tube side of the steam generator was completely vented within 2.5 s. It was analyzed that pressure of the tube side of the steam generator was higher than pressure of the shell side of the steam generator, which showed that sodium in the shell side did not flow into the tube side. Our results are expected to be used as basis information to performance analysis of Sodium-Water Reaction Pressure Relief System of Prototype Generation-IV Sodium-Cooled Fast Reactor.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.18 no.11
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• pp.941-946
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• 2006

Nowadays heat exchangers that have been applied for freon refrigerating systems, a shell and tube type condenser, but because of their large size, large space for installation and more amount of refrigerants are needed. Therefore, in this study, we will find the most suitable operating condition through the comparison of performance between the shell & tube type and shell & disk type heat exchanger with R22. The experiments are carried out for the condensing pressure of refrigeration system from 1,500 kPa to 1,600 kPa and for the degree of superheat from 0 to $10^{\circ}C$ at each condensing pressure. As a result of experiment, if the shell & disk type heat exchanger is applied for R22 refrigerating systems, minimized input of refrigerants and space required for installation will be secured, which will have a great contribute to financial improvement for industry.

• Journal of the Korean Institute of Telematics and Electronics C
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• v.34C no.1
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• pp.12-20
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• 1997

In this paper, we analyze the thermal deformation of mask frame assembly using finite element method(FEM) and predict the beam landing shift during tube operation. For realistic analysis, the apparent thermal conductivity and the apparent elastic modulus are calculated and the shadow mask is modeled as shell without aperatures. Also, all parts inside the tube are modeled and the each radiative effect is considered. Then the finite element analysis is performed for transient thermo-elastic deformation of the mask frame assembly and the beam landing shift is calculated. Experiments are eprformed for 17" cathode ray tube (CRT) to validate the FEM analysis. The temperatures of all parts inside the tube and beam landing shift on the panel are measured and the results are discussed in comparison with the results of the FEM analysis.ysis.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2001.05a
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• pp.681-687
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• 2001

Two-phase cross-flow exists in many shell-tube heat exchangers such as steam generators, condensers and reboilers. An understanding of flow-induced vibration excitation mechanism is necessary to avoid problems due to excessive tube vibration. This paper presents the results of a series of experiments done on tube bundles of different geometries subjected to two-phase cross-flow simulated by air-water mixtures. Normal(30$^{\circ}$) and rotated (60$^{\circ}$)triangular, and normal(90$^{\circ}$) and rotated (45$^{\circ}$) square tube bundle configurations of pitch-to-diameter ratio of 1.2 to 1.5 were tested over a range of mass fluxes from 0 to 1,000kg/$m^2$ㆍ s and void fraction from 0 to 100%. The effects of tube bundle geometry on vibration excitation mechanism such as fluidelastic instability and random turbulence, and on dynamic parameters such as damping and hydrodynamic mass are discussed. A lower pitch-to-diameter results in a higher hydrodynamic mass. The effect of tube bundle configurations on damping and random turbulence excitation is minor. The effect of pitch-to-diameter on the fluidelastic instability, however, is significant.

• Nuclear Engineering and Technology
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• v.35 no.5
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• pp.442-453
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• 2003

This study investigates the safety assessment of the potential for fretting-wear damages on steam generator (SG) U-tubes caused by foreign object in operating nuclear power plants. The operating SG shell-side flow field conditions are obtained from three-dimensional SG flow calculation using the ATHOS3 code. Modal analyses are performed for the finite element modelings of U-tubes to get the natural frequency, corresponding mode shape and participation factor. The wear rate of U-tube caused by foreign object is calculated using the Archard formula and the remaining life of the tube is predicted. Also, discussed in this study is the effect of the flow velocity and vibration of the tube on the remaining life of the tube.

• 한국태양에너지학회:학술대회논문집
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• 2011.11a
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• pp.68-73
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• 2011

This study was performed numerical analysis in order to analyze liquid film flow of heat exchanger tube arrangement and configuration of evaporative multi effect distillation system using medium-temperature. Simulation was accomplished the two-dimensional calculations using commercial analyses program FLUENT based on the FVM(finite volume method). Fresh water generator of this study used Shell & Tubes heat exchanger with Cu_Ni tube, configuration of tube used bare tube and corrugated tube, and arrangement of tube used in-line array and staggered array. Performance of heat exchanger through the formation of liquid film was compared and analyzed. Liquid film flow occurred that falling on heat exchanger tube wall. Result of simulation showed that liquid film thickness of in-line arrangement was found 0.57mm with bare tube and 0.67mm with corrugated tube, respectively. And liquid film thickness of staggered arrangement was found 0.39mm with bare tubes and 0.62mm with corrugated tubes, respectively. Liquid film thickness of corrugated tube showed thicker than bare tube, but heat transfer rates of corrugated tube showed higher than bare tube. The reason was considered that surface area of corrugated tube was wider than bare tube. And liquid film thickness of staggered arrangement showed thinner than in-line arrangement, so thermal performance of staggered arrangement showed higher than in-line arrangement.

• 한국신재생에너지학회:학술대회논문집
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• 2010.06a
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• pp.201-201
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• 2010

The evaporative desalination system with solar energy would be the efficient and attractive method to get fresh water. This study was described the development of Multi Effect Distillation(MED) with solar energy desalination system. The system was designed and manufactured Multi effect distillation on the capacity of $3m^3$/day. The experimental apparatus consists mainly of ejector pump, Hot water pump, flow meter, demister, cooler, evaporator and condenser. Evaporator and condenser were made Shell&Tube Heat Exchanger type with corrugated tube. The experimental variables were chosen $75^{\circ}C$ for hot water inlet temperature, 40, 60 and $80{\ell}$/min for hot water inlet volume flow rate, 6.0 and $8.0{\ell}$/min for evaporator feed seawater flow rate, $18^{\circ}C$ for sea water inlet temperature to cover the average sea water temperature and the salinity of sea water is measured about 33,000 PPM (parts per million). for a year in Korea. This study was analyzed the results of thermal performance of Multi Effect Distillation. The results are as follows, The experimental Multi effect distillation is required about 40 kW heat source for production of $3m^3$/day fresh water. Various operating flow rate was confirm in the experiments to get the optimum design data and the results showed that the optimum total flow was $8.0{\ell}$/min. Comparison of Single Effect Distillation with Multi Effect Distillation showed MED is at least more than double of SED.

• Proceedings of the SAREK Conference
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• 2009.06a
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• pp.1283-1287
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• 2009

In this study, an analysis was performed on an evaporative steam generator (concentrator), where natural circulation convective boiling occurs on tube-side by condensing hot steam on shell-side. Existing correlations on two-phase pressure drop, boiling or condensation heat transfer were used for the analysis. The effect of number of tubes, tube length, etc. on thermal performance was investigated. Simulation results reveal that steam generation rate increases almost proportionally to the tube length, or number of tubes. It is also shown that water circulation rate decreases as tube length increases.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.35 no.4
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• pp.361-369
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• 2011

The effect of an increase in the temperature of inlet air on the performance of a membrane humidifier for a PEMFC (Polymer Electrolyte Membrane Fuel Cell) vehicle was investigated both experimentally and numerically. A shell-and-tube type gas-to-gas humidifier with Nafion membrane was tested. The experimental result showed that water transfer varies nonlinearly with the temperature elevation. Numerical analysis based on detailed modeling was also conducted in simplified geometry of a single tube to explain this nonlinear behavior. The simulation revealed that the local water flux varies nonlinearly and dramatically along the tube. The analysis was based on the inverse relationship between the increase in temperature and decrease in relative humidity, both of which seriously affect the water conductivity of the membrane.