The changing energy paradigm, challenges, and new developments

Editorial of the Special Issue of the International Journal of Energy Researc

“Recent Advances in Energy Research”

The worldwide scarcity of fossil fuels regarding primary energy demand together with growing environmental concerns have raised new challenges to the world economy, and led to changes in the energy paradigm. Industry, services, researchers, and the Academy are challenged to envisage new solutions through setting up new conversion processes, designing new power systems, and investigating and developing new energy sources and vectors

Constructal theory and flow architectures in living systems

We apply Constructal theory to the study of the flow structure of the human respiratory tree. We show that the flow architecture that would perform oxygenation of the blood and removal of carbon dioxide best, i. e. with lowest resistance, would be composed of a channel system with 23 bifurcation with a diffusive zone (alveolus) at the end. As this tree matches the human respiratory tree we conclude that nature has optimized it in time. Two constructal relationships also emerge: (1) the length l, defined by the ratio of the square of the air way diameter to its length, is constant for all individuals of the same species, and (2) the length l is related to the volume of the space allocated to the respiratory process, to the length of the respiratory tree and to the area of the alveoli, and determines univocally the branching level of the respiratory tree

Transport and deposition of fine mode particles in porous filters

Transport and deposition of fine mode aerosol particles in porous filters was investigated analytically. The study was carried out by considering the transport of fine particles through the filter as a convective-dispersive phenomenon. Collector-particle and particle-particle interactions within the filter were considered while reentrainment of deposited particles was assumed to be negligible as compared to particle attachment. Based on these assumptions, transient equations that govern the amount of particles deposited within the filter, pressure drop through the filter, and the filter's permeability and performance are presented. The approach developed here confirms the significance of the Peclet number, the Sherwood number, and geometrical parameters on filtration processes. These results may be useful for filter design as well as for filtering operation monitoring

Analysis of loop heat pipe performance under varying wick load

Loop heat pipes (LHP) are heat transfer devices used to enhance cooling of small spaces and basically consist of sealed tubes connecting a heat source, the evaporator, whose major part is a porous wick, with a condenser that operates as heat sink. In this paper we analyse the effect of curvature of the liquid vapor interface upon the vapor pressure within wick pores. We show how this effect affects start-up by requiring a difference between wick and condenser temperatures as higher as wick pore width becomes smaller. We analysed also transient operation and found that idealy LHP are self-adjusting systems that tend to stable operation. We present a formula to describe the transient regime. The analysis provides also optimization of wick pore width for maximum heat transfer. Optimal pore width is shown to vary with temperature difference between wick and condenser. It is envisaged how this feature may help in LHP design

Numerical Particle Transport in Partitioned Room.

In this work, we solved particle transport in a two-zone enclosure numerically with different airflow pattems, particle properties and algo source positions. A discrete trajectory was employed for the particIe movement. Five isotropic line sources which are alI taken at different positions oftne same zone were festejo It was observed that for alI airflow pattems, residence time increases with decreasing size of particIes. Increase in size and mass increases the chaTIceof particles to get deposited auto the fIoor. Source locations should be chosen in the main stream of the fIow so that particles convect fast through and not contribute indoor polIutant concentration. ConcIusions were drawn for every numerical experiment in arder to show tendencies of particle dynamics within the encIosure

Influence of flow with suspended particles on temperature fields and convective heat transfer

The present paper reports the results of a numerical study of forced convection heat transfer between two plates filled with particles. We study the influence of particles suspended in flows on heat transfer enhancement. We consider steady-state fluid flow between two flat horizontal parallel plates with both plates kept at the same temperature. Mono-disperse particles with low and high thermal conductivities injected at the entrance are entrained with the flow. Their effects on temperature field and convective heat transfer are determined from the flow field

Optimal design of a heat exchanger network composed of parallel tubes

Networks of tubes for heat and mass transport abound both in nature and in engineered systems. In this paper we study the optimal design of heat exchanging flow networks composed of parallel tubes. The impact of the network size-limiting constrains (surface area, tubes diameter), fluid flow regime, as well as the fluid pumping power requirements is addressed in this paper for the cases when Biot number is smaller than 0.1

Particle deposition in airway bifurcations in different breathing conditions

In this paper, particle deposition in a rigid double bifurcation airway is studied experimentally. The effect of particle size and breathing conditions in the deposition are analyzed. Besides, the effect of airway obstruction (local reduction of airway diameter) that can be originated by some respiratory disorders is also studied. The experiments were performed in conditions of humidity near saturation in order to account for the conditions occurring in the respiratory tree

Some features of flow and particle transport in porous structures

There has been a growing interest in the study of porous and complex flow structures due to its impact in technology. This concerns not only environmental but also diagnostic and therapeutic exposure in medical research. Physics of flow within porous structures is especially important to model transport and deposition of viruses, pollutants and drugs deep in these structures. In this work we analyze numerically low and medium Reynolds number flows in axisymmetric cylindrical duct surrounded by a torus. We also consider three different particle sizes (0.02, 0.1 and 20 micron) for possible physiological and environmental applications