Dimpling Technique Research Articles

Dimples in turbulent pipe flows: experimental aero-thermal investigation

An experimental investigation is performed to study the effects of turbulent flow structures on the wall heat transfer, specifically inside the spherical cavities of partially dimpled tubes. The geometry under investigation consists of an array of spherical cavities distributed over the inner surface of half a tube. Each row has five indentations separated by an angular offset of 36° over the half circumference. The dimples are characterized by a depth-to-print diameter (d/Dp) of 0.18, a print diameter-to-pipe diameter (Dp/D) of 0.25, and a streamwise distance (xd/D) between consecutive cavities of 0.56. At Re=20000, flow separation, reattachment, and secondary flows are captured using both planar Particle Image Velocimetry (PIV) and stereo-PIV. The time-averaged flow field, the vorticity levels, and Turbulent Kinetic Energy (TKE) fields inside the dimples can be used for numerical validation. Moreover, the local heat transfer field inside the cavity is measured for Re=20000−80000, by using Liquid Crystals Thermography (LCTG). At the same Re and Pr, an overall heat transfer enhancement of 1.8 (1.8 times the Nusselt number value (Nu) in bare pipes) has been measured. The use of dimples in heat exchangers thus results in a rise in thermal efficiency at the cost of an increased pressure drop. Comparing the skin friction coefficient (Cf) of the dimpled pipe with the one measured in ribbed tubes for Re=20000−80000, it is shown that higher levels of the aerothermal performance (high heat transfer and low-pressure losses) are achieved by employing the dimple technique.

Numerical investigation on heat transfer performance and flow characteristics in circular tubes with dimpled twisted tapes using Al2O3-water nanofluid

The present study numerically examines heat transfer and flow in circular tubes fitted with dimpled twisted tape inserts, and Al2O3-water nanofluid is employed. Considering the effects of dimples, protrusions, nanofluid volume fraction α and nanoparticle diameter dp, the discussion and analysis on heat transfer, flow characteristics, turbulence kinetic energy TKE, thermal property, entropy generation and maximum local wall temperature Tmax are detailedly provided. The results show that dimple side and protrusion side both realize great heat transfer enhancement, and dimple side behaves better compared with protrusion side. Utilization of dimples leads to an increase by 25.53% in convective heat transfer coefficient h at most compared with smooth tape. Heat transfer performance is greatly improved on both tape wall and tube wall owing to disturbance to flow structures. The overall TKE level significantly rises especially close to the core flow region when dimples are adopted, and overall swirl flow intensity greatly increase, further resulting in enhancement of turbulent mixing and heat transfer. Remarkable decline in average heat transfer entropy generation rate Sah is identified, accompanied by slight rise in average friction entropy generation rate Saf, where average total entropy generation rate Sa inclines by 29.10% at most in comparison with smooth tape. Besides, the employment of nanofluids results in great improvement of heat transfer, with further enhanced effect when α increases, accompanied by slight growth in resistance. A maximum increase by 58.96% in h is identified compared with basefluid case, and it is quite helpful that in this case the maximum rise in friction factor is only 5.05%. The wall temperature distribution is greatly improved using nanofluid, and nanofluid case provides markedly improved thermal conductivity distribution in spite of slight growth in dynamic viscosity. The heat transfer in recirculation-caused low heat transfer regions is further promoted through nanofluids when dimple technique is adopted. Utilization of nanofluid brings about a significant reduction in Sah, the effect of which is further promoted by a rising α, with a slight increase in Saf, where Sa is reduced by 28.89% at most. The Tmax greatly declines using nanofluids with further enhanced effect when α ascends. Furthermore, utilization of smaller dp gives rise to significant heat transfer enhancement compared with the larger one, with extremely mild resistance increase. Lower Sa and lower Tmax are both realized when smaller dp is used, and the effect of dp reaches an extremely low level when it exceeds 40nm.

Focused intravascular ultrasonic probe using dimpled transducer elements

High-frequency focused intravascular ultrasonic probes were fabricated in this study using dimple technique based on PMN–PT single crystal and lead-free KNN–KBT–Mn ceramic. The center frequency, bandwidth, and insertion loss of the PMN–PT transducer were 34MHz, 75%, and 22.9dB, respectively. For the lead-free probe, the center frequency, bandwidth, and insertion loss were found to be 40MHz, 72%, and 28.8dB, respectively. The ultrasonic images of wire phantom and vessels with good resolution were obtained to evaluate the transducer performance. The −6dB axial and lateral resolutions of the PMN–PT probe were determined to be 58μm and 131μm, respectively. For the lead-free probe, the axial and lateral resolutions were found to be 44μm and 125μm, respectively. These results suggest that the mechanical dimpling technique has good potential in preparing focused transducers for intravascular ultrasound applications.

High frequency PMN–PT single crystal focusing transducer fabricated by a mechanical dimpling technique

High frequency (∼30MHz and ∼80MHz) focusing ultrasound transducers were fabricated using a PMN–0.28PT single crystal by a mechanical dimpling technique. The dimpled single crystal was used as an active element for the focusing transducer. Compared with a plane transducer, the focusing transducer fabricated with a dimpled active element exhibits much broader bandwidth and higher sensitivity. Besides, a high quality image can be obtained by the 30MHz focusing transducer, in which the −6dB axial and lateral resolution is 27μm and 139μm, respectively. These results prove that the dimpling technique is capable to fabricate the high frequency focusing transducers with excellent performance for imaging applications.

Optimization of the Natural Frequencies of Beams Via Dimpling Technique

In this paper, the natural frequencies of a beam, with different boundary conditions, are enhanced by creating cylindrical dimples on its surface. These dimples alter the local stiffness in the beam while keeping its mass the same. This method is cost-effective in comparison with other structural dynamics modification methods (SDM) because it is a one-step manufacturing method and because it enhances the dynamic behaviour of beam structures without additional weight or additional joints.The natural frequencies of dimpled beam are calculated by finite element method. In particular, ANSYS package is used in building the dimpled beam models for modal analysis. The effect of dimple location and size on the beam fundamental frequency is investigated. The simulation results indicated that creating dimples on simply supported and free–free beams decreases their fundamental frequencies, while creating dimples on clamped beams may increase their fundamental frequency.The optimal designs of dimpled beams are presented. The proposed method couples the finite element method for the modal analysis with an optimization technique based on genetic algorithm (GA). The optimization results show that dimpling technique is an effective technique to optimize the natural frequencies. The proposed technique is experimentally validated. The experimental results show a good agreement with the simulation results.

PMN–PT single crystal focusing transducer fabricated using a mechanical dimpling technique

A ∼5 MHz focusing PMN–PT single crystal ultrasound transducer has been fabricated utilizing a mechanical dimpling technique, where the dimpled crystal wafer was used as an active element of the focusing transducer. For the dimpled focusing transducer, the effective electromechanical coupling coefficient was enhanced significantly from 0.42 to 0.56. The dimpled transducer also yields a −6 dB bandwidth of 63.5% which is almost double the bandwidth of the plane transducer. An insertion loss of the dimpled transducer (−18.1 dB) is much lower than that of the plane transducer. Finite element simulation also reveals specific focused beam from concave crystal surface. These promising results show that the dimpling technique can be used to develop high-resolution focusing single crystal transducers.

Dentin exposure in tooth preparations for porcelain veneers: A pilot study

The various clinical techniques available for even reduction of a tooth surface to receive a porcelain veneer restoration do not produce a consistently even conservative reduction. In addition, it is not known which technique is most conservative of enamel. The purpose of this pilot study was to assess the effectiveness of 3 clinical techniques, namely, dimple, depth groove, and freehand, in producing an intraenamel preparation. The relation between overpreparation beyond the commonly accepted depth of preparation of 0.5 mm and dentin exposure was also examined. A single operator prepared 3 groups of 5 extracted maxillary central incisors to a depth of 0.5 mm using dimple, depth-groove, and freehand methods of tooth preparation. The prepared teeth were scanned using an x-ray microtomography scanner. The reconstructed images were studied using software that provided a volume-rendering routine so that, by choosing suitable x-ray linear attenuation coefficient thresholds, enamel (2.78 cm(-1) at 40 keV) and dentin (1.63 cm(-1) at 40 keV) surfaces could be viewed. The percentage area of enamel conserved was analyzed from these images. Coordinate metrology was used to produce color-coded images depicting the depth of preparation. The Kruskal-Wallis test was used to determine the statistical significance (alpha=.05) in the difference between the mean percentage area of enamel conserved in the 3 technique groups. The coordinate metrology and x-ray microtomography images were visually compared to study the correlation between overpreparation and dentin exposure. The Kruskal-Wallis test did not demonstrate significant difference (P=.07) between the 3 techniques in conserving enamel. However, the dimple technique showed a greater trend to retaining a larger mean percentage area of enamel (77.5% +/- 14.2) compared to depth-groove (50.1% +/- 17.5) and freehand (76.8% +/- 24.4) techniques. Preparation depth in the range of 0.4 to 0.6 mm was largely seen to be intraenamel, except in the cervical region. Within the limitations of this pilot study, the 3 different techniques tested did not differ significantly in conserving enamel.

Characterization of advanced complementary metal–oxide–semiconductor processes with reverse secondary ion mass spectrometry profiling

Secondary ion mass spectrometry (SIMS) profiling from the backside of a wafer containing the silicon-on-insulator structure has proven to be a unique way to achieve high accuracy in the characterization of a through-gate-oxide phosphorous profile in a complementary metal–oxide–semiconductor (CMOS) gate stack [P. Ronsheim et al., J. Vac. Sci. Technol. B 20, 448 (2002)]. In this work, we extended the sample preparation method for reverse SIMS by including the traditional transmission electron microscopy dimpling technique and generated large area openings with good reproducibility. Details about the flatness of sample surfaces, electrical conductivity near the surface of polycrystalline Si films, and difference between frontside and reverse SIMS data were elaborated by profiling an annealed P-type metal–oxide–semiconductor gate sample with polycrystalline Si doped with boron. The capability of reverse SIMS was further evaluated by characterizing the Hf distribution at the interface of the HfO2/Si substrate and Cu diffusion in a Cu/Ta/SiO2/Si stack, two typical analytical requests from CMOS front-end and back-end processes that have been challenges to SIMS. It was demonstrated that reverse SIMS was a promising solution to the characterization of abrupt interfaces that used to be hindered by the large decay lengths dominated by beam-bombardment-induced diffusion, segregation, preferential sputtering, etc.

Geographic distribution of porcelain veneer preparation depth with various clinical techniques

Statement of problem Various clinical techniques have been advocated for uniform reduction of the tooth surface before a porcelain veneer restoration. Often these techniques do not produce a consistently uniform labial reduction. Purpose The purpose of this study was to identify the degree of inconsistency on a geographic scale in the depth of labial reduction for porcelain veneers, resulting from the use of 3 clinical techniques. The technique of co-ordinate metrology was used to map the variations in the depth of the preparation. Material and methods A single operator using 3 techniques (dimples as depth guides, freehand, or depth grooves as depth guides) prepared 90 noncarious, unrestored extracted teeth to receive porcelain veneers (n=30). Impressions of the prepared and unprepared teeth were scanned with a co-ordinate measuring machine. In-house software was used to color-code the plotted images on the basis of the depth of preparation. Profile measurements were also made along the mid-labial sagital plane at the mid-labial, incisal, and cervical regions, as well as along the mesial proximal and distal proximal areas along the mid-labial horizontal plane. The ideal depth range for the labial reduction was chosen to be 0.4 to 0.6 mm. One-way analysis of variance and the Bonferroni test were performed to determine the significance ( P<.05) in the difference between the means of reductions achieved with the 3 techniques. Results There was no statistically significant difference in the mean percentage area prepared to the ideal depth range (0.4 mm-0.6 mm), between dimple (44.59%), freehand (36.35%), and depth groove (38.43%) techniques. The difference in the mean percentage area of reduction greater than 0.6 mm between dimple (12.98%), freehand (29.66%), and dimple and depth groove (37.32%) techniques were statistically significant ( P=.0000), but not between freehand and depth groove techniques. With the profile measurements it was seen that there were statistically significant differences in the mean depth between dimple (0.45 mm) and depth groove (0.63 mm), and freehand (0.51 mm) and depth groove in the mid-buccal ( P<.0004) and cervical (dimple = 0.48 mm, freehand = 0.52 mm, depth groove = 0.63 mm) ( P<.0005) regions. There was statistically significant difference ( P<.0000) in the mean depth between the dimple (0.39 mm) and freehand (0.30 mm), dimple and depth groove (0.50 mm), and freehand and depth groove techniques in the incisal area. In the mesial proximal region statistically significant difference ( P<.0034) in the mean depth was found between the dimple (0.52 mm) and freehand (0.68 mm), and dimple and depth groove (0.64 mm) techniques only. In the distal proximal region, there was no statistically significant difference in the mean depth between dimple (0.55 mm), freehand (0.66 mm), and depth groove (0.64 mm) techniques. Conclusion The use of dimple technique showed a trend to greater consistency and fidelity in labial reduction to a depth of 0.4 to 0.6 mm. The 3 techniques for veneer preparations studied were associated with varying degrees of inconsistency in the distribution of depth of preparation within a tooth and between teeth in the same technique group.

An Order of Magnitude Improvement in Detection Limits Achieved by Using a New Sample Support in Small Spot Xrf Analysis.

A new sample support film for small spot XRF analysis has been developed that improves detection limits by a factor of 10 over traditional polymer supports. The surface characteristics of this new film are excellent for retaining drops of sample solution in one place and allowing the solution to dry into a single spot A dimpling technique was developed to further aid in concentrating the evaporated samples to the prescribed spot size and position. The film showed good resistance to chemical attacfc from the solution, even some strong acids and bases. The detection limits achieved using micro sample XRF with the ultra thin sample support were sufficient to be a comparable alternative to ICP-MS and GFAAS for elemental analysis.

Preparation of Large Thin Area Vlsi Tem Specimens by Dimpling With A “Flatting Tool”

AbstractAn alternative VLSI TEM specimen preparation technique has been developed to produce 100μm diameter electron transparent thin area by using a conventional dimpler with a texmet padded ‘flatting tool’ for dimpling and a microcloth padded ‘flatting tool’ for polishing, followed by low angle ion milling. The advantages of this technique are a large sampling area and shorter milling times than conventional specimen preparation methods. In the following, we report the details of the modified dimpling technique. The improvements in available electron transparency, and a decrease in ion milling time are demonstrated with the preparation of planar and cross section VLSI device samples.

An improved dimpling technique for the preparation of TEM specimens

Traditional techniques for the preparation of TEM specimens have been electrolytic thinning or a combination of mechanical prethinning (dimpling) and ion-beam milling. The focus of discussion for this paper is an advanced technique for the mechanical dimpling procedure.A new device has been designed so that TEM specimens are consistently produced, thus minimizing the need for intensive operator intervention, trial and error methods, and ion-milling time. This instrument incorporates many of the features utilized in standard dimpling techniques. In addition, it provides the ability to simultaneously rotate and oscillate the specimen, resulting in an increased electron beam transparent area. Actual grinding rates are programmed with a resolution of 0.1 μ.m/min, thus eliminating the reliance on adjustable counterweight systems to control the grinding rate/force. A 40X microscope and movable magnetic specimen mount permit precise positioning that enables the dimple to be located at any point on the specimen. This is illustrated in Fig. 3, where the dimple is positioned on the interface of interest. An integral lamp back lights the specimen so that transparency can be detected without removing the specimen from the instrument. During the preparation process, the actual specimen thickness is continuously indicated on an alphanumeric display.

A study of a high repetition rate condensed arc source for the analysis of low alloy steels using different counter electrode sample configurations—I. A comparison between flat and dimple samples using a pointed tungsten counter electrode

A high repetition condensed arc source was investigated as a light source for the analysis of low alloy steel samples. The arc operated in an argon atmosphere using a sequential spectrometer as radiation recorder. Two techniques are compared viz. flat and dimple surface samples. Photographs of eroded surfaces are presented and discussed. Using manganese as test element present in a number of steel samples with different physical and chemical compositions, sample preparation, the experiments performed and an evaluation technique are described. The results are evaluated and discussed. It was found that long pre-arc times are necessary before relatively stable conditions set in and that the most satisfactory results are recorded using the line pair Mn I403.449/Fe I376.379 with the dimple technique.

The Effect of Interference on the Dimpled, Loaded-Hole Fatigue Strength of 2024-T3 Alclad® Aluminum Alloy

Abstract The effect of interference fit on the fatigue strength of loaded holes is well known. Recently a new technique has been developed for increasing this strength in thin sheet material. The technique consists of dimpling the material centering about the region where the hole is to be made and thus introducing tensile plastic strain. The dimple is then flattened and the hole drilled, leaving the region around the hole under residual compressive stress. Experiments were carried out to obtain the combined effect of interference and dimpling in loaded-hole fatigue applications. In zero-totension fatigue tests on nominally 1.60-mm (0.063-in.) thick 2024-T3 Alclad® aluminum alloy specimens, combined optimum tapered-pin interference and dimpling gave a fatigue strength improvement factor of 4.0 while the dimpling technique increased the fatigue strength by a factor of 2.85 at 106 cycles to failure.