Bulb-shaped field emission lamps (FELs) with a helical cathode filament were simulated and fabricated in this research. The light bulbs comprised a helical stainless steel filament cathode grown with carbon nano-coils (CNCs) and an Al anode deposited on the bottom hemisphere of a 60-mm-diameter glass bulb. White light was generated when the field-emitted electrons bombarded a layer of three-color phosphor coated on the anode. A numerical simulation model for the helical-cathode FELs was constructed, and the field emission (FE) performance was carefully studied. Due to the screening effect, the electric field strength as well as the FE current density on the inner side of the helix dramatically decreased with decreasing helical pitch. Real FELs using cathodes with various helical radii and pitches were fabricated and their FE currents were measured. The theoretical and experimental results were in good agreement. A maximum total FE current was found at a pitch of 16 mm (helical radius = 2 mm), where the optimum trade-off between a large total surface area and a small screening effect was obtained. The optimized FEL showed a total luminous flux of about 220 lm at an applied voltage of 8 kV and a color rendering index of 94. Compared to a straight filament cathode, a helical cathode offered a higher total FE current or, alternatively, a lower current density and a longer cathode life, if we fix the total current by using a lower voltage.
In current industries, sampling inspections of the quality of powders, such as superabsorbent polymers (SAPs) still are conducted via visual inspection. The size of samples and foreign matter are around 500 μm, making them difficult for humans to identify. An automatic foreign matter detection system for powder has been developed in the present study. The powder samples can be automatically delivered, distributed, and recycled, and images of them are captured through the hardware of the system, while the identification software of this system was developed based on diffusion adversarial representation learning (DARL). The background image is a foreign-matter-free powder image with an input image size of 1024 × 1024 × 3. Since DARL includes adversarial segmentation, a diffusion process, and synthetic image generation, the DARL model was trained using a diffusion block with the employment of a U-Net attention mechanism and a spatial-adaptation de-normalization (SPADE) layer through the adoption of a loss function from a vanilla generative adversarial network (GAN). This model was then compared with supervised models such as a fully convolutional network (FCN), U-Net, and DeepLABV3+, as well as with an unsupervised Otsu threshold segmentation. It should be noted that only 10% of the training samples were utilized for the DARL to learn and the intersection over union (IoU) of the DARL can reach up to 80.15%, which is much higher than the 59.00%, 53.47%, 49.39%, and 30.08% for the Otsu threshold segmentation, FCN, U-Net, and DeepLABV3+ models. Therefore, the performance of the model developed in the present study would not be degraded due to an insufficient number of samples containing foreign matter. In practical applications, there is no need to collect, label, and design features for a large number of foreign matter samples before using the developed system.
Fabrication and efficiency enhancement of tubal field emission lamps (FELs) using multi-walled carbon nanotubes (MWNTs) as the cathode field emitters were studied. The cathode filaments were prepared by eletrolessly plating a nickel (Ni) film on the cathode made of a 304 stainless steel wire dip-coated with MWNTs. The 304 wire was dip-coated with MWNTs and nano-sized Pd catalyst in a solution, and then eletrolessly plated with Ni to form an MWNT-embedded composite film. The MWNTs embedded in Ni not only had better adhesion but also exhibited a higher FE threshold voltage, which is beneficial to our FEL system and can increase the luminous efficiency of the anode phosphor. Our results show that the FE cathode prepared by dipping three times in a solution containing 400 ppm Pd nano-catalysts and 0.2 wt.% MWNTs and then eletrolessly plating a Ni film at a deposition temperature of 60 °C, pH value of 5, and deposition time of 7 min has the best FE uniformity and efficiency. Its emission current can stay as low as 2.5 mA at a high applied voltage of 7 kV, which conforms to the high-voltage-and-low-current requirement of the P22 phosphor and can therefore maximize the luminous efficiency of our FEL. We found that the MWNT cathodes prepared by this approach are suitable for making high-efficiency FELs.
Temperature non-uniformity on chips has drawn the attention of researchers due to unwanted thermal stress development on chips resulting in a reduction in their life cycle and performance. In the present investigation, the heat transfer and flow characteristics of the coolant in the micro-pin-fin heat sink with variable density arrangement have been conducted numerically. The dimensions of the micro-pin-fin heat sink are 18.0 mm × 19.0 mm × 4.0 mm, and the height of the micro-pin-fin is 2 mm. Circular micro-pin-fin with diameters of 400, 500, and 600 μm, respectively have been considered. The power supply is 50 W with a heat source area of 10.0 mm × 10.0 mm. Water was the working fluid used while aluminum was used for the solid part of the heat sink. The operating pressure drop between the inlet and the outlet of the heat sink is fixed at 1500 Pa, 3000 Pa, and 5000 Pa. Ansys-Fluent was employed for the analysis. The results indicate that the temperature uniformity on the heat source for heat sink with variable density arrangement is better than that with staggered arrangement for about the same number of micro-pin-fins. The best effective thermal resistance is noted as 0.258 K/W among the heat sinks with all the configurations. In addition, the temperature difference per unit length on the heat source for heat sink with convergent arrangement at the pressure difference of 5000Pa and micro-pin-fin diameter of 600 μm was 1.34 K/mm, which is lower than the previously reported literature.
A carbonyl iron/carbon fiber material consisting of carbon fibers grown on micrometer-sized carbonyl iron sphere, was synthesized by chemical vapor deposition using a mixture of C2H2 and H2. The hollow-core carbon fibers (outer diameter: 140 nm and inner diameter: 40 nm) were composed of well-ordered graphene layers which were almost parallel to the long axis of the fibers. A composite (2 mm thick) consisting of the carbonyl iron/carbon fibers and epoxy resin demonstrated excellent electromagnetic (EM) wave absorption. Minimum reflection losses of -36 dB (99.95% of EM wave absorption) at 7.6 GHz and -32 dB (99.92% of EM wave absorption) at 34.1 GHz were achieved. The well-dispersed and network-like carbon fibers in the resin matrix affected the dielectric loss of the EM wave while the carbonyl iron affected the magnetic loss.
A double-sided light source based on field emission (FE) using an alternating current (ac) power source is demonstrated. Electrode plates acted as cathode or anode consisting an indium tin oxide glass, a screen-printed ZnS phosphor layer and urchin-like α-Fe 2 O 3 emitters coated on the layer. Two pieces of the plates were assembled together with the coated surfaces facing each other to make a parallel-plate, diode-structure FE device with a gap distance of 300 μm. The 1- cm 2 device shows a double-sided luminance distribution with a turn-on field of 2.2 V/μm, 90.23% uniformity and a maximum luminance of 8750 cd/m 2 at 2 kV. The novel structure and ac model operation provide a double-sided luminance, high brightness, antiarcing, good thermal management, and long lifetime.
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