Perforated Flat Plates Research Articles

Numerical simulations on the performance of transpiration cooling implemented with perforated flat plates

Transpiration cooling is an effective method of protecting high-temperature components. However, this technology is currently not applicable to turbine blades because conventional sintered porous materials cannot precisely control the geometric parameters of the cooling channels and coolant outlets. In this study, numerical simulations using the conjugate heat transfer method were conducted to study the effects of hole diameter, injection ratio, and mainstream Reynolds number on the cooling performance of perforated flat plates. A novel optimisation method for the overall transpiration cooling efficiency that reduces coolant consumption through a nonuniform coolant allocation strategy was proposed. The effects of different pore diameters (0.15 mm, 0.2 mm, 0.25 mm, 0.3 mm) on transpiration cooling were investigated numerically. The results revealed that the hole diameter had a marginal effect on the average cooling efficiency of transpiration cooling under the same coolant-injection ratio. With dense heat transfer occurring within the solid matrix, the influence of variations in the pore size was diminished. However, the nonuniformity of the cooling efficiency on the hot wall surface increased with increasing pore size. A double coolant chamber non-uniform injection was adopted for the 0.3 mm perforated plate. The results indicated that there is an optimum coolant allocation ratio for achieving the highest average cooling efficiency with a certain coolant.

Experimental study on damage detectable brace-type shear fuses

This paper proposes new brace-type shear fuses (BSFs) in series connection. The BSF consists of 2 perforated flat plates, 2 middle bridging plates and 2 side bridging plates and it is designed to dissipate seismic input energy efficiently via shear and bending of its steel strips. The BSF combines the advantages of buckling-restrained braces and shear slit dampers as it merely needs a single brace for installation in a braced frame, and it is damage visible and detectable. Stiffness and strength of BSFs are uncoupled so that it can be designed with sufficient flexibility, and better ductility can be realized. Five specimens were designed with different lengths and widths for the steel strips. The proposed BSFs presented good energy dissipation capacity and ductility, and it was found that the length and width of steel strip have great effect on strength, stiffness, energy dissipation capacity and deformation capacity. Formulae to predict the initial stiffness, yield load and ultimate load of the BSF are proposed. A formula predicting the damage level of a building installed with BSFs is also proposed through residual plastic rotation angle of steel strips. A six-story BSF braced frame was studied numerically to examine the effect of BSFs on maximum and residual drift control. Finally, a step-by-step design procedure was proposed for BSF braced frames.

On the Morison hydrodynamic forces on perforated flat plates in combined steady, low frequency and high frequency motion

This paper aims to model the hydrodynamic forces on grids of perforated flat plates undergoing forced motions at three scales, namely steady (current), and combined low (wave) frequency and high (structural) frequency oscillatory motion. The intended application is the design and re-assessment of dynamically-responding offshore platforms. A recent set of experimental results by Santo et al. (2018c) is taken as the reference for comparison with the numerical predictions. A block of porous cells is used as a proxy to the grids of perforated plates in the numerical simulation, but with comparable resistance and added mass represented by equivalent Morison drag and inertia stresses both uniformly distributed over the porous cells. Both stresses are characterised by empirical force coefficients, F and Cm′, which correspond to Morison drag, Cd and inertia, Cm coefficients, respectively. Using these two adjustable empirical parameters, the simulated forces compare reasonably well with the measured hydrodynamic forces on the grids, both in terms of peak forces as well as the complete force–time histories for most of the flow conditions tested in the experiments. This is particularly true when the amplitude of wave velocity is larger than that of current velocity, a representation of large waves in a small current which is realistic for the harsh ocean environment. The porous block model is capable of capturing the global large-scale wake structures, which are responsible for the reduction in fluid flow velocity and associated forces on a structure. The simulated forces however only exhibit slight force asymmetry, unlike the measured forces, because the local fine-scale wake structures are not represented in the numerical modelling. For the scale of the experiments used for the comparison, the contribution from these small-scale wake structures to the global hydrodynamic forces can be quite significant, in particular when the amplitude of wave velocity is comparable to that of current velocity. Overall, this paper demonstrates the versatility of the porous block modelling approach in capturing most of the dominant flow physics and reproducing almost all the experimental results. The generality of the approach allows straightforward extension to wider range of flow conditions including three-dimensional flow.

Experimental evaluation of an unglazed solar air collector for building space heating in Iraq

The benefits of using an unglazed solar air collector (UTC) with a perforated absorber plate (PAP) are experimentally and theoretically investigated to evaluate this kind of collector under western Iraq climate conditions. The collector is inclined to 90° on the horizontal so that it can be easily placed on the wall of a building and to minimise its cost and weight. The thermal performance and economic characteristics of the collector are compared with other heating systems. The major results show that this type of collector offers advantages in economy and thermal performance under western Iraq climate conditions during both clear and cloudy winter days. In addition, the perforated flat plate absorber was effective and the UTC is effective in lowering both life cycle cost and energy used.

Comparative study on peak stress multipliers for perforated flat plate with various loadings

In this study, a mathematical approach is proposed to calculate the stress distributed around the circular hole of perforated flat plate. This analytical method allows an accurate evaluation of the stress state in the perforated plate. Besides, finite element analysis is carried out to determine the stress for perforated plate with different ligament efficiencies, various biaxiality ratios. After that, one dimensionless parameter named as peak stress multiplier (PSM) is analyzed with varying the ligament efficiency and biaxiality ratio for both numerical and analytical method. Through rigorous analysis, some important conclusions are summarized on the PSM. It is found that the PSM is not located at centric hole, and the one predicted by FEM is conservative.

Acoustic investigation of wall jet over a backward-facing step using a microphone phased array

The acoustic properties of a wall jet over a hard-walled backward-facing step of aspect ratios 6, 3, 2, and 1.5 are studied using a 24-channel microphone phased array at Mach numbers up to M=0.6. The Reynolds number based on inflow velocity and step height assumes values from Reh=3.0×104 to 7.2×105. Flow without and with side walls is considered. The experimental setup is open in the wall-normal direction and the expansion ratio is effectively 1. In case of flow through a duct, symmetry of the flow in the spanwise direction is lost downstream of separation at all but the largest aspect ratio as revealed by oil paint flow visualization. Hydrodynamic scattering of turbulence from the trailing edge of the step contributes significantly to the radiated sound. Reflection of acoustic waves from the bottom plate results in a modulation of power spectral densities. Acoustic source localization has been conducted using a 24-channel microphone phased array. Convective mean-flow effects on the apparent source origin have been assessed by placing a loudspeaker underneath a perforated flat plate and evaluating the displacement of the beamforming peak with inflow Mach number. Two source mechanisms are found near the step. One is due to interaction of the turbulent wall jet with the convex edge of the step. Free-stream turbulence sound is found to be peaked downstream of the step. Presence of the side walls increases free-stream sound. Results of the flow visualization are correlated with acoustic source maps. Trailing-edge sound and free-stream turbulence sound can be discriminated using source localization.

ASME Section III Stress Analysis of a Heat Exchanger Tubesheet with a Misdrilled Hole and Irregular or Thin Ligaments

A stress analysis is described for a nuclear steam generator tubesheet with a thin or irregular ligament associated with a mis-drilled hole using the rules of ASME B&PV Section III and Non-Mandatory Appendix A, Article A-8000 for Stresses in Perforated Flat Plates. The analysis demonstrates the proper application of the NB-3200 rules for this special application with discussion of the differences between an actual tube hole deviation from what is assumed in ASME Appendix A. This is a companion paper to “Technical Justification Supporting Operation with a Tube Installed in a Mis-Drilled Hole of a Steam Generator Tubesheet” NOMENCLATURE

Hydrodynamics of fluid around a collapsing bubble in the spark bubble droplet generation process

Summary This article aims to study in detail the bubble oscillation near confined free surfaces and the ensuing droplet formation using a combined boundary element-finite difference method. Three configurations are considered: (i) the bubble oscillation near a circular aperture made in a flat plate, (ii) the bubble oscillation inside and near the top opening of a vertical cylinder and (iii) the bubble oscillation between a perforated flat plate and a horizontal solid boundary. The effects of standoff distance on the bubble dynamics and on the surrounding fluid dynamics are examined. Completely different bubble shapes, free surface motions, jetting patterns and pressure distributions under different standoff distances could be observed in the present work. In addition, it was found that for the configurations (i) and (iii), the bubble reentrant jet is always directed away from the free surface. For the cylinder case, however, a critical standoff distance was found for which the pressure distribution in the fluid above and below the bubble are the same and the bubble takes the shape of an hourglass at the time of jet impact. For subcritical standoff distances the bubble reentrant jet is always away from the free surface. However, for supercritical standoff distances the direction of the reentrant jet is interestingly directed towards the free surface. Finally, the effect of plate and cylinder configurations on the resulting droplet dynamics was investigated. It was found that the driving force for the droplet formation is the initial velocity induced by the bubble reentrant jet rather than the pressure difference inside the liquid. Besides, in the cylinder case the droplet size is smaller and its pinch-off happens earlier than the plate case.

Study of the Performance Thermal Forced Unglazed Solar Air Collector

An experimental study is achieved to study the thermal performance of forced unglazed solar air collector supplied with perforated absorber flat plate. The study is carried under Iraqi circumferences in Al-Ramadi city .The collector is inclined (90o) on horizontal for the simplicity of setting such type of collector on the wall building and minimize its weight. The measurement is recorded on Winter season for two sunny days and two cloudy days in (January 2012). The results show that its possible to use this type of collectors for heating in Winter time because the maximum out air temperature reach to (34oC) when ambient air temperature at (17oC) in sunny days. A good agreement is shown with the published studies Finally its obtained a good effectiveness for perforated flat plate absorber with high system efficiency.

06/00884 Experimental heat transfer on the windward surface of a perforated flat plate: Dorignac, E. et al. International Journal of Thermal Sciences, 2005, 44, (9), 885–893.

06/00884 Experimental heat transfer on the windward surface of a perforated flat plate: Dorignac, E. et al. International Journal of Thermal Sciences, 2005, 44, (9), 885–893.

Experimental heat transfer on the windward surface of a perforated flat plate

Two techniques are described in this paper to determine convective transfer on a multiperforated plate; the perforations diameter can be small or large (from 1 millimeter to 1 centimeter). This study reports on heat transfer due to the air flow before it goes through the perforations. These perforations are perpendicular to the wall. For a large range of perforations spacings, an empirical relation is proposed for heat exchange at the windward surface of a perforated flat plate.

Experimental heat transfer on the windward surface of a perforated flat plate

Experimental heat transfer on the windward surface of a perforated flat plate

Transmission characteristics of dichroic filters measured by THz time-domain spectroscopy

The transmission characteristics of perforated flat plates which act as dichroic filters or frequency selective surfaces were measured in the far-infrared (FIR) region by Terahertz Time-Domain Spectroscopy (THz-TDS). The me- chanically made dichroic filters were designed for the cutoff frequencies of 155, 586 ,a nd773 GHz. Due to their sharp cut- off characteristics, dichroic filters are used in quasi-optical systems as compact, high-pass filters throughout the sub- millimeter wave and FIR region. Knowledge of the frequency response of such filters is important for various applications in frequency mixing and frequency multiplying experiments in the microwave region. The spectrum of a freely propa- gating THz pulse with and without filter was measured by electro-optic sampling in a ZnTe crystal. The experimental results for the frequency dependence of the transmittance of the dichroic filters are in good agreement with calculations based on the theory given by Chen (1).

Three-Dimensional Analysis of an Elastic Plate-Cylinder Intersection by the Boundary-Point-Least-Squares Technique

The boundary-point-least-squares technique is applied to the axisymmetric three-dimensional elasticity problem of a hollow circular cylinder normally intersecting with a perforated flat plate. The geometry of the intersection is partitioned into three parts. Boundary conditions on the middle part and continuity conditions between adjacent parts are satisfied using the numerical boundary-point-least-squares technique while the governing elasticity equations and all other boundary conditions are satisfied exactly. Sample theoretical results are presented for the case of axisymmetric radial tension loading on the plate. The results compare favorably with previously published experimental data and provide supplementary data to theoretical results obtained using existing shell theory solutions.

Transmission of Microwave Through Perforated Flat Plates of Finite Thickness

Transmission characteristics of a thick conducting plate perforated with either circular or rectangular holes are presented. Simple explicit formulas for predicting energy leakage through a reflector surface are derived.

A Study of Microwave Leakage through Perforated Flat Plates (Short Papers)

A simple formula useful for predicting leakage through a circular hole array in a metallic flat plate is presented. A correction is given for plate thickness. The formula is applicable to arrays having either a 60/spl deg/ (staggered) or 90/spl deg/ (square) hole pattern, but is restricted to the case of 1) an obliquely incident plane wave with the E field polarized normal to the plane of incidence, and 2) large transmission loss. When theoretical values were compared to experimental data obtained on test samples having transmission losses greater than 20 dB, the agreement between theory and experiment was typically better than 1 dB at S band and 2 dB at X band.

An experimental study of the rigidity of perforated plates

An experimental study of the effective rigidity of perforated flat plates is described, which forms part of a general study of perforated plates with particular reference to concrete reactor pressure vessels. Consideration is given to circular perforations on an equilateral triangular grid pattern, the perforation being unstiffened. The experimental results are compared with previous theories and with a new analytical approach based on a “thick cylinder” analogy.