Energy analysis of hydrogen production from a hybrid wind turbine-electrolyzer system

In this study, the energy performance of hybrid wind-hydrogen system is investigated. In addition to energy performance, a cost analysis of hydrogen production is also carried out for stand-alone system for different PEM electrolyzer capacities. Monthly efficiency variations for wind turbine operation for the total system are calculated and maximum efficiency values obtained as 22 % and 11.9 %, respectively. Energy efficiency of the PEM electrolyzer is determined for different temperature and electric current values. The results show that increasing the working temperature from 35 °C to 75 °C increases the energy efficiency of PEM electrolyzer from 62 % to 70 % at 30 A current. Hydrogen cost is calculated by economic analysis of wind-electrolysis-hydrogen production systems using the present-value method. The lowest cost at 6 m/s wind speed is calculated as 23.6 US$/kg. The size of electrolysis unit gains importance in regions with high annual average wind speed. In this regard, the optimum size is determined as 0.7 kW. The lowest cost at 6 m/s wind speed is calculated as 23.6 US$/kg. Furthermore, economics of wind-hydrogen system not only depends on the cost of wind turbine and electrolyzer but also on the configuration and resources. © Springer International Publishing Switzerland 2014

Review on modelling approaches based on computational fluid dynamics for biomass pyrolysis systems

Modelling is a complex task combining elements of knowledge in the field of computer science, mathematics and natural sciences (fluid dynamics, mass and heat transfer, chemistry). In order to correctly model the process of biomass thermal degradation, in-depth knowledge of multi-scale unit processes is necessary. A biomass conversion model can be divided into three main submodels depending on the scale of the unit processes: the molecular model, single particle model and reactor model. Molecular models describe the chemical changes in the biomass constituents. Single-particle models correspond to the description of the biomass structure and its influence on the thermo-physical behaviour and the subsequent reactions of the compounds released during decomposition of a single biomass particle. The largest scale submodel and at the same time, the most difficult to describe is the reactor model, which describes the behaviour of a vast number of particles, the flow of the reactor gases as well as the interaction between them and the reactor. This chapter contains a basic explanation about which models are currently available and how they work from a practical point of view

Recent advances in annular pathobiology provide insights into rim-lesion mediated intervertebral disc degeneration and potential new approaches to annular repair strategies

The objective of this study was to assess the impact of a landmark annular lesion model on our understanding of the etiopathogenesis of IVD degeneration and to appraise current IVD repairative strategies. A number of studies have utilised the Osti sheep model since its development in 1990. The experimental questions posed at that time are covered in this review, as are significant recent advances in annular repair strategies. The ovine model has provided important spatial and temporal insights into the longitudinal development of annular lesions and how they impact on other discal and paradiscal components such as the NP, cartilaginous end plates, zygapophyseal joints and vertebral bone and blood vessels. Important recent advances have been made in biomatrix design for IVD repair and in the oriented and dynamic culture of annular fibrochondrocytes into planar, spatially relevant, annular type structures. The development of hyaluronan hydrogels capable of rapid in situ gelation offer the possibility of supplementation of matrices with cells and other biomimetics and represent a significant advance in biopolymer design. New generation biological glues and self-curing acrylic formulations which may be augmented with slow delivery biomimetics in microcarriers may also find application in the non-surgical repair of annular defects. Despite major advances, significant technical challenges still have to be overcome before the biological repair of this intractable connective tissue becomes a realistic alternative to conventional surgical intervention for the treatment of chronic degenerate IVDs