Boiling heat transfer enhancement by nano-particles-assembled bi-porous layers

Nanoparticles-assembled bi-porous structure is newly proposed as boiling heat transfer enhancement technique. In order to assemble nanoparticles onto a heat transfer surface as a thin layer, a boiling adhesion method (BAM) is originally introduced in which, water or water/ethanol solution with mono-dispersed nanoparticles is dropped or sprayed onto a high temperature surface, and then the nanoparticles deposit onto the heat transfer surface during the boiling. In addition to that, it is expected that boiling bubbles can produce micro or milli scale of larger pores at the same time, which enables to fabricate bi-porous structure. Please download the full abstract below

Heat Transfer Enhancement Using Unidirectional Porous Media under High Heat Flux Conditions

In this chapter, new heat transfer enhancement technologies with unidirectional porous metal called “EVAPORON” and “Lotus’ Breathing” are introduced to remove and manage heat from high heat flux equipment. The unidirectional porous metals introduced here can be easily fabricated by unique techniques such as mold casting technique, explosive welding technique, and 3D printing technique. First of all, many kinds of porous media, which have been introduced by the author so far as a heat transfer promoter, are compared each other to clarify what kind of porous metal is more suitable for high heat flux removal and cooling by focusing on the permeability and the effective thermal conductivity. For the practical use of the unidirectional porous copper with high permeability and high thermal conductivity, at first, heat transfer performance of two-phase flow cooling using a heat removal device called “EVAPORON” is reviewed aiming at extremely high heat flux removal beyond 10 MW/m2. We have been proposing this device with the unidirectional porous copper fabricated by 3D printing technique as the heat sink of a nuclear fusion divertor and a continuous casting mold. Second, two-phase immersion cooling technique called “Lotus’ Breathing” utilizing “Breathing Phenomenon” is introduced targeting at thermal management of various electronics such as power electronics and high performance computers. The level of the heat flux is 0.1 MW/m2 to 5 MW/m2. In addition, as the other heat transfer enhancing technology with unidirectional porous metals, unidirectional porous copper pipes fabricated by explosive welding technique are also introduced for heat transfer enhancement of single-phase flow

Application of nanoparticles-assembled bi-porous structures to power electronics cooling

Nanoparticles-assembled bi-porous structure is newly proposed and its potential to enhance the boiling heat transfer is evaluated in order to develop a new cooling device toward 300W/cm2 of on-vehicle inverter cooling. In order to assemble nanoparticles on to a heat transfer surface as a thin layer, a boiling adhesion method (BAM) is originally introduced in which, water or water/ethanol solution with mono-dispersed nanoparticles is dropped or sprayed onto a high temperature surface, and then the nanoparticles deposit onto the heat transfer surface during the boiling. In addition to that, it is expected that boiling bubbles can produce micro or milli scale of pores at the same time. In order to evaluate the applicability of the nanoparticles-assembled bi-porous structures, droplet behavior on a high temperature surface is visualized with a high speed camera The experimental results show that the boiling adhesion method can produce multi-scale pore structures composed of nano-scale pores and micro-scale pores and that the water droplet intensely boils and evaporates on a high temperature of a wall with nanoparticles-assembled bi-porous layer even under Leidenfrost conditions, which proves that the nanoparticles-assembled bi-porous structure enables the increase in both the critical heat flux and the boiling heat transfer in a nucleate boiling regim

Interactions of the dynein-2 intermediate chain WDR34 with the light chains are required for ciliary retrograde protein trafficking

The dynein-2 complex drives retrograde ciliary protein trafficking by associating with the intraflagellar transport (IFT) machinery, containing IFT-A and IFT-B complexes. We recently showed that the dynein-2 complex, which comprises 11 subunits, can be divided into three subcomplexes: DYNC2H1–DYNC2LI1, WDR34–DYNLL1/DYNLL2–DYNLRB1/DYNLRB2, and WDR60–TCTEX1D2–DYNLT1/DYNLT3. In this study, we demonstrated that the WDR34 intermediate chain interacts with the two light chains, DYNLL1/DYNLL2 and DYNLRB1/DYNLRB2, via its distinct sites. Phenotypic analyses of WDR34-knockout cells exogenously expressing various WDR34 constructs showed that the interactions of the WDR34 intermediate chain with the light chains are crucial for ciliary retrograde protein trafficking. Furthermore, we found that expression of the WDR34 N-terminal construct encompassing the light chain–binding sites but lacking the WD40 repeat domain inhibits ciliary biogenesis and retrograde trafficking in a dominant-negative manner, probably by sequestering WDR60 or the light chains. Taken together with phenotypic differences of several WDR34-knockout cell lines, these results indicate that incorporation of DYNLL1/DYNLL2 and DYNLRB1/DYNLRB2 into the dynein-2 complex via interactions with the WDR34 intermediate chain is crucial for dynein-2 function in retrograde ciliary protein trafficking

Proposal of utilizing uni-directional porous copper for extremely high heat flux removal

This paper proposes new heat removal devices utilizing uni-directional porous copper against extremely high heat flux conditions. Before designing those, we discuss some key parameters of porous media to enable a high heat flux removal over 10 MW/m2 at a low flow rate of water, which are effective thermal conductivity, permeability, liquid supply to a heat transfer surface, and contact thermal resistance between the porous medium and the heat transfer surface. These discussions indicate utilizing the uni-directional porous media as shown in Fig. 1 from the view point of its higher thermal conductivity, direct supply of cooling liquid toward the heat transfer surface, discharge of vapor, reduction in flow resistance and the thermal contact resistance Please download the full abstract below

High-voltage scanning transmission electron microscopy: A tool for structural characterization of micrometer-thick specimens

Herein, the advantages of high-voltage scanning transmission electron microscopy (STEM) as a tool for structural characterization of micrometer-thick specimens are reported. Dislocations introduced in a wedge-shaped Si crystal were clearly observed by bright-field STEM operating at 1 MV. Many of the dislocations were straight and parallel to the 〈110〉, 〈112〉 or 〈113〉 directions. The widths of the dislocations in the STEM images were almost constant at 13–16 nm (i.e., 4–5 pixels) in the thickness range between 1 and 7.5 µm. The latest high-voltage STEM instrumentation is thus useful for imaging crystal defects in micrometer-thick materials, and enables multi-scale fields of view from a few nanometers squared to over 100 µm2

Maximum usable thickness revisited: Imaging dislocations in Si by modern high-voltage scanning transmission electron microscopy

This is the Accepted Manuscript version of an article accepted for publication in Japanese Journal of Applied Physics. IOP Publishing Ltd are not responsible for any errors or omissions in this version of the manuscript or any version derived from it. The Version of Record is available online at https://doi.org/10.7567/JJAP.56.100304.We have quantitatively evaluated the usable thickness of specimens in scanning transmission electron microscopy (STEM) at 1MV using a wedgeshaped Si(110) single crystal including artificially introduced high-density dislocations. The width of dislocation images was employed as a criterion for the quantitative evaluation of usable thickness. Superior usable thickness in STEM than in TEM was found; the obtained results were 14.7μm for STEM and 5.8μm for TEM. In particular, in STEM, dislocations can be observed as thin lines with 10-15nm width in the thickness range up to 10 μm. The latest high-voltage STEM is useful for imaging crystal defects in thick semiconductors