• Title/Summary/Keyword: Reverse flow

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Numerical Study on Flow and Heat Transfer Enhancement during Flow Boiling in Parallel Microchannels (병렬 미세관 흐름비등의 유동특성 및 열전달 향상에 대한 수치적 연구)

  • Jeon, Jin-Ho;Lee, Woo-Rim;Suh, Young-Ho;Son, Gi-Hun
    • 한국전산유체공학회:학술대회논문집
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    • 2008.03b
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    • pp.472-473
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    • 2008
  • Flow boiling in parallel microchannels has received attention as an effective heat sink mechanism for power-densities encountered in microelectronic equipment. the bubble dynamics coupled with boiling heat transfer in microchannels is still not well understood due to the technological difficulties in obtaining detailed measurements of microscale two-phase flows. In this study, complete numerical simulation is performed to further clarify the dynamics of flow boiling in microchannels. The level set method for tracking the liquid-vapor interface is modified to include the effects of phase change and contact angle. The method is further extended to treat the no-slip and contact angle conditions on the immersed solid. Also, the reverse flow observed during flow boiling in parallel microchannels has been investigated. Based on the numerical results, the effects of channel shape and inlet area restriction on the bubble growth, reverse flow and heat transfer are quantified.

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Simulation of $H_2O/LiBr$ Triple Effect Absorption Systems with a Modified Reverse Flow

  • Jo, Young-Kyong;Kim, Jin-Kyeong;Kang, Yang-Tae
    • International Journal of Air-Conditioning and Refrigeration
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    • v.15 no.3
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    • pp.114-121
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    • 2007
  • In this study, a modified reverse flow type, one of the triple effect absorption cycles, is studied for performance improvement. The cycle simulation is carried out by using EES(Engineering Equation Solver) program for the working fluid of $H_2O/LiBr$ solution. The split-ratios of solution flow rate, UA of each component, pumping mass flow rate of solution are considered as key parameters. The results show that the optimal SRH (split ratio of high side) and SRL (split ratio of low side) values are 0.596 and 0.521, respectively. Under these conditions, the COP is maximized to 2.1. The optimal pumping mass flow rate is selected as 3 kg/s and the corresponding UAEV A is 121 kW/K in the present system. The present simulation results are compared to the other literature results from Kaita's (2002) and Cho's (1998) triple effect absorption systems. The present system has a lower solution temperature and a higher COP than the Kaita's modified reverse flow, and it also gives a higher COP than the Cho's parallel flow by adjusting split ratios.

The Characteristics of Backfire for a Free-Piston Hydrogen Fueled Engine with Reverse Uni-flow Scavenging (Reverse uni-flow 소기방식을 갖는 2행정 프리피스톤 수소기관의 역화 현상에 관한 연구)

  • Byun, Chang-Hee;Choi, Kwan-Yeon;Back, Dae-Ha;Lee, Jong-Tae
    • Transactions of the Korean hydrogen and new energy society
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    • v.21 no.2
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    • pp.98-103
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    • 2010
  • In order to develop two-stroke free-piston hydrogen engine to obtain high thermal efficiency and low emission, backfire occurrence have to be prevented. In this research, backfire characteristics are analyzed as functions of the intake valve opening timing and compression chamber pressure under piston by using RICEM (Rapid Intake Compression Expansion Machine) that has reverse uni-flow scavenging. As the result, reverse uni-flow scavenging is advantage about back fire. but, it exists suitable intake valve opening timing and its timing become known that equivalence ratio 1 retard until the piston rises. Also, To rise chamber pressure of lower piston, this does not cause backfire occurs in equivalent ratio 0.6 observed back fire. Therefore, 2cycle hydrogen fueled free-piston engine is undesirable scavenging compression by compressing the piston.

A Study on the Reverse Engineering and Performance Test in the Development of Screw Flowmeter (스크류유량계 개발에서의 역공학 및 성능평가에 관한 연구)

  • Hwang, Jong-Dae;Jung, Jong-Yoon;Lee, Sang-Ryul;Jung, Yoon-Gyo
    • Journal of the Korean Society of Manufacturing Process Engineers
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    • v.4 no.2
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    • pp.24-30
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    • 2005
  • This research presents a modeling and a manufacturing method of screw flow meter. This paper introduces the efficient design and manufacturing method of screw type flow meter using reverse engineering and test technology. The methods introduced this paper utilize the reverse engineering that is increasing accuracy of modeling and manufacturing of reverse model. And then it can be used in performance test with hydraulic test equipment. Hence this can be used in the basic document for development of the quite accurate flowmeter.

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A Study on the Role of Notch and Radius Reduction Ratio in the Balanced Type Vane Pump (베인 펌프에서 노치와 반경 감소비의 역할에 관한 연구)

  • 김기동;조명래;한동철;최상현;문호지
    • Journal of the Korean Society for Precision Engineering
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    • v.15 no.1
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    • pp.87-93
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    • 1998
  • Pressure ripples of hydraulic vane pump results from flow ripples due to pump geometry and reverse flow through the discharge port due to compressibility of fluid and result in vibration and noise of connected hydraulic elements. In a balanced type vane pump, cam ring curve is important factor to influence the flow ripples. Therefore, to reduce the flow ripple, it has been required that optimal selection of seal region by proper design of cam ring and each port position, and notches for preventing the excessive reverse flow. This paper has been performed analytical study of compression characteristics with major design parameter in side plate and cam ring. and examined into the role of notch and radius reduction ratio.

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A Study on the Role of Notch and Radius Reduction Ratio in the Balanced Type Vane Pump (베인 펌프에서 노치와 반경 감소비의 역활에 관한 연구)

  • 김기동;조명래;문호지;배홍용
    • Proceedings of the Korean Society of Precision Engineering Conference
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    • 1997.04a
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    • pp.533-539
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    • 1997
  • Pressure ripple of hydraulic vane pump results form flow ripple due to pump geometry and reverse flow through the discharge port due to compressibility of fluid and result in vibration and noise of connected hydraulic elements. In a ba;anced type vane pump, cam ring curve is important factor to influence the flow ripple. Therefore, to reduce the now ripple, it has been required that optimal selection of seal region by proper design of cam ring and each port position, and notches for preventing the excessive reverse flow. This paper has been performed analytical study of compression characteristics with major design parameter in side plate and cam ring, and examined into the role of notch and radius reduction ratio.

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Investigation on reverse flow characteristics in U-tubes under two-phase natural circulation

  • Chu, Xi;Li, Mingrui;Chen, Wenzhen;Hao, Jianli
    • Nuclear Engineering and Technology
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    • v.52 no.5
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    • pp.889-896
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    • 2020
  • The vertically inverted U-tube steam generator (UTSG) is widely used in the pressurized water reactor (PWR). The reverse flow behavior generally exists in some U-tubes of a steam generator (SG) under both single- and two-phase natural circulations (NCs). The behavior increases the flow resistance in the primary loop and reduces the heat transfer in the SG. As a consequence, the NC ability as well as the inherent safety of nuclear reactors is faced with severe challenges. The theoretical models for calculating single- and two-phase flow pressure drops in U-tubes are developed and validated in this paper. The two-phase reverse flow characteristics in two types of SGs are investigated base on the theoretical models, and the effects of the U-tube height, bending radius, inlet steam quality and primary side pressure on the behavior are analyzed. The conclusions may provide some promising references for SG optimization to reduce the disadvantageous behavior. It is also of significance to improve the NC ability and ensure the PWR safety during some accidents.

Numerical Study on Reverse Flow Charcteristics in an Axial Compressor Cascade (축류압축기 익렬에서의 역류 유동 특성에 대한 수치적 연구)

  • Sohn, Chang-Hyun;Longley, John Peter
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.24 no.5
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    • pp.615-622
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    • 2000
  • Numerical simulation is performed with Denton's code to get pressure loss coefficients in wide range of reverse flow incidence(from -90 degree to +85 degree) for an axial compressor cascade. As a results, it is found that the pressure loss coefficient is increased with incidence and there exist critical incidence which corresponds to the maximum pressure loss coefficient. Pressure loss coefficient with bigger incidence than its critical value is decreased. The effect of increasing incidence in a cascade extremely reduce the mass flow rate by the large flow separation region. Consequently this effect reduce the portion of dynamic pressure in the total pressure loss and beyond the critical incidence the pressure loss coefficient decrease.

Fracture Behavior of the Cut Surface of a Flat Panel Glass according to Vibration Input (진동 인가에 따른 평판 유리 절단면의 파괴거동)

  • Choi, Seong-Dae;Cheong, Seon-Hwan;Kim, Gi-Man;Kweon, Hyun-Kyu;Jeon, Jae-Mock;Rho, Young-Jin
    • Journal of the Korean Society of Manufacturing Process Engineers
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    • v.4 no.3
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    • pp.51-56
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    • 2005
  • This research presents a modeling and a manufacturing method of screw flow meter. This paper introduces the efficient design and manufacturing method of screw type flow meter using reverse engineering and test technology. The methods introduced this paper utilize the reverse engineering that is increasing accuracy of modeling and manufacturing of reverse model. And then it can be used in performance test with hydraulic test equipment. Hence this can be used in the basic document for development of the quite accurate flowmeter.

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Effects of Operation Conditions on the Performance of Type II LiBr-H2O Absorption Heat Pump (제 2종 LiBr-H2O 흡수식 히트펌프의 운전 변수에 따른 성능 특성 수치 해석)

  • Yoon, Jun Seong;Kwon, Oh Kyung;Cha, Dong An;Bae, Kyung Jin;Kim, In Gwan;Kim, Min Soo;Park, Chan Woo
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.29 no.1
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    • pp.7-14
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    • 2017
  • This study carried out a numerical analysis of the effects of hot waste water supply on the performance of a Type II absorption heat pump. There are two types of hot waste water supply, regular series flow and reverse series flow. Also it investigated the interaction between each type of flow and heat exchange solutions. As the effectiveness of heat exchange solutions increase, the steam generation and (COP) increase as well. If the effectiveness of a heat exchange solution is lower than 0.566, the steam generation rate of the reverse flow is lower than that of the regular series flow. A high effectiveness of heat exchange solution is therefore required to make a larger amount of steam in reverse series flow than with ordinary series flow. The COP difference between the two types of flow decreases with the increasing effectiveness of the heat exchange solution. Thus, a reverse flow type absorption heat pump can match the high steam generation rate and COP of the ordinary flow type when a highly effective heat exchange solution is applied.