As electronic devices and mainboards become smaller, the need for thermal conductive materials having excellent internal heat dissipation is increasing. In this study, nano thermal grease was ...prepared by mixing in copper nanopowder, which is used as a heat transfer medium in thermal grease, which is a kind of thermal conductive material, with silicon oil. In addition, copper powder was mixed with graphene and alumina, respectively, and the thermal conductivity performance was compared. As a result, the thermal conductivity improved by 4.5 W/m·k over the silicon base, and the upward trend of thermal conductivity increased steadily up to 15 vol. %, and the increasing trend decreased after 20 vol. %. In addition, the increased rate of thermal conductivity from 0 to 5 vol. % and 10 to 15 vol. % was the largest.
The influence of surfactants on the dispersion, stability, and thermophysical characteristics of 0.5%-alumina/distilled water nanofluid was investigated. The study was conducted for a range of ...surfactant blending ratios (0.5, 1.0, and 1.5 wt%) with an amphoteric (LB) or anionic surfactant (SDS or SDBS). The results revealed that the nanofluids have different dispersion, stability, and thermophysical characteristics depending on the type of surfactant and the blending ratio. The amphoteric surfactant exhibited lower absorbance than the anionic surfactants did across a wavelength range of 650–1050 nm and rendered made the alumina nanofluid more unstable. The value of absolute zeta potential when using the anionic surfactants was higher than that of pure alumina nanofluid. The thermal conductivity of the alumina nanofluid with the amphoteric surfactant was higher than that with the anionic surfactants, although all the surfactants reduced the thermal conductivity of the 0.5 wt% alumina nanofluid at 293.15 K. However, regarding surface tension, there were no notable changes in the alumina nanofluids depending on the type of surfactant. Because surfactants have a significant effect on the properties of alumina nanofluids, this study provides a foundation for future applications of such mixtures in a variety of fields.
TiNi shape-memory-alloy thin films can be used as small high-speed actuators or sensors because they exhibit a rapid response rate. In recent years, the transformation temperature of these films, ...manufactured via a magnetron sputtering method, was found to be lower than that of the bulk alloys owing to the small size of the grain. In this study, deposition conditions (growth rate, film thickness, and substrate temperature) affecting the grain size of thin films were investigated. The grain size of the thin film alloys was found to be most responsive to the substrate temperature.
An experimental study was conducted to investigate the effect of surface tension and thermal conductivity of distilled water (DW) and 0.5 wt% alumina nanofluid with or without 1.5 wt% SDBS on a ...two-phase closed thermosyphon (TPCT). The TPCT thermal performance test was performed under varying conditions of filling ratio (30%, 50%, and 70%) and heat input power (5, 10, and 15 W). The surface tension and thermal conductivity of the working fluids were compared to confirm the effect of adding 1.5 wt% SDBS to DW and 0.5 wt% alumina nanofluid at 298 and 293 K, respectively. The surface tension of the DW decreased by approximately 58.7%, while the thermal conductivity decreased by approximately 2.1%. When the thermal conductivities of the DW and alumina nanofluids were almost the same, the decrease in the surface tension of the working fluids, approximately 6.7%, could reduce the thermal resistance. Even with a 58.7% decrease in surface tension and 2.1% decrease in thermal conductivity, the thermal resistance of the TPCT decreased. However, with a 58.3% decrease in surface tension and 5.6% decrease in thermal conductivity, the thermal resistance increased.
In earlier studies, much research has focused on increasing the efficiency of heat exchanger fields. Therefore, in this study, graphene nanofluid was fabricated for use as a heat transfer medium for ...a heat exchanger. Graphene has excellent electrical conductivity, mechanical properties, and heat transfer properties. It is expected that the heat transfer efficiency will be improved by fabricating the nanofluid. However, graphene is prone to sedimentation, because of its cohesion due to van der Waals binding force. In this experiment, a nanofluid was fabricated with enhanced dispersibility by surfactant and the ball-milling process. The zeta potential, absorbance, and thermal conductivity of the nanofluid were measured. As a result, when using the ratio of 2:1 (graphene:sodium dodecyl sulfate (SDS)), a higher thermal conductivity was obtained than in other conditions.
Aluminum alloy itself does not provide sufficient wear resistance for structural parts. Therefore, there is need to protect against the wear issue in practical applications. The objective of this ...study is to investigate different parameters wear characteristics of direct current (dc) magnetron sputtered titanium films on Al7075-T7351 using a wear test. Each parameter has three levels which include the direct current (DC) power, deposition time, and substrate surface roughness. The thickness of the coatings was measured using a focused ion beam scanning electron microscopy (FIB-SEM) from approximately 0.5 μm to 4.4 μm. The titanium thin film coatings were then evaluated using a PD102 wear tester under conditions of 60 rpm, 2N, 30 minutes. As a result, the coefficient of friction of the coating was reduced, and the wear resistance of the coating was improved as the applied power and deposition time increased. The hardness of titanium-coated specimens is increased significantly up to 272 HV, while the hardness of uncoated specimens was 160 HV.
High-thermal conductivity enhancement of nanofluid is one of the promising topics of the nanoscience research field. This work reports the experimental study on the preparation of graphene (GN) and ...multi-walled carbon nanotubes (MWCNTs) based nanofluids with the assistance of sodium dodecyl benzene sulfonate (SDBS) and sodium dodecyl sulfate (SDS) surfactants, and their thermal behaviors. The present work suggests not a solution, but a solution approach and deduces a new conclusion by trying to resolve the agglomeration problem and improve the dispersibility of nanoparticles in the base fluid. The analysis results of FESEM, thermal conductivity, diffusivity, effusivity and heat transfer coefficient enhancement ratio of nanofluid with surfactants SDS and SDBS expose strong evidence of the dispersing effect of surfactant on the making of nanofluid.
Ternary Ti-Nb-Zr alloys were prepared by a magnetron sputtering method with porous structures observed in some of them. In bulk, in order to control the porous structure, a space holder (NH₄HCO₃) is ...used in the sintering method. However, in the present work, we show that the porous structure is also dependent on alloy composition. The results from Young's modulus tests confirm that these alloys obey d-electrons alloy theory. However, the Young's modulus of ternary thin films (≈80⁻95 GPa) is lower than that for binary alloys (≈108⁻123 GPa). The depth recovery ratio of ternary Ti-Nb-Zr thin films is also higher than that for binary β-Ti-(25.9⁻34.2)Nb thin film alloys.
Nowadays the two-phase closed thermosyphon (TPCT) has been widely used as an important heat transfer medium for passive cooling systems. Since the enhancement of the performance of electronic device ...releases a considerable amount of heat, the development of working fluids which can improve thermal performance of the TPCT is necessary. In this experiment, two different type of MWCNT nanofluids were successfully made by using ball-mill process and alkaline treatment. The morphological and structural analysis were conducted by using transmission electron microscope (TEM), fourier-transform infrared spectroscopy (FT-IR). Also thermal conductivity of modified MWCNT nanofluids were investigated by introducing transient hot wire method. The results of TEM, FT-IR and thermal conductivity showed that the MWCNTs were successfully functionalized as well as had higher thermal conductivity. The TPCT was fabricated with copper tube and total length of the TPCT is 700mm, in which the evaporator section, the adiabatic section and the condenser section are 150mm, 400mm, and 150mm, respectively. The experiment of the thermal performance of the TPCT was evaluated by introducing RMS value of the temperature of the evaporation section, thermal resistance and heat transfer coefficient at five different filling ratios, 10%, 30%, 50% and 70% by ratcheting up heat loads in five levels, 5W, 8W, 10W, 13W and 15W. The overall results showed that the both of modified MWCNT nanofluids can decrease thermal resistance and increase the heat transfer coefficient, especially at 10% filling ratio with 8W. M-CNT nanofluid can even enhance the thermal performance of TPCT at 30% filling ratio with all heat loads.
Purpose
The purpose of this study is structural stability evaluation of umbilical winch. In accordance with the recent trend for developing natural resources, high-technology equipment on exploration ...ships is becoming more technologically advanced. One such piece of high-technology equipment is the umbilical winch. In this study, the umbilical winch is divided into two parts (drum and winch), where each is respectively designed with three dimensional models using CATIA, and dynamic simulation and structural analysis are performed using ANSYS.
Design/methodology/approach
In this paper, the winch is divided into two parts for finite element analysis, the drum and whole winch model, and the parts are designed as three-dimensional models except for some small parts, such as bolt holes. Dynamic simulation and structural analysis are then performed using ANSYS. The analysis results ensure the reliability of the design methods and will be used in the domestic localization of remote operated vehicle (ROV) launch and recovery systems (LARS).
Findings
The strain is identified from the results, but it is very small. Some stress is concentrated at the lower corner of the drum, but the maximum stress value is lower than the allowable stress; therefore, the structure has no impact on the strain and stress. Thus, it is determined that the designed structure is safe. The results ensure the reliability of the design methods and will be used in the domestic localization of ROV LARS.
Originality/value
Previous studies focus on the static and mechanic problems of the winch by considering winch and drum breakage in the umbilical winch system. However, ships have a nonlinear motion characteristic with six degrees of freedom according to the constant influence of the external environment. In addition, from a design perspective, the dynamic characteristics (e.g. the ship’s motions) are more important than the static characteristics. Thus, the authors focus on winch stability securement with variable loads, such as ships moving, wave disturbance and other such important environment conditions.
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