Roughness Geometry Research Articles

Effect of roughness geometry on friction during micro V-die bending by using finite element method

Interfacial conditions such as friction and roughness tend to be the dominant process characteristics when simulating sheet metal forming processes. Therefore, accurately modeling the tool workpiece interface is essential. Additionally, the accuracy of conventional methods of modeling the interface is insufficient for microforming. This work presents a novel approach for describing friction by modeling the geometric roughness of the tool surface instead of using the conventional friction coefficient or factor in dry contact. This finite element-based model was validated in terms of loads and metal flow in two cases of micro V-die bending processes. One process modeled a conventional flat tool surface with a friction coefficient. Another process modeled a rough tool surface described as roughness geometry with zero friction. In addition to elucidating how the roughness geometry of a tool surface affects friction during microforming, this work provides fundamental information about the interfacial conditions of the contact surface as well as improved accuracy and flexibility compared to conventional friction models. Another important application of the friction calculation results in this study is in microforming applications.

Heat Transfer and Thermal Efficiency of Solar Air Heater Having Artificial Roughness: A Review

Artificial roughness applied on the absorber plate is the most efficient method to improve thermal performance of solar air heaters .Experimental investigations appropriate to distinct roughness geometries shows that the enhancement in heat transfer is accompanied by considerable rise in pumping power. In view of the fact, a designer needs to carefully examine shape and orientation of roughness elements in order to choose the best fit roughness geometry for intended application. In this paper some distinguished roughness geometry has been compared on the basis of heat transfer enhancement and thermo hydraulic performance. The objective of this paper is to review various studies, in which different artificial roughness elements are used to enhance the heat transfer rate with little penalty of friction. Correlations developed by various researchers with the help of experimental results for heat transfer and friction factor for solar air heater ducts by taking different roughened surfaces geometries are given in tabular form. These correlations are used to predict the thermo hydraulic performance of solar air heaters having roughened ducts.

Superhydrophobic and superhygrophobic surfaces: from understanding non-wettability to design considerations

Current understanding of non-wettability of surfaces is presented and discussed. Three types of non-wettability are analysed: superhydrophobicity (drops on rough, hydrophobic surfaces), superhygrophobicity (drops on rough, hygrophilic surfaces), and under-water superhydrophobicity (rough, hydrophobic surfaces submerged in water). It is shown, based on quantitative work, that non-wettability must indeed be associated with the Cassie–Baxter state, and may be qualitatively defined by requiring the wetted area to be minimal. A quantitative definition is yet to be developed. The analysis is presented in terms of thermodynamic equilibrium and stability. To gain thermodynamic stability, the roughness geometry has to conform to a certain mathematical condition (for example, convex protrusions enable it while concave dents do not). The problem of optimal roughness geometry, including the issue of multi-scale roughness, is also discussed, concluding that the detailed optimal topography of non-wettable surfaces is yet to be elucidated. Finally, the fundamental principles underlying non-wettability are shown to be useful as design-guiding principles.

Experimental Investigations on Fusion Cutting Stainless Steel with Fiber and CO2 Laser Beams

First results of an experimental study on inert-gas fusion cutting stainless steel with different types of laser are presented. In particular, the cutting capabilities of a fiber and a CO2 laser beam with similar Rayleigh length have been compared as a function of material thickness with respect to achievable maximum cutting speed, cut edge surface roughness and cut kerf geometry. The most interesting finding achieved so far concerns the observation that the cut kerfs are nearly identical in size but differ qualitatively in shape for both laser teypes.

Effect of roughness geometry on heat transfer and friction characteristics of PCM storage unit for night coolness storage in summer season

This paper presents a theoretical analysis of thermal storage unit using phase change material (PCM) as storage medium. Storage unit consists of parallel rectangular channels for the air flow which are separated by phase change storage material. The purpose of storage unit is to absorb the night coolness and to provide cooled air at comfort temperature during day time in summer season. MATLsimulation tool has been used to compute the air temperature variation with location as well as time, charging and discharging time of storage unit. Phase change material used for analysis is selected in such a way that it?s Melting point lies between comfort temperature and minimum night ambient temperatures. The air flow rate needed for charging of PCM is approximately four times greater than the flow rate required during day time to achieve comfort temperature for approximately eight hours, due to limited summer night time (only eight hours). The length of storage unit for which NTU value is greater than or equal to five will give the exit air temperature equal to PCM temperature for the case of latent heat utilization. It is found that artificial roughness on the duct surface effectively reduces the length of storage unit in the cost of some extra pressure drop across the duct.

A review of various approaches to optimize the solar air heater

A comparative study of various approaches to optimise and increase the performance of solar air heater is carried out in the present work. Various types of artificial roughness geometries in the absorber plate of solar air heater duct and their characteristics have been investigated for the heat transfer improvement or enhance the performance by many researchers. However, exergy data are more practical and realistic in comparison with the respective energy values that have been found in this communication.

Effect of Roughness Geometry on Characteristics of Density Currents Head

Density currents occur when fluid of one density propagates along a horizontal boundary into fluid of a different density. The front part of a density current is deeper than the following steady fluid and this raised section of the flow is referred to as the head of the density current. In the present paper, the influence of roughness geometry on the head concentration, velocity and height are investigated experimentally. A total number of 21 experiments were performed using six rough beds as well as a smooth bed. The roughness elements were in cylindrical and conic shape. It was found that the head is influenced by height and project area of roughness elements. In a particular shape of roughness elements, the observed trend is that as the surface roughness increases the head concentration and velocity decrease while the head height increases. It was also found that the aforementioned trends occur at higher rates as the beds get rougher. In a given height of roughness elements, the head velocity and concentration decreases and head height rises when the project area of roughness elements increases. Keywords: Density current, Roughness geometry, Cylindrical roughness, Conic roughness

Effect of Roughness Geometry on Characteristics of Density Currents Head

Density currents occur when fluid of one density propagates along a horizontal boundary into fluid of a different density. The front part of a density current is deeper than the following steady fluid and this raised section of the flow is referred to as the head of the density current. In the present paper, the influence of roughness geometry on the head concentration, velocity and height are investigated experimentally. A total number of 21 experiments were performed using six rough beds as well as a smooth bed. The roughness elements were in cylindrical and conic shape. It was found that the head is influenced by height and project area of roughness elements. In a particular shape of roughness elements, the observed trend is that as the surface roughness increases the head concentration and velocity decrease while the head height increases. It was also found that the aforementioned trends occur at higher rates as the beds get rougher. In a given height of roughness elements, the head velocity and concentration decreases and head height rises when the project area of roughness elements increases.

Predictions of Sound from Rough Wall Boundary Layers

The Unified Theory of Roughness Noise is examined for the first time by making predictions of far-field noise normalized on the single-point rough wall pressure spectrum for a 40 grit stochastic sandpaper roughness and a 1-mm hemispherical element deterministic roughness with conditions ranging from transitionally to fully rough. These predictions are compared to experimentally measured values of noise from these surfaces in a wall-jet flow. Predicted values are within approximately 6 dB of the measured noise from the stochastic and deterministic roughness showing that reliable predictions of roughness noise can be completed using the Unified Theory for even fully rough conditions, as long as the roughness height to boundary-layer thicknesses are relatively moderate. The spectral shape of normalized roughness noise was found to be a predictable function of the relationship between the roughness geometry and the wall pressure wavenumber-frequency spectrum. The effect of the form of the wall pressure wavenumber-frequency spectrum on the predicted noise spectra was investigated finding that the convective velocity is the most significant parameter affecting the quality of predictions.

Thermal and thermohydraulic performance of roughened solar air heater having protruded absorber plate

Thermal performance of solar air heater does not take into account energy loss due to friction for propelling air through the duct. Therefore, it is necessary to evaluate thermohydraulic performance in order to investigate simultaneous effect of thermal and hydraulic characteristics on performance of solar air heater. In the present paper thermal and thermohydraulic performance of smooth as well as roughened solar air heater has been investigated with the help of a mathematical model. Absorber plate of solar air heater has been roughened with the formation of protrusions. Optimum value of each roughness geometry parameter has been obtained on the basis of thermal and effective efficiency of roughened solar air heater. Design plots have also been prepared in order to facilitate the designer for designing such type of roughened solar air heater within the investigated range of system and operating parameters.

Effect of surface roughness: comparison between continuum and kinetic approaches

In the present work a numerical analysis of the flow field in rough microchannels is carried out using two approaches: Navier-Stokes equations provided with first order slip-boundary condition and kinetic S-model equation with Maxwell diffuse reflecting boundary condition. An implicit scheme is used for the solution of S-model equation and an algorithm allowing massive parallelization in both physical and velocity spaces has been developed. The roughness geometry is modelled as a series of triangular obstructions with relative roughness ε equals to 1.25%, 2.5% and 5%. A wide range of Mach numbers is considered, from nearly incompressible to chocked flow conditions and a Reynolds number up to 170. To estimate rarefaction effect the flow at Knudsen number ranging from 0.01 to 0.08 and fixed pressure ratio has been considered. Accuracy and discrepancies between full Navier - Stokes and S-model solutions are discussed, assessing the range of applicability of first order slip condition in rough geometries. The effect of the roughness is discussed via Poiseuille number as a function of local Knudsen and Mach numbers.

Heat and fluid flow characteristics of roughened solar air heater ducts – A review

Abstract Artificial roughness in the form of repeated ribs is one of the effective way of improving the performance of a solar air heater ducts. Various studies have been carried out to determine the effect of different artificial roughness geometries on heat transfer and friction characteristics in solar air heater ducts. The objective of this paper is to review various studies, in which different artificial roughness elements are used to enhance the heat transfer coefficient with little penalty of friction factor. On the basis of correlations developed by various investigators for heat transfer coefficient and friction factor, an attempt has been made to compare the thermohydraulic performance of roughened solar air heater ducts. It has been found that lot of experimental and analytical studies reported in the literature.

Heat transfer and friction factor of solar air heater having duct roughened artificially with discrete multiple v-ribs

In this paper, results of an experimental investigation on heat transfer and friction in a rectangular duct roughened with discrete multi v-shaped rib on one of its broad wall are presented. The discretizing of multi v-shaped rib is done by providing small symmetrical gap equal to rib height in both legs of multi v-rib. The artificially roughened duct was investigated having width to height ratio (W/H) of 12, relative width ratio (W/w) of 6, relative roughness pitch (P/e) of 10, relative roughness height (e/Dh) of 0.0433, angle of attack (α) of 60°, and relative gap distance (Gd/Lv) of 0.55. The relative gap width (g/e) was varied from 0.5 to 1.5. The heat transfer and friction factor results obtained experimentally were compared with those of smooth duct under similar experimental conditions. It is seen that there is a significant change in Nusselt number and friction factor as a result of providing discrete multi v-shape ribs. The enhancement in Nusselt number is found to be 6.32 times (that of smooth surface) for discrete multi v-shaped rib with relative gap width of 1.0. It is also found that the duct having this roughness geometry results in best thermo-hydraulic performance in comparison to other geometries under similar operating conditions.

Effects of Structured Roughness on Fluid Flow at the Microscale Level

It has been well established that there are no differences between microscale and macroscale flows of incompressible liquids. However, surface roughness has been known to impact the transport phenomena. This work aims to systematically quantify the effect of structured roughness geometries on friction factor in the laminar and turbulent flows as a precursor to the detailed heat transfer studies on these geometries. Experiments were conducted by varying the pitch (150–400 μm) and height (36–131 μm) of transverse rib roughness structures in rectangular channels such that the pitch-to-height ratio ranged from 2 to 8. The channel width was fixed at 12.70 mm and the length at 152.4 mm, while the channel gap was varied (230–937 μm). Tests were conducted over a Reynolds number range of 5–3400. The results are compared to the existing models, which do not account for specific roughness features such as pitch and height. A theoretical model is developed to predict the effect of roughness pitch and height on pressure drop along the channel length. Validation of the proposed theory is carried out by comparing the predictions with the experimental results. The model and the experimental results provide an understanding of the effect of two-dimensional structured roughness on the frictional losses in fully developed laminar flow.

A Comprehensive Review on Roughness Geometries and Investigation Techniques Used in Artificially Roughened Solar Air Heaters

Artificial roughness applied on the absorber plate is the most acclaimed method to improve thermal performance of solar air heaters at the cost of low to moderate friction penalty. Experimental investigations pertinent to distinct roughness geometries unfolds that the enhancement in heat transfer is accompanied by considerable rise in pumping power. In view of the fact, a designer needs to carefully examine shape and orientation of roughness elements in order to choose the best fit roughness geometry for intended application. Moreover it is required to understand how flow field is affected by particular roughness geometry so that direction of future researches could be conceived. So as to elucidate the useful findings an attempt has been made to review roughness geometries employed in solar air heaters. Some distinguished roughness geometries have been compared on the basis of heat transfer enhancements and thermohaydraulic performance to draw attention towards their usefulness for specific applications. Furthermore, light is thrown on different investigation techniques adopted for prediction of heat transfer and friction characteristics of artificially roughened solar air heaters to recognize features and limitations of each technique.

Mass transfer through membranes with surface roughness

Abstract Surface roughness on membranes has been shown to increase flux, in part because surface area was increased. However, experimental studies of the relationship between flux and surface roughness have produced contradictory results in which flux did not always increase with increased surface roughness. Increases in flux that are greater than the increase in surface area also have been reported, with hydrogen flux through palladium and palladium–copper films as an example. A mathematical model was developed to examine two-dimensional diffusion through a roughened membrane when the surface is at local equilibrium with the feed. By comparing the results to a one-dimensional diffusion model, contributions of diffusion parallel to the plane of the membrane could be separated from that of a shorter diffusion path through the thin regions. Although lateral diffusion can be significant, more often the presence of thinner regions was the dominant factor for increased flux. The model calculations predict that membrane flux can increase by more or less than the increase in surface area depending on the geometry of the surface roughness. For the geometry of the surface structures in the hydrogen permeation experiments, model calculations indicate that flux increases larger than the increase in surface area could occur.

Two-Layer Wall Model for Large-Eddy Simulations of Flow over Rough Surfaces

Two-layer zonal near-wall treatment for flow over rough surfaces is proposed in a generalized coordinate largeeddy simulation framework. Rotta’s [Rotta, J. C., “Turbulent Boundary Layers in Incompressible Flow,” Progress in Aeronautical Sciences, Vol. 2, 1962, pp. 1–220.] approach to amplify the mixing length near the wall is used to model the eddy viscosity in the inner layer. Calculations are performed in a rod-roughened channel at high flow Reynolds numbers in the range of 6000 to 56,000 and in the fully rough regime. An equivalent sand-grain roughness is used to correlate the amplification in the wall shear stress with the roughness geometry. The roughness wall model predicts the skin-friction coefficient and the mean velocity profile, in close agreement with experiments. Turbulence statistics are also predicted with good accuracy. For the lowest Reynolds number investigated in the current study, the spatial resolution required bywall-modeled large-eddy simulation is three orders ofmagnitude smaller thanwith a direct simulation on the same geometry that resolves the roughness elements. This results in large savings in computational cost.

Analysis of exergy and parametric study of a v-corrugated solar air heater

Solar air heater requires investigation for enhancement of solar energy conversion into heat. Different configurations with various artificial roughness geometries are proposed to date. In present study attention is paid on ways leading to more delivery of exergy by a v-corrugated solar air heater through parametric study. Effects of aspect ratio of the collector, inlet air temperature, mass flow rate per collector area etc. are studied.

Refraction-enhanced x-ray radiography for density profile measurements at CH/Be interface

An x-ray radiographic technique utilizing refraction for phase contrast enhancement is developed. This technique is advantageous for study of discontinuities such as interfaces and shock fronts. Proof-of-principle experiment has been performed using OMEGA laser for CH/Be targets. The experimental design, including choice of backlighter, geometry and tolerance of surface roughness, is presented. Factors affecting the spatial resolution, background and sensitivity are discussed.

직사각형 형상의 표면조도 변화에 의한 난류변동분 해석

표면조도에 의해 발생하는 난류유동은 공학적, 물리적 분야에서 매우 중요하게 다루어지고 있다. 표면조도는 선박에서도 설계, 용접, 도장 등 각각의 단계에서 다양한 측면으로 고려되어야 할 중요한 요소이다. 본 연구는 표면조도 형상을 일반화하여 PIV기법을 적용하여 수조실험을 수행하였다. 표면조도 조건은 거칠기 형상의 간격에 대해 변화를 주었으며, 실험유속은 Re = <TEX>$1.1{\times}10^4$</TEX>, Re = <TEX>$2.0{\times}10^4$</TEX>, Re = <TEX>$2.9{\times}10^4$</TEX> 에서 시간평균에 대한 난류강도를 알아보았다. 거칠기 계수 증가에 따라 표면 거칠기 형상 근처에서 발생한 난류성분에 의해 난류강도는 강하게 나타났으며, 자유흐름 영역으로 갈수록 유동 방향의 변동이 전혀 없는 흐름이 나타났다. 실험유속 조건 변화에 대한 난류강도의 편차는 크게 영향을 받지 않았다. In physical engineering, the turbulent flow on the surface roughness is very important. With the welding, design and paint, the hull surface roughness at each stage in the various aspects are important factors to be considered. In this study, the hull surface roughness geometry that was generalized to the PIV was applied to the tank test. The roughness of the surface changed the distance of the interval. Experimental velocity is Re = <TEX>$1.1{\times}10^4$</TEX>, Re = <TEX>$2.0{\times}10^4$</TEX> and Re = <TEX>$2.9{\times}10^4$</TEX>. The turbulent intensity at the time-average were examined The roughness coefficient occurred with increasing turbulence intensities was stronger. The turbulence intensity away from the roughness in the shape was zero. The variation of turbulence intensity at the experimental flow conditions change was not affected.