The Experts below are selected from a list of 282 Experts worldwide ranked by ideXlab platform
C A Ward - One of the best experts on this subject based on the ideXlab platform.
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Surface Thermal Capacity and its effects on the boundary conditions at fluid-fluid interfaces.
Physical review. E Statistical nonlinear and soft matter physics, 2007Co-Authors: Kausik S Das, C A WardAbstract:We have formulated a generalization of the energy boundary condition for fluid-fluid interfaces that includes the transport of the Gibbs excess internal energy. A newly measured surface property - the surface Thermal Capacity c(sigma) - appears in the result, and couples the temperature and velocity fields. If this term is not included in the energy boundary condition at liquid-vapor interfaces, the energy-conservation principle cannot be satisfied during steady-state evaporation of H(2)O(l) or D(2)O(l) . The c(sigma) term is possibly important in a number of other circumstances, and its importance can be determined from the magnitude of two nondimensional numbers.
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Surface-Thermal Capacity of from measurements made during steady-state evaporation.
Physical review. E Statistical nonlinear and soft matter physics, 2005Co-Authors: Fei Duan, C A WardAbstract:When D2O(l) evaporates into its vapor under steady-state conditions with the temperature field in the liquid arranged so that there is no buoyancy-driven convection and the Marangoni number is less than approximately 100, it is found that the interface is quiescent and Thermal conduction to the interface supplies energy at a sufficient rate to evaporate the liquid. However, if the evaporation rate is raised so that the Marangoni number goes above approximately 100, the interface is transformed: a fluctuating thermocapillary flow occurs, and Thermal conduction no longer supplies energy at a sufficient rate to evaporate the liquid. An energy analysis indicates conservation of energy can be satisfied only if thermocapillary convection is taken into account, and the surface-Thermal Capacity csigma is assigned a value of 32.5+/-0.8 kJ/(m2 K) when the temperature is in the range -10 degrees C< or =TLV< or =3.7 degrees C. This value is consistent with that found previously for H2O, and application of the Gibbs model gives a qualitative explanation for the value. Once the value of the surface-Thermal Capacity is known, the local heat flux along the interface can be calculated and statistical rate theory can be used to predict the local vapor-phase pressure on the interface. Since this theory introduces no adjustable parameters, the predicted pressure can be compared directly with that measured: this comparison indicates the mean of the pressures predicted to exist on the interface is in close agreement with those measured approximately 20 cm above the interface, and the small pressure gradient along the interface is consistent with the thermocapillary convection predicted from the interfacial temperature gradient.
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surface Thermal Capacity of d 2 o from measurements made during steady state evaporation
Physical Review E, 2005Co-Authors: Fei Duan, C A WardAbstract:When ${\mathrm{D}}_{2}\mathrm{O}(l)$ evaporates into its vapor under steady-state conditions with the temperature field in the liquid arranged so that there is no buoyancy-driven convection and the Marangoni number is less than $\ensuremath{\sim}100$, it is found that the interface is quiescent and Thermal conduction to the interface supplies energy at a sufficient rate to evaporate the liquid. However, if the evaporation rate is raised so that the Marangoni number goes above $\ensuremath{\sim}100$, the interface is transformed: a fluctuating thermocapillary flow occurs, and Thermal conduction no longer supplies energy at a sufficient rate to evaporate the liquid. An energy analysis indicates conservation of energy can be satisfied only if thermocapillary convection is taken into account, and the surface-Thermal Capacity ${c}_{\ensuremath{\sigma}}$ is assigned a value of $32.5\ifmmode\pm\else\textpm\fi{}0.8\phantom{\rule{0.3em}{0ex}}\mathrm{kJ}∕({\mathrm{m}}^{2}\phantom{\rule{0.2em}{0ex}}\mathrm{K})$ when the temperature is in the range $\ensuremath{-}10\phantom{\rule{0.2em}{0ex}}\ifmmode^\circ\else\textdegree\fi{}\mathrm{C}\ensuremath{\leqslant}{T}^{LV}\ensuremath{\leqslant}3.7\phantom{\rule{0.2em}{0ex}}\ifmmode^\circ\else\textdegree\fi{}\mathrm{C}$. This value is consistent with that found previously for ${\mathrm{H}}_{2}\mathrm{O}$, and application of the Gibbs model gives a qualitative explanation for the value. Once the value of the surface-Thermal Capacity is known, the local heat flux along the interface can be calculated and statistical rate theory can be used to predict the local vapor-phase pressure on the interface. Since this theory introduces no adjustable parameters, the predicted pressure can be compared directly with that measured: this comparison indicates the mean of the pressures predicted to exist on the interface is in close agreement with those measured $\ensuremath{\sim}20\phantom{\rule{0.3em}{0ex}}\mathrm{cm}$ above the interface, and the small pressure gradient along the interface is consistent with the thermocapillary convection predicted from the interfacial temperature gradient.
Z.e. Da Silva - One of the best experts on this subject based on the ideXlab platform.
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Transient conduction in spherical fruits: method to estimate the Thermal conductivity and volumetric Thermal Capacity
Journal of Food Engineering, 2005Co-Authors: Stela De Lourdes Ribeiro De Mendonça, Celso Rosendo Bezerra Filho, Z.e. Da SilvaAbstract:Abstract A methodology to estimate the Thermal conductivity ( κ ) and volumetric Thermal Capacity ( ρc p ) of apples is described. The methodology is based in the inverse problem of heat conduction solution. The apples are considered as spherical objects. This approach relies on an analytical solution of the problem and on an optimization technique to estimate the two thermophysical properties. Typically, a test to measures the temperature response of a specimen subjected to transient heating by hot air to determine the properties directly as a function of temperature.
Stela De Lourdes Ribeiro De Mendonça - One of the best experts on this subject based on the ideXlab platform.
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Transient conduction in spherical fruits: method to estimate the Thermal conductivity and volumetric Thermal Capacity
Journal of Food Engineering, 2005Co-Authors: Stela De Lourdes Ribeiro De Mendonça, Celso Rosendo Bezerra Filho, Z.e. Da SilvaAbstract:Abstract A methodology to estimate the Thermal conductivity ( κ ) and volumetric Thermal Capacity ( ρc p ) of apples is described. The methodology is based in the inverse problem of heat conduction solution. The apples are considered as spherical objects. This approach relies on an analytical solution of the problem and on an optimization technique to estimate the two thermophysical properties. Typically, a test to measures the temperature response of a specimen subjected to transient heating by hot air to determine the properties directly as a function of temperature.
Shahab Teimourimanesh - One of the best experts on this subject based on the ideXlab platform.
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Thermal Capacity of tread-braked railway wheels. Part 1: Modelling
Proceedings of the Institution of Mechanical Engineers Part F: Journal of Rail and Rapid Transit, 2015Co-Authors: Shahab Teimourimanesh, Tore V Vernersson, Roger LundénAbstract:Tread brakes are still a common frictional braking system used on metro and suburban trains. Here the wheels are safety-related components and there is a need to develop design specifications and guidelines to ensure that the wheels perform properly under the service conditions to which they are exposed. In the present paper, a model is proposed and developed that represents typical conditions in metro and suburban operations, in particular during sequential stop braking. The analysis also considers drag braking, mechanical loading, residual stresses and wheel–axle interference fit. Finite element modelling, with an advanced temperature-dependent material model, together with a fatigue analysis is employed to quantify the wheel’s performance. An application example demonstrates the method for a typical metro wheel. In a companion paper, further applications are presented that demonstrate important aspects of the Thermal Capacity of tread-braked railway wheels.
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Thermal Capacity of tread-braked railway wheels. Part 2: Applications
Proceedings of the Institution of Mechanical Engineers Part F: Journal of Rail and Rapid Transit, 2015Co-Authors: Shahab Teimourimanesh, Tore V Vernersson, Roger LundénAbstract:Tread braking is a common friction-based braking system that finds use on metro and suburban trains. Here the wheels are safety-related components and there is a need to develop design specifications and guidelines to ensure that the wheels perform properly under the service conditions to which they are exposed. In the present paper, examples of applications are given that employ a modelling framework that was developed in a companion paper. The examples represent typical conditions in metro and suburban operations, in particular during sequential stop braking. Also results for drag braking, mechanical loading, residual stresses and wheel–axle interference fit are given. Parametric studies are performed to demonstrate the influence of load levels and other factors on the fatigue life of the wheels. The results should be useful for establishing design rules that consider the Thermal Capacity of tread-braked railway wheels.
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Thermal Capacity of Railway Wheels - Temperatures, residual stresses and fatigue damage with special focus on metro applications
2014Co-Authors: Shahab TeimourimaneshAbstract:Tread (block) braking is still one of the most common braking systems on railway vehicles. The action is carried out by pressing brake blocks against the tread of a wheel, which is also in rolling contact with the rail. The extensive use of tread brakes in metro and suburban applications has created a need for design guidelines or standards for wheels exposed to repeated stop braking. The Thermal Capacity of the wheels puts a limit to railway tread braking systems. With the exception of the drag braking cases described in the European standard EN 13979-1, there are no known standards or guidelines regarding the Thermal Capacity limits for wheels. In the present work, important aspects of the Thermal Capacity of tread braked railway wheels have been assessed in a literature survey. Then two different railway wheel designs, with typical characteristics of freight and metro wheels, have been numerically studied with respect to standard design criteria for load cases of drag braking and stop braking. The influence of brake block materials, Thermal parameters and brake pressure distribution on the wheel temperatures has been investigated. A general result is that hot spots only have a minor influence on the global heat partitioning in the wheel-block-rail system even though the hot spots have a major impact on local temperatures. Brake rig experiments and a field test campaign were performed and aimed at measuring wheel and brake block temperatures during different service conditions for a metro line. Simulation and calibration tools were employed in order to facilitate a comparison between measured temperatures. The results showed the importance of knowing the convection cooling parameters for different wagons if prolonged braking action is to be considered. In a pin-on-disc experimental study of railway braking materials, the heat partitioning characteristics between wheel and block material at controlled elevated disc temperatures were investigated by a finite element approach where a model was calibrated using measured temperatures. In the final part of the present thesis, a modelling framework was proposed and developed that represents typical conditions in metro and suburban operations, in particular during sequential stop braking. A parametric study was done for analysing the influence of various loading levels and other important factors on temperatures, axial flange deflection, residual stresses and the fatigue life of the wheels. The model and the numerical results will be useful for assessing the Thermal Capacity of wheels and for developing new design rules and standards. It was found that the mechanical and Thermal loadings have different influences on the web damage and on the estimated fatigue life depending on load cases and wheel design.
Fengrui Sun - One of the best experts on this subject based on the ideXlab platform.
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Extremal work of an endoreversible system with two finite Thermal Capacity reservoirs
Journal of the Energy Institute, 2009Co-Authors: Lingen Chen, Fengrui SunAbstract:AbstractExtremal work of two finite Thermal Capacity reservoirs is determined. It is obtained by using optimal control theory. It is shown that the temperature of driving fluid changes exponentially with respect to flow velocity and process duration. The extremal work for heat engine mode is different from that for heat pump mode. The obtained results are compared with those obtained with infinite low temperature heat reservoir. The model and analysis in this paper provide a means for improved evaluation of the mechanical energy limits in practical systems.
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Optimum work in real systems with a class of finite Thermal Capacity reservoirs
Mathematical and Computer Modelling, 2008Co-Authors: Lingen Chen, Fengrui SunAbstract:The optimum work in real systems with two finite Thermal Capacity reservoirs is determined. It is obtained by using optimal control theory. It is shown that the temperature of external working fluid changes exponentially with respect to flow velocity and process duration. The analysis proves that the optimum work is different for heat engine mode and heat pump mode. The recently obtained results are compared with those obtained previously. The models and results in this paper provide an approach to improve calculations of energy limits in real systems.
