Journal of Fluids Engineering-transactions of The Asme, Sep 1, 1981
The paper is a good comparative work, particularly in bringing out the features of transport {k-e... more The paper is a good comparative work, particularly in bringing out the features of transport {k-e and RS) models of turbulence and the nontransport model as they pertain to rectangular ducts. As a first reaction, one does have to be' wary of the greater amount of empiricism in the length scale model used without a significant gain in the computational ' costs. The author's comment regarding the use of planar, two-dimensional length scale models is probably the best alternative if one is committed to the use of nontransport models. Computational schemes for the prediction of duct flows that use stream function and vorticity (\j/, co) as dependent variables require the calculation of second derivatives of (v 2w 2) as source terms in the vorticity equation. In the Launder and Ying [6] model this is achieved by calculation of (v 2-w 2) using equation (14). It has to be noted that the anisotropy coefficient is built into this equation as an explicit constant (c) and L-Yused a much smaller value of this coefficient (0.01) than implied by experimental results (0.22). Schemes that use primitive variables have the more difficult task of calculating the first derivatives of the normal stresses v 2 , w 2 themselves as source terms in the secondary velocity equations. A k-e model that uses primitive equations includes algebraic equations for v 2 and w 2 and it is not possible to predict these normal stresses and secondary flows accurately without taking the near wall pressure-strain effects into consideration. Thus it appears it is more difficult to predict these parameters accurately in schemes that use primitive dependent variables and might explain some of the discrepancies in the paper. In this context it is interesting to note that though the absolute values of the normal stresses (Fig. 8(a)) are overpredicted, their gradients are in much better agreement, particularly away from the wall, and probably are a contributing factor for the successes reported here. Secondary flow computations are seen to be sensitive to the mesh size with the uniform grid used here and this reiterates the importance of near wall spatial resolution. Also, as mentioned by the authors, the underprediction of the secondary flows by the length scale model seems to confirm the advantage in using the transport equation models. The continued development of the secondary velocity profiles (Fig. 7(a)) after the axial velocity development is completed is cause for concern and warrants checking for continuity or continued minute changes in the axial velocity profiles.
The micro-arheometer (micro-array of rheometers) is a multi-functional system on a chip. It is ca... more The micro-arheometer (micro-array of rheometers) is a multi-functional system on a chip. It is capable of cell manipulation and sorting utilizing dielectrophoresis, as well as measuring frequency-dependent viscoelastic cell properties by applying a known force with the desired frequency (piezoelectric actuation) and measuring displacement using a piezoresistive read-out. The micro-arheometer will accelerate biomedical research generating a larger statistical data set in a shorter amount of time by automating the process of micro-rheology on multiple cells at a time.
Forced convective, nonequilibrium post-CHF heat transfer data (766 points) have been obtained at ... more Forced convective, nonequilibrium post-CHF heat transfer data (766 points) have been obtained at high pressure and low mass flux ranges not previously tested. The data are unique in that the superheated vapor temperature was measured at multiple elevations allowing the direct calculation of vapor generation rates. The data are useful for verification or development of nonequilibrium heat and mass transfer models. Current film boiling heat transfer correlations do not predict the data well. The Dougall-Rohsenow equilibrium correlation is the only one investigated that reasonably predicts the measured wall heat fluxes. Current vapor generation rate models do not adequately predict the measured vapor generation rates.
Geothermal energy piles are an environmentally friendly energy source and an innovative approach ... more Geothermal energy piles are an environmentally friendly energy source and an innovative approach to melt snow on the bridge surface and minimize or eliminate the use of deicing salt. However, the application potential of energy piles for bridge deicing or snow melting has not been fully explored for different climates. In this study, the feasibility of using energy piles for bridge deicing in eight cities of the United States was investigated. Temperature response function (G function) method was validated and used to estimate the extracted heat from energy piles installed in the soils with different thermal properties, which was used to heat the bridge deck during snowing. The results of numerical simulation and statistical analysis confirm that the performance of the geothermal deicing system depends on the weather conditions during snowing and thermal properties of soils. The coverage rate of the geothermal system (percentage of snowing time that the geothermal deicing system can keep the bridge surface above 0°C) increases with the increasing air temperature and thermal diffusivities of soils, and decreases with the increasing precipitation rate and wind speed. This deicing method is promising in cities with higher average air temperature and low precipitation rate during snowing.
• A novel phase change material (PCM) based cooling application is proposed. • A modeling method ... more • A novel phase change material (PCM) based cooling application is proposed. • A modeling method for a finned heat pipe assisted PCM system in 3D is developed. • Optimal design and cost sensitivity analysis of the system are presented.
The interaction between the cardiac hemodynamics and brain activity has been extensively studied ... more The interaction between the cardiac hemodynamics and brain activity has been extensively studied in the past. However these studies have involved not only an increase in heart rate but also an increase in blood pressure. One method to evaluate for underlying coronary artery disease is to perform stress testing. Often, myocardial stress is achieved by the patient walking on a treadmill or riding a stationary bicycle while being monitored. In patients that are unable to exercise, pharmacologic stress testing is performed, either with vasodilatory agents (e.g. adenosine) or dobutamine, which is a pro-inotropic and chronotropic drug. During dobutamine infusion, the heart rate increases, but there is a negligible increase in blood pressure. The result is that the heart rate increases as a function of the dosage. Thus by monitoring brain activity while patients are undergoing dobutamine stress testing the effect of increased blood pressure on the brain is removed. It was found in the results of one patient that there are fi ve areas of the brain which show a change in the frequency of EEG activity that is a function of dobutamine dosage. Using Fourier transforms it was established that this change occurred at a frequency around 12.5 Hz. The regions of the brain where the increased activity were a function of heart rate occurred in the CZ-PZ, C4-P4, T5-O1, T4-T6 and C3-P3 regions. In undertaking these calculations it was realized that the stress on the ventricle could be calculated. The physicians monitor ECG of the patient to evaluate the cardiac status of the patient. Since currently the attending physician does not have data on the stress being applied to the myocardium, it would be useful to have this calculated on a real time basis. The motivation for the present preliminary study is to both investigate the feasibility of producing such information for clinicians as well as to investigate the variation between different patients as the heart rate varies. It was found that generally the surface shear stress increased with heart rate around most of the left ventricle. While the time averaged shear stress may be important for diagnosis the maximum shear stress probably is the limiting factor in terminating testing.
A supplemental main steam condenser cooling system is under development, which utilizes a phase c... more A supplemental main steam condenser cooling system is under development, which utilizes a phase change material (PCM). This PCM rejects heat to the cool atmosphere at night until it is fully frozen. The frozen PCM is available for condenser cooling during peak daytime electric demand. Three calcium chloride hexahydrate (CaCl2·6H2O)-based PCMs were selected for development after being characterized using differential scanning calorimetry (DSC). Additives to minimize supercooling and phase separation have demonstrated good performance after long and short-term thermal cycling. Corrosion testing under both isothermal and cycling conditions was conducted to determine long-term compatibility between several common metals and the selected PCMs. Several metals were demonstrated to have acceptably low corrosion rates for long-term operation, despite continual immersion in the selected hydrated salts. A system optimization model was developed, which utilizes a 3D modeling approach called the Layered Thermal Resistance (LTR) model. This model efficiently models the nonlinear, transient solidification process by applying analytic equations to layers of PCM. Good agreement was found between this model and more traditional computational fluid dynamics (CFD) modeling. Next phases of the work includes prototype testing and a techno-economic analysis of the technology.
One of the challenges to design and control phase change material (PCM) based latent heat thermal... more One of the challenges to design and control phase change material (PCM) based latent heat thermal energy storage (LHTES) systems is to develop fast models to accurately represent their transient and nonlinear behaviors. In this paper, a fast explicit modeling approach for a multi-dimensional finned PCM system, called alternating front propagating, is proposed based on the concept of the alternating-direction implicit algorithm for multi-dimensional parabolic and elliptic differential equations. The proposed modeling method is employed to develop a fast explicit dynamic model for a large scale LHTES system, whose heat transfer is enhanced by imbedded circular finned heat pipes. The developed fast model has negligible computational cost and is of sufficient accuracy compared to high-fidelity numerical solutions. The fast explicit model of the LHTES system was employed in a model predictive control framework to determine the HTF flowrate so that its outlet temperature meets a target value. The controlled HTF flowrate can increase the usage efficiency of the stored heat in a LHTES system.
Forced convective, postcritical heat flux heat transfer experiments with water flowing upward in ... more Forced convective, postcritical heat flux heat transfer experiments with water flowing upward in a vertical tube have been conducted at the Idaho National Engineering Laboratory. Thermodynamic nonequilibrium in the form of superheated vapor temperatures was measured at a maximum of three different axial levels. Steady state experiments were conducted at pressures of 0.2 to 0.7 MPa, mass fluxes of 12
Forced-convective postcritical heat flux (CHF) heat transfer data have been obtained at low flow ... more Forced-convective postcritical heat flux (CHF) heat transfer data have been obtained at low flow rates and low pressures (0.2 to 0.7 MPa) for water flowing in a vertical tube. Significant magnitudes of superheat (up to 510 K) were found. The steady state data are in agreement with other reported low-flow and low-pressure nonequilibrium data. Nonequilibrium vapor temperatures were measured at
Two optical techniques for use in detecting liquid contacts in film and transition boiling regime... more Two optical techniques for use in detecting liquid contacts in film and transition boiling regimes were developed. The first optical method involves the measurements of liquid contacts on a high-temperature glass boiling surface in a transient experiment. The second technique utilizes a small fiber-optic probe mounted flush on a copper surface. Experiments have indicated the probe is sufficiently fast responding to provide accurate local measurements of liquid to solid contact in film and transition boiling regimes. The relationship between surface superheat and liquid contact time fraction was determined for both methods.
Journal of Fluids Engineering-transactions of The Asme, Sep 1, 1981
The paper is a good comparative work, particularly in bringing out the features of transport {k-e... more The paper is a good comparative work, particularly in bringing out the features of transport {k-e and RS) models of turbulence and the nontransport model as they pertain to rectangular ducts. As a first reaction, one does have to be' wary of the greater amount of empiricism in the length scale model used without a significant gain in the computational ' costs. The author's comment regarding the use of planar, two-dimensional length scale models is probably the best alternative if one is committed to the use of nontransport models. Computational schemes for the prediction of duct flows that use stream function and vorticity (\j/, co) as dependent variables require the calculation of second derivatives of (v 2w 2) as source terms in the vorticity equation. In the Launder and Ying [6] model this is achieved by calculation of (v 2-w 2) using equation (14). It has to be noted that the anisotropy coefficient is built into this equation as an explicit constant (c) and L-Yused a much smaller value of this coefficient (0.01) than implied by experimental results (0.22). Schemes that use primitive variables have the more difficult task of calculating the first derivatives of the normal stresses v 2 , w 2 themselves as source terms in the secondary velocity equations. A k-e model that uses primitive equations includes algebraic equations for v 2 and w 2 and it is not possible to predict these normal stresses and secondary flows accurately without taking the near wall pressure-strain effects into consideration. Thus it appears it is more difficult to predict these parameters accurately in schemes that use primitive dependent variables and might explain some of the discrepancies in the paper. In this context it is interesting to note that though the absolute values of the normal stresses (Fig. 8(a)) are overpredicted, their gradients are in much better agreement, particularly away from the wall, and probably are a contributing factor for the successes reported here. Secondary flow computations are seen to be sensitive to the mesh size with the uniform grid used here and this reiterates the importance of near wall spatial resolution. Also, as mentioned by the authors, the underprediction of the secondary flows by the length scale model seems to confirm the advantage in using the transport equation models. The continued development of the secondary velocity profiles (Fig. 7(a)) after the axial velocity development is completed is cause for concern and warrants checking for continuity or continued minute changes in the axial velocity profiles.
The micro-arheometer (micro-array of rheometers) is a multi-functional system on a chip. It is ca... more The micro-arheometer (micro-array of rheometers) is a multi-functional system on a chip. It is capable of cell manipulation and sorting utilizing dielectrophoresis, as well as measuring frequency-dependent viscoelastic cell properties by applying a known force with the desired frequency (piezoelectric actuation) and measuring displacement using a piezoresistive read-out. The micro-arheometer will accelerate biomedical research generating a larger statistical data set in a shorter amount of time by automating the process of micro-rheology on multiple cells at a time.
Forced convective, nonequilibrium post-CHF heat transfer data (766 points) have been obtained at ... more Forced convective, nonequilibrium post-CHF heat transfer data (766 points) have been obtained at high pressure and low mass flux ranges not previously tested. The data are unique in that the superheated vapor temperature was measured at multiple elevations allowing the direct calculation of vapor generation rates. The data are useful for verification or development of nonequilibrium heat and mass transfer models. Current film boiling heat transfer correlations do not predict the data well. The Dougall-Rohsenow equilibrium correlation is the only one investigated that reasonably predicts the measured wall heat fluxes. Current vapor generation rate models do not adequately predict the measured vapor generation rates.
Geothermal energy piles are an environmentally friendly energy source and an innovative approach ... more Geothermal energy piles are an environmentally friendly energy source and an innovative approach to melt snow on the bridge surface and minimize or eliminate the use of deicing salt. However, the application potential of energy piles for bridge deicing or snow melting has not been fully explored for different climates. In this study, the feasibility of using energy piles for bridge deicing in eight cities of the United States was investigated. Temperature response function (G function) method was validated and used to estimate the extracted heat from energy piles installed in the soils with different thermal properties, which was used to heat the bridge deck during snowing. The results of numerical simulation and statistical analysis confirm that the performance of the geothermal deicing system depends on the weather conditions during snowing and thermal properties of soils. The coverage rate of the geothermal system (percentage of snowing time that the geothermal deicing system can keep the bridge surface above 0°C) increases with the increasing air temperature and thermal diffusivities of soils, and decreases with the increasing precipitation rate and wind speed. This deicing method is promising in cities with higher average air temperature and low precipitation rate during snowing.
• A novel phase change material (PCM) based cooling application is proposed. • A modeling method ... more • A novel phase change material (PCM) based cooling application is proposed. • A modeling method for a finned heat pipe assisted PCM system in 3D is developed. • Optimal design and cost sensitivity analysis of the system are presented.
The interaction between the cardiac hemodynamics and brain activity has been extensively studied ... more The interaction between the cardiac hemodynamics and brain activity has been extensively studied in the past. However these studies have involved not only an increase in heart rate but also an increase in blood pressure. One method to evaluate for underlying coronary artery disease is to perform stress testing. Often, myocardial stress is achieved by the patient walking on a treadmill or riding a stationary bicycle while being monitored. In patients that are unable to exercise, pharmacologic stress testing is performed, either with vasodilatory agents (e.g. adenosine) or dobutamine, which is a pro-inotropic and chronotropic drug. During dobutamine infusion, the heart rate increases, but there is a negligible increase in blood pressure. The result is that the heart rate increases as a function of the dosage. Thus by monitoring brain activity while patients are undergoing dobutamine stress testing the effect of increased blood pressure on the brain is removed. It was found in the results of one patient that there are fi ve areas of the brain which show a change in the frequency of EEG activity that is a function of dobutamine dosage. Using Fourier transforms it was established that this change occurred at a frequency around 12.5 Hz. The regions of the brain where the increased activity were a function of heart rate occurred in the CZ-PZ, C4-P4, T5-O1, T4-T6 and C3-P3 regions. In undertaking these calculations it was realized that the stress on the ventricle could be calculated. The physicians monitor ECG of the patient to evaluate the cardiac status of the patient. Since currently the attending physician does not have data on the stress being applied to the myocardium, it would be useful to have this calculated on a real time basis. The motivation for the present preliminary study is to both investigate the feasibility of producing such information for clinicians as well as to investigate the variation between different patients as the heart rate varies. It was found that generally the surface shear stress increased with heart rate around most of the left ventricle. While the time averaged shear stress may be important for diagnosis the maximum shear stress probably is the limiting factor in terminating testing.
A supplemental main steam condenser cooling system is under development, which utilizes a phase c... more A supplemental main steam condenser cooling system is under development, which utilizes a phase change material (PCM). This PCM rejects heat to the cool atmosphere at night until it is fully frozen. The frozen PCM is available for condenser cooling during peak daytime electric demand. Three calcium chloride hexahydrate (CaCl2·6H2O)-based PCMs were selected for development after being characterized using differential scanning calorimetry (DSC). Additives to minimize supercooling and phase separation have demonstrated good performance after long and short-term thermal cycling. Corrosion testing under both isothermal and cycling conditions was conducted to determine long-term compatibility between several common metals and the selected PCMs. Several metals were demonstrated to have acceptably low corrosion rates for long-term operation, despite continual immersion in the selected hydrated salts. A system optimization model was developed, which utilizes a 3D modeling approach called the Layered Thermal Resistance (LTR) model. This model efficiently models the nonlinear, transient solidification process by applying analytic equations to layers of PCM. Good agreement was found between this model and more traditional computational fluid dynamics (CFD) modeling. Next phases of the work includes prototype testing and a techno-economic analysis of the technology.
One of the challenges to design and control phase change material (PCM) based latent heat thermal... more One of the challenges to design and control phase change material (PCM) based latent heat thermal energy storage (LHTES) systems is to develop fast models to accurately represent their transient and nonlinear behaviors. In this paper, a fast explicit modeling approach for a multi-dimensional finned PCM system, called alternating front propagating, is proposed based on the concept of the alternating-direction implicit algorithm for multi-dimensional parabolic and elliptic differential equations. The proposed modeling method is employed to develop a fast explicit dynamic model for a large scale LHTES system, whose heat transfer is enhanced by imbedded circular finned heat pipes. The developed fast model has negligible computational cost and is of sufficient accuracy compared to high-fidelity numerical solutions. The fast explicit model of the LHTES system was employed in a model predictive control framework to determine the HTF flowrate so that its outlet temperature meets a target value. The controlled HTF flowrate can increase the usage efficiency of the stored heat in a LHTES system.
Forced convective, postcritical heat flux heat transfer experiments with water flowing upward in ... more Forced convective, postcritical heat flux heat transfer experiments with water flowing upward in a vertical tube have been conducted at the Idaho National Engineering Laboratory. Thermodynamic nonequilibrium in the form of superheated vapor temperatures was measured at a maximum of three different axial levels. Steady state experiments were conducted at pressures of 0.2 to 0.7 MPa, mass fluxes of 12
Forced-convective postcritical heat flux (CHF) heat transfer data have been obtained at low flow ... more Forced-convective postcritical heat flux (CHF) heat transfer data have been obtained at low flow rates and low pressures (0.2 to 0.7 MPa) for water flowing in a vertical tube. Significant magnitudes of superheat (up to 510 K) were found. The steady state data are in agreement with other reported low-flow and low-pressure nonequilibrium data. Nonequilibrium vapor temperatures were measured at
Two optical techniques for use in detecting liquid contacts in film and transition boiling regime... more Two optical techniques for use in detecting liquid contacts in film and transition boiling regimes were developed. The first optical method involves the measurements of liquid contacts on a high-temperature glass boiling surface in a transient experiment. The second technique utilizes a small fiber-optic probe mounted flush on a copper surface. Experiments have indicated the probe is sufficiently fast responding to provide accurate local measurements of liquid to solid contact in film and transition boiling regimes. The relationship between surface superheat and liquid contact time fraction was determined for both methods.
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