Effects of spiral start number and depth ratio of corrugated tube on flow and heat transfer characteristics in turbulent flow region

Journal of Mechanical Science and Technology - Influence of spirally-corrugated tubes on heat transfer (Nu), pressure loss (f) and thermal enhancement factor (TEF) characteristics was numerically...     

Prediction of turbulent heat transfer in swirling flow downstream of an abrupt pipe expansion

Turbulent heat transfer characteristics in swirling flows downstream of an abrupt pipe expansion with a diameter ratio of 0.5 are predicted by full Reynolds stress model. The uniform heat flux condition is imposed on the downstream wall. The flows with weak and strong swirls as well as without swirl are computed. The governing differential equations are discretized by finite volume method. Results show that the Reynolds stress model predicts accurately the maximum local Nusselt number for the case with strong swirl, but that the effects of swirl are not fully accounted for the case with weak swirl.     

Static pressure measurement error for wall taps with high Reynolds number turbulent pipe flow

An experimental study on a static pressure measurement errors in wall taps was conducted using a high Reynolds number actual flow facility (Hi-Reff). The bulk Reynolds number Re_D examined was up to 1.3 × 10⁷ and tap Reynolds number Re_t was up to 8.5 × 10⁴. The behavior of the static pressure measurement error at high Reynolds numbers was clarified experimentally. The static pressure measurement error normalized by wall shear stress increases with Reynolds number and reaches an asymptotic value. Its maximum value is 7.1 at Re_t = 8470. The asymptotic value increases with the size of the tap diameter up to 6 mm and then becomes constant for tap diameters exceeding 6 mm. The universal curve reported in previous studies is observed for only a limited range of tap Reynolds numbers of below 700 and of tap diameters below 4 mm.     

Reynolds number effect on turbulent secondary flow in a duct

Numerical simulations of fully-developed turbulent flow through a straight square duct at three Reynolds numbers of 190, 300, and 550 based on the friction velocity averaged over the duct perimeter and duct half width are reported. The effect of Reynolds number on the mean and turbulence statistics and secondary flow is investigated. The mean streamwise-velocity profiles along the wall bisector are found to obey a logarithmic scaling when they are normalized by the friction velocity at the mid-wall. Magnitudes and spatial distributions of the peak production and diffusion terms in the mean streamwise-vorticity equation normalized by the wall units are found to be unaffected by the Reynolds-number variation when they are considered in wall-unit coordinates.     

Prediction of turbulent heat transfer downstream of an abrupt pipe expansion

Turbulent flow and heat transfer characteristics downstream of a sudden circular pipe expansion are predicted by using the full Reynolds stress model. The uniform wall temperature condition is imposed to the downstream wall. The governing differential equations are discretized by finite volume method with power-law scheme. The results show that the precise inlet conditions taken from the experimental data improve the results, but that the overall magnitude of Nusselt number is still under-predicted due to the use of conventional wall functions.     

Numerical investigations on swirl intensity decay rate for turbulent swirling flow in a fixed pipe

Due to the importance of predicting the SIDR¹ associated with engineering problems such as combustion chambers, draft tube of the Francis and Kaplan turbines, heat exchanger tubes, separators and so forth, in this research the trend of SIDR and its affecting factors, through a turbulent swirl decay pipe flow have been investigated. The swirling flow is created by means of a rotating honeycomb which produces solid body rotation at the inlet of a fixed pipe. First of all, turbulent swirling decay flow has been numerically surveyed using different flow conditions at the pipe inlet. The numerical results have been validated and compared with the existing experimental data and mathematical relations, showing satisfactory coincide. The obtained results show that, the SIDR depends mainly on the Reynolds number of the passing flow. On this basis, correlations have been proposed in order to improve the predictions of swirl intensity decay rate at upstream regions as well as those with high swirl intensity. In addition, conducted analyses demonstrates (analyses have been made to demonstrate) that the previous developed correlations for predicting swirl intensity decay rate, agree with those provided in this study only for regions far enough from downstream having the low swirl intensity. This implies that the swirl intensity decay rate should be a function of the type of swirl generator at the pipe inlet.     

Analysis of conjugate heat transfer and turbulent flow in mechanical seals

A numerical investigation of conjugate heat transfer of turbulent flow within a mechanical seal chamber is presented. The computational model takes into account the heat generation at the contact interface between the rotating ring and the stationary ring, heat conduction into the rings, and heat convection into the surrounding fluid in the chamber. Correlations are developed for predicting the average heat transfer coefficient on the wetted outer surfaces of the seal rings assuming that the flow in the seal chamber is turbulent.     

Heat transfer characteristics of liquid-solid suspension flow in a horizontal pipe

Particles in liquid-solid suspension flow might enhance or suppress the rate of heat transfer and turbulence depending on their size and concentration, The heat transfer characteristics of liquid-solid suspension in turbulent flow are not well understood due to the complexibility of interaction between solid particles and turbulence of the carrier fluid. In this study, the heat transfer coefficients of liquid-solid mixtures are investigated using a double pipe heat exchanger with suspension flows in the inner pipe. Experiments are carried out using spherical fly ash particles with mass median diameter ranging from 4 to 78 μm. The volume concentration of solids in the slurry ranged from 0 to 50% and Reynolds number ranged from 4,000 to 11,000. The heat transfer coefficient of liquid-solid suspension to water flow is found to increase with decreasing particle diameter. The heat transfer coefficient increases with particle volume concentration exhibiting the highest heat transfer enhancement at the 3% solid volume concentration and then gradually decreases. A correlation for heat transfer to liquid-solid flows in a horizontal pipe is presented.     

Heat transfer correlations for air-water two-phase flow of different flow patterns in a horizontal pipe

Heat transfer coefficients were measured and new correlations were developed for two-phase heat transfer in a horizontal pipe for different flow patterns. Flow patterns were observed in a transparent circular pipe (2.54 cm I. D. and L/D=96) using an air/water mixture. Visual identification of the flow patterns was supplemented with photographic data, and the results were plotted on the How regime map proposed by Taitel and Dukler and agreed quite well with each other. A two-phase heat transfer experimental setup was built for this study and a total of 150 two-phase heat transfer data with different flow patterns were obtained under a uniform wail heat 11 ux boundary condition. For these data, the superficial Reynolds number ranged from 640 to 35,500 for the liquid and from 540 to 21,200 for the gas. Our previously developed robust two-phase heat transfer correlation for a vertical pipe with modified constants predicted the horizontal pipe air-water heat transfer experimental data with good accuracy. Overall the proposed correlations predicted the data with a mean deviation of 1.0% and an rms deviation of 12%.     

Experimental study on flow and mass transfer in rotor-stator disk cavities

An experimental study has been performed in an attempt to seek some possibilities of obtaining the solutions of heat transfer problems related to rotor-stator disk cavity systems of gas turbine engines by analogy with corresponding problems in mass transfer which arises from using naphthalene sublimation technique. Measurements are made to examine the effects of rotational Reynolds number, the flow rate and the gap ratio on the radial pressure distributions. Pressure inversion phenomenon has been verified to exist for the case of shrouded disks with radial clearance, which perform better in terms of heat transfer, too, than those with axial clearance. The stator flow reattachment points are determined directly by the dual sensor pressure probes and compared well with those estimated from the distributions of static pressure and mass transfer coefficients.     

Improved convective heat transfer correlations for two-phase two-component pipe flow

In this study, six two-phase nonboiling heat transfer correlations obtained from the recommendations of our previous work were assessed. These correlations were modified using seven extensive sets of two-phase flow experimental data available from the literature, for vertical and horizontal tubes and different flow patterns and fluids. A total of 524 data points from five available experimental studies (which included the seven sets of data) were used for improvement of the six identified correlations. Based on the tabulated and graphical results of the comparisons between the predictions of the modified heat transfer correlations and the available experimental data, appropriate improved correlations for different flow patterns, tube orientations, and liquid-gas combinations were recommended.     

Modeling of Coriolis mass flow meter of a general plane-shape pipe

The vibration of a general plane tube with a flowing fluid, which is the measuring element in a Coriolis mass flow meter (CMF), is studied. The dynamic stiffness matrix method is used to model such a tube. The tube is divided into straight and circular elements. The elements dynamic stiffness matrices are derived from the equations of motion. By assembling the elements matrices into a global matrix the natural frequencies are obtained. The mode shapes are obtained by applying the boundary conditions at the supports and the compatibility conditions at the nodes. The effects of the flow velocity on the natural frequency and the relative phase difference are modeled. The method is applied to different tube shapes. The results are compared to the published data which reveals good agreement.     

Effects of the interface position of water-air flow on turbulent wall structures

Direct numerical simulations (DNS) are performed to investigate the effect of the interface position of water-air flow on turbulence statistics and flow structures in wall-bounded water-air turbulent flow through a straight channel. Water depths of 90 and 180 viscous wall units, referred to as shallow-water and deep-water cases, respectively, are examined. Water-to-air density and viscosity ratios of 831.7 and 55.56 are considered to model a realistic flow condition at temperature of 25 oC and pressure of 1 atm. The Reynolds number and Froude number are set to 180 and 1.22 x 10^-4, respectively, for both shallow-water and deep-water case, based on the friction velocity at the bottom wall, the half depth of the channel, and water density and viscosity. The Navier-Stokes equations are solved using a timesplitting projection method on an octree grid structure, while the deformation of the interface between water and air is computed using a volume-of-fluid method. With the presence of the water-air interface, velocity profiles in deep-water and shallow-water cases are found to slightly deviate from the log-law profile for a single phase turbulent flow in a channel. The deviation is magnified when the interface is placed closer to the log-law region. Turbulent velocity fluctuations in the water stream are found to be associated with quasi-streamwise vortices and hairpin vortices. The quasi-streamwise vortices which are attached close to the wall are found in both deep-water and shallow-water cases. However, the hairpin vortices of which leading portions are lifted away from the wall are found to be diminished in the shallow-water case while they are clearly observed in the deep-water case.     

Large eddy simulation of turbulent premixed flame in turbulent channel flow

Large eddy simulation of turbulent premixed flame in turbulent channel flow is studied by usingG-equation. A flamelet model for the premixed flame is combined with a dynamic subgrid combustion model for the filtered propagation flame speed. The objective of this work is to investigate the validity of the dynamic subgridG-equation model to a complex turbulent premixed flame. The effect of model parameters of the dynamic subgridG-equation on the turbulent flame speed is investigated. In order to consider quenching of laminar flames on the wall, wall-quenching damping function is employed in this calculation. In the present study, a constant density turbulent channel flow is used. The calculation results are evaluated by comparing with the DNS results of Bruneaux et al.     

Sheathed probe thermal gas mass flow meter heat transfer analysis

The thermal gas mass flow meter is an important meter used in industrial measurement. When the environmental temperature changes, the measured gas physical parameters change correspondingly and the thermal gas mass flow meter output signal is affected, causing large measurement error. The influence of gas temperature on the sheathed probe measurements is analyzed in this paper based on experiments and heat transfer theory using a three dimensional probe and gas heat transfer mathematical model based on the heat conduction equation. The probe heat transfer process is analyzed under convection heat transfer coupling conditions. The experimental data were analyzed and compared against the theoretical results, with a maximum average relative error of only 4.56%. The rationality of the theoretical method is thus verified.     

Theory of heat transfer in rough pipe

A method is developed for calculating the heat transfer in circular pipe with rough walls, by the superposition of the viscosity values for the sublayers within a turbulent layer.     

Effects of combustor-level high inlet turbulence on the endwall flow and heat/mass transfer of a high-turning turbine rotor cascade

Experimental data are presented which describe the effects of a combustor-level high free-stream turbulence on the near-wall flow structure and heat/mass transfer on the endwall of a linear high-turning turbine rotor cascade. The endwall flow structure is visualized by employing the partial- and total-coverage oil-film technique, and heat/mass transfer rate is measured by the naphthalene sublimation method. A turbulence generator is designed to provide a highly-turbulent flow which has free-stream turbulence intensity and integral length scale of 14.7% and 80mm, respectively, at the cascade entrance. The surface flow visualizations show that the high free-stream turbulence has little effect on the attachment line, but alters the separation line noticeably. Under high free-stream turbulence, the incoming near-wall flow upstream of the adjacent separation lines collides more obliquely with the suction surface. A weaker lift-up force arising from this more oblique collision results in the narrower suction-side corner vortex area in the high turbulence case. The high free-stream turbulence enhances the heat/mass transfer in the central area of the turbine passage, but only a slight augmentation is found in the endwall regions adjacent to the leading and trailing edges. Therefore, the high free-stream turbulence makes the endwall heat load more uniform. It is also observed that the heat/mass transfers along the locus of the pressure-side leg of the leading-edge horseshoe vortex and along the suctionside corner are influenced most strongly by the high free-stream turbulence. In this study, the endwall surface is classified into seven different regions based on the local heat/mass transfer distribution, and the effects of the high free-stream turbulence on the local heat/mass transfer in each region are discussed in detail.