Experimental investigation of non-uniform heating effect on flow boiling instabilities in a microchannel-based heat sink

Copyright @ 2011 ElsevierTwo-phase flow boiling in microchannels is one of the most promising cooling technologies for coping with high heat fluxes produced by the next generation of central processor units (CPUs). If flow boiling is to be used as a thermal management method for high heat flux electronics it is necessary to understand the behaviour of a non-uniform heat distribution, which is typically the case observed in a real operating CPU. The work presented is an experimental study of two-phase boiling in a multi-channel silicon heat sink with non-uniform heating, using water as the cooling liquid. Thin nickel film sensors, integrated on the back side of the heat sinks were used in order to gain insight related to temperature fluctuations caused by two-phase flow instabilities under non-uniform heating. The effect of various hotspot locations on the temperature profile and pressure drop has been investigated. It was observed that boiling inside microchannels with axially non-uniform heating leads to high temperature non-uniformity in the transverse direction.This research was supported by the UK Engineering and Physical Sciences Research Council through grant EP/D500109/1

Experimental investigation of non-uniform heating on flow boiling instabilities in a microchannels based heat sink

Two-phase flow boiling in microchannels is one of the most promising cooling technologies able to cope with high heat fluxes generated by the next generation of central processor units (CPU). If flow boiling is to be used as a thermal management method for high heat flux electronics it is necessary to understand the behaviour of a non-uniform heat distribution, which is typically the case observed in a real operating CPU. The work presented is an experimental study of two-phase boiling in a multi-channel silicon heat sink with non-uniform heating, using water as a cooling liquid. Thin nickel film sensors, integrated on the back side of the heat sinks were used in order to gain insight related to temperature fluctuations caused by two-phase flow instabilities under non-uniform heating. The effect of various hotspot locations on the temperature profile and pressure drop has been investigated, with hotspots located in different positions along the heat sink. It was observed that boiling inside microchannels with non-uniform heating led to high temperature non-uniformity in transverse direction

Grid Approach to Path Integral Monte Carlo Calculations

Approach taken for the gridification of the developed Monte Carlo code for calculation of path integrals is described. Brief introduction to path integrals and Grids is given, and details on the implementation of SPEEDUP in the Grid environment are described. The numerical results obtained by the gridified version of the application are shortly presented, demonstrating its usefulness in the research in physics and related areas

Effect of the Position in the Build Chamber on the Fatigue Strength of Additively Manufactured Maraging Steel MS1

The quality of additively produced parts and the achievable mechanical response may be affected by several factors, such as build orientation, heat treatment, or machining. A further rarely investigated factor is the position of the built part in the chamber with respect to inert gas flow. Previous studies have highlighted that the interaction between gas flow and laser track may induce an intense vaporization with consequent lack of fusion, particle entrainment, drop in density and denudation of the produced part, which is likely to detrimentally affect mechanical properties. This study addresses the effect of part position on the fatigue strength of heat-treated maraging steel MS1 produced by an EOSINT M280 machine in a nitrogen environment. Novelty arises from the lack of studies in this field, especially under fatigue. A factorial plan with subsequent statistical analysis highlighted that positioning the part upstream with respect to the gas flow leads to a slightly lower fatigue strength; however, no significant differences are observed. The failure mode, involving initiation from subsurface porosities of the same size, is also unaffected. Finally, a fatigue limit of 26% of the ultimate tensile strength is found, which is consistent with previous outcomes

Fatigue response of additively manufactured as-built 15-5 PH stainless steel and effects of machining and thermal and surface treatments

Additively produced 15-5 PH stainless steel has wide industrial applications, but the combined effects of heat treatment, machining, and shot-peening and their order have not been deeply investigated. This topic is addressed here by a 2-by-3 experimental plan that has involved S–N curve and fatigue limit determination, using vertically built cylindrical samples, tested under rotating bending. The obtained responses have been analyzed by an ANOVA-based statistical approach for comparison of fatigue trends. Results indicate that heat treatment without machining may be even detrimental for fatigue due to embrittlement. Conversely, machining with subsequent shot-peening, even without heat treatment, has a remarkable impact and leads to a doubled fatigue strength with respect to as-built material. This strength is also quite close to that achievable for wrought material. The study has been completed by micrography and fractography, to reveal the dependence of microstructure, crack initiation sites, and failure mode on the performed treatments

Fatigue response of additively manufactured Maraging Stainless Steel CX and effects of heat treatment and surface finishing

This paper deals with the novel topic of the fatigue response of additively manufactured Maraging Stainless Steel CX. A two-by-two factorial plan was arranged, to experimentally assess the effects of heat treatment and machining on the fatigue strength in both finite and infinite life domains. The two factors were regarded as on–off, taking the untreated unmachined condition as a reference for comparisons. Cylindrical specimens with vertical build orientation were involved in the fatigue campaign under four-point rotating bending. The results indicate that the fatigue strength may be remarkably incremented (up to five times) with respect to the as received conditions, especially thanks to surface smoothing and taking advantage of a very low porosity level. Heat treatment strengthening mechanisms were also interpreted in the light of optical and electron microscope observations. Fatigue enhancement arises from precipitate size increment throughout the conducted heat treatment, although the fracture mode turns to be more brittle

Advantages and Drawbacks of Additive Manufacturing

- This paper presents some various imperfections that can occur during Direct Metal Laser Sintering (DMLS) and their effects on part quality. Direct Metal Laser Sintering is one of the Additive Manufacturing (AM) technologies that enables fast production of an accurate, functional, complex shape parts and tools, without additional tooling, directly from 3D CAD model. This process is based on layer by layer manufacturing, where the fusion of the metal powder is performed by selective melting with laser beam. The laser beam moves and scans area that correspond to section of the part for the specific layer. In the DMLS the part is built layer by layer, where the process of the melting and solidification occur in small volume in relatively short time. Thanks to this kind of approach, the DMLS has much less limitations than the subtractive methods of part production. However, the production in the layers has some drawbacks, which can have a significantly influence on the part geometry, structural errors and part imperfections. Some of the advantages as well and drawback of the DMLS of metal parts has been presented in this paper.The authors wish to acknowledge the support of European Commission through the project “Advanced design rules for optimal dynamic properties of additive manufacturing products – A_MADAM”, which has received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No 734455.Publishe

Black Holes on Cylinders

We take steps toward constructing explicit solutions that describe non-extremal charged dilatonic branes of string/M-theory with a transverse circle. Using a new coordinate system we find an ansatz for the solutions with only one unknown function. We show that this function is independent of the charge and our ansatz can therefore also be used to construct neutral black holes on cylinders and near-extremal charged dilatonic branes with a transverse circle. For sufficiently large mass $M > M_c$ these solutions have a horizon that connects across the cylinder but they are not translationally invariant along the circle direction. We argue that the neutral solution has larger entropy than the neutral black string for any given mass. This means that for $M > M_c$ the neutral black string can gain entropy by redistributing its mass to a solution that breaks translational invariance along the circle, despite the fact that it is classically stable. We furthermore explain how our construction can be used to study the thermodynamics of Little String Theory.Comment: latex, 68 pages, 4 figures. v2: Typos fixed, argument about \chi corrected in sec. 7.4, discussion of space of physical solutions corrected and clarified in sec. 9; v3: v=\pi clarified, typos fixed, figure 1 change

Effects of Machining on the Fatigue Strength of Steel Components Produced by DMLS

Direct metal laser sintering (DMLS) is the additive manufacturing (AM) technology that allows production of metal machine components with complex geometry. Due to the layer-wise production principle, its products usually require post-processing, predominantly machining, to achieve uniform or requested surface quality. Given the increasing application of DMLS technology in industry and insufficient published data about the effects of machining on the fatigue properties of steel, the focus of this research is put to investigation of the influence of thickness of allowance for machining to fatigue strength of DMLS products. Previous studies revealed significant differences in the mechanical behaviour of samples made of different kinds of steels, both during production and testing. Unlike the samples made from maraging steel, the samples made from stainless steel often deformed during cooling due to the strong residual stresses, and revealed dependence of mechanical properties on orientation during production process. To improve the understanding of the differences, fatigue testing according to ISO 1143 was performed on samples manufactured from two kinds of steel, maraging steel 1.2709 and stainless steel 15-5. Twelve sets of samples were tested with the aim to investigate the effects of machining allowance and build orientation according to an extensive DoE experimental plan.The authors wish to acknowledge the support of European Commission through the project “Advanced design rules for optimal dynamic properties of additive manufacturing products – A_MADAM”, which has received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No 734455.Publishe