Prediction Of Friction Factor Research Articles

Prediction of Nusselt Number and Friction Factor of Water-Al2O3 Nanofluid Flow in Shell-and-Tube Heat Exchanger with Helical Baffles

Heat transfer and flow field of water-Al2O3 nanofluid were simulated three-dimensionally in the shell-side of shell-and-tube heat exchanger with helical baffles. The effects of Reynolds number and volume fraction on heat transfer and pressure drop were evaluated. Increasing the volume fraction and Reynolds number intensified both heat transfer and pressure drop. Reduction of the Reynolds number increased the friction factor, but no considerable change was observed in the friction factor by increasing the volume fraction at constant Reynolds number. Heat transfer of the nanofluid revealed greater dependency on the volume fraction of particles at lower Reynolds numbers. Models of Nusselt number and friction factor were obtained in the heat exchanger in terms of Reynolds number and volume fraction using neural network. The neural network predicted the output variables with great accuracy.

Creeping Flow of Viscoelastic Fluid through a Packed Bed

Experimental results on investigation of elastic effects in creeping flow of viscoelastic fluids through a packed bed of spherical particles are presented. A simple form of the corrective Weissenberg number (We) function is proposed to extend the use of the Ergun equation, applicable to fixed bed flow of purely viscous fluids, for the prediction of friction factor in creeping flow of viscoelastic fluids. In order to quantify the effect of fluid elasticity on frictional pressure drop, aqueous solutions of polyacrylamide in the concentration range of 0.25%–0.6% (wt/vol) were used as test fluids and an extensive pressure drop-flow rate data were generated. Friction factor or pressure drop exhibited asymptotic behavior with variation in We, depicting the onset of viscoelastic effects at critical We values with a magnitude of 0.1 and the dominance of elastic effects over inertial effects up to We = 1.1. The percentage drag enhancement, as a function of fluid relaxation time, in the applicable range of We, is also reported. The proposed correlation will be useful in the field of enhanced oil recovery.

Oblique fluid flow and heat transfer across a hollow fiber membrane bank under uniform temperature conditions

Hollow fiber membrane banks have been extensively used in various energy and environmental technologies. Fluid flow and heat and mass transfer in the tube bank have been a focus of study. Previous researches have been focused on either pure parallel flow or pure cross flow. However they are only very ideal flow conditions. This study addresses a more common condition: oblique flow, in which shell side flow impinges the fiber tubes with a skew angle. By solving the fluid flow and heat transfer equations in the shell side, convective coefficients are obtained for impinging angles from 0° to 90°. It is found that the oblique angle influences the heat transfer properties seriously. Heat transfer rates for oblique flows are higher than those for parallel flows but lower than those values for cross flows. Correlations are proposed for the prediction of friction factors and Nusselt numbers at various oblique angles, both for aligned and staggered arrays with various geometrical parameters. Then mass transfer coefficients can be obtained from the calculated Nusselt numbers with heat-mass analogy.

EVALUATION OF PRESSURE DROP IN FLOW OVER FIXED POROUS BED

Many studies are conducted about the dynamics of fluids in porous media, which generates a number of factors and problems are solved. In particular the phenomenon of pressure drop in flows on fixed bed, although fairly well in the form Ergun’s equation, still has certain inconsistencies with regard to the types of materials to be used in the packaging of the beds. The objective of this work is to study this phenomenon using some experiments reported in the literature to determine the pressure drop in fixed bed consisting of porous particles of açaí seed. Experimental studies were conducted to predict, and take into account the losses resulting from friction and inertia that showed strong dependence on velocity. The method of using the particular friction factor prediction as a way to replace the usual calculation and measurement of pressure drop. The analysis in the wind tunnel was made from different sizes of bed, with a decrease in arithmetic progressions corresponding to half the value of the diameter of the tube used in the test. Several bands of Reynolds number were also employed in order to be able to visualize how the phenomenon behaves on various tracks. For such a survey was necessary some parameters such as açaí seeds diameters, seed weight and volume occupied by the bed; these parameters are of vital importance in Ergun equation, because an important aspect of the phenomenon is the porosity which enters as a foundation in the theory of flow fixed bed. At the end of the study was found the divergence in big bands of the Reynolds number of the correlation between experimental data and the Ergun equation.

Laminar flow and heat transfer through a circular tube having integral transverse corrugations and fitted with centre-cleared twisted-tape

The experimental friction factor and Nusselt number data for laminar flow through a circular duct having integral transverse corrugation and fitted with centre-cleared twisted-tape has been presented. Predictive friction factor and Nusselt number correlations have also been presented. The thermohydraulic performance has been evaluated. The major findings of this experimental investigation are that the centre-cleared twisted tapes in combination with integral transverse corrugation perform better than the individual enhancement technique acting alone for laminar flow through a circular duct up to a certain amount of twisted-tape centre-clearance.

Experimental investigation of laminar flow of viscous oil through a circular tube having integral spiral corrugation roughness and fitted with twisted tapes with oblique teeth

The experimental friction factor and Nusselt number data for laminar flow of viscous oil through a circular duct having integral spiral corrugation roughness and fitted with twisted tapes with oblique teeth have been presented. Predictive friction factor and Nusselt number correlations have also been presented. The thermohydraulic performance has been evaluated. The major findings of this experimental investigation are that the twisted tapes with oblique teeth in combination with integral spiral corrugation roughness perform significantly better than the individual enhancement technique acting alone for laminar flow through a circular duct up to a certain value of fin parameter.

Prediction of heat transfer performance of CuO/water nanofluids flow in spirally corrugated helically coiled heat exchanger using fuzzy logic technique

This paper presents the fuzzy logic expert system (FLES) for heat transfer performance investigation in helically coiled heat exchanger with spirally corrugated wall operated with water and CuO/water nanofluids. Compared with traditional logic model, fuzzy logic is more efficient in connecting the multiple units to a single output and is invaluable supplements to classical hard computing techniques. Hence, the main objective of this analysis is to investigate the relationship between heat exchanger working parameters and performance characteristics, and to determine how fuzzy logic expert system plays a significant role in prediction of heat transfer performance. Analytical values are taken in helically coiled heat exchanger with spirally corrugated wall operated with water and CuO/water nanofluids for investigation of heat transfer performance. The heat transfer coefficients of CuO/water nanofluids significantly increased about 5.90–14.24% with the increase of volume concentrations compared to water and while the values of the friction factor decreased with the increase in volume flow rate and volume concentration by using nanofluid instead of water. A fuzzy logic expert system model has developed for the prediction of heat transfer coefficient and friction factor. Verification of the developed fuzzy logic model was carried out through various numerical error criteria. For all parameters, the relative error of predicted values are found to be less than and/or slightly above the acceptable limit (5%). The goodnesses of fit of the prediction values from the fuzzy logic expert system model are found to be close to 1.0 as expected, and hence demonstrated the good performance of the developed system.

Effect of surface roughness on liquid friction and transition characteristics in micro- and mini-channels

A general threshold was proposed to subdivide a flow in a smooth or a rough micro- and mini-channel. A database was setup based on the experimental results of liquid flow in rough micro- and mini-channels from the literature, which includes 5569 data and covers wide ranges of the relative roughness and the Reynolds number. The effect of roughness on a flow in micro- and mini-scale channels was investigated by in-depth analyzing the friction factor and the flowing transition characteristics. Existing prediction models were used to predict the friction factors of fully developed flow and critical Reynolds number. Both experimental data and the predictions showed that roughness had little effect on flow characteristics when the relative roughness (ε/Dh) is less than 1%, while for the relative roughness larger than 1%, the friction factor and critical Reynolds number gradually deviate from the prediction values of smooth tubes. It was recommended that ε/Dh = 1% could be set as a threshold to distinguish smooth and rough micro- and mini-channels. According to this criterion, new correlations to predict friction factor and critical Reynolds number were also fitted. Moreover, it was also concluded that geometries of the channels had little effects on this threshold.

Reply to discussion on paper: Prediction of friction factor and stage–discharge relationship in alluvial streams in ISH journal of hydraulic engineering, 19 (1), 49–54, Feb. 2013

Reply to discussion on paper: Prediction of friction factor and stage–discharge relationship in alluvial streams in ISH journal of hydraulic engineering, 19 (1), 49–54, Feb. 2013

Prediction of heat transfer coefficients and friction factors for evaporation of R-134a flowing inside corrugated tubes

In this study, experimental and simulation studies of the evaporation heat transfer coefficient and pressure drop of R-134a flowing through corrugated tubes are conducted. The test section is a horizontal counter-flow concentric tube-in-tube heat exchanger 2.0 m in length. A smooth tube and corrugated tubes with inner diameters of 8.7 mm are used as the inner tube. The outer tube is made from a smooth copper tube with an inner diameter of 21.2 mm. The corrugation pitches used in this study are 5.08, 6.35, and 8.46 mm. Similarly, the corrugation depths are 1, 1.25, and 1.5 mm, respectively. The results show that the maximum heat transfer coefficient and pressure drop obtained from the corrugated tube are up to 22 and 19 % higher than those obtained from the smooth tube, respec- tively. In addition, the average difference of the heat transfer coefficient and pressure drop between the simula- tion model and experimental data are about 10 and 15 %, respectively. List of symbols A Surface area of the test section (m 2 ) cp Specific heat at constant pressure (J/kg C) d Inner diameter (m) D Outer diameter (m) e Corrugation depth (mm) f Friction factor G Mass flux (kg/m 2 s) h Heat transfer coefficient (W/m 2 C) i Enthalpy (J/kg) if Enthalpy of the saturated liquid (J/kg) ifg Enthalpy of vaporization (J/kg) k Thermal conductivity (W/m C) L Length of the test tube (m) LMTD Logarithmic mean temperature difference m Mass flow rate (kg/s)

The importance of wall-normal Reynolds stress in turbulent rough channel flows

In this paper, it is demonstrated by DNS of turbulent rough channels that a proportionality between \documentclass[12pt]{minimal}\begin{document}$\widetilde{u}_2^\prime |_w$\end{document}ũ2′|w (the wall-normal Reynolds stress \documentclass[12pt]{minimal}\begin{document}$\widetilde{u}_2^\prime =\langle u_2^{\prime 2} \rangle ^{1/2}$\end{document}ũ2′=⟨u2′2⟩1/2 at the top of the roughness elements) and the roughness function does exist. This observation confirmed by experiments allows the derivation of a simple expression for the velocity profile in the log-region. This parameterization of rough walls through \documentclass[12pt]{minimal}\begin{document}$\widetilde{u}_2^\prime |_w$\end{document}ũ2′|w is suggested by the direct link between wall structures and \documentclass[12pt]{minimal}\begin{document}$\frac{\partial ^2 \widetilde{u_2^{\prime }}^2}{\partial x^2_{2}}$\end{document}∂2u2′̃2∂x22. Identification of the wall structures, near smooth and different kinds of rough surfaces, demonstrates flow isotropization near rough walls, corroborated by profiles of \documentclass[12pt]{minimal}\begin{document}$\frac{\partial ^2 \widetilde{u_2^{\prime }}^2}{\partial x^2_{2}}$\end{document}∂2u2′̃2∂x22, is depicted by visualizations of ∇2p. The relationship between the roughness function and \documentclass[12pt]{minimal}\begin{document}$\widetilde{u}_2^\prime |_w$\end{document}ũ2′|w allows the derivation of a new kind of Moody diagram, useful in the prediction of friction factors of rough flows at high Reynolds numbers.

Prediction of friction factor and stage–discharge relationship in alluvial streams

Development of predictors for frictional resistance in an alluvial channel is a challenging task because of the complex interaction of fluid, flow and sediment in the channel bed. In the present study, an effort has been made to develop a functional relationship for friction factor using relevant fluid, flow and sediment parameters. Using field data (years 1984–2002) and the said functional relationship, a predictor for friction factor is proposed for mobile boundary channels. Proposed predictors for friction factor and cross-sectional properties of a gauging station (Sarangkheda, Tapi River, India), in turn, have been used to develop stage–discharge relationship for the same station. The proposed relationship for friction factor and rating curve developed at the Sarangkheda gauging station has been validated using available independent data for years 2003–2007.

THERMOHYDRAULICS OF LAMINAR FLOW THROUGH A CIRCULAR TUBE HAVING INTEGRAL HELICAL CORRUGATIONS AND FITTED WITH HELICAL SCREW-TAPE INSERT

The experimental friction factor and Nusselt number data for laminar flow through a circular duct having integral helical corrugations and fitted with a helical screw-tape insert are presented. Predictive friction factor and Nusselt number correlations are also presented. The thermohydraulic performance was evaluated. The major findings of this experimental investigation are that the helical screw-tape insert in combination with integral helical corrugations performs significantly better than the individual enhancement technique acting alone for laminar flow through a circular duct up to a certain value of the fin parameter. This research finding is useful in designing tubes carrying solar thermal mass of viscous oil in a parabolic trough solar collector used in environmentally sound and increasingly cost-effective solar thermal electric power plants. The result is also useful in designing heat exchangers used in process industries.

Enhancement of heat transfer of laminar flow of viscous oil through a circular tube having integral helical rib roughness and fitted with helical screw-tapes

The experimental friction factor and Nusselt number data for laminar flow of viscous oil through a circular duct having integral helical rib roughness and fitted with helical screw-tape insert have been presented. Predictive friction factor and Nusselt number correlations have also been presented. The thermohydraulic performance has been evaluated. The major findings of this experimental investigation are that the helical screw-tape inserts in combination with integral helical rib roughness perform significantly better than the individual enhancement technique acting alone for laminar flow through a circular duct up to a certain value of fin parameter.

Laminar Flow Heat Transfer and Pressure Drop in a Circular Tube Having Wire-Coil and Helical Screw-Tape Inserts

The experimental friction factor and Nusselt number data for laminar flow through a circular duct having wire-coil and helical screw-tape inserts have been presented. Peripherally and axially local temperatures on the duct outside wall have been measured. The temperature drop across the duct wall has been calculated to obtain the duct inside wall temperatures. Peripherally averaged and axially local temperatures have been used to get axially local Nusselt numbers. These axially local Nusselt numbers have been averaged over the whole length of the duct to get the mean Nusselt number. Predictive friction factor and Nusselt number correlations developed by log-regression analysis have also been presented. Nusselt number correlation takes care of the thermal development length represented by the Graetz number, swirl and inertia force due to forced convection at large Reynolds number, buoyancy force due to natural convection at low Reynolds number represented by Rayleigh number and the geometrical parameters of wire-coil and helical screw-tape inserts. The thermohydraulic performance has been evaluated. The helical screw-tape inserts in combination with wire-coil inserts perform better than the individual enhancement technique acting alone for laminar flow through a circular tube up to a certain value of fin parameter.

Wave energy and wave-induced flow reduction by full-scale model Posidonia oceanica seagrass

This paper presents results from experiments in a large flume on wave and flow attenuation by a full-scale artificial Posidonia oceanica seagrass meadow in shallow water. Wave height and in-canopy wave-induced flows were reduced by the meadow under all tested regular and irregular wave conditions, and were affected by seagrass density, submergence and distance from the leading edge. The energy of irregular waves was reduced at all components of the spectra, but reduction was greater at the peak spectral frequency. Energy dissipation factors were largest for waves with small orbital amplitudes and at low wave Reynolds numbers. An empirical model, commonly applied to predict friction factors by rough beds, proved applicable to the P. oceanica bed. However at the lowest Reynolds numbers, under irregular waves, the data deviated significantly from the model. In addition, the wave-induced flow dissipation in the lower canopy increased with increasing wave orbital amplitude and increasing density of the mimics. The analysis of the wave-induced flow spectra confirm this trend: the reduction of flow was greatest at the longer period component of the spectra. Finally, we discuss the implications of these findings for sediment dynamics and the role of P. oceanica beds in protecting the shore from erosion.

Laminar flow heat transfer enhancement in a circular tube having integral transverse rib roughness and fitted with centre-cleared twisted-tape

The experimental friction factor and Nusselt number data for laminar flow through a circular duct having integral transverse ribs and fitted with centre-cleared twisted-tape have been presented. Predictive friction factor and Nusselt number correlations have also been presented. The thermohydraulic performance has been evaluated. The major findings of this experimental investigation are that the centre-cleared twisted tapes in combination with transverse ribs perform significantly better than the individual enhancement technique acting alone for laminar flow through a circular duct up to a certain amount of centre-clearance. This result is useful for the design of solar thermal heaters and heat exchangers.

Gene-expression programming to predict friction factor for Southern Italian rivers

This briefing article presents gene-expression programming (GEP), which is an extension to genetic programming, as an alternative approach to predict friction factor for Southern Italian rivers. Published data were compiled for the friction for 43 gravel-bed rivers of Calabria. The proposed GEP approach produces satisfactory results (R 2 = 0.958 and RMSE = 0.079) compared with existing predictors.

Thermo-fluid characteristics of laminar flow of viscous oil through a circular tube having integral helical corrugations and fitted with centre-cleared twisted-tape

The experimental friction factor and Nusselt number data for laminar flow through a circular duct having integral helical corrugation and fitted with centre-cleared twisted-tape has been presented. Predictive friction factor and Nusselt number correlations have also been presented. The thermohydraulic performance has been evaluated. The major findings of this experimental investigation are that the centre-cleared twisted tapes in combination with integral helical corrugation perform better than the individual enhancement technique acting alone for laminar flow through a circular duct up to a certain amount of twisted-tape centre-clearance.

Heat Transfer Enhancement of Laminar Flow Through a Circular Tube Having Wire Coil Inserts and Fitted With Center-Cleared Twisted Tape

The experimental friction factor and Nusselt number data for laminar flow through a circular duct having wire coil inserts and fitted with center-cleared twisted tape have been presented. Predictive friction factor and Nusselt number correlations have also been presented. The thermohydraulic performance has been evaluated. The major findings of this experimental investigation are the center-cleared twisted tapes in combination with wire coil inserts perform better than the individual enhancement technique acting alone for laminar flow through a circular duct up to a certain amount of center-clearance.