Hwan-Seong Kim

Experimental Investigation of Heat Transfer in Two-phase Flow Boiling

In this article, an experimental investigation is performed to measure the boiling heat transfer coefficient of water flow in a microchannel with a hydraulic diameter of 500 μm. Experimental tests are conducted with heat fluxes ranging from 100 to 400 kW/m2, vapor quality from 0 to 0.2, and mass fluxes of 200, 400, and 600 kg/m2s. Also, this study has modified the liquid Froude number to present a flow pattern transition toward an annular flow. Experimental results show that the flow boiling heat transfer coefficient is not dependent on mass flux and vapor quality but on heat flux to a certain degree. The measured heat transfer coefficient is compared with a few available correlations proposed for macroscales, and it is found that previous correlations have overestimated the flow boiling heat transfer coefficient for the test conditions considered in this work. This article proposes a new correlation model regarding the boiling heat transfer coefficient in mini- and microchannels using boiling number, Reynolds number, and modified Froude number.

Active steering for intelligent vehicles using advanced control synthesis

This paper considers the design of an active steering controller of an intelligent vehicle for general lane change manoeuvres. First, we present a unified formulation of lateral vehicle dynamics. Next, the design method includes the 2-DOF H∞ loop-shaping control scheme for lane change manoeuvres, in the face of co-prime factorisation perturbations. Furthermore, the controller has been reduced to a reasonable order before real implementation. The resulting controller is then evaluated in both frequency- and time-domains. Finally, it is shown that the presented controller provides excellent performance over a wide range of simulated manoeuvring conditions.

Experimental and Numerical Analysis for Single-phase Flow Pressure Drop in Parallel Micro-channels

The experimental and numerical studies of the single-phase flow pressure drop in parallel micro-channels were performed. The parallel micro-channels consisted of 15 channels with depth 0.2mm, width 0.45mm and length 60mm. The FC-72 was used as the working fluid and the mass fluxes ranged from 62.8 to 1371.6kg/m 2 s. The numerical analysis was performed iterative calculations to solve governing equations and finds the appropriate value. The experimental data was compared with the numerical data, the results showed good agreement with the numerical data.

Two-phase Pressure Drop in Horizontal Rectangular Channel

Two-phase pressure drop experiments were performed during flow boiling to deionized water in a microchannel having a hydraulic diameter of . Tests were made in the ranges of heat fluxes from 100 to , vapor qualities from 0 to 0.2 and mass fluxes of 200, 400 and . The frictional pressure drop during flow boiling is predicted by using two models; the homogeneous model that assumes equal phase velocity and the separate flow model that allows a slip velocity between two phases. From the experimental results, it is found that the two phase multiplier decreases with an increase in mass flux. Measured data of pressure drop are compared to a few available correlations proposed for macroscale and mini/microscale. Among the separated flow models, the correlation model suggested by Lee and Garimella predicted the frictional pressure drop within MAE of 47.2%, which is better than other correlations.

A study on the analysis of galloping for power transmission line

In this paper, the authors deal with a new type of modelling method for the analysis of galloping in power transmission lines (PTL). The single mass model is obtained under the linearization method and is applied into an f-order model. In these models, the natural frequencies of PTL are obtained which have an effect on the galloping directly. In simulation, they verify that the maximum magnitude of natural frequency depends on the galloping distance of PTL. Also, from the analysis of frequency response, a reduction method for galloping is introduced which is affected by the distance of PTL, wind velocity and icing types.

Two-phase flow boiling heat transfer of FC-72 in parallel micro-channels

ABSTRACT Experimental research is performed on two-phase flow boiling heat transfer in micro-channels. FC-72 is used as the working fluid. In order to analyze the heat transfer mechanism during two-phase flow boiling, the dimensionless parameters, e.g., boiling number and convection number, are used, and the effect of these parameters on the heat transfer can be confirmed during flow boiling in the micro-channel. In addition, the transition criterion from bubbly/slug flow to annular flow is proposed from the modified Weber number. Based on the boiling heat transfer mechanism obtained from the experiments, a new correlation is proposed to predict the heat transfer coefficient. The new correlation predicts well the experimental results within a mean absolute error of 5.2%.

Modified PID control with H∞ loop shaping synthesis for RO desalination plants

AbstractThis paper deals with the PID control synthesis with robust (H∞) loop shaping framework to manage MIMO reverse osmosis (RO) desalination plants. This new method takes advantage of the robust controller which has a fixed low order of conventional PID scheme guaranteeing robust stability and performance under large parametric uncertainties, external disturbances, and sensor noises. The coprime factor uncertainty description in H∞ loop shaping methodology can cover a wide variety of uncertainties over all frequencies for the RO plants. The test results demonstrate that the achieved controller has high stability margin, showing disturbance and noise attenuation abilities. Furthermore, most interactions between control channels have been decoupled in the complete control system. The presented control approach can help reduce membrane cleaning, save energy, and reduce product water costs for the RO plants. Note that weather changes increase unstableness in RO plants but the water treatment facilities ar...

Analysis of Galloping Amplitude for Conductors With Inter-phase Spacers

The main purpose of this paper is to calculate the behaviors of interphase spacers to reduce the amplitude of galloping in conductors. In simulation, three phases and iced-single/two-bundles conductors with/without spacers are considered in viewpoint of standard cases. The implicit/explicit finite element methods are used to calculate the transient response with geometric nonlinear behavior. ANSYS/LS-DYNA program is also applied. Calculation results can be used to predict the positions to insert the interphase spacers between conductors.

Analysis of galloping amplitude for conductors with interphase spacers

The main purpose of this paper is to calculate the behaviors of interphase spacers to reduce the amplitude of galloping in conductors. In simulation, three phases and iced-single/two-bundles conductors with/without spacers are considered in viewpoint of standard cases. The implicit/explicit finite element methods are used to calculate the transient response with geometric nonlinear behavior. ANSYS/LS-DYNA program is also applied. Calculation results can be used to predict the positions to insert the interphase spacers between conductors.

Pressure drop characteristics for two-phase flow of FC-72 in microchannel

In this paper, an experimental study on two-phase flow pressure drop of refrigerant FC-72 is carried out in a microchannel. The microchannel has a width and depth of 0.45 and 0.2 mm respectively, and comprises 15 parallel channels with a length of 60 mm. The experiment is conducted under the condition of mass flux of 100.3–458.0 kg/m2s and heat flux of 3.2–49.0 kW/m2. This study analyzed the pressure drop characteristics for two-phase flow by using a separated flow model. To predict the frictional pressure drop, two-phase frictional multiplier obtained from experiments is compared with the existing correlations. The experimental results show that two-phase frictional multipliers rely heavily on the vapor quality. Fractional pressure drop increases as the vapor quality increases. However, the rate of increase in the high vapor quality region decreases as the vapor quality increases. Based on pressure drop characteristics obtained from the experiments, a new correlation is proposed to predict the frictional pressure drop. Two-phase multiplier is modified with the dimensionless parameters such as Reynolds number, Weber number, and Martinelli parameter. The newly developed correlation predicts the experimental results well within a mean absolute error of 8.0%.