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• 1. [Article] Fully developed laminar natural convection in a vertical parallel plate channel with symmetric uniform wall temperature

  Described in this thesis is an investigation of the fully developed natural convection heat transfer in a vertical channel formed by two infinitely wide parallel plates maintained at a uniform wall temperature. ...

  Citation × Citation Citation Abstract Copy Title: Fully developed laminar natural convection in a vertical parallel plate channel with symmetric uniform wall temperature Author: Willie, Robert H. Described in this thesis is an investigation of the fully developed natural convection heat transfer in a vertical channel formed by two infinitely wide parallel plates maintained at a uniform wall temperature. Closed-form solutions for the velocity and temperature profiles are developed along with local and averaged Nusselt numbers. The local Nusselt number based on bulk temperature is found to be 3.77. This result is an analog corresponding to 7.60 for fully developed laminar forced convection in a parallel plate channel with uniform wall temperature boundary condition. The local Nusselt number based on the ambient temperature is deduced as a function of flowwise location. Results are compared with existing numerical and experimental data to find good agreement. Title: Fully developed laminar natural convection in a vertical parallel plate channel with symmetric uniform wall temperature Author: Willie, Robert H. Described in this thesis is an investigation of the fully developed natural convection heat transfer in a vertical channel formed by two infinitely wide parallel plates maintained at a uniform wall temperature. Closed-form solutions for the velocity and temperature profiles are developed along with local and averaged Nusselt numbers. The local Nusselt number based on bulk temperature is found to be 3.77. This result is an analog corresponding to 7.60 for fully developed laminar forced convection in a parallel plate channel with uniform wall temperature boundary condition. The local Nusselt number based on the ambient temperature is deduced as a function of flowwise location. Results are compared with existing numerical and experimental data to find good agreement. Close

• 2. [Article] Spatio – temporal temperature variations during droplet impingement evaporation : effects of nanofluid and nano-structured surface

  Droplet and spray impingement cooling are typically used in high heat flux thermal management. In this thesis, droplet impingement and evaporation heat transfer characteristics are determined from measured ...

  Citation × Citation Citation Abstract Copy Title: Spatio – temporal temperature variations during droplet impingement evaporation : effects of nanofluid and nano-structured surface Author: Graber, Christof Droplet and spray impingement cooling are typically used in high heat flux thermal management. In this thesis, droplet impingement and evaporation heat transfer characteristics are determined from measured spatially- and temporally- varying fluid and surface temperatures. Unique to this study is the documentation of the effects of using a nanofluid and a nano-structured surface for dropwise cooling by comparison of heat transfer characteristics with that of water droplet impingement on a polished surface. Temperatures were determined using radiation intensities recorded using an Infrared (IR) camera. The impingement surface is either comprised of IR transparent silicon, which permits near-surface fluid temperature measurements, or an IR opaque gold coated surface, which permits surface temperature measurements. A range of surface heat fluxes, resulting in both single-phase and boiling conditions are studied. Three different impingement surfaces have been tested, including polished silicon, nano-structured porous silicon, and gold coated polished silicon. The nanofluid is a water-based carbon nanotube suspension. Five major droplet impingement and evaporation stages have been identified: initial impact, boiling (if the surface temperature was sufficiently high), approximately constant diameter evaporation, stepwise fast receding contact line evaporation, and simultaneously decaying diameter and contact angle final dryout period. The surface temperature spatial distribution shows the lowest temperature values within the contact area bulk region and increasing temperature values toward the contact line region and beyond. The basic temperature trends and evaporation behavior are similar for the polished and nano-structured surface while the nanofluid exhibits some distinction. Evaporation times are reduced up to 20% and 37% using the nanostructured surface and nanofluid, respectively. Considering the evaporation time reduction as a measure of droplet cooling performance, the nano-enhanced surface and nanofluid may improve heat transfer in droplet impingement and spray cooling applications. Title: Spatio – temporal temperature variations during droplet impingement evaporation : effects of nanofluid and nano-structured surface Author: Graber, Christof Droplet and spray impingement cooling are typically used in high heat flux thermal management. In this thesis, droplet impingement and evaporation heat transfer characteristics are determined from measured spatially- and temporally- varying fluid and surface temperatures. Unique to this study is the documentation of the effects of using a nanofluid and a nano-structured surface for dropwise cooling by comparison of heat transfer characteristics with that of water droplet impingement on a polished surface. Temperatures were determined using radiation intensities recorded using an Infrared (IR) camera. The impingement surface is either comprised of IR transparent silicon, which permits near-surface fluid temperature measurements, or an IR opaque gold coated surface, which permits surface temperature measurements. A range of surface heat fluxes, resulting in both single-phase and boiling conditions are studied. Three different impingement surfaces have been tested, including polished silicon, nano-structured porous silicon, and gold coated polished silicon. The nanofluid is a water-based carbon nanotube suspension. Five major droplet impingement and evaporation stages have been identified: initial impact, boiling (if the surface temperature was sufficiently high), approximately constant diameter evaporation, stepwise fast receding contact line evaporation, and simultaneously decaying diameter and contact angle final dryout period. The surface temperature spatial distribution shows the lowest temperature values within the contact area bulk region and increasing temperature values toward the contact line region and beyond. The basic temperature trends and evaporation behavior are similar for the polished and nano-structured surface while the nanofluid exhibits some distinction. Evaporation times are reduced up to 20% and 37% using the nanostructured surface and nanofluid, respectively. Considering the evaporation time reduction as a measure of droplet cooling performance, the nano-enhanced surface and nanofluid may improve heat transfer in droplet impingement and spray cooling applications. Close

• 3. [Article] An experimental study of radiative and total heat transfer between a high temperature fluidized bed and an array of immersed tubes

  Experimental data are reported for the time-averaged local radiative and total heat transfer coefficients for both an array of horizontal tubes as well as a single horizontal tube immersed in a large-particle ...

  Citation × Citation Citation Abstract Copy Title: An experimental study of radiative and total heat transfer between a high temperature fluidized bed and an array of immersed tubes Author: Lei, David Hsien-Yu Experimental data are reported for the time-averaged local radiative and total heat transfer coefficients for both an array of horizontal tubes as well as a single horizontal tube immersed in a large-particle fluidized bed at elevated temperatures. Spatial-averaged heat transfer coefficients computed from the local values, using a simple trapezoidal rule integration, are reported. An instrumented tube was used to measure both the radiative and total heat transfer rates simultaneously. Three different window materials, silicon, sapphire, and quartz, have been tested in order to examine some key design decisions made in the development of the radiation detector. It is concluded that the radiation detector employing silicon as the window material is most suitable to achieve accurate measurements of the radiative heat transfer between a fluidized bed and immersed surfaces. Experiments were conducted at the Oregon State University high temperature fluidized bed facility employing Tone grain as the bed material. Measurements were made for two particle sizes (2.14 mm and 3.23 mm) and at three different bed temperatures (812 K, 925 K, and 1000 K). The radiative heat transfer results for tube arrays are believed to be the first of their kind. In comparing these results with those for a single tube, it was found that the radiative heat transfer coefficient decreases with increases in both bed temperature and particle size due to the presence of neighboring "cool" tubes in a hot bed and the greater "see through" effect of the larger particles. Radiation contributions for a bubbling bed were calculated for various test conditions. The effects of superficial velocity, bed temperature, particle size, and adjacent "cool" tubes on both the radiative and total heat transfer performance are described with comparisons made between the results of this study and available literature data or correlations. Title: An experimental study of radiative and total heat transfer between a high temperature fluidized bed and an array of immersed tubes Author: Lei, David Hsien-Yu Experimental data are reported for the time-averaged local radiative and total heat transfer coefficients for both an array of horizontal tubes as well as a single horizontal tube immersed in a large-particle fluidized bed at elevated temperatures. Spatial-averaged heat transfer coefficients computed from the local values, using a simple trapezoidal rule integration, are reported. An instrumented tube was used to measure both the radiative and total heat transfer rates simultaneously. Three different window materials, silicon, sapphire, and quartz, have been tested in order to examine some key design decisions made in the development of the radiation detector. It is concluded that the radiation detector employing silicon as the window material is most suitable to achieve accurate measurements of the radiative heat transfer between a fluidized bed and immersed surfaces. Experiments were conducted at the Oregon State University high temperature fluidized bed facility employing Tone grain as the bed material. Measurements were made for two particle sizes (2.14 mm and 3.23 mm) and at three different bed temperatures (812 K, 925 K, and 1000 K). The radiative heat transfer results for tube arrays are believed to be the first of their kind. In comparing these results with those for a single tube, it was found that the radiative heat transfer coefficient decreases with increases in both bed temperature and particle size due to the presence of neighboring "cool" tubes in a hot bed and the greater "see through" effect of the larger particles. Radiation contributions for a bubbling bed were calculated for various test conditions. The effects of superficial velocity, bed temperature, particle size, and adjacent "cool" tubes on both the radiative and total heat transfer performance are described with comparisons made between the results of this study and available literature data or correlations. Close

• 4. [Article] An experimental investigation of transition pool boiling

  The heat-transfer phenomena studied in this work were associated with pool boiling from a flat horizontal surface facing upward with the bulk liquid at its saturation temperature. The analysis of boiling ...

  Citation × Citation Citation Abstract Copy Title: An experimental investigation of transition pool boiling Author: Aoki, Tadao The heat-transfer phenomena studied in this work were associated with pool boiling from a flat horizontal surface facing upward with the bulk liquid at its saturation temperature. The analysis of boiling sound and the investigation of the transition boiling mechanism constituted the essence of the present study. The distinctively large sound intensity with predominant frequency components of 250 Hz and 500 Hz was observed during transition boiling. From the photographic studies of surface temperature variation, it was concluded that the heat transfer mechanism at relatively low heat flux levels of transition boiling involves the direct contact between liquid and the hot surface followed by a spheroidal state of the liquid. At higher heat flux levels while the liquid was in the spheroidal state, its contribution to total heat transfer increased with a decrease in surface temperature. Title: An experimental investigation of transition pool boiling Author: Aoki, Tadao The heat-transfer phenomena studied in this work were associated with pool boiling from a flat horizontal surface facing upward with the bulk liquid at its saturation temperature. The analysis of boiling sound and the investigation of the transition boiling mechanism constituted the essence of the present study. The distinctively large sound intensity with predominant frequency components of 250 Hz and 500 Hz was observed during transition boiling. From the photographic studies of surface temperature variation, it was concluded that the heat transfer mechanism at relatively low heat flux levels of transition boiling involves the direct contact between liquid and the hot surface followed by a spheroidal state of the liquid. At higher heat flux levels while the liquid was in the spheroidal state, its contribution to total heat transfer increased with a decrease in surface temperature. Close

• 5. [Article] Applications of the thermal wave technique in liquid thermal conductivity measurements and flow field diagnostics

  The thermal wave technique has been explored for the use of liquid thermal conductivity measurement and flow property diagnostics in this dissertation. For liquid thermal conductivity measurements, an ...

  Citation × Citation Citation Abstract Copy Title: Applications of the thermal wave technique in liquid thermal conductivity measurements and flow field diagnostics Author: Wang, Zhefu The thermal wave technique has been explored for the use of liquid thermal conductivity measurement and flow property diagnostics in this dissertation. For liquid thermal conductivity measurements, an experimental technique based on the thermal wave approach is developed. A stainless steel strip functions as both a heating element and a sealing cover for a chamber containing a test liquid. A periodic current passing through this metal strip generates a periodic Joule heating source. An infrared detector measures the temperature response at the front surface of the stainless steel strip. The phase and magnitude of the temperature response were measured by a lock-in amplifier at various frequencies. A one-dimensional, two-layered transient heat conduction model is developed to predict the temperature response. The phase information of this temperature response shows high sensitivity to the change of thermal properties of the liquid layer and is employed to match experimental data to find the thermal properties of the test liquid. The measured thermal conductivities of water and ethylene glycol agree quite well with data from the literature and support the validity of this measurement technique. An aqueous fluid consisting of gold nanoparticles was also tested and anomalous thermal conductivity enhancement was observed. Our measurement results also showed a divergence of thermal transport behavior between nanofluids and pure liquids. This suggests a need to carefully examine the role of the measurement technique in the heat transfer experimental studies of nanofluids. For the study of flow property diagnostics, a heat transfer system with a periodic boundary condition in a steady flow field is examined. Due to linearity and homogeneity of the heat transfer system under certain conditions, a thermal wave field generated by a periodic heating flux at the boundary of the flow field may be used to detect important flow field parameters, such as the velocity gradient at the wall, and therefore, the wall shear stress. A wall shear stress sensor design with a heater and two temperature sensors on a silicon dioxide substrate is analyzed. The heater with a periodic heating source generates an oscillating temperature field which interacts with the flow field. The temperature sensors pick up the temperature response that contains information on the velocity gradient at the wall. Based on the above sensor design, a two-dimensional conjugate heat convection model is developed with a periodic heating flux at the solid/fluid interface and a linear velocity profile in the fluid domain. Two designs are studied, one with a silicon heat sink under the silicon dioxide substrate and another without the heat sink. The effects of the two main design parameters, the operating frequency and the distance between the heater and the temperature sensor, are discussed. A reasonable sensitivity of the phase information to the velocity gradient suggests a practical sensor design. A preliminary experimental test on a water channel flow has been conducted to support the concept of applying the thermal wave method to wall shear stress measurements. Title: Applications of the thermal wave technique in liquid thermal conductivity measurements and flow field diagnostics Author: Wang, Zhefu The thermal wave technique has been explored for the use of liquid thermal conductivity measurement and flow property diagnostics in this dissertation. For liquid thermal conductivity measurements, an experimental technique based on the thermal wave approach is developed. A stainless steel strip functions as both a heating element and a sealing cover for a chamber containing a test liquid. A periodic current passing through this metal strip generates a periodic Joule heating source. An infrared detector measures the temperature response at the front surface of the stainless steel strip. The phase and magnitude of the temperature response were measured by a lock-in amplifier at various frequencies. A one-dimensional, two-layered transient heat conduction model is developed to predict the temperature response. The phase information of this temperature response shows high sensitivity to the change of thermal properties of the liquid layer and is employed to match experimental data to find the thermal properties of the test liquid. The measured thermal conductivities of water and ethylene glycol agree quite well with data from the literature and support the validity of this measurement technique. An aqueous fluid consisting of gold nanoparticles was also tested and anomalous thermal conductivity enhancement was observed. Our measurement results also showed a divergence of thermal transport behavior between nanofluids and pure liquids. This suggests a need to carefully examine the role of the measurement technique in the heat transfer experimental studies of nanofluids. For the study of flow property diagnostics, a heat transfer system with a periodic boundary condition in a steady flow field is examined. Due to linearity and homogeneity of the heat transfer system under certain conditions, a thermal wave field generated by a periodic heating flux at the boundary of the flow field may be used to detect important flow field parameters, such as the velocity gradient at the wall, and therefore, the wall shear stress. A wall shear stress sensor design with a heater and two temperature sensors on a silicon dioxide substrate is analyzed. The heater with a periodic heating source generates an oscillating temperature field which interacts with the flow field. The temperature sensors pick up the temperature response that contains information on the velocity gradient at the wall. Based on the above sensor design, a two-dimensional conjugate heat convection model is developed with a periodic heating flux at the solid/fluid interface and a linear velocity profile in the fluid domain. Two designs are studied, one with a silicon heat sink under the silicon dioxide substrate and another without the heat sink. The effects of the two main design parameters, the operating frequency and the distance between the heater and the temperature sensor, are discussed. A reasonable sensitivity of the phase information to the velocity gradient suggests a practical sensor design. A preliminary experimental test on a water channel flow has been conducted to support the concept of applying the thermal wave method to wall shear stress measurements. Close

• 6. [Article] A numerical solution for heat transfer to non-Newtonian fluids with temperature-dependent viscosity for arbitrary conditions of heat flux and surface temperature

  Citation × Citation Citation Abstract Copy Title: A numerical solution for heat transfer to non-Newtonian fluids with temperature-dependent viscosity for arbitrary conditions of heat flux and surface temperature Author: Cochrane, G. F. (Glenn Frank) Title: A numerical solution for heat transfer to non-Newtonian fluids with temperature-dependent viscosity for arbitrary conditions of heat flux and surface temperature Author: Cochrane, G. F. (Glenn Frank) Close

• 7. [Article] Studies of homogeneous nucleation and transient heat transfer in cryogenic liquids

  We report the results of a series of experimental studies in two interrelated areas: homogeneous nucleation and transient heat transfer in cryogenic liquids. We report the first determination of the homogeneous ...

  Citation × Citation Citation Abstract Copy Title: Studies of homogeneous nucleation and transient heat transfer in cryogenic liquids Author: Sinha, Dipen N. Year: 1980 We report the results of a series of experimental studies in two interrelated areas: homogeneous nucleation and transient heat transfer in cryogenic liquids. We report the first determination of the homogeneous nucleation temperature of liquid helium I and liquid nitrogen employing a transient superheating technique. This technique in liquid helium involved the development of a new transient magnetoresistive thermometer which relies on the strong temperaure dependence of magnetoresistance in bismuth as a thermometric property. Our measurements of the homogeneous nucleation temperature for both liquid helium I and nitrogen are in good agreement with the predictions from the Becker-Doring Volmer-Zel'dovich-Frenkel nucleation theory. On the basis of such agreement between theory and experiment in both liquid helium and liquid nitrogen we have developed a corresponding state analysis applicable to the case of homogeneous nucleation in liquid noble gases, both quantum and classical. Predictions of the homogeneous nucleation temperature and surface tension of several hydrogen isotopes are made from such a quantum mechanical law of corresponding states. We also comment on the limiting superheat temperature of liquid helium I. It is suggested that a comparison between the limiting superheat temperaure and the peak nucleate boiling temperature is meaningless and that the reported agreement between the two is largely fortuitous. In the studies of transient heat transfer in helium we find that the heat transfer from a solid into liquid helium is markedly enhanced by the application of a visible pulse of light. In liquid nitrogen we find that a transition to stable film boiling can be observed for power values as low as 40 per cent of the steady-state peak heat flux. Title: Studies of homogeneous nucleation and transient heat transfer in cryogenic liquids Author: Sinha, Dipen N. Year: 1980 We report the results of a series of experimental studies in two interrelated areas: homogeneous nucleation and transient heat transfer in cryogenic liquids. We report the first determination of the homogeneous nucleation temperature of liquid helium I and liquid nitrogen employing a transient superheating technique. This technique in liquid helium involved the development of a new transient magnetoresistive thermometer which relies on the strong temperaure dependence of magnetoresistance in bismuth as a thermometric property. Our measurements of the homogeneous nucleation temperature for both liquid helium I and nitrogen are in good agreement with the predictions from the Becker-Doring Volmer-Zel'dovich-Frenkel nucleation theory. On the basis of such agreement between theory and experiment in both liquid helium and liquid nitrogen we have developed a corresponding state analysis applicable to the case of homogeneous nucleation in liquid noble gases, both quantum and classical. Predictions of the homogeneous nucleation temperature and surface tension of several hydrogen isotopes are made from such a quantum mechanical law of corresponding states. We also comment on the limiting superheat temperature of liquid helium I. It is suggested that a comparison between the limiting superheat temperaure and the peak nucleate boiling temperature is meaningless and that the reported agreement between the two is largely fortuitous. In the studies of transient heat transfer in helium we find that the heat transfer from a solid into liquid helium is markedly enhanced by the application of a visible pulse of light. In liquid nitrogen we find that a transition to stable film boiling can be observed for power values as low as 40 per cent of the steady-state peak heat flux. Close

• 8. [Article] Studies of nucleation and heat transfer in liquid helium isotopes 3 and 4

  We report the results of a series of experiments in three interrelated areas: light induced nucleation of vapor bubbles in superheated liquid helium 4, transient heat transfer in liquid helium isotopes ...

  Citation × Citation Citation Abstract Copy Title: Studies of nucleation and heat transfer in liquid helium isotopes 3 and 4 Author: Lezak, David Year: 1985 We report the results of a series of experiments in three interrelated areas: light induced nucleation of vapor bubbles in superheated liquid helium 4, transient heat transfer in liquid helium isotopes 3 and 4, and homogeneous nucleation of vapor bubbles in superheated liquid helium 3. This work has resulted in significant contributions in each of these particular areas. Our transient heat transfer work has resulted in extremely high temperature measurements of the Kapitza thermal boundary conductance limits in helium 3 and 4, in measurements of the delay time to the onset of film boiling over a wide range of bath temperatures in helium 4, and in a determination of bubble growth rates in helium 4. These measurements have been compared with theory and have in some cases allowed the extension or elucidation of that theory. We have characterized the so called "light effect" and established photographically that small amounts of visible light will cause the formation of vapor bubbles at the interface of a solid and superheated liquid helium 4 and that this vapor can influence the quasi-steady-state heat flux vs temperature hysteresis curve. Finally, we have measured the homogeneous nucleation temperature of liquid helium 3 and found good agreement with the predictions of the Becker-Doring-Volmer-Zel'dovich Frenkel nucleation theory. This work is shown to have applications to practical cryogenic engineering, to further understanding of basic heat transfer and nucleation theory, and to practical and theoretical environmental and resource considerations. Title: Studies of nucleation and heat transfer in liquid helium isotopes 3 and 4 Author: Lezak, David Year: 1985 We report the results of a series of experiments in three interrelated areas: light induced nucleation of vapor bubbles in superheated liquid helium 4, transient heat transfer in liquid helium isotopes 3 and 4, and homogeneous nucleation of vapor bubbles in superheated liquid helium 3. This work has resulted in significant contributions in each of these particular areas. Our transient heat transfer work has resulted in extremely high temperature measurements of the Kapitza thermal boundary conductance limits in helium 3 and 4, in measurements of the delay time to the onset of film boiling over a wide range of bath temperatures in helium 4, and in a determination of bubble growth rates in helium 4. These measurements have been compared with theory and have in some cases allowed the extension or elucidation of that theory. We have characterized the so called "light effect" and established photographically that small amounts of visible light will cause the formation of vapor bubbles at the interface of a solid and superheated liquid helium 4 and that this vapor can influence the quasi-steady-state heat flux vs temperature hysteresis curve. Finally, we have measured the homogeneous nucleation temperature of liquid helium 3 and found good agreement with the predictions of the Becker-Doring-Volmer-Zel'dovich Frenkel nucleation theory. This work is shown to have applications to practical cryogenic engineering, to further understanding of basic heat transfer and nucleation theory, and to practical and theoretical environmental and resource considerations. Close

• 9. [Article] Coupled momentum and heat transport in laminar axisymmetric pipe flow of ferrofluids in non-uniform magnetic fields : theory and simulation

  The effect of a non-uniform magnetic field on the coupled transport of momentum and heat is studied for the case of laminar pipe flow of a magnetically susceptible ferrofluid. The momentum and heat transport equations ...

  Citation × Citation Citation Abstract Copy Title: Coupled momentum and heat transport in laminar axisymmetric pipe flow of ferrofluids in non-uniform magnetic fields : theory and simulation Author: Cruz-Fierro, Carlos Francisco The effect of a non-uniform magnetic field on the coupled transport of momentum and heat is studied for the case of laminar pipe flow of a magnetically susceptible ferrofluid. The momentum and heat transport equations are complemented with the necessary electromagnetic terms and used to develop a computer simulation of the velocity profile and temperature distribution in the fluid. Two magnetic field configurations are studied. The first configuration is produced by a single short solenoid, located around the pipe. The magnetic field produced has both radial and axial components. For the second configuration, the electric current is inverted in one half of the solenoid, creating much stronger field gradients in both directions. The flow is laminar, driven by a constant pressure difference between the ends of the pipe. The apparent viscosity of the ferrofluid is modeled as dependent on temperature and magnetic field. In simulations involving heat transfer, a section of the pipe is maintained at higher constant temperature. The rest of the wall is adiabatic. A Visual-Basic code, FiRMa (Flow in Response to Magnetic field), was developed to perform the numerical simulations. For the water-based ferrofluid, results show reduction of average velocity and small deviations from the parabolic velocity profile as the result of vortex viscosity. Heat transfer calculations show a decrease in the heat transfer coefficient and an increase in the fluid exit temperature. These effects are due to the change in flow pattern and average velocity. Current research aims for the development of a stable liquid-metal based ferrofluid, because of the high electric and thermal conductivities. The FiRMa code is used to examine the expected response of a mercury-based ferrofluid to the magnetic fields under study. Results show that the electromagnetic effects on the liquid metal-based ferrofluid are much stronger, due to induced electric currents and the Lorentz force acting on them. Title: Coupled momentum and heat transport in laminar axisymmetric pipe flow of ferrofluids in non-uniform magnetic fields : theory and simulation Author: Cruz-Fierro, Carlos Francisco The effect of a non-uniform magnetic field on the coupled transport of momentum and heat is studied for the case of laminar pipe flow of a magnetically susceptible ferrofluid. The momentum and heat transport equations are complemented with the necessary electromagnetic terms and used to develop a computer simulation of the velocity profile and temperature distribution in the fluid. Two magnetic field configurations are studied. The first configuration is produced by a single short solenoid, located around the pipe. The magnetic field produced has both radial and axial components. For the second configuration, the electric current is inverted in one half of the solenoid, creating much stronger field gradients in both directions. The flow is laminar, driven by a constant pressure difference between the ends of the pipe. The apparent viscosity of the ferrofluid is modeled as dependent on temperature and magnetic field. In simulations involving heat transfer, a section of the pipe is maintained at higher constant temperature. The rest of the wall is adiabatic. A Visual-Basic code, FiRMa (Flow in Response to Magnetic field), was developed to perform the numerical simulations. For the water-based ferrofluid, results show reduction of average velocity and small deviations from the parabolic velocity profile as the result of vortex viscosity. Heat transfer calculations show a decrease in the heat transfer coefficient and an increase in the fluid exit temperature. These effects are due to the change in flow pattern and average velocity. Current research aims for the development of a stable liquid-metal based ferrofluid, because of the high electric and thermal conductivities. The FiRMa code is used to examine the expected response of a mercury-based ferrofluid to the magnetic fields under study. Results show that the electromagnetic effects on the liquid metal-based ferrofluid are much stronger, due to induced electric currents and the Lorentz force acting on them. Close

• 10. [Article] An experimental study of heat transfer to a horizontal tube in a large particle fluidized bed at elevated temperature

  Citation × Citation Citation Abstract Copy Title: An experimental study of heat transfer to a horizontal tube in a large particle fluidized bed at elevated temperature Author: George, Alan Herbert Title: An experimental study of heat transfer to a horizontal tube in a large particle fluidized bed at elevated temperature Author: George, Alan Herbert Close