Flexible Thermoelectric Devices of Ultrahigh Power Factor by Scalable Printing and Interface Engineering

Printing is a versatile method to transform semiconducting nanoparticle inks into functional and flexible devices. In particular, thermoelectric nanoparticles are attractive building blocks to fabricate flexible devices for energy harvesting and cooling applications. However, the performance of printed devices are plagued by poor interfacial connections between nanoparticles and resulting low carrier mobility. While many rigid bulk materials have shown a thermoelectric figure of merit ZT greater than unity, it is an exacting challenge to develop flexible materials with ZT near unity. Here, a scalable screen‐printing method to fabricate high‐performance and flexible thermoelectric devices is reported. A tellurium‐based nanosolder approach is employed to bridge the interfaces between the BiSbTe particles during the postprinting sintering process. The printed BiSbTe flexible films demonstrate an ultrahigh room‐temperature power factor of 3 mW m^?1 K^?2 and ZT about 1, significantly higher than the best reported values for flexible films. A fully printed thermoelectric generator produces a high power density of 18.8 mW cm^?2 achievable with a small temperature gradient of 80 °C. This screen‐printing method, which directly transforms thermoelectric nanoparticles into high‐performance and flexible devices, presents a significant leap to make thermoelectrics a commercially viable technology for a broad range of energy harvesting and cooling applications.     

Route planning model of multi-agent system for a supply chain management

Sometimes in travel planning, finding the best route to the road transportation network by considering the environmental conditions that are affecting the actual time travel of the travellers are vital especially in handling the logistic operations in supply chain management (SCM). Furthermore, the policy strategy is needed in order to influence the managers or drivers to find the optimum and the most effective route for a trip plan in supporting the logistic operations of SCM. In this paper we analyze the effectiveness of the coordination model of the environmental conditions that are affecting for the travelling time based on multi-agent system for a road transportation network for supply chain management. A number of experimental cases have been used to evaluate the proposed approach transportation network problems in some Malaysian cities. Finally, experimental results affirmed that the proposed approach is practical and efficient.     

Study on fracture behaviour of Al–15%Mg<Subscript>2</Subscript>Si metal matrix composite with and without beryllium additions

In this study, the influence of Beryllium (Be) content on the fracture behaviour of Al–15%Mg₂Si composite was investigated. The results showed an increase in mechanical properties with increasing of Be content. The stress–strain curves of samples showed a same category of serrations reflecting non-uniform deformation. Scanning electron microscopy was employed to examine the crack nucleation and fracture model. The results indicate that Al–15%Mg₂Si composite shows different behaviours of crack initiation and fracture for samples with and without Be. Differences observed in the fracture behaviour were attributed to microstructural changes as well as morphological aspects of primary Mg₂Si particles.     

Effects of Micro Silica on Permeability of Plastic Concrete

Water tightness and seepage control are important considerations in the design and construction of dams. Plastic concrete cut-off walls are one of the effective means for seepage control in earth dams constructed on permeable substrate. An important requirement for the plastic concrete in such applications is adequate strength for the design loads and low enough permeability to meet the water tightness requirements of the dam. As permeability of cement-based materials, such as concrete, is mainly dependent on water to cement ratio, the permeability of plastic concretes is much higher than those of normal concretes. It is thus apparent that the achieving to low permeability is an important problem in plastic concrete. So a method, which could reduce the permeability of plastic concretes without unduly increasing their elastic modulus, would provide considerable technical advantages. In the present research, the possibility of lowering the permeability of plastic concrete thorough replacement of a portion of cement by micro silica was investigated. The aim of the experimental research was to investigate the effects of various levels of cement replacement by micro silica, including 0%, 3%, 6%, 9%, 12% and 15% on strength and permeability of plastic concrete. The results illustrate that the use of micro silica for replacement of some of the cement content in plastic concrete results in very substantial decrease in permeability. Obtained results show that through the use of micro silica in plastic concrete, it is possible to keep the strength and elastic modulus at the level of control mix and still achieve to reduction in permeability.     

Thermodynamic analysis and optimization of novel ejector-expansion TRCC (transcritical CO2) cascade refrigeration cycles (Novel transcritical CO2 cycle)

In this paper, two new CO₂ cascade refrigeration cycles are proposed and analyzed. In both these cycles the top cycle is an ejector-expansion transcritical cycle and the bottom cycle is a sub-critical CO₂ cycle. In one of these proposed cycles the waste heat from the gas cooler is utilized to drive a supercritical CO₂ power cycle making the plant a combination of three cycles. Using the first and second laws of thermodynamics, theoretical analyses on the performance characteristics of the cycles are carried out. Also a parametric study is conducted to optimize the performance of each cycle under various operating conditions. The proposed cycles exhibit a reasonable value of COP (coefficient of performance) with a much less value of compressor discharge temperature, compared to the conventional cycles.     

CFD simulation of gas-solid bubbling fluidized bed containing FCC particles

The hydrodynamics of a bubbling gas-solid fluidized bed of 57.4 μm FCC particles was simulated by using a state-of-the-art two-fluid model integrating the kinetic theory of granular flow for particulate phase stresses. The overestimation of the bed expansion was resolved by using a suitable scale factor in the drag model as suggested by McKeen and Pugsley (T.R. McKeen, T.S. Pugsley, Powder Technol., 129, 139 (2003)). This study showed that the method was appropriate in simulation of a gas-solid fluidized bed of Geldart A particles at high gas velocities (0.3 to 0.61 m/s). The reduction of computational time especially for simulation of large-scale systems was achieved. The time-averaged local voidage was compared with the experimental data and the trend of varying several parameters on the hydrodynamic of the bed was investigated. The simulation results showed both qualitative and quantitative agreement with the literature.     

Gasification of wastes: The impact of the feedstock type and co-gasification on the formation of volatiles and char

A gasification pilot plant was built up in order to investigate the influence of both feedstock type and co-gasification on the distribution and composition of the products. The results showed that at the same process condition, different feedstocks could result in different product yields. For instance, the highest gas yield was obtained from tire gasification, while the lowest one belonged to weed gasification. The characterization of the products showed the presence of different components and functionalities in the samples produced. In addition, the co-gasification of the feedstocks resulted in the products with different specifications than single feeding, proving the existence of different reaction pathways. This means that feedstocks and their derivatives could interact with each other and resulted in nonproportional yields and composition for the char, tar, and gaseous products in comparison with the products from the gasification of the single feedstocks. As an example, the tar from co-gasification had a lower content of acids but a higher content of amines and amides. This confirmed that co-gasification influenced the reaction network significantly, impacting the formation of gases, tar, and char, originated from the cross-interaction among the reaction intermediates derived from the pyrolysis/gasification of the various feedstocks.     

CFD studies of solids hold-up distribution and circulation patterns in gas-solid fluidized beds

Numerical results for a gas-fluidized bed using a 2D Eulerian model including the kinetic theory for the particulate phase were provided. The circulation patterns for various operating conditions were discussed. Modeling parameters of drag function, algebraic and transport equations of granular temperature, frictional stress model, turbulent model and discretization scheme were investigated for a bed with different gas distributors and a slotted draft tube. CFD results showed that the drag model is an important hydrodynamics parameter for gas-fluidized beds with various gas distributors. Transport and algebraic equations for granular temperature should be utilized, respectively, for beds including partial and complete sparging at U_g = 2.18 m/s. Frictional stresses play an important role for the beds containing partial sparging with and without draft tube. Discretization schemes should be examined to achieve better results. The Simonin and k-ε turbulent models can improve the CFD results at high gas velocities. Considering perforated plate distributor improves the results.     

Optimization of an Artificial Neural Network Topology for Predicting Drying Kinetics of Carrot Cubes Using Combined Response Surface and Genetic Algorithm

In this study, the advantages of integrated response surface methodology (RSM) and genetic algorithm (GA) for optimizing artificial neural network (ANN) topology of convective drying kinetic of carrot cubes were investigated. A multilayer feed-forward ANN trained by back-propagation algorithms was developed to correlate output (moisture ratio) to the four exogenous input variables (drying time, drying air temperature, air velocity, and cube size). A predictive response surface model for ANN topologies was created using RSM. The response surface model was interfaced with an effective GA to find the optimum topology of ANN. The factors considered for building a relationship of ANN topology were the number of neurons, momentum coefficient, step size, number of training epochs, and number of training runs. A second-order polynomial model was developed from training results for mean square error (MSE) of 50 developed ANNs to generate 3D response surfaces and contour plots. The optimum ANN had minimum MSE when the number of neurons, step size, momentum coefficient, number of epochs, and number of training runs were 23, 0.37, 0.68, 2,482, and 2, respectively. The results confirmed that the optimal ANN topology was more precise for predicting convective drying kinetics of carrot cubes.     

Simultaneous confidence bands for all contrasts of three or more simple linear regression models over an interval

Simultaneous confidence intervals are used in Scheffé (1953) to assess any contrasts of several normal means. In this paper, the problem of assessing any contrasts of several simple linear regression models by using simultaneous confidence bands is considered. Using numerical integration, Spurrier (1999) constructed exact simultaneous confidence bands for all the contrasts of several regression lines over the whole range (−∞,∞) of the explanatory variable when the design matrices of the regression lines are all equal. In this paper, a simulation-based method is proposed to construct simultaneous confidence bands for all the contrasts of the regression lines when the explanatory variable is restricted to an interval and the design matrices of the regression lines may be different. The critical value calculated by this method can be as close to the exact critical value as required if the number of replications in the simulation is chosen sufficiently large. The methodology is illustrated with a real problem in which sizes of the left atrium of infants in three diagnostic groups (severely impaired, mildly impaired and normal) are compared.