Sheam Chyun Lin

Flow characteristics of a two stage EHD gas pump in circular pipe

Flow characteristics of a two-stage electrohydro-dynamic (EHD) gas pump in a circular tube has been experimentally investigated for two different sizes (61.8 mm and 127.8 mm in diameter). Each stage uses eight emitting electrodes flush mounted on the tube wall. Two electrode configurations, aligned and offset, with fixed spacing between electrodes have been considered in this study. The main objective of the study is to verify if a two-stage EHD pump can sustain or even increase the volume flow rate produced by a single-stage pump over a greater tube length. To this end, electrodes at both stages are charged at the same voltages in positive polarity from 18 kV to 22 kV. Velocities are measured at three cross-sections along the tube length and then integrated to obtain the volume flow rate. The velocity profile and volume flow rate delivered by the single top stage of the pump are compared with those produced by the two stages combined to give additional insight to the problem. The results obtained have important implications for practical applications of EHD gas pump.

Effects of Number of Porous Insert, Spindle Speed and Gap Thickness on Characteristics of a Partially Porous Aerostatic Journal Bearing

The effects of the rotating speed of the spindle, the number of the porous medium inserted into the partially porous aerostatic journal bearing and the thickness of the bearing gap on the characteristics of the bearing such as the pressure distribution, the load carrying capacity and the stiffness of the bearing were studied. Based on the finite volume method and the pressure-velocity coupling scheme of the SIMPLE algorithm with the standard k-ε turbulent model, the CFD software was used to solve the Navier-Stokes equations to calculate the pressure field in the bearing gap. The computed results revealed the faster the spindle rotated, the higher the gap pressure. As the gap thickness increased, the gap pressure, the load carrying capacity and the stiffness of the bearing decreased. The more the porous inserts, the higher the gap pressure and the load carrying capacity, but the less the bearing stiffness would be.

Variation of Entrance Length Effect on EHD Gas Pump Performance

The effects of entrance length on performance and flow characteristic of EHD gas pump has been experimentally examined in this study. A 61.8mm-in-diameter EHD gas pump with eight evenly spaced emitting electrodes and flush mounted on the tube inner wall is used for this investigation. The experiment is conducted for two applied voltages 19 kV and 20kV with positive polarity. Several (L/D) ratios are used aiming at picking the appropriate length to achieve highest ionic discharge and maximum pump performance. Results show that the lowest (L/D) ratio gives the best pump performance with highest discharge managed.

Effect of Electrode Length on the Performance of EHD Gas Pump

The effects of electrode length on the characteristics of flow induced by an electrohydrodynamic (EHD) gas pump in circular pipe have been experimentally examined in this study. The gas pump has a diameter of 61.8 mm and uses eight evenly spaced emitting electrodes which are flush mounted on the tube inner wall. The gap distance between emitting and ground electrodes is fixed at 25 mm and two emitting electrode lengths (15 mm and 40 mm) are considered. Experiments are conducted using positive corona discharge with voltage varying from 17.5 kV to 23 kV. Several important implications from the present results for practical engineering applications are presented.

Performance Enhancement of a Small Centrifugal Cooling Fan

Under the rapid enhancement of CPU performance, the thermal management on the CPU becomes a challenging task, especially for the industrial PC with a high system resistance. The traditional axial fan with heat sink assembly is not capable to solve this difficult thermal-dissipation problem. Thus, a combination of centrifugal fan and heat sink is utilized to solve this high system-resistance for a server. A centrifugal fan is utilized to offer extra static pressure for drawing the hot air inside this compact enclosure and discharging to the atmosphere. In this study, experimental measurement and numerical simulation are integrated to improve the aerodynamic performance of a blower (80x 80x15 mm3) by redesigning its housing and rotor. Also, fan performance and acoustic experiment are conducted in an AMCA 210-99 test chamber and a semi-anechoic chamber following CNS-8753 code for ensuring a reliable test platform. In conclusion, based on experimental and CFD outcomes, the maximum flow rate and the static pressure of the improved design alternative are successfully increased by 19.5% and 25.53%, respectively.

Pressure Distribution in the Air Film and the Porous Conveyor Air Bearing

The porous aerostatic conveyor bearings are used to feed large substrates such as the flat panel display glass sheets and the silicon wafers by supporting them with compressed air in a non-contact condition. Due to unevenly distributed pressure in the air film between the substrate and the porous aerostatic conveyor bearing, the soft substrate often deforms and tilts on the bearing pad during the feeding process. In order to investigate the pressure distribution in the air gap, the CFD software, FLUENT, was employed to simulate the operation of the porous aerostatic conveyor bearing during the feeding process. In addition, the load capacity of the conveyor air bearing was calculated. The results show there is low vacuum pressure around the air discharge holes. The high pressure above the air supply holes forms two paraboloidal distributions in the air film. For design modification, the air supply and the air discharge holes need to be rearranged and/or relocated to improve the pressure distribution in the air film for more stable feeding of the substrate.

Performance of a two-stage EHD gas pump in a circular pipe operating at uneven applied voltages

The performance of a two-stage electrohydro-dynamic (EHD) gas pump in a circular tube has been investigated for operating conditions in which each stage is charged at a different voltage. The main objective of the study is to examine the characteristics of resulting flow as well as the efficient use of energy in sustaining and improving the volume flow rate produced by a single-stage pump over a greater distance. To this end, two different sizes of tube are employed (61.8 mm and 127.8 mm in diameter). Each stage uses eight emitting electrodes flush mounted on the tube wall. In addition, two electrode configurations, aligned and offset, with fixed electrode spacing have been considered. The electrodes at both stages are charged at voltages in positive polarity from 18 kV to 22 kV. The velocity profile and volume flow rate delivered are compared with those produced by the same pump operating at even voltages to provide additional insight to the problem. The results thus obtained have important implications for practical use of EHD gas pump.

The Effect of Rotational Speed on Fluid Compressibility and Gap Pressure of a Partially Porous Aerostatic Thrust Bearing

This study investigated the effect of the spindle speed on pressure distribution in the air gap and the load carrying capacity of a porous aerostatic annular thrust bearing. Based on the finite volume method and the pressure-velocity coupling scheme of the SIMPLE algorithm with the standard k-ε turbulent model, a CFD software was used to solve the Navier-Stokes equations to calculate pressure and velocity of the air flow. The results revealed there were positive pressure zones and vacuum pressure zones in the air gap between the thrust disk and the bearing. Under the same spindle speed, the pressure difference between the positive peak and the negative peak in the case of incompressible air was greater than that in the case of compressible air. The averaged pressure on the surface of the thrust disk with compressible air flow was higher than that with incompressible air flow. So was the load carrying capacity of the bearing, which increased when the spindle rotated faster.

Noise Reduction on Centrifugal Fan via the Quarter-Wave Resonator

The purpose of this work is to improve flow-induced noise for the centrifugal fan with quarter-wave resonator by design scheme, mockup fabrication, and experimental test. At first, the cascade theory is utilized to generate the three-dimensional fan configuration which is fabricated for performance and acoustic tests later. Next, FFT is applied to measure the noise for comparison and evaluating the effect of quarter-wave resonator. To reduce the fan noise, a set of quarter-wave resonator of this centrifugal fan are designed and fabricated on the centrifugal fan. Consequently, the flow-induced-noise reduction due to the aerodynamics is examined and discussed in details. In conclusions, a comprehensive parametric study on quarter-wave resonator is carried out and summarized for attaining a design guideline for its application on centrifugal fan. The accomplishment of this study provides a systematic scheme of noise reduction for a centrifugal fan with the addition of quarter-wave resonator design.

A New Design for Enhancing the Performance of Hidden Ceiling Fan

The new axial-flow fans are designed by following a systematic procedure to construct the 3D multi-airfoil impeller, which is constructed by NACA four-digital series of 2D profiles. Also a new housing is proposed for enhancing the performance. The numerical flow visualization is observed carefully for modifying the design parameters when the undesirable flow pattern appeared. After that a CNC-fabricated prototype consisting of new housing and axial-flow fan is served for performance comparison. The results show that data from experiment and simulation have the same trend and in good agreement. Furthermore, the airflow rate for mockup is largely improved by 64.57% after imposing the new axial-flow fan and the new housing. Moreover, for design of single axial-flow fan, the maximum static pressure and maximum airflow rate are increased by a significant 33.7% and 55.48%, both much higher than the commercial products, respectively. In conclusion, the enhancement of hidden ceiling fan has been accomplished successfully via the systematic scheme proposed in this effort.