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• Vertical downward condensation plate heat exchanger. • Electrochemical etching generates microscale roughness. • Enhance thermal-hydraulic performance of plate heat exchanger. • Analyze effect of heat flux, mass flux, vapor quality and surface roughness on heat transfer. • Multi-objective generic algorithm optimized designed roughness. • Pareto front solutions for maximizing performance. This research employed electrochemical etching to generate microscale roughness on a plate heat exchanger (PHE) thereby enhancing condensation heat transfer in a vertical downward flow. The effects of the mass flux, vapor quality, heat flux, saturation temperature and microscale surface roughness on the condensation heat transfer coefficient (HTC) and frictional pressure drop (FPD) of R-513a flowing through a PHE was experimentally investigated. Experimental measurements were made under various heat fluxes of 5–15 kW/m2, mass fluxes of 60–80 kg/m2s, saturation temperatures of 40–50 °C, and mean vapor qualities of 0.1–0.7. HTC increased by up to 28, 26, 74, and 32.5 % as the heat flux, mass flux, average quality, and microscale surface roughness were respectively increased, but decreased by 19 % with the saturation temperature. FPD increased as the mass flux and average vapor quality increased, whereas it was reduced as the refrigerant saturation temperature increased. In contrast, the heat flux had little to no influence on FPD. Correlations for predicting the Nusselt number and friction factor were postulated by considering influential dimensionless numbers during heat transfer. Maximizing the Nusselt number and thermal performance factor was ultimately resolved using a multi-objective genetic algorithm to find a Pareto front solution. Consequently, the optimal surface roughness was found to be 9.94 μm. [ABSTRACT FROM AUTHOR]

A hydrophobic surface promotes bubble nucleation due to hydrophobicity. Thus, a hydrophobic surface has a higher boiling heat transfer coefficient (BHTC) than a hydrophilic surface. In contrast, a hydrophilic surface supplies liquid to a heating surface. This mechanism enhances the critical heat flux (CHF). In this respect, there is a trade-off between a hydrophobic and a hydrophilic surface. In this study, we examined the effect of heterogeneous wetting surfaces on flow boiling performance. We designed four types of hydrophobic stripes; there are two directions, parallel and crossed to the flow, and the width (the pitch) of the hydrophobic stripes in each direction is 3 or 1 mm. In the macro-channel, the flow boiling performance on the surfaces depended on the patterns. The parallel striped surfaces had higher CHFs than the crossed striped surfaces. In addition, the narrow patterns in each direction had higher CHFs than the wide patterns. The difference in BHTC among the parallel striped surfaces was not large, but the difference in BHTC among the crossed striped surfaces was considerable. A visualization technique revealed that the merging and confinement of bubbles were key factors in explaining the boiling characteristics. Considering the drag coefficient and bubble breakup, we suggest appropriate designs of the hydrophobic pattern for the improvement of BHTC and CHF in the flow boiling performance. [ABSTRACT FROM AUTHOR]

A smart surface that is a TiO 2 -coated surface (TCS) is a hydrophobic surface initially, but becomes a hydrophilic surface when heated. Therefore, such a surface can be used to enhance both boiling heat transfer (BHT) and critical heat flux (CHF) in pool boiling. In the present study, the time effect of the wetting transition of TCS was focused on. The CHF on TCS was enhanced more when the holding time of the heat flux in high-temperature regime was increased. By observing changes in contact angles on TCS through heat treatment in air, it was found that the wetting transition was affected not only by the temperature, but also by the time. Thus, a variation of the receding contact angle was correlated in the form of an exponential function. The suggested empirical correlation includes temperature and time, and it describes the transition of the receding contact angle. The correlation was also used to predict the CHF on TCS in pool boiling. As a result, CHFs on TCS could be explained using the correlation. [ABSTRACT FROM AUTHOR]

Modified surfaces with graphene coatings were evaluated experimentally to enhance nucleate boiling performance on an orientated surface, from upward to downward (0°, 45°, 90°, 120°, 135°, 150°, 160°, and 170°). Two-dimensional (2D) laminate and three-dimensional (3D) porous graphene were prepared for surface modification, and their boiling heat transfer coefficient (BHTC) and critical heat flux (CHF) values were evaluated according to orientation angle. Moreover, their boiling structures were observed and analyzed using high-speed visualization. The results showed that the surfaces coated with 2D and 3D graphene had enhanced BHTC and CHF performance in comparison with the bare surface with no graphene modification. The 2D graphene surface showed increased nucleate site density and early onset of nucleate boiling, resulting in enhanced BHTC, by 40%, in the downward condition. The enhancement ratio of CHF was 40% on 2D graphene and 20–25% on 3D graphene. [ABSTRACT FROM AUTHOR]

We report nucleate pool boiling experiments using reduced graphene oxide (RGO) colloidal suspensions on a silicon dioxide plate surface, in order to describe a kind of quasi-transition boiling phenomenon, whereby the wall temperature gradually increased as a function of time without a rapid increase in temperature at the critical heat flux (CHF). Under boiling conditions, the RGO flakes formed a three-dimensional (3D) graphene structure at the surface, so that the RGO colloidal suspension exhibited a larger boiling heat transfer coefficient and larger CHF with the quasi-transition boiling phenomenon than when the working fluid was deionized water. To evaluate the effect of the heat flux conditions on the phenomenon, various heat fluxes were investigated, and the transient behavior of the boiling heat transfer characteristics was observed. We found that the rate of change of the wall temperature in the quasi-transition boiling regime was proportional to the heat flux, even if the higher heat flux was applied following the onset of the increase in the wall temperature. [ABSTRACT FROM AUTHOR]

Abstract: Although titanosaurs represent one of the most diverse radiations of non-avian dinosaurs during the Cretaceous, our knowledge of their early developmental stages was restricted to the Auca Mahuevo (Argentina) embryos in ovo. Here, we present the first complete lithostrotia titanosaur embryo in ovo. The relatively small spherical 87.07 to 91.1mm egg was discovered at the Lower Cretaceous locality Algui Ulaan Tsav in Mongolia, and is, to date, the smallest positively identified titanosaur egg. Through taphonomic processes, the egg was transformed into a calcite geode at the bottom of which the embryonic bones settled down and are now partially exposed on the lower egg surface. Neutron tomography characterization reveals a fully developed embryo fossilized within a thin (7.6mm–8.6mm) calcite layer. EBSD, a SEM-based diffraction technique, which measures the complete crystallographic orientation of the crystal lattice from a submicron area on the sample surface, is used for the first time on an extinct dinosaur eggshell. Observations of the egg and its embryo combined with eggshell microcharacterizations suggest that this new embryo was a lithostrotia titanosaur with an intermediate robusticity index that shares a mosaic of skeletal characters with Diamantinasaurus matildae from Queensland (Australia) and the nemegtosaurid Rapetosaurus krausei (Madagascar) more than with any other titanosaurs. The Early Cretaceous age of Algui Ulaan Tsav implies that this specimen greatly predates the previously described lithostrotian titanosaurs from the Late Cretaceous sediments of Mongolia. In addition, the recognized amount of similar eggs that has been recovered during the last 70years at Algui Ulaan Tsav suggests that a well-established population of lithostrotian titanosaurs used this site as a nesting site. The combined observations provide an important addition to Mongolian fossil richness and alter our understanding of the paleodispersion of this sauropod group. It now appears that lithostrotian sauropods would have reached Mongolia during the Aptian–Albian, thus suggesting the existence of a passage before the complete separation of the Laurasian and Gondwanan continents. Possibly, the lithostrotian north and eastward migration could have occurred between North Africa, Spain, and the rest of Europe prior to its fragmentation in large islands during the Cretaceous, thus justifying the presence of lithostrotians in the Cretaceous Romanian Hateg Island. [Copyright &y& Elsevier]

Abstract: An investigation into the water discharge characteristics of proton exchange membrane (PEM) fuel cells is carried out by using a feasibility test apparatus and the Neutron Radiography Facility (NRF) at HANARO. The feasibility test apparatus was composed of a distilled water supply line, a compressed air supply line, heating systems, and single PEM fuel cells, which were a 1-parallel serpentine type with a 100cm2 active area. Three kinds of methods were used: compressed air supply-only; heating-only; and a combination of the methods of a compressed air supply and heating, respectively. The resultant water discharge characteristics are different according to the applied methods. The compressed air supply only is suitable for removing the water at a flow field and a heating only is suitable for water at the MEA. Therefore, in order to remove all the water at PEM fuel cells, the combination method is needed at the moment. [Copyright &y& Elsevier]

Abstracts An experimental study was carried out to measure the boiling heat transfer and critical heat flux on serpentine-pattern thin film heater having a 120 nm thick platinum under pool boiling. Pool boiling critical heat flux experiments were performed using plain heater, 2-serpentine, 4-serpentine, and 6-serpentine pattern thin film heater. From the experimental results, it is found that the measured boiling heat transfer performance and critical heat flux are dependent of serpentine pattern, however critical heat flux is independent of the number of serpentine pattern. Measured data of critical heat flux are compared with classical model of critical heat flux, and degradation phenomena of boiling heat transfer and critical heat flux on serpentine-pattern thin film heater under pool boiling analyzed in this work. [ABSTRACT FROM AUTHOR]

• Experimental investigation of air natural convection in a turning L-shape channel. • Vertical/horizontal gaps as experimental parameters and varying heat load conditions. • Critical parameter of cooling performance/thermal behavior estimated from measured wall/air temperatures. • Transition phenomenon eliminating the entrance effect near the mid-height of the vertical channel. • Cooling performance enhanced by minimizing the entrance effect as recognized from air temperature profiles. The geometrical effect of natural convection in an air channel with a cavity at the turning section was investigated experimentally by controlling the vertical upper gap (G, 100–75 mm) and horizontal lower channel gap (B, 100 - 300 mm) and varying the heat load conditions (P, 1.35–6.20 kW). The thermal behavior in the channel was considered in terms of the temperature distributions of the walls, and the air temperature field was estimated from the measured air temperature. Additionally, the heat removal performance was analyzed for changes in each parameter to find the critical design parameter on cooling performance. The heat load condition positively affected the heat removal performance, but it did not affect the trend of the wall temperature distributions or the shape of the temperature field in the channel. A lower channel gap directly affected the cooling in the lower channel (cavity) between the lower curved wall and bottom but did not appreciably affect the cooling in the upper vertical channel between both vertical walls and overall heat removal performance (RSD Max = 3.2 %). As a result, the most critical parameter was the upper vertical channel gap because it affected both lower and upper channels and played a vital role in determining the overall heat transfer performance (RSD Max = 11.0 %). Additionally, it was confirmed that the location where the peak wall temperature appeared changed as the vertical gap size was altered. Interestingly, we found that the transition phenomenon eliminating the entrance effect occurred above the mid-height of the vertical channel in all experimental cases, and it was directly related to the heat removal performance. The temperature profiles developed smoothly along the height in only the G175 cases, which were the maximum heat removal performance cases, owing to the minimized entrance effect in the channel. In contrast, the temperature profiles below the mid-height of the vertical channel changed rapidly due to the entrance effect in other cases. [ABSTRACT FROM AUTHOR]

The graphene has been interested world-widely for the superb mechanical and electrical properties. Among them, the thermal conductivity of graphene was often reported as the 500–5000 W/mK. We tried to apply the graphene to the thermal application of boiling heat transfer through the graphene coating. The graphene was used for the reduced graphene oxide flakes in water (RGO colloid). The RGO colloid boiling on silicon-dioxide heater (substrate) showed both the boiling heat transfer and the critical heat flux enhancement as 65% and 70%, respectively. After RGO colloid boiling, the base graphene layer (BGL) with 10–100 nm thickness below the self-assembled foam-like graphene (SFG) was observed. In order to confirm the effect of BGL on the enhanced boiling performance, the only water boiling on an artificial graphene multilayers (RGO film) coated heater was conducted, and shows the similar result with the RGO colloid boiling. [ABSTRACT FROM AUTHOR]

Abstract: X-ray imaging detectors in combination with scintillator screens have been widely used in digital X-ray imaging applications. Gd2O2S:Tb was used as scintillation material for pixelated scintillator screens based on silicon substrates (wafer) with a micropore array of various dimensions fabricated using the photolithography and deep reactive ion etching (DRIE) process. The relative light output and the modulation transfer function (MTF) of each fabricated scintillator screen were measured by a cooled CCD and compared with those of Lanex screens. The spatial resolution of our scintillator screens was higher but their light outputs were lower than those of Lanex screen probably due to the loss of light at the wall surfaces. Therefore further treatment of the wall surface, such as reflective coating, seems necessary to compensate the light loss. [Copyright &y& Elsevier]