Laminar Flow In Circular Tube Research Articles

Comprehensive heat transfer performance analysis of liquid metal based nanofluid laminar flow in circular tube

Liquid metal based nanofluid is expected to be the ultimate coolant, however, till date a comprehensive heat transfer analysis of this fluid flow is still lacking. The paper presents the comprehensive analysis of heat transfer, entropy generation and performance evaluation of liquid metal nanofluid laminar flow in a circular tube subject to constant wall heat flux, in which the two-phase mixture model is adopted to simulate the nanofluid flow, and three types of nanoparticles (namely Alumina (Al2O3), Diamond (Diam), Carbon nanotubes (CNT)) is considered. The computational results show that, as nanoparticles volume fraction increases, the average heat transfer coefficient of Ga-Diam and Ga-CNT increases, but that of Ga-Al2O3 decreases. The corresponding total entropy generation of Ga-Diam and Ga-CNT decreases, and that of Ga-Al2O3 increases. Particularly, as Re = 1000 and αp=0.06 the average Nusselt number of nanofluids Ga-CNT, Ga-Diam and Ga-Al2O3 relative to that of pure liquid metal Ga are increased by 17.3%, 16.1% and −2.1%, respectively. In general, the liquid metal based nanofluid with high concentration carbon nanotubes nanoparticles is a better choice for heat transfer enhancement, however, from the view point of energy utilization efficiency low concentration nanoparticles is more suitable.

Heat Transfer Enhancement for Laminar Flow in Circular Tubes with Twisted-Tape Inserts

This paper presents the results of a comprehensive study of heat transfer and pressure drop for the laminar flow of water in circular tubes with twisted-tape inserts. Three different twist ratios and tape thicknesses were considered. Experiments were performed for two different tube diameters with Reynolds numbers ranging from 500 to 2200 under constant-wall-temperature boundary condition. The fully developed Nusselt number and friction factor were found to be influenced by the twist ratio and the tape thickness-to-diameter ratio. The Nusselt number increases with a decreasing twist ratio, increasing tape thickness, and increasing Reynolds number; whereas the friction factor increases with an increasing twist ratio and tape thickness. Correlations for the Nusselt number and friction factor are developed for a tube with inserted-tape inserts. The present correlations consider the effects of the tape thickness-to-diameter ratio and the twist ratio on the Nusselt number and friction factor. The thermal-hydraulic performance ratio decreases with an increasing Reynolds number and twist ratio, whereas the tape thickness has a slight effect on the thermal performance ratio.

Laminar flow in circular tube with internal solidification of a binary mixture

Laminar flow heat transfer in circular tube with internal solidification of a binary mixture of paraffin is investigated numerically. The problem of the solidification process is formulated using the enthalpy–porosity based method. The influence of various parameters such as: wall temperature, inlet maximal velocity, initial temperature and initial concentration of the binary mixture, on the solidification process is analyzed in detail. It is found that the initial temperature has less important effect on the solidification progress than the wall pipe temperature, the initial concentration and the inlet velocity of the binary mixture.

Accuracy enhancement of thermal dispersion model in prediction of convective heat transfer for nanofluids considering the effects of particle migration

A thermal dispersion model is utilized for simulation of convective heat transfer of water-TiO2 nanofluid for laminar flow in circular tube. Concentration distribution at cross section of the tube was obtained considering the effects of particle migration, and this concentration distribution was applied in the numerical solution. Numerical solution was done at Reynolds numbers of 500 to 2000 and mean concentrations of 0.5 to 3%. Meanwhile, an experimental study was conducted to investigate the accuracy of the results obtained from the numerical solution. Non-uniformity of the concentration distribution increases with raising mean concentration and Reynolds number. Thereby, for mean concentration of 3%, at Reynolds numbers of 500 and 2000, the concentration from wall to center of the tube increases 2.6 and 30.9%, respectively. In the dispersion model, application of non-uniform concentration distribution improves the accuracy in prediction of the convective heat transfer coefficient in comparison with applying uniform concentration.

Flow transitions and combined free and forced convective heat transfer in a rotating curved circular tube

The simultaneous effects of curvature, rotation and heating/cooling of the tube complicate the flow and heat transfer characteristics beyond those observed in the tubes with simple curvature, rotation or heating/cooling. The phenomena encountered are investigated for steady, hydrodynamically and thermally fully developed laminar flow in circular tubes. A full second-order perturbation solution is obtained under the condition that the wall heat flux is uniform with peripherally uniform wall temperature. The results cover both the nature of flow transitions and the effect of these transitions on temperature distribution, friction factor and Nusselt number. When the rotation is in the same direction as the main flow imposed by a pressure gradient and the fluid is heated, the flow and heat transfer remain similar to those observed in stationary curved tubes, radially rotating straight tubes or mixed convection in stationary straight tubes. There are, however, quantitative changes due to the combined effects of centrifugal, Coriolis and buoyancy forces. A more complex behaviour is possible when the rotation is opposite to the flow due to the pressure gradient or when the fluid is cooled. In particular, the inward Coriolis force and/or buoyancy force may cause the direction of the secondary flow to reverse. The flow reversal occurs by passing through a four-cell vortex flow region where overall, the centrifugal, Coriolis and buoyancy forces just neutralize each other.

Deposition of ions from laminar flow in circular tubes made of various materials

Deposition of ions from laminar flow in circular tubes made of various materials

Finite difference analysis for developing laminar flow in circular tubes applied to forced and combined convection

AbstractThe complete two‐dimensional partial differential equations for developing laminar flow in a circular tube have been treated by a finite difference analysis. Property variation with temperature, especially that of viscosity, is allowed for in a flexible manner. The continuity and momentum equations, and then the energy equations, are solved by direct elimination at each axial step, and marching procedure used in the axial direction. A new technique is that the stepwise energy balance is rigidly satisfied throughout by using it as a constituent equation in place of the ‘explicit’ wall thermal boundary condition normally used.The analysis predicts the complete developing hydrodynamic and thermal fields, together with friction factors and heat transfer coefficients. It has been tested for a range of fluid velocity and thermal boundary conditions and for various fluids, including high viscosity oils, water and air.Data for constant wall heat flux have already been published. 1,2 Predictions for constant wall temperature presented here are for forced and combined convection and are compared with experimental data of Test3 and Zeldin and Schmidt4.

Laminar Heat Transfer Data with a Step-Varying Wall Heat Flux

In 1958 Siegel et al. derived a thermal-entry-length integral solution for laminar flow in circular tubes with an arbitrary wall heat flux. From this we derived a solution for a step-varying flux. The objective of this research was to obtain experimental data to verify the accuracy of the above solution. The steps used were a good approximation of the sinusoidal heat flux, which exists along the cooling tube in nuclear reactors. The experimental results fell above the theoretical solution, the average difference being 10.9%. Thus, the step-varying wall heat flux solution may be used for the design of cooling systems within that uncertainty.

Tracer concentration responses and moments for measurements of laminar flow in circular tubes

Abstract Expressions are derived for the response to a tracer pulse injection into a fluid flowing with a prabolic velocity profile in cylindrical channel. Injections of finite duration and a finite monitored volume are considered, and the injection and detection are each either uniform or proportional to velocity across the channel cross section. Methods are suggested whereby yhe derived responses and their moments, for which expressions are also given, may be used in conjunction with experimental data to determine the flow rate and channel volume under laminar flow conditions. Of particular interet is the application of radioactive tracers to the measurement of blood flow. Feasibility experiments in a 3 4 -in. pipe indicate that reproducible results that approach the idealized case of uniform injection and detection can be obtained with syringe injections.

Heat transfer in laminar flow in circular and flat conduits with (constant) surface resistance

Graetz's solution is extended to include surface resistance to heat transfer in laminar flow in circular tubes and flat conduits. The computed eigenvalues, eigenfunctions, coefficients and average mean temperatures for various surface resistances are presented. The solution presented is general and contains Graetz's solution as a particular case of zero boundary resistance.