Marcelo Risso Errera

Deterministic Tree Networks for Fluid Flow: Geometry for Minimal Flow Resistance Between a Volume and One Point

The function of many natural flow systems is to connect by a fluid flow a nite-size volume and one point. This paper outlines a strategy for constructing the architecture of the volume-topoint path such that the flow resistance is minimal (constructal theory 1 ). The given volume is viewed as an assembly of volume elements of various sizes. The main discovery is that the shape of each element can be optimized such that the elemental volume-to-point flow resistance is minimal. This optimization principle applies at every volume scale. The smallest volume element contains a fluid saturated porous medium with Darcy flow, which is collected by and channeled through a high permeability path (e.g., ssure) to one point on the element boundary. The geometric optimization is repeated for larger volume elements, which are constructs (assemblies) of optimized smaller volumes. The flow integrated over each new assembly is channeled through a high-permeability path to a point on the side of the assembly. One remarkable feature of the emerging minimal-resistance flow path is that the highpermeability channels of the various volume elements form a tree network which is completely deterministic. The interstices of the network are lled with low permeability porous medium. The method is extended to applications where the high-permeability paths are empty spaces (e.g., parallel-plate channels). It is shown that when the total void volume is constrained it can be distributed optimally among the volume elements to further decrease the overall flow resistance.

Convective trees of fluid channels for volumetric cooling

Abstract This paper describes the geometric optimization of the internal structure of a volume that generates heat at every point and is cooled by a single stream. According to the constructal method, the optimization of the cooling design is organized in a sequence of steps that begins with the smallest volume element and continues with larger assemblies (constructs) of previously optimized building blocks. Optimized at each level of assembly are the external shape of the construct and the relative thickness of each duct for fluid flow. It is shown that in the end the fluid channels form a tree network that cools every point of the given volume. Length scales smaller than the thickness of the elemental volume are reached by conduction through the solid heat-generating material. Two fluid channel geometries are optimized: parallel-plate channels and round tubes.

DETERMINISTIC TREE NETWORKS FOR RIVER DRAINAGE BASINS

This paper shows that the dendritic patterns formed by low-resistance channels in a river drainage basin are reproducible and can be deduced from a single principle that acts at every step in the development of the pattern: the constrained minimization of global resistance in area-to-point flow. The river basin is modeled as a two-dimensional territory with Darcy flow through a saturated heterogeneous porous medium with uniform flow addition per unit area. From one step to the next, small elements of the porous medium are dislodged and removed in ways that minimize the global flow resistance. The removed elements are replaced by channels with lower flow resistance. The channels form a dendritic pattern that is deterministic, not random. The finest details of this structure are sensitive to internal properties and external forcing, i.e. variations in the local properties of the flow medium, and the manner in which the total area-to-point flow rate varies as the structure develops. Remarkably insensitive to such effects are the basic type and rough size of the flow structure (channels versus no channels, dendrite, number of branches) and the minimized global resistance to flow.

Maximum power from a hot stream

Abstract This paper reports the solution to the fundamental problem of how to maximize the mechanical power extracted from a hot single-phase stream when the total heat transfer area bathed by the stream is constrained. It is shown that the optimization has two degrees of freedom: the shape of the stream temperature distribution as a function of the length ( x ) traveled along the heat transfer surface, and the position of this distribution on the absolute temperature scale. The optimal stream temperature distribution is exponential in x , and so is the temperature distribution along the hot end of the system that converts the heat transfer into mechanical power. At any x , the temperature difference across the heat exchanger is proportional to the local absolute temperature. Similar conclusions are reached for the cold end heat exchanger, when the power system rejects heat to a cold single-phase stream. It is shown that the optimal solution can be implemented in practice by using two counterflow heat exchangers. Each counterflow is imbalanced to a degree recommended by thermodynamic optimization. The effect of the sizes and capacity rates of the two heat exchangers is documented.

Complexity, organization, evolution, and constructal law

Physics is concise, simple, unambiguous, and constantly improving. Yet, confusion reigns in the field especially with respect to complexity and the second law of thermodynamics. In this paper, we step back and take a look at these notions—their meaning and definition—on the background provided by nature and thermodynamics. We review the central concepts and words that underpin the physics of evolutionary design today: information, knowledge, evolution, change, arrow of time, pattern, organization, drawings, complexity, fractal dimension, object, icon, model, empiricism, theory, disorder, second law, the “any” system in thermodynamics, morphing freely, and the constructal law. We show, for example, that information is not knowledge, fractal dimension is not a measure of complexity, and pattern is not a live flow architecture. Drawings, as physical means to facilitate the flow of knowledge, are subject to the natural tendency toward design evolution. Complexity, organization, and evolution in nature are most powerful and useful when pursued as a discipline, with precise terms, rules, and principles.

Gaseous emissions from a heavy-duty engine equipped with SCR aftertreatment system and fuelled with diesel and biodiesel: Assessment of pollutant dispersion and health risk

The changes in the composition of fuels in combination with selective catalytic reduction (SCR) emission control systems bring new insights into the emission of gaseous and particulate pollutants. The major goal of our study was to quantify NOx, NO, NO2, NH3 and N2O emissions from a four-cylinder diesel engine operated with diesel and a blend of 20% soybean biodiesel. Exhaust fume samples were collected from bench dynamometer tests using a heavy-duty diesel engine equipped with SCR. The target gases were quantified by means of Fourier transform infrared spectrometry (FTIR). The use of biodiesel blend presented lower concentrations in the exhaust fumes than using ultra-low sulfur diesel. NOx and NO concentrations were 68% to 93% lower in all experiments using SCR, when compared to no exhaust aftertreatment. All fuels increased NH3 and N2O emission due to SCR, a precursor secondary aerosol, and major greenhouse gas, respectively. An AERMOD dispersion model analysis was performed on each compound results for the City of Curitiba, assumed to have a bus fleet equipped with diesel engines and SCR system, in winter and summer seasons. The health risks of the target gases were assessed using the Risk Assessment Information System For 1-h exposure of NH3, considering the use of low sulfur diesel in buses equipped with SCR, the results indicated low risk to develop a chronic non-cancer disease. The NOx and NO emissions were the lowest when SCR was used; however, it yielded the highest NH3 concentration. The current results have paramount importance, mainly for countries that have not yet adopted the Euro V emission standards like China, India, Australia, or Russia, as well as those already adopting it. These findings are equally important for government agencies to alert the need of improvements in aftertreatment technologies to reduce pollutants emissions.

Wealth inequality: The physics basis

“Inequality” is a common observation about us, as members of society. In this article, we unify physics with economics by showing that the distribution of wealth is related proportionally to the movement of all the streams of a live society. The hierarchical distribution of wealth on the earth happens naturally. Hierarchy is unavoidable, with staying power, and difficult to efface. We illustrate this with two architectures, river basins and the movement of freight. The physical flow architecture that emerges is hierarchical on the surface of the earth and in everything that flows inside the live human bodies, the movement of humans and their belongings, and the engines that drive the movement. The nonuniform distribution of wealth becomes more accentuated as the economy becomes more developed, i.e., as its flow architecture becomes more complex for the purpose of covering smaller and smaller interstices of the overall (fixed) territory. It takes a relatively modest complexity for the nonuniformity in the ...

Emissions of Criteria and Non-Criteria Pollutants by a Flex-Fuel Motorcycle

While criteria pollutants have established emission limits for motorcycles in Brazil, aldehydes limits have not been established and conclusive studies have not been found in the existing literature, despite the growing number of motorcycles using flex fuel in Brazil. This work presents results for the emissions of criteria pollutants, such as carbon monoxide, hydrocarbons and nitrogen oxides, acetaldehyde and formaldehyde. The motorcycle was tested with 22, 61, and 100% of ethanol in gasoline blends. Fourier transform infrared (FTIR) and high performance liquid chromatography (HPLC) were used to determine the pre- and post-catalytic converter emissions. Aldehyde emissions directly increased with the ethanol content in the fuel blend. The tailpipe aldehyde emissions for 22, 61, and 100% of ethanol in gasoline were 3.9, 8.5, and 38.8 mg km-1, respectively. These results demonstrated that aldehyde emissions in motorcycles are not negligible, and higher emissions are observed during the cold phase of the engine.

Analysis of capacitive measurements at low frequencies for moisture content determination in soybeans

This study aims to evaluate the capacitive measurement method at low frequencies for determining the moisture content in soybeans. Furthermore, a technique for measuring the moisture content of soybeans at different temperatures is proposed. A practical cylindrical capacitor was designed for the experiments. Capacitive measurements at frequencies of 1 kHz, 10 kHz and 100 kHz were performed using an LCR meter. Two varieties of soybeans were used in the tests, and the differences were evaluated. The errors of the proposed method were analyzed, and the correlation between moisture content and capacitance was verified. The influence of temperature on the measurements was also quantified. Polynomial models are proposed to compensate for temperature variations. It was found that reasonable precision can be achieved at 100 kHz using the temperature compensation provided by the designed models.