Friction Factor Values Research Articles

Experimental investigation of thermophysical properties and heat transfer characteristics of hybrid nanofluids based on particle size

In heat transfer applications, nanofluids are utilized to increase thermal conductivity and heat transfer coefficient. The difficulty of nanoparticle stabilization in the fluids is a significant problem in heat transfer applications. Heat exchanger materials may wear and erode as a result of the additional nanoparticle. When compared to mono nanofluids, this can be lowered by using hybrid nanofluids. In this work, hybrid nanofluids are used in a radiator under laminar flow at 75?C, and the effect of volume concentration on heat transfer enhancement is investigated. The thermophysical characteristics of hybrid nanofluids are investigated using SiC and Al2O3 at 0.1 vol.% and 0.2 vol.%. The results revealed that a hybrid nanofluid with a higher volume concentration improves heat transfer. Finally, regression analysis for laminar flow is carried out and correlations for experimental Nusselt number and friction factor values were developed. The impact of particle size, flow rate, and temperature on the radiator?s heat transfer enhancement is investigated using hybrid nanofluid at 75?C. It is observed that the size of the nanoparticle has a substantial effect on heat transfer characteristics. It is concluded that using smaller-sized hybrid nanoparticles of Al2O3/SiC-S with less volume concentration enhances heat transfer and reduces radiator size compared to conventional coolants.

Friction factor from velocity profiles in smooth turbulent channel flows

Fluid dynamics plays an important role in many Renewable energies studies, i.e. wind and tidal turbines, wave energy geothermal and solar power, …). Friction factor f is an important parameter for the determination of pressure drop in different processes and systems. In this study, we use DNS data of turbulent smooth channels to evaluate different methods. First, a recalibration of Dean’s correlation (Dean, 1978) is proposed. The aim of the study is to obtain accurate wall friction factors from velocity profiles. On the one hand, we obtained two implicit analytical relations based on the law-of-the-wall: a logarithmic friction relation similar to that of pipes and a linear-logarithmic friction relation. On the other hand, we obtained f from the computation of the average velocity. It is first calculated from the law-of-the-wall and allows a good prediction of f for Reτ > 395 but presents a gap for low Reτ which is related to inaccurate velocities. Low-Reynolds number effect in channel flows has been previously observed in different experimental and computational studies. In order to provide suitable friction factor values, it is important to predict velocities accurately on the overall channel height. We used therefore a more appropriate method which consists to use for y+ < 20 the momentum equation with an eddy viscosity formulation (Absi, 2019) and the log-wake law for high y+ values. This method provides accurate friction factor values and allows good agreement with DNS data.

Friction factor and heat transfer evaluation of cross-corrugated triangular flow channels with trapezoidal baffles

Heat recovery ventilator (HRV) with cross-corrugated triangular flow channels has the advantages of high heat transfer coefficient and high mechanical strength, but it also has the disadvantages of uneven internal temperature distribution and large pressure loss. In this paper, a kind of cross-corrugated triangular flow channel with trapezoidal baffle is proposed, and the influence of the trapezoidal baffle on the flow and heat transfer characteristics of the cross-corrugated triangular flow channel is comprehensively studied by numerical simulation. The Nusselt number (Nu), friction factor (f) and Performance Evaluation Criteria (PEC) value of the flow channel with trapezoidal baffles and the original flow channel were compared. The synergistic effect of the trapezoidal baffle on the flow and heat transfer in the flow channel was analyzed. The results show that the trapezoidal baffle can promote fluid mixing and momentum exchange, thus enhancing the field synergistic effect and improving the comprehensive heat transfer performance of the flow channel. The Nu and f of flow channels with trapezoidal baffles are more than 1.7 and 3.5 times of those without baffles, and the PEC value can be increased by 30%. The data and empirical formulas of this study can provide a guideline for HRVs design.

Experimental Investigation of Pressure Drop Performance of Smooth and Dimpled Single Plate-Fin Heat Exchangers

Passive heat exchangers (HXs) form an inseparable part of the manufacturing industry as they provide high-efficiency cooling at minimal overhead costs. Along with the aspects of high thermal cooling, it is essential to monitor pressure loss while using plate-fin HXs because pressure loss can introduce additional power costs to a system. In this paper, an experimental study was conducted to look at the effects of dimples on the pressure drop characteristics of single plate-fin heat exchangers. To enable this, different configurations of National Advisory Committee for Aeronautics (NACA) fins with smooth surfaces and 2 mm-diameter dimples, 4 mm-diameter dimples and 6 mm-diameter dimples were designed and 3D printed using fused deposition modelling (FDM) of ABS plastic. The depth to diameter ratio for these dimples was kept constant at 0.3 with varied diameters and depths. These were then tested using a subsonic wind tunnel comprised of inlet and outlet pressure taps as well as a hot wire velocimeter. Measurements were taken for pressure differences as well as average velocity. These were then used to calculate friction factor values and to compare the smooth fin to the dimpled fins in relation to their relative pressure drop performance. It was observed that for lower velocities the 4 mm dimples provided minimum pressure drop, with a difference of 58% when compared to smooth fins. At higher velocities, 6 mm dimples increased the pressure drop by approximately 34% when compared to smooth fins. It can also be concluded from the observed data in this study that shallower dimples produce lower pressure drops compared to deeper dimples when the depth to diameter ratio is kept constant. Accordingly, deeper dimples are more effective in providing drag reduction at lower velocities, whereas shallower dimples are more effective for drag reduction at higher velocities.

Effects of Biochar Addition on Rill Flow Resistance

The development of rills on a hillslope whose soil is amended by biochar remains a topic to be developed. A theoretical rill flow resistance equation, obtained by the integration of a power velocity distribution, was assessed using available measurements at plot scale with a biochar added soil. The biochar was incorporated and mixed with the arable soil using a biochar content BC of 6 and 12 kg m−2. The developed analysis demonstrated that an accurate estimate of the velocity profile parameter Гv can be obtained by the proposed power equation using an exponent e of the Reynolds number which decreases for increasing BC values. This result pointed out that the increase of biochar content dumps flow turbulence. The agreement between the measured friction factor values and those calculated by the proposed flow resistance equation, with Гv values estimated by the power equation calibrated on the available measurements, is characterized by errors which are always less than or equal to ±10% and less than or equal to ±3% for 75.0% of cases. In conclusion, the available measurements and the developed analysis allowed for (i) the calibration of the relationship between Гv, the bed slope, the flow Froude number, and the Reynolds number, (ii) the assessment of the influence of biochar content on flow resistance and, (iii) stating that the theoretical flow resistance equation gives an accurate estimate of the Darcy–Weisbach friction factor for rill flows on biochar added soils.

Numerical Investigation of Thermal-Flow Characteristics in Heat Exchanger with Various Tube Shapes

In this study, eight configurations of oval and flat tubes in annular finned-tube thermal devices are examined and compared with the conventional circular tube. The objective is to assess the effect of tube flatness and axis ratio of the oval tube on thermal-flow characteristics of a three-row staggered bank for Re (2600 ≤ Re ≤ 10,200). It has been observed that the thermal exchange rate and Colburn factor increase according to the axis ratio and the flatness, where O1 and F1 provide the highest values. O1 produces the lowest friction factor values of all the oval tubes at all Re, and F4 gives 13.2–18.5% less friction than the other tube forms. In terms of performance evaluation criterion, all of the tested tubes outperformed the conventional circular tube (O5), with O1 and F1 obtaining the highest values. The global performance criterion of O1 has been found to be 9.6–45.9% higher as compared to the other oval tube geometries at lower values of Re, and the global performance criterion increases with the increase in flatness. The F1 tube shape outperforms all the examined tube designs; thus, this tube geometry suggests that it be used in energy systems.

Experimental Study of Flow Characteristics in A Rectangular Gravel Bed Channel

In an open channel flow, the characteristics of flow resistance are greatly affected by the roughness of the base and the walls of the channel. The existence of an object or other material, including gravel, also influenced the resistance of flow, therefore the purpose of this study is to examine the flow characteristics (flow velocity and flow resistance) in gravel open channel by using experimental study. A laboratory study to explore the effect of channel bed in terms of roughness of types of sediment on the hydraulics flow in 8 m length x 40 cm width a rectangular channel is presented. The study consists of an extensive set of rectangular flume experiments for flows with certain slope and sediment bed. The study was using the Before After Control Impact (BACI) method by set up five different scenarios. The results show that the lowest flow velocity (v=0.3041 m/sec) was occurred in the scenario 3 (50%sand and 50% gravel). Based on the Manning’ coefficient (n), it was also found that at the 100% discharge flow condition, the highest value of friction factor (f=0.0780) within 5 scenarios was scenario 3 with the sediment consisted of 50%sand and 50%gravel. Whereas the value of the lowest friction factor(f=0.0652) was scenario 1 with the sediment only gravel within. It concluded that the results gave the lower value of Manning’ coefficient (n) compared to the table of Manning’s coefficient (f= 0.04) for the channel with gravel base condition.

Hydrothermal characteristics of a double flow parabolic trough solar collector equipped with sinusoidal-wavy grooved absorber tube and twisted tape insert

PurposePresent investigation conducts a study on the hydrothermal features of a double flow Parabolic Trough Solar Collector (PTSC) equipped with sinusoidal-wavy grooved absorber tube and twisted tape insert filled with nanofluid. This paper aims to present an effectual PTSC which is comprised by nanofluid numerically by means of finite volume method.Design/methodology/approachThe beneficial results such as pressure drop inside the absorber tube, mean predicted friction factor, predicted average Nusselt number and hydrothermal Performance Evaluation Criteria (PEC) are evaluated and reported to present the influences of numerous factors on studied interest outcomes. Effects of different Reynolds numbers and environmental conditions are also determined in this investigation.FindingsIt is found that using the absorber roof (canopy) can enhance the heat transfer ratio of PTSCs significantly during all studied Reynolds numbers. Also, it is realized that the combination of inner grooved surface, outer corrugated surface and inserting turbulator can improve the thermal-hydraulic characteristics of PTSCs sharply.Originality/valueNovel PTSC (N.PTSC) filling with two Heat Transfer Fluids (HTFs), inner and outer surface corrugated absorber tube, absorber roof and inserting twisted tape (N.PTSC.f) has the highest PEC values among all novel configurations along all investigated Reynolds numbers which is followed by configurations N.PTSC with two HTFs and inserting twisted tape (N.PTSC.e), N.PTSC with two HTFs and outer surface corrugated absorber tube (N.PTSC.b) and N.PTSC with two HTFs and inner surface corrugated absorber tube (N.PTSC.c), respectively. N.PTSC.f Nusselt number values can overcome the high values of friction factor, and therefore is introduced as the most efficient model in the current study.

Effect of particle size on thermophysical and heat transfer properties of Ag nanofluid in a radiator – an experimental investigation

In this experimental and statistical investigation, Silver (Ag) nanoparticles with varying particle sizes of 20 nm with the base fluid of EG and DI water are tested to improve the heat transfer properties of the car radiator. The thermophysical properties are tested at temperatures varying from 35 to 75 °C. Results showed that small nanoparticles had higher thermophysical properties than large nanoparticles. The heat transfer properties along with friction factor characteristics are measured. A total of 20 nm of Ag has higher thermal transfer properties than other nanofluids; it can be concluded that smaller nanoparticles can improve thermal properties and minimize the radiator size compared to traditional coolants. A systematic optimized RSM-based architecture has been developed to define the quantitative estimate of the specific design parameters influencing nanofluid heat transfer properties and friction factor characteristics. Finally, correlations are developed for experimental Nusselt number and friction factor values by regression analysis.

Local & Average Heat Transfer and Friction Factor Characteristics of a Flow through a Helical Wire Coil for Turbulent Flow Conditions

Heat transfer augmentation is essential for numerous industrial applications. The flow through a helical coil is one of the most efficient and effective techniques of heat transfer enhancement due to the provision of a large surface area. The present study is focused on the thermo-hydraulic performance of turbulent flow through a helical coil, made up of copper with a curvature ratio of 0.0519 (d/D) and pitch equal to 50 mm using water as a test fluid. The objective of the present study is to reveal the influence of secondary flow, centrifugal force, and Reynolds number (Re) on local velocity, local heat transfer coefficient in a helical coil. The values of average heat transfer and friction factor at different Re for a flow through a helical coil are compared with corresponding values for a flow through a smooth tube. The numerical results are presented for the Re number range at inlet conditions of the helical coil from 5000 to 20000 in the increment of 2500 under constant heat flux conditions. Numerical results indicate that there is a circumferential variation of local velocity and local Nusselt number (Nu) values concerningthe inner and outer sides of the helical coil. The values of average heat transfer are observed to be 150 to 200% more than the smooth tube values with increased pressure drop.

Effect of straight slot rib height on heat transfer enhancement of nanofluid flow through rectangular channel

The present work deals with the numerical analysis of thermohydraulic performance of Al2O3-H2O based nanofluid flow through straight slot rib rectangular channel. The integration of the artificial roughness on the heated surface and use of the nanofluid as a heat transferring medium makes the present system efficient. Important parameters such as Reynolds number (Re) is selected in the range of 5000–8000, relative slot rib height (HSSR/DH) in the range of 0.060–0.084 and other parameters have been fixed are spanwise pitch (Pspan/HSSR) 4.07, streamwise pitch (PStream/HSSR) is 7.6, nanoparticle concentration (∅) is 3% and nanoparticle diameter (nd) of 40 nm. The analysis resulted in the maximum value of Nusselt number (Nurough) and friction factor (frough) at value of Relative height ratio (HSSR/DH) of 0.084 and 0.06, respectively. It is found that the value of relative slot rib height 0.084 delivers the highest thermohydraulic performance (η) in comparison to other values of geometric parameters.

Heat transfer augmentation using periodically spherical dimple-protrusion patterned walls of twisted tape

The heat transfer performances of pipes with twisted tape inserts having periodically spherical dimple-protrusion patterned walls are numerically investigated by Ansys Fluent under a constant heat flux of 5 W/cm2. The inserts having three different densities (N = 0, 30, and 45) and three different kinds of arrangement (composed of only dimples, only protrusions, and a combination of dimples and protrusions) with a constant twist ratio of 3 were tested for Reynolds numbers (Re) within the range from 3000 to 27000. Comparing the turbulence models proposed the validated realizable k-ϵ model coupled with enhanced wall function to employ on the numerical simulations. While the highest Nusselt number (Nu) and friction factor (f) values for the presented study were found for the dense protruded twisted tape (D-PT) arrangement at Re values lower than 18000 and for dense dimpled-protruded twisted tape (D-DPT) arrangement for the Re greater than 18000, dimpled-protruded twisted tape (DPT) and dimpled twisted tape (DT) sequences reached the lowest f values of 0.365 and 0.322 at Re = 3000, respectively. D-DPT and D-PT sequences reached the highest thermal performance factor (TPF) values of 1.508 and 1.478 at Re = 3000, respectively. All patterned twisted tapes performed better Nu than conventional twisted tapes in the analyzing range and performed better TPF than typically twisted tapes in the Re region of less than 6000.

Experimental investigation of the thermal performance in a single-component two-phase flow in multistream multi-fluid plate-fin heat exchangers

This paper focuses on evaluating the effects of flow rate and temperature changes of hot and cold fluid flows in multistream multi-fluid plate-fin heat exchangers with a single-component two-phase flow in the middle heat exchanger. This three-fluid heat exchanger included three layers with offset strip and wavy fin configurations. In the adjacent heat exchanger with offset strip fins, hot and cold fluids were flowing, while the middle heat exchanger with wavy fins contained a single-component two-phase flow (condensed vapor). The Nusselt number, friction factor, the thermal performance factor, and the heat transfer surface contribution of the middle heat exchanger with each of the adjacent heat exchangers, were obtained using the measured experimental data. The results indicate that the two-phase Reynolds number was between 500 and 1800, and the vapor quality varied in the range of 0.17–0.56. Also, the heat transfer surface contribution of the adjacent cold and hot fluids was between 0.18 and 0.5. The two-phase flow in the wavy channel has a wavy and stratified pattern. The examinations showed that raising the Reynolds number of hot and cold fluids, respectively, led to maximum 13.8 % and 9.5 % of reduction in the vapor quality, 8.8 % and 9 % of increase in the two-phase Nusselt number, and 18 % and 12 % of reduction in the average value of friction factor. The domain change in the two-phase vapor quality, the two-phase fluid heat transfer surface contribution, and the flow pattern determination parameters including the dimensionless mass parameter and the Lockhart-Martinelli parameter was 33.67 %, 80.81 %, 32.72 %, and 19.09 %, respectively. As the Reynolds number of the cold fluid was changed, the variation domain of these parameters was higher compared to when the Reynolds number of the hot fluid was altered. Increasing the dimensionless temperature of the hot and cold raised the vapor quality by 12–16 %. The experimental results revealed that by decreasing the temperature of adjacent fluids and increasing their Reynolds number, the thermal performance factor of the two-phase flow was increased.

Heat transfer, friction factor and thermal efficiency results of air flowing through three sides concave dimple roughened duct

The present work is an outcome of experimental investigations conducted upon three sides concave dimple roughened solar collector. The results reveal that three sides roughened solar air heaters have high values of heat transfer compared to one side roughened ones in the range of 25–86 % for varying relative roughness pitch and 21–81% for varying relative roughness height. The rise in friction factor of three sides over one side roughened duct for varying relative roughness pitch and relative roughness height was 11–34% and 15–41%, respectively. Maximum Nusselt number is obtained at a relative roughness pitch of 12 and a relative roughness height of 0.036. Maximum values of friction factor are obtained at a relative roughness pitch of 8 and a relative roughness height of 0.045. Augmentation in thermal efficiency in three sides over one side duct is 44–56 % for a varying relative roughness pitch and 39–51 % for a varying relative roughness height.

Analysis on flow structure and improvement of heat transfer in 3D circular tube with varying axial groove turbulator configurations

AbstractUsing passive devices are an efficient method to enhance streamline behavior when liquid flows through the circular pipe. The interrupted structure groove is usually used to change the flow patterns. In this analysis, a heat performance numerical technique is applied to study the characteristics of fluid flow and heat transfer of the circular pipe using different axial groove geometrical configurations with different axial groove numbers, including 2, 3, and 4, under different conditions. The number of annular grooves and circumferential positions are the important parameters to analyse with varying operating conditions, with the Reynolds number (Re) range from 1500 to 23,000. A three‐dimensional coordinate pipe system is applied using tetrahedron grids. The discretization equations are obtained by deriving algebraic approximations to integral conservation equations. Results observed that using this type of passive method has a low effect on pressure dope compared to the normal one (smooth pipe). The flow change occurs near and closed to the axial groove parameters. Moreover, the Nusselt number (Nu) value for the groove turbulators was higher than the normal one, about 14.5%–21%. The friction factor (f) value for the groove turbulators was higher than the normal one, were about 7.5%–24%. Most friction losses are caused by dynamical pressure dissipation owing to more viscous losses closed to the wall surfaces. The improvement of heat performance using this type of passing method was more than 1.2%.

CFD investigation on characteristics of heavy crude oil flow through a horizontal pipe

Transportation of heavy crude oil via pipelines possesses many technological issues that are inherently flow related. Accurate prediction of flow characteristics is an essential step for a reliable piping design of transporting the crude oil. A rheology-based Computational Fluid Dynamics (CFD) model of the Iraqi heavy crude oil flow through a horizontal pipe (1 m length of 3/4 in. inside diameter) was developed using the commercial software Ansys 15 Fluent. By using power law rheological model, the Iraqi heavy crude oil exhibits a non-Newtonian dilatant behavior over the examined shear rate range of 1–40 s−1. The proposed axi-symmetric CFD model identifies velocity profile and generates values of friction factor, which are validated with experimental measurements. Additionally, wall shear stress and entrance length were numerically predicted and compared with well-established correlations from the literature for Non-Newtonian flow. Detailed results of the CFD model exhibited a reliable prediction of the characteristics of heavy crude oil flow.

Experimental study of heat transfer and friction factor in a double pipe heat exchanger using twisted tape with dimple inserts

ABSTRACT The present experimental work deals with heat transfer and friction factor analysis of water flowing in double pipe heat exchanger with dimpled twisted tape inserts. The investigated parameters are twist ratio of 5.5, Reynolds number (Re) of 6000–14,000, dimple diameter (D) of 3 mm, 5 mm, and 7 mm and dimple diameter-to-depth ratio (D/H) of 1.5, 3, and 6. Nine dimpled twisted tapes were tested and a comparison was made between these twisted tapes and plain twisted tape along with plain tube. Nusselt number (Nu) is found to be maximum (113.68 at Re 14,000 and 59.56 at Re 6000) for D = 5 mm and D/H = 3. This highest value of Nu is 1.50–1.82, 1.37–1.46, 1.24–1.19 and 1.18–1.10 times greater than the values for Nu for plain tube, twisted tape without dimple, dimpled twisted tape with D = 3 mm (D/H = 3) and dimpled twisted tape with D = 7 mm (D/H = 3) respectively. Based on the analysis, the friction factor (f) is found directly proportional to the depth and diameter of the dimple, consequently, maximum value of friction factor (f) is found at 7 mm diameter and D/H 1.5. In addition, it is observed that maximum value of performance evaluation criteria (PEC) is found at dimple diameter of 5 mm (D/H = 3). The correlations for heat transfer and friction factor have been established in terms of dimple geometry (D and D/H) and Reynolds number (Re).

Explicit Equations for Estimating Resistance to Flow in Open Channel with Moveable Bed Based on Artificial Neural Networks Procedure

The resistance to flow in an open channel is associated with the value of the Darcy-Weisbach friction factor f. For natural channels with a movable bed, the f value depends on the grain size of the bed materials and the bedforms, such as ripple, dune, or anti-dune. The total resistance to flow is the sum of the resistance due to grain roughness and bedform. Several researchers have proposed several graphs to determine the friction factor value due to the bedforms. Still, using these graphs requires graphical interpolation, which is inconvenient and difficult to apply to the flow and sediment transport calculation. This study proposes two explicit equations, ANN models 1 and 2, to compute the friction factor due to the bedform based on artificial neural networks (ANN) procedure. The data used to build the equations were obtained by digitizing the graph proposed by Alan and Kennedy. The explicit ANN equations are in the form of a series of hyperbolic tangent functions. The resulting equations can predict the friction factor value due to bedform satisfactorily.

Experimental implementation of thermal enhancement performance of air heat exchanger’s pipes utilizing unconventional turbulator

Heat exchangers are widely used in industry, however, raising their performance are important for the variety of applications. Consequently, efficiency improvement associated with low production cost is considered in this experimental work. The current study aims to enhance the rate of heat transfer in pipe-type heat exchangers experimentally by using a novel nozzle as a turbulator. The cross-sectional shape of the nozzle is hexagonal, and the diameter ratio DR is equal to 0.5. Constant heat flux was maintained in the vicinity of the section of the test tube, while the working fluid was pumped into the open system at six discrete Reynolds number values ranging from 6000 to 19500. To investigate the effect of distance among the pieces, three turbulators with different numbers were assigned and named as (N=4, 5 and 6). The results indicated an increase of 172 %, 194 % and 216 % of the heat transfer rate for cases 4, 5 and 6 respectively comparing to the benchmark tube. On the other hand, the friction factor values increased remarkably due to the inserting of turbulators by about of 722.9 % for N=4, 823.9 % for N=5 and 886.7 % for N=6 compared to a plain tube case. Moreover, it has been established that with the insertion of 6 pieces two enhancements was observed; heat transfer rate and thermal performance, where, thermal performance of all cases exceeds unity (maximum thermal performance of 1.62 has been obtained by inserting 6 pieces of hexagonal nozzles turbulators). A comparison with another types of vortex generators shows the gap between the turbulator and heated surface offers a solution for problems occurred in the pipes of heat exchanger. The study therefore suggests a wider practical implementation of the turbulators

Heat transfer augmentation in a circular tube fitted with tri-partition flow splitters

This paper focuses on the numerical and experimental study of a heated tubes heat transfer and flow characteristics with a novel tri-partition flow splitter under forced convection. A low thermal conducting fluid like air is considered to be a working fluid. Tri-partition flow splitters were manufactured with different thickness and arranged alternatively with 180° rotations to change the direction of airflow. Seven Reynolds number in the range of 5000–15,000 were considered as an operating parameter. The results of the plain tube are validated with the standard Dittus–Boelter and Gnielinski equations available in literature. In addition, the experimental results with tri-partition flow splitters are used to validate the computational fluid dynamics model used to examine the flow characteristics in the heated tube. The overall thermal performance enhancement is evaluated by the performance evaluation criteria (PEC). The results showed that the Nusselt number (Nu) is increased with an increase in Reynolds number. The maximum PEC 1.98 is obtained for 2 mm thickness splitters. The highest Nusselt number (Nu = 271.99) is found for 10 mm thickness with a higher friction drop. Friction factor values are found dropped by reducing the thickness of the splitters.