• Nuclear Engineering and Technology
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• v.38 no.1
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• pp.69-80
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• 2006

Fluid-elastic instability in an air-water two-phase cross-flow has been experimentally investigated using two different arrays of straight tube bundles: normal square (NS) array and rotated square (RS) array tube bundles with the same pitch-to-diameter ratio of 1.633. Experiments have been performed over wide ranges of mass flux and void fraction. The quantitative tube vibration displacement was measured using a pair of strain gages and the detailed orbit of the tube motion was analyzed from high-speed video recordings. The present study provides the flow pattern, detailed tube vibration response, damping ratio, hydrodynamic mass, and the fluid-elastic instability for each tube bundle. Tube vibration characteristics of the RS array tube bundle in the two-phase flow condition were quite different from those of the NS array tube bundle with respect to the vortex shedding induced vibration and the shape of the oval orbit of the tube motion at the fluid-elastic instability as well as the fluid-elastic instability constant.

• Journal of Advanced Marine Engineering and Technology
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• v.29 no.3
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• pp.275-280
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• 2005

Recently there has been a growing interest in the design and manufacturing of the muffler tube due to the strict environment regulations, A muffler is an important part used to reduce noise and to purify exhaust gas in cars and heavy equipment. The shape of the muffler tube and the number of the tube hole has been made variously according to the weight and function of the car. The perforating technique of the muffler tube has a great influence on the manufacturing cost. In this study, metal forming analysis has been carried out to investigate the perforating process for the muffler tube and predict an optimal forming conditions of the muffler tube, Also its simulation results by the finite element method were reflected to the die design and the manufacturing system for the muffler tube. The perforating process is performed in the longitudinal direction of the tube. According to the simulation results, when the shear angle of punch was similar to the tube curvature, the optimal shape was obtained. Also when the clearance of die was 0.2mm, the burr was minimized and optimal shear section was obtained.

• Proceedings of the SAREK Conference
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• 2006.06a
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• pp.657-662
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• 2006

The present paper dealt with an experimental study of condensation heat transfer coefficients with refrigerant R-22, R-407C and R-410A, and was focused on pressure gradient and heat transfer coefficient in horizontal tube-in-tube heat exchangers using inner diameter of 4 mm, 3 mm and 2 mm in a 16.91 mm tube and length of 3,000 mm. Experiments were performed at inlet saturation temperature of 35 to $45^{\circ}C$ and mass flux ranges from 200 to $600 kg/m^2s$. The pressure gradient with inner tube diameter of 4.0 mm is higher 2.5 times than that of 8.0 mm. In tube-in-tube HEX, the pressure gradient of R-410A were lower than those of R-22 and R-407C. The condensation heat transfer coefficients increased with mass flux increase, but they decreased with saturation temperature increased. Condensation heat transfer coefficients of R-410A were a little higher than those of R-22 and R-407C. The condensation heat transfer coefficients of tube-in-tube HEX were about 40% higher than those of double tube HEX.

• 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.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.2 no.4
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• pp.316-326
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• 1990

The measurements of heat transfer and pressure drop were performed on ripple tube with air flow. The results with the tube were compared with the performance of smooth tube. The enhancements in heat transfer coefficient for ripple tube, being compared with smooth tube, was ranged from 7.4 to 39 percent. The local Nusselt number for the inner fin tube, being compared with that for smooth tube, varied from 7.4% to 39%, while the corresponding increase in friction factors were 4.1 to 8.1%. One of the most direct indications of Nusselt number of ripple tube is given as following equation: $$Nu=0.061Re^{0.75}Pr^{0.4}(Tb/Tw)^{0.5}$$ We can see that Nusselt number for ripple tube in this experiment is consistent with the theoretical one taken from Walkinson's equation at Reynolds number range from 8,000 to 20,000.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
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• 2002.10a
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• pp.53-57
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• 2002

Brake tube is considered one of the most important parts in automobile. The shape of brake tube-end has a great influence on the function of brake, and the quality and productivity of brake tube have relation to die design. The forming process of brake tube-end is peformed by hydraulic press forming machine. In this paper, the forming processes of tube-end for automobile is analyzed and designed to make the optimal form of brake tube-end. Also, finite element analysis has been carried out using DEFORM-3D$\^$TM/ to predict the optimal shape of brake tube-end and the results obtained showed the optimal length between punch and chuck is 1.0 ∼ 1.2mm. The shape of tube-end is in good agreement with the finite element simulations and the experimental results.

• Nuclear Engineering and Technology
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• v.51 no.6
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• pp.1650-1657
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• 2019

Fluidelastic instability and nonlinear dynamics of tube bundles is a key issue in a steam generator. Especially, once the post-instability motion of the tube becomes larger than the clearance gap to other tubes, effective contact or impact between the tubes under consideration and the other tube inevitable. There is seldom theoretical analysis to the nonlinear dynamic characteristics of a tube array in two-phase flow. In this paper, experimental and numerical studies were utilized to obtain the critical velocity of the flow-induced instability of a rotated triangular tube array. The calculation results agreed well with the experimental data. To explore the post-instability dynamics of the tube array system, a Runge-Kutta scheme was used to solve the nonlinear governing equations of tube motion. The numerical results indicated that, when the flow pitch velocity is larger than the critical velocity, the tube array system is undergoing a limit cycle motion, and the dynamic characteristics of the tube array are almost similar for different void fractions.

• Progress in Superconductivity and Cryogenics
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• v.13 no.2
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• pp.25-28
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• 2011

A compact phase controller of pulse tube refrigerator is proposed in this paper. Most pulse tube refrigerators available now consist of a long inertance tube and reservoir as the phase controller. The long inertance tube and reservoir present a challenge for compact packaging in some applications. To overcome this disadvantage, the long inertance tube and reservoir are replaced with the compact phase controller consisted of mass, spring and damper in pulse tube refrigerator. This process is achieved using similarity of mechanical, electrical, and acoustic system and the specific configuration of the compact phase controller is designed. From the simulation code in this paper, the performance of pulse tube refrigerator with the designed compact phase controller is confirmed to be comparable to pulse tube refrigerator with the long inertance tube and reservoir.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.24 no.7
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• pp.553-559
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• 2012

A plate-fin heat exchanger is a type of heat exchanger widely used in air conditioners, and tubes and fins are tightly assembled by the mechanical expansion process of tubes. The tube expansion process deforms the grooves inside the tube, and the groove shapes also affect the adhesion between tubes and fins. In this study, the adhesion and heat transfer performance affected by the tube expansion of the non-uniform groove shape tube with different heights are investigated by both analysis and experiments. From the analysis method, it was shown that the contact pressure of non-uniform groove tube is higher than that of the uniform groove tube, and the most appropriate high groove number of the non-uniform groove tube is designed for the maximum contact pressure. From the experimental results, the decreasing rate of the condensation heat transfer coefficient is smaller in the non-uniform groove tube with different heights, compared to the conventional uniform groove tube. Also, the air-side heat transfer coefficient of the non-uniform groove tube with different heights is higher than that of the uniform groove tubes.

• 연구논문집
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• s.29
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• pp.17-27
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• 1999

The experimental results of the 17K inertance tube pulse tube cryocooler for cooling cryosensors are presented in this paper. In prototype experiments, linear compressor is driven by linear motor, and inertance tubes are inserted between one liter reservoir and pulse tube. Design of the inertance tube pulse tube cryo-cooler is conducted by ARCOPTR program of NASA Ames Research Center. To find optimal conditions of inertance tube pulse tube cryocooler, no load temperature and refrigeration capacity according to the variations of inertance tube volume, reservoir volume and charging pressure are measured. and the cool down and load characteristics at the particular conditions are presented. As the representative results, no load temperature of the cold end is 52.7K and refrigeration capacity is 5W at 72K..