Results 1 - 10 of 21
Results 1 - 10 of 21. Search took: 0.017 seconds
|Sort by: date | relevance|
[en] Highlights: • A novel microchannel with interlaced configuration is fabricated. • Side walls of channel as the main heat transfer surfaces is realized. • Experimental investigation on the thermal and hydraulic performance is performed. • A better heat transfer performance of interlaced microchannel is obtained. - Abstract: In this study, a novel interlaced microchannel with a “cold water-hot water-cold water” counterflow arrangement was designed. The influences of microchannel configurations on the thermal and hydraulic performance were studied by comparing the proposed microchannel configuration with parallel and traditional spiral configurations. The results showed that the effective heat transfer area of the interlaced microchannel was 6.4 and 8.4 times that of the parallel and spiral configurations, respectively. For interlaced microchannels, the maximum temperature difference between the cross sections was 0.07 °C, and the temperature rise along the flow direction was only 6 °C. When the Reynolds number was 492, the Nusselt number of the interlaced microchannels was 2 and 10 times that of the parallel and spiral microchannels, respectively. The heat transfer performance of interlaced microchannels was improved by 83.46% compared with that in the literature. The influence of microchannel configurations on the pressure drop and the entrance length were negligible. The interlaced microchannel exhibited its lowest thermal resistance of 0.015 °C/W and lowest entropy production of 22.6 W/ °C at a Reynolds number of 492. The heat transfer enhancement coefficient of the interlaced microchannel and parallel microchannel were 5 and 2.8 times that of the traditional spiral microchannel, respectively. The maximum heat load of loop heat pipe was enhanced by 4 times with the integration of interlaced microchannel as the condenser.
[en] Highlights: • Smooth and rough porous copper fiber sintered sheets as wicks are fabricated. • Capillary pumping performance of porous copper fiber sintered sheets are tested and discussed. • Effects of different parameters on thermal performance of loop heat pipes are studied. • Better thermal performance with rough porous copper fiber sintered sheets as wick is obtained. • Deionized water with a 30% filling ratio is the optimal combination for designed loop heat pipe. - Abstract: Smooth and rough porous copper fiber sintered sheets, employed here as wicks for loop heat pipes for the first time, were fabricated using a low-temperature solid-phase sintering method. The capillary performance of these porous copper fiber sintered sheets were analyzed and discussed. The influence of the surface morphology, filling ratio, and working fluid on the thermal resistance, evaporator wall temperature, and start-up time of the loop heat pipes were investigated. The results showed that the capillary pumping amount of working fluid for both smooth and rough porous copper fiber sintered sheets initially increases rapidly, and then gradually attains a stable state. The curve of the capillary pumping amount of working fluid can be described as a function that increases exponentially over time. When rough porous copper fiber sintered sheets are used as wicks and deionized water is used as the working fluid, the capillary pumping amount is maximized. Compared to smooth porous copper fiber sintered sheets, loop heat pipes with rough porous copper fiber sintered sheets exhibit a shorter start-up time, lower thermal resistance, and lower evaporator wall temperature. For a filling ratio in the range of 15–45%, loop heat pipes with rough porous copper fiber sintered sheets and a 30% filling ratio show lower thermal resistance and a lower evaporator wall temperature. Ultimately, the use of deionized water as the working fluid with a 30% filling ratio enables loop heat pipes with rough porous copper fiber sintered sheets to be stably operated at a heat load of 200 W.
[en] Single phase chamfered-edge zeolite 4A samples in pure form with a high crystallinity were synthesized by applying step-change of synthesis temperature during hydrothermal treatment of coal fly ash. The calcium binding capacity of these zeolite 4A samples (prepared from coal fly ash) and the commercial detergent grade zeolite 4A were tested for usage as a detergent builder. The results show that these zeolite 4A samples behaved similarly as the commercial one in removing calcium ions during the washing cycle. Moreover, from the leaching tests (evaluation of toxicological safety), the results show that these zeolite 4A samples leached the same elements (Sb, As, Se and Tl) as the commercial one with the concentrations in the same order of magnitude. This shows that the toxicological effect of the coal fly ash converted zeolite 4A was not worse than that of the commercial sample. Finally, economic and environmental aspects of converting coal fly ash to useful products were discussed
[en] A proof-of-concept of applying laser micro-machining to fabricate high performance GaN light-emitting diode (LED) was presented in this study. Laser micro-machining was applied to fabricate GaN LED chip with angled sidewalls (ALED). The inclined sapphire sidewalls were coated with highly reflective silver film which functions as an efficient light out-coupling medium for photons within the LED structure. Thus, more laterally-propagating photons can be redirected to the upward direction of the ALED with silver coating (Ag-ALED). Performances of the Ag-ALED, ALED and conventional planar GaN LED were evaluated. At an injection current of 30 mA, the light output intensity of Ag-ALED was significantly improved by 97% and 195% as compared to ALED and conventional planar LED, respectively. The corresponding wall-plug efficiency of Ag-ALED was remarkably increased by 95% and 193% as compared to ALED and conventional planar LED, respectively. The results of this study demonstrated that the Ag-ALED showed a pronounced increase in light output intensity compared to conventional planar LED, which may have many potential applications in the field of display engineering.
[en] Many 2D graphene-based catalysts for electrooxidation of glucose involved the use of binders and toxic reducing agents in the preparation of the electrodes, which potentially causes the masking of original activity of the electrocatalysts. In this study, a green method was developed to prepare binder-free 3D graphene aerogel/nickel foam electrodes in which bimetallic Pd-Pt NP alloy with different at% ratios were loaded on 3D graphene aerogel. The influence of Pd/Pt ratio (at%: 1:2.9, 1:1.31, 1:1.03), glucose concentration (30 mM, 75 mM, 300 mM, 500 mM) and NaOH concentration (0.1 M, 1 M) on electrooxidation of glucose were investigated. The catalytic activity of the electrodes was enhanced with increasing the Pd/Pt ratio from 1:2.9 to 1:1.03, and changing the NaOH/glucose concentration from 75 mM glucose/0.1 M NaOH to 300 mM glucose/1 M NaOH. The Pd1Pt1.03/GA/NF electrode achieved a high current density of 388.59 A g−1 under the 300 mM glucose/1 M NaOH condition. The stability of the electrodes was also evaluated over 1000 cycles. This study demonstrated that the Pd1Pt1.03/GA/NF electrode could be used as an anodic electrode in glucose-based fuel cells.
[en] This study investigated the performance of a combined ozone and zeolite system in eliminating gaseous toluene which is a major contaminant in many industrial and indoor environments. The hypothesis that the removal of toluene by ozone can be substantially affected by confining the oxidation reaction in a zeolite structure was evaluated. The degradation of toluene seemed to be contributed by the active oxygen atom generated from the decomposition of ozone at the Lewis acid sites in the zeolite 13X. Air containing toluene levels at 1.5, 2 and 3 ppm was injected with ozone in the range of 0-6 ppm before being vented into a fixed amount of 3600 g zeolite 13X with 90 mm bed-length. The experimental results showed that the elimination rate of toluene was significantly enhanced when compared to using zeolite or ozone alone. In particular, over 90% of the 1.5 ppm toluene was removed when 6 ppm ozone was used at 40% relative humidity level. Deactivation of the zeolite 13X after a few hours of reactions under the current experimental conditions was probably due to the adsorbed water, carbon dioxide and the reaction by-products. The residue species left in the zeolite and the intermediate species in the exhaust gas stream were characterized by FT-IR, GC-MS and HP-LC methods, respectively. A distinctive peak of O atom attached to the Lewis acid site at 1380 cm-1 was found in the FT-IR spectrum and trace amount of aldehydes was found to be the reaction by-products
[en] Graphical abstract: Display Omitted Highlights: ► Cu2O doped p-type AZO films was first prepared by sol–gel method. ► AZO:Cu2O films showed a polycrystalline Cu2O (1 1 0) and Cu (2 0 0) phases. ► p-Type conductivity was achieved by annealing in N2/H2 forming gas at 400 °C. ► p–n junction (ITO/AZO:Cu2O) revealed rectifying I–V characteristics. ► The mean optical transmittance of AZO:Cu2Ofilms was >90%. -- Abstract: Highly transparent Cu2O-doped p-type Zn1−xAlxO (AZO; Al/Zn = 1.5 at%) conducting oxide films were synthesized on glass substrates using a cost effective low temperature sol–gel method. X-ray diffraction of the Cu2O-doped AZO (AZO:Cu2O) films revealed a polycrystalline Cu2O (1 1 0) peak. The I–V measurements of the p–n junction (ITO/AZO:Cu2O) revealed rectifying I–V characteristics, showing that these AZO:Cu2O films exhibit p-type conductivity. p-Type conductivity was achieved by annealing the AZO:Cu2O films in N2/H2 forming gas at 400 °C. The hole concentration, hole mobility and resistivity of the 0.5–2 mol% AZO:Cu2O films were 5.41 × 1018 to 1.99 × 1020 cm−3, 8.36–21.6 cm2/V s and 1.66 × 10−2 to 6.94 × 10−3 Ω cm, respectively. These results show that post-annealing in a forming gas is effective and practicable in producing p-type AZO.
[en] We report the synthesized mixture of MXene and NiCo LDH on nickel foam by an electrodeposition technique. The specific capacitance of the mixture attained 983.6 F g−1 at a discharge current of 2 A g−1, which is greater than that of pure MXene. Compared to NiCo LDH, the sample created through electrodeposition provided a better rate capability of 983.6 F g−1 at 2 A g−1 and 536.6 F g−1 at 50 A g−1 and cycling stability with 76% retention after 5000 cycles at 30 A g−1. Moreover, a solid-state asymmetric supercapacitor with MXene-LDH as the positive electrode and multi-walled carbon nanotube coated on the nickel foam as the negative electrode delivers high energy density (36.70 Wh kg−1 at the power density of 1.44 kW kg−1), which outperforms the other devices reported previously.
[en] Highlights: ► High-quality ZnO thin films were deposited at room temperature. ► Effect of O2 flow and RF sputtering voltages on properties of ZnO films were studied. ► O2/Ar ratios played a key role in controlling optical properties of ZnO films. ► Photoluminescence intensity of the ZnO films strongly depended on O2/Ar ratios. ► Crystallite size, stress and strain strongly depended on O2/Ar ratios. - Abstract: ZnO thin films were deposited onto quartz substrates by radio frequency (RF) reactive magnetron sputtering using a Zn target. The structural and optical properties of the ZnO thin films were investigated comprehensively by X-ray diffraction (XRD), ultraviolet–visible and photoluminescence (PL) measurements. The effects of the oxygen content of the total oxygen–argon mixture and sputtering voltage in the sputtering process on the structural and optical properties of the ZnO films were studied systemically. The microstructural parameters, such as the lattice constant, crystallite size, stress and strain, were also calculated and correlated with the structural and optical properties of the ZnO films. In addition, the results showed that the crystalline quality of ZnO thin films improved with increasing O2/Ar gas flow ratio from 2:8 to 8:2. XRD and PL spectroscopy revealed 800 V to be the most appropriate sputtering voltage for ZnO thin film growth. High-quality ZnO films with a good crystalline structure, tunable optical band gap as well as high transmittance could be fabricated easily by RF reactive magnetron sputtering, paving the way to obtaining cost-effective ZnO thin films transparent conducting oxides for optoelectronics applications
[en] Hydrogen energy technology can be one of the best key players related to the sector of the United Nations Framework Convention on Climate Change (UNFCCC) and the hydrogen economy. Comparing to other technologies, hydrogen energy technology is more environmentally sound and friendly energy technology and has great potential as a future dominant energy carrier. Advanced nations including Korea have been focusing on the development of hydrogen energy technology R and D for the sustainable development and low carbon green society. In this paper, we applied the integrated fuzzy analytic hierarchy process (Fuzzy AHP) and the data envelopment analysis (DEA) for measuring the relative efficiency of the R and D performance in the national hydrogen energy technology development. On the first stage, the fuzzy AHP effectively reflects the vagueness of human thought. On the second stage, the DEA approach measures the relative efficiency of the national R and D performance in the sector of hydrogen energy technology development with economic viewpoints. The efficiency score can be the fundamental data for policymakers for the well focused R and D planning. (author)