The present research is an experimental study of “double enhancement” behavior in pool boiling from heater surfaces simulating microelectronic devices immersed in saturated FC-72 at atmospheric pressure. The term “double enhancement” refers to the combination of two different enhancement techniques: a large-scale area enhancement (square pin fin array) and a small-scale surface enhancement (microporous coating). Fin lengths were varied from 0 (flat surface) to 8 mm. Effects of this double enhancement technique on critical heat flux (CHF) and nucleate boiling heat transfer in the horizontal orientation (fins are vertical) are investigated. Results showed significant increases in nucleate boiling heat transfer coefficients with the application of the microporous coating to the heater surfaces. CHF was found to be relatively insensitive to surface microstructure for the finned surfaces except in the case of the surface with 8 mm long fins. The nucleate boiling and CHF behavior has been found to be the result of multiple, counteracting mechanisms: surface area enhancement, fin efficiency, surface microstructure (active nucleation site density), vapor bubble departure resistance, and re-wetting liquid flow resistance.
{"title":"Pool Boiling Heat Transfer From Plain and Microporous, Square Pin Finned Surfaces in Saturated FC-72","authors":"K. Rainey, S. M. You","doi":"10.1115/1.1288708","DOIUrl":"https://doi.org/10.1115/1.1288708","url":null,"abstract":"\u0000 The present research is an experimental study of “double enhancement” behavior in pool boiling from heater surfaces simulating microelectronic devices immersed in saturated FC-72 at atmospheric pressure. The term “double enhancement” refers to the combination of two different enhancement techniques: a large-scale area enhancement (square pin fin array) and a small-scale surface enhancement (microporous coating). Fin lengths were varied from 0 (flat surface) to 8 mm. Effects of this double enhancement technique on critical heat flux (CHF) and nucleate boiling heat transfer in the horizontal orientation (fins are vertical) are investigated. Results showed significant increases in nucleate boiling heat transfer coefficients with the application of the microporous coating to the heater surfaces. CHF was found to be relatively insensitive to surface microstructure for the finned surfaces except in the case of the surface with 8 mm long fins. The nucleate boiling and CHF behavior has been found to be the result of multiple, counteracting mechanisms: surface area enhancement, fin efficiency, surface microstructure (active nucleation site density), vapor bubble departure resistance, and re-wetting liquid flow resistance.","PeriodicalId":120929,"journal":{"name":"Heat Transfer: Volume 4","volume":"21 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1999-11-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"134116013","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}
Results from the first part of an experimental study of flame spread instability are presented. The instabilities were investigated in the NASA drop facilities because the particular instabilities being examined were most pronounced in microgravity, when the influences of buoyancy were minimized. The flame front over thin cellulosic samples broke apart into separate flamelets which interacted with one another and oscillated (frequency ∼ 1 Hz). Different heat-sink backings, which were used to promote flame instability and flamelet productions are examined and described. Preliminary experiments in the NASA 5 second drop tower (Zero-G) drop facility are discussed.
{"title":"Instability of Flame Spread in Microgravity","authors":"L. Oravecz, I. Wichman, S. Olson","doi":"10.1115/imece1999-1118","DOIUrl":"https://doi.org/10.1115/imece1999-1118","url":null,"abstract":"\u0000 Results from the first part of an experimental study of flame spread instability are presented. The instabilities were investigated in the NASA drop facilities because the particular instabilities being examined were most pronounced in microgravity, when the influences of buoyancy were minimized. The flame front over thin cellulosic samples broke apart into separate flamelets which interacted with one another and oscillated (frequency ∼ 1 Hz). Different heat-sink backings, which were used to promote flame instability and flamelet productions are examined and described. Preliminary experiments in the NASA 5 second drop tower (Zero-G) drop facility are discussed.","PeriodicalId":120929,"journal":{"name":"Heat Transfer: Volume 4","volume":"37 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1999-11-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"134462171","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}
Liquid crystal thermography generates two-dimensional temperature information in a fluid layer. Three-dimensional temperature field can be reconstructed using the two-dimensional temperature fields obtained at various locations with the help of synchronized transverse movements of the light sheet and camera (Lutjen et al., 1999). However, it is not feasible to generate a large number of liquid crystal thermographs that are needed for the reconstruction of a high resolution three-dimensional temperature field. A tomographic reconstruction method is suggested here that can be appropriately used to produce a high resolution three-dimensional reconstruction from a limited number of two-dimensional images of the full temperature field. The two-dimensional temperature fields generated from the experiments can be used to obtain an integrated information of the three-dimensional field from various directions known as projections of the actual three-dimensional field and can be used to reconstruct a high resolution volumetric temperature field.
液晶热成像在流体层中产生二维温度信息。利用在不同位置获得的二维温度场，借助光片和相机的同步横向运动，可以重建三维温度场(Lutjen et al.， 1999)。然而，要产生大量的液晶热像仪来重建高分辨率的三维温度场是不可行的。本文提出了一种层析重建方法，可以适当地从有限数量的全温度场二维图像中产生高分辨率的三维重建。实验生成的二维温度场可用于从不同方向获得三维场的综合信息，即实际三维场的投影，可用于重建高分辨率的体温场。
{"title":"A Tomographic Reconstruction Method for Three-Dimensional Liquid Crystal Thermography","authors":"D. Mishra, P. M. Lutjen, V. Prasad","doi":"10.1115/imece1999-1100","DOIUrl":"https://doi.org/10.1115/imece1999-1100","url":null,"abstract":"\u0000 Liquid crystal thermography generates two-dimensional temperature information in a fluid layer. Three-dimensional temperature field can be reconstructed using the two-dimensional temperature fields obtained at various locations with the help of synchronized transverse movements of the light sheet and camera (Lutjen et al., 1999). However, it is not feasible to generate a large number of liquid crystal thermographs that are needed for the reconstruction of a high resolution three-dimensional temperature field. A tomographic reconstruction method is suggested here that can be appropriately used to produce a high resolution three-dimensional reconstruction from a limited number of two-dimensional images of the full temperature field. The two-dimensional temperature fields generated from the experiments can be used to obtain an integrated information of the three-dimensional field from various directions known as projections of the actual three-dimensional field and can be used to reconstruct a high resolution volumetric temperature field.","PeriodicalId":120929,"journal":{"name":"Heat Transfer: Volume 4","volume":"19 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1999-11-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"123892143","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 new experimental technique has been developed that permits the determination of local surface heat transfer coefficients on surfaces without requirement for calibration of the temperature-sensing device. The technique uses the phase delay that develops between the surface temperature response and an imposed periodic surface heat flux. This phase delay is dependent upon the thermophysical properties of the model, the heat flux driving frequency and the local heat transfer coefficient. It is not a function of magnitude of the local heat flux. Since only phase differences are being measured there is no requirement to calibrate the temperature sensor, in this instance a thermochromic liquid crystal. Application of a periodic surface heat flux to a flat plate resulted in a surface colour response that was a function of time. This response was captured using a standard colour CCD camera and the phase delay angles were determined using Fourier analysis. Only the 8 bit G component of the captured RGB signal was required, there being no need to determine a Hue value. From these experimentally obtained phase delay angles it was possible to determine heat transfer coefficients that compared well with those predicted using a standard correlation.
{"title":"A New Experimental Technique for Measuring Surface Heat Transfer Coefficients Using Uncalibrated Liquid Crystals","authors":"W. Turnbull, P. Oosthuizen","doi":"10.1115/imece1999-1111","DOIUrl":"https://doi.org/10.1115/imece1999-1111","url":null,"abstract":"\u0000 A new experimental technique has been developed that permits the determination of local surface heat transfer coefficients on surfaces without requirement for calibration of the temperature-sensing device. The technique uses the phase delay that develops between the surface temperature response and an imposed periodic surface heat flux. This phase delay is dependent upon the thermophysical properties of the model, the heat flux driving frequency and the local heat transfer coefficient. It is not a function of magnitude of the local heat flux. Since only phase differences are being measured there is no requirement to calibrate the temperature sensor, in this instance a thermochromic liquid crystal. Application of a periodic surface heat flux to a flat plate resulted in a surface colour response that was a function of time. This response was captured using a standard colour CCD camera and the phase delay angles were determined using Fourier analysis. Only the 8 bit G component of the captured RGB signal was required, there being no need to determine a Hue value. From these experimentally obtained phase delay angles it was possible to determine heat transfer coefficients that compared well with those predicted using a standard correlation.","PeriodicalId":120929,"journal":{"name":"Heat Transfer: Volume 4","volume":"34 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1999-11-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"124827349","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 description is given of an introductory heat transfer class offered in a “cooperative learning” format. The emphasis of the course was to develop analysis skills of the class members. Groups of three students spent most of the class time working problems collectively. Various aspects of arranging this type of course are summarized, including the steps to be taken prior to the beginning of the term, as well as those elements that were handled on a day-today basis. The benefits and drawbacks of this type of approach are outlined.
{"title":"Cooperative Learning in an Introductory Heat Transfer Class","authors":"R. Boehm","doi":"10.1115/imece1999-1135","DOIUrl":"https://doi.org/10.1115/imece1999-1135","url":null,"abstract":"\u0000 A description is given of an introductory heat transfer class offered in a “cooperative learning” format. The emphasis of the course was to develop analysis skills of the class members. Groups of three students spent most of the class time working problems collectively. Various aspects of arranging this type of course are summarized, including the steps to be taken prior to the beginning of the term, as well as those elements that were handled on a day-today basis. The benefits and drawbacks of this type of approach are outlined.","PeriodicalId":120929,"journal":{"name":"Heat Transfer: Volume 4","volume":"51 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1999-11-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"127282481","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}
R. Ambrosek, F. W. Ingram, G. Hawkes, J. Sterbentz
Safety requirements many times require specific evaluations for experiment operating conditions during periods of postulated off-normal operation. A unique experimental facility in the Advanced Test Reactor was designed for enhancement of the neutron flux in an irradiation position, large “I”, in the reflector region. Requirements for the facility necessitated analysis of the enhancement fuel to demonstrate that melting of the fuel element cladding would not occur during a loss of coolant event during reactor shutdown. The response of the fuel elements was evaluated using computer software that allowed detailed evaluations of the gamma heating magnitude and deposition fraction, natural convection cooling, prediction of heat transfer coefficients, and detailed finite element modeling for prediction of the temperature magnitudes and profile.
{"title":"Thermal Margin Evaluation for FELI Fuel Assemblies During an Accidental Vessel Draining","authors":"R. Ambrosek, F. W. Ingram, G. Hawkes, J. Sterbentz","doi":"10.1115/imece1999-1128","DOIUrl":"https://doi.org/10.1115/imece1999-1128","url":null,"abstract":"\u0000 Safety requirements many times require specific evaluations for experiment operating conditions during periods of postulated off-normal operation. A unique experimental facility in the Advanced Test Reactor was designed for enhancement of the neutron flux in an irradiation position, large “I”, in the reflector region. Requirements for the facility necessitated analysis of the enhancement fuel to demonstrate that melting of the fuel element cladding would not occur during a loss of coolant event during reactor shutdown. The response of the fuel elements was evaluated using computer software that allowed detailed evaluations of the gamma heating magnitude and deposition fraction, natural convection cooling, prediction of heat transfer coefficients, and detailed finite element modeling for prediction of the temperature magnitudes and profile.","PeriodicalId":120929,"journal":{"name":"Heat Transfer: Volume 4","volume":"47 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1999-11-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"126636657","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}
Button gages have been extensively used to measure convective heat transfer coefficients in a number of short duration experiments. A button gage consists of a small insert made from an insulator material, typically Pyrex, with a thin film of Platinum active element painted on its surface. In a typical short duration experiment, gages are initially at the same temperature as the test article. As the flow is established, convective heat flux results in the surface temperature of the gage to rise much more rapidly than the surrounding metal walls. The influence of this non-isothermal wall condition on the local thermal boundary layer and hence the measured data is the focus of the present program. A detailed experimental study of the influence of local non-isothermal conditions on the inferred heat flux from button heat-flux gages is performed. An existing wind tunnel capable of generating subsonic through transonic flow conditions has been modified to include an isothermal flat plate test section with a row of surface flush-mounted button heat-flux gages. In addition to the button gages, a uniform sheet of two-layered Kapton heat-flux gages, operating under isothermal conditions, are also applied to the flat plate surface. A detailed study of the uncertainties of experimental results is performed. As part of this study, flow Mach number and Reynolds number are varied and their relative significance upon the deviation in the response of the gages is quantified. The measured heat flux did show a deviation from the isothermal measured values. It is further shown that a correction term based on classical heat transfer theory will adjust the measured heat flux on the flat plate to match isothermal values for a range of Reynolds numbers and temperature ratios.
{"title":"Influence of Non-Isothermal Button Gage Surface Temperature in Heat Flux Measurement Applications","authors":"David A. Zilles, R. Abhari","doi":"10.1115/imece1999-1107","DOIUrl":"https://doi.org/10.1115/imece1999-1107","url":null,"abstract":"\u0000 Button gages have been extensively used to measure convective heat transfer coefficients in a number of short duration experiments. A button gage consists of a small insert made from an insulator material, typically Pyrex, with a thin film of Platinum active element painted on its surface. In a typical short duration experiment, gages are initially at the same temperature as the test article. As the flow is established, convective heat flux results in the surface temperature of the gage to rise much more rapidly than the surrounding metal walls. The influence of this non-isothermal wall condition on the local thermal boundary layer and hence the measured data is the focus of the present program.\u0000 A detailed experimental study of the influence of local non-isothermal conditions on the inferred heat flux from button heat-flux gages is performed. An existing wind tunnel capable of generating subsonic through transonic flow conditions has been modified to include an isothermal flat plate test section with a row of surface flush-mounted button heat-flux gages. In addition to the button gages, a uniform sheet of two-layered Kapton heat-flux gages, operating under isothermal conditions, are also applied to the flat plate surface. A detailed study of the uncertainties of experimental results is performed. As part of this study, flow Mach number and Reynolds number are varied and their relative significance upon the deviation in the response of the gages is quantified. The measured heat flux did show a deviation from the isothermal measured values. It is further shown that a correction term based on classical heat transfer theory will adjust the measured heat flux on the flat plate to match isothermal values for a range of Reynolds numbers and temperature ratios.","PeriodicalId":120929,"journal":{"name":"Heat Transfer: Volume 4","volume":"114 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1999-11-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"115629361","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}
Earlier laboratory studies were carried out to determine the effectiveness of implementing the use of tree barriers to protect open areas such as parks and schoolyards from large wind-driven urban fires. Numerical simulations based on a field fire model also produced promising results which corresponded well with the laboratory experimental observations and measurement data The confidence gained in these earlier studies has led to the present study to simulate the implementation of various tree-barrier configurations in an actual park in Kobe City, Japan under real-scale fire and prevailing wind conditions similar to those encountered in the 1995 Great Kobe Earthquake. Among the various barrier configurations studied, it has been demonstrated that the best configuration is the one using a dual barrier system to reduce the temperatures in the open park downwind from the barriers to safe levels.
{"title":"Reduction of Fire Hazards Downwind of Wind-Driven Fires by Tree Barriers: Part IV — Numerical Simulation of Real-Scale Fires Located in Kobe City, Japan","authors":"K. Satoh, H. Yoshihara, K. Sagae","doi":"10.1115/imece1999-1117","DOIUrl":"https://doi.org/10.1115/imece1999-1117","url":null,"abstract":"\u0000 Earlier laboratory studies were carried out to determine the effectiveness of implementing the use of tree barriers to protect open areas such as parks and schoolyards from large wind-driven urban fires. Numerical simulations based on a field fire model also produced promising results which corresponded well with the laboratory experimental observations and measurement data The confidence gained in these earlier studies has led to the present study to simulate the implementation of various tree-barrier configurations in an actual park in Kobe City, Japan under real-scale fire and prevailing wind conditions similar to those encountered in the 1995 Great Kobe Earthquake. Among the various barrier configurations studied, it has been demonstrated that the best configuration is the one using a dual barrier system to reduce the temperatures in the open park downwind from the barriers to safe levels.","PeriodicalId":120929,"journal":{"name":"Heat Transfer: Volume 4","volume":"49 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1999-11-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"116753544","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 novel research apparatus is developed to measure the fluid thermal conductivity while in shearing flow, and to determine its dependence on the shearing itself, contrary to the current state-of-the-art of measuring thermal conductivity under the condition of motionless fluid. A concentric cylinders’ apparatus was developed to provide controlled heat transfer in the radial direction, orthogonal to the circumferential fluid velocity, thus virtually preserving pure conductive heat transfer mode. The measurement and control are accomplished and integrated by using a computerized data acquisition system and a comprehensive virtual instrument, developed using the LabVIEW application software. It was found that the thermal conductivity of a Newtonian fluid, such as distilled water, was virtually independent of the fluid motion, as expected. However, for non-Newtonian fluids such as 1000 and 2000 wppm aqueous polyacrylamide (Praestol) solutions, there was up to 10–20% increase of thermal conductivity in the operating shear rate range (40 ≤ γ ≤ 510 sec−1) at 27°C average fluid temperature.
{"title":"Investigation of Thermal Conductivity of a Polymer Solution as Function of Shearing Rate","authors":"M. Kostic, H. Tong, Vapor Corp, A. Westinghouse","doi":"10.1115/imece1999-1099","DOIUrl":"https://doi.org/10.1115/imece1999-1099","url":null,"abstract":"\u0000 A novel research apparatus is developed to measure the fluid thermal conductivity while in shearing flow, and to determine its dependence on the shearing itself, contrary to the current state-of-the-art of measuring thermal conductivity under the condition of motionless fluid.\u0000 A concentric cylinders’ apparatus was developed to provide controlled heat transfer in the radial direction, orthogonal to the circumferential fluid velocity, thus virtually preserving pure conductive heat transfer mode. The measurement and control are accomplished and integrated by using a computerized data acquisition system and a comprehensive virtual instrument, developed using the LabVIEW application software.\u0000 It was found that the thermal conductivity of a Newtonian fluid, such as distilled water, was virtually independent of the fluid motion, as expected. However, for non-Newtonian fluids such as 1000 and 2000 wppm aqueous polyacrylamide (Praestol) solutions, there was up to 10–20% increase of thermal conductivity in the operating shear rate range (40 ≤ γ ≤ 510 sec−1) at 27°C average fluid temperature.","PeriodicalId":120929,"journal":{"name":"Heat Transfer: Volume 4","volume":"25 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1999-11-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"122139364","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}
Electrostatically positioned droplets are very useful for the fundamental study of solidification phenomena and the measurement of thermal physical properties. This paper descries a numerical analysis of surface deformation and surface tension driven flows in electrostatically positioned droplets in microgravity. The analysis is based on a fully coupled boundary element and finite element solution of the Maxwell equations, the Navier-Stokes equations and the energy balance equation. Results show that an applied electrostatic field results in a nonuniform electric stress distribution along the droplet surface, which, combined with surface tension, causes the droplet to deform into an ellipsoidal shape in microgravity. Laser heating induces a non-uniform temperature distribution in the droplet, which in turn produces Marangoni convection in the droplet. It is found that the viscous stress contribution to the deformation is small for a majority of cases. Also, a higher temperature gradient produces a stronger Marangoni convection in droplets with higher melting points that require more laser power. The internal recirculating flow may be reduced by more uniform laser heating. During the undercooling of the droplet, both temperature and fluid flow fields evolve in time such that the temperature gradient and the tangential velocities along the droplet surface subside in magnitude and reverse their directions.
{"title":"Surface Deformation and Thermal Convection in Electrostatically-Positioned Droplets Under Microgravity","authors":"Su-Ae Song, Ben Q. Li","doi":"10.1115/imece1999-1120","DOIUrl":"https://doi.org/10.1115/imece1999-1120","url":null,"abstract":"\u0000 Electrostatically positioned droplets are very useful for the fundamental study of solidification phenomena and the measurement of thermal physical properties. This paper descries a numerical analysis of surface deformation and surface tension driven flows in electrostatically positioned droplets in microgravity. The analysis is based on a fully coupled boundary element and finite element solution of the Maxwell equations, the Navier-Stokes equations and the energy balance equation. Results show that an applied electrostatic field results in a nonuniform electric stress distribution along the droplet surface, which, combined with surface tension, causes the droplet to deform into an ellipsoidal shape in microgravity. Laser heating induces a non-uniform temperature distribution in the droplet, which in turn produces Marangoni convection in the droplet. It is found that the viscous stress contribution to the deformation is small for a majority of cases. Also, a higher temperature gradient produces a stronger Marangoni convection in droplets with higher melting points that require more laser power. The internal recirculating flow may be reduced by more uniform laser heating. During the undercooling of the droplet, both temperature and fluid flow fields evolve in time such that the temperature gradient and the tangential velocities along the droplet surface subside in magnitude and reverse their directions.","PeriodicalId":120929,"journal":{"name":"Heat Transfer: Volume 4","volume":"13 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1999-11-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"126819316","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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