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A new thermochromic liquid crystal temperature identification technique using color space interpolations and its application to film cooling effectiveness measurements
Abstract
A new color-temperature identification technique using thermochromic liquid crystals (TLC) and image processing has been developed. The technique is based on the finding that there exists a one-to-one correspondence between a temperature value and a set of TLC tristimulus values (rgb) in a color space (rgb space). Calibration points expressed in terms of rgb values corresponding to various temperatures are plotted in rgb space and then interpolated to obtain a smooth space calibration curve. This space calibration curve does not generally intersect with itself, and therefore the entire reflection region, which is not effectively used by the conventional hue-capturing technique, becomes available. Also, because the calibration curve can be obtained by simple algebraic interpolation, a more complex approach such as a neural network is not required. Moreover, the acceptable region around the calibration curve is clearly defined, and so doubtful pixel information is easily excluded by controlling this region. A temperature measurement system based on this technique has been established using a CCD color camera, image analyzing application board, and Visual C++ programs. With this system, film cooling effectiveness over a flat plate through a round hole, a diffusion-shaped hole, and a diffusion-shaped hole with a vortex generator was studied.
... Hue-temperature calibration is the most common technique used for almost all applications of LCT [3][4][5][7][8][9]. However, other colour maps such as RGB [10] and artificial intelligence techniques such as neural networks [11] have also been used. Matsuda et al [10] used normalized RGB values to develop a smooth calibration curve in three dimensions by interpolating the missing values. ...
... However, other colour maps such as RGB [10] and artificial intelligence techniques such as neural networks [11] have also been used. Matsuda et al [10] used normalized RGB values to develop a smooth calibration curve in three dimensions by interpolating the missing values. The advantage of this technique is that the entire colour bandwidth can be used unlike the hue-temperature calibration. ...
... The advantage of this technique is that the entire colour bandwidth can be used unlike the hue-temperature calibration. However, Matsuda et al [10] have not considered the high standard deviation in RGB values leading to higher uncertainty in the measured temperature. Small variations in light intensity will further affect the RGB values, increasing uncertainty in the measured temperature. ...
Liquid crystal thermography (LCT) is a common surface temperature measurement technique. Typically, the colour response is calibrated against temperature by building an analytical relation between the temperature and the hue of the colour. A suitable polynomial fit is then used to describe this relation after removing the discontinuity in the hue. The variability of hue at each calibration point determines the temperature resolution. However, this technique does not take into consideration the variability in R, G and B intensities used to determine the hue, leading to uncertainty in the measured temperature. This paper describes a novel technique using neural networks to calibrate thermochromic liquid crystal (TLC) material and compensate for high variability in RGB intensities along with other sources of noise in the data. A TLC-based temperature measurement system and calibration results are presented. In our measurements, the lighting intensity (8-bit mean intensity of black surface ± standard deviation) is changed from a minimum of 16.65 ± 2.30 to a maximum of 31.41 ± 3.85. The neural networks were trained on the steady-state TLC calibration system. The results indicate that the neural networks can cope with the variation in lighting by merging the shifted hue curves into a single curve determined by the regression analysis of the test data. Performance characteristics studied on various network configurations relevant to the analysis are described. This approach may be useful in developing liquid crystal thermography for various biomedical applications.
... perienced by the CNLCs within the experimental facility should be within its active temperature range, and that the CNLC first be '''reset'' to below their active temperature range before obtaining a heated calibration curve. This calibration curve can then be used as long as the CNLCs' temperature cycles stay within their active temperature range. Matsuda et al. (2000) have also shown that when operating within the active CNLC temperature range, that hysteresis is negligible. ...
... Other such studies have yielded similar results (Fujisawa and Adrian 1999; Fujisawa and Funatani 2000; Fujisawa et al. 2005; Vejrazka and Marty 2007). Multi-variable calibration curves within the rgb color space have also been studied by Matsuda et al. (2000) and Park et al. (2001) Unlike the previous results, Park et al. (2001) found that their rgb-temperature calibration curve produced larger uncertainties than their hue-temperature calibration curve. They attributed this to the fact that the training vectors to their neural network represented only a narrow set of input values, which when combined with the large uncertainties in their individual r-, g-, b-temperature curves, produced larger uncertainties. ...
Digital particle image thermometry/velocimetry (DPIT/V) is a relatively new methodology that allows for measurements of simultaneous
temperature and velocity within a two-dimensional domain, using thermochromic liquid crystal tracer particles as the temperature
and velocity sensors. Extensive research has been carried out over recent years that have allowed the methodology and its
implementation to grow and evolve. While there have been several reviews on the topic of liquid crystal thermometry (Moffat
in Exp Therm Fluid Sci 3:14–32, 1990; Baughn in Int J Heat Fluid Flow 16:365–375, 1995; Roberts and East in J Spacecr Rockets 33:761–768, 1996; Wozniak et al. in Appl Sci Res 56:145–156, 1996; Behle et al. in Appl Sci Res 56:113–143, 1996; Stasiek in Heat Mass Transf 33:27–39, 1997; Stasiek and Kowalewski in Opto Electron Rev 10:1–10, 2002; Stasiek et al. in Opt Laser Technol 38:243–256, 2006; Smith et al. in Exp Fluids 30:190–201, 2001; Kowalewski et al. in Springer handbook of experimental fluid mechanics, 1st edn. Springer, Berlin, pp 487–561, 2007), the focus of the present review is to provide a relevant discussion of liquid crystals pertinent to DPIT/V. This includes
a background on liquid crystals and color theory, a discussion of experimental setup parameters, a description of the methodology’s
most recent advances and processing methods affecting temperature measurements, and finally an explanation of its various
implementations and applications.
... In an experimental investigation by Matsuda et al. [15], a diffusion-shaped hole with a vortex generator placed inside the diffusor part of the hole exhibited the best film cooling effectiveness compared to a diffusion-shaped hole without vortex generator and a cylindrical hole configuration. In 2006, Kusterer et al. [16] have introduced the Double-Jet Film Cooling (DJFC) technology. ...
In modern gas turbines, film cooling technology is essential for the protection of hot parts. Today, shaped holes are widely used, but besides others, the NEKOMIMI-shaped cooling holes have shown that there is still potential to increase the film cooling effectiveness significantly by generation of Anti-Counter-Rotating Vortices (ACRV). Within the past decade, the technology has been improved step by step at B&B-AGEMA and Kawasaki Heavy Industries Ltd.; mainly by means of numerical simulations. The laterally averaged film cooling effectiveness is typically captured with acceptable accuracy, but the experimental measurements still show a deviation from the numerically obtained results with respect to the local film cooling effectiveness distribution behind the film cooling hole. Nevertheless, the film cooling air spread out in the lateral direction is one of the keys for enhancement of the film cooling performance. Thus, more precise simulations are consequently necessary for improvement of the hole shape configuration.
The present study involves simulations of a baseline fan shaped hole configuration (“777 hole” investigated by Schroeder and Thole [1][2]) using different turbulence models available in STAR-CCM+ with isotropic and anisotropic turbulence consideration (constitutive relations). Distinct differences with respect to flow phenomena (detachments and vortex creation) can be observed depending on the applied turbulence model. In total, the results show that anisotropic viscosity strongly influences the film cooling performance prediction by CFD for prediction of the film cooling effectiveness, but none of the models provides acceptable accuracy in this regard.
... Another method in order to achieve an antikidney vortex structure has been introduced by Rigby and Heidmann [19], who have placed a delta vortex generator downstream of the ejection hole and have found that the vortex generator has been very effective at producing an anti-kidney vortex pair. In an experimental investigation by Matsuda et al. [20], a diffusion-shaped hole with a vortex generator placed inside the shaped part of the hole exhibited the best film cooling effectiveness compared to the diffusion-shaped hole without the vortex generator and a cylindrical hole configuration. ...
In modern gas turbines, the film cooling technology is essential for the protection of the hot parts, in particular of the first stage vanes and blades of the turbine, against the hot gases from the combustion process in order to reach an acceptable life span of the components. As the cooling air is usually extracted from the compressor, the reduction of the cooling effort would directly result in increased thermal efficiency of the gas turbine. Understanding of the fundamental physics of film cooling is necessary for the improvement of the state-of-the-art. Thus, huge research efforts by industry as well as research organizations have been undertaken to establish high efficient film cooling technologies. Today it is common knowledge that film cooling effectiveness degradation is caused by secondary flows inside the cooling jets, i.e. the Counter-Rotating Vortices (CRV) or sometimes also called kidney-vortices, which induce a lift-off of the jet. Further understanding of the secondary flow development inside the jet and how this could be influenced, has led to hole configurations, which can induce Anti-Counter-Rotating Vortices (ACRV) in the cooling jets. As a result, the cooling air remains close to the wall and is additionally distributed flatly along the surface. Beside different other technologies, the NEKOMIMI cooling technology is a promising approach to establish the desired ACRVs. It consists of a combination of two holes in just one configuration so that the air is distributed mainly on two cooling air streaks following the special shape of the generated geometry.
The NEKOMIMI configuration and two conventional cooling hole configurations (cylindrical and shaped holes) has been investigated numerically under adiabatic and conjugate heat transfer conditions. The influence of the conjugate heat transfer on the secondary flow structure has been analysed.
In conjugate heat transfer calculations, it cannot directly derived from the surface temperature distribution if the reached cooling effectiveness values are due to the improved hole configuration with improved secondary flow structure or due to the heat conduction in the material. Therefore, a methodology has been developed, to distinguish between cooling effectiveness due to heat conduction in the material and film cooling flow over the surface. The numerical results shows that for the NEKOMIMI configuration, 77% of the reached overall cooling effectiveness is due to film cooling with improved flow structure in the secondary flow (ACRV) and 23% due to heat conduction in the material. For the cylindrical hole configuration, 10% of the reached overall cooling effectiveness is due to the film cooling flow structure and 90% due to heat conduction in the material.
... Another method in order to achieve an antikidney vortex structure has been introduced by Rigby and Heidmann [19], who have placed a delta vortex generator downstream of the ejection hole and have found that the vortex generator has been very effective at producing an anti-kidney vortex pair. In an experimental investigation by Matsuda et al. [20], a diffusion-shaped hole with a vortex generator placed inside the shaped part of the hole exhibited the best film cooling effectiveness compared to the diffusion-shaped hole without the vortex generator and a cylindrical hole configuration. ...
In modern gas turbines, the film cooling technology is essential for the protection of the hot parts, in particular of the first stage vanes and blades of the turbine, against the hot gases from the combustion process in order to reach an acceptable life span of the components. As the cooling air is usually extracted from the compressor, the reduction of the cooling effort would directly result to an increased thermal efficiency of the gas turbine. Understanding of the fundamental physics of film cooling is necessary for the improvement of the state-of-the-art. Thus, huge research efforts by industry as well as research organizations have been undertaken to establish high efficient film cooling technologies. It is common knowledge today that film cooling effectiveness degradation is caused by secondary flows inside the cooling jets, i.e. the Counter-Rotating Vortices (CRV) or sometimes also mentioned as kidney-vortices, which induce a lift-off of the jet. Further understanding of the secondary flow development inside the jet and how this could be influenced, has led to hole configurations, which can induce Anti-counter-rotating Vortices (ACRV) in the cooling jets. As a result, the cooling air remains close to the wall and is additionally distributed flatly along the surface. Beside different other technologies, the NEKOMIMI cooling technology is a promising approach to establish the desired ACRV. It consists of a combination of two holes in just one configuration so that the air is distributed mainly on two cooling air streaks following the special shape of the generated geometry. The original configuration was found to be difficult for fabrication by advanced machining processes. Thus, the improvement of this configuration has been reached by a set of geometry parameters, which lead to configurations easier to be manufactured but preserving the principle of the NEKOMIMI technology. Within a numerical parametric study several advanced configurations have been obtained and investigated under hot gas flow conditions. By systematic variation of the parameters a further optimization with respect to highest film cooling effectiveness has been performed. The best configuration outperforms the basic configuration by more than 20% regarding the overall averaged adiabatic film cooling effectiveness.
... A delta vortex generator was placed downstream of the ejection hole and, thus, they found that the vortex generator has been very effective at producing an anti-kidney vortex pair. In an experimental investigation by Matsuda et al. [31], a diffusion-shaped hole with a vortex generator placed inside the shaped part of the hole exhibited the best film cooling effectiveness compared to the diffusion-shaped hole without the vortex generator and a cylindrical hole configuration. ...
In modern gas turbines, the film cooling technology is essential for the protection of the hot parts, in particular of the first stage vanes and blades of the turbine, against the hot gases from the combustion process in order to reach an acceptable life span of the components. As the cooling air is usually extracted from the compressor, the reduction of the cooling effort would directly result to an increased thermal efficiency of the gas turbine. Understanding of the fundamental physics of film cooling is necessary for the improvement of the state-of-the-art. Thus, huge research efforts by industry as well as research organizations have been undertaken to establish high efficient film cooling technologies. It is a today common knowledge that film cooling effectiveness degradation is caused by secondary flows inside the cooling jets, i.e. the Counter-Rotating Vortices (CRV) or sometimes also mentioned as kidney-vortices, which induce a lift-off of the jet. Further understanding of the secondary flow development inside the jet and how this could be influenced, has led to hole configurations, which can induce Anti-Counter-Rotating Vortices (ACRV) in the cooling jets. As a result, the cooling air remains close to the wall and is additionally distributed flatly along the surface. Beside different other technologies, the NEKOMIMI cooling technology is a promising approach to establish the desired ACRV. It consists of a combination of two holes in just one configuration so that the air is distributed mainly on two cooling air streaks following the special shape of the generated geometry. The original configuration was found to be difficult for manufacturing even by advanced manufacturing processes. Thus, the improvement of this configuration has been reached by a set of geometry parameters, which lead to configurations much easier to be manufactured but preserving the principle of the NEKOMIMI technology. Within a numerical parametric study several advanced configurations have been obtained and investigated under ambient air flow conditions similar to conditions for a wind tunnel test rig. By systematic variation of the parameters a further optimization with respect to highest film cooling effectiveness has been performed. A set of most promising configurations has been also investigated experimentally in the test rig. The best configuration outperforms the basic configuration by 17% regarding the overall averaged adiabatic film cooling effectiveness under the experimental conditions.
The heat transfer capability was investigated for water flow across a cylinder under the influence of 25 kHz ultrasound in a rectangular duct with a Reynolds number (Re) in the range of 110–2,140. A heating cylinder with constant heat flux was set at the center of the duct. The transducer was mounted on the top wall, and its location was set at -2, -1, 0, +1, and +2 diameters from the cylinder in the streamwise direction. Thermocouples and thermochromic liquid crystals (TLCs) were used to characterize the heat transfer mechanism on the heating surface. In particular, a visualization technique using TLCs was developed to obtain temperature results on a cylindrical surface. The temperature of the heating surface was reduced by the acoustic cavitation process with ultrasonic involvement. The local Nusselt number was increased by 2.37-fold by the waves at a cylindrical angle of 90° and Re value of 110 when the transducer was also located in the middle of the duct. Furthermore, the results indicated that ultrasonic effects could be transported along with the flow when the transducer was located upstream. In addition, when the waves were released downstream, they affected the heat transfer of the cylindrical surface at low Re values. The friction loss in the system was investigated by comparing the pressure drops with and without ultrasound. Depending on the position of the ultrasonic transducer, the pressure drop ratio was in the range 0.88–1.27. Furthermore, the areas most affected by ultrasound were identified using the TLC measurement method, and regions of augmented heat transfer were detected locally on the shaded and unshaded sides of the cylinder. A predictive formula was proposed for the local Nusselt number ratio with and without ultrasound as a function of the Re value, spanwise direction, and cylindrical angle.
This paper describes the conceptual design and cooling blade development of a 1700 °C-class high-temperature gas turbine in the ACRO-GT-2000 (Advanced Carbon Dioxide Recovery System of Closed-Cycle Gas Turbine Aiming 2000K) project. In the ACRO-GT closed cycle power plant system, the thermal efficiency aimed at is more than 60% of higher heating value of fuel (HHV). Because of the high thermal efficiency requirement, the 1700 °C-class high-temperature gas turbine must be designed with the minimum amount of cooling and seal steam consumption. The hybrid cooling scheme, which is a combination of closed loop internal cooling and film ejection cooling, was chosen from among several cooling schemes. The elemental experiments and numerical studies, such as those on blade surface heat transfer, internal cooling channel heat transfer and pressure loss and rotor coolant passage distribution flow phenomena, were conducted and the results were applied to the conceptual design advancement. As a result, the cooling steam consumption in the first stage nozzle and blade was reduced by about 40% compared with the previous design that was performed in the WE-NET (World Energy Network) Phase-I.
The heat transfer characteristics and flow behavior in a rectangular passage with two opposite 45° skewed ribs for turbine rotor blade have been investigated for Reynolds numbers from 7800 to 19,000. In this blade, the spanwise coolant passage at the trailing edge region whose thickness is very thin is chosen, so the channel aspect ratio (=width/height of channel) is extremely high, 4.76. Therefore the heat transfer experiment in the high-aspect-ratio cooling channel was performed using thermochromic liquid crystal and thermocouples. Furthermore, the calculation of flow and heat transfer was carried out using CFD analysis code to understand the heat transfer experimental results. The enhanced heat transfer coefficients on the smooth side wall at the rib's leading end were the same level as those on the rib-roughened walls. © 2002 Scripta Technica, Heat Trans Asian Res, 31(2): 89–104, 2002; DOI 10.1002/htj.10018
There are currently 3 established techniques employed routinely to determine the risk of foot ulceration in the patient with diabetes mellitus. These are the assessment of circulation, neuropathy, and foot pressure. These assessments are widely used clinically as well as in the research domain with an aim to prevent the onset of foot ulceration. Routine neuropathic evaluation includes the assessment of sensory loss in the plantar skin of the foot using both the Semmes Weinstein monofilament and the biothesiometer. Thermological measurements of the foot to assess responses to thermal stimuli and cutaneous thermal discrimination threshold are relatively uncommon. Indeed, there remains uncertainty regarding the importance of thermal changes in the development of foot ulcers. Applications of thermography and thermometry in lower extremity wounds, vascular complications, and neuropathic complications have progressed as a result of improved imaging software and transducer technology. However, the uncertainty associated with the specific thermal modality, the costs, and processing times render its adaptation to the clinic. Therefore, wider adoption of thermological measurements has been limited. This article reviews thermal measurement techniques specific to diabetic foot such as electrical contact thermometry, cutaneous thermal discrimination thresholds, infrared thermography, and liquid crystal thermography.
A wide-band liquid crystal paint was calibrated for its temperature versus color (wavelength) relationship and then used with a true-color digital image processing technique to measure the temperature distribution on a specimen from its color video image. The specimen was a flat, electrically heated sheet with a known heat release (W/m2) so the heat transfer coefficient distribution could be deduced from the temperature distribution, pixel by pixel. The measurement uncertainty of the present procedure is estimated to be about ±10% on each value but that can probably be significantly improved. The present method offers a practical alternative to infra-red thermal imaging. The calibration of the paint was expressed in terms of the 'hue angle' versus temperature using a standard chromaticity representation based on the RGB trichromic decomposition of color.
Some cholesteric liquid crystals change their color according to temperature and are used to show temperature distribution on a surface qualitatively. The present study developed a quantitative method by which temperature distribution can be displayed just like an infra-red thermo-camera. At first, the theoretical ground is presented. The spectral properties of liquid crystal and optical filters are determined. Calibration methods are described and the accuracy of this method is evaluated as 0.2°C, and the order of resolution is 0.01°C. For application, temperature distributions on heated surfaces attached by a cylinder are measured in detail.