Volume 45, Issue 2

The present mathematical simulation deals with the study of heat transfer characteristics of the shape of gold nanoparticles (Au-NPs) on blood flow past an exponentially stretching sheet using Sisko nanofluid taking into account the Biot number effect. Influences of non-linear thermal radiation and suction/injection are considered. The one-phase model is used to describe the Sisko nanofluid flow. Similarity variables are performed to convert the non-linear PDEs into ordinary ones. These equations together with initial and boundary conditions are provided in a non-dimensional form and then resolved numerically utilizing the fourth–fifth-order Runge–Kutta–Fehlberg (RKF45) technique. The attitude of diverse flow quantities is investigated and examined via the study of parameters like the Au-NP volume fraction, the non-linear stretching parameter, and the Biot number. It is found that the Biot number improves the heat transfer rate markedly. In the blowing case, the blade-shaped Au-NPs show the highest heat transfer rate; in the suction case, the contrary is observed for spherical Au-NPs.

In this study, the effect of magnetic field on an incompressible ferrofluid flow along a vertical wavy surface saturated in a porous medium is investigated. Ferrofluid is made by incorporating magnetic particles, in this case cobalt, at the nanoscale level into a base fluid. For the study of porous medium two well-known models, namely, Darcy and non-Darcy, are used. The mathematical model in terms of governing partial differential equations which are based on conservation laws in mechanics according to the assumption is developed, and this model is converted into a dimensionless form by suitable transformations. Due to the complex non-linear partial differential equations, the numerical solution is calculated by using an implicit finite difference scheme. The impact of involved parameters, namely, magnetic parameter, nanoparticle volume fraction parameter, the amplitude of the wavy surface, and the Grashof number, on Nusselt and average Nusselt numbers are studied through graphs and tables. The results show that for large values of the magnetic parameter, both the Nusselt number and the average Nusselt number decrease in ferrofluid flow. The value of the Nusselt number in the Darcy model is higher than the value of the Nusselt number in the non-Darcy model.

Canonical statistical mechanics hinges on two quantities, i. e., state degeneracy and the Boltzmann factor, the latter of which usually dominates thermodynamic behaviors. A recently identified phenomenon ( supradegeneracy ) reverses this order of dominance and predicts effects for equilibrium that are normally associated with non-equilibrium, including population inversion and steady-state particle and energy currents. This study examines two thermodynamic paradoxes that arise from supradegeneracy and proposes laboratory experiments by which they might be resolved.

First, the special-relativistic Theory of Irreversible Processes for a multi-component fluid is formulated. It is based on (i) the balance equations of the particle number and the energy-momentum for the total system (i. e., the mixture of the components) as well as the sub-systems (i. e., the components) and (ii) the dissipation inequality and the Gibbs equation for the mixture. In order to allow for reactions between the single components, in contrast to the total system, the sub-systems are assumed to be open, which means that their particle number and energy-momentum are not constrained by conservation laws. Without making any assumptions on the thermodynamic behavior of the interacting components, one arrives at a thermodynamic description of the mixture showing now heat conduction and viscosity. In particular, this makes it possible to calculate the entropy production and, thus, to identify thermodynamic currents and forces. In a second part, the post-Newtonian limit of this theory is calculated to show that for the mixture there result relations known from classical Extended Thermodynamics that partly are corrected by entrainment terms. The mathematical origin and physical consequences of these terms are discussed.

This work proposes a structure synthesis and surface distribution algorithm in a heat exchange system for the case when all heat capacity rates and inlet temperatures of the hot streams are constant, while cold streams also have outlet temperatures set. The algorithm includes the possibility of changing the phase state of the contacting streams. The synthesis is based on minimization of dissipation for a given total heat load in the form of minimum total contact surface area, which again correlates with the cost of the heat exchange system. The proposed algorithm can be considered to follow a thermodynamic rationale and as development of pinch analysis.

The main aim of this research work is to show the simultaneous effects of ferro-particles (Fe3O4{\text{Fe}_{3}}{\text{O}_{4}}) and thermal radiation on the natural convection of non-Newtonian nanofluid flow between two vertical flat plates. The studied nanofluid is created by dispersing ferro-particles (Fe3O4{\text{Fe}_{3}}{\text{O}_{4}}) in sodium alginate (SA), which is considered as a non-Newtonian base fluid. Resolution of the resulting set of coupled non-linear second order differential equations characterizing dynamic and thermal distributions (velocity/temperature) is ensured via the Adomian decomposition method (ADM). Thereafter the obtained ADM results are compared to the Runge–Kutta–Feldberg based shooting data. In this investigation, a parametric study was conducted showing the influence of varying physical parameters, such as volumic fraction of Fe3O4{\text{Fe}_{3}}{\text{O}_{4}} nanoparticles, Eckert number (Ec{E_{c}}) and thermal radiation parameter ( N ), on the velocity distribution, the skin friction coefficient, the heat transfer rate and the temperature distribution. Results obtained also show the advantages of ferro-particles over other types of standard nanoparticles. On the other hand, this investigation demonstrates the accuracy of the adopted analytical ADM technique.

Thermodynamic performance analysis of microscopic Feynman’s engine has always been a hot topic, since it can reveal the operating mechanism of the system and give out the suggestions of performance improvement. The present work explores the optimal performance regions of the ratchet operating, respectively, as heat engine and refrigerator. The major purpose is to obtain the optimal performance bunds and provide theoretical guidelines for the designs of practical microscopic ratchet engine systems. Based on an irreversible Feynman’s ratchet engine, the optimal power output versus thermal efficiency performance and the optimal cooling load versus COP performance in different operation modes are analyzed. The effects of irreversible heat leakage and major design parameters are also explored. By further introducing the ecological function, efficient power, and figure of merit criteria, performance characteristics of ratchet device with different optimization indexes are analyzed and compared with each other. The optimal performance regions concerning different optimization criteria are obtained. The results show that by reasonably selecting design parameters, Feynman’s ratchet can attain the optimal operation conditions for different design purposes.