Textured Sidewalls Research Articles

The research for the recommended flush flow of high-speed mechanical seal with textured side-wall

For mechanical seals used in high-speed turbo pumps, it is often observed that the seal face will fail due to high temperatures before excessive wear occurs. The textured side-wall with low dissipation and high heat transfer can effectively extend the life of high-speed mechanical seal. Numerical research is carried out with SST k-ω model and turbulence dissipation. The numerical results have been validated with published experiments and achieved good validity. The textured side-wall shows an excellent cooling effect over a wide range of flush flow. Even when the flush channel is narrow and flush flow almost non-existent, the reduction in the temperature of seal face is still significant. The flow field and turbulence dissipation of three different channels are analyzed under different flush flow. By means of commonly used design, the maximum temperature of seal face can be reduced by over 40 °C (22.2 %) when flush flow is nearly non-existent. The recommended flush flow is approximately 15 L/min, ignoring the shape of the flow channel. It can simultaneously achieve a more effective cooling effect and a reduction in turbulence dissipation.

The influence of cooling medium and cooling channel on heat transfer of textured seal in presence of viscous dissipation

When operating at high speed, the mechanical seal produces a large amount of frictional heat on the seal face. If the heat is not dissipated in time, it could lead to the thermal failure of the seal face. In the field of tribology research, the technology of textured surface is a method to enhance the heat dissipation rate. Numerical analysis is carried out based on the SST k-ω turbulence model and the energy equation with viscous dissipation term, and the results are validated by the experimental data published in the reference. In a wide range of rotational speeds, cooling medium with varied Pr numbers is employed to confirm the performance of textured side-wall in heat transfer enhancement. The shape of the seal chamber is also changed to provide guidance for the design of the cooling channel. The results show that a larger Pr number increases the heat transfer enhancement of the textures; it is advisable to utilize a cooling channel that gradually decreases in size; and the flushing should not be perpendicular to the stator; additionally, it is important to ensure that the cooling channel is not too narrow. By means of appropriate design, the maximum temperature of seal face can be reduced by over 40 °C (22.2 %) at 20,000 rpm.

Influence of Cavitation on the Heat Transfer of High-Speed Mechanical Seal with Textured Side Wall

By setting textures on the side walls of a rotor, based on SST k-ω turbulence and the mixture model, the effects of depth-to-diameter ratio, shape, and rotational speed on interface temperature are analyzed. Local Nu number, flow field in textures, and gas distribution are used to verify the conclusion. When rotational speed increases, there are three different stages on the surface: liquid-dominated, mixed two-phase, and gas-dominated. This leads to a big difference in heat transfer on the side wall and causes the temperature on the seal face to increase when cavitation is considered. The distribution of the gas phase is explained through drag reduction, which has a high correlation with the velocity gradient near the surface. For several common shapes, heat transfer enhancement of textures is compared under high speed. The key influencing factor is the depth-to-diameter ratio, which causes flow stratification and reduces heat transfer. Flow stratification leads to different results of maximum temperature on the seal face when cavitation is considered. Results show that at high speed, a deep, circular texture is better when cavitation does not occur, and a shallow triangular texture is recommended when cavitation occurs; a textured side wall can reduce the maximum temperature of the seal face by about 10 °C.

Characteristics of Micro LEDs With Snowflake p-Electrode and Composite Textured Sidewalls

We demonstrate a hybrid structure incorporating concave-convex circular composite textured sidewalls and snowflake-like p-electrode, which is an effective approach to improve optical properties without deteriorating the electrical characteristics for micro-LEDs. Compared to the device with flat sidewalls and disk p-electrode, the device with concave-convex circular composite textured sidewalls and 6-branches snowflake-like p-electrode exhibits a saturation light output power enhancement of 36.85%. And the forward voltage decreases by 7.6% at current density of 1732.4 A/cm2. The enhanced performances are mainly attributed to the decrease of total internal reflection at the concave-convex circular composite textured sidewalls and improvement of current distribution provided by 6-branches snowflake-like p-electrode.

Enhanced Light Extraction of GaN-Based Light-Emitting Diodes With a Hybrid Structure Incorporating Microhole Arrays and Textured Sidewalls

GaN-based light-emitting diodes (LEDs) with a hybrid structure, including a microhole array and textured sidewalls (45° angle and convex patterns), are fabricated and studied. The use of this hybrid structure, formed using an inductively coupled plasma etching approach, causes reduced total internal reflection and increased scattering probability of photons at the GaN/air interface. Therefore, the opportunity for photons to find an escape cone and the related light extraction efficiency can be effectively increased. This designed hybrid structure provides substantial improvements in optical performance without any degradation in electrical properties. For instance, as compared with a conventional LED, the studied device with this hybrid structure (45° angle sidewalls) shows remarkable improvements of 20.9%, 24.3%, 20.5%, and 21.3% in light output power, luminous fluxes, external quantum efficiency, and wall-plug efficiency, respectively. In addition, higher intensities in the light emission mapping images and far-field patterns of the studied device are found. Therefore, the studied hybrid structure is promising for high-performance GaN-based LED applications.

Implementation of light extraction improvements of GaN-based light-emitting diodes with specific textured sidewalls

Textured-sidewall GaN-based light-emitting diodes (LEDs) with various sidewall angles (15–90°) and convex or concave sidewalls prepared using an inductively-coupled-plasma approach are comprehensively fabricated and studied. The device with 45° sidewalls (Device F) and that with convex sidewalls (Device B) show significant improvements in optical properties. Experiments show that, at an injection current of 350 mA, the light output power, external quantum efficiency, wall-plug efficiency, and luminous flux of Device F (Device B) are greatly improved by 18.3% (18.2%), 18.2% (18.2%), 17.3% (19.8%), and 16.6% (18.4%), respectively, compared to those of a conventional LED with flat sidewalls. In addition, negligible degradation in electrical properties is found. The enhanced optical performance is mainly attributed to increased light extraction in the horizontal direction due to a significant reduction in total internal reflection at the textured sidewalls. Therefore, the reported specific textured-sidewall structures (Devices B and F) are promising for high-power GaN-based LED applications.

Light Extraction Enhancement of GaN-Based Light-Emitting Diodes With Textured Sidewalls and ICP-Transferred Nanohemispherical Backside Reflector

Textured-sidewall GaN-based light-emitting diodes (LEDs) with convex and 45° patterns and an inductively coupled plasma (ICP)-transferred nanohemispherical backside reflector, formed using an ICP etching process, are fabricated and studied. For devices with textured sidewalls, the scattering probability of photons at the GaN/air interface is increased and the light extraction efficiency is enhanced since photons are allowed to find escape cones in the horizontal direction. With the ICP-transferred nanohemispherical backside reflector, reflected photons can be easily scattered and redirected in arbitrary directions for light extraction and thus have more opportunities to escape the devices. The LED with 45° sidewalls and a backside reflector exhibited the significant improvements of 55.8%, 49.3%, 47.2%, and 55.4% in light output power, luminous flux, external quantum efficiency, and wall-plug efficiency, respectively, compared to those of a conventional LED without these specific designs (Device A). In addition, the higher intensities in a light emission mapping image and improved far-field patterns are obtained for the studied device. The enhanced optical performance is mainly attributed to the increased light extraction in all directions due to a significant reduction in the total internal reflection by the textured sidewalls and a backside reflector. Therefore, textured-sidewall structures and an ICP-transferred nanohemispherical backside reflector are promising for high-power GaN-based LED applications.

Implementation of Light Extraction Improvements of GaN-based Light-Emitting Diodes with Specific Textured Sidewalls

Implementation of Light Extraction Improvements of GaN-based Light-Emitting Diodes with Specific Textured Sidewalls

Thermal performance of mechanical seals with textured side-wall

Experimental measurements and numerical simulations are presented to show the effectiveness of cooling of a mechanical seal's active surface by means of cylindrically shaped dimples engraved circumferentially on the outside diameter of the mating ring. The working fluid is propylene glycol solution (70% in water by volume) and the flush rate is 107 cm 3/s. A commercially available CFD code (FLUENT) is employed to numerically confirm the experimental measurements, and the numerical and experimental results are in agreement. Results of this study demonstrate the heat augmentation effectiveness of surface texture techniques on the mechanical seals.

Enhanced luminescence of GaN-based light-emitting diodes by selective wet etching of GaN/sapphire interface using direct heteroepitaxy laterally overgrowth technique

We introduce a method to enhance the luminescence of GaN-based LEDs by combining the direct heteroepitaxy laterally overgrowth (DHELO) technique with selective wet etching process. The epitaxial overgrowth of GaN layers on sapphire substrate with SiO 2 micro-rods array exhibited a reduced dislocation density and improved the crystal quality. The EL intensity of LEDs with SiO 2 micro-rods array was 6.5% higher than conventional LEDs at 20 mA. The selective wet etching process was then used to texture the LED sidewalls into inverted pyramid shape. Finally, the EL intensity could be further enhanced about 12.5% as compared with LEDs with SiO 2 micro-rods array when adopting the textured sidewalls.

GaN-Based Light-Emitting Diodes With Pillar Structures Around the Mesa Region

This study presents the numerical and experimental demonstrations for the enhancement of light extraction efficiency in nitride-based light-emitting diodes (LEDs) with textured sidewall and micro-sized pillar waveguides (TSMPW) and nano-textured sidewall and nano-pillars (NTSNP) around the mesa. Using hydrothermal ZnO nanorods as the etching hard mask, the authors successfully formed vertical GaN nano-pillars on the mesa-etched regions. It was found that electrical characteristics observed from the proposed LEDs were near the same as the control samples without the pillars. Output power enhancement of LED with TSMPW was about 11% compared with conventional LEDs, and the output power enhancement of LED was greater than 45% upon replacement of TSMPW with the NTSNP structure. The light extraction efficiency enhancement factors of the LEDs with TSMPW and NTSNP structures simulated by finite-difference time-domain analysis were 16.6% and 23%, respectively.

A low damage GaN-based light-emitting diode with textured/inclined sidewalls and an air–buffer layer

A GaN-based light-emitting diode (LED) with an air–buffer layer and textured sidewalls is fabricated and investigated. After the deposition of a 1-μm silicon dioxide (SiO 2) passivation layer on the whole device region except for the sidewall, a hot KOH etching solution is used to develop the desired textured sidewall. Many sidewalls with triangular-like shape are produced along the specific direction of 〈 1 1 ¯ 0 0 〉 , where photons introduced within multiple-quantum-well (MQW) exhibit more opportunities to scatter into the air. Based on the lateral etching, many triangular-shaped cones are formed on the patterned sapphire substrate (PSS). The device sidewall inclines with a 24° angle which results in an improved reemission of photons in the vertical/lateral direction. At 20 mA, as compared with the LED without KOH treatment, the studied device exhibits improved output power by 11.7% without deteriorating its electrical characteristics. This phenomenon can be attributed to the enhanced output light from vertical and lateral directions due to the formation of an air–buffer layer, textured and inclined sidewalls.

III-Nitride-Based Light-Emitting Diodes With GaN Micropillars Around Mesa and Patterned Substrate

In this paper, the textured-sidewall mesa and GaN microsize pillars (?-pillars) around the mesa region were fabricated on III-nitride light-emitting diodes (LEDs) with a patterned sapphire substrate (PSS). We demonstrated that the light-waveguide mode outside the mesa region of III-nitride LEDs could be disrupted by a GaN ?-pillar around the mesa region and PSS. We found that the power enhancement of LEDs with textured sidewall, ?-pillars around the mesa, and PSS from ray-tracing simulation was about 65% larger than that of conventional LEDs. It was found that we could achieve a high power enhancement of about 60% of LEDs with textured sidewall, ? -pillars around the mesa, and a patterned substrate, and it was close to the result of simulation. It was also found that the light intensity outside the mesa region with ? -pillars of LEDs with or without a patterned substrate would decay in proportion to the distance away from the mesa edge, by studying the light emission intensity image of the whole LEDs. The decay lengths for the textured sidewall and ?-pillars around the mesa LEDs with or without a patterned substrate are 12 and 17 ?m, respectively. We understand that the light outside the mesa region could be extracted earlier by introducing the GaN ?-pillars and patterned substrate together.

Efficiency Improvement of GaN-Based LEDs With $ \hbox{SiO}_{2}$ Microrod Array and Textured Sidewalls

High-performance nitride-based light-emitting diodes (LEDs) grown with SiO2 microrod array have been demonstrated. The light output power of LEDs with SiO2 microrod array was 9.03% higher than conventional LEDs at the injection current of 20 mA. The improvement contributed to the enhancement of the light extraction efficiency, and epitaxial GaN film quality improved by direct heteroepitaxial lateral overgrowth with SiO2 microrod array. The light output power could be further enhanced by about 18.36% as compared with the conventional LEDs when adopting the textured sidewall surface which use buffered oxide etch to remove SiO2 microrod arrays and use NaOH to etch the sidewall again into an inverted pyramid shape. After the texturing process, the LEDs show higher electroluminescence intensity and broader far-field pattern. Furthermore, the LEDs with SiO2 microrod array and additional wet-etching process will not affect the electrical property.

GaN-Based LEDs With GaN $\mu$-Pillars Around Mesa, Patterned Substrate, and Reflector Under Pads

Nitride-based light-emitting diodes (LEDs) with textured sidewall, GaN mu-pillars around mesa region, patterned sapphire substrate (PSS), and highly reflective Ag-Cr-Au electrode pads were fabricated using the conventional lithography method (labeled as experimental LEDs). When a 20-mA injection current was applied, forward voltages were 3.18 and 3.4 V for the conventional and experimental LEDs, respectively. The high 20-mA Vf of LEDs with Ag-Cr-Au electrode pads could be attributed to the fact that the specific contact resistance of n+-GaN-Ag-Cr-Au is slightly higher than that of the n+ -GaN-Cr-Au contact. It was found that we could achieve much stronger LED output power with textured sidewalls, GaN mu-pillars around mesa region, PSS, and highly reflective Ag-Cr-Au electrode pads. It was also found that we could enhance LED output power by more than 80% compared with the conventional LEDs.

Characteristics of a Low-Damage GaN-Based Light-Emitting Diode Using a KOH-Treated Wet-Etching Approach

A GaN-based light emitting diode (LED) with an air-buffer layer and textured sidewalls is fabricated and investigated. A hot KOH etching solution is used to develop the desired textured sidewalls. Many sidewalls with triangular-like shape are produced along the specific direction of <1100 >, where photons introduced within multiple-quantum-well (MQW) exhibit more opportunities to scatter into the air. Based on the lateral etching, many triangular-shaped cones are formed on the patterned sapphire substrate (PSS). At 20 mA, as compared with the LED without KOH treatment, the studied device exhibits improved output power by 11.7% without deteriorating its electrical characteristics. This phenomenon can be attributed to the enhanced output light from vertical and lateral directions due to the formation of an air-buffer layer as well as textured sidewalls. The thermal reliability of the studied device is also comparable to the one without KOH-treated process.

Nitride-Based Light Emitting Diodes With Textured Sidewalls and Pillar Waveguides

Nitride-based light emitting diodes (LEDs) with sidewall texture and pillar waveguides (STPW) were fabricated using conventional lithography method. With 20-mA injection current, it was found that forward voltages were 3.16 and 3.15 V for the conventional LED and the LED with STPW, respectively. It was also found that 20-mA LED output powers were 8.4 and 10.1 mW for conventional LED and the LED with STPW, respectively. The enhancement is attributed to the out-coupling of lateral waveguide mode in the near horizontal directions

Nitride-based LEDs with nano-scale textured sidewalls using natural lithography

This investigation describes the development of a InGaN/GaN light-emitting diode (LED)with textured sidewalls using natural lithography with polystyrene spheres (PSs) as theetching mask and dry etching the epitaxial layers of LEDs to achieve nano-scale texturedsidewalls. The LED with textured sidewalls increased the output power of theInGaN–GaN multiple quantum well (MQW) LEDs by a factor of 1.3, indicating that theLED with nano-scale textured sidewalls had larger light extraction efficiency. Thewall-plug efficiency of nitride-based LEDs was increased by 30% using texturedsidewalls.

Nitride-Based LEDs With Textured Side Walls

Nitride-based light-emitting diodes (LEDs) with textured side walls were fabricated. By using plasma-enhanced chemical vapor deposition SiO/sub 2/ layer as the etching mask, we successfully etched the nitride epitaxial layers to achieve wavelike side walls. It was found that such wavelike side walls could mainly enhance the light output at the horizontal directions. With a 20-mA current injection, it was found that the output powers of the LED with textured side walls and normal LED were 9.3 and 8.4 mW, respectively. Furthermore, it was found that such textured side walls will not result in a higher operation voltage.