Test Section Of Channel Research Articles

Thermal analysis of metal foam and nanofluid integration in an asymmetrical heated channel

The flow and heat transport presentation of the nanofluid flowing through the metal foam (MF) positioned inside the asymmetrical heated horizontal channel is evaluated computationally in the current study. The MF of 20 pores per inch (PPI) with porosity 0.918 is inserted into horizontal channel test section. The test segment is heated from the top wall with the help of plate (aluminum) heater assemblage positioned at the top of the channel. The novelty of the current examination is to extract the consequences of nanofluids such as Al2O3-H2O and CuO-H2O flowing through the MF filled test segment at various velocities ranging from 0.02 to 0.15 m/s. The conjugate heat transport examination is executed through MF region using integrated DEF (Darcy Extended Forchheimer) with LTE (local thermal equilibrium models). The improvement in thermal presentation achieved for nanofluids are likened with H2O and H2O-C2H6O2 (water with 50 % ethylene glycol) solution and also with clear channel. The procedure adopted in the current analysis is initially confirmed with the help of comparison of present work result with literature upshots. The outcomes are presented in terms of friction factor (FF), Nusselt number (Nu), Colburn j factor, performance evaluation criteria (PEC) and pumping power (PP). The CuO-H2O nanofluid showed the best performance (average PEC of 1.4) among all the fluids considered in the present examination.

Conceptual design of narrow rectangular channel test section for research reactor application

Conceptual design was carried out on test section for studying heat transfer characteristics of narrow rectangular channel for research reactor application. Thermal hydraulic design requirements were specified through literature study on mid- to high-powered research reactors currently under operation or design. Engineering design was then carried out in streamlined fashion with help of in-house design code and computational fluid dynamics analysis. Considering various constraints and uncertainties in terms of engineering hot channel factors, sensitivity studies were performed and realistic test section design was obtained. For final design, stochastic operable heater power map is generated by merging individual operable ranges from each constraint, with random sampling of hot channel factors.

Effects of polymer addition on transition and length scales of flow structures in transitional channel flow

The effect of polymer addition on transition to turbulence in a two-dimensional water-flow channel was experimentally investigated by flow visualization using reflective flakes. The flow entering the channel test section maintains a high disturbance level by expanding laterally after reaching a high Reynolds number upstream the test section. In order to obtain the intermittency factor (turbulence fraction), the visualized images were classified into non-turbulent and turbulent regions, and the streamwise scale of the streaks appearing in the non-turbulent region was estimated from the autocorrelation coefficient computed by shifting the images in the streamwise direction. The visualization results show that similar to the pure water case, intermittent flow with a patch-like distribution of turbulent and non-turbulent areas clustered by streamwise streaks is observed. The Reynolds number at which the intermittency increases shifts toward higher Reynolds numbers with increasing polymer concentration, indicating a delay of transition. The streaks appearing in the non-turbulent region elongate with increasing polymer concentration. At high concentrations, straight elongated streaks penetrate through the turbulent regions, suggesting that the polymer addition affects the stability of the streaks. These changes of the streak behavior indicate that the polymer affects not only the transition Reynolds number but also the flow structure during the transition process.

Conceptual Design of Narrow Rectangular Channel Test Section for Research Reactor Application

Conceptual Design of Narrow Rectangular Channel Test Section for Research Reactor Application

Benchmark Validation Experiment of Plenum-to-Plenum Flow Through Heated Parallel Channels

Abstract This paper documents a computational fluid dynamics (CFD) validation benchmark experiment for flow through three parallel, heated channels from one plenum to another. The test section was installed into a facility designed for natural convection benchmark validation experiments. The focus of these experiments was the highly-coupled thermal-fluid dynamics that occur between mixing jets in the upper plenum of the wind tunnel. A thermal instability in mixing jets, called thermal striping, can cause damage to structures which is a concern for high temperature gas reactors. Nine experimental cases were explored by varying the relative channel temperature or blower speed. The boundary conditions for CFD validation were measured and tabulated along with an uncertainty. Geometry measurements of the triple channel test section were used to make an as-built solid model for use in simulation. The outer tunnel and channel surface temperatures, the pressure drop across the test section, atmospheric conditions, and inflow into the upper plenum were measured or calculated for the boundary conditions. The air velocity and temperature were measured in the jet mixing region of the upper plenum as system response quantities.

Flow analysis of a shock wave at pulse ionization: Riemann problem implementation

An experimental study of the plasma-gas dynamic fluid formed after pulse ionization of the gas flow with a plane shock wave with Mach number 2.2–4.8 is carried out. Nanosecond volume discharge with UV preionization was switched on when the shock moved in a tube channel test section. Energy input occurs in the low-pressure gas volume separated by the shock surface within a time less than 200–300 ns; a single shock wave breaks into three discontinuities in accordance with the 1D Riemann problem solution. The initial (plasma-dynamic) stage of the flow in the nanosecond time range is visualized by glow recording; the supersonic gas processes in the microsecond time range are recorded using high-speed shadow imaging. Quantitative information about the dynamics of the shocks and contact surface (plots of horizontal distance) was obtained within time up to 25 µs. A region with an increased gas-discharge plasma glow intensity, after the discharge electric current termination, was recorded in the time interval from 0.3 to 1.5 µs; it was explained by a jump in gas temperature and density between the new shock wave and the contact discontinuity.

Statistical description of morphological characteristics of bedforms in seepage affected alluvial channels

In this study, experiments were performed in a curvilinear cross-sectional threshold alluvial channel with no seepage and with seepage conditions to understand the influence of downward seepage in an alluvial channel. We observed that a stable channel during the no seepage condition started to approach a stable channel in the transporting stage with downward seepage. Increased value of Shields stress was observed after the application of seepage. In addition, this study deals with the effect of downward seepage on the evolution of alluvial bedforms. In this regard, multi-temporal bed elevation profiles were collected along the test section of channel, which are used to characterize migrating bedforms. Results reveal greater fluctuations and variability on the channel bed under the influence of increased seepage discharge. Slope of the power spectral density with wave number was significantly increased with an increment in seepage percentage, showing more inhomogeneous arrangement of bedforms and larger roughness over the channel boundary.

Experimental study on electrohydrodynamically induced heat transfer enhancement in a minichannel

Effect of electric field on heat transfer enhancement and pressure drop for different Reynolds numbers is experimentally investigated in a minichannel for laminar flow. The test section consists of a square channel with a heater embedded in its bottom. The high voltage electrode is a wire, placed on top of the test section of channel and the bottom is considered as ground. The side walls in the test section are thermally and electrically insulated. Secondary flow, as a result of charge injection from high voltage electrode through the liquid, disrupts the boundary layer and leads to higher convective heat transfer coefficients and higher amounts of pressure drop. By increasing electric field intensity cooling performance was improved for all Reynolds numbers. Results show that presence of electric field is more effective in lower Reynolds numbers and as the mass flow rate increases the effect of electric field decreases. Performance Evaluation Criterion (PEC) is calculated and as an outstanding result its values were upper than unity which in most of the enhancement techniques is not. PEC value increases by raising electric field intensity or decreasing Reynolds number.

Experimental Characterisation of the Interfacial Structure during Counter-Current Flow Limitation in a Model of the Hot Leg of a PWR

In order to investigate the two-phase flow behaviour during counter-current flow limitation in the hot leg of a pressurised water reactor, dedicated experiments were performed in a scaled down model ofKobe University. The experiments were performed with air and water at atmospheric pressure and room temperature. At high flow rates, CCFL occurs and the discharge of water to the reactor pressure vessel simulator is limited by the formation of slugs carrying liquid back to the steam generator. The structure of the interface was observed from the side of the channel test section using a high-speed video camera. An algorithm was developed to recognise the stratified interface in the camera frames after background subtraction. This method allows extracting the water level at any position in the image as well as performing further statistical treatments. The evolution of the interfacial structure along the horizontal part of the hot leg is shown by the visualisation of the probability distribution of the water level and analysed in function of the liquid and gas flow rates. The data achieved are useful for the analysis of the flow conditions as well as for the validation of modelling approaches like computational fluid dynamics.

Microflow-based control of near-wall fluctuations for large viscous drag reduction

The stabilizing effect of microgroove surface morphology on viscous drag reduction was studied experimentally in the inlet region of a plane channel flow. The stabilization is thought to be due to the ability of a microgrooved surface pattern to suppress the velocity fluctuations in the spanwise direction on a restricted portion of the wetted surface, which prevents vorticity development at the wall and consequently across the entire flow field. This smart microflow control strategy, which works successfully only under very particular circumstances, was implemented in a microgroove-modified channel flow in which the front part has a microgrooved surface topology. The results of pressure drop measurements indicate that microgrooved surfaces can effectively stabilize laminar boundary layer development, leading to a significant reduction in the viscous drag. In the rear flat part of the microgroove-modified channel test section, a maximum drag reduction of \({\rm DR\simeq 35\%}\) was measured. This corresponds to an overall drag reduction of \({\rm DR\simeq 16\%}\) at a length Reynolds number of \(Re_x\simeq 10^6. \) The drag reduction effect persisted in a narrow range of flow velocities and for the reported experimental conditions corresponds to microgroove dimensions between 1.5 and 2.5 viscous length-scales.

Turbulent flow over transverse ribs in open channel with converging side walls

This paper reports an experimental study of favorable pressure gradient turbulent flow over transverse square ribs in an open channel. The first half of the channel test section has straight parallel side walls, and each of the side walls of the second half of the test section converges linearly to produce the favorable pressure gradient. Two different values of half-angle ( α = 1° and 2°) of the converging side walls were used to vary the pressure gradient. For each value of α, transverse square ribs were glued onto the bottom wall both upstream of and within the converging sections. The pitch-to-height ratio of the ribs was varied to produce d-type, intermediate and k-type rib roughness. A particle image velocimetry was used to conduct detailed measurements over the ribs at several planes upstream of and within the converging sections. From these measurements, mean velocities and turbulent quantities were extracted at selected streamwise locations. The distributions of the mean velocities, turbulent intensities, and the mean and turbulent momentum fluxes at the interface between the rib cavities and the overlying boundary layer were used to provide insight into the interaction between the shear layers. The profiles of mean velocity, turbulent intensities, Reynolds shear stress and triple products were obtained to document the characteristics of favorable pressure gradient turbulent flow over square ribs in an open channel.

Nusselt Numbers and Flow Structure on and Above a Shallow Dimpled Surface Within a Channel Including Effects of Inlet Turbulence Intensity Level

Abstract Experimental results from a channel with shallow dimples placed on one wall are given for Reynolds numbers based on channel height from 3,700 to 20,000, levels of longitudinal turbulence intensity from 3% to 11% (at the entrance of the channel test section), and a ratio of air inlet stagnation temperature to surface temperature of approximately 0.94. The ratio of dimple depth to dimple print diameter δ∕D is 0.1, and the ratio of channel height to dimple print diameter H∕D is 1.00. The data presented include friction factors, local Nusselt numbers, spatially averaged Nusselt numbers, a number of time-averaged flow structural characteristics, flow visualization results, and spectra of longitudinal velocity fluctuations which, at a Reynolds number of 20,000, show a primary vortex shedding frequency of 8.0Hz and a dimple edge vortex pair oscillation frequency of approximately 6.5Hz. The local flow structure shows some qualitative similarity to characteristics measured with deeper dimples (δ∕D of 0.2 and 0.3), with smaller quantitative changes from the dimples as δ∕D decreases. A similar conclusion is reached regarding qualitative and quantitative variations of local Nusselt number ratio data, which show that the highest local values are present within the downstream portions of dimples, as well as near dimple spanwise and downstream edges. Local and spatially averaged Nusselt number ratios sometimes change by small amounts as the channel inlet turbulence intensity level is altered, whereas friction factor ratios increase somewhat at the channel inlet turbulence intensity level increases. These changes to local Nusselt number data (with changing turbulence intensity level) are present at the same locations where the vortex pairs appear to originate, where they have the greatest influences on local flow and heat transfer behavior.

An Experimental Analysis of Vortex Trapping Techniques

An experimental verification is presented for the theoretical vortex trapping concept. A suction orifice located along one wall of a water channel test section was used to simulate a point sink to trap spanwise vortices downstream of a backward-facing step and between two parallel fences. Results from the backward-facing step geometry indicated an increase in the sink strength required to hold a vortex as the sink is positioned closer to the step, closely following previous theoretical predictions made using conformal mapping. The experimental data also showed reasonable agreement with the theoretical position for optimum vortex trapping. Flow visualization has shown a three-dimensional cross-stream effect due to bending of the forced-vortex core by suction. Results from the dual-fence geometry, on the other hand, verified the ability to use a lower level of suction for vortex trapping when compared with the backward-facing step.

Experimental and theoretical investigation of backward-facing step flow

Laser-Doppler measurements of velocity distribution and reattachment length are reported downstream of a single backward-facing step mounted in a two-dimensional channel. Results are presented for laminar, transitional and turbulent flow of air in a Reynolds-number range of 70 < Re < 8000. The experimental results show that the various flow regimes are characterized by typical variations of the separation length with Reynolds number. The reported laser-Doppler measurements do not only yield the expected primary zone of recirculating flow attached to the backward-facing step but also show additional regions of flow separation downstream of the step and on both sides of the channel test section. These additional separation regions have not been previously reported in the literature.Although the high aspect ratio of the test section (1:36) ensured that the oncoming flow was fully developed and two-dimensional, the experiments showed that the flow downstream of the step only remained two-dimensional at low and high Reynolds numbers.The present study also included numerical predictions of backward-facing step flow. The two-dimensional steady differential equations for conservation of mass and momentum were solved. Results are reported and are compared with experiments for those Reynolds numbers for which the flow maintained its two-dimensionality in the experiments. Under these circumstances, good agreement between experimental and numerical results is obtained.

Response of gravity water waves to wind excitation

The primary objective of this work was to study the response of gravity water waves to wind excitation and, in particular, the applicability of the Miles inviscid shear-flow theory of gravity wave growth, by conducting experiments in a laboratory wind-wave channel under conditions approximating the assumptions of the mathematical model. Mechanically generated wave profiles subjected to wind action were measured with capacitance wire sensors and wave energy was calculated at seven stations spaced at 10ft. intervals along the channel test section. Waves varied in length from about 2·5 to 6·5 ft. and maximum wind speeds ranged from 12 to 44 ft./sec. Vertical mean air velocity profiles were taken at six stations in the channel, fitted near the air-water interface with semi-logarithmic profiles, and used in a stepwise computation of theoretical wave growth. The results show that the measured wave energy growth is exponential but considerably larger than the growth predictions of Miles's theory. Derived experimental values of the phase-shifted pressure component β are greater than theoretical values by a factor varying from 1 to 10, with a mean of about 3. Wind mean velocity profiles appear to be closely logarithmic near the air-water interface. Wind-generated ripples superposed on mechanically generated waves created a rough water surface with standard deviation larger, in all cases, than the respective critical-layer thickness.

Magneto-Fluid-Mechanic Channel Flow. I. Experiment

An experiment is described in which fully developed turbulent channel flow of mercury was investigated in the presence of a uniform transverse magnetic field. The channel test section was constructed from an electrical insulator and was rectangular in cross section. The flow was studied in the range of Reynolds numbers: 58 000–180 000, based on channel equivalent diameter. Hartmann number was varied between zero and values sufficiently high to change the flow from turbulent to laminar at the corresponding Reynolds number. Skin friction coefficients were deduced from static pressure measurements along the length of the channel. Velocity profiles were obtained from traversing probe total head measurements.