Massimo Capobianchi

Predictions of pressure drop and heat transfer in concentric annular ducts with modified power law fluids

The following numerical analysis examines the pressure drop and heat transfer characteristics associated with flows of modified power law fluids through concentric annular ducts. The flows considered are steady, fully developed and laminar with constant properties, except for viscosity. The boundary conditions for the heat transfer problem are constant heat flux at the inner tube, and an adiabatic outer tube.Results are presented for the friction factor-Reynolds number product and for the Nusselt number as a function of a dimensionless shear rate parameter. These are expressed as correlation equations which give a convenient description of the results throughout the complete domain of the analysis: from low shear rates where the viscosity is Newtonian, to the higher shear rates where the behavior is purely power law, and at the intermediate shear rates where the viscosity is transitional.ZusammenfassungDie folgenden numerischen Berechnungen untersuchen für die Strömung in konzentrischen Ringkanälen den Druckverlust und die Wärmeübertragungscharakteristik von Fluiden, die mit dem modifizierten Potenz-Ansatz beschrieben werden. Die betrachtete Strömung ist stationär, voll ausgebildet und laminar. Alle Stoffwerte außer der Viskosität sind konstant. Die Randbedingungen für den Wärmeübergang sind konstante Wärmestromdichte am inneren Rohr und ein adiabates äußeres Rohr.Ergebnisse werden für das Produkt Reibungsfaktor—Reynoldszahl und für die Nusselt-Zahl als Funktion eines dimensionslosen Parameters für den Geschwindigkeitsgradienten gezeigt. Diese werden als Korrelationsgleichungen formuliert, die eine gebräuchliche Darstellung der Ergebnisse des kompletten Berechnungsgebietes ergeben: von niedrigen Geschwindigkeitsgradienten, wo die Viskosität dem Ansatz nach Newton folgt, zu den höheren Geschwindigkeitsgradienten, wo das Verhalten dem reinen Potenzansatz entspricht, und bei einem Zwischenstadium, in dem die Viskosität in einem Übergangsbereich liegh.

A new technique for measuring the Fickian diffusion coefficient in binary liquid solutions

The present study details the development of a new technique for measuring the Fickian diffusion coefficient in binary liquid solutions, and reports the coefficients obtained using this new technique for two electrolytic systems. The new method, called the decaying pulse technique, takes advantage of the behavior of a semi-infinite system exposed to a transient concentration pulse. The method permits simple, direct, and absolute determination of the diffusion coefficient, and requires measurement of only time and distance. It is applicable to many different types of fluid pairs, and requires no knowledge of solution properties. The decaying pulse technique was used to measure the average diffusion coefficient of potassium chloride in water and sodium chloride in water, at 18.5, 25.0, and 30.0°C. The current experimental results were compared to those from other published investigations, and were generally found to agree within the predicted uncertainty of the current measurements ±7.6%.

Laminar Natural Convection From an Isothermal Vertical Surface to Pseudoplastic and Dilatant Fluids

This paper reports the results of a numerical study of natural convective heat transfer from a vertical isothermal surface to pseudoplastic and dilatant fluids. The analysis calculates the average Nusselt number in the laminar regime when the surface is exposed to an otherwise quiescent fluid. Because the solution utilizes constitutive equations that are valid over the entire shear rate range, the results map the behavior regardless of the shear rates that exist in the flow field. The Nusselt number is shown to approach Newtonian values when the shear rates throughout the flow field are predominantly either in the zero or in the high shear rate Newtonian regions of the flow curve. When they are principally in the power law regime, and if the fluid is also strongly non-Newtonian, then the Nusselt number approaches power law values. For all other cases, it is seen to attain intermediate values. Furthermore, a shear rate parameter is identified that determines the shear rate regime where the system is operating. The average Nusselt number is presented in both graphical and tabular forms over a broad range of system parameters.

Simulating the Electrical Behavior of Integrated Circuit Devices in the Presence of Thermal Interactions

This paper describes a cosimulation methodology for modeling the electrical behavior of integrated circuit devices in the presence of thermal interactions. The methodology consists of linking a custom finite-volume thermal simulator to a commercially available electrical simulator (Saber, Synopsys, Inc.). Specifically, this paper delineates the techniques developed to resolve the time- and length-scale issues associated with this type of cosimulation that, if left unresolved, typically lead to poor computational performance. These problems, their solutions, and their implementation into the thermal simulator are exposed in detail

A Modification of Murray's Law for Shear-Thinning Rheology

This study reformulates Murrays well-known principle of minimum work as applied to the cardiovascular system to include the effects of the shear-thinning rheology of blood. The viscous behavior is described using the extended modified power law (EMPL), which is a time-independent, but shear-thinning rheological constitutive equation. The resulting minimization problem is solved numerically for typical parameter ranges. The non-Newtonian analysis still predicts the classical cubic diameter dependence of the volume flow rate and the cubic branching law. The current analysis also predicts a constant wall shear stress throughout the vascular tree, albeit with a numerical value about 15-25% higher than the Newtonian analysis. Thus, experimentally observed deviations from the cubic branching law or the predicted constant wall shear stress in the vasculature cannot likely be attributed to bloods shear-thinning behavior. Further differences between the predictions of the non-Newtonian and the Newtonian analyses are highlighted, and the limitations of the Newtonian analysis are discussed. Finally, the range and limits of applicability of the current results as applied to the human arterial tree are also discussed.