Pressure Drop For Turbulent Flow Research Articles

Comparative study of heat transfer and pressure drop in turbulent flow of a singular and hybrid nanofluids into a horizontal pipe

Comparative study of heat transfer and pressure drop in turbulent flow of a singular and hybrid nanofluids into a horizontal pipe

Pressure drop of turbulent flow across pipe bends

Pressure drop of turbulent flow across 90[Formula: see text] round bends with 10mm inside diameter investigated by employing the shear stress transport [Formula: see text] turbulent model for numerous curvature ratios and flow conditions. A total of 10 flow velocities varied from 1 to 10 m/s and 17 curvature radii between 5 and 300 mm were examined. Velocity profiles were evaluated at eight locations to examine the entrance effect. The simulation results were verified by comparing the evaluated Darcy friction factor with a well-known published correlation. The obtained results of bend pressure drop demonstrate the domination of the curvature ratio effect on the pressure drop over the influence of other factors. The computed pressure loss across the bend in terms of pressure loss coefficient [Formula: see text] and equivalent length to diameter ratio [Formula: see text] shows a good agreement with various published data in the literature with [Formula: see text] maximum average error. The coincidence between the results and the published data verifies the accuracy of the employed model to evaluate the pressure drop of turbulent flow throughout 90[Formula: see text] bends for the applied boundary conditions.

Thermal Performance Investigation in Circular Tube with Stationary and Rotating Conical-Obstacle Inserts

In the present study, the effect of conical obstacles on heat transfer and flow characteristics in a circular tube was investigated. In most previous studies, stationary obstacles were used to stimulate the flow and to investigate heat transfer and pressure drop. In the present paper, in addition to investigating the effect of a stationary obstacle, the effect of using moving obstacles was studied, both empirically and numerically, as a new topic on heat transfer and pressure drop in turbulent flow inside the pipe. In this study, the rotating speed of the obstacle ranged from 50 to 100 rpm, and the ranged from 4000 to 24,000. The results revealed that the heat transfer and friction factor changed by 2.2–3.95 and 17.2–22.2 times relative to the smooth tube, respectively. Also, the thermal performance coefficient was 120% more than the stationary obstacles. According to the findings of the current study, studying the effect of obstacle rotation on thermohydraulic characteristics is an innovative and useful topic. Altogether, besides its easy construction, compared to previous reports, the conical obstacle is a suitable obstacle that can be employed to improve thermal performance.

Measurements for verification and validation of thermal-hydraulic computer code used for thermal-hydraulic analysis of VVER440 typical fuel assembly

The paper contains experimental data and analysis of the velocity distribution and pressure drop of turbulent flow through a fuel bundle of 19 rods as a partial model of the VVER-440 reactor core. Also, results from the code calculations at the outlet of the test assembly at different flow rates and comparison with experimental data are presented. A pitot tube was used to measure the velocity and pressure drop. Detailed measurements of the velocity distribution in a fuel bundle are done in a fully developed turbulent flow region. Moreover, detailed measurements of the pressure drop of wire and spacer grids typical for PWRs are discussed together with the total pressure drops performance. The experimental result was compared with the predictions by our code and good agreement was found. The calibration protocol and uncertainties of the measurements are presented.

The Application of the Integral Momentum Balance on the Pressure Drop of a Sudden Contraction

Abstract A new approach based on the momentum balance to calculate the pressure drop in turbulent flow through sharp-edged axisymmetric sudden contractions is presented. The momentum balance needs the velocity as well as the pressure distributions on the boundaries of the control volume. These distributions are obtained by a series of numerical simulations with different settings for the discharge, as well as the contraction ratio. The numerical model itself is validated by the comparison of the simulated and measured pressure drops in a laboratory experiment at different positions. To get easily applicable hydraulic formulations for the pressure drop depending on the discharge and the contraction ratio, the missing momentum and pressure coefficients are determined from the simulated velocity and pressure distributions. Only the pressure coefficient shows a dependency on the contraction ratio. After fitting the dependency by a simple analytical expression, a new formulation for the hydraulics of a sharp-edged sudden contraction based solely on momentum balance was obtained. The comparison with own experimental results as well as the classical parameterization of Idelchik show in both cases very good agreement.

Experimental investigation of heat transfer enhancement in heat exchanger due to air bubbles injection

The present work experimentally investigated air bubbles injection on heat transfer enhancement and pressure drop of turbulent flow in two helical coils heat exchanger. The experience is accomplished for turbulent flow with Reynolds number (Re) of (9000 to 50000) for hot water and constant mass flow rate of cold water 0.0331 kg/s .Air bubbles injection in hot water in the range of (1.5, 2.5, and 3.5) lit/min. Experimental results represented by Nusselt number(NU), effectiveness (ε), number of thermal units (NTU) and exergy losses. It was evinced that, the presence of air bubbles in hot water causes enhanced in Nusselt number from (64 to 126) % and increased the friction factor from (66 to 85) % in the Reynolds number range from (9000 to 50000). Bubbles injection has a positive effect on enhanced heat transfer and negative effect of increased friction factor and this represent by thermal enhancement factor which was increased about (1.13 to 1.29) in mass flow rate of hot water of 0.0163 kg/s by using values of air bubbles from (1.5 to 3.5) lit/min. A quantity of number of thermal units (NTU) and effectiveness (ε) appreciably enhanced due to air bubbles. Furthermore, exergy loss with air bubbles was higher than without air bubble injection.

Generalized correlations for predicting heat transfer and friction factor of turbulent flow in tubes with inner helical ribs

Generalized correlations for predicting heat transfer and pressure drop for turbulent flow of Newtonian fluid through tubes with inner helical ribs are presented. A comparison with existing correlations in the literature shows that revealed correlations allow decreasing the data deviation and cover the wide ranges of working fluids, operational conditions, and different dimensions of helical ribs.

Convection Heat Transfer Enhancement in Square Cross-Section with Obstacle Using Nanofluids

The characteristics of heat transfer and pressure drop in turbulent flow of Al2O3 and CuO/water nanofluid that flowing in a horizontal straight square cross-section duct with obstacle has been studied experimentally and numerically. The experimental work is attempted by using a water and nanoparticles concentration of (φ = 0.5 to 2.0 % vol.) that flows in an aluminium square duct with side dimensions of a = 20 mm and length of L = 1000 mm. The obstacle located at the middle of the duct with different obstacle height to pipe side ratio varied as (h/a = 0.0, 0.25, 0.5 and 0.75). The water entered to the duct with inlet Reynolds number of turbulent flow of 3500, 4300, 5200 and 6800. Constant heat flux of 6500 W/m2 is applied upon the external walls of the duct. The numerical finite volume method with appropriate boundary conditions used with ANSYS-Fluent v.16.2 was employed to simulate the temperatures and velocity of the nanofluids. The experimental and numerical results showed that the average Nusselt number increases with increasing the obstacle height ratio and with using nanofluids as compared with pure water. Moreover, the Nusselt number increases with increasing the nanoparticles concentrations in the nanofluids. In addition, the results indicated that increasing in the obstacle height ratio and increasing the nanoparticles, concentration leads to increasing the friction factor and pressure drop. Finally, the numerical results give good indication to the presence of the recirculation cell zone behind the obstacle.

Studies on heat transfer and pressure drop in turbulent flow of silver - water nanofluids through a circular tube at constant wall heat flux

In the present study, performance of convective heat transfer and friction factor of silver-water nanofluids in a horizontal circular pipe under turbulent flow were investigated experimentally under uniform heat flux condition. The volume concentration of silver nanoparticles is varied as 0.01, 0.05 and 0.1%. Heat transfer coefficient and friction factor of nanofluids were measured experimentally by varying the Reynolds number from 3000 to 21,000. It is observed that the addition of even low volume fraction of silver nanoparticles increases both Nusselt number and heat transfer coefficient of the nanofluid significantly. Nusselt number of silver-water nanofluid increases up to 32.6% for 0.1% volume fraction at Reynolds number of 21,000. However, the addition of nanoparticles in the base fluid increases the friction factor slightly. New empirical correlations are also proposed for the estimation of Nusselt number and friction factor of silver-water nanofluid based on the data of present experimental investigation. The proposed correlations of Nusselt number and friction factor show good agreement with their experimental data.

Investigation of heat transfer and pressure drop of turbulent flow in tubes with successive alternating wall deformation under constant wall temperature boundary conditions

In this study, the effects of the presence of multi-longitudinal vortex and various rotation angles between the pitches of alternating elliptical axis (AEA) tubes on heat transfer and pressure drop of turbulent flow were numerically investigated. Turbulent flow of water fluid was simulated at Reynolds numbers of 10,000–60,000. The turbulent flow and heat transfer in the tubes were discussed in terms of parameters such as static pressure, velocity magnitude, wall shear stress, turbulent intensity, performance evaluation criterion and the field synergy principle. The results demonstrate that most heat transfer occurs in the transition zone, but this also caused a high rate of pressure drop. Increasing the rotation angle between pitches from 60° to 80° increased the heat transfer, which increased the number of the multi-longitudinal vortices from four to eight and better mixed the cold fluid with the hot fluid near the tube wall on more paths. The friction factor decreased and the average Nusselt number increased as the Reynolds number increased. Both parameters increased as the angle of the pitch rotation increased. The performance evaluation criteria for all AEA tubes at a constant pumping power showed that the highest value (1.09) was achieved at a low Reynolds number (Re = 10,000) in the AEA 90° tube.

The numerical investigation of heat transfer and pressure drop of turbulent flow in a triangular microchannel

In this presentation, the flow and heat transfer inside a microchannel with a triangular section, have been numerically simulated. In this three-dimensional simulation, the flow has been considered turbulent. In order to increase the heat transfer of the channel walls, the semi-truncated and semi-attached ribs have been placed inside the channel and the effect of forms and numbers of ribs has been studied. In this research, the base fluid is Water and the effect of volume fraction of Al2O3 nanoparticles on the amount of heat transfer and physics of flow have been investigated. The presented results are including of the distribution of Nusselt number in the channel, friction coefficient and Performance Evaluation Criterion of each different arrangement. The results indicate that, the ribs affect the physics of flow and their influence is absolutely related to Reynolds number of flow. Also, the investigation of the used semi-truncated and semi-attached ribs in Reynolds number indicates that, although heat transfer increases, but more pressure drop arises. Therefore, in this method, in order to improve the heat transfer from the walls of microchannel on the constant heat flux, using the pump is demanded.

Transient aspects of drag reducing plane Couette flows

The addition of a small amount of polymers of high molecular weight can lead to a decrease in the pressure drop in turbulent flows. Over the years, numerous studies have been conducted in attempts to make practical use of polymer-induced drag reduction. However, many aspects concerning its main mechanism are still unclear. One of those aspects is the development of the turbulent structures and polymer deformation over time in the beginning of the phenomenon. As an attempt to further understand the drag reduction over this developing time, we analyse a turbulent Couette flow of a FENE-P fluid with the aid of direct numerical simulations. We show that the initial interactions between the mean shear flow, turbulent structures, and polymer stretching are the key to understanding the step-by-step evolution of the drag reduction (DR). A few instants after the beginning of the simulation, the DR assumes a significantly negative value before starting to increase and reaches its maximum. When the DR is a minimum, the polymers experience their highest deformation state. The energy necessary to initially stretch them comes mainly from the mean shear flow, which causes a decrease of the DR until its minimum and negative value. After this point, the polymers start to strongly interact with the turbulent structures, which are partially suppressed, and the DR starts to increase. Part of the energy stored by the molecules is then released to the mean flow, increasing the DR to a maximum level while the polymer extension decreases. Lastly, DR reduces, reaching an asymptotic and positive value, which indicates the beginning of the statistical steady flow state.

3-D numerical study of the effect of Reynolds number and baffle angle on heat transfer and pressure drop of turbulent flow of air through rectangular duct of very small height

Summary Present article illustrates a computational study of three-dimensional steady state heat transfer and high turbulent flow characteristics through a rectangular duct with constant heat fluxed upper wall and single rectangular cross-sectioned baffle insertion at different angles. RNG k–ɛ model along with standard wall function based computations has been accomplished applying the finite volume method, and SIMPLE algorithm has been executed for solving the governing equations. For a Reynolds number, Re of 10,000 to 50,000, Prandtl Number, Pr of 0.707 and baffle angle, α of 30°, 60°, 90°, 120°, 150°, computational studies are executed, centred onto the hydraulic diameter, D h , test section and hydrodynamic entry length of the duct. Flow field has been solved using Ansys Fluent 14.0 software. Study exposes that baffled rectangular duct has a higher average Nusselt number, Nu and Darcy friction factor, f compared to a smooth rectangular duct. Nu as well as f are found to be maximum at 90° baffle angle. Results illustrate that both α and Re play a significant role in heat transfer as well as flow characteristics and also effects TEF. The correctness of the results attained in this study is corroborated by comparing the results with those existing in the literature for smooth rectangular duct within a precision of ±2% for f and ±4% for Nu .

Numerical–Theoretical Analysis of Heat Transfer, Pressure Drop, and Fouling in Internal Helically Ribbed Tubes of Different Geometries

A numerical analysis of heat transfer and pressure drop for turbulent flow in a series of 15.54-mm inside diameter helically ribbed tubes has been performed. The ranges of geometric parameters were number of rib starts (10 to 40), helix angle (25 to 55 degrees), and rib height (0.3 to 0.6 mm). The effect of grid independence was extensively examined. The computational results match well with the experimental data to validate the accuracy of the numerical model. The effect of each main parameter, rib starts, helix angle, and rib height, on heat transfer and pressure drop is investigated. Considering fouling in practical situations, the ratio of pitch over rib height is an important parameter to select the tubes. It is advisable to select tubes with pitch over rib height ratio greater than 3.5, which have better heat transfer and lower fouling potential.

Drag Reduction and Velocity Profiles Distribution of Crude Oil Flow in Spiral Pipes

One of the main problems that occur in the fluid flow in the pipeline industry is a high consumption on pump power due to high frictional pressure drop in turbulent flow. So many applications that related to fluids transportation in oil and gas industry such as crude oil, oil and gas refinery product, moreover in drilling fluid that contains mud slurry. Therefore it is required to use DRA (Drag Reducing Agent) as method to improve pumping efficiency. Another problem in fluid flow such as crude oil and drilling fluid is the weight concentration of suspension particles, when the speed of flow is not sufficient enough can end with sedimentation in bottom side of pipe so that increased drag. Drag Reducing Agent (DRA) is used as a solution towards reduce the power losses in the piping system. One of the most popular DRA is biopolymer due to its environment friendly and inexpensive. The aims of this study is to investigate the reduction of pressure drop using consentration of additive CMC 250 ppm, 500 ppm and 750 ppm into crude oil flow in the straight spiral pipe with diameter ratio P/Di=3,5;5,4; and 7,6, and circular pipe with diameter Di=17 mm. The effectiveness of DRA is analyzed by measuring the profile of velocity distributionsusing pitot tube. The results showed that the maximum DR percentage of 750 ppm for circular pipe is 35,8%, for spiral pipes with ratio P/Di 3,5=20,3%, P/Di 5,4=25,6%, P/Di 7,6=32,5%. Increasing of DR is presented by the data of velocity distribution profiles that increased by increasing CMC concentration.The important of this research is the application of spiral pipe offers the best solution for the flow of crude oil containing a heavy concentration of particles in suspension. Certain ratios of spiral pipe and additives CMC can be obtained without sedimentation of crude oil flow and flow with lower drag.

Prediction of local pressure drop for turbulent flow in axisymmetric sudden expansions with chamfered edge

The present study numerically investigates the turbulent flow in axisymmetric sudden expansions with a chamfered edge. With the aid of commercial CFD software, Fluent 12.0, an extensive set of numerical simulations is carried out for dimensionless chamfer lengths varying from 0.02 to 0.5, expansion ratios between 2 and 6, and chamfer angles of up to 45° at a Reynolds number of 3×105. First, we present and analyze the local pressure drop across the sudden expansions without a chamfer. The dependence of the pressure drop coefficient on the main geometric parameters is then thoroughly investigated. Finally, a new correlation is proposed for the local loss coefficient in sudden expansions with a chamfered edge, along with a discussion of the optimal chamfer angle.

Experimental study of convective heat transfer and pressure drop of TiO2/water nanofluid

In this paper, an experimental study of convective heat transfer and pressure drop of turbulent flow of TiO2-water nanofluid through a uniformly heated horizontal circular tube has been performed. The spherical TiO2 nanoparticles with a nominal diameter of 15nm are functionalized by a new chemical treatment and then dispersed in distilled water to form stable suspensions containing 0.1, 0.5, 1.0, 1.5 and 2.0% volume concentrations of nanoparticles. Results indicate that heat transfer coefficients increase with increasing the nanofluid volume fraction and it is not changed with altering the Reynolds number. The enhancement of the Nusselt number is about 8% for nanofluid with 2.0% nanoparticle volume fraction at Re=11,800.

Experimental studies on heat transfer and friction factor characteristics of Al2O3/water nanofluid under turbulent flow with spiraled rod inserts

An experimental investigation on the convective heat transfer and friction factor characteristics in circular tube with spiraled rod inserts (pitch=15mm, 30mm) under turbulent flow with constant heat flux is carried out with distilled water and Al2O3/water nanofluids. For this purpose, Al2O3 nanoparticles were synthesized by using chemical precipitation method. The average size of particle is found to be 40.3nm. The nanoparticles are then dispersed in distilled water to form stable suspension of Al2O3/water nanofluids with 0.3, 0.4 and 0.5% volume concentration of nanoparticles. It is found that (i) heat transfer enhancement is caused by suspending nanoparticles and becomes more pronounced with the increase of the particle volume concentration (ii) the Nusselt number for spiraled rod inserts under turbulent flow showed an increase of about 10–48% compared to the Nusselt numbers obtained with plain tube (iii) the isothermal pressure drop for turbulent flow with spiraled rod inserts were found to be between 2 and 8% higher than the plain tube.

Computing the Pressure Drop of Nanofluid Turbulent Flows in a Pipe Using an Artificial Neural Network Model

In this study, an Artificial Neural Network (ANN) model to predict the pressure drop of turbulent flow of titanium dioxide-water (TiO2-water) is presented. Experimental measurements of TiO2-water under fully developed turbulent flow regime in pipe with different particle volumetric concentrations, nanoparticle diameters, nanofluid temperatures and Reynolds numbers have been used to construct the proposed ANN model. The ANN model was then tested by comparing the predicted results with the measured values at different experimental conditions. The predicted values of pressure drop agreed almost completely with the measured values.

Pressure drop of TiO 2 nanofluid in circular pipes

This paper discusses the pressure drop in circular pipes of TiO 2/water nanofluid for both laminar and turbulent flows at different temperatures and TiO 2 weight fractions. This study shows that TiO 2/water nanofluid causes enhancement, but temperature rise reduces pressure drop. The proportional increase in pressure drop for turbulent flow is lower than that for laminar flow. The traditional equation for pressure drop fails to accurately estimate the pressure drop for laminar and turbulent flows. Accordingly, this study developed new empirical equations for the friction factor for both laminar and turbulent flows, and the maximum deviations between calculated and experimental results were reduced to within the ranges of −6.17% to 3.55% and −3.08% to 3.81%, respectively, that is, for TiO 2/water nanofluid, the correlations apply better to turbulent than to laminar flow.