Largest Exergy Loss Research Articles

Analysis of entropy generation and exergy loss during combustion

The analysis of entropy generation and exergy loss is used for optimizing the performance of energy conversion systems such as gas turbines. Exergy loss in the combustor of 20%–30% is the largest of all component losses in the gas turbine systems. The sources of the large exergy loss during the combustion process can be evaluated by analyzing local entropy generation of irreversible processes. Multicomponent flow with chemical reactions such as combustion involves four irreversible processes: viscous dissipation, heat conduction, mass diffusion, and chemical reaction. In this study, we analyzed local entropy generation and exergy loss due to these processes in premixed and diffusion flames in order to clarify the reasons for large exergy destruction during combustion processes, taking into account detailed chemical kinetics and multicomponent diffusion. The effects of fuels, equivalence ratio, and inlet fluid temperature on local entropy generation and exergy loss were evaluated for premixed flames. Chemical reaction is the dominant process for exergy loss in premixed flames, and the fraction of it changes in relation to the flame structure modification and temperature. On the contrary, for diffusion flames, heat conduction instead of chemical reaction is the major process for exergy loss.

New Graphical Method for Representing Characteristic Features of Extraction

The effect of solvent species (i.e., cyclohexanol, nitromethane, and α-furan aldehyde) on the extraction of acetic acid from its aqueous solution is analyzed with a new graphical method using a material-utilization diagram (or MUD) for each individual component. The abscissa and ordinate of MUD are a flow rate and a logarithm of concentration, respectively. Their scales are properly set to have a common scale of area on MUDs. This new method graphically and precisely provides important properties such as changes in concentration of each component in two phases, the distribution coefficient, selectivity, and exergy loss. MUDs for both water and acetic acid reflect the effect of the solvent species. They depict a factor of selectivity attained in the system. Changes in the concentration of a solvent give rise to a large exergy loss, indicating the importance of the solvent selection. The small exergy loss is accomplished by cyclohexanol in a countercurrent multistage scheme. This relates to a small amount o...

96/01949 District heating and cooling systems

District energy systems can potentially decrease the CO2 emissions linked to energy services, thanks to the implementation of large polygeneration energy conversion technologies connected to buildings over a network. To transfer the energy from these large technologies to the users, conventional district energy systems use water with often two independent supply and return piping systems for heat and cold. However, sharing energy or interacting with decentralised heat pump units often results in relatively large heat transfer exergy losses due to the large temperature differences that are economically required from the water network. Besides, the implementation of two independent supply and return piping systems for heat and cold, results in large space requirements in underground technical galleries. Using refrigerants as a district heating or cooling fluid at an intermediate temperature could alleviate some of these drawbacks. A new system has been developed, that requires only two pipes, filled with refrigerant, to meet heating, hot water and cooling requirements. Because of the environmental concerns about conventional refrigerants, CO2, a natural refrigerant, used under its critical point, is considered an interesting candidate. A comparative analysis shows that both in terms of exergy efficiency and costs the proposed CO2 network is favourable.

General theory of exergy-balance analysis and application to solar collectors

Valuable results have been obtained by applying exergy concepts to thermodynamic systems. Second-law analyses are not easily applied to the overall system. The general theory of exergy balance is established and applied to solar collectors. Large and small exergy losses are identified for optimum design.

焼成および非焼成ペレットを使用した還元鉄製造プロセスのエクセルギー評価

In order to make a clear evaluation of overall energy requirement for the production system of directly reduced iron through pellet from iron ore powders, exergy analysis was applied to the two systems. The first one consists of pelletizing, firing and reduction processes (Fired pellets method) and the second one includes pellets curing process instead of firing process (Cement bonded pellets method).Being compared with enthalpy balance, exergy analysis has two advantages in that the exergy expresses the quality of energy and evaluates different kinds of energy like chemical, thermal, pressure, mixing energies and so on by a unified measure.As a result of exergy analysis, fired pellets lose less exergy than cement bonded pellets in the reduction process in a shaft furnace. As the overall system, however, exergy requirement in the cement bonded pellets method is about 50% of that in the fired pellets method. This marked difference is caused by the large exergy loss in the firing process. Furthermore, exergy loss in the production of cement bonded pellets will be decreased by decreasing the amount of cement added as binder.