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An updated model of the hybrid system consisting of a vacuum TIG (thermionic generator) and a multi-couple TEG (thermoelectric generator) is proposed, in which the main internal and external irreversible losses of the system are considered and the temperatures of the electrode plates of the TIG and the cold side of the TEG are determined by energy balance equations rather than some specified parameters. Analytical expressions for the power output and efficiency of the TIG, TEG, and hybrid system are derived. The effects of the voltage output and work functions of the TIG and the electric current of the TEG on the power output and efficiency are discussed. The maximum power output and efficiency of the hybrid system are numerically calculated. The optimally operating regions of main parameters are determined.

Abstract High coulombic efficiency (CE) usually indicates a long battery cycle life. However, the relationship between long-term CE evolution and battery degradation is not fully understood yet. This paper explores the behavior of long-term CE and clarifies its relationship with capacity degradation. Cycle life tests are conducted on two types of mainstream commercial lithium-ion batteries. An incremental capacity (IC) analysis is then employed to identify battery aging mechanisms. Experimental observations along with in-depth discussions are presented regarding battery degradation, aging mechanisms, and CE evolution. From the experimental results, two typical degradation patterns are recognized. From the IC analysis, we observed that, in addition to a loss of lithium inventory, a loss of active material accelerates battery degradation and brings down CE values. From an electrochemical perspective, this paper establishes the relationship between CE evolution and capacity degradation. This relationship can help develop battery degradation models, estimate battery health states, and provide early failure warnings for a battery management system.

Abstract Combustion optimization by fine tuning combustion parameters of boilers can cut down NO x emissions effectively with little cost. Coal qualities, which change from time to time, have great influences on NO x emissions. However, the current NO x reduction optimization model cannot handle with this problem well. What is more, the output load would deviate from the demand load as the boiler efficiency is also affected by the optimized manipulated variables (MVs). In this paper, an on-line method to calculate coal qualities based on reverse balance thermal efficiency model was integrated into the optimization model. Furthermore, a new constraint was added to the optimization model to meet the demand load. NO x emission characteristics of some 600 MW capacity utility boiler were investigated. Fine selected MVs were taken as the inputs of support vector machines (SVM) and NO x emission was taken as the output, respectively. Parameters of SVM were fine tuned by particle swarm optimization algorithm (PSO). Combustion optimization for the studied boiler was undertaken based on the proposed optimization model. Results showed that the new model can provide lower NO x emissions and meet demand loads at the same time.

Abstract With the encouragement of LNG (liquefied natural gas) application in China, CCHP (combined cooling heating and power) system fueled by natural gas has been receiving increasing attention. This paper presents optimization of CCHP system on their design and operation from energetic analysis, economic operation and environment effect viewpoints. CCHP system for hotels, offices and residential buildings in Dalian (China) is given to ascertain the effectiveness of the model. Weighting method and fuzzy optimum selection theory are employed to evaluate the integrated performances of CCHP systems with various operation strategies. Results show that: (1) Hotels have the greatest contribution (42.28%) to the energy savings based on energetic analysis sub-model because of their relatively stable electricity loads. (2) CCHP systems reduce the annual total costs for all operation cases compared with the reference system for hotels and offices. However, CCHP system achieves no economic merits for residential buildings. (3) The applications of the CCHP system decrease pollutant emissions in all operation cases for the studied buildings. (4) CCHP system driven by gas engine has better performance than driven by gas turbine. Coupled with renewable energy sources and with thermal storage tank are mostly optimum operation cases from energetic, economic and environment criteria.

The production of synthesis gas has gained increasing importance because of its use as raw material for various industrial syntheses. In this paper synthesis gas generation during the reaction of a coal/methane with steam and oxygen, which is called the co-gasification of coal and natural gas, was investigated using a laboratory scale fixed bed reactor. It is found that about 95% methane conversion and 80% steam decomposition have been achieved when the space velocity of input gas (oxygen and methane) is less than 200 h(-1) and reaction temperature about 1000 degrees C. The product gas contains about 95% carbon monoxide and hydrogen. The reaction system is near the equilibrium when leaving the reactor. (c) 2007 Elsevier Ltd. All rights reserved.