Entrance Region Of Pipe Research Articles

Reproduction of air velocity in the entrance region of the test pipe in a wind tunnel

The airflow development in the pipe, in the entrance region of the wind tunnel located in the Lithuanian Energy Institute, the laboratory of Heat Equipment Research and Testing is investigated to analyze the conditions for the reproduction of air velocity values. The analysis is performed to reveal undeveloped flow conditions where the calibration of the devices is usually made, the entrance region of the pipes, or free stream from the nozzles. In this study, different flow regimes have been investigated using different air velocity measurement methods. Experimental and numerical results clearly show the features of the developing flow. They both demonstrate the stable core of the velocity profile up to 5 D in the pipe and ≤1 D from the entrance into the free stream in the testing chamber. Ultrasonic anemometer (UA) installed in the aerodynamic test facility shows reliable and highly comparable results with another non-intrusive device – laser Doppler velocimeter (LDA) in a range of velocities from 0.05 m/s up to 30 m/s. UA integrated into the wind tunnel is not found to be used for metrological issues for air velocity. Due to the fast response, they both enabled to analyze fluctuations in the flow. Local vortices identified in the flow have influenced the low-frequency fluctuations and the scatter of measurement results. Moreover, high-frequency fluctuations found in the flow originated from the flow turbulence and might be due to the electronic or acoustic noise. The stabilization of the entrance region in the pipe influences the mean value of air velocity, the transversal distribution of velocity and the development of axial velocity in different test sections of the pipe in a wind tunnel. Along with the recirculation zones in cavities of ultrasonic transducers, these factors are essential that make an impact on the reproduction of air velocity value.

Bingham Fluid Flow in the Entrance Region of a Pipe

Abstract Laminar Bingham fluid flow in the entrance region of a circular pipe is investigated using a momentum integral model. The fully developed flow is uniform in the core region, while the velocity changes in the annular part of the cross section of the pipe. The inlet-filled region concept is adopted. In the inlet region, the boundary layer thickness increases until the size of the plug flow area reaches the fully developed flow size. The model converges to the fully developed solution in the filled region. The model provides the velocity, pressure drop, and skin friction coefficient profiles. The pressure drop results are in good agreement with published experimental data. The flow results asymptotically converge to the fully developed values. In addition, the results are consistent with published Newtonian fluid flow experimental data and theoretical results for the boundary layer thickness, pressure drop, and centerline velocity for small values of the Bingham number.

DNS study on turbulent heat transfer induced by turbulence at the inlet in entrance region of pipe

DNS study on turbulent heat transfer induced by turbulence at the inlet in entrance region of pipe

Numerical study of heat transfer enhancement in the entrance region for low-pressure gaseous laminar pipe flows using Al2O3–air nanofluid

The gaseous low-pressure nanofluid flow of a steady-state two-dimensional laminar forced convection heat transfer in the entrance region of pipes is numerically investigated. Such flows are of interest for many engineering applications like the nuclear reactor and electronic equipment cooling, heat exchangers, and many others. Physical parameters considered in this study are Reynolds number ( Re), Prandtl number ( Pr), nanosolid particles volume fraction [Formula: see text], Knudsen number ( Kn), and the aspect ratio ( AR). These parameters ranges are as follows: [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text], and [Formula: see text]. The outcome of this study shows that by increasing Kn, velocity slip and temperature jump at the solid boundaries increase. In addition, heat transfer is enhanced by dispersing Al2O3 nanoparticles in the base low-pressure gaseous flow. Results show that there is no effect of the nanoparticles volume fraction with values below 0.03 on the average Nusselt number. The average Nusselt number increases [Formula: see text] as the value of the nanoparticles volume fraction exceeds 0.03. For instance, at Re = 1000, results show that when dispersing Al2O3 nanosolid particles with volume fractions of 0.3 and 0.5; there is an enhancement in the average Nusselt number of 30.35% and 136.74%, respectively, when compared to the case of dispersing Al2O3 nanosolid particles of 0.03 volume fraction.. Moreover, it is concluded that the average Nusselt number [Formula: see text] depends directly on Reynolds ( Re), Prandtl ( Pr) numbers, and the nanoparticles volume fraction [Formula: see text] and inversely on Knudsen number ( Kn) and the aspect ratio ( AR) for the investigated range of parameters considered in this study. Finally, a correlation of Nusselt number among all the investigated parameters in this study is proposed as [Formula: see text].

Numerical study of turbulent nanofluid flow at the entrance region of a ribbed pipe

In this paper, we perform a numerical study on the heat transfer and pressure drop in hydraulically and thermally developing turbulent flow of nanofluid through an internally ribbed pipe. The effects of volume fraction of nanoparticles and the distance between the ribs are investigated on the heat transfer and skin friction coefficients at the entrance region of the pipe. The set of governing equations followed by a two-layer zonal turbulence model are solved numerically by a velocity-pressure coupling algorithm based on finite-volume method. Moreover, available empirical relations are used to calculate the nanofluid properties in terms of the nanoparticles and the base fluid. The obtained results illustrate that increasing the volume fraction of nanoparticles makes the thermal entrance length decrease and consequently, the heat transfer increases. It reveals that 10% increase in the volume fraction of nanoparticles causes about 15% rise in average Nusselt number. In addition, it is found that the friction factor rises by increasing the volume fraction of nanoparticles compared with turbulent flow of the base-fluid. Also, the average Nusselt number in nanofluid flow increases with the interval between the ribs compared with pure-fluid flow.

The Entrance Region of Circular Pipes Revisited

The laminar flow in the entrance region of pipes having a circular cross section is investigated by the use of finite element solutions to the full Navier-Stokes equations in cylindrical coordinates. Because these solutions cover the complete three-dimensional geometry the usual development length is no longer a very interesting parameter as explained herein. The velocities and pressures are determined throughout the pipe and presented in graphic form.

J057044 円管内共存対流温度助走区間の乱流熱伝達構造(〔J057-04〕乱流における運動量、熱、物質の輸送現象(4))

In order to investigate and observe turbulent heat transfer in the entrance region of combined pipe flow, direct numerical simulations (DNS) are carried out. The DNS results show the quantitative statistics of turbulent heat transfer in the pipe flow in detail. In the present DNS, since the pipe is uniformly heated at the wall, both stable and unstable thermal stratifications are formed in the pipe, i.e., the wall temperature is higher than the temperature of inlet fluid. The velocity field is affected by the thermal stratifications, in which the secondary flow clearly appears in the pipe, while the thermal field develops in the entrance region of pipe. The DNS clearly demonstrates distributions of Reynolds shear stress and turbulent heat flux in the entrance region of combined pipe flow.

Transient conjugated heat transfer in thick walled pipes with convective boundary conditions

Transient conjugated heat transfer for laminar flow in the thermal entrance region of pipes is investigated by considering two dimensional wall and axial fluid conduction. The problem is handled for an initially isothermal, infinitely long, thick-walled and two-regional pipe for which the upstream region is insulated and solved numerically by a finite difference method for hydrodynamically developed flow with a step change in the ambient fluid temperature in the heated downstream region. A parametric study is done to analyse the effects of five defining parameters namely, wall thickness ratio, wall-to-fluid conductivity ratio, wall-to-fluid thermal diffusivity ratio, the Peclet number and the Biot number.

Forced-convection heat transfer in the entrance region of pipes

The steady-state local heat transfer characteristics for air flowing turbulently inside an electrically heated pipe have been determined experimentally over a range of Reynolds numbers from 12000 to 56000. A surface-boundary heating condition of uniform heat flux was employed. The entrance configuration of the heat transfer pipe was either a similar pipe of L D = 50, 30, 15 ; or a sharp edge (i.e. L D = 0 ). Based on the obtained experimental data, a correlation for predicting the rate of heat transfer was developed.

NUMERICAL SOLUTION OF GRAETZ PROBLEM WITH AXIAL CONDUCTION

Heat transfer in the thermal entrance region of pipes is analyzed by the finite-difference method including the effect of axial fluid conduction. A hydrodynamically developed flow through a two-region pipe is investigated for constant surface temperatures by a step change and for insulated upstream and uniform wall heat flux in the downstream region. The rate of convergence is enhanced by discretizing the governing differential equation by an exact profile obtained from the analytical solution of the one-dimensional conduction-convection problem.

An assessment of the accuracy of numerical solutions to the graetz problem

It has been well documented in prior studies that numerical solutions to the classical Graetz problem in the entrance region of pipes produce estimates of Nusselt number that are greatly in error. In this report, we examine this problem and attempt to provide plausible explanation for the discrepancy.

Unsteady thermal entrance heat transfer of power-law fluids in pipes and plate slits

An instant-local similarity method is proposed to analyze the unsteady state Graetz problems. Unsteady heat transfer for fully-developed laminar flow of power-law non-Newtonian fluids in the thermal entrance region of pipes and plate slits, with viscous dissipation considered, is studied. For the unsteady thermal entrance heat transfer problems, only large Graetz numbers (small normalized axial distance) are concerned and the normalized time from transient up to steady state is of order 10 −1; therefore, the instant-local similarity approach gives results of high accuracy. The effects of the flow index, viscous dissipation and Graetz number on the heat transfer rate are demonstrated with numerical solutions. The corresponding steady-state Graetz problems are studied by the local similarity method whose solutions agree very well with the extended Leveque solutions particularly for large Graetz number and Brinkman number.

Joule‐Thomson effects on turbulent graetz problem for gas flows in pipes with uniform wall temperature

AbstractThe Joule‐Thomson effect is known to be important in arctic gas pipelines. The Joule‐Thomson effects on forced convective heat transfer in the thermal entrance region of pipes with uniform wall temperature are studied for steady fully developed turbulent gas flows by the Graetz method. Thermal entrance heat transfer results are presented for Prandtl number 0.72, Reynolds number 105 and Brinkman number ± 0.1, ± 1.0 with Joule‐Thomson parameter Jμ ranging from 0 to 1.0 to cover the possible range in practical applications. Bulk temperatures and Nusselt numbers are also presented for fully developed flow with Reynolds numbers from 5 × 103 to 106. For given Prandtl and Reynolds numbers, the asymptotic Nusselt number is found to be dependent on the Joule‐Thomson parameter only and is independent of Brinkman number. The fully developed bulk temperature is a linear function of Brinkman number and a linear relationship exists between the bulk temperature parameter (‐θbf/Br) and the Joule‐Thomson parameter Jμ for given Prandtl and Reynolds numbers.

Effect of Temperature-Dependent Viscosity on Laminar Forced Convection in the Entrance Region of a Circular Pipe

Predictions and measurements are reported of heat transfer to a viscous oil at uniform wall-heat flux in the entrance region of a pipe of circular cross-section. This work extends an earlier investigation of isothermal flow to simultaneous development of the hydrodynamic and thermal boundary layers where the extent of viscosity variation is influenced both by the applied heat flux and the viscous heat generation. The effect of the contribution of viscous heating to the delay in flow development at high Prandtl numbers is also discussed.

Deep Ocean Work Boat (DOWB), an Advanced Deep Submergence Vehicle

4 Metzner, A. B., of Fluids, Sec. 7, Handbook of Fluid Dynamics, edited by V. L. Streeter, McGrawHill, New York, 1961. 5 Wells, C. S., Jr., On the Shear Flow of an ElasticoViscous Fluid, Paper 64-36, 1964, AIAA; also AIAA Journal, Vol. 3, No. 10, Oct. 1965, pp. 1800-1805. 6 Giles, W. B., Viscoelastic Boundary Layers with Roughness, Rept. 64GL51, March 11, 1964, General Electric Co. 7 Fabula, A. G., Toms Phenomenon in the Flow of Very Dilute Proceedings Fourth International Congress of Rheology, Part 3, Interscience, New York, 1965, pp. 455-479. 8 Hoyt, J. W. and Fabula, A. G., of Additives on Fluid Friction, NAVWEPS Rept. 8636, ASTIA AD 612 056, Dec. 1964, Naval Ordnance Test Station, China Lake, Calif. 9 Shin, H., of in by Dilute Polymer Doctoral thesis, June 1965, Massachusetts Institute of Technology; also Transactions of the Rheological Society, Vol. 10,1966, pp. 335-351. 10 Gadd, G. E., Turbulence Damping and Reduction Produced by Certain Additives in Water, Nature, May 1, 1965, pp. 463-467,. 11 Patrick. H. V. L., of High Molecular Weight Polymer Additives on the Performance of a Conical Diffuser, Paper 66-658, June 1966, AIAA. 12 Lang, T. G., Drag of Blunt Bodies in Polymer Solutions, 66-WA/FE-33, 1966, American Society of Mechanical Engineers New York. 13 Ripken, J. F. and Pilch, M., Non-Newtonian Pipe Frictio Studies with Various Dilute Polymer Water Rept. 7] BuShips Contract S-R009-01-01, June 1964, St. Anthony Fall Hydrodynamics Lab., University of Minnesota. 14 Pruitt, G. T. and Crawford, H. R., Effect of Molecula Weight and Segmental Constitution on the Reduction c Water Soluble Polymers, DTMB Contract NONR-4306(00 ASTIA AD 625 801, April 1965, The Western Co. 15 Schlichting, H., Boundary Layer Theory, 4th ed., McGra Hill, New York, 1960, pp. 505, 506. 16 Ross, D., Turbulent Flow in the Entrance Region of Pipe, Paper 54-H-89, 1954, American Society of Mechanical Ei gineers, New York. 17 Shapiro, A. H., Siegel, R., and Kline, S. J., Factoi in the Laminar Entry Region of a Smooth Tube, Proceeding 2nd National Congress of Applied Mechanics, 1954, America Society of Mechanical Engineers, New York. 18 Astarita, G. and Nicodemo, L., Velocity Distributions an Normal Stresses in Viscoelastic Pipe Flow, AlCh Journal, Vol. 12, No. 3, May 1966, pp. 478-483. 19 von Kdrma'n, T., On Laminar and Friction TM1093, Sept. 1946, NAG A; also Zeitschrift fur Mathematik u? Mechanik, Vol. 1, No. 4, Aug. 1921.