Browsing by Author "Liao, Ying-Hao"

Now showing 1 - 10 of 10

A novel micro-channel heat sink with trapezoid drainage for enhancing condensation heat transfer of dielectric fluid
(2019-09-01)
Chu, Wen-Xiao
;
Chen, Chuan-Yu
;
Liao, Ying-Hao
;
Wang, Chi-Chuan
;
機械工程學系
This study experimentally investigates the condensation of dielectric fluid HFE-7100 in a micro-channel heat sink with the hydraulic diameter of 1.21 mm. Tests are conducted at a fixed pressure of 110 kPa, with vapor mass quality (x(in)) ranging from 0.1 to 0.9, mass fluxes (G) from 150 to 250 kg.m(-2).s(-1), inclined angle ( theta) from -90 degrees to +90 degrees. A novel trapezoid drainage design is proposed to enhance the condensation heat transfer by effectively entraining condensation film. When G is lower than 200 kg.m(-2).s(-1), the two phase heat transfer coefficient (h(tp)) for the trapezoid drainage design exceeds the conventional rectangular micro-channel heat sink by 10-26% while the corresponding pressure drop is about 22-45% lower. When G is increased to 250 kg.m(-2).s(-1), the drainage design can still dramatically decrease the pressure drop, however, it shows a negative effect on h(tp) when the x(in) is greater than 0.2. With inclined arrangements, the pressure drop would dramatically increase due to gravity effect. Besides, at the conditions of theta = -45 degrees and -90 degrees, the trapezoid drainage channel can improve the h(tp) by 43-45% when G is lower than 200 kg.m(-2).s(-1). On the contrary, with the arrangement of theta = +45 degrees and +90 degrees, the trapezoid drainage channels may decrease the h(tp) by 8-15%. This phenomenon is especially pronounced at a high z i p. In addition, the heat transfer enhancement and deterioration are both analyzed based on stress distribution at vapor phase and condensation film.
A study on the influence of gas mixtures on the property of plasma-activated water
(1970-01-01)
Lai, Cheng-Chun
;
Deng, Yong-Xin
;
Liao, Ying-Hao
;
機械工程學系
;
Department of Mechanical Engineering
The present study applying a plasma jet to activate water in a controllable environment is aimed to investigate the effect of a combination of (working/chamber gas) on the properties of plasma-activated water. After 10 min of activation, results reveal that a significant decrease in solution pH is observed with the presence of N-2. Hydrogen peroxide appears to be the major species for most gas mixtures, except [Ar + air/Ar] and [Ar + air/air], where nitrite and nitrate dominate. A gas mixture of [Ar + air/Ar] produces the maximum concentration of NO2-, while the maximum NO3- and H2O2 are observed for [Ar + air/air] and (Ar/Ar), respectively. Overall, the antibacterial efficacy correlates well with NO2- concentration.
An Investigation on the Application of Plasma-Activated Gas to Laminar Lifted Nonpremixed Jet Flames
(2019-11-01)
Liao, Ying-Hao
;
Kuo, Hsin-Te
;
機械工程學系
;
Department of Mechanical Engineering
This paper is to experimentally investigate the effect of plasma-activated gas on the characteristics of a laminar lifted nonpremixed jet flame in a coflow stream. A coaxial dielectric-barrier discharge is employed to activate fuel (C3H8) and oxidizer, respectively. It is shown that an enhancement of 12% and 50% in the liftoff velocity is observed for oxidizer and fuel activation, respectively. With the addition of O-3 (1650 ppm) by oxidizer activation, the flame liftoff height is continuously decreased and the blowout velocity is extended. In contrast, a larger liftoff height, accompanied with a smaller blowout velocity, exhibits for flames with fuel activation. The inconsistent effect of fuel activation on the flame liftoff is presumably a contribution of the gas expansion, the conversion rate, and the corresponding product selectivity. The gas expansion is due to the fuel activation that produces lighter hydrocarbons than propane. The conversion rate and the H-2 and CH4 selectivities are found to be associated with the plasma energy density. The flame propagation can be greatly enhanced to produce a nozzle-attached flame when the plasma energy density is high enough to effectively decompose C3H8 into H-2. Nevertheless, a decrease in plasma energy is more sufficient for the cleavage of C-C bonds, resulting in a significant decrease in H-2 selectivity, but a nearly unaltered CH4 selectivity. The reduced conversion due to the lower plasma energy, along with the gas expansion, produces a lifted flame with a larger liftoff height than the nonactivated flame.
APPLICATION OF PLASMA DISCHARGES TO THE IGNITION OF A JET DIFFUSION FLAME
(2017-01-01)
Liao, Ying-Hao
;
Sun, Ming-Chien
;
Lai, Ru-Yi
;
機械工程學系
;
Department of Mechanical Engineering
The present study experimentally investigates the effect of plasma discharges on the ignition of a laminar methane jet diffusion flame in a stream of co-flow air. The Reynolds number of the jet flame, based on the nominal jet velocity and the nozzle diameter, is approximately Re = 2000. The plasma discharge, a corona type, is produced between two tungsten wires with a diameter of 0.5 mm and a gap of 15 mm. Results show that the application of plasma discharge in a near-nozzle region can ignite the flame. A non-reacting free jet similarity solution is applied to examine the ignition locations and it shows that many of the locations are outside the jet boundary, where the mixture is leaner than stoichiometry. The minimum input power required for flame ignition is seen to increase with radial distance away from the nozzle and decrease with downstream locations. A high input power required for ignition is found to be close to the nozzle exit, where a high strain can be expected. Spectroscopic study confirms the emission spectra in non-thermal air plasma and shows the intensity difference in spectra between discharges that ignite and do not ignite flames.
Effects of Plasma Discharges on the Ignition of a Laminar Nonpremixed Jet Flame
(2018-08-01)
Liao, Ying-Hao
;
Sun, Ming-Chien
;
Lai, Ru-Yi
;
機械工程學系
;
Department of Mechanical Engineering
This paper experimentally investigates the effect of plasma discharges on the ignition of a laminar nonpremixed methane jet flame in a stream of co-flow air. The Reynolds number of the jet flame, based on the nominal jet velocity and the nozzle diameter, is approximately Re- j = 2000. The plasma discharge, a corona type, is produced between two tungsten wires with a diameter of 0.5 mm and a gap of 15 mm. Results show that the application of plasma discharge in a near-nozzle region is capable of ignition of the flame studied here, even though most of the ignition locations are in the lean side of the stoichiometric methane mass fraction. In general, the ignition probability (i.e., flame ignition is successfully achieved) is relatively larger as the discharge is closer to the stoichiometric methane mass fraction. In addition, the ignition probability is seen to increase with the discharge energy density. Results of the most probable ignition time, defined as the mode of the probability density function of the required flame ignition time, are consistent with those of the ignition probability. The most probable ignition time is seen to decrease with the increased ignition probability. Overall, the shorter ignition time occurs when the discharge is closer to the stoichiometric methane mass fraction or when the discharge energy density becomes larger. The estimated reduced electric field suggests the importance of the electron-impact dissociation induced by plasma discharges to the flame ignition.
Guest Editorial Introduction to the Special Issue on the 10th Asia-Pacific Symposium on Plasma Technology (APSPT 2017)
(2019-02-01)
Hsu, Cheng-Che
;
Wei, Ta-Chin
;
Liao, Ying-Hao
;
Tanaka, Yasunori
;
Teii, Kungen
OH-PLIF Imaging of the Reaction Zone in Swirled, Strongly-Pulsed Jet Diffusion Flames with a Low Reynolds Number
(2018-01-01)
Liao, Ying-Hao
;
Hermanson, James C.
;
機械工程學系
;
Department of Mechanical Engineering
Planar laser-induced fluorescence (PLIF) imaging of the OH radical was used to study the reaction-zone structure in the near-nozzle region of strongly-pulsed jet diffusion flames in the presence of a swirling coflow. The nominal steady jet velocity at the nozzle exit leads to a Reynolds number of Re-jet = 5000. Ethylene-fueled flames were investigated over a wide range of injection conditions and different swirl levels. OH PLIF imaging was successfully employed in these highly sooting flames by careful selection of the laser fluence and camera gate width to minimize soot-related signal interference. The reaction-zone structure, as indicated by OH PLIF, is broadly consistent with the observation of luminous flame structure for these types of flames under the same injection conditions. The overall area of the reaction zones, as indicated by statistics generated from the OH PLIF signals, is generally higher for strongly-pulsed flames compared to steady flames. In addition, the measured reaction-zone area generally increases with increased swirl level, consistent with a broader and more convoluted reaction-zone structure for flames with swirl. The root mean square of the reaction-zone area, which is broadly indicative of the degree to which the reaction zones are impacted by the local flow fluctuations, is generally higher for flames with swirl than for those without swirl, suggesting a relatively stronger impact of flow turbulence on the flame structure of swirled flames. In many cases, the reaction zones were observed to exhibit discontinuities (i.e., non-ignition of fuel) at the instantaneous flame tip in the early period of fuel injection. The discontinuities are less evident for the case of flames with swirl.
Parametric Study on Thrust Vectoring with a Secondary Injection in a Convergent-Divergent Nozzle
(2020-07-01)
Chen, Jun-Lin
;
Liao, Ying-Hao
;
機械工程學系
;
Department of Mechanical Engineering
This work investigated the performance of thrust vectoring with a secondary injection in a convergent-divergent nozzle. Analytical modeling was conducted to determine the shock location and shock angle, providing a guideline for system design and performance. Thereafter, numerical simulation was performed to understand the effects of the injection pressure, injection location, injection angle, and injectant on thrust vectoring performance. Satisfactory agreement between the analytical modeling and numerical simulation suggests that shock reflection within the nozzle must be avoided to produce efficient thrust vectoring. Numerical results showed that both the injection pressure and the injection location have significant impacts on the thrust angle. The lateral thrust, and hence the thrust angle, was found to increase with the injection pressure and to be larger when the injection was situated closer to the nozzle exit. Impacts of the injection angle and the injectant on the thrust angle were found to be insignificant. However, hydrogen peroxide (H2O2) can be more effective at producing a side thrust than can air.
Plasma-Assisted Stabilization of Lifted Non-premixed Jet Flames
(2018-03-01)
Liao, Ying-Hao
;
Zhao, Xiang-Hong
;
機械工程學系
;
Department of Mechanical Engineering
The present study experimentally investigates the effects of plasma discharges on the stabilization of lifted non premixed jet flames in a stream of co-flow air. The plasma discharge is produced on the sharp edge of the fuel nozzle exit, facilitating its impact on flame stabilization. It is observed that the application of plasma discharges has an impact on the enhancement of flame lift-off velocity, lift-off height, and hysteresis phenomenon and leads to plasma-attached flames, plasma enhanced lifted flames, and plasma-ineffective lifted flames, depending on flame lift-off conditions. A maximum enhancement of approximately 84% is observed for the flame lift-off velocity when the co-flow velocity is sufficiently low. As the co-flow velocity or the jet Reynolds number is low, the flame is anchored at the nozzle by the discharge. As the co-flow velocity or the jet Reynolds number is increased, the flame detaches but with a decrease in lift-off height compared to the flame without the discharge. If the co-flow velocity of the jet Reynolds number is continuously increased such that the flame lift-off height is beyond a critical value, the effect of plasma discharges diminishes and the flame lift-off height becomes comparable to that without plasma discharges. In flame hysteresis studies, both of the flame lift-off and reattachment velocities are increased with 2-fold enhancement when the discharge is present. Spectroscopic study shows that the emission characteristics, particularly for those between 400 and 800 nm, in flames are intensified with the presence of plasma discharge, consistent with the flame luminosity visualization, probably due to the reduced lift-off height that leads to reduced air premixing, resulting in increased soot formation.
Propagation of tribrachial flames with ozone in a laminar non-premixed jet
(2020-05-01)
Tsai, Tsung-Feng
;
Liao, Ying-Hao
;
機械工程學系
;
Department of Mechanical Engineering
Effects of ozone on the propagation characteristics of the tribrachial flame in a laminar co-flow jet are experimentally investigated. Ozone is generated by a coaxial plasma reactor which can produce a maximum O-3 concentration of 2850 ppm with a power consumption of 76.5 W. A high-speed camera is employed to record the stationary and propagating flames both with and without ozone, by which the flame displacement and propagation speeds can be determined. It is shown that the flame stability characteristics are altered with the addition of O-3, in which a flame with decreased lift-off height and enhanced lift-off, reattachment and blowout velocities is observed. The enhanced flame stability with O-3 addition is due to an increase in flame displacement and propagation speeds. A scaling argument shows that the enhanced flame propagation speed is strongly related to the O-3 kinetic enhancement on laminar flame speed. Due to the distinct flame structure, the accompanied hydrodynamic enhancement by O-3 addition facilitates the tribrachial flame propagation, implying an over-prediction of the O-3 kinetic enhancement. The hydrodynamic enhancement with O-3 presence originates from a stronger flow redirection, due to the higher sensitivity of off-stoichiometric flames to O-3 enhancement on laminar flame speed, and a more slanted flame front, due to the increased velocity gradient.