Use of a fictitious Marangoni number for natural convection simulation

In this paper, a method based on the use of a fictitious Marangoni number is proposed for the simulation of natural thermocapillary convection as an alternative to the traditional effective diffusivity approach. The fundamental difference between these two methods is that the new method adopts convective mass flows in simulating natural convection. Heat transfer in the natural convection simulation is calculated through the mass transport. Therefore, empirical Nusselt numbers correlations required in the effective diffusivity method are eliminated. This represents a clear advantage in the context of design studies where flexibility in varying the geometry unconstrained by the availability of appropriate correlations is highly desirable. The new method is demonstrated using a simple geometrical model. An analytical expression of the fictitious Marangoni number associated with convection between vertical plates is derived and a computational fluid dynamics (CFD) simulation is performed to study the efficacy of the proposed method. The results show that the new method can approximate real natural convection quite accurately and can be used to simulate the convective flow in complex, obstructed or finned structures where the specific Nusselt correlation is not known.This is the author accepted manuscript. The final version is available from Elsevier via http://dx.doi.org/10.1016/j.ijheatmasstransfer.2015.04.08

Magnetic separation for a continuous solar-two-step thermochemical cycle for solar hydrogen/CO production using ferrites

A novel solar-two-step thermochemical concept for continuous production of H2 or CO from solar energy and H2O or CO2 using the redox pair MOFe2O3/MO as reactive particles is proposed and assessed. Here, an efficient continuous separation mechanism is devised by the use of an external magnetic field and the weak magnetization of MOFe2O3 at the working temperatures. The mechanism is suitable for systems of ferrites with a Curie temperature in the range 500–800 ∘C where water or CO2 decomposition occurs. One of the most promising candidates is the Fe3O4/FeO system. Pyromagnetic coefficients for Fe3O4 were obtained experimentally. A simple magnetic trap was employed and the separation ratios Fe3O4/FeO were obtained. The results are encouraging and motivate the development of full-scale solar reactor prototypes.This is the final published version of the article. It was originally published in the International Journal of Energy and Environmental Engineering (Arias FJ, Parks GT, International Journal of Energy and Environmental Engineering, 2015, doi:10.1007/s40095-015-0177-x). The final version is available at http://dx.doi.org/10.1007/s40095-015-0177-

On the Feasibility of Self-Sustainable Deuterium Production in Fusion Reactors Using an Ionization Chamber

In this technical note we examine a method for self-sustainable (in-situ) deuterium production in a fusion reactor, using a very different approach to those considered in previous studies. Here, instead of pursuing the production of deuterium via neutron capture (H + n ! D) inside and/or outside the fusion chamber, the deuterium is obtained by ionization induced by the neutronic flux in an ionization chamber and then electromagnetically separated. Using conservative modelling assumptions, an estimate of the amount of deuterium obtainable per day is made. The results show the feasibility of this approach, encouraging further research. Using the proposed method in combination with the use of lithium blankets for tritium breeding opens a new possibility for integral in-situ production of all the nuclear fuel required for fusion.This is the accepted manuscript. The final version is available from Springer at http://link.springer.com/article/10.1007%2Fs10894-015-9874-y

On the use of stimulated thermocapillary currents and virtual walls as computational tools for natural convection simulation in enclosed spaces

A new, alternative approach is proposed for natural convection simulation by means of stimulated thermocapillary currents created by virtual walls. In contrast to the well-known effective thermal conductivity model, in the proposed approach it is the mass motion due to the convective currents which is intended to be simulated and the heat flux is a consequence of such flows. As a result, no a priori knowledge of the Nusselt number is needed and thus the approach is more suitable for complex geometries. Utilizing a simplified physical model and the definition of hydraulic diameter, a generalized expression for enclosed geometries is derived which offers thermal engineers a powerful analysis tool that can use virtual walls with an associated fictitious Marangoni stress for pre-screening and estimation of Nusselt numbers.This is the accepted manuscript. The final version is available at http://www.sciencedirect.com/science/article/pii/S129007291500112X

The behavior of radiogenic particles at solidification fronts

The thermal behavior of insoluble radiogenic particles at the solid-liquid interface of an advancing solidification front and its significance with regard to environmental impact are discussed. It is shown that, unlike classical particles, where the most probable behavior is engulfing by the solidification front, radiogenic particles are more likely to be rejected by the solidification front. Utilizing a simplified physical model, an adaptation of classical theoretical models is performed, where it is shown that, unlike classical particles, for radiogenic particles the mechanism is thermally driven. An analytical expression for the critical velocity of the solidification front for engulfing/rejection to occur is derived. The study could be potentially important to several fields, e.g. in engineering applications where technological processes for the physical removal of radionuclide particles dispersed throughout another substance by inducing solidification could be envisaged, in planetary science where the occurrence of radiogenic concentration could result in the possibility of the eruption of primordial comet/planetoids, or, if specific conditions are suitable, particle ejection may result in an increase in concentration as the front moves, which can translate into the formation of hot spots.This research was supported by the Spanish Ministry of Economy and Competitiveness under fellowship grant Ramon y Cajal: RYC-2013-13459

Cause of Death Affects Racial Classification on Death Certificates

Recent research suggests racial classification is responsive to social stereotypes, but how this affects racial classification in national vital statistics is unknown. This study examines whether cause of death influences racial classification on death certificates. We analyze the racial classifications from a nationally representative sample of death certificates and subsequent interviews with the decedents' next of kin and find notable discrepancies between the two racial classifications by cause of death. Cirrhosis decedents are more likely to be recorded as American Indian on their death certificates, and homicide victims are more likely to be recorded as Black; these results remain net of controls for followback survey racial classification, indicating that the relationship we reveal is not simply a restatement of the fact that these causes of death are more prevalent among certain groups. Our findings suggest that seemingly non-racial characteristics, such as cause of death, affect how people are racially perceived by others and thus shape U.S. official statistics

Markov Influence Diagrams.

Markov influence diagrams (MIDs) are a new type of probabilistic graphical model that extends influence diagrams in the same way that Markov decision trees extend decision trees. They have been designed to build state-transition models, mainly in medicine, and perform cost-effectiveness analyses. Using a causal graph that may contain several variables per cycle, MIDs can model various patient characteristics without multiplying the number of states; in particular, they can represent the history of the patient without using tunnel states. OpenMarkov, an open-source tool, allows the decision analyst to build and evaluate MIDs-including cost-effectiveness analysis and several types of deterministic and probabilistic sensitivity analysis-with a graphical user interface, without writing any code. This way, MIDs can be used to easily build and evaluate complex models whose implementation as spreadsheets or decision trees would be cumbersome or unfeasible in practice. Furthermore, many problems that previously required discrete event simulation can be solved with MIDs; i.e., within the paradigm of state-transition models, in which many health economists feel more comfortable