• Transactions of the Korean Society of Mechanical Engineers A
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• v.31 no.5
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• pp.570-577
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• 2007

A micromachined convective accelerometer is a recently developed device. Typical micromachined accelerometers use a solid proof mass for measuring acceleration. But a micromachined convective accelerometer does not use a solid proof mass. A micromachined convective accelerometer is composed of a heating resistor and temperature sensors. This device measures acceleration by using convective heat transfer phenomenon. Therefore characteristics of a micromachined convective accelerometer are different as compared with typical micromachined accelerometer. In this research, we analyze the convective accelerometer by using transient convective heat transfer analysis. Based on the results of a convective accelerometer, we propose a new model which has improved performance.

• Journal of Ocean Engineering and Technology
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• v.25 no.3
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• pp.11-18
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• 2011

The rogue wave was generated in a two-dimensional wave tank the rogue wave kinematics was investigated including local and convective accelerations of the water particle and verification of existing prediction methods. PIV technique was applied to measure the wave kinematics near the wave crest which extended to compute the local and convective accelerations. The experimental results were compared with several analytical predictions. The convective acceleration under the crest of rogue wave has a similar magnitude with the local acceleration.

• Proceedings of the Korea Water Resources Association Conference
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• 2008.05a
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• pp.1111-1115
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• 2008

The relative magnitudes of the individual terms of the momentum equation are analyzed and compared by the analytical methods in open channel flow. The temporal variations of each term(local acceleration term, convective acceleration term, pressure force term, gravity force term, and friction force term) are analyzed for the influence factors to runoff expressed by the parameters of the momentum equation, stream slopes and roughness coefficients. The magnitudes of each term vary with the channel characteristics, especially when the roughness coefficients are dominant or for the mild stream slopes the pressure term can not be negligible. As a result of the characteristics of momentum equation in open channel flow, the acceleration terms are very small compared with the other terms. The magnitudes of local acceleration and convective acceleration offsets each other. The peak time of each term except the gravity term coincides with inflection point of the hydrograph rising limb each other.

• Journal of Ocean Engineering and Technology
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• v.24 no.1
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• pp.1-9
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• 2010

A series of experiments employing particle image velocimetry (PIV) technique was conducted to produce benchmark wave kinematics data for regular waves having four different wave slopes in 2-D wave tank. Water velocities and accelerations near the free surface of regular waves were computed from image pair obtained by PIV systems. With the measured wave velocity field, the wave accelerations were computed using a centered finite difference scheme. Both local and convective components of the total accelerations are obtained from experimental data. With increasing the wave slope, the horizontal velocity and the vertical accelerations near the wave crest obtained by PIV technique became larger than theoretical results, which are well-known phenomena of the wave nonlinearity. It is noted that the relative magnitude of convective acceleration to the local acceleration became larger with increasing wave slope.

• Journal of Mechanical Science and Technology
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• v.17 no.11
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• pp.1756-1766
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• 2003

Numerical modeling is carried out to investigate forced convective heat transfer to near-critical water in developing laminar flow through a circular tube. Due to large variations of thermo-physical properties such as density, specific heat, viscosity, and thermal conductivity near thermodynamic critical point, heat transfer characteristics show quite different behavior compared with pure forced convection. With flow acceleration along the tube unusual behavior of heat transfer coefficient and friction factor occurs when the fluid enthalpy passes through pseudocritical point of pressure in the tube. There is also a transition behavior from liquid-like phase to gas-like phase in the developing region. Numerical results with constant heat flux boundary conditions are obtained for reduced pressures from 1.09 to 1.99. Graphical results for velocity, temperature, and heat transfer coefficient with Stanton number are presented and analyzed.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.36 no.5
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• pp.477-485
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• 2012

Fluid flow and heat transfer in horizontal ducts are strongly coupled with large changes in thermodynamic and transport properties near the critical region as well as the gravity force. Numerical analysis has been carried out to investigate convective heat transfer in horizontal rectangular ducts for water near the thermodynamic critical point. Convective heat transfer characteristics, including velocity, temperature, and the properties as well as local heat transfer coefficients along the ducts are compared with the effect of proximity on the critical point. When there is flow acceleration because of a density decrease, convective heat transfer characteristics in the ducts show transition behavior between liquid-like and gas-like phases. There is a large variation in the local heat transfer coefficient distributions at the top, side, and bottom surfaces, and close to the pseudocritical temperature, a peak in the heat transfer coefficient distribution resulting from improved turbulent transport is observed. The Nusselt number distribution depends on pressure and duct aspect ratio, while the Nusselt number peak rapidly increases as the pressure approaches the critical pressure. The predicted Nusselt number is also compared with other heat transfer correlations.

• Water for future
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• v.29 no.1
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• pp.163-179
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• 1996

Flood flow characteristics of the Han River (from Goan to Indo Bridge) are analyzed using 1-dimensional St. Venant equations. NETWORK, a finite difference model, is used to calculate each term (local acceleration term, convective acceleration term, pressure force term, gravity force term, and friction force term) of the momentum equation and to analyze the flow characteristics. By the result of the study, as the general characteristics of flow in a channel that acceleration terms are very small and the other three terms are much greater is presented, three terms(pressure force term, gravity force term, friction force term) are to be main terms which decide the characteristics of flow. Specially in this region the acceleration term is noted so large that it cannot be ignored according to the shape of hydrograph and the region.

• 한국연소학회:학술대회논문집
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• 2004.06a
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• pp.183-191
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• 2004

The burning characteristics of interacting droplets with internal circulation in a convective flow are numerically investigated at various Reynolds numbers. The transient combustion of 2-dimensionally arranged droplets, both the fixed droplet distances of 5 radii to 40 radii horizontally and 4 radii to 24 radii vertically, is studied. The results obtained from the present numerical analysis reveal that the transient flame configuration and retardation of droplet internal motion with the horizontal or vertical droplet spacing substantially influence lifetime of interacting droplets. At a low Reynolds number, lifetime of the two droplets with decreasing horizontal droplet spacing increases monotonically, whereas their lifetime with decreasing vertical droplet spacing decreases due to flow acceleration. This flow acceleration effect is reversed when the vertical droplet spacing is smaller than 5 radii in which decreasing flame penetration depth causes the reduction of heat transfer from flame to droplets. At a high Reynolds number, however, lifetime of the first droplet is hardly affected by either the horizontal droplet spacing or flow acceleration effect. Lifetime with decreasing vertical droplet spacing increases due to reduction of flame penetration depth. Lifetime of interacting droplets exhibits a strong dependence on Reynolds number, the horizontal droplet spacing and the vertical droplet spacing and can be con-elated well with these conditions to that of single burning droplet.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.22 no.1
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• pp.29-35
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• 2012

Special attention in the role of convection in vapor crystal growth has been paid since some single crystals under high gravity acceleration of $10g_0$ appear considerably larger than those under normal gravity acceleration ($1g_0$). With increasing the gravity acceleration from $1g_0$ up to $10g_0$, the total molar flux for ${\Delta}T$ = 30 K increases by a factor of 4, while for ${\Delta}T$ = 90, by a factor of 3. The maximum molar fluxes for three different gravity levels of $1g_0$, $4g_0$ and $10g_0$, appear approximately in the neighborhood of y = 0.5 cm, and the molar fluxes show asymmetrical patterns, which indicate the occurrence of either one single or more than one convective cell. As the gravitational level is enhanced form $1g_0$ up to $10g_0$, the intensity of convection is increased significantly through the maximum molar fluxes for ${\Delta}T$ = 30 K and 90 K. At $10g_0$, the maximum total molar flux is nearly invariant for for ${\Delta}T$ = 30 K and 90 K. The total molar flux increases with increasing the gravity acceleration, for $1g_0{\leq}g_y{\leq}10g_0$, and decreases with increasing the partial pressure of component B, a noble gas called as Kr (Krypton), $P_B$. The ${{\mid}U{\mid}}_{max}$ is directly proportional to the gravity acceleration for 20 Torr $P_B{\leq}300$ Torr. As the partial pressure of $P_B$ (Torr) decreases from 300 Torr to 20 Torr, the slopes of the ${{\mid}U{\mid}}_{max}s$ versus the gravity accelerations increase from 0.29 sec to 0.54 sec, i.e. by a factor of 2. The total molar flux of $Hg_2Cl_2$ is first order exponentially decayed with increasing the partial pressure of component B, $P_B$ (Torr) from 20 Torr up to 300 Torr.

• Journal of the Korean Society of Hazard Mitigation
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• v.8 no.3
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• pp.137-147
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• 2008

The relative magnitudes of the individual terms of the momentum equation are analyzed and compared by analytical methods. The temporal variations of each term are analyzed for the influence factors to runoff expressed by the parameters of the momentum equation, stream slopes and roughness coefficients. The magnitudes of local acceleration and convective acceleration offset each other. The peak time of each term except the gravity term coincides with inflection point of the hydrograph rising limb each other. The magnitudes of each term vary with the channel characteristics, especially when the roughness coefficients are dominant or for the mild stream slopes the pressure term can not be negligible.