The Experts below are selected from a list of 2235 Experts worldwide ranked by ideXlab platform
David L Ross - One of the best experts on this subject based on the ideXlab platform.
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high spatial resolution thermal mapping of radiofrequency ablation lesions using a novel Thermochromic Liquid Crystal myocardial phantom
Journal of Cardiovascular Electrophysiology, 2013Co-Authors: W Chik, M A Barry, Sujitha Thavapalachandran, Christine Midekin, Jim Pouliopoulos, Gopal Sivagangabalan, Stuart P Thomas, David L RossAbstract:BACKGROUND: Radiofrequency (RF) ablation causes thermal mediated irreversible myocardial necrosis. This study aimed to (i) characterize the thermal characteristics of RF ablation lesions with high spatial resolution using a Thermochromic Liquid Crystal (TLC) myocardial phantom; and (ii) compare the Thermochromic lesions with in vivo and in vitro ablation lesions. METHODS AND RESULTS: The myocardial phantom was constructed from a vertical sheet of TLC film, with color change between 50 °C (red) to 78 °C (black), embedded within a gel matrix, with impedance titrated to equal that of myocardium. Saline, with impedance titrated to blood values at 37 °C, was used as supernatant. A total of 51 RF ablations were performed. This comprised 17 ablations in the Thermochromic gel phantom, bovine myocardial in vitro targets and ovine in vivo ablations, respectively. There was no difference in lesion dimensions between the Thermochromic gel and in vivo ablations (lesion width 10.2 ± 0.2 vs 10.2 ± 2.4, P = 0.93; and depth 6.3 ± 0.1 vs 6.5 ± 1.7, P = 0.74). The spatial resolution of the Thermochromic film was tested using 2 thermal point-sources that were progressively opposed and was demonstrated to be <300 μm. CONCLUSIONS: High spatial resolution thermal mapping of in vitro RF lesions with spatial resolution of at least 300 μm is possible using a Thermochromic Liquid Crystal myocardial phantom model, with a good correlation to in vivo RF ablations. This model may be useful for assessing the thermal characteristics of RF lesions created using different ablation parameters and catheter technologies.
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High Spatial Resolution Thermal Mapping of Radiofrequency Ablation Lesions Using a Novel Thermochromic Liquid Crystal Myocardial Phantom
Journal of Cardiovascular Electrophysiology, 2013Co-Authors: W Chik, M A Barry, Sujitha Thavapalachandran, Christine Midekin, Jim Pouliopoulos, Gopal Sivagangabalan, Stuart P Thomas, David L Ross, Alistair McewanAbstract:BACKGROUND: Radiofrequency (RF) ablation causes thermal mediated irreversible myocardial necrosis. This study aimed to (i) characterize the thermal characteristics of RF ablation lesions with high spatial resolution using a Thermochromic Liquid Crystal (TLC) myocardial phantom; and (ii) compare the Thermochromic lesions with in vivo and in vitro ablation lesions. METHODS AND RESULTS: The myocardial phantom was constructed from a vertical sheet of TLC film, with color change between 50 °C (red) to 78 °C (black), embedded within a gel matrix, with impedance titrated to equal that of myocardium. Saline, with impedance titrated to blood values at 37 °C, was used as supernatant. A total of 51 RF ablations were performed. This comprised 17 ablations in the Thermochromic gel phantom, bovine myocardial in vitro targets and ovine in vivo ablations, respectively. There was no difference in lesion dimensions between the Thermochromic gel and in vivo ablations (lesion width 10.2 ± 0.2 vs 10.2 ± 2.4, P = 0.93; and depth 6.3 ± 0.1 vs 6.5 ± 1.7, P = 0.74). The spatial resolution of the Thermochromic film was tested using 2 thermal point-sources that were progressively opposed and was demonstrated to be
Michael J Owen - One of the best experts on this subject based on the ideXlab platform.
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solutions of fourier s equation appropriate for experiments using Thermochromic Liquid Crystal
International Journal of Heat and Mass Transfer, 2012Co-Authors: Oliver Pountney, Gary D Lock, Michael J OwenAbstract:Abstract In transient heat-transfer experiments, the time to activate the Thermochromic Liquid Crystal (TLC) can be used to evaluate h , the heat transfer coefficient. Most experimenters use the solution of Fourier’s equation for a semi-infinite substrate with a step-change in the temperature of the fluid to determine h . The ‘semi-infinite solution’ can also be used to determine T ad , the adiabatic surface temperature, but this is an error-prone method suitable only for experiments with relatively large values of Bi, the Biot number. For Bi > 2, which covers most practical cases, more accurate results could be achieved using a composite substrate of two materials. Using TLC to determine the temperature–time history of the surface of the composite substrate, h and T ad could be computed from the numerical solution of Fourier’s equation. Alternatively, h and T ad could be determined analytically from a combination of the semi-infinite and steady-state solutions.
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transient heat transfer measurements using Thermochromic Liquid Crystal lateral conduction error
International Journal of Heat and Fluid Flow, 2005Co-Authors: James R Kingsleyrowe, Gary D Lock, Michael J OwenAbstract:Abstract Thermochromic Liquid Crystal (TLC) can be used to measure the surface temperature in transient heat transfer experiments. Knowing the time at which the TLC changes colour, hence knowing the surface temperature at that time, it is possible to calculate the heat transfer coefficient, h , and the analytical one-dimensional solution of Fourier’s conduction equation for a semi-infinite wall is often used for this purpose. However, the 1D solution disregards lateral variations of the surface temperature (that is, those variations parallel to the surface), which can cause a bias, or lateral-conduction error, in the calculated value of h . This paper shows how the 1D analytical solution can be used to estimate, and to provide a correction for, the error. An approximate two-dimensional analysis (which could be readily extended to three dimensions) is used to calculate the error, and a 2D finite-difference solution of Fourier’s equation is used to validate the method.
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transient heat transfer measurements using Thermochromic Liquid Crystal part 1 an improved technique
International Journal of Heat and Fluid Flow, 2003Co-Authors: P J Newton, Gary D Lock, Nia E Stevens, Simon T Evatt, Michael J OwenAbstract:Abstract It is common practice to employ Thermochromic Liquid Crystal (TLC) to determine heat transfer coefficients, h , in transient experiments. The method relies on the solution of Fourier’s conduction equation, usually with the boundary condition of a step-change in air temperature. In practice a step-change can be difficult to achieve, and a more general solution to the one-dimensional conduction equation is presented here for a “slow transient,” where the rise in air temperature is represented by an exponential series. An experimental method, based on this technique, requires only a single measurement of surface temperature history, and this has the advantage that narrow-band TLC can be used. As an example, measurements of h are presented from an experiment modelling the internal flow of cooling air inside a gas turbine engine. The measurements are analysed using both the conventional step-change method and the exponential-series technique, and the results show that using the step-change method can give rise to significant errors in the calculated values of h . The new technique should be applicable to many other slow transient heat transfer measurements.
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transient heat transfer measurements using Thermochromic Liquid Crystal part 2 experimental uncertainties
International Journal of Heat and Fluid Flow, 2003Co-Authors: Michael J Owen, P J Newton, Gary D LockAbstract:Abstract In Part 1 of this two-part paper, an “exponential-series technique” was used to calculate heat transfer coefficient, h , for the so-called slow transient case where it is not possible to generate a step-change in the air temperature. Small uncertainties in the measured temperatures can, however, create large uncertainties in the calculated value of h , and the amplification parameter, Φ h , is defined as the ratio of the relative uncertainty in h to the relative uncertainties in the temperatures. Using an uncertainty analysis, theoretical expressions for Φ h are found for the slow transient case, and these expressions are in excellent agreement with values computed using a Monte Carlo method. The results provide guidance in the selection of design parameters for an experiment and for the calculation and minimisation of the uncertainty in h .
Nadia Abdullah - One of the best experts on this subject based on the ideXlab platform.
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the basics and issues of Thermochromic Liquid Crystal calibrations
Experimental Thermal and Fluid Science, 2010Co-Authors: Nadia Abdullah, Abd Rahim Abu Talib, Abdul Aziz Jaafar, Mohamad Amran Mohd Salleh, W T ChongAbstract:Thermochromic Liquid Crystals (TLCs) have been widely used by researchers in heat transfer and fluid flow communities as a thermal imaging tool for mapping surface and spatial temperature distributions. In order to utilize TLCs for quantitative temperature measurements, calibration is first necessary to determine the colour–temperature relationship of TLCs. This paper is aimed to provide novice and intermediate users of TLCs with a review on the basics and issues pertaining to calibrations of TLCs, particularly for surface thermography. A general overview of TLCs, the basic elements of a TLC calibration rig, and the common calibration methods of TLCs are described. The crucial issues associated with calibrations of TLCs, namely, imaging, colourimetry, illumination, hysteresis, film thickness and aging, and the methods used to compensate for these effects are discussed. This paper is intended to provide useful information to novice and intermediate users of TLCs, particularly on TLC calibrations.
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erratum to film thickness effects on calibrations of a narrowband Thermochromic Liquid Crystal experimental thermal and fluid science 33 2009 561 578
Experimental Thermal and Fluid Science, 2010Co-Authors: Nadia Abdullah, Abd Rahim Abu Talib, Abdul Aziz Jaafar, Helmey Ramdhaney Mohd Saiah, Mohamad Amran Mohd SallehAbstract:Department of Mechanical Engineering, Faculty of Engineering, Universiti Malaya, 50603 Kuala Lumpur, Malaysia b Propulsion and Thermo-Fluids Research Group, Department of Aerospace Engineering, Faculty of Engineering, Universiti Putra Malaysia, 43400 Serdang, Selangor, Malaysia Department of Chemical and Environmental Engineering, Faculty of Engineering, Universiti Putra Malaysia, 43400 Serdang, Selangor, Malaysia
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film thickness effects on calibrations of a narrowband Thermochromic Liquid Crystal
Experimental Thermal and Fluid Science, 2009Co-Authors: Nadia Abdullah, Abd Rahim Abu Talib, Abdul Aziz Jaafar, Helmey Ramdhaney Mohd Saiah, Mohamad Amran Mohd SallehAbstract:Thermochromic Liquid Crystals (TLCs) have been widely employed by researchers in heat transfer and fluid flow communities as a reliable and non-intrusive temperature measurement tool due to their unique optical properties such as birefringence, optical activity, circular dichroism and selective reflection of colours in the visible spectrum as function of temperature. The use of narrowband TLCs are attractive for temperature and heat transfer measurements due to their higher precision in temperature measurements and due to the fact that narrowband TLCs are less affected by variations in illumination-viewing angles and illumination disturbances. Narrowband TLCs have been used with full intensity-matching methods to provide robust image processing for measurements of thermal parameters in transient heat transfer tests. Calibration of narrowband TLCs is necessary in order to obtain the intensity-temperature relationship of the TLCs. Film thickness is one of the factors which affects calibrations of TLCs. In this research, film thicknesses of 10, 20, 30, 40 and 50 μm were investigated on green intensity-based calibrations of R35C1W TLC during heating and cooling. Results showed an increase in magnitude of peak green intensity with increasing film thickness, with a percentage increase of nearly 18% when film thickness increased from 10 to 50 μm. Results also showed an inconsistent shift in temperature at which peak green intensity occurs, with a maximum shift of 0.40 °C, suggesting that film thickness effects may be insignificant for narrowband TLCs compared with wideband TLCs. A theoretical method for estimating the volume of TLC coating required to achieve a desired film thickness has also been described in this paper, based on the surface area and dry solids content of the TLC. The method is easily implemented and applicable for sprayable TLC coatings.
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effect of film thickness on narrowband Thermochromic Liquid Crystal calibration
2009Co-Authors: Nadia AbdullahAbstract:Thermochromic Liquid Crystals (TLCs or TLC) are complex organic substances which selectively reflect visible light as function of temperature. Narrowband TLCs are attractive for temperature measurements due to their higher precision in temperature measurements associated with their narrow bandwidths, and calibrations of narrowband TLCs are less affected by variations in illumination-viewing angles and background illumination. In order to properly utilize narrowband TLCs and intensitymatching methods for quantitative temperature measurements, it is important to investigate film thickness effects on intensity-based calibrations of narrowband TLCs, which have been previously ignored in previous research. Film thicknesses of 10, 20, 30, 40 and 50 μm were investigated on green intensity-based calibrations of R35C1W narrowband TLC during heating and cooling. The results showed an increase in magnitude of peak green intensity with increasing film thickness, with a percentage increase of approximately 18% when film thickness increased from 10 μm to 50 μm. The results also showed an inconsistent shift in peak green temperature, with a maximum temperature shift of 0.40oC, suggesting that film thickness effects may be insignificant for narrowband TLCs compared with wideband TLCs. A theoretical method for estimating the volume of coating formulation required to achieve a desired film thickness was presented in this research, based on the film coverage and dry solids content of the TLCs. Results were presented for seven samples of sprayable narrowband TLCs with desired film thicknesses of 10, 20, 30, 40 and 50 μm based on a square shaped model surface area. The percentage uncertainties in volume of coating formulation was obtained to be significant, within 57 – 67%, however, the results were attributed mainly to the lack in accuracy of the electronic balance, which was ± 1 g. Simulation results showed that if the accuracy was increased to ± 0.001 g, the percentage uncertainties decreased to less than 5% for all samples. The method is easily implemented, and is likely to be beneficial to users intending to employ sprayable TLCs for temperature measurements. In this research, a graphical user interface (GUI) was developed to process images and data in transient calibration of TLCs. The GUI functions to generate full intensity-based calibration curves based on single colour intensity in the Red-Green- Blue (RGB) colour space. The GUI greatly simplifies, streamlines and automates image and data processing, which at present, is carried out by low-level programming and keyboard-entered commands. The GUI is likely to be a useful tool for users intending to utilize TLCs for temperature measurements.
Gary D Lock - One of the best experts on this subject based on the ideXlab platform.
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Solutions of Fourier’s equation appropriate for experiments using Thermochromic Liquid Crystal
International Journal of Heat and Mass Transfer, 2012Co-Authors: Oliver Pountney, Gary D Lock, J M OwenAbstract:Abstract In transient heat-transfer experiments, the time to activate the Thermochromic Liquid Crystal (TLC) can be used to evaluate h , the heat transfer coefficient. Most experimenters use the solution of Fourier’s equation for a semi-infinite substrate with a step-change in the temperature of the fluid to determine h . The ‘semi-infinite solution’ can also be used to determine T ad , the adiabatic surface temperature, but this is an error-prone method suitable only for experiments with relatively large values of Bi, the Biot number. For Bi > 2, which covers most practical cases, more accurate results could be achieved using a composite substrate of two materials. Using TLC to determine the temperature–time history of the surface of the composite substrate, h and T ad could be computed from the numerical solution of Fourier’s equation. Alternatively, h and T ad could be determined analytically from a combination of the semi-infinite and steady-state solutions.
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solutions of fourier s equation appropriate for experiments using Thermochromic Liquid Crystal
International Journal of Heat and Mass Transfer, 2012Co-Authors: Oliver Pountney, Gary D Lock, Michael J OwenAbstract:Abstract In transient heat-transfer experiments, the time to activate the Thermochromic Liquid Crystal (TLC) can be used to evaluate h , the heat transfer coefficient. Most experimenters use the solution of Fourier’s equation for a semi-infinite substrate with a step-change in the temperature of the fluid to determine h . The ‘semi-infinite solution’ can also be used to determine T ad , the adiabatic surface temperature, but this is an error-prone method suitable only for experiments with relatively large values of Bi, the Biot number. For Bi > 2, which covers most practical cases, more accurate results could be achieved using a composite substrate of two materials. Using TLC to determine the temperature–time history of the surface of the composite substrate, h and T ad could be computed from the numerical solution of Fourier’s equation. Alternatively, h and T ad could be determined analytically from a combination of the semi-infinite and steady-state solutions.
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accurate heat transfer measurements using Thermochromic Liquid Crystal part 2 application to a rotating disc
International Journal of Heat and Fluid Flow, 2009Co-Authors: Vinod U Kakade, Gary D Lock, Michael T Wilson, J M Owen, J E MayhewAbstract:Abstract Encapsulated Thermochromic Liquid Crystal (TLC) can accurately measure surface temperature in a variety of heat transfer and fluid-flow experiments. In Part 1 of this two-part paper, two narrow-band Liquid Crystals were specifically calibrated for application to experiments on a disc rotating at high speed (∼5000 rpm). Part 2 describes how these Crystals were used to measure the surface temperature on the disc in a transient experiment that models the flow of internal cooling air in a gas turbine. The TLC was viewed through the transparent polycarbonate disc using a digital video camera and strobe light synchronised to the disc frequency. The convective heat transfer coefficient, h, was subsequently calculated from the one-dimensional solution of Fourier’s conduction equation for a semi-infinite wall. The analysis accounted for the exponential rise in the air temperature driving the heat transfer, and for experimental uncertainties in the measured values of h. The paper focuses on the method used, and sample experimental results are provided to demonstrate the accuracy and potency of the technique.
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accurate heat transfer measurements using Thermochromic Liquid Crystal part 1 calibration and characteristics of Crystals
International Journal of Heat and Fluid Flow, 2009Co-Authors: Vinod U Kakade, Gary D Lock, Michael T Wilson, J M Owen, J E MayhewAbstract:Abstract Encapsulated Thermochromic Liquid Crystal (TLC) can accurately measure surface temperature in a variety of heat transfer and fluid flow experiments. Narrow-band TLC, where the colour changes over a temperature range of ∼1 °C, can be used to determine surface temperature within an uncertainty of 0.1 °C. Wide-band TLC, typically active over 5–20 °C, allow the possibility of mapping surface temperature distributions. In part 1 of this two-part paper, an extensive set of calibrations for narrow-band and wide-band TLC is reported. This generic study provides insight into the importance and influence of the various factors governing the colour–temperature relationship. These governing effects include the variation in optical path, the spectrum of the illumination source, the lighting and viewing angles, the differences between cooling or heating cycles (hysteresis), the variation with the number of heating or cooling cycles (aging) and how this varies with TLC film thickness. Two narrow-band Crystals are also specifically calibrated for application to experiments on a transparent disc rotating at high speed (∼5000 rpm). Part 2 of this paper describes how these accurately-calibrated Crystals were used to measure the transient surface temperature on, and heat transfer to, a rotating disc.
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transient heat transfer measurements using Thermochromic Liquid Crystal lateral conduction error
International Journal of Heat and Fluid Flow, 2005Co-Authors: James R Kingsleyrowe, Gary D Lock, Michael J OwenAbstract:Abstract Thermochromic Liquid Crystal (TLC) can be used to measure the surface temperature in transient heat transfer experiments. Knowing the time at which the TLC changes colour, hence knowing the surface temperature at that time, it is possible to calculate the heat transfer coefficient, h , and the analytical one-dimensional solution of Fourier’s conduction equation for a semi-infinite wall is often used for this purpose. However, the 1D solution disregards lateral variations of the surface temperature (that is, those variations parallel to the surface), which can cause a bias, or lateral-conduction error, in the calculated value of h . This paper shows how the 1D analytical solution can be used to estimate, and to provide a correction for, the error. An approximate two-dimensional analysis (which could be readily extended to three dimensions) is used to calculate the error, and a 2D finite-difference solution of Fourier’s equation is used to validate the method.
Smith Eiamsaard - One of the best experts on this subject based on the ideXlab platform.
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visualization of heat transfer characteristics using Thermochromic Liquid Crystal temperature measurements in channels with inclined and transverse twisted baffles
International Journal of Thermal Sciences, 2020Co-Authors: Smith Eiamsaard, V ChuwattanakulAbstract:Abstract Channels with ribs/baffles are widely applied in thermal engineering applications such as heat exchangers, solar water/air heaters and gas turbine cooling. In the present work, inclined and transverse twisted-baffles (I-TBs/T-TBs) are developed for heat transfer enhancement in a channel. The effects of Reynolds number (Re = 4000, 8000, 12,000, 16,000 and 20,000) roughness pitch ratios (p/w = 4.0, 6.0, 8.0, 10.0 and 12.0) and baffle twist ratios (y/w = 2.0, 3.0, 4.0 and 5.0 corresponding to twisted-baffle loop numbers (N) of 5, 7, 8 and 9) were investigated using air (Prandtl number, Pr = 0.7) as a working fluid. Heat transfer behavior was examined using Thermochromic Liquid Crystal temperature measurements. Typical transverse and inclined baffles were also tested for comparison. Heat transfer, flow friction and thermal performance are reported in terms of Nusselt numbers (Nu), Nusselt number ratios (Nu/Nus), friction factors (f), friction factor ratios (f/fs) and thermal performance indices (η). Experimental results reveal that under most conditions examined, I-TBs show better heat transfer, lower frictional losses and higher thermal performance than TBs, IBs and T-TBs. For I-TBs, maximum heat transfer and thermal performance are obtained at a moderate pitch ratio (p/w = 6.0). However, in cases of T-TBs, heat transfer and thermal performance monotonically increase with a decreasing pitch ratio. Friction losses caused by both I-TBs and T-TBs decrease considerably with increasing pitch ratio. For I-TBs, heat transfer and thermal performance monotonically increase with increasing twist ratios. However, for T-TBs, maximum heat transfer and thermal performance are obtained at y/w = 3.0. Over the present studied range, a channel with I-TBs having optimal geometry (p/w = 6.0 and y/w = 5.0) yields maximum thermal performance indices, as high as 1.98, which is greater than the maximum values yielded by channels with T-TBs, TBs, IBs, and smooth channels, by around 74.1%, 98%, 52.5% and 98.3%.
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heat transfer visualization of co counter dual swirling impinging jets by Thermochromic Liquid Crystal method
International Journal of Heat and Mass Transfer, 2015Co-Authors: Smith Eiamsaard, K Nanan, Khwanchit WongchareeAbstract:The objective of the experimental study is to investigate heat transfer of co/counter-dual swirling impinging jets (Co-DSIJs/C-DSIJs) on the impingement surfaces under uniform wall heat flux boundary condition. Two twisted-tapes were inserted into pipe nozzles with different arrangements: (1) each tape was twisted in the same direction as the co-dual tapes for producing co dual swirls and (2) each tape was twisted in the different directions as the counter-dual tapes for inducing counter dual swirls. The effect of the Co-DSIJs/C-DSIJs with baffles placed between the tapes for jet confinement on heat transfer was also investigated. The effects of jet Reynolds number (5000 ⩽ Re ⩽ 20,000), jet-to-plate spacing (1 < L/D < 8) and tape twist ratio (y/W = 3, 4, 5 and 6) were examined. In addition, the experiments using a single swirling impinging jet (SIJ) and a conventional impinging jet (CIJ) were also carried out, for comparison. The temperature distributions on impinged surfaces were recorded via a Thermochromic Liquid Crystal (TLC) sheet and then Nusselt number distributions were obtained by a Liquid Crystal thermography technique. The experimental results revealed that for all Co-DSIJs and C-DSIJs, heat transfer increased with decreasing nozzle-to-plate spacing (L/D) and increasing Reynolds number. For the Co-DSIJs and C-DSIJs without baffle, heat transfer increased with increasing twist ratio (decreasing swirl number) while the opposite trend was found for the Co-DSIJs and C-DSIJs with baffle. At similar conditions, the Co-DSIJs and C-DSIJs with baffles offered higher heat transfer than the ones without baffle, owing to the combined effect of swirling flow and jet confinement. For small jet-to-plate spacings (L/D = 1 and 2), all swirling jets possessed considerably higher average Nusselt numbers than the conventional jets, at similar conditions. At large jet-to-plate spacings (L/D = 4, 6 and 8), the average Nusselt numbers of the conventional and swirling jets became comparable. For the studied range, the maximum average Nusselt number of 110 was achieved by using C-DSIJs with baffle at L/D = 1, y/W = 3 and Re = 20,000.
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effect of cross flow velocity on flow and heat transfer characteristics of impinging jet with low jet to plate distance
Journal of Mechanical Science and Technology, 2014Co-Authors: Makatar Waehayee, Smith Eiamsaard, Perapong Tekasakul, Chayut NuntadusitAbstract:An effect of cross-flow velocity on flow and heat transfer characteristics of impinging jet in the case of low jet-to-plate distance at H = 2D was experimentally and numerically investigated. In the experiments, the air jet from orifice impingement on the wall of wind tunnel while a cross-flow was simultaneously induced normal to the jet flow. The jet velocity was fixed while the cross-flow velocity was varied corresponding to velocity ratios (jet velocity/cross-flow velocity) VR = 3, 5 and 7. The temperature distribution on an impinged surface was visualized by using Thermochromic Liquid Crystal sheet (TLCs), and Nusselt number distribution was evaluated by using image processing method. The flow pattern on impingement surface was visualized by using oil film technique. The numerical simulation was carried out for a better understanding of the jet flow in the cross-flow. The results show that Nusselt number peak shifts downstream and the Nusselt number peak increases with increasing cross-flow velocity.
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visualization of flow and heat transfer characteristics for swirling impinging jet
International Communications in Heat and Mass Transfer, 2012Co-Authors: Chayut Nuntadusit, Makatar Waehayee, Asi Bunyajitradulya, Smith EiamsaardAbstract:Abstract Flow and heat transfer characteristics of swirling impinging jet (SIJ) were studied experimentally at constant nozzle-to-plate distance of L = 4D. The swirling jet is generated by inserting twisted tapes within a pipe nozzle. Effects of swirl on the impinged surface are investigated at twist ratios (y/W) of ∞ (straight tape), 3.64, 2.27, 1.82, and 1.52. The flow patterns of the free swirling jet and the swirling impinging jet were visualized by mixing dye with the jet flow. Distributions of temperature and convective heat transfer coefficient on the impinged surface were measured with Thermochromic Liquid Crystal (TLC) sheet and image processing technique. Additionally, an oil film technique was performed as a complementary technique for flow visualization on the impinged surface. The experimental results reveal that there appear to be two peaks of heat transfer in the jet impingement region. The heat transfer enhancements in jet impingement region can be achieved at a low twist ratio of 3.64 which corresponds to the swirl number of 0.4.
