Toni Pujol

Bio: Toni Pujol is an academic researcher from University of Girona. The author has contributed to research in topics: Thermoelectric generator & Pressure drop. The author has an hindex of 17, co-authored 67 publications receiving 1198 citations. Previous affiliations of Toni Pujol include Texas A&M University.

The second law of thermodynamics and the global climate system: A review of the maximum entropy production principle

Abstract: [1] The long-term mean properties of the global climate system and those of turbulent fluid systems are reviewed from a thermodynamic viewpoint. Two general expressions are derived for a rate of entropy production due to thermal and viscous dissipation (turbulent dissipation) in a fluid system. It is shown with these expressions that maximum entropy production in the Earth's climate system suggested by Paltridge, as well as maximum transport properties of heat or momentum in a turbulent system suggested by Malkus and Busse, correspond to a state in which the rate of entropy production due to the turbulent dissipation is at a maximum. Entropy production due to absorption of solar radiation in the climate system is found to be irrelevant to the maximized properties associated with turbulence. The hypothesis of maximum entropy production also seems to be applicable to the planetary atmospheres of Mars and Titan and perhaps to mantle convection. Lorenz's conjecture on maximum generation of available potential energy is shown to be akin to this hypothesis with a few minor approximations. A possible mechanism by which turbulent fluid systems adjust themselves to the states of maximum entropy production is presented as a self-feedback mechanism for the generation of available potential energy. These results tend to support the hypothesis of maximum entropy production that underlies a wide variety of nonlinear fluid systems, including our planet as well as other planets and stars.

Palaeolithic Populations and Waves of Advance

Abstract: The wave-of-advance model has been previously applied to Neolithic human range expansions, yielding good agreement to the speeds inferred from archaeological data. Here, we apply it for the first time to Palaeolithic human expansions by using reproduction and mobility parameters appropriate to hunter-gatherers (instead of the corresponding values for preindustrial farmers). The order of magnitude of the predicted speed is in agreement with that implied by the AMS radiocarbon dating of the lateglacial human recolonization of northern Europe (14.2–12.5 kyr bp). We argue that this makes it implausible for climate change to have limited the speed of the recolonization front. It is pointed out that a similar value for the speed can be tentatively inferred from the archaeological data on the expansion of modern humans into the Levant and Europe (42–36 kyr bp).

Progress in front propagation research

Abstract: We review the progress in the field of front propagation in recent years. We survey many physical, biophysical and cross-disciplinary applications, including reduced-variable models of combustion flames, Reid's paradox of rapid forest range expansions, the European colonization of North America during the 19th century, the Neolithic transition in Europe from 13 000 to 5000 years ago, the description of subsistence boundaries, the formation of cultural boundaries, the spread of genetic mutations, theory and experiments on virus infections, models of cancer tumors, etc. Recent theoretical advances are unified in a single framework, encompassing very diverse systems such as those with biased random walks, distributed delays, sequential reaction and dispersion, cohabitation models, age structure and systems with several interacting species. Directions for future progress are outlined.

A method to assess the fuel economy of automotive thermoelectric generators

Abstract: For the widespread application of thermoelectric generators, it is of vital importance to have convenient simulation tools in order to test the behavioral consequences of a thermoelectric generator in almost real conditions. The simulation by numerical methods of the performance of automotive thermoelectric generators (ATEG) allows for time- and cost-saving assessment of material combinations and variations of crucial design parameters. However, even in the case of promising simulation results, it is complicated to guarantee the ATEG capacity for reducing the vehicle’s fuel consumption. This work presents a method to assess the fuel economy of an ATEG design. The procedure, which takes into account the ATEG power generation, backpressure, weight and the coolant pumping power, reveals that the maximum fuel economy value does not occur with the maximum ATEG power generation point. The method applied to the ATEG presented predicts a maximum fuel economy value of 0.18%.

Transient behavior under a normalized driving cycle of an automotive thermoelectric generator

Abstract: Thermoelectric generators (TEGs) have become a promising technology for vehicle exhaust heat recovery. Many models and prototypes have been developed and validated with very promising results. The majority of them have been tested under steady-state engine conditions. However, light-duty vehicles operate under wide variable loads, causing significant variation of TEG performance. The purpose of this study is to test and analyze an automotive thermoelectric generator (ATEG) under different steady-state engine conditions and under the transient New European Driving Cycle (NEDC). Results show that both thermal inertia and pressure drop play a key role in designing an ATEG for real applications. Variations on exhaust temperature and mass flow rate prevent achievement of thermal steady state. Consequently, total energy generated during the NEDC is lower than that expected from a steady-state analysis. On the other hand, excessive pressure loss on the exhaust considerably minimizes engine performance. Results show that the overall power generation of the ATEG can be significantly improved by maximizing the heat transfer through TEMs using a finned geometry, employing lower temperature thermoelectric materials and including a hot-side temperature control.

Maximum entropy production principle in physics, chemistry and biology

Abstract: The tendency of the entropy to a maximum as an isolated system is relaxed to the equilibrium (the second law of thermodynamics) has been known since the mid-19th century. However, independent theoretical and applied studies, which suggested the maximization of the entropy production during nonequilibrium processes (the so-called maximum entropy production principle, MEPP), appeared in the 20th century. Publications on this topic were fragmented and different research teams, which were concerned with this principle, were unaware of studies performed by other scientists. As a result, the recognition and the use of MEPP by a wider circle of researchers were considerably delayed. The objectives of the present review consist in summation and analysis of studies dealing with MEPP. The first part of the review is concerned with the thermodynamic and statistical basis of the principle (including the relationship of MEPP with the second law of thermodynamics and Prigogine’s principle). Various existing applications of the principle to analysis of nonequilibrium systems will be discussed in the second part.

The Fate of Mutations Surfing on the Wave of a Range Expansion

Abstract: Many species, including humans, have dramatically expanded their range in the past, and such range expansions had certainly an impact on their genetic diversity. For example, mutations arising in populations at the edge of a range expansion can sometimes surf on the wave of advance and thus reach a larger spatial distribution and a much higher frequency than would be expected in stationary populations. We study here this surfing phenomenon in more detail, by performing extensive computer simulations under a two-dimensional stepping-stone model. We find that the probability of survival of a new mutation depends to a large degree on its proximity to the edge of the wave. Demographic factors such as deme size, migration rate, and local growth rate also influence the fate of these new mutations. We also find that the final spatial and frequency distributions depend on the local deme size of a subdivided population. This latter result is discussed in the light of human expansions in Europe as it should allow one to distinguish between mutations having spread with Paleolithic or Neolithic expansions. By favoring the spread of new mutations, a consequence of the surfing phenomenon is to increase the rate of evolution of spatially expanding populations.

Linked magma ocean solidification and atmospheric growth for Earth and Mars

Abstract: Early in terrestrial planet evolution energetic impact, radiodecay, and core formation may have created one or more whole or partial silicate mantle magma oceans. The time to mantle solidification and then to clement surface conditions allowing liquid water is highly dependent upon heat flux from the planetary surface through a growing primitive atmosphere. Here we model the time to clement conditions for whole and partial magma oceans on the Earth and Mars, and the resulting silicate mantle volatile compositions. Included in our calculations are partitioning of water and carbon dioxide between solidifying mantle cumulate mineral assemblages, evolving liquid compositions, and a growing atmosphere. We find that small initial volatile contents (0.05 wt.% H 2 O, 0.01 wt.% CO 2 ) can produce atmospheres in excess of 100 bars, and that mantle solidification is 98% complete in less than 5 Myr for all magma oceans investigated on both Earth and Mars, and less than 100,000 yr for low-volatile magma oceans. Subsequent cooling to clement surface conditions occurs in five to tens of Ma, underscoring the likelihood of serial magma oceans and punctuated clement conditions in the early planets. Cumulate mantles are volatile-bearing and stably stratified following solidification, inhibiting the onset of thermal convection but allowing for further water and carbon emissions from volcanoes even in the absence of plate tectonics. Models thus produce a new hypothetical starting point for mantle evolution in the terrestrial planets.