Application of hybrid friction stir channeling technique to improve the cooling efficiency of electronic components

Hybrid friction stir channeling (HFSC) is a new friction stir-based method for producing internal, closed channels created simultaneously during welding of multiple metal plates. Differently from conventional friction stir channeling, that is only able to produce channels in a monolithic component, HFSC can be applied to complex structural systems involving multiple components made of similar or dissimilar materials. In this study, the channels manufactured by HFSC were open in a structural system made of AA5083, with one base plate of 5 mm thick, and one overlapping plate of 8 mm thick, used as a rib, containing the channel along conformal cooling path. The thermal performance of the HFSC channel is compared with a conventional channel, with similar shape and path, produced by milling. The channels being tested are part of an electronic device containing multiple heat sources. The HFSC channel presents 30 to 40% lower steady-state temperature and 33% higher cooling rate during the transient period than thoseof the milled version. Compared with the milled channel, the heat extraction capacity, per unit of mechanical pumping power, is higher for the HFSC channel. Surface roughness, microhardness, and microstructural analysis of HFSC channels are investigated to characterize the HFSC channel.Peer reviewe

Long-term changes in space weather effects on the Earth’s ionosphere

Abstract Certain limitations that have been identified in existing ionospheric prediction capabilities indicate that the deeper understanding and the accurate formulation of the ionospheric response to external forcing remain always high priority tasks for the research community. In this respect, this paper attempts an investigation of the long-term behavior of the ionospheric disturbances from the solar minimum between the solar cycles 23 and 24 up to the solar maximum of solar cycle 24. The analysis is based on observations of the foF2 critical frequency and the hmF2 peak electron density height obtained in the European region, records of the Dst and AE indices, as well as measurements of energetic particle fluxes from NOAA/POES satellites fleet. The discussion of the ionospheric behavior in a wide range of geophysical conditions within the same solar cycle facilitates the determination of general trends in the ionospheric response to different faces of space weather driving. According to the evidence, the disturbances in the peak electron density reflect mainly the impact of geoeffective solar wind structures on the Earth’s ionosphere. The intensity of the disturbances may be significant (greater than 20% with respect to normal conditions) in all cases, but the ionospheric response tends to have different characteristics between solar minimum and solar maximum conditions. In particular, in contrast to the situation in solar maximum, in solar minimum years the solar wind impact on the Earth’s ionosphere is mainly built on the occurrence of ionization increases, which appear more frequent and intense than ionization depletions. The ionization enhancements are apparent in all local time sectors, but they peak in the afternoon hours, while a significant part of them seems not related with an F2 layer uplifting. Taking into account the main interplanetary drivers of the disturbances in each case, i.e. high speed streams (HSSs) and corotating interaction regions (CIRs) in solar minimum and coronal mass ejections (CME) in solar maximum, we argue that the identified tendency may be considered as evidence of the ionospheric response to different solar wind drivers

Small Wind Turbines on Pylon Powering Base Transceiver Stations: A Study of Radio Interactions

International audienceIn radio cellular networks, base transceiver station (BTS) powered by hybrid energy (solar/wind/fuel) has become an efficient and attractive solution to help reduce the use of fossil fuel based energy. Such hybrid energy BTSs have been deployed in remote areas with small wind turbines (SWT) located on top of BTS pylon or on a separate mast. Because megawatt WTs or wind farm disturb various radio systems (radars, TVs), the proximity between SWT and BTS raises questions about electromagnetic compatibility. In the context of the OPERA-Net2 European project, these questions are being studied through this original work. Based on the conclusions, for the first time ever installation recommendations could be proposed to reduce the radio impact of SWTs. Compared to megawatt WTs, SWTs whose nominal power is in the range of 1.5 - 7.5 kW are much more diverse (shapes, materials). Thus, a representative model (RSWT) has been designed. Its size was optimized to improve the match with realistic models, notably the Nheowind 3D100 wind turbine (NHEOLIS - IDSUD ENERGIES). A prototype of the RSWT with dimensions scaled down by 10 was manufactured. Based on the RCS of this prototype measured in an anechoic chamber at 9 GHz and 17 GHz, the scattering (or RCS) of the designed RSWT at radio cellular frequencies could be determined. Comparisons between simulation and measure-ment at these frequencies show good agreement thus validate the RSWT modelling