Turbulent Flow In Circular Tube Research Articles

Heat transfer augmentation for turbulent flow in circular tubes using inserts with multiple curved vortex generator elements

Measurements of local heat transfer coefficients on the circumference of a circular tube, fitted with two modified versions of an already existing axially inline curved Vortex Generator (VG) element insert are reported in this study. Measurements for average pressure drop are also presented and the air was used as the working fluid. The first modified insert is manufactured with a pair of two VG elements spaced symmetrically 180° apart but with the subsequent pairs along the axis staggered at an angle of 90°. The geometric features for the staggered insert were identical to the optimal one for the existing inline one. The staggered insert gives a more uniform circumferential and axial Nusselt number distribution. The ratio of the highest and lowest Nusselt number values for the staggered and inline case is equal to approximately 1.3 and 1.6 respectively. The average Nusselt number ratio at constant Reynolds number (10,000 < Re < 45,000) and constant pumping power however remained the same at about 2.6 and 1.5 respectively. The second modified insert was manufactured with three vortex generators placed symmetrically 120°apart at each axial location with all subsequent locations in line with one another. Two angles of attack 30°and 45° were used for the vortex generator elements and the pitch to projected length ratio of the VGs was varied between 1.6 and 12.2. The average heat transfer coefficient augmentation ratio using this insert at the equal Reynolds number and constant pumping power was obtained in the range of 1.5–5.5 and 1.0 - 1.8, respectively. The experimental data is presented in the form of empirical correlations for Nusselt number, and friction factor as a function of tube flow parameters, and non-dimensional geometrical parameters of VG inserts, which predict the data with an accuracy equal to ±20 %.

Heat transfer coefficients of laminar, transitional, quasi-turbulent and turbulent flow in circular tubes

Several well-known correlations to determine the heat transfer coefficients of quasi-turbulent and turbulent flow in smooth tubes are available in literature. However, when these correlations are compared with each other, the results vary over a considerable range. The purpose of this study was therefore to conduct heat transfer and pressure drop experiments in the quasi-turbulent and turbulent flow regimes and to develop an accurate heat transfer correlation that can be combined with recently developed laminar and transitional flow correlations to obtain a single correlation that is valid for all flow regimes. A total of 1180 experimental data points were collected from careful experiments that were conducted ourselves using two different test section configurations. The first test section configuration consisted of a tube-in-tube test section on which the wall temperatures were obtained either indirectly using the Wilson plot method or by direct surface temperature measurements. The second test section configuration consisted of single tubes being electrically heated at a constant heat flux. Different test sections covering a range of tube diameters from 4 mm to 19 mm and a range of tube lengths from 1 m to 9.5 m, were used. Experiments were conducted from a Reynolds number of 2445, which corresponded to the start of the quasi-turbulent flow regime, up to 220,800, which was well into the turbulent flow regime. Water, as well as different concentrations of multi-walled carbon nanotubes, were used as the test fluid, which gave a Prandtl number range of 3–10. A new correlation was developed that could estimate 95% of all the experimental data points within 10% and an average deviation of <5%. Furthermore, it was able to predict experimental data in literature with a Prandtl number range of 0.47–276 and Reynolds number range of 3000–401,600 with an average deviation of 14%.

Numerical investigation of heat transfer in supercritical CO2 and water turbulent flow in circular tubes

This study presents a numerical investigation of heat transfer in supercritical CO2 and water turbulent flow in a circular tube. To solve two-dimensional grid systems, RSM turbulent models were used. The effect of mass flow rate and pressure on heat transfer coefficient, flow acceleration and buoyancy parameter were investigated. The numerical results demonstrated that increasing the mass flux causes to decrease buoyancy and flow acceleration. In addition, an increase in pressure results in a decrease in buoyancy and flow acceleration terms. Finally, a new correlation is proposed to enumerate the effect of flow acceleration and buoyancy on heat transfer phenomena in a vertical upward flow of a supercritical fluid.

Improvement of Prandtl mixing length theory and application in modeling of turbulent flow in circular tubes

In order to correctly predict tube cross section time-smoothed velocity distribution, friction factor and mass transfer behavior, two models for turbulent flow in circular tubes based on classical Prandtl mixing length theory and a modified mixing length were established. The results show that the modified mixing length includes the introduction of a damping function for the viscous sublayer and the second-order derivative to approximate eddy velocity. The calculated dimensionless time-smoothed velocity from the model based on Prandtl mixing length is much better than the result from the concept of eddy viscosity. The calculated eddy viscosity from the model based on modified mixing length is much better than the result from the model based on the classical Prandtl mixing length theory. And the friction factor calculated from the model based on the modified mixing length agrees well with the reported empirical relationships.

97/05008 Heat transfer and friction characteristics of turbulent flow in circular tubes with twisted-tape inserts and axial interrupted ribs: Zhang, Y. M. et al. Enhanced Heat Transfer, 1997, 4, (4), 297–308

97/05008 Heat transfer and friction characteristics of turbulent flow in circular tubes with twisted-tape inserts and axial interrupted ribs: Zhang, Y. M. et al. Enhanced Heat Transfer, 1997, 4, (4), 297–308

Heat Transfer and Friction Characteristics of Turbulent Flow in Circular Tubes with Twisted-Tape Inserts and Axial Interrupted Ribs

Heat Transfer and Friction Characteristics of Turbulent Flow in Circular Tubes with Twisted-Tape Inserts and Axial Interrupted Ribs

Comparison of Turbulent Thermal Entrance Regions for Pipe Flows With Developed Velocity and Velocity Developing From a Sharp-Edged Inlet

The thermal entrance region for turbulent flow in circular tube has been analytically investigated for two types of velocity distributions. In one case, the flow is hydrodynamically developed throughout the entire length of the thermal entrance region. In the other, the velocity is uniform at the inlet of the heated section, so that there is a hydrodynamic development of the flow which occurs simultaneously with the thermal development. The latter situation is rarely, if ever, encountered in practice and is, in fact, difficult to achieve in a laboratory experiment. The effect of various types of velocity distributions on the turbulent heat transfer coefficients in the thermal entrance region of an isothermal-walled tube was investigated experimentally by Boelter et al. The different velocity distributions were attained by use of different configurations of the inlet of the heated section. As noted in Kays and Crawford, the insufficiencies of the experimental technique used by Boelter et al. suggest that the results be regarded as qualitative rather than quantitative. The objective of the present research is to provide definitive thermal entrance region heat transfer results for an isothermal-walled tube for two types of turbulent velocity distributions that are of practical relevance. The two setsmore » of results will be compared to yield the quantitative response of the thermal entrance region to the nature of the velocity condition at the tube inlet. The work to be reported here is experimental and covers the Reynolds number range from approximately 5,000 to 85,000.« less

Turbulent heat transfer in a circular tube with circumferentially varying thermal boundary conditions

An analysis has been carried out to determine the heat-transfer characteristics for turbulent flow in circular tube with circumferentially varying boundary conditions of first and second kind. Fully developed flow and heat transfer is considered. Contrary to prior investigations of this problem, anisotropy of turbulent energy transport has been taken into account employing theoretical results for eddy diffusivity in the various directions from an analysis of Ramm and Johannsen which are shown to be in satisfactory agreement with recent experimental data. Results for heat transfer at both constant and varying boundary conditions are presented over a wide range of Reynolds number (if10 4⩽ Re ⩽10 6) and Prandtl number (0 ⩽ Pr ⩽ 100) and compared to empirical data.