• Journal of Advanced Marine Engineering and Technology
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• v.28 no.8
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• pp.1195-1202
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• 2004

In this paper an experimental study was investigated for two-phase flow distribution in compact heat exchanger header. A test section was consisted of the horizontal bottom dividing header($\phi$: 5 mm, L: 80 mm) and 10 upward circular mini channels ($\phi$: 1.5 mm, L: 850 mm) using an acrylic tube. Three different types of tube intrusion depth were tested for the mass flux and inlet mass quality ranges of 50 - 200 kg/$m^2$s and 0.1 - 0.3, respectively. Air and water were used as the test fluids. The distribution of vapor and liquid is obtained by measurement of the total mass flow rate and the calculation of the quality. Two-phase flow pattern was observed, and pressure drop of each channel was measured. By adjusting the intrusion depth of each channel an uniform liquid flow distribution through the each channel was able to solve the mal-distribution problem.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.16 no.9
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• pp.828-837
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• 2004

The present study investigated two-phase flow distribution, phase separation and pressure drop in multi-microchannel tubes under adiabatic condition. The test section consisted of inlet and outlet headers with the inner diameter of 19.4㎜ and 15 parallel microchannel tubes. Each microchannel tube brazed to the inlet and outlet headers and had 8 rectangular ports with the hydraulic diameter of 1.32㎜. The key experimental parameters were orientation of header (horizontal and vertical), flow direction of refrigerant into the inlet header (in-line, parallel and cross flow) and inlet quality (0.1, 0.2 and 0.3). It was found that the orientation of the header had relatively large effect on the flow distribution and phase separation, while the inlet quality didn't affect much on them. The horizontal header showed the better flow distribution and phase separation characteristics than the vertical one. The parallel flow condition with the horizontal header showed the best performance for the flow distribution and phase separation characteristics under the test conditions. Two-phase pressure drops through the microchannel tubes with the horizontal header were higher than those of the microchennel tubes with the vertical header due to gravitational effect.

• Journal of Electrical Engineering and Technology
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• v.13 no.6
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• pp.2364-2375
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• 2018

Two-phase simultaneous excitation mode of the switched reluctance motor (SRM) has been shown to effectively improve the average torque output compared with traditional single-phase excitation mode. But the torque ripple of the two-phase excitation SRM with traditional winding distribution increases because of the inconsistent electromagnetic field. To reduce the torque ripple, a two-phase excitation 8/6 SRM with novel winding distribution is proposed in this paper. The static torques generated by various magnetic circuits are analyzed and obtained to verify the torque increase. Then the electromagnetic characteristics of the proposed SRM are investigated by the numerical calculation method in detail, including flux linkage, inductance, and torque. Finally, an experiment for measuring the SRM static electromagnetic characteristics and dynamic performance is designed and performed based on the novel mode, and the comparing results show that the proposed two-phase SRM is effective.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.30 no.5A
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• pp.425-431
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• 2010

The phase distribution in a multi-phase material strongly affects its material properties. Therefore, a proper method to describe the phase distribution of a material is needed. In this research, probability distribution functions, two-point correlation and lineal-path functions, are used to represent the probabilistic phase distributions of a material. The probability distribution function is calculated using a numerical method and is described as an analytical form via exponential curve fitting with three parameters. Application of analytical form of probability distribution function is investigated using two-phase polycrystalline solids and soil samples. It is confirmed that the probability distribution functions can be represented as an exponential form using curve fitting which helps identifying the applicability of a representative volume element(RVE).

• Journal of Mechanical Science and Technology
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• v.17 no.8
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• pp.1211-1218
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• 2003

The present study investigated two-phase flow distribution and phase separation of R-22 refrigerant through various types of branch tubes. The key experimental parameters were the orientation of inlet and branch tubes (horizontal and vertical), diameter ratio of branch tube to inlet tube (1 and 0.61), mass flux (200-500 kg/㎡s), and inlet quality (0.1-0.4). The predicted local pressure profile in the tube with junction was compared and generally agreed with the measured data. The local pressure profile within the pressure recovery region after the junction has to be carefully investigated for modeling the pressure drop through the branch. The equal flow distribution case can be found by adjusting the orientation of the inlet and branch tubes and the diameter ratio of the branch tube to the inlet tube. The T-junction with horizontal inlet and branch tubes showed the nearly equal phase distribution ratio. The quality at the branch tube varied from 0 to 1 as the orientation of the branch tube changed, while it varied within${\pm}$50% as the orientation of the inlet tube changed.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.30 no.8 s.251
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• pp.780-787
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• 2006

Several types of different header designs are numerically studied to have uniform distribution of two phase flow in the evaporator header having multi-channels. The different geometries include the inlet tube position into the header and the width of header. In the numerical calculation, two types of two-phase model such as homogeneous model and VOF(Volume Of Fluid) model are employed. In this study, the mal-distribution number, $M_d$, is newly defined to evaluate the averaged level of the flow distribution in the whole passes of the evaporator. As results, two phase flow in the header can be visualized using post-processing of numerical results. Furthermore, the optimum position of the inlet tube into the header and the width of header can be proposed for the better distribution of refrigerant(R-134a) flow.

• Transactions of the Korean Society of Mechanical Engineers
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• v.19 no.10
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• pp.2586-2594
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• 1995

Two phase flow phenomena are observed in many industrial facilities and make much importance of optimum design for nuclear power plant and various heat exchangers. This experimental study has been investigated the classification of the flow pattern, the local void distribution and convective heat transfer in swirl and non-swirl two phase flow under the isothermal and nonisothermal conditions. The convective heat transfer coefficients in the single phase water flow were measured and compared with the calculated results from the Sieder-Tate correlation. These coefficients were used for comparisons with the two-phase heat transfer coefficients in the flow orientations. The experimental results indicate, that the void probe signal and probability density function of void distribution can used into classify the flow patterns, no significant difference in voidage distribution was observed between isothermal and non-isothermal condition in non-swirl flow, the values of two phase heat transfer coefficients increase when superficial air velocities increase, and the enhancement of the values is observed to be most pronounced at the highest superficial water velocity in non-swirl flow. Also two phase heat transfer coefficients in swirl flow are increased when the twist ratios are decreased.

• Journal of Mechanical Science and Technology
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• v.20 no.6
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• pp.840-848
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• 2006

We carried out numerical studies to investigate the single- and two-phase flow characteristics in the single- and multi-channels. We used the finite volume method to solve the mass and momentum conservation equations. The volume of fluid model is used to predict the two-phase flow in the channel. We obtained the distribution of velocity fields, pressure drop and air volume fraction for different water mass flow rates. We also calculated the distribution of mass flow rates in the multi-channels to understand how the flow is distributed in the channels. The calculated results for the single- and two-phase flow are partly compared with the present experimental data both qualitatively and quantitatively, showing relatively good agreement between them. The numerical scheme used in this study predicts well the characteristics of single-and two-phase flow in a multi-channel.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.18 no.1
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• pp.31-37
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• 2006

The present study has been experimentally investigated the effect of geometric and operating parameters on the two-phase flow distribution of refrigerants in a horizontal T-junction. The operating parameters were the kind of refrigerants (R-22, R- l34a, and R-410A), saturated temperature, and the inlet mass flux and quality. The geometric parameters were the tube diameter and the tube diameter ratio. The measured data of refrigerants were compared with the values predicted using the models developed by several researchers for air/water or steani/water two-phase flow. Among the operating parameters, the inlet Quality was the most sensitive to the mass flow rate ratio. Between the geometric parameters, the tube diameter ratio was more sensitive than tube diameter.

• Transactions of the Korean Society of Automotive Engineers
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• v.4 no.1
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• pp.187-197
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• 1996

Many investigations have been made to determine the pressure drop and heat transfer characteristics for single phase flow in tape generated swirl flow. But few studies have been carried out to investigate the heat transfer in two component, two phase swirl flow with non-boiling. An experimental study has been conducted to determine the effects of tape twist ratios on two phase convective heat transfer coefficients, pressure drop, and void fraction distribution in a non-boiling, air-water, two phase flow. The flow conditions were both swirl and non swirl flows. The internal diameter of the test section is 42.5mm. The tape twist ratios of pitch to diameter ratio varied from 4.0 to 10.6. The heating conditions were isothermal and nonisothermal. The flow patterns identified with experiments were bubbly, bubbly-slug, slug, and slug-annular flow in up-flow. This study has concluded that no significant difference in void fraction distribution were observed both isothermal and nonisothermal conditions, the pressure drop for two phase flow with twisted tape swirler increase as the tape twist ratio decrease, and that values of two phase heat transfer coefficient increase when the tape twist ratio decreases.