Some basic ideas of the heat transfer of ice slurries are discussed. The equations des-cribing a ... more Some basic ideas of the heat transfer of ice slurries are discussed. The equations des-cribing a flow of a Bingham fluid through a tube with a heat flux over the boundary are presented. The theory shows that familiar Relations known in the field of heat exchangers, e.g. the logarithmic-mean temperature difference, do not always apply. – With a device, designed to measure the heat transfer coefficients in tubes, first exper-imental data on the specific heat capacity have been obtained. They are compared with model results. The velocity profile of a laminar ice slurry flow has been mesured with an ultra-sound velocity profile sensor. Furthermore, ice particles of a water/etha-nol ice slurry have been observed under a microscope.
In an earlier contribution it was shown that the Continuous-Properties Model (CPM) is an ideal th... more In an earlier contribution it was shown that the Continuous-Properties Model (CPM) is an ideal theoretical model to calculate melting of ice slurries. Now with a shock-theoretical approach, it is proven that the CPM - in the limit toward a discontinuous melting - just yields the Stefan problem. This limit corresponds to the case when the additive content in an ice slurry tends toward zero. In heat exchangers the ice fraction of an ice slurry is a decreasing function of the downstream space coordinate. The specific pressure drop R=-dp/dx can differ from the inlet to the outlet by more than a factor ten, because the viscosity and the critical shear stress decrease with increasing temperature. A simple analytical model to calculate the overall pressure drop of a cylindrical heat exchanger (with different boundary conditions) is presented.
To measure enthalpy densities, respectively overall specific heats, frequently the differential s... more To measure enthalpy densities, respectively overall specific heats, frequently the differential scanning thermal analysisis (DSC) is applied. Other useful methods are also available, but all of them have disadvantages. Therefore, an alternative measurement procedure - the online enthalpy measurment method - which was presented six years ago, has now been further improved. The quality of the results can be essentially increased by evaluating the experimental data according to a specially developed method. It is analogous to a method of numerical mathematics. The new evaluation procedure is presented and applied to measurements of the enthalpy density of two different phase change slurries, an ice slurry and a water suspension containing micro-encapsulated paraffin wax.
The heat transport to a talin/water ice slurry in a cylindrical heat exchanger was determined by ... more The heat transport to a talin/water ice slurry in a cylindrical heat exchanger was determined by theory and experiment. The theory based on perturbation analysis is only valid for small heat transfer rates. Direchlet and Neumann boundary conditions are applied to numerically calculate temperature profiles at different distances downstream. For the constant-heat-flux-density Neumann boundary condition, numerical results were compared with measured profiles. For laminar and low-Reynolds-number turbulent flows, heat transfer coefficients are presented as a function of the Hedstrom number.
At the University of Applied Scierices in Yverdon, Switzerland for five years theo retical and ex... more At the University of Applied Scierices in Yverdon, Switzerland for five years theo retical and experimental investigatiens of heat transfer to ice sluries in pipes are performed. If only small heat fluxe occur, the velocity profile of laminar flows in tubes are stable. This result leads to a theory for the calculation of pressure drops in heat exchangers. It is presented in detail in this article.
In this article we propose to generalize Reynolds shear stresses in local zero-equation turbulenc... more In this article we propose to generalize Reynolds shear stresses in local zero-equation turbulence models to nonlocal and fractional forms. In the well-accepted general method, starting with a Kraichnanian convolution-integral as Reynolds shear stress, different weighting functions are possible candidates to serve this purpose; e.g. the Liouville weighting function leads to the left-handed Riemann–Liouville fractional derivative and the Heaviside distribution to a mean velocity difference, respectively a difference quotient. Therefore, this weighting function transforms the first gradient (the one in the eddy diffusivity) of Prandtl’s 1925 mixing-length model to an eddy diffusivity with a mean velocity difference and, thereby, directly leads to the (modified) Prandtl shear-layer model of 1942. Prandtl’s intuitive development—which is in agreement with fractional calculus—does not serve as a proof of correctness, but is a welcome coincidence. By further following Prandtl’s intuition and applying the Heaviside distribution also to the remaining driving gradient, yields the Difference-Quotient Turbulence Model (DQTM), which was discovered by other means and had been published by Egolf in 1991. As a result, it becomes clear that the DQTM is a natural nonlocal extension of Prandtl’s models and contains a special case of a simple fractional derivative, namely a difference quotient, which stands for the highest possible nonlocality and minimum calculation time to solve a turbulent flow problem.
Visualization of ice particles in a rectangular cavity and ice slurry flows in a pipe are perform... more Visualization of ice particles in a rectangular cavity and ice slurry flows in a pipe are performed. The form and size of ice particles is investigated by optical microscopy, which permits a statistical evaluation of the geometrical shapes of the ice crystals. The observed particle densities and the size distributions correspond with the theoretically determined ice fractions. A method applied to measure ice slurry velocity fields is based on ultrasound Doppler echography. The velocity profile, determined by the velocity of ice particles, is measured and several features which are related to Bingham flows are observed. With these experimental results, complete rheograms can be constructed.
Experimental results on storage and mixing of ten-percent-talin/water ice slurries are presented.... more Experimental results on storage and mixing of ten-percent-talin/water ice slurries are presented. For this purpose a system with a storage tank, with a volume of 1000 liters and a mixing device containing three slightly inclined cones, was investigated. In first experiments the angular velocity of the mixing device was varied. The variance of numerous temperatures (measured at different locations with different heights in the tank) yields a suitable measure to quantify the stratification. Above a critical rotation frequency, which is a function of the ice fraction, the entire fluid gets into motion and very good mixing is obtained.
Publications on magnetocaloric materials, magnetic refrigerators, magnetic heat pumps and magneti... more Publications on magnetocaloric materials, magnetic refrigerators, magnetic heat pumps and magnetic power conversion machines contain experimental results as well as solutions obtained by physical modelling, analytical and numerical calculations. Whereas material scientists usually aim for physical property data, thermal and electrical engineers are interested in the efficiency of the operation and economists in both, production and operation costs of a machine. However, without exact data of the magnetocaloric and magnetic materials, no precise determination of the energy consumption of a magnetic refrigerator can be achieved. Magnetic and thermodynamic measurement techniques must be reviewed and discussed. In the article, a method for an accurate determination of a global COP of a magnetic refrigerator, heat pump, respectively energy conversion machine is proposed, taking all possible losses of the machines into consideration. Only a full account in a machine characterization gives...
Keywords: magnetocaloric ; entropy ; second-order magnetic phase transition ; standardization Ref... more Keywords: magnetocaloric ; entropy ; second-order magnetic phase transition ; standardization Reference EPFL-CONF-213544 Record created on 2015-11-09, modified on 2017-05-08
Even though applications of direct numerical simulations are on the rise, today the most usual me... more Even though applications of direct numerical simulations are on the rise, today the most usual method to solve turbulence problems is still to apply a closure scheme of a defined order. It is not the case that a rising order of a turbulence model is always related to a quality improvement. Even more, a conceptual advantage of applying a lowest order turbulence model is that it represents the analogous method to the procedure of introducing a constitutive equation which has brought success to many other areas of physics. First order turbulence models were developed in the 1920s and today seem to be outdated by newer and more sophisticated mathematical-physical closure schemes. However, with the new knowledge of fractal geometry and fractional dynamics, it is worthwhile to step back and reinvestigate these lowest order models. As a result of this and simultaneously introducing generalizations by multiscale analysis, the first order, nonlinear, nonlocal, and fractional Difference-Quoti...
Wireless capsule endoscopy (WCE) is a powerful tool for medical screening and diagnosis, where a ... more Wireless capsule endoscopy (WCE) is a powerful tool for medical screening and diagnosis, where a small capsule is swallowed and moved by means of natural peristalsis and gravity through the human gastrointestinal (GI) tract. The camera-integrated capsule allows for visualization of the small intestine, a region which was previously inaccessible to classical flexible endoscopy. As a diagnostic tool, it allows to localize the sources of bleedings in the middle part of the gastrointestinal tract and to identify diseases, such as inflammatory bowel disease (Crohn's disease), polyposis syndrome, and tumors. The screening and diagnostic efficacy of the WCE, especially in the stomach region, is hampered by a variety of technical challenges like the lack of active capsular position and orientation control. Therapeutic functionality is absent in most commercial capsules, due to constraints in capsular volume and energy storage. The possibility of using body-exogenous magnetic fields to guide, orient, power, and operate the capsule and its mechanisms has led to increasing research in Magnetically Guided Capsule Endoscopy (MGCE). This work shortly reviews the history and state-of-art in WCE technology. It highlights the magnetic technologies for advancing diagnostic and therapeutic functionalities of WCE. Not restricting itself to the GI tract, the review further investigates the technological developments in magnetically guided microrobots that can navigate through the various air- and fluid-filled lumina and cavities in the body for minimally invasive medicine.
ABSTRACT Un producto de fase cambiante PCM y un modulo de acumulación basados en un modelo para f... more ABSTRACT Un producto de fase cambiante PCM y un modulo de acumulación basados en un modelo para fusión/congelación se han fabricado e implementado dentro del programa informático Dymola-Modelica. Este programa ofrece un conjunto de bibliotecas de datos térmicos con componentes estándar como tubos, bombas, intercambiadores de calor etc. Los resultados de interés procedentes de la simulación principal incluyen el cambio de fase (tiempo de retardo) causado por cilindros rellenos con un PCM y colocados en el aparato de acumulación / desfasaje. Además, se ha elaborado un modelo completo de casa MinergieTM mediante un modelo bastante simple (económico en términos del tiempo de la CPU), pero siendo muy efectivo térmicamente. Esta casa está conectada a un sistema idóneo de ventilación seleccionado a partir de una lista de tipos diferentes. Por consiguiente, también gracias a los recursos gráficos en una interfase, es posible crear una casa MinergieTM con una conmutación integrada de bajada térmica de temperatura/fase y un aparato de recuperación de calor. Se han estudiado las diferencias de temperatura entre la casa MinergieTM conectada a un aparato de almacenamiento – acumulador – una casa sin dicho acumulador. Dichos sistemas están planificados para ser utilizados principalmente para enfriamiento híbrido de casas suizas MinergieTM en época de verano. En caso de una aplicación multifuncional, pueden también aplicarse en invierno como apoyo a la calefacción. Se analizan los numerosos resultados de la simulación y se presentan las soluciones óptimas.
Some basic ideas of the heat transfer of ice slurries are discussed. The equations des-cribing a ... more Some basic ideas of the heat transfer of ice slurries are discussed. The equations des-cribing a flow of a Bingham fluid through a tube with a heat flux over the boundary are presented. The theory shows that familiar Relations known in the field of heat exchangers, e.g. the logarithmic-mean temperature difference, do not always apply. – With a device, designed to measure the heat transfer coefficients in tubes, first exper-imental data on the specific heat capacity have been obtained. They are compared with model results. The velocity profile of a laminar ice slurry flow has been mesured with an ultra-sound velocity profile sensor. Furthermore, ice particles of a water/etha-nol ice slurry have been observed under a microscope.
In an earlier contribution it was shown that the Continuous-Properties Model (CPM) is an ideal th... more In an earlier contribution it was shown that the Continuous-Properties Model (CPM) is an ideal theoretical model to calculate melting of ice slurries. Now with a shock-theoretical approach, it is proven that the CPM - in the limit toward a discontinuous melting - just yields the Stefan problem. This limit corresponds to the case when the additive content in an ice slurry tends toward zero. In heat exchangers the ice fraction of an ice slurry is a decreasing function of the downstream space coordinate. The specific pressure drop R=-dp/dx can differ from the inlet to the outlet by more than a factor ten, because the viscosity and the critical shear stress decrease with increasing temperature. A simple analytical model to calculate the overall pressure drop of a cylindrical heat exchanger (with different boundary conditions) is presented.
To measure enthalpy densities, respectively overall specific heats, frequently the differential s... more To measure enthalpy densities, respectively overall specific heats, frequently the differential scanning thermal analysisis (DSC) is applied. Other useful methods are also available, but all of them have disadvantages. Therefore, an alternative measurement procedure - the online enthalpy measurment method - which was presented six years ago, has now been further improved. The quality of the results can be essentially increased by evaluating the experimental data according to a specially developed method. It is analogous to a method of numerical mathematics. The new evaluation procedure is presented and applied to measurements of the enthalpy density of two different phase change slurries, an ice slurry and a water suspension containing micro-encapsulated paraffin wax.
The heat transport to a talin/water ice slurry in a cylindrical heat exchanger was determined by ... more The heat transport to a talin/water ice slurry in a cylindrical heat exchanger was determined by theory and experiment. The theory based on perturbation analysis is only valid for small heat transfer rates. Direchlet and Neumann boundary conditions are applied to numerically calculate temperature profiles at different distances downstream. For the constant-heat-flux-density Neumann boundary condition, numerical results were compared with measured profiles. For laminar and low-Reynolds-number turbulent flows, heat transfer coefficients are presented as a function of the Hedstrom number.
At the University of Applied Scierices in Yverdon, Switzerland for five years theo retical and ex... more At the University of Applied Scierices in Yverdon, Switzerland for five years theo retical and experimental investigatiens of heat transfer to ice sluries in pipes are performed. If only small heat fluxe occur, the velocity profile of laminar flows in tubes are stable. This result leads to a theory for the calculation of pressure drops in heat exchangers. It is presented in detail in this article.
In this article we propose to generalize Reynolds shear stresses in local zero-equation turbulenc... more In this article we propose to generalize Reynolds shear stresses in local zero-equation turbulence models to nonlocal and fractional forms. In the well-accepted general method, starting with a Kraichnanian convolution-integral as Reynolds shear stress, different weighting functions are possible candidates to serve this purpose; e.g. the Liouville weighting function leads to the left-handed Riemann–Liouville fractional derivative and the Heaviside distribution to a mean velocity difference, respectively a difference quotient. Therefore, this weighting function transforms the first gradient (the one in the eddy diffusivity) of Prandtl’s 1925 mixing-length model to an eddy diffusivity with a mean velocity difference and, thereby, directly leads to the (modified) Prandtl shear-layer model of 1942. Prandtl’s intuitive development—which is in agreement with fractional calculus—does not serve as a proof of correctness, but is a welcome coincidence. By further following Prandtl’s intuition and applying the Heaviside distribution also to the remaining driving gradient, yields the Difference-Quotient Turbulence Model (DQTM), which was discovered by other means and had been published by Egolf in 1991. As a result, it becomes clear that the DQTM is a natural nonlocal extension of Prandtl’s models and contains a special case of a simple fractional derivative, namely a difference quotient, which stands for the highest possible nonlocality and minimum calculation time to solve a turbulent flow problem.
Visualization of ice particles in a rectangular cavity and ice slurry flows in a pipe are perform... more Visualization of ice particles in a rectangular cavity and ice slurry flows in a pipe are performed. The form and size of ice particles is investigated by optical microscopy, which permits a statistical evaluation of the geometrical shapes of the ice crystals. The observed particle densities and the size distributions correspond with the theoretically determined ice fractions. A method applied to measure ice slurry velocity fields is based on ultrasound Doppler echography. The velocity profile, determined by the velocity of ice particles, is measured and several features which are related to Bingham flows are observed. With these experimental results, complete rheograms can be constructed.
Experimental results on storage and mixing of ten-percent-talin/water ice slurries are presented.... more Experimental results on storage and mixing of ten-percent-talin/water ice slurries are presented. For this purpose a system with a storage tank, with a volume of 1000 liters and a mixing device containing three slightly inclined cones, was investigated. In first experiments the angular velocity of the mixing device was varied. The variance of numerous temperatures (measured at different locations with different heights in the tank) yields a suitable measure to quantify the stratification. Above a critical rotation frequency, which is a function of the ice fraction, the entire fluid gets into motion and very good mixing is obtained.
Publications on magnetocaloric materials, magnetic refrigerators, magnetic heat pumps and magneti... more Publications on magnetocaloric materials, magnetic refrigerators, magnetic heat pumps and magnetic power conversion machines contain experimental results as well as solutions obtained by physical modelling, analytical and numerical calculations. Whereas material scientists usually aim for physical property data, thermal and electrical engineers are interested in the efficiency of the operation and economists in both, production and operation costs of a machine. However, without exact data of the magnetocaloric and magnetic materials, no precise determination of the energy consumption of a magnetic refrigerator can be achieved. Magnetic and thermodynamic measurement techniques must be reviewed and discussed. In the article, a method for an accurate determination of a global COP of a magnetic refrigerator, heat pump, respectively energy conversion machine is proposed, taking all possible losses of the machines into consideration. Only a full account in a machine characterization gives...
Keywords: magnetocaloric ; entropy ; second-order magnetic phase transition ; standardization Ref... more Keywords: magnetocaloric ; entropy ; second-order magnetic phase transition ; standardization Reference EPFL-CONF-213544 Record created on 2015-11-09, modified on 2017-05-08
Even though applications of direct numerical simulations are on the rise, today the most usual me... more Even though applications of direct numerical simulations are on the rise, today the most usual method to solve turbulence problems is still to apply a closure scheme of a defined order. It is not the case that a rising order of a turbulence model is always related to a quality improvement. Even more, a conceptual advantage of applying a lowest order turbulence model is that it represents the analogous method to the procedure of introducing a constitutive equation which has brought success to many other areas of physics. First order turbulence models were developed in the 1920s and today seem to be outdated by newer and more sophisticated mathematical-physical closure schemes. However, with the new knowledge of fractal geometry and fractional dynamics, it is worthwhile to step back and reinvestigate these lowest order models. As a result of this and simultaneously introducing generalizations by multiscale analysis, the first order, nonlinear, nonlocal, and fractional Difference-Quoti...
Wireless capsule endoscopy (WCE) is a powerful tool for medical screening and diagnosis, where a ... more Wireless capsule endoscopy (WCE) is a powerful tool for medical screening and diagnosis, where a small capsule is swallowed and moved by means of natural peristalsis and gravity through the human gastrointestinal (GI) tract. The camera-integrated capsule allows for visualization of the small intestine, a region which was previously inaccessible to classical flexible endoscopy. As a diagnostic tool, it allows to localize the sources of bleedings in the middle part of the gastrointestinal tract and to identify diseases, such as inflammatory bowel disease (Crohn's disease), polyposis syndrome, and tumors. The screening and diagnostic efficacy of the WCE, especially in the stomach region, is hampered by a variety of technical challenges like the lack of active capsular position and orientation control. Therapeutic functionality is absent in most commercial capsules, due to constraints in capsular volume and energy storage. The possibility of using body-exogenous magnetic fields to guide, orient, power, and operate the capsule and its mechanisms has led to increasing research in Magnetically Guided Capsule Endoscopy (MGCE). This work shortly reviews the history and state-of-art in WCE technology. It highlights the magnetic technologies for advancing diagnostic and therapeutic functionalities of WCE. Not restricting itself to the GI tract, the review further investigates the technological developments in magnetically guided microrobots that can navigate through the various air- and fluid-filled lumina and cavities in the body for minimally invasive medicine.
ABSTRACT Un producto de fase cambiante PCM y un modulo de acumulación basados en un modelo para f... more ABSTRACT Un producto de fase cambiante PCM y un modulo de acumulación basados en un modelo para fusión/congelación se han fabricado e implementado dentro del programa informático Dymola-Modelica. Este programa ofrece un conjunto de bibliotecas de datos térmicos con componentes estándar como tubos, bombas, intercambiadores de calor etc. Los resultados de interés procedentes de la simulación principal incluyen el cambio de fase (tiempo de retardo) causado por cilindros rellenos con un PCM y colocados en el aparato de acumulación / desfasaje. Además, se ha elaborado un modelo completo de casa MinergieTM mediante un modelo bastante simple (económico en términos del tiempo de la CPU), pero siendo muy efectivo térmicamente. Esta casa está conectada a un sistema idóneo de ventilación seleccionado a partir de una lista de tipos diferentes. Por consiguiente, también gracias a los recursos gráficos en una interfase, es posible crear una casa MinergieTM con una conmutación integrada de bajada térmica de temperatura/fase y un aparato de recuperación de calor. Se han estudiado las diferencias de temperatura entre la casa MinergieTM conectada a un aparato de almacenamiento – acumulador – una casa sin dicho acumulador. Dichos sistemas están planificados para ser utilizados principalmente para enfriamiento híbrido de casas suizas MinergieTM en época de verano. En caso de una aplicación multifuncional, pueden también aplicarse en invierno como apoyo a la calefacción. Se analizan los numerosos resultados de la simulación y se presentan las soluciones óptimas.
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