Natural convection of non-Newtonian power-law fluid in a square cavity with a heat-generating element

Development of modern technology in microelectronics and power engineering necessitates the creation of effective cooling systems. This is made possible by the use of the special fins technology within the cavity or special heat transfer liquids in order to intensify the heat removal from the heat-generating elements. The present work is devoted to the mathematical modeling of thermogravitational convection of a non-Newtonian fluid in a closed square cavity with a local source of internal volumetric heat generation. The behavior of the fluid is described by the Ostwald-de Waele power law model. The defining Navier–Stokes equations written using the dimensionless stream function, vorticity and temperature are solved using the finite difference method. The effects of the Rayleigh number, power-law index, and thermal conductivity ratio on heat transfer and the flow structure are studied. The obtained results are presented in the form of isolines of the stream function and temperature, as well as the dependences of the average Nusselt number and average temperature on the governing parameters

A Distinctive Fatigue Failure Criterion

Abstract This paper presents a new fatigue failure criterion for asphalt paving mixtures that is simple, unique, and distinctive. Bending beam fatigue testing in the controlled strain mode at a 1000-microstrain level and 19C temperature was performed on eleven asphalt mixtures that included unmodified and modified binders. Analysis of fatigue load-deformation raw data for each fatigue load cycle was conducted to determine the true point of fatigue failure. With application of a sinusoidal strain on a sample, a sinusoidal response stress is expected even for a heterogeneous material like asphalt concrete. In such a case, a smooth traditional load-deformation (or stress-strain) hysteresis loop is anticipated. This holds true as long as there is no fatigue damage induced in the material. With repeated load applications, the sample starts to fatigue and microcracks are induced. These microcracks introduce discontinuities in the stress paths and the stress response starts to distort. This gets reflected in the load-deformation hysteresis loop, which in turn shows this distortion. Similar distortion can also be seen by observing the sinusoidal load-deformation waveform, where the stress response is no longer dependent on the strain input due to the formation of interconnected fatigue cracks. By tracking the distortion in the hysteresis loop or in the waveform, one is able to get a clear indication of when the first microcracks appeared, and how they progressed up to the point of complete fatigue failure

Engineering estimate of hydrodynamic entrance lengths in non-Newtonian turbulent flow

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Natural convection in a wavy open porous cavity filled with a nanofluid: Tiwari and Das' nanofluid model

Natural convective heat transfer and fluid flow in an open porous cavity filled with a nanofluid is studied numerically using the Tiwari and Das nanofluid model. The transport equations for mass, momentum and energy formulated in dimensionless stream function and temperature are solved numerically using a second-order accurate finite difference method. Particular efforts are focused on the effects of the governing parameters on the heat and fluid flow. It is found that an increase in undulation number of the wavy vertical wall leads to an attenuation of convective flow and a decrease in the heat transfer rate

Unsteady free convection in a porous open wavy cavity filled with a nanofluid using Buongiorno's mathematical model

A numerical investigation is performed on the unsteady free convection heat transfer characteristics of a nanofluid confined within a porous open wavy cavity using the mathematical nanofluid model proposed by Buongiorno. In modeling the cavity, it is assumed that the left wall has a wavy surface, while the right wall is flat. In addition, it is assumed that the two vertical walls of the cavity are impermeable and isothermal, while the bottom wall is adiabatic. In performing the analysis, the governing equations are modeled using the Boussinesq approximation and are solved numerically using the finite-difference method with the second-order differencing schemes.The simulations focus on the respective effects of the undulations number, shape coefficient, and dimensionless time. Particular efforts have been focused on the effects of these parameters on the fluid flow, heat, and mass transfer characteristics.The results show that the average Nusselt and Sherwood numbers decrease with an increase in the undulations number. At the same time, the average Nusselt and Sherwood numbers can be optimized via an appropriate tuning of the wavy surface geometry parameters

Unsteady free convection in a porous open wavy cavity filled with a nanofluid using Buongiorno's mathematical model

A numerical investigation is performed on the unsteady free convection heat transfer characteristics of a nanofluid confined within a porous open wavy cavity using the mathematical nanofluid model proposed by Buongiorno. In modeling the cavity, it is assumed that the left wall has a wavy surface, while the right wall is flat. In addition, it is assumed that the two vertical walls of the cavity are impermeable and isothermal, while the bottom wall is adiabatic. In performing the analysis, the governing equations are modeled using the Boussinesq approximation and are solved numerically using the finite-difference method with the second-order differencing schemes.The simulations focus on the respective effects of the undulations number, shape coefficient, and dimensionless time. Particular efforts have been focused on the effects of these parameters on the fluid flow, heat, and mass transfer characteristics.The results show that the average Nusselt and Sherwood numbers decrease with an increase in the undulations number. At the same time, the average Nusselt and Sherwood numbers can be optimized via an appropriate tuning of the wavy surface geometry parameters

Influence of the chamber inclination angle and heat-generating element location on thermal convection of power-law medium in a chamber

Purpose This paper aims to study the mathematical modeling of passive cooling systems for electronic devices. Improving heat transfer is facilitated by the correct choice of the working fluid and the geometric configuration of the engineering cavity; therefore, this work is devoted to the analysis of the influence of the position of the heat-generating element and the tilted angle of the electronic cabinet on the thermal convection of a non-Newtonian fluid. Design/methodology/approach The area of interest is a square cavity with two cold vertical walls, while the horizontal boundaries are adiabatic. An element of constant volumetric heat generation is placed on the lower wall of the chamber. The problem is described by Navier–Stokes partial differential equations using dimensionless stream function and vorticity. The numerical solution is based on the developed computational code using the finite difference technique and a uniform rectangular grid. Findings The key conclusions of this work are the results of a detailed analysis of streamlines and isotherms, the average Nusselt number and profiles of the average heater temperature. It was found that more intensive cooling of the heat-generating element occurs when the cavity is filled with a pseudoplastic fluid (n < 1) and not inclined (α = 0). The Rayleigh number of Ra = 105 and the thermal conductivity ratio of k = 100 are characterized by the most positive effect. Originality/value The originality of the research lies in both the study of thermal convection in a square chamber filled with power-law fluid under the influence of a volumetric heat production element and the analysis of the influence of geometric and thermophysical parameters characterizing the considered process