Comparative study on the globally optimal performance of cryogenic energy storage systems with different working media

Cryogenic energy storage(CES)has garnered attention as a large-scale electric energy storage technology for the storage and regulation of intermittent renewable electric energy in power networks.Nitrogen and argon can be found in the air,whereas methane is the primary component of natural gas,an important clean energy resource.Most research on CES focuses on liquid air energy storage(LAES),with its typical round-trip efficiency(RTE)being approximately 50%(theoretical).This study aims to explore the feasibility of using different gases as working media in CES systems,and consequently,to achieve a high system efficiency by constructing four steady-state process models for the CES systems with air,nitrogen,argon,and methane as working media using Aspen HYSYS.A combined single-parameter analysis and multi-parameter global optimization method was used for system optimization.Further,a group of key independent variables were analysed carefully to determine their reasonable ranges to achieve the ideal system performance,that is,RTE and liquefaction ratio through a single-parameter analysis.Consequently,a multi-parameter genetic algorithm was adopted to globally optimize the CES systems with different working media,and the energy and exergy analyses were conducted for the CES systems under their optimal conditions.The results indicated the high cycle efficiency of methane and a low irreversible loss in the liquefaction cycle.Moreover,the Joule-Thomson valve inlet temperature and charging and discharging pressures considerably affected the system performance.However,exergy loss in the CES system occurred primarily in the compressor,turbine,and liquefaction processes.The maximum optimal RTE of 55.84%was achieved in the liquid methane energy storage(LMES)system.Therefore,the LMES system is expected to exhibit potential for application in the CES technology to realize the integration of natural gas pipelines with renewable power grids on a large scale.Moreover,the results of study have important theoretical significance for the innovation of the CES technology.

The Role of Voluntary Youth Work in Media in Professional Development of Young People and Documentation of Urban Space in Wroclaw （Poland）

Wroclaw is mostly known for being a university town. In addition, the city is known in Poland for its sports history--basketball and football-and for many cultural events such as the Review of Stage Songs or African Culture Brave Festival. Because of the fact that Wroclaw is one of the largest and most important cities in Poland, it quickly becomes a subject of interest in new media, including the Internet, which becomes a field for community projects. This gives a tremendous opportunity to Wroclaw＇s youth who can participate in the life of Wroclaw, as well as by volunteering learn the basics of journalism and pursue their passions in an active and creative way. In perspective of those fact, the main aim of the planned paper is to describe evolution process of possibilities which Internet media gives to young people who would like to be a journalist. It is also a trial of analysis on how citizen journalism destroyed media voluntary youth work in Wroclaw, where in fact real citizen journalism was started by young people. What is more, paper＇s goal is to present methods of urban space documentation created by teenage journalists to show multicultural spectrum of Wroclaw.