• Title, Summary, Keyword: Two-phase

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Stratified Steady and Unsteady Two-Phase Flows Between Two Parallel Plates

  • Sim Woo-Gun
    • Journal of Mechanical Science and Technology
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    • v.20 no.1
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    • pp.125-132
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    • 2006
  • To understand fluid dynamic forces acting on a structure subjected to two-phase flow, it is essential to get detailed information about the characteristics of two-phase flow. Stratified steady and unsteady two-phase flows between two parallel plates have been studied to investigate the general characteristics of the flow related to flow-induced vibration. Based on the spectral collocation method, a numerical approach has been developed for the unsteady two-phase flow. The method is validated by comparing numerical result to analytical one given for a simple harmonic two-phase flow. The flow parameters for the steady two-phase flow, such as void fraction and two-phase frictional multiplier, are evaluated. The dynamic characteristics of the unsteady two-phase flow, including the void fraction effect on the complex unsteady pressure, are illustrated.

Space-vector PWM Techniques for a Two-Phase Permanent Magnet Synchronous Motor Considering a Reduction in Switching Losses

  • Lin, Hai;Zhao, Fei;Kwon, Byung-il
    • Journal of Electrical Engineering and Technology
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    • v.10 no.3
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    • pp.905-915
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    • 2015
  • Two PWM techniques using space vector pulse-width modulation (SVPWM) are proposed for a two-phase permanent magnet synchronous motor (PMSM) driven by a two-phase eight-switch inverter. A two-phase motor with two symmetric stator windings is usually driven by a two-phase four-, six-, or eight-switch inverter. Compared with a four- and six-switch inverter, a two-phase eight-switch inverter can achieve larger power output. For two-phase motor drives, the SVPWM technique achieves more efficient DC bus voltage utilization and less harmonic distortion of the output voltage. For a two-phase PMSM fed by a two-phase eight-switch inverter under a normal SVPWM scheme, each of the eight PWM trigger signals for the inverter have to be changed twice in a cycle, causing a higher PWM frequency. Based on the normal SVPWM scheme, two effective SVPWM schemes are investigated in order to reduce the PWM frequency by rearranging four comparison values, while achieving the same function as the normal PWM scheme. A detailed explanation of the normal and two proposed SVPWM schemes is illustrated in the paper. The experimental results demonstrate that the proposed schemes achieve a better steady performance with lower switching losses compared with the normal scheme.

Space Vector PWM Technique for Two-Phase Inverter-Fed Two-Phase Induction Motors (2상 유도전동기의 구동을 위한 2상 인버터의 2상 공간전압벡터 PWM 방식)

  • 장도현;윤덕용
    • The Transactions of the Korean Institute of Power Electronics
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    • v.7 no.1
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    • pp.1-10
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    • 2002
  • In this paper the space voltage vector pulsewidth modulation(SVPWM) technique for two-phase inverter is proposed. The two-phase SVPWM technique is applicable to two-phase induction motor drives. The two-phase inverter using two-phase SVPWM technique cannot generate zero voltage vectors, but four space vectors. A reference voltage vector in the square locus is realized by adjusting four space vectors. The switching sequence "two-phase symmetrical modulation" used in two-phase SVPWM is proposed. Practical verification of theoretical predictions is presented to conform the capabilities of the new technique.technique.

Phase Current Reconstruction Techniques for Two-Phase Inverters using a Single Current Sensor

  • Cho, Young-Hoon;Cho, Kwan-Yuhl;Mok, Hyung-Soo;Kim, Kyeong-Hwa;Lai, Jih-Shen
    • Journal of Power Electronics
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    • v.11 no.6
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    • pp.837-845
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    • 2011
  • This paper proposes phase current reconstruction techniques for two-phase two-leg and two-phase four-leg inverters using a single current sensor. In the proposed methods, one phase current is sampled simultaneously with a particular branch current by using only one current sensor, and then current reconstruction algorithms are applied to extract the information on two phase currents from the sensor output. The sampled current information is periodically updated at the peak and the valley of the triangular carrier waveform in each switching cycle of pulse-width modulation (PWM). The voltage vector spaces where the phase currents can be reconstructed are evaluated. Compared to the existing method using two individual current sensors in two phases, the proposed schemes can save implementation cost since it is possible to remove one current sensor. In addition, the proposed methods are free from gain discrepancy issues between two current sensors. Simulations and experiments show excellent current reconstruction performance of the proposed methods.

Digital Implementation of PWM Techniques for Two-phase Eight-switch Inverter fed Brushless DC Motor Drives

  • Lin, Hai;You, Yong-Min;Cheon, Sung-Rock;Kwon, Byung-Il
    • Journal of Electrical Engineering and Technology
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    • v.8 no.2
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    • pp.295-303
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    • 2013
  • This paper reports an investigation of pulse width modulation (PWM) techniques for two-phase brushless DC (BLDC) motors fed by a two-phase eight-switch inverter in a fan application. The three-phase BLDC motor is widely applied in industry; however, a lower-cost two-phase BLDC motor and drive circuit has been greatly in demand in recent years. In this paper, we introduce a mathematical model of the two-phase BLDC motor with sinusoidal back electromotive forces (EMFs) based on traditional three-phase BLDC motors. To simplify the drive algorithm and speed up its application, we analyze the principle of block commutation for a two-phase BLDC motor drive in the 180-electrical-degree conduction mode, and we further propose five PWM schemes to improve the commutation performance of the two-phase BLDC drive. The effectiveness of the proposed PWM methods is verified through experiments.

Experimental measurements of R-22 two-phase friction factor in plate heat exchangers (판형열교환기에서 R-22 냉매의 이상 압력 손실계수 평가)

  • Yoo, Sang-Roon;Jeong, Ji-Rwan
    • Proceedings of the KSME Conference
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    • pp.2273-2278
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    • 2007
  • Brazed Plate Heat Exchanger (BPHE) is a type of compact plate heat exchanger with parallel corrugated plates which are brazed together in series. Each plate hascorrugation called herringbone pattern. Inside a BPHE, hot fluid and cold fluid alternate its flow direction to establish counter current flow configuration. Two-phase flow heat transfer and pressure drop of R-22 in BPHE were experimentally measured in this study. In the present experiments, single-phase region and two-phase region coexist in a BPHE. Therefore, the inside of a BPHE have to be divided into single phase region and two phase region and analyzed accordingly. The results from the single phase flow analysis are then extended to the two phase flow analysis to correlate the condensation and evaporation heat transfer and pressure drop for the refrigerant R-22 in the BPHEs. Previous models for two- phase friction factor have been compared with the present experimental results.

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A Novel PWM Method for Three-Leg Two-Phase Inverter Fed Two-Phase Induction Motor (2상 유도전동기 구동 2상 인버터를 위한 새로운 PWM제어방식 II - 3-레그 타입의 경우 -)

  • Jang Do-Hyun
    • The Transactions of the Korean Institute of Power Electronics
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    • v.10 no.4
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    • pp.339-346
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    • 2005
  • It is complex to realize the reference voltage vector by the space vector PWM method in three-leg two-phase inverter In this paper a new PWM technique for three-leg two-phase inverter fed two-phase induction motor is poroposed assuming that three-leg two-phase inverter is equivalent circuit for 'four-leg two-phase inverter with the connected two windings'. From assumption, six sectors are decreased to four sectors, and simple sinusoidal PWM method instead of SVPWM is applied to three-leg two-phase inverter. Also, the switching pattern to determine the switching periods at each sector is proposed. Practical verification of theoretical predictions is presented to confirm the capabilities of the new techniques.

New PWM Technique for Two-Phase Brushless DC Motor Drives

  • Lin, Hai;Kwon, Byung-Il
    • Journal of Electrical Engineering and Technology
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    • v.8 no.5
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    • pp.1107-1115
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    • 2013
  • A new PWM technique for a two-phase BLDC motor fed by a two-phase eight-switch inverter is proposed in this paper. It is well known that a two-phase eight-switch inverter can significantly improve power output compared with a two-phase six-switch inverter in a two-phase motor drive. To drive the two-phase BLDC motor simply and effectively, two normal PWM strategies are investigated to manage speed regulation. However, under the conditions of low speed and light load, especially during the braking process, the current in a short time of one period is near zero, which is a discontinuous waveform every half period. To solve it, a novel PWM technique is investigated to improve the operational performance of normal technique. Using the new PWM scheme, the current continues every half period and the braking performance is improved. The effectiveness of the proposed PWM method is verified through the experiments.

A Review on Two-Phase Flow Analysis using Chaos Theory (카오스 이론을 이용한 2상 유동 해석)

  • Kwon, Jeong-Tae;Kwon, Young-Chul;Kim, Kyoung-Min
    • The Transactions of the Korean Institute of Electrical Engineers P
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    • v.56 no.1
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    • pp.23-27
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    • 2007
  • This article presents a review on chaos analysis of two-phase flow. Chaos theory has recently been applied to two-phase flow analysis, and it gives promising measures to quantitatively identify two-phase flow patterns and pool boiling behaviors. But, consistency of the calculated chaotic measures were not completely confirmed yet. More experimental data are requested for chaos analysis of two-phase flow. Also, chaos analysis methodology should be developed by experimental verification.

Study on Design of Air-water Two-phase Flow Centrifugal Pump Based on Similarity Law

  • Matsushita, Naoki;Furukawa, Akinori;Watanabe, Satoshi;Okuma, Kusuo
    • International Journal of Fluid Machinery and Systems
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    • v.2 no.2
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    • pp.127-135
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    • 2009
  • A conventional centrifugal pump causes a drastic deterioration of air-water two-phase flow performances even at an air-water two-phase flow condition of inlet void fraction less than 10% in the range of relatively low water flow rate. Then we have developed a two-phase flow centrifugal pump which consists of a tandem arrangement of double rotating cascades and blades of outer cascade have higher outlet angle more than $90^{\circ}$. In design of the two-phase flow pump for various sized and operating conditions, similarity relations of geometric dimensions to hydraulic performances is very useful. The similarity relations of rotational speed, impeller diameter and blade height are investigated for the developed impeller in the present paper. As the results, the similarity law of rotational speed and impeller diameter is clarified experimentally even in two-phase flow condition. In addition, influences of blade height on air-water two-phase flow performances indicate a little difference from the similarity relations.