An Experimentally Validated Model for Two-Phase Sudden Contraction Pressure Drop in Microchannel Tube Headers

2003 ◽  
Author(s):  
John Wesley Coleman
Keyword(s):  
Pressure Loss ◽  
Accurate Determination ◽  
Time Data ◽  
Two Phase ◽  
Pressure Transducers ◽  
Pressure Losses ◽  
Mass Fluxes ◽  
Data Points ◽  
Minor Losses ◽  
Phase Pressure

This paper presents the results of an experimental investigation of two-phase pressure loss of R134a in microchannel headers using various end-cut techniques. Novel experimental techniques and test sections were developed to enable the accurate determination of the minor losses without obfuscating the problem with a lengthwise pressure gradient. This technique represents a departure from approaches used by other investigators that have extrapolated minor losses from air-water experiments and the combined effects of expansion, contraction, deceleration, and lengthwise pressure gradients. Pressure losses were recorded over the entire range of qualities from 100% vapor to 100% liquid. In addition, the tests were conducted for five different refrigerant mass fluxes between 185 kg/m2-s and 785 kg/m2-s using two differnt end-cut techniques. More than 790 data points were recorded to obtain a comprehensive understanding of the effects of mass flux and quality on minor pressure losses. High accuracy instrumentation such as coriolis mass flowmeters, RTDs, pressure transducers, and real-time data analyses were used to ensure accuracy in the results. The results show that many of the commonly used correlations for estimating two-phase pressure losses significantly underpredict the pressure losses found in compact microchannel tube headers. Furthermore, the results show that the end-cut technique can substantially affect the pressure losses in microchannel headers. A new model for estimating the pressure loss in microchannel headers is presented and a comparison of the end-cut techniques on the minor losses is reported.

Experimental and Analytical Studies on Frictional Pressure Drops of Gas-Liquid Two-Phase Flow at Vena Contract and Expansion

2008 ◽  
Author(s):  
Hiroyasu Ohtake ◽  
Masato Hagiwarai ◽  
Yasuo Koizumi
Keyword(s):  
Pressure Loss ◽  
Two Phase Flow ◽  
Test Tube ◽  
Experimental Results ◽  
Phase Flow ◽  
Two Phase ◽  
Pressure Drops ◽  
Pressure Losses ◽  
Sudden Contraction ◽  
Sudden Enlargement

The frictional pressure drops of gas-liquid two-phase flow in mini-micro pipes and at vena contract and expansion were investigated experimentally and analytically. Pressure drops of straight pipe, sudden enlargement and sudden contraction of gas-liquid two-phase flow in mini-pipes were measured. Test liquid was water at room temperature; test gas was argon. The diameter of the test mini-pipe was 1.0 and 0.5 mm, respectively. Each test tube was connected at both ends to small tanks. The diameter of the small tank was 15 mm for 1.0 mm diameter of test tube and 5 mm for 0.5 mm diameter of test tube, respectively. Thus, the cross-sectional ratio of the contraction was about 1000; the ratio of the enlargement was about 0.001. The pressure drop data were collected over 3.0 < UG < 130 m/s for the superficial gas velocity and 0.02 < UL < 6.0 m/s for the superficial liquid velocity. The present experimental results of sudden contraction pressure loss factor Kc and sudden enlargement pressure loss factor Ke of single-phase liquid flow in mini-pipes differed from the conventional values, Kc = 0.5 and Ke = 1.0. The calculated results by using a commercial code, STAR-CD, agreed with the present experimental results for mini-pipes. Assuming to homogenous flow and incompressible flow, sudden contraction pressure loss, sudden enlargement pressure loss and their factors Kc, Ke for gas-liquid two-phase flow were estimated by using momentum equation and energy equation. The contraction pressure losses by Hewitt’s correlation for conventional pipes were similar to the present experimental results of the contraction for mini-circular pipe. Collier’s correlation of the enlargement pressure loss for conventional pipes underpredicted the present experimental results of the enlargement for mini-tube. Based on the present experimental results, new correlations were obtained for the enlargement and the contraction pressure losses in mini-channel.

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

2016 ◽  
Vol 24 (01) ◽  
pp. 1630002 ◽  
Author(s):  
Jung Hoon Yun ◽  
Ji Hwan Jeong
Keyword(s):  
Experimental Data ◽  
Pressure Drop ◽  
Pressure Loss ◽  
Separated Flow ◽  
Empirical Correlations ◽  
Two Phase ◽  
Flow Models ◽  
Micro Channels ◽  
Extensive Experimental Data ◽  
Phase Pressure

Previous methods and correlations for predicting two-phase frictional pressure loss in mini/micro-channels are reviewed and compared. The empirical correlations are classified into four groups of modeling approaches: Homogeneous equilibrium models (HEMs), separated flow models (SFMs), direct empirical correlations, and flow pattern specific 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 flows, respectively, are gathered from 15 papers and reports. The results present that the size of the channel significantly influences 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 3[Formula: see text]mm.

scholarly journals Robust and universal predictive models for frictional pressure drop during two-phase flow in smooth helically coiled tube heat exchangers

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
M. A. Moradkhani ◽  
Seyyed Hossein Hosseini ◽  
M. Mansouri ◽  
G. Ahmadi ◽  
Mengjie Song
Keyword(s):  
Pressure Drop ◽  
Sensitivity Analyses ◽  
Two Phase ◽  
Neural Network Approach ◽  
Frictional Pressure Drop ◽  
Mass Fluxes ◽  
The Neural Network ◽  
Coil Axis ◽  
Data Points ◽  
Intelligent Models

AbstractThere is a lack of well-verified models in the literature for the prediction of the frictional pressure drop (FPD) in the helically coiled tubes at different conditions/orientations. In this study, the robust and universal models for estimating two-phase FPD in smooth coiled tubes with different orientations were developed using several intelligent approaches. For this reason, a databank comprising 1267 experimental data samples was collected from 12 independent studies, which covers a broad range of fluids, tube diameters, coil diameters, coil axis inclinations, mass fluxes, saturation temperatures, and vapor qualities. The earlier models for straight and coiled tubes were examined using the collected database, which showed absolute average relative error (AARE) higher than 21%. The most relevant dimensionless groups were used as models’ inputs, and the neural network approach of multilayer perceptron and radial basis functions (RBF) were developed based on the homogenous equilibrium method. Although both intelligent models exhibited excellent accuracy, the RBF model predicted the best results with AARE 4.73% for the testing process. In addition, an explicit FPD model was developed by the genetic programming (GP), which showed the AARE of 14.97% for all data points. Capabilities of the proposed models under different conditions were described and, the sensitivity analyses were performed.

Condensation Pressure Drops in Circular Microchannels

2004 ◽  
Author(s):  
Srinivas Garimella ◽  
Akhil Agarwal ◽  
Jesse D. Killion
Keyword(s):  
Pressure Drop ◽  
Flow Regime ◽  
Intermittent Flow ◽  
Condensation Process ◽  
Two Phase ◽  
Pressure Drops ◽  
Mass Fluxes ◽  
Flow Mechanisms ◽  
Data Points ◽  
Smooth Transitions

This paper presents a multiple flow-regime model for pressure drop during condensation of refrigerant R134a in horizontal microchannels. Two-phase pressure drops were measured in five circular channels ranging in hydraulic diameter from 0.5 mm to 4.91 mm. For each tube under consideration, pressure drop measurements were first taken over the entire range of qualities from 100% vapor to 100% liquid for five different refrigerant mass fluxes between 150 kg/m2-s and 750 kg/m2-s. Results from previous work by the author on condensation flow mechanisms in microchannel geometries were used to assign the applicable flow regime to the data points. Pressure drop models for intermittent (Garimella et al. 2002) and annular (Garimella et al. 2003a) flow reported earlier by the authors were modified and combined to develop a comprehensive model that addresses the entire progression of the condensation process from the vapor phase to the liquid phase. This combined model accurately predicts condensation pressure drops in the annular, disperse wave, mist, discrete wave, and intermittent flow regimes. Overlap and transition regions between the respective regimes are also addressed using an appropriate interpolation technique that results in relatively smooth transitions between the predicted pressure drops. The resulting model predicts 82% of the data within ±20%.

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