• Bulletin of the Korean Chemical Society
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• v.34 no.2
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• pp.379-383
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• 2013

For the production of ethanol from freshwater cyanobacteria, a new pretreatment method using supercritical fluid was introduced. In this study, it was found that the supercritical fluid could penetrate inside the cell wall and help to liberate starch from cyanobacterial cells which resulted in the increase of the efficiency of ethanol production. For Microcystis aeruginosa, supercritical fluid pretreatment increased the amount of ethanol produced from cyanobacteria from 1.53 g/L to 2.66 g/L. For Anabaena variabilis, the amount of ethanol was increased from 1.25 g/L to 2.28 g/L. With use of supercritical fluid pretreatment, the efficiency of the process to obtain higher ethanol yields from freshwater cyanobacteria was improved upto 80%. The optimum temperature and pressure conditions for supercritical fluid pretreatment were determined as the temperature of $40^{\circ}C$ and the pressure of 120 atm. This study demonstrates the feasibility of using supercritical fluid pretreatment for ethanol production using freshwater cyanobacteria.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.24 no.1
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• pp.69-74
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• 2015

This study examined the fluid flow characteristics of a hydraulic retarder adapted as an auxiliary brake for heavy vehicles. The commercial computational fluid dynamics (CFD) software STAR-CCM+ was used to investigate the torque performance and flow characteristics of the hydraulic retarder. The numerical results showed that the pressure distribution was higher near the inner wall surface of the rotor and stator. The pressure of the working fluid increased in the radial direction of the rotor and stator. The variation in the fluid velocity intensity showed a similar trend to that of the fluid pressure, but the maximum velocity appeared near the outer wall surface of the rotor and stator interface. The numerical results showed that increasing the revolution speed of the retarder greatly increased the rate of torque generation.

• Journal of Magnetics
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• v.22 no.1
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• pp.133-140
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• 2017

Split magnetic fluid sealing is a combination of magnetic fluid rotary and plane sealing. Using the theory of equivalent magnetic circuit design as basis, the author theorized the pressure resistance performance of magnetic fluid plane sealing. To determine the pressure resistance of magnetic fluid plane sealing, the author adopted the method of finite element analysis to calculate the magnetic field intensity in the gap between plane sealing structures. The author also analyzed the effect of different sealing gaps, as well as different ratios between the sealing gap and tooth and solt width, on the sealing performance of split magnetic fluid. Results showed that the wider the sealing gap, the lower the sealing performance. Tooth width strongly affects sealing performance; the sealing performance is best when the ratio between tooth width and sealing gap is 2, whereas the sealing performance is poor when the ratio is over 8. The sealing performance is best when the ratio between the solt width and sealing gap is 4, indicating a slight effect on sealing performance when the ratio between the solt width and sealing gap is higher. Theoretical analysis and simulation results provide reference for the performance evaluation of different sealing equipment and estimation of critical pressure at interface failure.

• Structural Engineering and Mechanics
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• v.85 no.2
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• pp.247-263
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• 2023

The paper deals with the study of the mechanical time-harmonic forced vibration of the hydro-piezoelectric system consisting of the piezoelectric plate and compressible viscous fluid with finite depth. The exact equations of motion of the theory of linear electro-elasticity for piezoelectric materials are employed for describing the plate motion, however, the fluid flow is described by employing the linearized Navier-Stokes equations for a compressible (barotropic) viscous fluid. The plane-strain state in the plate and the plane flow of the fluid are considered and the corresponding mathematical problems are solved by employing the Fourier transform with respect to the space coordinate which is on the coordinate axis directed along the platelying direction. The expressions of the corresponding Fourier transform are determined analytically, however, the inverse transforms are found numerically. Numerical results on the interface pressure and the electrical potential are obtained for various PZT materials and these results are discussed. According to these results, in particular, it is established that the electromechanical coupling effect can significantly decrease the interface pressure.

• Proceedings of the KSME Conference
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• 2007.05b
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• pp.2879-2884
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• 2007

Dynamic responses of electrorheological (ER) fluids in steady pressure flow to stepwise electric field excitations are investigated experimentally. The transient periods under various applied electric fields and flow velocities were determined from the pressure behavior of the ER fluid in the flow channel with two parallel-plate electrodes. The pressure response times were exponentially decreased with the increase of the flow velocity, but increased with the increase of the applied electric field strength. In order to investigate the cluster structure formation of the ER particles, it was verified using the flow visualization technique that the transient response of ER fluids in the flow mode is assigned to the densification process in the competition of the electric field-induced particle attractive interaction forces and the hydrodynamic forces, unlike that in the shear mode determined by the aggregation process.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2008.04a
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• pp.579-584
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• 2008

The importance and the interest of wind load have emphasized since the damage of the Jeju World cup Stadium and Main Stadium of Busan Asiad in 2002, and the appearance of high-rise buildings. In general, a evaluation for the wind load acting on structures have been carried out mainly through the wind tunnel test, but this technique has the huge shortcomings that consume too much cost and experimental time. However, with the rapid advances on computers, it is possible to analyze the wind pressure distribution acting on structures by numerical scheme. In this paper, to predict the wind pressure distribution acting on shell structures having the various shape by numerical simulation, governing equations of fluid flow and turbulent model is formulated. Also, evaluates the wind pressure coefficient in accordance with the structural shape for shell structures like as a membrane structures and dome structures.

• Journal of Power System Engineering
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• v.12 no.3
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• pp.32-37
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• 2008

The present work aims to determine the overall pressure losses in the shell from the point of entry of the fluid to the outlet point of fluid of shell and tube heat exchanger. The main contribution of the present work is concerned with calculating the pressure drop in the interior section and window section. Shell-side flow velocity distributions have been evaluated. We assume that the shell-side fluid is turbulent. The calculation procedure is based upon the Delaware method. Evaluation of pressure drop on the shell side will be helpful for a designer or manufacturer of a heat exchanger.

• International Journal of Fluid Machinery and Systems
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• v.1 no.1
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• pp.109-120
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• 2008

An innovative method of changing a centrifugal low specific speed pump performance and pressure fluctuation by applying outlet flaps to impeller exit has been investigated. The outlet blade edge section corresponds to the trailing edge of wing on the circular-cascade, which dominates the pump performance and pressure fluctuation. Computational fluid dynamics (CFD) analysis of the entire impeller and volute casing and an experimental investigation are conducted. The pressure fluctuation and the vibration of the shaft are measured simultaneously. Kurtosis is applied as a dimensionless parameter with which the unevenness of velocity distribution at impeller outlet is indicated. The influence of the flaps on the pressure fluctuation is explained by the kurtosis. This paper presents a theoretical method of predicting the pump performance related to the attachment of a flap at impeller outlet.

• KSTLE International Journal
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• v.10 no.1_2
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• pp.37-42
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• 2009

This paper presents the characteristics of volumetric efficiency of an axial type piston pump considering the piston tilting. A numerical analysis is carried out in order to obtain the pressure distribution considering the fluid inertia at the notch of the valve plate. The cylinder pressure variation and the discharge flow rate are measured experimentally according to the operating conditions such as supply pressure, rotational speed, and viscosity of the working fluid by using the cam type test apparatus. Leakage is also measured considering piston tilting. The characteristics of the volumetric efficiency are analyzed with respect to various operating conditions and leakage is also analyzed according to the piston tilting angle. Results are applicable to improve the design of an axial type piston pump.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.23 no.6
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• pp.675-682
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• 2010

The flood impact pressure acting on a vertical wall resulting from a dam-breaking problem is simulated using a navier-Stokes(N-S) solver. The N-S solver uses Eulerian Finite Volume Method(FVM) along with Volume Of Fluid(VOF) method for 2-D incompressible free surface flows. A Split Lagrangian Advection(SLA) scheme for VOF method is implemented in this paper. The SLA scheme is developed based on an algorithm of Piecewise Linear Interface Calculation(PLIC). The coupling between the continuity and momentum equations is affected by using a well-known Semi-Implicit Method for Pressure-Linked Equations (SIMPLE) algorithm. Several two-dimensional numerical simulations of the dam-breaking problem are presented to validate the accuracy and demonstrate the capability of the present algorithm. The significance of the time step and grid resolution are also discussed. The computational results are compared with experimental data and with computations by other numerical methods. The results showed a favorable agreement of water impact pressure as well as the global fluid motion.