Two-phase Flow Frictional Pressure Research Articles

FRICTIONAL PRESSURE DROP DURING CONDENSING FLOW INSIDE MINI/MICRO-CHANNELS: PREDICTIVE TOOLS ASSESSMENT AND DATA TREATMENT

A total of 1210 new condensation friction pressure gradient points (database) is collected from 12 open articles on mini/micro-channels literature. The database covered a wide range of thermophysical properties associated with low-GWP refrigerants, physical dimension, mass velocity and vapor quality. A comparison of the experimental database against eleven two-phase flow frictional pressure drop prediction tools is carried out. Based on that, the mini/micro-channel developed by Xu and Fang exhibited the best ability to capture the tendency of the database with a mean absolute relative deviation of (36.59%) for all data. Keywords: Two-phase flow frictional pressure gradient; Mini/micro-channels; Condensing flow; New refrigerant fluid; Heat transfer; Collect database.

Pressure Drop in Horizontal Two-Phase Flow

In an artificial environment, the most important key in the process equipment design is determining gas-liquid two-phase flow frictional pressure drop of pipes. To achieve this, an experimental investigation was carried out in this study to analyze the pressure drops of air-water two-phase flow in a 30mm internal diameter horizontal pipe with a length of 6m at different flow conditions. The study was carried out at 20Co using tap water and air. To cover the slug flow pattern, the volumetric flow rate of water varied from 30 to 80 LPM, and the volumetric flow rate of air from 40 to 200 LPM. Pressure transmitters were used to measure pressure at four different points along the test section, each 2m apart. The results of the experiments were compared to 8 models using 3 distinct methods: Mean Absolute Percentage Error (MAPE), Relative Performance Factor (RPF), and the percentage of data included in the range of the 30% error band. All methods produced similar results, with the Sun-Mishima model being the most accurate.

Experimental study and general correlation for frictional pressure drop of two-phase flow inside microfin tubes

The adiabatic pressure drop in a microfin tube with an outside diameter of 3.5 mm was experimentally studied herein. The experiments were conducted using R1234yf as a working fluid at saturation temperatures of 20 °C and 30 °C with varying mass velocities from 50 to 300 kg m−2s−1 and vapor qualities ranging from 0.1 to 0.9. The effects of experimental conditions were analyzed and discussed with present and previous data. A new two-phase flow frictional pressure drop correlation has been developed using the data with tube diameter of 2.5–9.52 mm, mass velocity of 50–1000 kg m−2s−1, and many kinds of refrigerants. The proposed correlation predicts the experimental data of other researchers with mean deviation of 17.6%.

Single-Phase and Two-Phase Flow Pressure Drop in a Long Double Helicoidally Coiled Tube

Abstract Single-phase and two-phase frictional pressure drop in horizontally oriented double helically coiled tubes confined in a cylindrical shell are experimentally studied using an instrumented test loop that represents a prototypical liquified natural gas (LNG) fuel delivery system for internal combustion (IC) engines. Adiabatic experimental data addressing liquid (water) and gas (nitrogen) single-phase flows, as well as two-phase flows (air–water) in the helicoidally coiled tubes are presented. The range of Reynold numbers for single-phase flow experiments is 2600–4800. In two-phase flow experiments, the only liquid and only gas Reynolds numbers varied in 1030–6600 and 1700–17700 ranges, respectively. In a laminar single-phase flow regime, the measured friction factors are in relatively good agreement with well-established correlations. In the turbulent flow regime, the measured friction factors are moderately higher than the prediction of well-established published correlations. Two-phase flow frictional pressure drops are compared with some relevant correlations, with the poor agreement. The generated experimental data are empirically correlated based on the two-phase flow multiplier concept.

Combined APSO-ANN and APSO-ANFIS models for prediction of pressure loss in air-water two-phase slug flow in a horizontal pipeline

Abstract Prediction of air-water two-phase flow frictional pressure loss in pressurized tunnels and pipelines is essentially in the design of proper hydraulic structures and pump systems. In the present study artificial neural networks (ANN) and adaptive neuro-fuzzy inference system (ANFIS) are employed to predict pressure loss in air-water two-phase slug flow. Adaptive particle swarm optimization (APSO) is also applied to optimize the results of the ANN and ANFIS models. To predict the pressure loss in two-phase flow, the frictional pressure loss coefficient needs to be determined with respect to the effective dimensionless parameters including two-phase flow Froude and Weber numbers and the air concentration. Laboratory test results are used to determine and validate the findings of this study. The performances of the ANN-APSO and ANFIS-APSO models are compared with those of the ANN and ANFIS models. Different comparison criteria are used to evaluate the performances of developed models, suggesting that all the models successfully determine the air-water two-phase slug flow pressure loss coefficient. However, the ANFIS-APSO performs better than other models. Good agreement is obtained between estimated and measured values, indicating that the APSO with a conjugated ANFIS model successfully estimates the air-water two-phase slug flow pressure loss coefficient as a complex hydraulic problem. Results suggest that the proposed models are more accurate compared to former empirical correlations in the literature.

Two-phase flow frictional pressure drop prediction in helical coiled tubes

Based on the construction of different experimental databases, the frictional pressure drop in helical tubes for single-phase and water-steam two-phase flow was analyzed empirically. The aim of the present study is to provide the scientific community with a reliable and simple to use predictive tool for estimating frictional pressure drop in helical tubes covering operating conditions of interest for the design and operation of coiled tube once-through steam generators, as those used in small modular advanced nuclear reactors.The single-phase database contains around 2000 data points from 14 different sources, including data measured with air and water as working fluids, covering Reynolds numbers ranging from 40 to 145,000 and curvatures between 0.0027 and 0.3. The prediction capability of some existing correlations for simple phase flow was analyzed, concluding that Ito correlations for laminar and turbulent regime (1959) are the best ones fitting the experimental data. The average difference between experimental data and Ito correlations was 3.75% for laminar regime and 2.11% for turbulent regime.The two-phase flow database was built with data available from open literature works. Due to the fact no existing correlation was found to successfully predict the available data, a new prediction tool based on the homogeneous equilibrium model was developed for water-steam flows at conditions of interest.The proposed tool, so-called FEMA correlation, converges to the Ito correlations for single phase flow, i.e. for thermodynamic qualities equal to 0 and 1. In addition, the correlation successfully fits the experimental data with an average error of 7.4% which is smaller than any other existing correlation. In addition, the new correlation is recommended for water-steam flow in vertical helical tubes with liquid only Reynolds numbers ranging from 20000 and 124000, pressures between 1 and 8 MPa, curvatures between 0.01 and 0.08, and thermodynamic qualities ranging from 0 to 1.

Experimental investigation on two-phase frictional pressure drop of R600a and R600a/3GS oil mixture in a smooth horizontal tube

Abstract The current work demonstrates an empirical investigation on the two-phase flow frictional pressure drops attributes of the R600a/3GS oil within an inner diameter horizontal tube, sized 8 mm. Furthermore, experiments were carried out at the nominal oil concentrations between 0% and 4% at the saturation temperature of 20 °C, having the heat flux amounting to 10.0 kW·m−2, together with the mass flux that ranged between 150 and 300 kg·m−2·s−1. Moreover, the impact of the nominal oil concentration, together with the mass flux and quality on the frictional pressure drops were not only investigated but also debated. As the findings indicate, the existence of oil augments the two-phase frictional pressure drop approximately between 0 and 60% with the present test conditions. Meanwhile, the comparison of the experimental data of the two-phase frictional pressure drops was carried out with some of the relationships present in literatures. The result showed the fact that the experimental data reasonably agree with the correlation of Schlager, with 95% of the empirical points being in an error bandwidth amounting to ±25%. Besides that, a new correlation for predicting the frictional pressure drop of R600a/oil mixture was modified on the basis of the local attributes of the oil. In accordance with the forecasted values from the modified correlation, there is an acceptable agreement with the empirical data. Moreover, the deviations are located within –20%–+15%. Accordingly, it could be put to use for predicting the frictional pressure drops of R600a/oil mixture in evaporator while designing a refrigeration system.

Operational behavior and heat transfer in a thermosiphon desorber at sub-atmospheric pressure. Part I: The model

The thermosiphon desorber or bubble pump is advantageous in absorption cooling devices, since the processes of refrigerant desorption and solution pumping is combined in one hermetical unit. This supersedes the necessity of a mechanical solution pump. In the application with NH3/H2O the thermosiphon desorber typically operates at a pressure of around 15 bar with a liquid vapor density ratio in the range of 102, which is in a well-known regime of two phase flow. Nevertheless, for the application of thermosiphon desorbers in H2O/LiBr absorption chillers, which are commonly operated at a pressure below 0.1 bar with the liquid vapor density ratio in the range of 104, there is a lack of heat transfer correlations for two-phase flow.First attempts to fill this gap of flow boiling heat transfer correlations in the thermosiphon desorber at sub-atmospheric pressures is presented in this paper. A model is formed by solving simultaneously the mass, energy, and momentum equations. The well-known correlations for predicting single-phase and two-phase flow heat transfer coefficient and frictional pressure drop have been reviewed to find a possibility for applying them to the thermosiphon desorber. The mass flow rate and heat transfer behavior with the different flow length of the riser tube and with changing the pressure has been theoretically studied in the model. For verification, the model has been compared to experimental data using pure water. This will be presented in the second part of the paper.

Two-phase flow frictional pressure drop of FC-14 in horizontal tubes

Experimental measurements on the two-phase flow frictional pressure drop of tetrafluoromethane, FC-14, were carried out with a pressure of 0.4 MPa and the mass-flow rates ranging from 240-785 kg/m2s. The influences of the mass-flow rate and quality on the frictional pressure drop were analyzed. The experimental results have been compared with three widely used correlations, of which proposed by Zhang and Webb (2001) gave a best agreement with the deviation in 16%.

수평 원관 내 공기-오일 이상유동 양식과 마찰 압력강하에 관한 실험적 연구

This study examines the air-oil two-phase flow regime and frictional pressure drop in a horizontal circular pipe with a diameter of 40 mm. The pressure drop fluctuation characteristics for different air and oil superficial velocities are investigated. Observed flow regimes and frictional pressure drop data are compared with previous flow regime maps and frictional pressure drop correlations, respectively.

Two-phase Frictional Pressure Drop of Propane with Prediction Methods of Viscosity and Density in 500 μm Diameter Tube

The experimental study of frictional pressure drop of two-phase flow with propane on the microchannel has been done. The aim of the present research is to characterize pressure drop of evaporative propane in microchannel with 500 μm diameter and 0.5 m length. The experimental apparatus used heating process in the test section with closed loop process system. Variable of research are mass flux of 360 to 915 kg/m2s and vapor quality of 0 to unity. The homogeneous and separated model used to determine the two-phase flow frictional pressure drop. Some existing correlations of two-phase flow viscosity and density used to predict frictional pressure drop, including parameter C that used non-dimensional parameter of two-phase viscosity number Nμtp which developed as a function of two-phase viscosity and density. The comparison of prediction frictional pressure drop showed that the Hibiki, Xuejiao and Pamitran correlation from separated model.

Newton-Krylov method in solving drift-flux two-phase flow problems for both pre-CHF and post-CHF conditions at steady state

This paper presents numerical simulations of two-phase flow heat transfer for both pre-CHF and post-CHF conditions typical in light water nuclear reactors. The conjugate heat transfer problem is modeled with one-dimensional four-equation drift-flux two-phase flow model for coolant flow and two-dimensional heat conduction equation in solid walls/rods. Fully implicit time integration schemes were employed, and the resulted non-linear equations were solved with a Newton-Krylov method. For the drift-flux two-phase flow model, the EPRI drift-flux closure correlation is used to model the relative motion between the two phases. Additional closure correlations were adopted from REALP5-3D to further improve the model accuracy in complex two-phase flow applications. These correlations are applied to determine two-phase flow regime, wall boiling heat and mass transfer, interfacial heat and mass transfer, and two-phase flow frictional pressure drop. Three sets of experiments were used for code validation, including Bartolomei subcooled flow boiling in vertical pipes, FRIGG boiling tests in vertical bundles, and Bennett heated tube tests. RELAP5-3D simulation results were also provided to perform code-to-code benchmark. Overall, numerical results of this work showed good agreements with both experimental data and RELAP5-3D simulation results. Discrepancy between them were also identified in post-CHF region, which suggests necessary further improvement. This work represents the first successful application of Newton-Krylov method in solving four-equation drift-flux two-phase flow problems with a full realistic boiling curve.

Experiment investigation of two-phase flow pattern transition and frictional pressure drop of R600a in a horizontal tube

With the growing concern of environment problems, there are urgent demands for environment-friendly refrigerants in the refrigeration industry. As a natural refrigerant, R600a not only has zero ozone depletion potential and quite low global warming potential, but also has better cooling performance than other refrigerants. Due to its good cooling performance and environment-friendly characteristics, R600a has been used as an alternative refrigerant in heat transfer applications such as refrigerators, freezers, and heat pumps. It is known that accurate prediction of two phase flow pattern transition and frictional pressure drop of R600a in a horizontal tube play an important role in design and optimization of refrigerators, freezers, and heat pumps. According to this issue, a detailed experimental study was carried out to investigate the two-phase flow pattern transition and frictional pressure drop characteristics of R600a in a smooth horizontal tube with an inner diameter of 6 mm. The experiments were performed at conditions covering saturation temperature from 282.4 to 304 K, mass fluxes from 67 to 194 kg/(m2 s). Based on a high speed camera, four main flow regimes can be observed: plug flow, stratified-wavy flow, slug flow and annular flow. The flow map of R600a has been drawn and comparisons between the experimental data of flow patterns and transition lines in the literature have been made. The results showed that with the increase of mass flux, the inception of the annular flow regime occurs earlier. The intermittent flow regime takes place over a narrow range of vapor quality and annular flow regime occupies a wide range of vapor quality. In addition, the trend of Barbieri and Ong and Thome I / A transitions lines are consistent with the experimental data. However, both of them overestimate the inception of the annular flow regime. After taking the influence of vapor inertia, liquid viscous and surface tension forces into account, a modified Weber number We * has been introduced to the new flow pattern transition model. Based on the relationship of X tt and We *, a new correlation has been proposed and it can well fit with the experimental data of flow pattern. Furthermore, a detailed discuss of frictional pressure drop of annular flow and non-annular flow has been made. The results indicated that frictional pressure drop increases with the increases of vapor quality. The tendency of frictional pressure drop presents different the changing laws in different flow regime. The frictional pressure drop increases slowly in the non-annular flow regime while it increases rapidly when the flow pattern turns into the annular flow regime. The reason is that the vapor-phase pressure drop often dominates the total two-phase frictional pressure drop. The annular flow regime owns higher void fraction than the non-annular flow regime. Nine classic prediction correlations of pressure drop were evaluated and the results showed that the correlation of Gronnerud and Muller-Steinhagen and Heck give the best fit to the experimental frictional pressure drop of annular flow and non-annular flow with a mean absolute relative deviation of 38.5% and 19.7% respectively.

Frictional pressure drop correlation for two-phase flows in mini and micro multi-channels

1029 frictional pressure drop data of two-phase flow in mini/micro multi-channels were collected from 11 literatures. This database included 8 working fluids: R134a, R22, R404a, FC-72, water, CO2, R236fa and R245fa. The channel dimension ranged from 0.109 to 2.13mm. Frictional pressure drop range of the database was from 5 to 150kPa. The applicability of 11 existing correlations developed for mini/micro single channels to mini/micro multi-channels were evaluated with the multi-channel database. Among the existing correlations, the correlation of Lee-Mudawar predicted the database with the mean absolute percentage error (MAPE) of 35.3%, the correlations of Lee-Garimella and Sun-Mishima had MAPEs within 45.0%. In the process of new correlation development, the database was divided into three categories (namely, 1: gas laminar-liquid laminar, 2: gas turbulent-liquid laminar, 3: gas turbulent-liquid turbulent) in terms of liquid Reynolds number and gas Reynolds number, since gas laminar-liquid turbulent data did not exist in the literature. The newly developed correlation was formulated by a function of the two-phase Reynolds number, Retp, the two-phase viscosity number, Nμtp, and the vapor quality, x. The correlation could predict the measured frictional pressure drop with the MAPE of 18.9%. The correlation demonstrated an excellent performance of the two-phase flow frictional pressure drop prediction in mini/micro multi-channels.

ANALYSIS OF OUTCOMES OF THE FRICTIONAL PRESSURE DROP PREDICTION USING DIFFERENT DATA SOURCE

Predictions of the frictional pressure drop using friction factor correlations that have been developed based on past experimental data have always been found to disagree with recent experimental data. Thus, new correlations are continuously being developed to generalize their applications across refrigerants and flow regimes. The friction factor is dependent on the Reynolds number and relative roughness, therefore consequently depends on the applied equation and fluid data. This research shows the outcome of the analysis of the frictional pressure drop prediction when different data source as well as different friction factor equations for smooth and rough pipes are utilized. The R-22 data used for comparison are experimental data from a past report, NIST (Standard Reference Database), and experimental data from University of Indonesia. The used e friction factor equations are Blasius and Fang et al. (2011) in smooth and rough pipe respectively. The mass flux is ranging from 200 to 600 kg/m2s and vapor quality from 0.0001 to 0.5, the latter of which is assumed constant along the pipe length of 2000 mm at the saturation temperature of 10°C. The pipe material is stainless steel with an absolute roughness of 0.03 mm. The minimization of the friction factor and two-phase flow frictional pressure drop is achieved by applying Genetic Algorithm (GA). The comparisons reveal that the differences are an indication of the appropriate data source necessary so that the frictional pressure drop can be accurately predicted. The results showed that in 1.5 mm pipe diameter, the Blasius equation gives the lower percentage of differences in the range of 0.69 – 1.47 % when the data from NIST and UI are used. While the lower percentage of differences gives Fang et al. (2011) equation in the range of 1.47 – 2.61% when data from Pamitran et al. (2010) and UI are used. In the 3 mm inner diameter, also Blasius equation gives the lower percentage of differences in the range of 0.89 – 2.52% when the data from Pamitran et al. (2010) and UI are used. While Fang et al. (2011) gives the lower percentage of differences in the range of 1.56 – 1.33% when the data from Pamitran et al. (2010) and UI are used. The proposed method is predictable to raise the accuracy of the prediction and decrease the time of testing. The results are compared between each other’s for different data sources. For most situations, the percentage difference, as well as for laminar and turbulent flows are between 91 – 97% and 88 – 95% in 1.5 and 3 mm pipe diameter respectively.

R32 and R410A condensation heat transfer coefficient and pressure drop within minichannel multiport tube. Experimental technique and measurements

The present paper reports the construction of an experimental installation to measure local condensing two-phase flow heat transfer coefficient and frictional pressure drop within mini-channel tubes, the validation measurements developed with R134a and the experimental measurements of heat transfer coefficient and frictional pressure drop made with R32 and R410A.This experimental work is carried out in a test apparatus which allows determining the local heat flux extracted from the condensing fluid. For this purpose, the wall temperature is measured along the test section in several points.The saturation temperature is determined from the saturation pressure, which is measured at the inlet and the outlet of the test channel.Experimental data of R32 and R410A are also compared with some predicting models widely accepted in the literature.

Effect of the bend geometry on the two-phase frictional pressure drop and flow behaviour in the vicinity of the bend

The effect of a sharp return bend on the two-phase flow frictional pressure drop close up-and downstream of the bend is investigated. The measurements are performed for refrigerant R134a at mass fluxes ranging from 200 to 500kg/m2s. Four bend geometries are tested, with inner channel diameters ranging from 4.93mm to 8.1mm and the curvature ratio between 2.55 and 4.43. For both up-and downward oriented flow the main bend effect on the frictional pressure drop is observed close downstream of the return bend. However, for downward oriented flow a decrease in pressure drop is observed and for upward flow an increase is found. To assess the effect the underlying flow behaviour, the void fraction time trace is analysed. The average void fraction and wavelet variance of the void fraction signal can be used to explain the trends in the frictional pressure drop. The correlation between the frictional pressure drop and the flow behaviour indicators is investigated quantitatively for the different geometries.

Two-phase frictional pressure drop and flow behaviour up- and downstream of a sharp return bend

In this work, the two-phase flow frictional pressure drop of a refrigerant flow up- and downstream of a sharp return bend is studied. The radius of the return bend is 10.2 mm and the channel inner diameter measures 8 mm. The refrigerant is R134a, the mass flux is varied between 200 and 500 kg/m2 s and the vapour quality x is varied between 0 and 1. The bend orientation is vertical. Upward flow as well as downward flow through the bend is studied. To be able to explain the effect of the return bend on the frictional pressure drop, the two-phase flow behaviour is measured at several locations up- and downstream of the return bend by means of a capacitance sensor. From this capacitance signal, the void fraction and wavelet variance are derived. Close downstream of the return bend the measured pressure gradient is lower than the reference for downward oriented flow. At these locations the void fraction is higher compared to the reference and the wavelet variance is lower compared to the reference measurement, which is consistent with a lower pressure gradient. For upward oriented flow an increase in pressure gradient compared to the reference measurement is observed close downstream of the return bend. At these locations an increase in wavelet variance compared to the reference is observed, which is consistent with the increase in frictional pressure gradient. Upstream the affected length is rather small, less than 10 diameters upstream, downstream the bend effect is more pronounced and present for more than 30 diameters.

Two-phase flow pattern and pressure drop in silicon multi-microchannel with expansion–constriction cross-section

Gas–liquid two-phase intermittent flow pattern and frictional pressure drop in new silicon multi-microchannel were investigated experimentally by means of the IDT high-speed camera mounted together with a Nikon microscope. Each test section consisted of 10 parallel microchannels with 0.1mm wide and 0.2mm deep in constant cross-section segment and each microchannel consisted of an array of periodic reentrant cavities. The major two-phase flow pattern observed was intermittent in the test sections, and the intermittent sub regimes in the new microchannels were different from those displayed in the rectangular straight microchannel. Using nitrogen and deionized water as working fluids, the intermittent sub regime maps for the new multi-microchannel were obtained. Meanwhile, the pressure drops were compared with several existing correlations based on the homogeneous or separated mixture assumption. Results show that the homogeneous flow model cannot predict the two-phase pressure drop data well, while the separated flow model is proposed to provide a better prediction of the two-phase frictional pressure drop. Among the separated flow models investigated, the best two correlations of C value can provide mean deviations within less than 16% for all the three microchannels and all the predictions lie in the bound of ±30%.

Experimental study of saturated boiling heat transfer and pressure drop in vertical rectangular channel

Experimental study has been conducted about the boiling heat transfer and pressure drop in a vertical rectangular channel with the cross-section of 2mm×40mm. The experiments are conducted with the pressure range from 0.1 to 2MPa, mass flux range from 500 to 2500kg/(m2s). The relationships of the boiling heat transfer coefficient and two-phase flow frictional pressure drop multiplier with mass flux, pressure and mass quality are analyzed according to the results. In addition, the effect of void fraction models on the two-phase flow pressure drop calculation is also assessed. Furthermore, the boiling heat transfer and friction pressure drop experimental data are compared with the classical correlations. Based on the experimental data, the new correlations for calculating the boiling heat transfer and pressure drop are developed.