Search

The conventional theory of droplet collision with an object can be used only down to a collision efficiency of about 0.1. Therefore, no accurate modelling of in-cloud icing has been possible when droplets are small, wind speed is low, or the object is large. This has also put a limit on the size of an ice accretion on e.g. a power line cable up to which its growth can be simulated. We utilize results of icing wind tunnel experiments and fluid dynamics simulations to explain the differences between the experiments and the theory when the collision efficiency is small. We confirm that the history term in the droplet trajectory equations becomes relevant at small collision efficiencies. Including this term, and applying the integral over the size distribution instead of using the median volume diameter, shows that accurate modelling of icing at very small collision efficiencies is feasible. This makes it possible to estimate large rime ice loads relevant to structural design. [ABSTRACT FROM AUTHOR]

Small wind turbines (SWTs) have been a common option for rural electrification during recent decades. Recently, an application for connecting these devices to the grid was proposed. This requires an AC-coupled configuration, which brings the need for a power converter necessary for connection to the AC bus. This publication analyzes the requirements and commercial availability of such power converters, coming first to a conclusion on the lack of existing electronic power converters for SWTs, mainly in the lowest power range (<1 kW). As a result of this need, PV power converters were proposed, as they are both economically competitive and commercially available. The use of PV power converters for SWT AC-coupled applications is therefore analyzed as well, bringing a second conclusion: their use is possible but not straightforward, as some adaptations have to be taken into account. Finally, a suggested adaptation is proposed, in terms of hardware and software; the first field results of a prototype are presented, and they look very promising. [ABSTRACT FROM AUTHOR]