This paper utilizes the experimental and numerical results obtained during quenching of stainless steel (SS) probes in carbon nanotube (CNT) nanofluids to arrive at an optimum CNT concentration and bath temperature for maximum quenching heat transfer rate. The individual effect of CNT concentration and bath temperature on the quenching heat transfer rate has recently been published by the authors. The objective of this work is to study the combined effect of CNT concentration and bath temperature on the heat transfer rate during quenching. For this purpose, CNT nanofluids were prepared by suspending chemically treated CNTs in de-ionized (DI) water without any surfactant at 0.50 and 0.75 wt. % of CNTs. Cylindrical quench probes made of SS 304L with a diameter of 20 mm and an aspect ratio of 2.5 were quenched in the CNT nanofluids by maintaining at 30, 40, and 50°C using an external water bath. The recorded time-temperature data during quenching were used as input and the heat flux and temperature at the quenched surface were estimated based on the inverse heat conduction (IHC) method. The computed boiling curves during quenching were used in conjunction with the boiling curves published in literature to arrive at an optimum CNT concentration and bath temperature for maximum heat transfer rates. The computational results showed that the peak heat flux during quenching of SS probes in CNT nanofluids increased when the CNT nanofluid was maintained at 40 than at 30°C and it started decreasing with further increase in the bath temperature irrespective of the CNT concentration. The enhanced heat transfer performance of CNT nanofluid at a slightly higher temperature during quenching is attributed to the enhanced Brownian motion of CNTs in nanofluid.
{"title":"Optimum CNT Concentration and Bath Temperature for Maximum Heat Transfer Rate during Quenching in CNT Nanofluids","authors":"K. Babu, T. Kumar","doi":"10.1520/JAI104442","DOIUrl":"https://doi.org/10.1520/JAI104442","url":null,"abstract":"This paper utilizes the experimental and numerical results obtained during quenching of stainless steel (SS) probes in carbon nanotube (CNT) nanofluids to arrive at an optimum CNT concentration and bath temperature for maximum quenching heat transfer rate. The individual effect of CNT concentration and bath temperature on the quenching heat transfer rate has recently been published by the authors. The objective of this work is to study the combined effect of CNT concentration and bath temperature on the heat transfer rate during quenching. For this purpose, CNT nanofluids were prepared by suspending chemically treated CNTs in de-ionized (DI) water without any surfactant at 0.50 and 0.75 wt. % of CNTs. Cylindrical quench probes made of SS 304L with a diameter of 20 mm and an aspect ratio of 2.5 were quenched in the CNT nanofluids by maintaining at 30, 40, and 50°C using an external water bath. The recorded time-temperature data during quenching were used as input and the heat flux and temperature at the quenched surface were estimated based on the inverse heat conduction (IHC) method. The computed boiling curves during quenching were used in conjunction with the boiling curves published in literature to arrive at an optimum CNT concentration and bath temperature for maximum heat transfer rates. The computational results showed that the peak heat flux during quenching of SS probes in CNT nanofluids increased when the CNT nanofluid was maintained at 40 than at 30°C and it started decreasing with further increase in the bath temperature irrespective of the CNT concentration. The enhanced heat transfer performance of CNT nanofluid at a slightly higher temperature during quenching is attributed to the enhanced Brownian motion of CNTs in nanofluid.","PeriodicalId":15057,"journal":{"name":"Journal of Astm International","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2012-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"86778410","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
C. White, D. Hunston, K. Tan, J. Filliben, A. Pintar, G. Schueneman
An accurate service life prediction model is needed for building joint sealants in order to greatly reduce the time to market of a new product and reduce the risk of introducing a poorly performing product into the marketplace. A stepping stone to the success of this effort is the precise control of environmental variables in a laboratory accelerated test apparatus in order to produce reliable weathering data that can be used to generate a predictive model. This contribution reports a systematic study, using a novel laboratory test apparatus, investigating the individual and synergistic impacts of four environmental factors (cyclic movement, temperature, relative humidity, and ultraviolet radiation) on the durability of a sealant system. The apparatus used is unique because it not only allows the precise control of environmental factors but also permits in situ characterization tests so that the specimens need not be removed from the apparatus chamber. Graphical and quantitative statistical approaches have been used to analyze the data. The study shows that the critical role of each individual factor, as well as synergism among the different factors, can be readily quantified, and modes of degradation possibly can be identified.
{"title":"A Systematic Approach to the Study of Accelerated Weathering of Building Joint Sealants","authors":"C. White, D. Hunston, K. Tan, J. Filliben, A. Pintar, G. Schueneman","doi":"10.1520/JAI104091","DOIUrl":"https://doi.org/10.1520/JAI104091","url":null,"abstract":"An accurate service life prediction model is needed for building joint sealants in order to greatly reduce the time to market of a new product and reduce the risk of introducing a poorly performing product into the marketplace. A stepping stone to the success of this effort is the precise control of environmental variables in a laboratory accelerated test apparatus in order to produce reliable weathering data that can be used to generate a predictive model. This contribution reports a systematic study, using a novel laboratory test apparatus, investigating the individual and synergistic impacts of four environmental factors (cyclic movement, temperature, relative humidity, and ultraviolet radiation) on the durability of a sealant system. The apparatus used is unique because it not only allows the precise control of environmental factors but also permits in situ characterization tests so that the specimens need not be removed from the apparatus chamber. Graphical and quantitative statistical approaches have been used to analyze the data. The study shows that the critical role of each individual factor, as well as synergism among the different factors, can be readily quantified, and modes of degradation possibly can be identified.","PeriodicalId":15057,"journal":{"name":"Journal of Astm International","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2012-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"76593734","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
D. Ehntholt, K. Beltis, Michaela Jakubowski, John F. Martin, M. Mccomish
After an event involving the deliberate release of toxic chemicals, there is a need to collect samples at the affected site for preservation, recovery, and analysis of the chemical species of interest. These would likely include the active or toxic species as well as chemicals that could serve as chemical attribution signatures that would be important in assigning responsibility for the release. In this preliminary study, a standard gauze pad surface sampling material and technique was compared with the use of silicone rubber samplers placed on glass and coated steel solid surfaces. A range of commercially available silicone rubbers was examined for possible use and one was selected for more extensive evaluation due to its relative ease of handling and minimal interferences with the analytical process. The experiments were conducted with organic chemical species that covered a range of volatilities; two contaminant challenge concentrations were used. The silicone rubber samplers, as applied, were found to consistently collect higher quantities of organic chemicals from the solid surfaces than did the gauze pads. Results of these initial experiments are discussed and ongoing efforts are briefly described.
{"title":"New Surface Samplers for Use in Forensic Sampling after a Chemical Incident","authors":"D. Ehntholt, K. Beltis, Michaela Jakubowski, John F. Martin, M. Mccomish","doi":"10.1520/JAI104217","DOIUrl":"https://doi.org/10.1520/JAI104217","url":null,"abstract":"After an event involving the deliberate release of toxic chemicals, there is a need to collect samples at the affected site for preservation, recovery, and analysis of the chemical species of interest. These would likely include the active or toxic species as well as chemicals that could serve as chemical attribution signatures that would be important in assigning responsibility for the release. In this preliminary study, a standard gauze pad surface sampling material and technique was compared with the use of silicone rubber samplers placed on glass and coated steel solid surfaces. A range of commercially available silicone rubbers was examined for possible use and one was selected for more extensive evaluation due to its relative ease of handling and minimal interferences with the analytical process. The experiments were conducted with organic chemical species that covered a range of volatilities; two contaminant challenge concentrations were used. The silicone rubber samplers, as applied, were found to consistently collect higher quantities of organic chemicals from the solid surfaces than did the gauze pads. Results of these initial experiments are discussed and ongoing efforts are briefly described.","PeriodicalId":15057,"journal":{"name":"Journal of Astm International","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2012-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"73449948","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
M. Filippini, S. Beretta, L. Patriarca, G. Pasquero, S. Sabbadini
The fatigue properties of a Ti-48Al-2Cr-2Nb alloy obtained by electron-beam melting (EBM) with a patented process has been examined by conducting high cycle fatigue tests performed at different R ratios at room temperature. Fatigue-crack propagation tests have been performed for the purpose of characterizing the fatigue-crack growth rate and threshold of the material. Additionally, specimens with artificially introduced defects have been fatigue tested with the objective of studying the growth behavior of small cracks. Artificial defects with different sizes have been generated in the gauge section of the specimens by electron-discharge machining (EDM). After EDM defects are produced, the specimens are pre-cracked in cyclic compression, so that small cracks can be generated at the root of the EDM starter defects. Fatigue tests are conducted by applying the staircase technique with the number of cycles of censored test (runout) fixed at 107 cycles. By employing the Murakami model for the calculation of the range of stress intensity factor, the threshold stress intensity factor range dependence on the loading ratio R and on the defect size is evaluated, highlighting the relevant parameters that govern the specific mechanisms of failure of the novel γ–TiAl alloy studied in the present work.
{"title":"Fatigue Sensitivity to Small Defects of a Gamma–Titanium–Aluminide Alloy","authors":"M. Filippini, S. Beretta, L. Patriarca, G. Pasquero, S. Sabbadini","doi":"10.1520/JAI104293","DOIUrl":"https://doi.org/10.1520/JAI104293","url":null,"abstract":"The fatigue properties of a Ti-48Al-2Cr-2Nb alloy obtained by electron-beam melting (EBM) with a patented process has been examined by conducting high cycle fatigue tests performed at different R ratios at room temperature. Fatigue-crack propagation tests have been performed for the purpose of characterizing the fatigue-crack growth rate and threshold of the material. Additionally, specimens with artificially introduced defects have been fatigue tested with the objective of studying the growth behavior of small cracks. Artificial defects with different sizes have been generated in the gauge section of the specimens by electron-discharge machining (EDM). After EDM defects are produced, the specimens are pre-cracked in cyclic compression, so that small cracks can be generated at the root of the EDM starter defects. Fatigue tests are conducted by applying the staircase technique with the number of cycles of censored test (runout) fixed at 107 cycles. By employing the Murakami model for the calculation of the range of stress intensity factor, the threshold stress intensity factor range dependence on the loading ratio R and on the defect size is evaluated, highlighting the relevant parameters that govern the specific mechanisms of failure of the novel γ–TiAl alloy studied in the present work.","PeriodicalId":15057,"journal":{"name":"Journal of Astm International","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2012-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"84430756","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Bone surrogates are proposed alternatives to human cadaveric vertebrae for assessing interbody device subsidence. Polyurethane foam blocks are an accepted surrogate for cancellous bone but do not share their heterogeneous bone density distribution. Synthetic vertebrae have been recently developed as an alternative bone surrogate with representations of cortices, endplates, and cancellous bone. The efficacy of each surrogate was evaluated by uniaxially indenting it with an interbody device. The force-displacement curve profiles, failure forces, and depth of implant subsidence were compared for devices seated centrally and peripherally on the surrogates. The synthetic endplate mimicked human endplates through a gradually increasing endplate thickness toward the periphery. This enabled the synthetic vertebrae to provide additional subsidence resistance to implants seated at the periphery. By contrast, the foam block was insensitive to implant placement. Absence of failure in synthetic vertebrae from peripheral implant indentation suggests the synthetic endplate is stronger than human endplates but further study with human cadaveric vertebrae is needed.
{"title":"Comparison of Two Bone Surrogates for Interbody Device Subsidence Testing","authors":"A. Aiyangar, A. Au, P. Anderson, H. Ploeg","doi":"10.1520/JAI103498","DOIUrl":"https://doi.org/10.1520/JAI103498","url":null,"abstract":"Bone surrogates are proposed alternatives to human cadaveric vertebrae for assessing interbody device subsidence. Polyurethane foam blocks are an accepted surrogate for cancellous bone but do not share their heterogeneous bone density distribution. Synthetic vertebrae have been recently developed as an alternative bone surrogate with representations of cortices, endplates, and cancellous bone. The efficacy of each surrogate was evaluated by uniaxially indenting it with an interbody device. The force-displacement curve profiles, failure forces, and depth of implant subsidence were compared for devices seated centrally and peripherally on the surrogates. The synthetic endplate mimicked human endplates through a gradually increasing endplate thickness toward the periphery. This enabled the synthetic vertebrae to provide additional subsidence resistance to implants seated at the periphery. By contrast, the foam block was insensitive to implant placement. Absence of failure in synthetic vertebrae from peripheral implant indentation suggests the synthetic endplate is stronger than human endplates but further study with human cadaveric vertebrae is needed.","PeriodicalId":15057,"journal":{"name":"Journal of Astm International","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2012-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"84518685","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Corrosion fatigue-crack growth characteristics are important for the design of marine and off-shore structures. Design of critical components requires data on fatigue-crack growth rate at very low frequencies of the order of 10−2 to 10−3 Hz. Experiments at low frequencies pose practical difficulties of enormous test duration. To address this, it is proposed to estimate corrosion crack growth characteristics using a frequency shedding method where the frequency is shed with crack advance using an exponential law. Fatigue-crack growth rate tests have been conducted on Ni–Mn–Cr steel at a constant ΔK range of 18 MPa√m (lower Paris regime) under lab air conditions as well as 3.5 % NaCl solution. Crack growth rate data plotted as a function of test frequency presents a straight-line trend in log–log scale for a frequency range of 1–0.1 Hz; however, there is a change in trend when the frequencies are dropped further, which could be due to domination of corrosion mechanism. To understand the role of crack closure, crack closure estimates were obtained at periodic intervals of crack length and the effective stress intensity graphs suggest acceleration in crack growth rate due to corrosion as the frequency is reduced.
{"title":"Estimation of Corrosion Fatigue-Crack Growth through Frequency Shedding Method","authors":"R. Prakash, S. Dhinakaran","doi":"10.1520/JAI103988","DOIUrl":"https://doi.org/10.1520/JAI103988","url":null,"abstract":"Corrosion fatigue-crack growth characteristics are important for the design of marine and off-shore structures. Design of critical components requires data on fatigue-crack growth rate at very low frequencies of the order of 10−2 to 10−3 Hz. Experiments at low frequencies pose practical difficulties of enormous test duration. To address this, it is proposed to estimate corrosion crack growth characteristics using a frequency shedding method where the frequency is shed with crack advance using an exponential law. Fatigue-crack growth rate tests have been conducted on Ni–Mn–Cr steel at a constant ΔK range of 18 MPa√m (lower Paris regime) under lab air conditions as well as 3.5 % NaCl solution. Crack growth rate data plotted as a function of test frequency presents a straight-line trend in log–log scale for a frequency range of 1–0.1 Hz; however, there is a change in trend when the frequencies are dropped further, which could be due to domination of corrosion mechanism. To understand the role of crack closure, crack closure estimates were obtained at periodic intervals of crack length and the effective stress intensity graphs suggest acceleration in crack growth rate due to corrosion as the frequency is reduced.","PeriodicalId":15057,"journal":{"name":"Journal of Astm International","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2012-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"84821351","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
There are several methods available to measure residual stress fields present within a structural component. Recently a new so called on-line crack compliance technique has been proposed, which is based on linear elastic fracture mechanics. This experimental method uses incremental crack mouth opening displacements measured during fatigue crack growth testing to generate information on the existing residual stresses along the crack line. The present study employs two dimensional (2D) plane stress finite element simulations of fatigue crack growth from a cold worked hole to investigate the performance of this technique. Using the simulation results, the stress intensity factors due to the residual stress field normalized by the maximum applied stress intensity factor KIrs/KImax were obtained from the on-line crack compliance method. For validation, the J-integral approach was used to calculate KIrs/KImax values from fatigue crack growth simulations in an elastic material. The two methods generated nearly identical results. Fatigue crack growth was also simulated in an elastic-plastic material. Even though the stress intensity factor is not the appropriate crack tip characterizing technique for elastic-plastic material conditions, it is still investigated here to approximate the actual testing conditions, where plastic deformation near the crack tip is unavoidable. The KIrs/KImax solutions are presented for different cold work levels and applied loadings. Results indicate that the agreement between the elastic and elastic-plastic crack growth solutions is dependent on the maximum applied loading level, as might be expected.
{"title":"Study of an On-Line Crack Compliance Technique for Residual Stress Measurement Using 2D Finite Element Simulations of Fatigue Crack Growth","authors":"S. Ismonov, S. Daniewicz","doi":"10.1520/JAI103952","DOIUrl":"https://doi.org/10.1520/JAI103952","url":null,"abstract":"There are several methods available to measure residual stress fields present within a structural component. Recently a new so called on-line crack compliance technique has been proposed, which is based on linear elastic fracture mechanics. This experimental method uses incremental crack mouth opening displacements measured during fatigue crack growth testing to generate information on the existing residual stresses along the crack line. The present study employs two dimensional (2D) plane stress finite element simulations of fatigue crack growth from a cold worked hole to investigate the performance of this technique. Using the simulation results, the stress intensity factors due to the residual stress field normalized by the maximum applied stress intensity factor KIrs/KImax were obtained from the on-line crack compliance method. For validation, the J-integral approach was used to calculate KIrs/KImax values from fatigue crack growth simulations in an elastic material. The two methods generated nearly identical results. Fatigue crack growth was also simulated in an elastic-plastic material. Even though the stress intensity factor is not the appropriate crack tip characterizing technique for elastic-plastic material conditions, it is still investigated here to approximate the actual testing conditions, where plastic deformation near the crack tip is unavoidable. The KIrs/KImax solutions are presented for different cold work levels and applied loadings. Results indicate that the agreement between the elastic and elastic-plastic crack growth solutions is dependent on the maximum applied loading level, as might be expected.","PeriodicalId":15057,"journal":{"name":"Journal of Astm International","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2012-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"75495735","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Farzad Baratzadeh, Christian Widener, H. Lankarani, D. Burford
The purpose of this study was to obtain a better understanding of crack initiation at friction stir weld exit holes in no-load transfer coupons as a first-order approximation of the potential performance of friction stir welding (FSW) joints employed for aircraft fuselage applications. In order to meet this goal, the effects of weld exit location on fatigue life in discontinuous friction stir lap-welded panels were documented. Sheets of aluminum alloys 7075-T6 and 2024-T3 were chosen for the FSW lap welds. Constant amplitude fatigue tests were carried out in order to determine the effect of various welding scenarios on fatigue crack initiation. A number of weld exit strategies were investigated, as well as another FSW tool design called a retractable pin tool (RPT). This tool was shown to eliminate the exit hole and reduce the stress concentration around the weld exit location. Prior to this work, none of the attempted exit strategies was found to delay or eliminate the initiation of fatigue cracks at the exit holes of discontinuous FSW lap welds. Only by using the RPT, which is able to eliminate the exit hole completely, was it possible to produce fatigue life results in coupons with a tool extraction zone that were comparable to those in baseline coupons containing no extraction zone.
{"title":"Methods to Increase the Fatigue Life of Friction Stir Lap Welds in No-load Transfer Coupons Using a Retractable Pin Tool","authors":"Farzad Baratzadeh, Christian Widener, H. Lankarani, D. Burford","doi":"10.1520/JAI103899","DOIUrl":"https://doi.org/10.1520/JAI103899","url":null,"abstract":"The purpose of this study was to obtain a better understanding of crack initiation at friction stir weld exit holes in no-load transfer coupons as a first-order approximation of the potential performance of friction stir welding (FSW) joints employed for aircraft fuselage applications. In order to meet this goal, the effects of weld exit location on fatigue life in discontinuous friction stir lap-welded panels were documented. Sheets of aluminum alloys 7075-T6 and 2024-T3 were chosen for the FSW lap welds. Constant amplitude fatigue tests were carried out in order to determine the effect of various welding scenarios on fatigue crack initiation. A number of weld exit strategies were investigated, as well as another FSW tool design called a retractable pin tool (RPT). This tool was shown to eliminate the exit hole and reduce the stress concentration around the weld exit location. Prior to this work, none of the attempted exit strategies was found to delay or eliminate the initiation of fatigue cracks at the exit holes of discontinuous FSW lap welds. Only by using the RPT, which is able to eliminate the exit hole completely, was it possible to produce fatigue life results in coupons with a tool extraction zone that were comparable to those in baseline coupons containing no extraction zone.","PeriodicalId":15057,"journal":{"name":"Journal of Astm International","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2012-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"76271392","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
A simple one step solution phase approach to synthesize copper nanofluids has been developed, involving simultaneous in situ synthesis of nanoparticles and their dispersion in the base fluid. Copper nitrate has been reduced using ascorbic acid in ethylene glycol under thermal as well as microwave conditions. Sodium lauryl sulfate has been used to control the size of the particle as well as to act as a stabilizing agent. The effect of ratio of the reactants, pH, power of microwave, reaction time, and dilution on the size of the particles has been studied using X-ray diffraction, transmission electron microscopy, and field-emission scanning electron microscopy. The characterization of the fluids has also been done using Fourier transform infrared spectrometry, ultraviolet-visible spectroscopy, selected area electron diffraction, and energy dispersive X-ray analysis. The thermal conductivity and viscosity of the fluid were also measured at various particle concentrations. The copper particles in the fluid were found to have size less than 50nm and were well dispersed in the fluid. Thus this method was found to preserve the advantages of the polyol process and aqueous chemical reduction method as well. The fluid was stable up to 5 weeks under stationary conditions at room temperature. This method employs fast, inexpensive, extendible process for the synthesis of copper nanofluids and also overcomes the drawbacks of two step process.
{"title":"Synthesis of Copper Nanofluids Using Ascorbic Acid Reduction Method Via One Step Solution Phase Approach","authors":"Sandhya Shenoy, A. N. Shetty","doi":"10.1520/JAI104416","DOIUrl":"https://doi.org/10.1520/JAI104416","url":null,"abstract":"A simple one step solution phase approach to synthesize copper nanofluids has been developed, involving simultaneous in situ synthesis of nanoparticles and their dispersion in the base fluid. Copper nitrate has been reduced using ascorbic acid in ethylene glycol under thermal as well as microwave conditions. Sodium lauryl sulfate has been used to control the size of the particle as well as to act as a stabilizing agent. The effect of ratio of the reactants, pH, power of microwave, reaction time, and dilution on the size of the particles has been studied using X-ray diffraction, transmission electron microscopy, and field-emission scanning electron microscopy. The characterization of the fluids has also been done using Fourier transform infrared spectrometry, ultraviolet-visible spectroscopy, selected area electron diffraction, and energy dispersive X-ray analysis. The thermal conductivity and viscosity of the fluid were also measured at various particle concentrations. The copper particles in the fluid were found to have size less than 50nm and were well dispersed in the fluid. Thus this method was found to preserve the advantages of the polyol process and aqueous chemical reduction method as well. The fluid was stable up to 5 weeks under stationary conditions at room temperature. This method employs fast, inexpensive, extendible process for the synthesis of copper nanofluids and also overcomes the drawbacks of two step process.","PeriodicalId":15057,"journal":{"name":"Journal of Astm International","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2012-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"73859679","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Nanofluids are being evaluated as alternative heat transfer fluids, and thus their behavior during storage or low velocity applications in which natural convection can be significant has to be known and documented. Buoyancy induced flows in rectangular enclosures using nanofluids can be studied experimentally using thermocouples, thermistors, surface heat flux sensors, and ultrasound thermometry. The effects of the mass fraction concentration of nanoparticles, the enclosure aspect ratio, and the inclination have been studied experimentally, but more could be done. The opacity of nanofluids does not permit the use of particle image velocimetry, laser induced fluorescence, or any other means of flow visualization or visual temperature measurement of the local fluid temperature. However, the temperature field can be observed using a non-invasive method such as ultrasound thermometry. The experimental enclosure here was validated using water as the initial fluid; measured values of the local fluid temperature were compared with numerical simulations utilizing commercial software. Nanofluid mass fractions of 10% and 25% were used for comparative purposes to study the effects of concentration on the temperature field. Buoyancy force reversal effects were witnessed in both 10% and 25% concentrations. The nanofluid also prolonged the multicellular effects that occur in buoyancy inversion flows. A Rayleigh number inversion was observed with the 25% mass fraction nanofluid. The multicellular regime transitions to a boundary layer regime at about Ra = 1 × 107 when the aspect ratio is 2.625 and at about Ra = 2 × 108 when the aspect ratio is 1.000 for different concentrations of nanofluid. The observations could be physically explained. The current work confirms that temperature measurements of the flow field can be made to assess convective regimes and flow phenomena that induce significant temperature variations. The use of ultrasound thermometry is successfully demonstrated for opaque nanofluid.
{"title":"Use of Ultrasound Thermometry to Study Natural Convection in Opaque Nanofluids","authors":"K. Wong, B. Bon","doi":"10.1520/JAI104320","DOIUrl":"https://doi.org/10.1520/JAI104320","url":null,"abstract":"Nanofluids are being evaluated as alternative heat transfer fluids, and thus their behavior during storage or low velocity applications in which natural convection can be significant has to be known and documented. Buoyancy induced flows in rectangular enclosures using nanofluids can be studied experimentally using thermocouples, thermistors, surface heat flux sensors, and ultrasound thermometry. The effects of the mass fraction concentration of nanoparticles, the enclosure aspect ratio, and the inclination have been studied experimentally, but more could be done. The opacity of nanofluids does not permit the use of particle image velocimetry, laser induced fluorescence, or any other means of flow visualization or visual temperature measurement of the local fluid temperature. However, the temperature field can be observed using a non-invasive method such as ultrasound thermometry. The experimental enclosure here was validated using water as the initial fluid; measured values of the local fluid temperature were compared with numerical simulations utilizing commercial software. Nanofluid mass fractions of 10% and 25% were used for comparative purposes to study the effects of concentration on the temperature field. Buoyancy force reversal effects were witnessed in both 10% and 25% concentrations. The nanofluid also prolonged the multicellular effects that occur in buoyancy inversion flows. A Rayleigh number inversion was observed with the 25% mass fraction nanofluid. The multicellular regime transitions to a boundary layer regime at about Ra = 1 × 107 when the aspect ratio is 2.625 and at about Ra = 2 × 108 when the aspect ratio is 1.000 for different concentrations of nanofluid. The observations could be physically explained. The current work confirms that temperature measurements of the flow field can be made to assess convective regimes and flow phenomena that induce significant temperature variations. The use of ultrasound thermometry is successfully demonstrated for opaque nanofluid.","PeriodicalId":15057,"journal":{"name":"Journal of Astm International","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2012-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"86984329","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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