•A micro-bolometer and a simple script are used for thermoelastic stress analysis.•A camera dependent calibration allows quantitative stress measurements.•Spectral leakage and frames missing errors ...have been quantified and corrected.•The SIF and crack tip position in fatigue tests are obtained from infrared data only.
A low-cost Thermoelastic Stress Analysis (TSA) experimental setup is proposed which uses an ordinary micro-bolometer and in-house developed signal processing scripts. The setup is evaluated by analysing the thermoelastic signal from a tensile and a SENT specimen made of stainless steel AISI 304L, and the bolometer performances are compared with those of a state of the art photon detector. Signal processing is based on off-line cross-correlation, using a self-reference signal which is retrieved from the acquired thermal data. Procedures are in particular developed to recognise, quantify and correct errors due to spectral leakage and loss of streamed frames. The thermoelastic signal amplitude/phase, the thermoelastic constant and the Mode I Stress Intensity Factor (SIF) from the bolometer and photonic cameras are evaluated considering the influence of loading frequency, sampling frequency, detector array sub-windowing and acquisition interval duration. A camera-specific linear calibration procedure is applied to correct the thermoelastic signal obtained with the bolometer. The procedure is extended to correct also SIF values, finding a good match with the SIFs obtained by the photon detector. An automatic iterative algorithm, based on the least square fitting of Williams’ series functions, is proposed to identify the crack tip position. An estimation of processing times of the developed signal processing scripts has been carried out, finding that a full crack characterisation (TSA maps, crack tip position, SIF) can be performed with a data acquisition time of 10-20 s, a post-processing time of less than 2 s and an overall hardware cost under 10 k€.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Twelve ITER-like plasma-facing units made of tungsten were exposed in the WEST tokamak divertor, with three plasma-facing units (PFUs) significantly overexposed to plasma heat flux: one sharp-edged ...PFU (vertical misalignment h = 0.8 mm) and two chamfered PFUs (h =0.6 mm and 0.3 mm, respectively). This paper describes the first temperature analysis obtained with a very high spatial resolution infrared camera (pixel size ∼ 0.1 mm) on the misaligned PFU edges and shows the consistency obtained on the parallel heat flux derived from these measurements. The analysis is focused on the hottest areas of the PFU misaligned leading edges, since the temperature detection threshold of the VHR camera is high (Tthreshold,BB ≈ 370 °C). The heat flux parallel to the magnetic field lines is assessed by matching the toroidal temperature profile in the vicinity of the leading edge with 3D finite element modelling. The tungsten emissivity assumed in this study is 0.6, which is consistent with laboratory measurements for damaged PFUs. For the three PFUs studied (with different vertical misalignments, incident angles, geometries), the derived parallel heat flux is similar, and consistent with independent measurements by a Fiber Bragg grating embedded in a graphite PFU at another toroidal location, giving confidence in future experiments using the same settings.
In the present experimental investigation, the flow and heat transfer characteristics of synthetic jet (SJ) issuing from different lobed (3–10) star-shaped orifices are studied. Tests are performed ...by actuating the SJ actuator at constant input power of 4Vrms, with varied range of orifice to surface spacings (1–16) and numerous values of Reynolds number (8692–10746). The synthetic jet's flow characteristics are studied using hot-wire anemometry, while the thermal characteristics are analyzed using an IR camera. Distinct peaks in turbulence intensity are observed in major and minor planes for different lobed (3–6) star orifices; this may be due to the development of two shear layers in such orifices, which consequently merges into a single shear layer for higher lobed (8–10) star orifice. The 6-lobed star orifice is found to exhibit maximum heat transfer performance at z/d varying between 2 and 14. At z/d = 2, the 6-lobed star orifice exhibit 7.6% and 10.1% improvement in average Nusselt number compared to circular and 10-lobed star orifice respectively, which may be due to formation of vortical structures along the lobed edges and subsequent switching of axes between the major and minor planes. To comprehend the energy associated with the issuing vortices, the power spectral density of the velocity signal at the orifice exit is examined. A unified correlation for the average Nusselt number is also derived for various star-shaped orifices.
•Reports flow and thermal behavior of synthetic jet with various lobed star-shaped orifices.•Tests are performed for different orifice to surface spacing and Reynolds number.•Hot-wire anemometry and thermal imaging techniques are employed to measure the flow velocity and temperature, respectively.•The 6-lobed star orifice exhibits maximum average Nusselt number.•The PSD of the velocity signal at orifice exit is analyzed to understand the energy associated with the emanating vortices.•A correlation is proposed for average Nusselt number.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
The paper analyses the possibilities and effectiveness of using infrared thermography with optical thermal excitation by reflection approach in the case of multilayer composites reinforced fibers. ...The advantages and limitations of this technique have been demonstrated via composites reinforced with three types of fibers: glass, aramid, and carbon. The most common defects in such structures are: delaminations, fiber cracks, matrix cracks, and separation of fibers from the matrix. The paper describes some results of the numerical simulations of defects detection using optical IR thermography with the emphasis made on the inspection of multi-layer composite materials. The simulations were conducted in order to determine the detection of defects depending on the depth of their location under the front surface of composite material as well as their geometrical dimensions.
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•Passive controlled impinging jets were experimentally and numerically studied.•The passive-passive controlled jet ECJ triggered an earlier axis switching.•ECJ exhibited the largest heat transfer ...improvement around the stagnation region•The chevron jets lost the uniform distribution of the impinging thermal imprint.
The present study experimentally and numerically investigated the passive control on flow structure evolution and convective heat transfer enhancement for impinging jet. Four different impinging jets, including a baseline circular jet (CJ) and three passive controlled jets, i.e., an elliptic jet (EJ), a circular-chevron jet (CCJ) and an elliptic-chevron jet (ECJ), were comparatively analyzed by utilizing the Particle Image Velocimetry (PIV) technique, infrared (IR) thermography and large eddy simulation (LES) over a wide range of jet-to-wall distances (H/D) at the jet Reynolds number (Re) of 20,000. The results showed that, unlike CJ which presented a general shedding of axisymmetric toroidal vortices, EJ showed highly deformed toroidal structures accompanied with the axis switching effect, both CCJ and ECJ exhibited the well-organized counterrotating streamwise vortex pairs developing from the chevron notches. All the three passive controlled strategies were found to induce a stronger mixing and fluctuating activity near around the stagnation region, especially for ECJ (i.e., the passive–passive controlled device) which showed the highest turbulence level approaching the target wall due to the double-passive enhancement. Moreover, compared with the baseline jet CJ, all the passive controlled jets achieved a significant heat transfer improvement in the vicinity of the stagnation point, particularly for ECJ which presented the highest heat transfer enhancement of about 41% at H/D=5. Whereas both CCJ and ECJ were found to exhibit a less-than-ideal heat transfer performance at a small H when the heat transfer uniformity was specifically considered, due to the anisotropic thermal imprint distributions.
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This paper investigates the surface heat transfer caused by interaction of a jet and a supersonic crossflow near the jet injection hole. A sonic jet with different momentum ratios (J=0.510, 1.018, ...1.477) was injected perpendicularly into a crossflow with a Mach number of 3.0 in a supersonic wind tunnel. Surface temperature through time measured by infrared thermography was used to deduce surface heat flux. In addition, heat transfer coefficients and adiabatic wall temperatures were derived from time histories of surface heat flux and temperature. In order to consider an effect of conduction from the inner hole surface, a three-dimensional energy conservation is considered in the deduction process of the heat flux. As a result, the characteristics of the heat transfer near the hole and the change in the heat transfer with momentum ratios are presented. The separation vortex and recirculation vortex are found to be dominant flow features in terms of the augmentation of the heat transfer. The maximum heat transfer is observed at the immediate vicinity of the hole due to the flow oscillation from a jet-mixing layer. This oscillation resulted in a 390% of augmentation of the heat transfer near the hole compared to the freestream even at the lowest momentum ratio. Also, the augmentation near the hole is more susceptible to change of momentum ratio compared to the augmentation on the overall interaction area.
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An experimental study was performed to understand heat transfer characteristics of inclined liquid jet impingement on heated semi-cylindrical convex curved and flat surfaces in free surface ...configuration (unconfined). In experiments, curvature ratio of D/d = 7 along with the flat surface (D/d → ∞) were considered, here d is the hydraulic diameter of the circular pipe used to produce a liquid jet, and D is the cylindrical surface's diameter. Jet to plate spacing (H) was held constant to 24 mm (H/d = 4). Results are presented for four different inclination angles 0° (orthogonal jet), 15°, 30°, 45°, and Reynolds numbers (17,036 to 42,590). Applicability of inclined jet impingement on a curved and flat surface, their advantage, disadvantages in terms of heat removal rate (Nusselt number) are discussed. A Parametric study was performed by varying Reynolds number, inclination angle, and curvature ratios (D/d) to understand these parameters' effect on heat transfer. Findings revealed that higher inclination angle cases (θ = 30° and θ = 45°) could give an overall high heat removal rate from the cylindrical surface as compared to the orthogonal jet case, especially for higher Reynolds numbers. However, there are no advantages in terms of the heat removal rate by using an inclined jet for lower Reynolds number cases.
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High porosity nanostructured coatings have been extensively studied for their use in enhancing liquid-to-vapor phase change due to their ability to wick liquids laterally across surfaces during ...boiling. Although the effect of these coatings on the maximum heat transfer rate achievable (the critical heat flux) is now well understood, the impact on boiling efficiency (the heat transfer coefficient) is less clear. In this work, a novel experimental apparatus is used to take heat transfer measurements beneath growing and departing bubbles on nanostructured surfaces. By independently tuning the surface heat flux and bubble departure time, IR thermography is used to directly visualize and characterize surface superheat, heat flux, and heat transfer coefficient during the highly transient bubble ebullition cycle. It is shown that although flat surfaces exhibit large spatial and temporal variations in surface temperature and heat flux, the nanostructured coatings produce a uniform temperature profile with enhanced heat transfer due to evaporation from the nanostructure-supported liquid films beneath the bubble. This work demonstrates the relative importance of advancing and receding contact lines, as well as the quenching process, on the overall thermal performance of structured and nonstructured surfaces. It is seen that the combined effects produce a net increase in heat transfer coefficient of over 30%, averaged over the entire ebullition cycle and throughout the entire area of influence. Additionally, the impact of viscous resistance and the importance of the nanostructure dry-out has been studied by tuning the ebullition cycle time to create dry spots. This work shows for the first time the role of nanostructured coatings and thin-film evaporation during nucleate boiling, and it provides a framework to understand the complicated nature of nanostructured boiling across all portions of the boiling curve from nucleation to critical heat flux.
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