purpose of this study is to experimentally determine the optimal blend rate of ethanol-gasoline fuels in order to maximize the brake thermal efficiency of a commercial SI engine. In this study, the engine performance, in terms of brake torque and brake specific fuel consumption, has been investigated with variation of volumetric mixing ratio between 87.5-octane gasoline and 99.5%-purity ethanol (E10, E20, E30, E40, E50, E60, E70, E85, and E100). The experiment has been conducted at different engine speeds and percentages of intake-throttle opening. The tests were performed at a constant compression ratio. The relative air-fuel ratio was tuned to unity and the ignition timing was tuned for maximum engine torque. The experimental results indicated that the appropriate ethanol-gasoline mixing ratio can enhance engine torque output, especially at low engine speed. The brake thermal efficiency is maximum when the engine operates at 58-73% of WOT with an engine speed of 2000-2500 rpm, using E40 and E50 fuels. This paper also provides a guideline for a suitable ethanol-gasoline blend rate at a certain engine load and speed. (C) 2016 Elsevier Ltd. All rights reserved.

Here we develop analytically the formulas for effective permeability in several configurations using the closed-form description of tree networks designed to provide flow access. The objective was to find the relation between the permeability and porosity of tree-shaped fissures. We found the effect of the fracture size on the permeability for fixed number of bifurcation and the results showed that the permeability of the fracture network increased rapidly with the size of the fracture. Next, we found a relation between the Reservoir Quality Index (RQI) and the porosity of the fracture. The results in this paper have been validated by comparison with experimental and numerical results. We show that the permeability formulas do not vary much from one tree design to the next, suggesting that similar formulas may apply to naturally fissured porous media with unknown precise details, which occur in natural reservoirs. (C) 2015 Elsevier Ltd. All rights reserved.

This research is aimed to study the transient behavior of air flow through the intake manifold of a heavy duty diesel engine according to the step of valve opening. The numerical study of air flow through the intake manifold was done on the 6SD-1 Isuzu engine. Two numerical techniques, finite element and finite volume methods were used in comparison and tendency confirmation of air flow characteristics inside the manifold. The transient air flow was studied at the engine speed of 1,000 rpm, 1,500 and 2,000 rpm. The numerical results from both numerical techniques agree exceptionally well with each other. The transient behavior of air flow according to the step of valve opening is well illustrated.

A microscale model of a solid oxide fuel cell (SOFC) involving the mass transfer together with the electrochemical reaction, the transportation of electrons and ions through the respective spherical shaped electron conducting and ion conducting particles inside the electrodes was mathematically developed. Couples of useful parameters were introduced in order to represent the characteristics of the cell. The predicted cell performance was showed according to various operating and design conditions. The effects of microscale electrode geometry on the cell performance were also taken into account. Parametric study according to the volumetric fraction of ionic and electronic conducting particles was conducted in order to examine the effects of operating conditions on the cell overpotentials. The study results substantiate the fact that SOFC overpotential could be effectively decreased by increasing the operating temperature as well as operating pressure. This present study reveals the working mechanisms of SOFC at the microscale level, while demonstrating the use of microscale relations to enhance the SOFC performance. The accuracy of the presented model was validated by comparing with already existing experimental results from the available literatures.

A micro-scale model of a solid oxide fuel cell (SOFC) involving the mass transfer together with the electrochemical reaction, the electron and ion transports through the respective spherically shaped electron-and ion-conducting particles inside the electrodes was mathematically developed. Couples of useful dimensionless parameters were introduced in order to represent the characteristics of the cell. The predicted cell performance was showed according to various operating and design conditions. The effects of micro-scale electrode geometry on the cell performance were also taken into account. Parametric study according to the volumetric fraction of ionic and electronic conducting particles was conducted in order to examine the effects of operating conditions on the cell overpotentials. The study results substantiate the fact that SOFC overpotential could be effectively decreased by increasing the operating temperature as well as operating pressure. This present study reveals the working mechanisms of SOFC at the micro-scale level, while demonstrating the use of micro-scale relations to enhance the SOFC performance. The accuracy of the presented model was validated by comparing to already existing experimental results from the available literatures.

Solid Oxide Fuel Cells (SOFCs) are of great interest due to their high energy efficiency, low emission level, and multiple fuel utilization. SOFC can operate with various kinds of fuels such as natural gas, carbon monoxide, methanol, ethanol, and hydrocarbon compounds, and they are becoming one of the main competitors among environmentally friendly energy sources for the future. In this study, a mathematical model of a co-flow planar anode-supported solid oxide fuel cell with internal reforming of natural gas has been developed. The model simultaneously solves mass, energy transport equations, and chemical as well as electrochemical reactions. The model can effectively predict the compound species distributions as well as the cell performance under specific operating conditions. The main result is a rather small temperature gradient obtained at 800 degrees C with S/C = 1 in classical operating conditions. The cell performance is reported for several operating temperatures and pressures. The cell performance is specified in terms of cell voltage and power density at any specific current density. The influence of electrode microstructure on cell performance was investigated. The simulation results show that the steady state performance is almost insensitive to microstructure of cells such as porosity and tortuosity unlike the operating pressure and temperature. However, for SOFC power output enhancement, the power output could be maximized by adjusting the pore size to an optimal value, similarly to porosity and tortuosity. At standard operating pressure (1 atm) and 800 degrees C with 48% fuel utilization, when an output cell voltage was 0.73 V, a current density of 0.38 Acm(-2) with a power density of 0.28 Wcm(-2) was predicted. The accuracy of the model was validated by comparing with existing experimental results from the available literature.

This paper reports optimal bifurcation shapes (T and Y) in turbulent regime of tree-shaped flows. Unlike earlier studies of T and Y constructs, here the effect of pressure losses at the junction is taken into account, and the wall roughness and duct cross-sectional shapes are free to vary. The optimal ratio of duct cross-sectional areas (as a generalization of Murray's law), the optimal ratio of duct lengths, and the optimal angle between the branches of the Y are presented. These optimal geometrical features are reported as functions of the flow direction (splitting flow versus merging flow), wall roughness, duct cross-sectional shape, and svelteness. The svelteness, Sv, is a global property defined as the external length scale of the flow construct divided by the internal length scale. It is shown that the effect of junction pressure losses on the optimized architecture can be neglected when Sv(3/2) is greater than approximately 10(4). Two dimensionless terms are introduced and shown to be useful for the optimization of flow networks.

Solid oxide fuel cells (SOFCs) are an alternative distributed power source due to their high thermal efficiency, low emission and multiple fuel utilization. SOFC can be supplied with various kinds of fuels such as natural gas, carbon monoxide, methanol, ethanol and hydrocarbon compounds. In this study, a mathematical model of a co–flow planar anode supported solid oxide fuel cell with internal reformation of natural gas has been developed in MATLAB code. The model solves simultaneously mass and energy transport equations, chemical as well as electrochemical reactions. The model can predict effectively the temperature and compound specie distributions as well as the SOFC cell performance under specific operating conditions. The cell performance is reported for several operating temperature and pressure. The cell performance is specified in term of cell voltage and power density at any specific current density. The influence of electrode microstructure on cell performance was investigated. The simulation results show that the steady state performance is almost insensitive to microstructure of cells such as porosity and tortousity. At standard operating pressure (1 atm) and 800 oC with 41% fuel utilization, an output cell voltage of 0.73 volt, a current density of 0.38 A/cm with a power density of 0.2774 W/cm was predicted.

This paper is a fundamental study of the effect of junction losses on the optimized geometry of tree-shaped flows. Several classes of flows are investigated systematically in a T-shaped construct with fixed internal and external size: laminar with non-negligible entrance and junction losses, and turbulent in tubes with smooth and rough walls. It is shown that in all cases junction losses have a sizeable effect on optimized geometry when Sv2 < 10, where the svelteness Sv is a global property of the entire flow system: Sv = external length scale/internal length scale. The relationship between the global Sv and the slenderness of individual channels is discussed. The study shows that, in general, the duct slenderness decreases as the tree architecture becomes finer and more complex. In conclusion, miniaturization pushes flow architectures not only toward the smaller, finer and more complex, but also toward the domain in which junction losses must be taken into account in the optimization of geometry.

This paper considers the fundamental question of whether the optimal geometry of dendritic tree networks is symmetric or asymmetric. Asymmetry of dendritic networks is a result of the relation between flow resistance and flow fraction at each bifurcation node. Asymmetry of bifurcation (asymmetry of Y-shaped assemblies) appears when the flow fraction at each bifurcation node is not equal to one-half. Asymmetric bifurcation provides lower flow resistance than symmetric bifurcation. Murray’s law of bifurcation (Di+1∕Di=2−1∕3) is valid only when the flow fraction at every bifurcation node in dendritic networks is one-half and the networks are symmetric. General rules to construct asymmetric trees are developed and reported in this paper. It is shown that even through pressure drops across round and square cross-sectional shape channels are different; their flow resistances can be expressed by similar relations.

Dendritic flow architectures are being contemplated for thermal designs that provide high heat transfer densities for the cooling of electronics. Optimized tree networks maximize the flow access between one point (source, sink) and an infinity of points (line, area, volume). This paper is a fundamental study of a new class of dendritic flow architectures for thermal design: trees combined with closed-loop structures, as in the venation of leaves. The loops provide robustness to the design: the network continues to serve its assigned area even if one or more ducts are damaged. The study documents the achievement of performance and robustness systematically, by starting from the simplest architectures and proceeding toward the more complex, namely, point-circle networks with one loop size and two loop sizes, and networks with loops without and with branching levels. It is shown that the use of loops increases the global flow resistance relative to the dendritic design without loops. Damage, or removal of a duct from the network, also leads to an increase in global flow resistance. These effects become less important as complexity increases, provided that the network is optimized. A damaged peripheral duct induces a smaller penalty than a damaged duct that is situated close to the center of the network. In summary, optimized complex flow structures are robust. Loops are an attractive design feature for maintaining a high level of global performance when the structure experiences local damage.

This article is about novel applications of computational heat transfer and fluid dynamics: the optimization and design of complex tree-shaped flow structures for cooling high-density heat-generating volumes (e.g., electronics). The focus is on computational cost, and how to reduce it by devising effective strategies for identifying paths that lead to the optimal complex flow structure. The method is illustrated by considering dendritic architectures that connect with laminar fluid flow the center of a circle with points distributed equidistantly on the circle. Optimal architectures are pursued numerically based on several methods. the optimization of every geometric detail of the complex structure, the minimization of every duct length, and the optimization of every angle of bifurcation. It is shown that strategy leads to dramatic increases in optimization speed, and provides an effective albeit approximate description of the optimal complex flow structure.

Constructal theory is applied to the cooling of a disc where heat is uniformly generated. The disc size and the total volume occupied by the ducts (distributing the flow from the centre to the periphery) are constrained. It is shown that when the objective is to minimise the global thermal resistance, the best design is the one built with radial ducts. On the other hand, the minimisation of the pumping power leads to tree-shaped structures. The results show that the two optimisation approaches, thermal and fluid-mechanical, generate results with nearly the same global performance. Yet, when the scale of the problem becomes smaller and smaller and dendritic flows perform better, demonstrating the usefulness and robustness of tree-shaped structures.

In this paper we develop the optimal tree-shaped flow paths for cooling a disc-shaped body by convection. Heat is generated uniformly over the disc area. The coolant enters through the center of the disc, and exits through ports positioned equidistantly along the perimeter. The unknown is the flow architecture. The constraints are the disc size and the total volume occupied by the ducts. It is assumed that the ducts are narrow enough so that the flow is hydrodynamically and thermally fully developed. The ultimate goal is to determine flow architectures that reach simultaneously two objectives: (i) minimal global fluid flow resistance (or pumping power), and (ii) minimal global thermal resistance. When the architecture is optimized for (i), the result is a dendritic structure in which every geometric feature is uniquely determined. The corresponding thermal resistance decreases as the total mass flow rate and the pumping power increase. When the objective is (ii), the optimal architecture has radial ducts, not dendrites. The corresponding fluid-flow resistance increases as the flow rate increases and the global thermal resistance decreases. Put together, these geometric results show that methods (i) and (ii) lead to nearly the same combined performance (thermal and fluid). Examined more closely, the dendrites produced by method (i) perform progressively better as the length scales become smaller. Optimized increasing complexity is the route to high thermal and fluid-flow performance in the limit of decreasing scales.

In this paper. we review the fundamental problem of how to design a flow path with minimum overall resistance between one point (O) and many points situated equidistantly on a circle centred at O. This is a fundamental problem in energy engineering: the distribution of fluid, energy, electric power, etc., from points to Surrounding areas. This problem is also fundamental in heat transfer and electronics cooling: how to bathe and cool with a single stream of coolant a disc-shaped area or volume that generates heat at every point. This paper outlines, first, a direct route to the construction of effective tree-shaped flow structures. The starting point is the optimization of the shape of each elemental area, such that the length of the flow path housed by the element is minimized. Proceeding towards larger and more complex structures-from elements to first constructs, second constructs, etc.-the paper develops tree-shaped flow structures between one point and a straight line, as an elemental problem, and a circle and its centre. We also consider the equivalent tree-shaped networks obtained by minimizing the pressure drop at every step of the construction, in accordance with geometric constraints. The construction method is applied to a fluid flow configuration with laminar fully developed flow. It is shown that there is little difference between the two methods. The minimal-length structures perform very close to the fully optimized designs. These results emphasize the robustness of optimized tree-shaped flows. Copyright (C) 2003 John Wiley Sons, Ltd.

In this paper we consider the fundamental problem of how to design a flow path with minimum overall resistance between one point (O) and many points situated equidistantly on a circle centered at O. The flow may proceed in either direction, from the center to the perimeter, or from the perimeter to the center. This problem is an integral component of the electronics cooling problem of how to bathe and cool with a single stream of coolant a disc-shaped area or volume that generates heat at every point. The smallest length scale of the flow structure is fixed (d), and represents the distance between two flow ports on the circular perimeter. The paper documents a large number of optimized dendritic flow structures that occupy a disc-shaped area of radius R. The flow is laminar and fully developed in every tube. The complexity of each structure is indicated by the number of ducts (n0) that reach the central point, the number of levels of confluence or branching between the center and the perimeter, and the number of branches or tributaries (e.g., doubling vs. tripling) at each level. The results show that as R/d increases and the overall size of the structure grows, the best performance is provided by increasingly more complex structures. The transition from one level of complexity to the next, higher one is abrupt. Generally, the use of fewer channels is better, e.g., using two branches at one point is better than using three branches. As the best designs become more complex, the difference between optimized competitors becomes small. These results emphasize the robustness of optimized tree-shaped networks for fluid flow.

This paper outlines a direct route to the construction of effective tree-shaped flow structures. Dendritic flow structures dominate the design of natural and engineered flow systems, especially in thermal and fluid systems. The starting point is the optimization of the shape of each elemental area or volume, such that the length of the flow path housed by the element is minimized. Proceeding toward larger and more complex structures – from elements, to first constructs, second constructs, etc. – the paper develops tree-shaped flow structures between one point and a straight line, one point and a plane, a circle and its center, and a point and many points distributed uniformly over an area. In the latter, the construction method is applied to a fluid flow configuration with laminar fully developed flow. The constructions reveal several features that are supported by empirical observations of natural tree-shaped flows: asymmetry, flow rate imbalance, pairing or bifurcation, angles between branches, and Y-shaped constructs that lie in a plane. It is shown that these basic features are necessary because of “packing”, i.e., assembling optimized elements into a fixed space, and filling the space completely. For the flow between an area and one point, the best elemental shape is the regular hexagon. It is shown that the emergence of string-shaped links that connect two or more elements are necessary features, which are also required by packing. Strings cover some of the inner zones of the tree network, particularly the inner zones of large and complex trees. Dichotomous Y-shaped constructs dominate the tree structure, especially the peripheral zones of the tree canopy. The practical importance of the simplified design method is discussed.