Impact of Two Drops on a Dry Surface

( Chun-kuei Chen ),( Sheng-qi Chen ),( Ta-hui Lin ) 한국액체미립화학회 2017 한국액체미립화학회 학술강연회 논문집 Vol.2017 No.-

A group of two streamwise drops could be successfully generated by using the free-falling drops technique incorporated with a drop severance device in this study. Therefore, the impact characteristics of a group of two streamwise drops impinging on a dry surface will be experimentally examined and analyzed in this study. The water was considered as the working fluid, and the velocity of the drop was fixed to 1.9 ± 0.1 m/s. The initial diameter of the drop was fixed to 930 ± 30 ㎛ and 1025 ± 5 ㎛, respectively. This study focused on four cases of two drops impinging on a dry surface which classified by space difference (ㅿt). Conditions respectively being Case 1: single drop impinging, Case 2: ㅿt = 0.5 ms, Case 3: ㅿt = 1 ms and Case 4: ㅿt = 2.5 ms. The results showed two drops impinging on a dry surface for Case 2~4, the maximum spread diameter of drop was 1.3 times compared with the single drop at the same initial drop diameter, but the variation process of two drops impinging on a dry surface was different to the single drop.

Two-phase pressure drop due to friction in micro-channel

Lim, Tae-Woo,You, Sam-Sang,Kim, Jong-Su,Moon, Serng-Bae,Seo, Dong-Hoan SAGE Publications 2014 Proceedings of the Institution of Mechanical Engin Vol.228 No.5

<P>This paper deals with an experimental investigation to measure the frictional pressure drops for two-phase flow boiling in a micro-channel with a hydraulic diameter of 500 µm. First, the experimental study is performed under the test conditions: heat fluxes ranging from 100 to 400 kW/m<SUP>2</SUP>, vapor qualities from 0 to 0.2, and mass fluxes of 200, 400 and 600 kg/m<SUP>2</SUP>s. Then, the frictional pressure drop during flow boiling is estimated using two models: the homogeneous model and the separated flow model. The experimental results show that the two-phase multiplier decreases with the increase of mass flux. In addition, the measured pressure drops are compared with those from a few correlation models available for macro-scales and mini/micro-scales. Finally, the present paper proposes a new correlation for two-phase frictional pressure drops in mini/micro-scales. This correlation model is developed based on the Chisholm constant C as a function of two-phase Reynolds and Weber numbers. It is found that the new correlation satisfactorily predicts the experimental data within mean absolute error (MAE) of 3.9%.</P>

A Review of Prediction Methods for Two-Phase Pressure Loss in Mini/Micro-Channels

윤정훈,정지환 대한설비공학회 2016 International Journal of Air-Conditioning and Refr Vol.24 No.1

Previous methods and correlations for predicting two-phase frictional pressure loss in mini/ micro-channels are reviewed and compared. The empirical correlations are classi¯ed into four groups of modeling approaches: Homogeneous equilibrium models (HEMs), separated °ow models (SFMs), direct empirical correlations, and °ow pattern speci¯c correlations. In order to examine the characteristics of the predictive methods for two-phase pressure loss in mini-channels and to assess the accuracy of the previous models and correlations, extensive experimental data and correlations that are available in the open literature are collected. The 1175 and 1304 experimental data for the two-phase pressure drop for condensing and boiling °ows, respectively, are gathered from 15 papers and reports. The results present that the size of the channel signi¯cantly in°uences the pressure drop. The comparison demonstrates that Cicchitti et al.'s two-phase viscosity model is recommended for predicting two-phase pressure loss when the HEM is used. In general, the SFM with the two-phase multipliers of Muller– Steinhagen and Heck and Kim and Mudawar outperforms others for channel diameters of less than 3mm.

Development of a prediction model relating the two-phase pressure drop in a moisture separator using an air/water test facility

김기환,이재봉,김우식,최해섭,김종인 한국원자력학회 2021 Nuclear Engineering and Technology Vol.53 No.12

The pressure drop of a moisture separator in a steam generator is the important design parameter toensure the successful performance of a nuclear power plant. The moisture separators have a wide rangeof operating conditions based on the arrangement of them. The prediction of the pressure drop in amoisture separator is challenging due to the complexity of the multi-dimensional two-phase vortex flow. In this study, the moisture separator test facility using the air/water two-phase flow was used to predictthe pressure drop of a moisture separator in a Korean OPR-1000 reactor. The prototypical steam/watertwo-phase flow conditions in a steam generator were simulated as air/water two-phase flow conditionsby preserving the centrifugal force and vapor quality. A series of experiments were carried out toinvestigate the effect of hydraulic characteristics such as the quality and liquid mass flux on the twophase pressure drop. A new prediction model based on the scaling law was suggested and validatedexperimentally using the full and half scale of separators. The suggested prediction model showed goodagreement with the steam/water experimental results, and it can be extended to predict the steam/watertwo-phase pressure drop for moisture separators

사다리꼴 미세유로의 대류비등 2상유동:1부-압력강하 특성

김병주(Byong Joo Kim),김건일(Geonil Kim) 대한설비공학회 2011 설비공학 논문집 Vol.23 No.1

Characteristics of two-phase pressure drop in microchannels were investigated experimentally. The microchannels consisted of 9 parallel trapezoidal channels with each channel having 205 ㎛ of bottom width, 800 ㎛ of depth, 3.6° of sidewall angle, and 7 ㎝ of length. Pressure drops in convective boiling of Refrigerant 113 were measured in the range of inlet pressure 105~195 ㎪, mass velocity 150~920 ㎏/㎡s, and heat flux 10~100 ㎾/㎡. The total pressure drop generally increased with increasing mass velocity and/or heat flux. Two-phase frictional pressure drop across the microchannels increased rapidly with exit quality and showed bigger gradient at higher mass velocity. A critical review of correlations in the literature suggested that existing correlations were not able to match the experimental results obtained for two-phase pressure drop associated with convective boiling in microchannels. A new correlation suitable for predicting two-phase friction multiplier was developed based on the separated flow model and showed good agreement with the experimental data.

Pressure Drop in Two-Phase Flow Boiling of R134a, R123 and Their Mixture in Horizontal Tube

Lim, Tae-Woo The Society of Air-Conditioning and Refrigerating 2004 International Journal Of Air-Conditioning and Refr Vol.12 No.2

An experimental study on the pressure drop during flow boiling for pure refrigerants Rl34a and R123, and their mixture was carried out in a uniformly heated horizontal tube. Tests were run at a pressure of 0.6㎫ and in the ranges of heat flux 5-50㎾/$m^2$, vapor quality 0-100 percent and mass velocity of 150-600 kg/$m^2$s. Generally, the two-phase frictional multiplier is used to predict the frictional pressure drop during the two-phase flow boiling. The obtained results have been compared to the existing various correlations for the two-phase multiplier. Also, the frictional pressure drop was compared to a few available correlations; The Lockhart-Martinelli correlation considerally overpredicted the frictional pressure drop data for mixture as well as pure components in the entire mass velocity ranges employed in the present study, while the Chisholm correlation underpredicted the present data. The Friedel correlation was found to satisfactorily correlate the frictional pressure drop data except for a low quality region.

The Review of Studies on Pressure Drop and Heat Transfer In Microchannels

Hwang, Yun-Wook,Kim, Min-Soo The Society of Air-Conditioning and Refrigerating 2005 International Journal Of Air-Conditioning and Refr Vol.13 No.1

This paper reviews the studies on the pressure drop and the heat transfer in microchannels. Although a lot of studies about the single-phase flow have been done until now, conflicting results are occasionally reported about flow transition from laminar flow to turbulent flow, friction factor, and Nusselt number. Some studies reported the early flow transition due to relatively greater wall effect like surface roughness, but the other studies showed that the flow transition occurred at the Reynolds number of about 2300 and the early flow transition might be due to less accurate measurement of the channel geometry. Also, there have been arguments whether the conventional relation based upon continuum theory can be applied to the fluid flow and the heat transfer in microchannels without modification or not. The studies about the two-phase flow in microchannels have been mostly about investigating the flow pattern and the pressure drop in rectangular channels using two-component, two-phase flow like air/water mixture. Some studies proposed correlations to predict two-phase flow pressure drop in microchannels. They were mostly based on Lockhart-Martinelli model with modification on C-coefficient, which was dependent on channel geometry, Reynolds number, surface tension, and so on. Others investigated the characteristics of flow boiling heat transfer in microchannels with respect to test parameters such as mass flux, heat flux, system pressure, and so on. The existing studies have not been fully satisfactory in providing consistent results about the pressure drop and the heat transfer in microchannels. Therefore, more in-depth studies should be done for understanding the fundamentals of the transport phenomena in the microchannels and giving the basic guidelines to design the micro devices.

기액 이상류를 응용한 우주용 열관리 시스템의 개발

최부홍(B. H. Choi) 한국동력기계공학회 2004 한국동력기계공학회 학술대회 논문집 Vol.- No.-

Necessities of high power level demands for thermal management systems in future space applications have stimulated research on gas-liquid two-phase flows under microgravity condition. Two-phase flow is an excellent alternative to the conventional single-phase system in transporting large amount of thermal energy at a uniform temperature regardless of variations in the heat loads. In addition, two-phase flows exist in a wide range of applications and enabling technologies in space. These include material processing and ceramics at ultra high temperatures, life-support systems, storage and transport of cryogenics, and in the design of many cold plate assemblies where heating or cooling takes place at the instrument interface. More reliable design of such systems requires a through understanding of the mechanics of the two-phase flow at variable gravity conditions, since two-phase flow characteristics differ when subjected to earth gravity, to hyper-gravity, to Moon or Mars gravity, or to microgravity environment. The essential factors to the designers of such systems are also the flow patterns in a conduit, the void fraction, and the pressure drop at different gas and liquid flow rates. Recent progress in the study of gas-liquid two-phase flows at variable gravity conditions will be reviewed and discussed in this paper.

연결세경관을 이용한 휜관형 열교환기의 기계확관에 의한 전열특성

이상무(Sangmu Lee),박병덕(Byung-Duck Park) 대한설비공학회 2016 설비공학 논문집 Vol.28 No.11

The fin and tube heat exchanger using a two-port tube has in air-conditioner heat exchanger because heat transfer performance. This study investigates the feasibility of a fin and tube heat exchanger using two-port copper tube by mechanical expansion. The optimum size of the tube-expanding bullet for the heat exchanger using two-port tube was through numerical calculation. The heat exchanger using a two-port tube was fabricated by mechanical expansion, and the heat exchanger performance was evaluated condensation and evaporation experiments. Compared to the heat exchanger of a conventional circular tube, the pressure drop per unit length of the heat exchanger with a two-port tube decreased. Compared to the heat exchanger using a conventional circular tube, the overall heat transfer coefficient of heat exchanger with a two-port tube increased up to 13% in the case of condensation, and up to 25% in the case of evaporation. The two-port tube heat exchanger outperforms conventional heat exchanger for air conditioner with a inner grooved circular tube.

미니채널에서 공기-물 혼합물의 마찰압력강하에 관한 실험적 연구

신홍철,김성민 한국유체기계학회 2018 한국유체기계학회 논문집 Vol.21 No.2

This study explores the frictional pressure gradient of air-water mixture in a horizontal rectangular mini-channel with a height of 2 mm and a width of 1 mm. Two absolute pressure transducers are used to measure the frictional pressure drop of two-phase flow. Six representative photos of two-phase flow pattern including elongated bubbly, slug, semi-annular, annular, slug/dispersed and annular/dispersed flows are obtained with the aid of high speed camera. The measured frictional pressure gradients increased with increasing the superficial gas velocity, and were also compared with predictions of previous correlations for two-phase frictional pressure gradient. Predictive capability of previous correlations for two-phase frictional pressure gradient showed dependence on flow patterns of two-phase flow. Among all previous correlations, the correlation of Kim and Mudawar showed the best predictions for the present data.