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Abstract The analysis and optimization of flat plate fins of constant thickness and straight base has been conducted for different fin’s shapes. Performance of the fins is quantified through effectiveness and expressed as a function of fin’s shape, width, and area. A linear piecewise function with varying number of evenly spaced sections is used to generate shapes with different number of degrees of freedom, which are classified as constrained- or unconstrained-base depending on the width of the fin at the constant temperature base location. For one- and two-degrees of freedom shapes, a variety of rectangular, triangular, trapezoidal, and rhomboidal geometries are considered and optimized. For more than two-degrees of freedom, more complex resulting shapes are also considered. By adjusting the value of the corresponding shape parameters, the best possible distributions of available area to maximize heat transfer are obtained, which produce significant improvements favored by smaller width and larger area. Unconstrained-base performs better than constrained-base configurations as they allow the distribution of a larger area close to the high-temperature base. Optimal shape of unconstrained-base fins is in general convergent with non-zero wide tip, while, for constrained-base fins, it is divergent in the first linear section from the base and convergent in the remaining ones. For increasing number of degrees of freedom the optimized shapes tend to resemble natural structures while effectiveness increases asymptotically to a limit for constant width and area. Besides determining the optimal configurations, consideration has been made about the optimal regions where a variety of shapes produce virtually the same effectiveness of the absolute maximum, which can be used to design fins with almost maximum performance but having simpler shapes or being functional under possible space restrictions. The dimensionless model and the systematic analysis proposed in this work are not only appropriate to study a wide range of flat plate fins but also can be implemented to analyze and perform optimization over other type of fins and fins configurations.

Abstract Dimethyl ether appears to be a better choice among various diesel alternatives due to its high cetane number and sootless combustion. However, the physical and chemical properties of dimethyl ether are very different from those of diesel. The physical properties influence spray formation and atomization characteristics, while chemical properties determine combustion and emission formation characteristics. Thus, fuel's physical and chemical properties significantly determine engine performance and emissions. In the present work, spray combustion and emission formation characteristics of n-heptane, dimethyl ether, and their blends (10, 25, and 50% dimethyl ether in n-heptane) were numerically studied in a constant volume chamber. Results show that the n-heptane spray combustion has the highest heat release rate with an intense premix combustion phase, whereas dimethyl ether spray combustion has the lowest heat release rate and shortest premix combustion phase. The magnitude of the premixed phase and heat release rate decreases with the increase in dimethyl ether mass fraction in the blends. Soot, carbon monoxide (CO), unburned hydrocarbon (UHC), and nitric oxide (NO) emissions decreased with the increase in the dimethyl ether mass fraction in the blends and were lowest for the dimethyl ether.

Abstract This study investigates the non-linear relationship between urbanization paths and CO2 emissions in selected South, South-East, and East Asian countries over the period 1971–2014. Based on the STIRPAT (Stochastic Impacts by Regression on Population, Affluence, and Technology) framework, we applied the advanced and robust methods of dynamic seemingly unrelated regression (DSUR), dynamic OLS (DOLS), and fully modified OLS (FMOLS) to estimate the long-term effects. The empirical findings revealed the inverted U-shaped effects of urbanization and urban agglomeration and the U-shaped impact of the largest city ratio on CO2 emissions. Urbanization and urban agglomerations improve environmental quality in the long-run and support ecological modernization theory. However, excessive concentration in the largest cities have severely affected the environmental quality and violates the notion of compact-city efficiencies. Moreover, energy intensity and economic growth positively affect CO2 emissions, while trade openness negatively influences CO2 emissions. Our robustness analysis at the country-level applies the augmented mean group (AMG) panel ARDL technique, which further supports the non-linear effect of urbanization paths on CO2 emissions except for a few countries. The results of the panel Granger non-causality approach unveil bidirectional causality of energy efficiency, economic growth, urbanization, and largest city ratio with CO2 emissions. In contrast, unidirectional causality runs from urban agglomeration to CO2 emissions. Our findings have important policy implications as we suggest green urban infrastructures, eco-friendly dwellings, smart cities, country-specific trade policies, and renewable energy options to improve the environmental quality.