نشریه فناوری های نوین در سیستم های انرژی
سال یکم شماره 2 (پیاپی 102، تابستان 1394)

Heat transfer from surfaces of the sphere is the most important topics in chemical engineering and industry. In this paper, heat transfer rate from these surfaces were studied by computational fluid dynamics (CFD). The effect of nano-particles concentrations and kinds on the rate of heat transfer was investigated numerically. Different models were used in order to access optimum results in simulations. The results of these simulations were compared with the well-known empirical relationships and showed a good adaptation. Finally, the RNG k-&epsilon model was chosen to simulate the heat transfer from spherical surface in the turbulent regimes. Nano-fluid with different kinds of nano-particle as well as various concentrations was used to improve the heat transfer rate from spherical surfaces. The results showed that heat transfer rate was improved by using nano-fluids. Heat transfer rate increased with increasing nano-particle concentrations. At low Reynolds number, the nano-particles effect was significant. The enhancement in heat transfer rate was negligible when using the nano-particle with lower thermal conductivity. Nusselt numbers were not change with the nano-particles concentrations at constant Reynolds numbers. The Nusselt numbers also increased by Reynolds numbers.

In order to build complex relationships between cyclone pressure drop coefficient (PDC) and geometrical dimensions, representative artificial neural networks (ANNs), including back propagation neural network (BPNN), radial basic functions neural network (RBFNN) and generalized regression neural network (GRNN), are developed. Multi Step Search Method (MSSM) configures the optimal parameters for designing ANNs. To choose the network with best performance of prediction, mean square error and correlation coefficient of three networks is compared. It is found that, the RBFNN provides higher generalization performance than the BPNN and GRNN. And BPNN has the least precision. Comparing proposed RBFNN simulation results with three semi-empirical models shows the great vantages for RBFNN. In next step, using RBFNN and genetic algorithm, optimized geometrical parameters for minimizing pressure drop of cyclone are found. A comparison between the new design and the standard Stairmand design shows that the new cyclone design results in about 80% of the PDC obtained by the old Stairmand design at almost the same cut-off diameter and the same volume flow rate.

In this research Modeling and simulation software of methanol fuel cells using MATLAB and Kamsvel has been done. The model was verified with experimental data using MATLAB software and then parameters of this model is used for the study of cell function. The effect of concentration on the polarization chart, the effect of density on the conversion and transfer coefficient on pressure loss, the impact of using conventional carbon and carbon nanotubes on waste catalyst-voltage and temperature drop effect on potential loss have been studied

Numerical method of thermal energy storage for decreasing the melting time of phase changing material by using of two tubes heat exchanger with fluent software has been investigated in this article. Due to the addition of aluminum oxide nano particles and copper nano particles to phase changing material with different volume percent, the melting time of phase changing material has been studied. In this study, two different phase changing materials are used: paraffin and n- octane, and Also for modeling thermal energy storage system, these results are compared with experimental results of Jace Matthew and his colleagues model that Shows the numerical results are in good agreement with the experimental results, and then the effects of parameters such as input, the input fluid temperature on decrease of melting time of phase change material has been investigated. The results show that paraffin phase changing material with copper nano particles have a better heat conductivity than paraffin and aluminum nano particles and by increasing the flow, heat transfer rate and paraffin liquefying rate are reduced. Also, increasing a low percentage volume of nano particles in the mixture causes a significant increase in heat transfer and using nano particles with thermal conductivity increases the efficiency of this method.

In this paper, first, the history of emergy concept formation is described and then, tried to be the superficies of subjects more than their depth with knowing approach of different sections of emergy. Therefore, the principles of emergy are discussed, briefly and then, the language of energy systems is expressed and the method of ecology energy calculations also mentioned. In addition, decision making procedure based on emergy assessment is introduced and its indices are defined. Eventually, the emergy concept is described as a function of exergy in order to two different study solutions.