Joon Yong Yoon

Experimental study for flow characteristics of eccentric butterfly valves

An experimental study was performed to investigate the flow characteristics of single, double, and triple eccentric butterfly valves and concentric inclined disc butterfly valves. Valve flow coefficients, relative valve flow coefficients, and valve loss coefficients are compared between each type of butterfly valve in detail. These coefficient curves are quite different from those of conventional butterfly valves. Finally, the triple eccentric butterfly valve is recommended for use in flow rate or pressure controls, while single or double eccentric butterfly valves are better used in on–off regulation of large flow rates.

Numerical Investigation of Mixing Characteristics in a Cavity Flow by Using Hybrid Lattice Boltzmann Method

Key Words: Hybrid Lattice Boltzmann Method(혼성격자볼츠만방법), Multiple-Relaxtion-Time(다중완화시간), Cavity flow(공동형상유동), Mixing Characteristics(혼합특성)초록: 본연구에서는혼성격자볼츠만방법(HLBM)을이용하여상판이일정한속도로움직이는공동형상내부에서의혼합특성에대하여수치적으로연구하였다. 먼저, 공동형상에서기존의신뢰성있는유동장결과와의비교를통해LB-SRT 모델과LB-MRT 모델의신뢰성을검토하였다. 두모델모두기존의연구결과와유사한결과를보였으나, LB-MRT 모델이LB-SRT 모델보다높은Re수에서는수치적안정성이높은것을확인하였다. 수치적안정성이좋은LB-MRT 모델을토대로유한차분법을적용한HLBM을이용하여공동형상내부에서의농도장을수치해석하였다. Re수와Pe수를변화하여공동형상내부의혼합특성과물질전달형태에대하여파악하였다.Abstract: In this study, the mixing characteristics in lid-driven cavity flows were studied numerically by using a hybridlattice Boltzmann method (HLBM). First, we compared the numerical results from single-relaxation-time (LB-SRT) andmulti-relaxation-time (LB-MRT) models to examine their reliability. In most of the cavity flow, the results from boththe LB-SRT and the LB-MRT models were in good agreement with those using a Navier–Stokes solver for Re=100–5000. However, the LB-MRT model was superior to the LB-SRT model for the simulation of higher Reynolds numberflows having a geometrical singularity with much lesser spatial oscillations. For this reason, the LB-MRT model wasselected to study the mass transport in lid-driven cavity flows, and it was demonstrated that mass transport in the fluidwas activated by a recirculation zone in the cavity, which is connected from the top to the bottom surfaces throughtwo boundary layers. Various mixing characteristics such as the concentration profiles, mean Sherwood (Sh) numbers,and velocity were computed. Finally, the detailed transport mechanism and solutions for the concentration profile in thecavity were presented.

Surface Modification Effect of Wettability on the Performance of PDMS-Based Valveless Micropump

Experimental investigation and numerical simulation on the effect of surface wettability on the performance of a polydimethylsiloxane (PDMS) based diffuser micropump are presented. A valveless micro membrane pump with piezoelectric actuation has been examined. Using a replica molding technique, the valveless micropump was made of PDMS on a Pyrex glass substrate. A thin piezoelectric (PZT) disc was used as an actuator. Poly vinyl alcohol (PVA) and octadecyltrichlorosilane (OTS) coatings, which make the coated surface hydrophilic and hydrophobic, respectively, were used to modify the surface wettability inside the pump. In our experiments, the contact angle of the PDMS surface changed from 96.6 o to 29.1 o and 99.6 o by PVA and OTS coatings, respectively, and the contact angle of glass changed from 33.2 o to 17.5 o and 141.8 o. A self-priming process was numerically simulated in a diffuser element using a computational fluid dynamics program (CFD-ACE+). The results show that fewer gas bubbles were created in the hydrophilic coated pump than in the hydrophobic coated one as time progressed. This agrees well with experimental observations. Steady-state flow rates of the micropump were measured. Compared to the non-coated pump, the flow rate increased slightly with the hydrophobic coating but decreased with the hydrophilic coating. We determine that surface wettability significantly affects the performance of a PDMS-based micropump.

Experimental study of a cavitation heat generator

Recent research has investigated the use of ultrasonic or hydrodynamic cavitation for chemical reactors, water treatment equipment, and heat generators. In this article, a new cavitation heat generator is introduced. The proposed system utilizes an electric motor to rotate the generator, and various experiments are performed by changing the flow conditions such as inlet pressure and rotating velocity to evaluate the performance of it. In addition, the amount of heat generation is measured and the thermal efficiency is evaluated. The result is a highly efficient heat generator that can reach 90% thermal efficiency.

Experimental Investigation of the Thermal and Disinfection Performances of a Novel Hydrodynamic Cavitation Reactor

In the present study, we proposed an effective, efficient, and economical approach to disinfect water using a novel, advanced, rotational hydrodynamic cavitation reactor (HCR). First, analyses of the flow field and cavitation generation mechanism in the HCR were conducted through visualization of the reactor flow field using a high-speed camera. Second, the thermal performance was tested in 20 experiments with various rotational speeds of the rotor (2700, 3000, 3300, and 3600 rpm) and pump pressure settings (0.0, 0.5, 0.7, 1.0, and 1.5 bar gauge pressure). The HCR maximally achieved a heat generation rate of 48.15 MJ/h and thermal efficiency of 82.18%. Then, the disinfection effect was evaluated using water that simulated an effluent containing Escherichia coli (E. coli) for various flow rates (8, 11, and 14 L/min), a pump pressure setting fixed at 0.5 bar, and a rotational speed of 3600 rpm. In addition, an economical assessment of the disinfection processes was performed by considering the measured electric consumption. The thermal effect generated by the HCR was the dominant factor affecting the concentration of E. coli. The HCR achieved a 100% disinfection rate with a 4.3 L/min treatment rate and a cost of US

A Numerical Simulation Study on the Shape of the Rotor in Hydraulic Cavitation Heat Generator

3.019/m3 at the optimal flow rate. The effects of the pressure setting and rotational speed on the performance were discussed in detail. Finally, compared to the recent studies, the treatment rate of the HCR is several hundred times greater than that obtained by the HCRs utilized in those studies, and also has a reasonable cost.

Numerical performance and safety analyses of a retainer-type ball valve for use in a high-pressure district heating pipeline:

This paper presents a numerical investigation on the local hydraulic cavitation phenomena of water resulting from the rotor with high rotational speed in the hydraulic cavitation heat generator. The numerical simulation utilizes the standard k-epsilon turbulence model, the mixture multiphase model and the Schnerr-Sauer cavitation model to simulate the complex cavitation phenomena in the generator. For exploring the efficient shape of the dimples on the rotor to causing cavitation phenomena artificially, the pressure distributions and the volume fractions of the vapor on the rotor are investigated respectively about different shapes of the rotor in the generator. The optimum shape of the dimple to causing cavitation phenomena in the selected shapes is obtained by the means of the numerical simulation.

Numerical Investigation of Mixing Characteristics in Cavity Flow at Various Aspect Ratios

The performance and safety of a retainer-type ball valve have been evaluated for use in a high-pressure pipeline to a district heating plant. The retainer-type ball valve is a developed valve improving the defects of the leaks that may occur in the general valves such as the floating ball valve or trunnion ball valve. To verify the valve design, a numerical analysis of the design has been applied to investigate safety factors and to determine the flow coefficients for the DN300 and DN400 standard sizes. The conditions used for the numerical analysis was based on the international standards ISO 5208, IEC 60534-2-3, and a high-pressure pipeline to a district heating plant. The structural analysis results comprise deformations, equivalent stresses, and safety factors, and the flow analysis results show the flow coefficient, the pressure distribution, the velocity vectors, and the flow patterns for each rotation angle. These results confirmed the characteristics and reliability of the retainer-type ball valve and, based on these studies, we proposed a retainer-type ball valve as a solution to solve the leakage problem.

Investigation of the Performance for a Heat Generator Using Hydrodynamic Cavitation

* School of Mechanical Engineering, Dongyang Mirae Univ., ** Dept. of Mechanical Engineering, Hanyang Univ. (Received July 24, 2014 ; Revised September 26, 2014 ; Accepted September 30, 2014)Key Words: Hybrid Lattice Boltzmann Method(혼성 격자볼츠만 방법), Rectangular cavity flow(직사각 공동형상 유동), Mixing characteristics(혼합특성)초록: 본 연구에서는 유한차분법(FDM)을 적용한 혼성 격자볼츠만 방법(HLBM)을 이용하여 직사각 형태를 갖는 공동형상 내 혼합특성에 대하여 수치적으로 연구하였다. 유동장은 다중 완화시간을 적용한 격자볼츠만 방법(LB-MRT)을 사용하였으며, 농도장은 두 물질의 질량은 같고 두 물질 사이의 상호작용이 없다고 가정한 Passive Scalar 방법을 사용하였다. 먼저, 정사각형과 종횡비가 2인 직사각형의 공동형상 내 유동해석 결과를 기존의 신뢰성 있는 연구결과와 비교하여 HLBM의 신뢰성을 검토하였다. 이를 토대로 다양한 종횡비를 갖는 공동형상에서 Pe수를 변화시키며 공동형상 내부에서의 혼합특성과 물질전달 형태에 대하여 파악하였다.Abstract: This study numerically examined the mixing characteristics of rectangular cavity flows by using the hybrid lattice Boltzmann method (HLBM) applied to the finite difference method (FDM). Multi-relaxation time was used along with a passive scalar method which assumes that two substances have the same mass and that there is no interaction. First, we studied numerical results such as the stream function, position of vortices, and velocity profile for a square cavity and rectangular cavity with an aspect ratio of 2. The data were compared with previous numerical results that have been proven to be reliable. We also studied the mixing characteristics of a rectangular cavity flow such as the concentration profile and average Sherwood number at various Pe numbers and aspect ratios.

Thermal, mechanical and rheological properties of poly (lactic acid)/epoxidized soybean oil blends

Cavitation occurs typically when pressure is lower than the saturated vapor pressure. Generally, cavitation used to be a phenomenon engineer should avoid when they design fluid machinery because it creates erosion, vibration and noise that make performance of the machineries worse. Recently, study about generating energy with cavitaion is being proceeded like heat generating machinery which is the most typical. There is little academic research, although study about these has some commercial documents or patents. In this study, we proceed experimental study for the heat generator connected to electrical motor which generates heat from cavitaion using a fast rotating device. We used 15 kW and 55 kW electric motors to rotate the generator. The experiments performed changing flow conditions such as pressure at entering position by using a booster pump and rotating velocity of the motors by an inverter. We analyzed heat production and thermal efficiency according to the flow conditions. The front cover of the heater is made of acrylic plate so that we can use high speed photography to observe the relation between cavitation and generator shape. We made sure that these conditions can affect performance and especially pressure at entrance or rotating velocity affect heat production. Existing theory of cavitation and results of this study were discussed. These results could be useful for design process of the machine using cavitation such as a cavitation heat generator and a chemical reactor etc.Copyright