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We do not pretend to be exhaustive on the investigated subject, not even one volume would be enough. In this paper we want to present some reflections on the energy, environmental and climatic problems of our time (in particular those less studied), starting from the knowledge of the past. The contribution provided by non-renewable energy sources to the development of our civilization is analyzed, underlining that their replacement is not feasible in a short time in order not to cause a drastic shortage of the resources necessary for a still growing world population. The difference between environmental and climatic problems and the need to deepen knowledge of the latter ones is emphasized, in order to better understand their causes, predict future developments and take preventive actions to reduce their impact on our environment and our lives. Finally, mention is made of the need to establish priorities in addressing the great problems of our time, in a global vision of human society.

In this paper, a detailed investigation on MHD flow over a porous stretching sheet was conducted by taking power-law heat flux and heat source into account. Series solutions are achieved for the reduced nondimensional ordinary differential equations by admitting an analytical technique known as a homotopy analysis method (HAM). A precise way of convergence of series solutions is also furnished. The attained results of the present study are in excellent connection with the previous results. Nature of magnetic parameter, permeability parameter, radiation parameter, Prandtl number, Eckert number, heat generation parameter and suction/injection parameters on velocity, temperature, skin friction coefficient and Nusselt number are presented in tables and graphs.

The motivation behind this article is to research the Newtonian liquid flow porous stretching/shrinking sheet utilizing a Brinkman model. The leading system of non-linear partial differential equations relating the article is mapped to standard ordinary differential equations via similarity transformations. Exact result is obtained for velocity. The effects of the Brinkman number or viscosity ratio, slip parameter, Darcy number, suction/injection (mass transpiration) parameter and the mass suction parameter on the velocity dispersion are introduced graphically and talked about. The outcomes have conceivable innovative applications in extrusion process and such other unified zones and in the fluid based frameworks including stretchable materials. Examination of fluid flow past a permeable stretching/shrinking sheet embedded in a non-Darcy permeable medium has been performed for a wide scope of various parameters. Exact solution has been obtained.

It is our great pleasure and honor to present this special issue of Heat Transfer Engineering to highlight some of the research works presented at the AIGE 2016 Conference on Energy Conversion, Man...

The qualitative effect of variable internal heat source and variable gravity on the onset of convection in a horizontal fluid saturated sparsely packed porous layer is investigated using linear stability analysis. The single term Galerkin technique is used to compute the value of the critical Rayleigh number and the corresponding wave number. Three different sets of variable gravity and heat source functions are chosen and their influence on the onset of convection is discussed. The eigenvalues are obtained for free-free velocity boundary conditions with isothermal temperature conditions on the boundaries. The influence of porous parameter on the onset of convection is brought out. It is found that the variable heat source and variable gravity does not affect the shape and size of the convective cell at the onset of convection. However the porous parameter do so.

A theoretical analysis is performed for studying the flow and heat and mass transfer characteristics of Maxwell fluid over a cylinder with Cattaneo–Christov and non-uniform heat source/sink. The Brownian motion and thermophoresis parameters also considered into account. Numerical solutions are carried out by using Runge–Kutta-based shooting technique. The effects of various governing parameters on the flow and temperature profiles are demonstrated graphically. We also computed the friction factor coefficient, local Nusselt and Sherwood numbers for the permeable and impermeable flow over a cylinder cases. It is found that the rising values of Biot number, non-uniform heat source/sink and thermophoresis parameters reduce the rate of heat transfer. It is also found that the friction factor coefficient is high in impermeable flow over a cylinder case when compared with the permeable flow over a cylinder case.

The magnetohydrodynamic (MHD) stagnation point flow of Casson nanofluid over a nonlinear stretching sheet in the presence of velocity slip and convective boundary condition is examined. In this analysis, various effects such as velocity ratio, viscous dissipation, heat generation/absorption and chemical reaction are accentuated. Possessions of Brownian motion and thermophoresis are also depicted in this study. A uniform magnetic field as well as suction is taken into account. Suitable similarity transformations are availed to convert the governing nonlinear partial differential equations to a system of nonlinear ordinary differential equations and then series solutions are secured using a homotopy analysis method (HAM). Notable accuracy of the present results has been obtained with the earlier results. Impact of distinct parameters on velocity, temperature, concentration, skin friction coefficient,Nusselt number and Sherwood number is canvassed through graphs and tabular forms.

Carbon nanotubes are allotropes of carbon with a cylindrical nanostructure. These cylindrical carbon molecules have unusual properties, which are valuable for nanotechnology, electronics, optics and other fields of materials science and technology. With this intention, we investigate the three-dimensional magnetohydrodynamic convective heat and mass transfer of nanofluid over a slendering stretching sheet filled with porous medium and heat source/sink. For balancing the flow, temperature and concentration slip mechanisms are also taken into account. In this investigation simulation performed by mixing the two types of carbon nanotubes, namely single- and multi-walled carbon nanotubes, into water as base fluid. The governing system of partial differential equations is transformed into nonlinear ordinary differential equations which answered by using R–K–Fehlberg-integration scheme. The impact of various pertinent parameters on velocity, temperature and concentration as well as the friction factor coefficient, local Nusselt and local Sherwood number is derived and discussed through graphs and tables for both single- and multi-walled carbon nanotubes cases. It is found that the momentum boundary layer thickness of SWCNTs is thicker than MWCNTs. These results can help us to conclude that SWCNTs are helpful for minimizing the friction between the particles, whereas MWCNTs are helpful for boosting the heat and mass transfer rate.

In this study, we proposed a theoretical investigation on the temperature-dependent viscosity effect on magnetohydrodynamic dissipative nanofluid over a truncated cone with heat source/sink. The involving set of nonlinear partial differential equations is transforming to set of nonlinear ordinary differential equations by using self-similarity solutions. The transformed governing equations are solved numerically using Runge–Kutta-based Newton’s technique. The effects of various dimensionless parameters on the skin friction coefficient and the local Nusselt number profiles are discussed and presented with the support of graphs. We also obtained the validation of the current solutions with existing solution under some special cases. The water-based titanium alloy has a lesser friction factor coefficient as compared with kerosene-based titanium alloy, whereas the rate of heat transfer is higher in water-based titanium alloy compared with kerosene-based titanium alloy. From this we can highlight that depending on the industrial needs cooling/heating chooses the water- or kerosene-based titanium alloys.

One of the main issues regarding the design of LFR is the corrosion-erosion behaviour of materials in contact with high temperature and high velocity lead, such as pump impeller and bearing materials. Those materials will worked in Lead at about 480°C with a velocity relative to impeller blade in the magnitude of 10m/s. Ti3 SiC2 , a ternary compound was selected as one of the most promising candidate material, the most significant aspect of Ti3 SiC2 is that it combines some of the most attractive proprieties of ceramics with those of metals. This material was already applied in industry but more effort is needed to qualify its performance when compared with candidate structural stainless steel available in Europe. With the purpose of evaluating the corrosion resistance of Ti3 SiC2 , a preliminary screening test was carried out at ENEA Brasimone in fluent lead under oxidation conditions (oxygen concentration of about 10−6 wt% in the melt), with an average temperature of 500°C and a stream velocity of about 1 m/s.Copyright © 2009 by ASME

Carbon nanotubes are allotropes of carbon with a cylindrical nanostructure. These cylindrical carbon molecules have unusual properties, which are valuable for nanotechnology, electronics, optics and other fields of materials science and technology. With this intention, we investigate the three-dimensional magnetohydrodynamic convective heat and mass transfer of nanofluid over a slendering stretching sheet filled with porous medium and heat source/sink. For balancing the flow, temperature and concentration slip mechanisms are also taken into account. In this investigation simulation performed by mixing the two types of carbon nanotubes, namely single- and multi-walled carbon nanotubes, into water as base fluid. The governing system of partial differential equations is transformed into nonlinear ordinary differential equations which answered by using R–K–Fehlberg-integration scheme. The impact of various pertinent parameters on velocity, temperature and concentration as well as the friction factor coefficient, local Nusselt and local Sherwood number is derived and discussed through graphs and tables for both single- and multi-walled carbon nanotubes cases. It is found that the momentum boundary layer thickness of SWCNTs is thicker than MWCNTs. These results can help us to conclude that SWCNTs are helpful for minimizing the friction between the particles, whereas MWCNTs are helpful for boosting the heat and mass transfer rate.

In this paper, we use Bejan’s Constructal theory to optimize the geometry of a H-shaped cavity that intrudes into a solid conducting wall. The objective is to minimize the global thermal resistance between the solid and the cavity. Internal heat generation is distributed uniformly throughout the solid wall. The cavity surface is isothermal, while the solid wall has adiabatic conditions on the outer surface. The total volume and the volume of the H-shaped cavity are fixed, while the geometry of the H-shaped cavity is free to vary. Numerical results show that the optimal H-shaped configuration performs better than an optimal T-shaped cavity. The performance of the optimal H-shaped cavity is also superior to the performance of optimal rectangular and C-shaped cavities, which may be regarded as “elemental” configurations. Each of the optimized cavities, C-shaped, T-shaped and H-shaped, performs better when it penetrates the solid completely: this means that the geometrical complexity must evolve in order for the global flow system performance to improve.

In this study, we proposed a theoretical investigation on the temperature-dependent viscosity effect on magnetohydrodynamic dissipative nanofluid over a truncated cone with heat source/sink. The involving set of nonlinear partial differential equations is transforming to set of nonlinear ordinary differential equations by using self-similarity solutions. The transformed governing equations are solved numerically using Runge–Kutta-based Newton’s technique. The effects of various dimensionless parameters on the skin friction coefficient and the local Nusselt number profiles are discussed and presented with the support of graphs. We also obtained the validation of the current solutions with existing solution under some special cases. The water-based titanium alloy has a lesser friction factor coefficient as compared with kerosene-based titanium alloy, whereas the rate of heat transfer is higher in water-based titanium alloy compared with kerosene-based titanium alloy. From this we can highlight that depending on the industrial needs cooling/heating chooses the water- or kerosene-based titanium alloys.

A new formulation of the spacecraft relative motion for a generic orbit is presented based on the orbital propagation method proposed by Peláez et al. in 2006 [1]. Two models have been developed. In the first model the method is applied to each spacecraft using a time synchronization of the system dynamical states. In the second model we employ a local orbital reference frame with a linearization of gravitational terms, apply the method to the formation center of mass and propagate the relative dynamics with respect to the center of mass reference orbit. The models are compared in terms of computational speed for the case of a bounded triangular formation

This work reports, according to Bejan’s Constructal theory, the geometric optimization of an elliptical cavity that intrudes into a solid conducting wall. The objective is to minimize the global thermal resistance between the solid and the cavity. There is uniform heat generation on the solid wall. The cavity is optimized for two sets of thermal conditions: isothermal cavity and cavity bathed by a steady stream of fluid. The solid conducting wall is isolated on the external perimeter. The total volume and the elliptical cavity volume are fixed while the geometry of the cavity is free to vary. The results show that the optimized geometrical shapes are relatively robust, i.e., insensitive to changes in some of the design parameters: the cavity shape is optimal when penetrates the conducting wall almost completely.

This study presents a novel approach for the analysis of the experimental dynamical behaviour of a system exhibiting Vapotron effect. This phenomenon occurs as a subcooled boiling of a refrigerant fluid entrapped in the cavities of a non-isothermally heated finned surface. A preliminary characterisation of the experimental time series has been carried out to detect the existence of a low dimensional source of the dynamics, through the adoption of non-linear time series analysis techniques. In this way the existence of chaos has been observed in the system in study, which is therefore non-linear. As a second step, a low-order non-linear model has been developed for the identification of the system dynamics. In particular, the NARMAX (Non-linear Auto-Regressive Moving Average with eXogenous inputs) identification strategy has been chosen for its flexibility, and has been implemented and generalised by means of Multilayer Perceptron neural networks. The neural model has been tested with satisfactory performances, showing the suitability of non-linear identification strategies as a reliable predictive tools for the dynamics of such kind of systems.

This paper documents the optimization of architecture in accordance with Bejan's Constructal theory. For illustration, we consider the optimization of a cavity that intrudes into a solid conducting wall, having internal heat generation and adiabatic conditions on the outer surfaces. The cavity is rectangular, with fixed volume and variable aspect ratio, and the solid is trapezoidal. The objective is to minimize the global thermal resistance between the volume of the entire system (cavity and solid) and the surroundings. The performance improves as the cavity becomes slender. The geometry is optimal when the cavity penetrates the conducting wall completely.

The dependence of the transition conditions between annular and fog flow on the parameters of a system with boiling flow are analysed in order to extend the applicability of a physical model of the two-phase flow recently proposed by the authors to calculate the friction coefficient. Having suitably represented the phenomenon, examination is made as to its influence on the analytical development of the model, the results obtainable from the latter being compared with those of the relations usually employed and with experimental indications, thus showing the broad field of validity of the formulae presented.

The paper deals with the analytical determination of time dependent temperature distribution in a sample placed in the focal plane of the paraboloidal mirror of a solar furnace. Several different heat pulses are considered and some graphs are shown.

The object of the present paper is to look into the thermal and thermoelastic state in a nuclear fuel rod with gap and cladding, including a neutron flux distribution deduced by diffusion theory. The steady state temperature and the thermal stresses in the rod are analytically determined solving a set of differential and integral equations, deriving from heat conduction and Hooke's law. The mathematical technique here utilized is based on the modified first kind Bessel functions theory; the solution presents a very compact and simple form. The results so obtained are related and a comparison is made with the analogous results deduced implying a constant heat source distribution in the fuel, i.e., neglecting the actual neutron flux distribution. Some numerical results are finally reported with reference to a common boiling water reactor and shortly discussed.

A short outline of the instability phenomenon is given. Two methods are explained for the problem solution, i.e. the practical determination of the existence or not of an aperiodic instability and, in the case of existence, what to do to eliminate it. The first method substantially comes from that used by boiler designers. A second, new method is suggested: this is a manual, simple method. The two methods are compared: the new one is reliable, and has the great advantage of the simplicity and the possibility of specifying the diaphragm at the pipe mouth for eliminating the two-phase flow instability.

The thermal unsteady regimes in one-dimensional flow of heat generating fluids, caused by flow-rate changes, are studied when heat is transferred to surroundings of constant temperature. The heat generation is a function of time and temperature. General results are then applied to solve particular situations. Some numerical results are related and a short discussion is given.

The nonlinear equation of heat conduction is solved by the method of finite differences. The results are compared with the solution to the same problem obtained by the variational method.

Con una formulazione variazionale viene affrontato il problema della conduzione stazionaria e transitoria con conducibilita termica variabile comunque con la temperatura in un mezzo di volume arbitrario con una funzione di generazione interna di calore qualsiasi. Si considera poi, la applicazione della teoria precedente all'elemento cilindrico, riportando quindi in grafici i risultati ottenuti., Par une formulation variationnelle on aborde le problème de la conduction stationnaire et transitoire avec conductibilité thermique variable de toute façon avec la température dans un milieu de volume arbitraire avec n'importe quelle fonction de génération intérieure de chaleur. On considère ensuite, l'application de la théorie précédente à l'élément cylindrique, rapportant par conséquent en graphiques les résultats obtenus., Lorenzini Enrico. A variational formulation applied to heat conduction equation. In: Bulletin de la Classe des sciences, tome 56, 1970. pp. 367-379.

In Low Earth Orbit, it is possible to use the ambient plasma and the geomagnetic field to exchange momentum with the Earth's magnetosphere without using propellant. A device that allows an efficient momentum exchange is the electrodynamic tether (EDT), a long conductor attached to the satellite. EDT technology has been demonstrated in several past missions, being the Plasma Motor Generator mission (NASA 1993) one of the most successful. Nevertheless, it is not until today that reality has imposed a strong need and a concrete use case for developing this technology. In March 2019, the European Commission project Electrodynamic Tether technology for PAssive Consumable-less deorbit Kit (E.T.PACK) started the design of a new generation EDT. After completing the design phase, the consortium manufactured and is currently testing a Deorbit Kit Demonstrator (DKD) breadboard based on EDT technology. The objective of E.T.PACK is to reach Technology Readiness Level equal to 4 by 2022. The DKD is a standalone 24-kg satellite with the objective to demonstrate the performances of the improved EDT solution and validate its ultra-compact deployment system. The DKD is composed of two modules that will separate in orbit extending a 500-m long tape-like tether. The deployed bare-Aluminium tether will capture electrons from the ambient plasma passively and the circuit will be closed with the ionospheric plasma by using an active electron emitter. E.T.PACK tether will take advantage of several novelties with respect to the mission flown in the past that will allow to optimize the system volume and mass. Once successful demonstrated in orbit, the team plans to develop a suite of EDT systems capable of deorbiting satellites between 200 and 1000 kg from an altitude up to 1200 km in a few months. The work presents the current design status of the de-orbit kit demonstrator breadboard, the simulations of the system deorbit performances and the development approach. This work was supported by the European Union's Horizon 2020 Research and Innovation Programme under grant agreement No.828902 (3M€ E.T.PACK project) and No.101034874 (100K€ BMOM project). SG is supported by an Industrial Ph.D funded by Comunidad de Madrid (135K€ IND2019/TIC17198). The team has recently got 2.5M€ additional financial support from European Union (ETPACK-F project No. 101058166) for the manufacturing and qualification of the In Orbit Demonstration (IOD) by the end of 2025.

A simple model is applied for the analysis of radiative heat transfer in a pressurized water reactor fuel assembly during steady state and under a loss-of-coolant accident. The method includes a matrix calculation of view factors, performed dividing the bundle into unit cells composed by portions of fuel rods and by a coolant subchannel. The cells are correlated considering imaginary faces among them, and the pertinent equations are simultaneously solved for the whole assembly. Some results are related for various values of the heat flux in different operational and accidental conditions.