1,721,019 research outputs found
Effect of Particle Size Distribution on Laser Powder Bed Fusion Manufacturability of Copper
Get PDFOne of the major benefits of the Laser Powder Bed Fusion (LPBF) technology is the possibility of fabrication of complex geometries and features in only one-step of production. In the case of heat exchangers in particular, this is very convenient for the fabrication of conformal cooling channels which can improve the performance of the heat transfer capability. Yet, obtaining dense copper parts printed via LPBF presents two major problems: the high reflectivity of 1 μm (the wavelength of commonly used laser sources) and the high thermal conductivity of copper that limits the maximum local temperature that can be attained. This leads to the formation of porous parts.
In this contribution, the influence of the particle size distribution of the powder on the physical and mechanical properties of parts produced via LPBF is studied. Three copper powders lots with different particle size distributions are used in this study. The effect on densification from two laser scan parameters (scan speed and hatching distance) and the influence of contours scans on the lateral surface roughness is reported. Subsequently, samples manufactured with the optimal process parameters are tested for thermal and mechanical properties evaluation
Production quality controls and geometric characterization of the IFMIF-RFQ modules via the usage of a Coordinate Measuring Machine
No full textThe RFQ of the IFMIF/EVEDA project (Pérez et al., 2015) [1] is a 9.8 m long cavity able to accelerate a 125 mA deuteron beam from the input energy of 50 keV/u to the output energy of 2.5 MeV/u. Such RFQ operates at the frequency of 175 MHz and is composed of 18 mechanical modules approximately 0.55 long each (Pepato et al., 2010) [2]. The RFQ realization involves the I.N.F.N. Sections of Padova, Torino and Bologna, as well as the Legnaro National Laboratories (L.N.L.). The metrological measurements via CMM (Coordinate Measuring Machine) provided to be a very effective tool both for quality controls along the RFQ production phases and in the reconstruction of the cavity geometric profile for each RFQ module. The scans in the most sensitive regions with respect to RF frequency, such as modulation, tips, base-vane width and vessel height provided the values of the cavity deviations from nominal geometry to be compared with design physic-driven tolerances and with RF measurements. Moreover..
Local heat transfer measurements during in-tube condensation of refrigerants in a new test section made by additive manufacturing
Get PDFCondensation process inside small diameter channels is nowadays of considerable interest in refrigeration, heat
pumps and cooling applications. The reduced cross-sectional area of the channels enables compact heat exchangers design but it makes local heat transfer coefficient measurements more difficult during condensation.
High-quality data collection is essential for developing and validating predictive models for heat exchangers’
design. To address this challenge, a novel test section having a 2.76 mm inner diameter channel was built by
additive manufacturing for accurate local heat transfer coefficient measurements with refrigerants and using
water as secondary fluid for heat rejection. The design, optimized by computational fluid dynamics (CFD)
simulations, resulted in a complex finned geometry of the water side. The fabrication of the test section was
achieved using laser powder bed fusion with AlSi10Mg alloy. Given the limited number of experimental data
available for the low-GWP (Global Warming Potential) refrigerants in small-diameter channels, condensation
tests were performed with R1234ze(E) and R1233zd(E) at 40 ◦C saturation temperature and mass flux ranging
from 30 to 350 kg m-2 s-1. Results at 0.5 vapour quality show that, R1233zd(E) achieves 62 % higher heat transfer
coefficients than R1234ze(E) at high mass flux (330–350 kg m-2 s-1) and 18 % higher at low mass flux (60 kg m-2 s
-1). High-speed videos revealed distinct flow patterns that can be linked to the heat transfer coefficient trends.
Finally, the accuracy of selected heat transfer coefficient correlations was assessed, showing good predictive
capability for R1234ze(E) but lower accuracy in the case of R1233zd(E)
Effects of micro-sized TiC on the cracking behavior of additively manufactured tungsten
Get PDFIn this study, the effects of the addition of TiC micro-sized particles on the printability of tungsten via Laser-Based Powder Bed Fusion are presented. Micrographic analyses were carried out on pure tungsten and W-TiC samples to study the evolution of the microstructure. It is well known that additively manufactured tungsten has a high cracking tendency due to the rapid solidification rate during the process, and the intrinsic brittleness of the grain boundaries. The addition of titanium carbide helped to reduce the cracks within the material, and microcracks were completely eliminated. However, some segregation areas of titanium were noticed, and this phenomenon is strongly correlated to the formation of voids in the metal
A New Efficient Mirror Cooling for the Transmission Line of Fusion Reactor ECH Systems Based on Triply Periodic Minimal Surfaces
Get PDFAn innovative cooling strategy for the mirrors of the transmission line of the electron cyclotron heating (ECH) of a fusion research reactor, the divertor tokamak test (DTT) facility, is presented and investigated here based on triply periodic minimal surfaces (TPMSs). After the check on the manufacturability of gyroid and Split-P lattices of unit cell size ranging from 3 to 8 mm, extensive numerical investigations by conjugate heat transfer analyses have been performed. The heat removal capability has been assessed together with the pressure drop for all heat sinks. The temperature field in the mirror has been evaluated and used for the assessment of the deformation of the mirror reflective surface. The results show that all tested TPMSs are highly efficient in the heat removal, with low hotspot temperatures, minimal pressure drop, and low deformation of the reflective surface
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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