Numerical solution of MHD slip flow of a nanofluid past a radiating plate with Newtonian heating : a lie group approach

In this paper, we have examined the magnetohydrodynamic flow of a nanofluid past a radiating sheet. The Navier velocity slip, Newtonian heating and passively controlled wall boundary conditions are considered. The governing equations are reduced into similarity equations with the help of Lie group. A collocation method is used for simulation. The influence of emerging parameters on velocity, temperature, nanoparticle volumetric fraction profiles, as well as on local skin friction factor and local Nusselt number are illustrated in detail. It is found that the friction (heat transfer rate) is lower (higher) for passively controlled boundary conditions as compared to the case of an actively controlled boundary condition. The magnetic field decreases both the skin friction and the rate of heat transfer. The findings are validated with existing results and found an excellent agreement. The model explores new applications in solar collectors with direct solar radiative input using magnetic nanofluids

Zrównoważony rozwój jako czynnik konkurencyjności : ilościowa analiza międzykrajowa

That sustainability is an essential competitive advantage is a common dictum in politics and some areas of academic research. The past few decades have made more and more dispersed ‘hard’ and soft data available, indicating not only more details on the economic performance of coun-tries, but also on their sustainability performance. This study aims to examine whether there is a rela-tionship between sustainability performance and national competitiveness by analysing economic, environmental, and social indicators from four data sources, including economic and sustainability data from G-20 countries for the period 2010 to 2019, representing 73% of the global GDP in 2020. The research design is based on several stepwise regression analyses to explore the pooled data set. The data analysis concludes that the effects of sustainability on competitiveness are hardly confirmed or rejected, contrary to classic economic predictors.Stwierdzenie, że zrównoważony rozwój stanowi istotną przewagę konkurencyjną, jest powszechną tezą obecną w polityce i niektórych obszarach badań naukowych. W ciągu ostatnich kilku dekad udostępniono coraz więcej rozproszonych danych „twardych” i „miękkich”, wskazujących więcej szczegółów nie tylko na temat wyników gospodarczych krajów, ale także na temat ich wyników w zakresie zrównoważonego rozwoju. Celem badania jest sprawdzenie, czy istnieje związek między wynikami w zakresie zrównoważonego rozwoju a konkurencyjnością kraju poprzez analizę wskaźni-ków ekonomicznych, środowiskowych i społecznych z czterech źródeł danych, w tym danych ekono-micznych i danych dotyczących zrównoważonego rozwoju z krajów G-20 w okresie od 2010 do 2019 roku, reprezentujących 73% globalnego PKB w 2020 roku. Badanie opiera się na kilku analizach regresji wykonanych w celu analizy zbioru danych, która prowadzi do wniosku, że wpływ wyników zrównowa-żonego rozwoju na konkurencyjność jest trudny do potwierdzenia lub odrzucenia, w przeciwieństwie do klasycznych predyktorów ekonomicznych

Hydrodynamic Instability and Heat Transfer Analysis of Nanoflow in Semi-Porous Microchannels

This dissertation focuses on the simulation of nanofluid and fluid flow in a semi-porous microchannel. Despite the wide applications of nanoparticles in recent years, there are still some nano-exclusive phenomena which render the performance of the nanofluid unpredictable. The nano-scale specific properties can be positive or negative depending on the nanoparticle and the surrounding conditions, ignoring which, result in imprecise predictions. Therefore, this dissertation analyzes the hydrodynamic and thermal behavior of nanofluid and fluid flow in semi-porous microchannels, employing the Lattice Boltzmann method. First, the flow instabilities in nanofluid flow in a porous microchannel are studied. It is shown that the nanoparticle effect on instability is highly-dependent on its properties and the surrounding conditions. It is also revealed that nanoparticles behave differently at various viscous regimes, and the instability is controlled by the physical and chemical properties of the nanoparticles. The second part focuses on the heat transfer behavior of the porous microchannel in the presence of nanofluid. It is shown that the nanoparticle distribution plays important roles in heat transfer. Particle size and surface energy are also found to change the whole picture of heat transfer and therefore, a characteristic curve is introduced, using which, nanoparticles can safely improve heat removal. In the third section, the analysis of the second part is extended to randomly distributed pin-based microchannels with special attention to nanoparticle adsorption on pin surfaces. Statistical analysis shows that various random realizations behave differently, and an averaged behavior can be found. Nanoparticle adsorption on the pin surface is found to have double-edged effects and can be beneficial or detrimental to heat removal. Finally, the hydrodynamic and thermal behavior of partially-porous microchannel are analyzed. It is revealed that, unlike the fully-porous microchannel, the thermal performance of these systems is complicated. The study shows existence of hydrodynamic and thermal critical porous medium heights where the impact of the porous medium becomes imperative. A particle tracing technique is adopted to explain the underlying physics and a mathematical model is proposed to explain the interplay between the critical points and the hydrodynamic, geometric, and thermal parameters

Numerical and Experimental Analyses of Shear-thinning Viscoelastic Fluid Flow in Confined Geometries

This thesis focuses on numerical and experimental investigations of shear-thinning viscoelastic (VE) fluid flow in confined geometries, such as porous media and microchannels for applications in polymer processing, heat transfer devices, biological and biomedical systems, and enhanced oil recovery. The numerical research focuses on the hydrodynamic performance of a VE fluid with particular attention to vortex patterns that develop downstream of smooth contractions/expansions. It was found that there are critical regions, in which the behavior of VE fluid flow is subjected to a change through different pore geometries. The experimental work focuses on the retention phenomenon of hydrolyzed polyacrylamide polymers, using microfluidic chips in which the effect of single pore size on retention is measured. From these experiments, the contribution of different retention mechanisms was reported through different sizes of microchannel. It was found that polymer orientation plays a role in the measured absolute and relative adsorption in different concentrations

Dynamic Modelling of Axle Tramp in a Sport Type Car

One of the most significant dynamic aspects of coupled vibration of transmission system and dependent type suspension systems is axle tramp. The tramp is defined as undesirable oscillation of rigid live axle around roll axis. In spite of utilizing powerful engines in some type of sport cars, tramp occurrence causes loss of longitudinal performance. The aim of this paper is to derive a mathematical model for predicting and classifying of the tramp. A parameter study reveals that, some parameters such as engine torque, moving parts moment of inertia, car and wheels weight and the material used in suspension system play important role in controlling the tramp. It is shown that large difference between sprung and unsprung mass moment of inertia around the roll-axis, low vehicle mass, short rear track and medium damping values have significant effects on the severity of tramp

Dynamic modelling of axle tramp in a sport type car

Abstract. One of the most significant dynamic aspects of coupled vibration of transmission system and dependent type suspension systems is axle tramp. The tramp is defined as undesirable oscillation of rigid live axle around roll axis. In spite of utilizing powerful engines in some type of sport cars, tramp occurrence causes loss of longitudinal performance. The aim of this paper is to derive a mathematical model for predicting and classifying of the tramp. A parameter study reveals that, some parameters such as engine torque, moving parts moment of inertia, car and wheels weight and the material used in suspension system play important role in controlling the tramp. It is shown that large difference between sprung and unsprung mass moment of inertia around the roll-axis, low vehicle mass, short rear track and medium damping values have significant effects on the severity of tramp