Two-phase Pressure Research Articles

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.

R1234yf Flow Boiling Heat Transfer Inside a 2.4-mm Microfin Tube

ABSTRACTThis paper presents an experimental study on R1234yf flow boiling inside a mini microfin tube with an inner diameter at the fin tip of 2.4 mm. R1234yf is a new refrigerant with an extremely low global warming potential (GWP <1), proposed as a possible substitute for the common R134a, whose GWP is about 1300. The mass flux was varied between 375 and 940 kg m−2 s−1, heat flux from 10 to 50 kW m−2, and vapor quality from 0.1 to 1. The saturation temperature at the inlet of the test section was kept constant and equal to 30°C. The wide range of operative test conditions permitted highlighting the effects of mass flux, heat flux, and vapor quality on the thermal and hydraulic behavior during the flow boiling mechanism inside such a mini microfin tube. The results show that at low heat flux the phase-change process is mainly controlled by two-phase forced convection, and at high heat flux by nucleate boiling. The two-phase frictional pressure drop increases with increasing both mass velocity and vapor quality. Dry-out was observed only at the highest heat flux, at vapor qualities of around 0.94–0.95.

MODELING OF THE MINIMIZED TWO-PHASE FLOW FRICTIONAL PRESSURE DROP IN A SMALL TUBE WITH DIFFERENT CORRELATIONS

The major parameters of interest in heat transfer research are the refrigerant charge, pressure drop, and heat transfer capacity. Smaller channels reduce the refrigerant charge with higher heat transfer capability due to the increased in surface area to volume ratio but at the expense of a higher pressure drop. Differences between the predicted and experimental frictional pressure drop of two-phase flow in small tubes have frequently been discussed. Factors that could have contributed to that effect have been attributed to the correlations used to model the flow, some being modified from the originals developed for a macro system. Experimental test-rigs have varied in channel geometry, refrigerant type, and flow conditions. Thousands of data have been collected to find a common point among the differences. This paper reports an investigation of four different two-phase friction factor correlations used in the modeling of the frictional two-phase flow pressure drop of refrigerant R-22. One had been specifically developed for laminar flow in a smooth channel, another was modified from a laminar flow in a smooth pipe to be used for a rough channel, and two correlations are specific for turbulent flow that consider internal pipe surface roughness. Genetic algorithm, an optimization scheme, is used to search for the minimum friction factor and minimum frictional pressure drop under optimized conditions of the mass flux and vapor quality. The results show that a larger pressure drop does come with a smaller channel. A large discrepancy exists between the correlations investigated; between the ones that does not consider surface roughness and that which does, as well as between flow under laminar and turbulent flow conditions.

Optimization of the Friction Factor and Frictional Pressure Drop of R22 and R290

Today, the air-conditioning and refrigeration industry is still searching for the environmentally friendly refrigerants that could replace the hazardous coolants that are ozone depleting – refrigerants that behave similarly, if not better than the present ones. The present study includes optimization of the frictional pressure drop of R22 and R290 using genetic algorithm. Parametric analysis have been conducted in order to determine the difference in the case of the use of genetic algorithms. The outcomes are compared against that of the measured pressure drop, the latter obtained from a horizontal 7.6 mm channel with a length of 1.07 meter. Three equations have been used for calculating the Darcy friction factor and two-phase flow pressure drop for both laminar and turbulent flow regimes in smooth and rough tubes. The effects of the different correlations for the friction factor and the pressure drop utilized are demonstrated. The results illustrate that the differences between values of the Darcy friction factor are very small for the two refrigerants, and the frictional pressure of R-290 higher than R-22. Smaller channel induced much higher frictional pressure drop too.

Characteristics of Two-Phase Flow Pressure Drop of Propane in Horizontal Circular Small Tube

This study experimentally investigated two-phase flow pressure drop of propane as refrigerant in horizontal small tube. Inner diameter and length of the tube were 7.6 mm and 1.07 m, respectively. In order to get pressure drop data, the experiment was conducted in various conditions of 10 to 25 kW m-2 heat flux, 200 to 628 kg m-2 s-1 mass flux, and 4.0 to 11.7°C saturation temperature. This study clearly showed the effect of heat flux, mass flux, and saturation temperature on the pressure drop of propane. This study also investigated which fluid properties gave higher effect on the frictional pressure drop due to its change over the process based on the recent experiment data. The existing pressure drop correlations were evaluated against the experimental result.

A Note on Mixture Density Using the Shannak Definition

In this study, a note on mixture density using the Shannak definition of the Froude number is presented (Shannak, B., 2009, “Dimensionless Numbers for Two-Phase and Multiphase Flow,” Proceedings of the International Conference on Applications and Design in Mechanical Engineering (ICADME), Penang, Malaysia, Oct. 11–13, 2009). From the definition of the two-phase Froude number, an expression of the two-phase density is obtained. The definition of the two-phase density can be used to compute the two-phase frictional pressure gradient using the homogeneous modeling approach in circular pipes, minichannels, and microchannels. We cannot have gas density≤two-phase density≤liquid density for 0≤mass quality≤1. Therefore, attention must be paid when using the obtained expression of the two-phase density in this note at any x value.

Thermal Characteristics of a Chip-Scale Two-Phase Microgap Cooler

Two-phase heat transfer and pressure drop results for a chip-scale, uniformly heated, microgap channel, with nominal gap heights of 100, 200, and 500 μm and using HFE-7100 and FC-87 as the working fluids, are reported. Average heat transfer coefficients in the range of 5 to 30 kW/m2-K were observed, for exit qualities up to 60%. Local heat transfer coefficients, obtained through an inverse computational technique, are found to vary strongly with thermodynamic quality and to fall within ±30% of the predictions of the venerable Chen correlation.

RELAP5 Analyses of ROSA/LSTF Experiments on AM Measures during PWR Vessel Bottom Small-Break LOCAs with Gas Inflow

RELAP5 code posttest analyses were performed on ROSA/LSTF experiments that simulated PWR 0.2% vessel bottom small-break loss-of-coolant accidents with different accident management (AM) measures under assumptions of noncondensable gas inflow and total failure of high-pressure injection system. Depressurization of and auxiliary feedwater (AFW) injection into the secondary-side of both steam generators (SGs) as the AM measures were taken 10 min after a safety injection signal. The primary depressurization rate of 55 K/h caused rather slow primary depressurization being obstructed by the gas accumulation in the SG U-tubes after the completion of accumulator coolant injection. Core temperature excursion thus took place by core boil-off before the actuation of low-pressure injection (LPI) system. The fast primary depressurization by fully opening the relief valves in both SGs with continuous AFW injection led to long-term core cooling by the LPI actuation even under the gas accumulation in the SG U-tubes. The code indicated remaining problems in the predictions of break flow rate during two-phase flow discharge period and primary pressure after the gas inflow. Influences of the primary depressurization rate with continuous AFW injection onto the long-term core cooling were clarified by the sensitivity analyses.

Two-phase flow pressure drop of liquid nitrogen boiling in the straight section downstream of U-bend

The gas-liquid (two-phase) flow pressure drop of liquid nitrogen boiling in the straight section downstream of U-bend is investigated experimentally. The mass flux ranges from 32 to 280 kg/(m2· s). The inlet pressure of U-tube is from 140 to 272 kPa. And the curvature ratio is from 6.67 to 15. The tube wall including the U-bend is heated uniformly and the heat flux ranges from 0 to 22 kW/m2. The tube with higher inlet pressure has higher pressure drop in the downstream section of the bend. The bended degree of the U-bend influences the pressure drop in the downstream straight section of U-bend. A new correlation taking the effect of the secondary flow into account is proposed for the two-phase slip speed ratio. The pressure drop in the straight section downstream of U-bend calculated by the new correlation agrees well with experimental measurements.

Mixers based on a variable geometry ejector

A mathematical model, which permits the ejector geometry to be optimized, has been designed in the framework of the inverse problem with the use of a non-equilibrium model of the two-phase gas-droplet medium and pressure law. A conventional ejector with a cylindrical chamber and diffuser is compared to the optimum geometry ejector based on numerical studies.

Prediction of Two-Phase Heat Transfer and Pressure Drop in Dilute Gas–Solid Flows: A Numerical Investigation

In this article, numerical simulations are performed using a Euler-Euler approach for the gas–solid flows in a horizontal pipe accounting for four-way coupling. The computational domain is a 55-mm-diameter pipe with a length-to-diameter ratio of 100. The effects of two important flow parameters, gas Reynolds number (in the range 37,640–94,100) and particulate loading (in the range 1–20), on the overall pressure drop and heat transfer are investigated. It is observed that the addition of solid particles (spherical fly ash particles of size 30–50 µm) to the gas flow resulted in an increase in pressure drop as well as heat transfer in comparison to single-phase flow. A simplified correlation is also developed for two-phase Nusselt number using nonlinear regression analysis in a non-dimensional form.

Two-phase flow dynamics in a micro channel with heterogeneous surfaces

In this paper, two-phase flows in a micro channel with heterogeneous surfaces are investigated both experimentally and numerically. The heterogeneity in a micro rectangular channel is characterized by three hydrophilic channel walls plus one hydrophobic one; and the hydrophobic surface is either smooth or rough (roughness: 226–550nmrms for the smooth surface and 21.5–28.9μmrms for the rough). Results on an entirely hydrophilic smooth channel (roughness ∼1.3nmrms) are also presented for comparison. Two-phase flows are visualized through two different angles: (1) a top view; and (2) a cross-sectional view. It is observed that the surface wetting property and roughness affect the presence site of liquid water flow: liquid water is preferentially present in the two hydrophilic corners when one channel wall is hydrophobic. As a result, two-phase pressure, patterns, and stability differ from the purely hydrophilic channel. Rough surface is found to affect two-phase flow. Model predictions, obtained from both empirical formula based on the Lockhart–Martinelli parameter and two-fluid approach, along with model parameters optimization using experimental data. Real-time pressures are presented to show the effects of channel surface properties on pressure drop.

Bounds on Two-Phase Frictional Pressure Gradient and Void Fraction in Circular Pipes

Simple rules are developed for obtaining rational bounds for two-phase frictional pressure gradient and void fraction in circular pipes. The bounds are based on turbulent-turbulent flow assumption. Both the lower and upper bounds for frictional pressure gradient are based on the separate cylinders formulation. For frictional pressure gradient, the lower bound is based on the separate cylinders formulation that uses the Blasius equation to represent the Fanning friction factor while the upper bound is based on the separate cylinders equation that represents well the Lockhart-Martinelli correlation for turbulent-turbulent flow. For void fraction, the lower bound is based on the separate cylinders formulation that uses the Blasius equation to predict the Fanning friction factor while the upper bound is based on the Butterworth relationship that represents well the Lockhart-Martinelli correlation. These two bounds are reversed in the case of liquid fraction (1-α). For frictional pressure gradient, the model is verified using published experimental data of two-phase frictional pressure gradient versus mass flux at constant mass quality. The published data include different working fluids such as R-12, R-22, and Argon at different mass qualities, different pipe diameters, and different saturation temperatures. The bounds models are also presented in a dimensionless form as two-phase frictional multiplier (ϕ l and ϕ g) versus Lockhart-Martinelli parameter ( X) for different working fluids such as R-12, R-22, and air-water and steam mixtures. For void fraction, the bounds models are verified using published experimental data of void fraction versus mass quality at constant mass flow rate. The published data include different working fluids such as steam, R-12, R-22, and R-410A at different pipe diameters, different pressures, and different mass flow rates. It is shown that the published data can be well bounded for a wide range of mass fluxes, mass qualities, pipe diameters, and saturation temperatures.

Prediction of Flowing Bottomhole Pressures for Two‐Phase Coalbed Methane Wells

Abstract:A method is proposed to predict the flowing bottomhole pressures (FBHPs) for two‐phase coalbed methane (CBM) wells. The mathematical models for both gas column pressure and two‐phase fluid column pressure were developed based on the well liquid flow equation. FBHPs during the production were predicted by considering the effect of entrained liquid on gravitational gradients. Comparison of calculated BHPs by Cullender‐Smith and proposed method was also studied. The results show that the proposed algorithm gives the desired accuracy of calculating BHPs in the low‐productivity and low‐pressure CBM wells. FBHP is resulted from the combined action of wellhead pressure, gas column pressure and fluid column pressure. Variation of kinetic energy term, compressibility and friction factors with depth increments and liquid holdup with velocity should be considered to simulate the real BHPs adequately. BHP is a function of depth of each column segment. The small errors of less than 1.5% between the calculated and measured values are obtained with each segment within 25 m. Adjusting BHPs can effectively increase production pressure drop, which is beneficial to CBM desorption and enhances reservoir productivity. The increment of pressure drop from 5.37 MPa2 to 8.66 MPa2 leads to an increase of CBM production from 3270 m3/d to 6700 m3/d and is attributed to a decrease in BHP from 2.25 MPa to 1.33 MPa.

Comments on “Analyses of single- and two-phase flow pressure drops in helical pipes using a modified RELAP5 code”

Comments on “Analyses of single- and two-phase flow pressure drops in helical pipes using a modified RELAP5 code”

Three-Dimensional Numerical Simulation of Fluid with Sparse Particles' Erosion to Pipelines

A three dimensional fluid flow model was set up in this paper, based on the computational fluid dynamics (CFD) and the elasticity theory. Using the finite volume method, a 120° bend was taken as a research object to simulate the erosion to the wall of fluid with sparse particles, finally, to determine the most severe wear areas.At the same time, the distribution of two-phase flows pressure and velocity was analyzed in 45° and 90° bends, then tracked the trajectory of the particles. The results show that the 90°bend has the smallest wear area and particle distribution or combination property is the best.

Comparison of Property Parameters of Pre-mixed Abrasive Water Jet Nozzles by Simulation Approach

Properties of four traditional pre-mixed abrasive water jet nozzles were compared by theory analysis and experimental approach in this paper. Based on the result, Six types of optimized nozzles were designed and simulated under steady state, turbulent, two-phase flow conditions by standard k-e Equation Model and SIMPLE algorithm of pressure coupling. Two-phase flow dynamic pressure and velocity of different nozzles were gained. After the comparison and analysis of the results, a new combinative way was given for the design of nozzle configuration, which may offer evidences for nozzles design.

Enhancement of Interphase Transport in Mini-/Microscale Applications Using Passive Mixing

Structured mini-/microscale reactors continue to receive attention from both industry and academia due to their low pressure drop, high heat and mass transfer rates, and ease of scale-up relative to conventional reactor technology. Commonly considered for reactions such as hydrogenations, hydrodesulfurization, oxidations, and Fischer–Tropsch synthesis, the performance of these systems is highly dependent on mixing and the interfacial area between phases. While existing literature describes the initial flow patterns generated by a broad range of two-phase contactors, few studies explore the dynamic impacts of downstream passive mixing elements. Experimental and computational methodologies for characterizing two-phase flow pattern transitions, pressure drop, and heat and mass transfer are discussed, with relevant examples for serpentine and Venturi-based passive mixing designs. The efficacies of these two configurations are explored in the context of pressure drop, conditions leading to significant interface renewal, and design considerations for optimizing mass transfer. Challenges associate with the characterization of multiphase flow through these systems are highlighted, and strategies suggested for both experimental and computational analysis of dynamic flow patterns and fluid–fluid interactions.

Two-phase frictional pressure drops in U-bends and contiguous straight tubes for different refrigerants, orientations, tube, and bend diameters: Part 1. Experimental results (RP-1444)

Over the years, much research has been conducted on two-phase flows in straight tubes because these tend, in length, to be predominant in two-phase systems. However, two-phase heat exchangers can also have singularity elements, where the most common type is typically a U-bend. The importance of these elements on the design of a system is that their frictional pressure gradients are much higher than those occurring in straight tubes. Therefore, in this study, pressure drop measurements were made for U-bends and their contiguous straight tubes with two-phase refrigerants. The experiments were made with R410A and R134a at two saturation temperatures (5°C and 10°C [41°F and 50°F]) flowing at three mass fluxes (150, 300, and 500 kg s−1m−2 [110.6·103, 221.2·103, and 368.7·103 lb h−1 ft−2]) inside five different test sections with three different internal diameters (13.4, 10.7, and 7.8 mm [0.527, 0.421, and 0.307 in.]) and five different bend diameters (66.1, 54.8, 38.1, 31.7, and 24.8 mm [2.602, 2.157, 1.5, 1.248, and 0.976 in.]) in three different orientations (horizontal, vertical upflow, and vertical downflow) with vapor qualities ranging from 0.05 to 0.95. The first part of this article focuses on the experimental pressure drop results, while the second part presents a new flow pattern based frictional pressure drop model for U-bends and an updated version of the straight tube frictional pressure drop model of Moreno Quibén and Thome (2007b).

The Effect of Heat Exchanger Type on Two-Phase Heat Transfer Coefficient and Pressure Drop

Three different types of heat exchangers were tested experimentally to investigate two-phase heat transfer coefficient and pressure drop during the condensation process of CO2 gas. Experimental results revealed that the convection heat transfer coefficient was enhanced by a factor of four due to the existence of porous media and by a factor of seven due to the use of micro-pipes when compared to the normal macro-tubes. The pressure drop was measured and noticed only in porous tubes and micro-pipes, reaching about 17.5 kPa/m and 8.4 kPa/m, respectively. Comparisons between experimental and correlated results were conducted.