• Journal of the Korea Academia-Industrial cooperation Society
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• v.16 no.5
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• pp.3014-3021
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• 2015

Shell-tube heat exchanger is widely applied in industrial field by easily manufacturing as to various size and flow patterns. In this study, by changing baffle's cut direction, tilt angle and rotational angle as well as by using SST (Shear Stress Transport) $k-{\omega}$ turbulence model in ANSYS FLUENT v.14, the heat transfer rate and pressure drop characteristics of inner shell will be analyzed to improve heat transfer ability. As a result of analysis, heat transfer performance according to cut direction of baffle has been improved with vertical model B and angle $45^{\circ}$ model C than horizontal model A. In addition, the tilt $10^{\circ}$ of the baffle and rotational angle $0^{\circ}-90^{\circ}-180^{\circ}-270^{\circ}$ of model D showed better result in heat transfer rate and pressure drop.

• Journal of the Society of Naval Architects of Korea
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• v.47 no.5
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• pp.647-655
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• 2010

In this paper, a numerical study is carried out for super-pipe, flat plate and axisymmetric body flows to investigate a validity of using wall function and high $y_1^+$ in calculation of high Reynolds number flow. The velocity profiles in boundary layer agree well with the law of the wall. And it is found that the range of $y^+$��which validated the logarithmic law of the wall grows with increasing Reynolds number. From the result, an equation is suggested that can be used to estimate a maximum $y^+$ value of validity of the log law. And the slope(1/$\kappa$) of the log region of the numerical result is larger than that of experimental data. On the other hand, as $y_1^+$ is increasing, both the friction and the pressure resistances tend to increase finely. When using $y_1^+$ value beyond the range of log law, the surface shear stress shows a significant error and the pressure resistance increases rapidly. However, when using $y_1^+$ value in the range, the computational result is reasonable. From this study, the use of the wall function with high value of $y_1^+$ can be justified for a full scale Reynolds number ship flow.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.29 no.3B
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• pp.239-245
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• 2009

Levees, the hydro-engineering structure, are similar to earth dams in aspects of shape and structure. However, they are different from earth dams in the external force conditions. As a levee is the structure that is complexly affected by the flow and the water stage in the river, it may be unreasonable to analyze the seepage safety as previous studies derived from the neglect of river flow. In this study, an experiment was conducted to investigate flow structures in a trapezoidal open-channel and the influence of the channel flow on the seepage through a levee. Flow structures in a trapezoidal open-channel were distinguished from a rectangular open-channel such as velocity and bottom shear stress distributions. In case with the flow velocity of 0.5 m/s, seepage water heads were higher 10 percent as compared with the stagnant case. This result is caused by dynamic heads, secondary currents, turbulent fluctuation forces, and various physical factors. It is suggested that external force boundary considered in terms of the flow as well as the water stage is proper to seepage analyses.

• 한국해양학회지
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• v.19 no.2
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• pp.141-152
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• 1984

In order to investigate the circulation dynamics of the Keum River estuary, 300velocity fields obtained at six sites over two tidal cycles by using instantaneous profiling technique were analyzed in detail. In this investigation, the variability of shear velocity, bottom shear stress, drag coefficient, and roughness length scale were confirmed. The measured values of the bottom boundary drag coefficient show wide range of variations, i.e., C$\_$100/=6.78${\times}$10$\^$-5/∼1.15${\times}$10$\^$-1/, and the mean of 300 measurements is 1.6${\times}$10$\^$-2/. The relationship between U* and C$\_$100/ also show the scatter in values. However, overall mean values over two tidal cycles at 6 stations show that if U* 1cm/s, C$\_$100/ is unpredictable, if U* 1cm/s, C$\_$100/ increase with U*. The values of Re$\_$100/ and C$\_$100/ have scatter. But the overall mean values over two tidal cycles show that if Re$\_$100/ 3.6${\times}$10$\^$5/, C$\_$100/ is unpredictable, if Re$\_$100/ 3.6${\times}$10$\^$5/, C$\_$100/=1.4${\times}$10$\^$-2/. Finally the flow regime of the Keum River estuary was classified as "subcritical fully turbulent" flow.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.14 no.6
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• pp.528-535
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• 2004

Ultrasonic Vibrator is designed to achieve the maximum vibration amplitude at 30 kHz by in-cluding a horn (diameter, 40 mm), mechanical vibration amplifier at the top of the ultrasonic vibrator in the system and making the complete system resonate. In addition, it is experimentally visualized by particle imaging velocimetry (PIV) that the acoustic streaming velocity in the gap is at maximum when the gap between the ultrasonic vibrator and stationary plate agrees with the multiples of half-wavelength of the ultrasonic wave. This fact results from the resonance of the sound wave and the theoretical analysis of that is also accomplished and verified by experiment. It is observed that the magnitude of the acoustic streaming dependent upon the gap between the ultrasonic vibrator and stationary plate possibly changes due to the measurement of the average velocity fields of the acoustic streaming induced by the ultrasonic vibration at resonance and non-resonance. There exists extremely small average velocity at non-resonant gaps while the relatively large average velocity exists at resonant gaps compared with non-resonant gaps. It also reveals that there should be larger axial turbulent intensity at the hub region of the vibrator and at the edge of it in the resonant gap where the air streaming velocity is maximized and the flow phenomena is conspicuous than that at the other region. Because the variation of the acoustic streaming velocity at resonant gap is more distinctive than that at non-resonant gap, shear stress increases more in the resonant gap and is also maximized at the center region of the vibrator except the local position of center (r〓0). At the non-resonant gap there should be low values of vorticity distribution, but in contrast to the non-resonant gap, high and negative values of it exist at the center region of the vibrator with respect to the radial direction and in the vicinity of the middle region with respect to the axial direction. Acoustic streaming is noise-free due to the ultrasonic vibration and maintenance-free because of the absence of moving parts. Moreover, the proposed method by acoustic streaming can be utilized to the nano and micro-electro mechanical systems as a driving mechanism in addition to the augmentation of the streaming velocity.