ABSTRACT
The needle valve, serving as the flow control unit of the thruster system, is a crucial component of the entire thruster. Its performance directly impacts the flow state of the rarefied gas in the micro-nozzle structure of the cold gas micro-thruster, thereby exerting a significant influence on the high precision and stability of the propulsion system as a whole. This study examines the impact of different needle valve structures on the flow and thrust in micro-nozzles using the DSMC method. The analysis includes discussions on the spatial distribution, Kn distribution, slip velocity distribution, and pressure distribution of the micro-nozzle's flow mechanism. Notably, increased curvature of the needle valve enhances the flow velocity in the throat and expansion section. The magnitude of the curvature directly affects the flow velocity, with larger curvatures resulting in higher velocities. Comparing different spool shapes, the conical spool shape minimizes the velocity gradient in the high-speed region at the junction between the spool area and the outlet pipe, particularly with a wide opening. Increasing the curvature of the spool leads to a higher velocity in the expansion section. Consequently, an arc-shaped spool valve maximizes the nitrogen flow at the nozzle during wide openings, thereby enhancing thrust. These research findings serve as a valuable reference for the structural design of the needle valve in the micro-nozzle of the cold gas micro-thruster.
ABSTRACT
When the satellite is in orbit, the thruster will experience drastic temperature changes (100-1000 K) under solar radiation, which will affect the rarefied gas flow state in the micro-nozzle structure of the cold gas micro-thruster. In this study, the effect of different wall temperatures on the rarefied flow and heat transfer in the micro-nozzle is investigated based on the DSMC method. The micro-nozzle structure in this paper has a micro-channel with a large length-to-diameter ratio of 10 and a micro-scale needle valve displacement (maximum needle valve displacement up to 4 µm). This leads to more pronounced multiscale flow characteristics in the micro-nozzle, which is more influenced by the change in wall temperature. At wall temperatures ranging from 100 K to 1000 K, the spatial distribution of local Kn distribution, slip velocity distribution, temperature, and wall heat flux distribution in the micro-nozzle were calculated. The slip flow region is located in the flow channel and transforms into transition flow as the slip velocity reaches approximately 50 m/s. The spatial distribution of the flow pattern is dominated by the wall temperature at small needle valve opening ratios. The higher the wall temperature, the smaller the temperature drop ratio in the low-temperature region inside the micro-nozzle. The results of the study provide a reference for the design of temperature control of micro-nozzles in cold gas micro-thrusters.
ABSTRACT
For mass production of liposomes, we designed a plastic micro-channel device on the basis of 5 µm of micro-nozzle array forming T-junction with 100 µm depth of micro-channel. A micro-channel unit for synthesizing liposomes consisted of two micro-nozzle arrays for mixing two solutions as well as delivery and recovery channels for supplying solutions and collecting liposome suspension. The number of micro-nozzles was approximately 2400 for a micro-channel unit, and seven units were applied independently on a micro-channel plate. The plastic micro-channel plate was injection-molded for mass production using a micro-channel stamper previously fabricated by UV lithography and nickel electroforming process. A plastic cover plate with seven pairs of inlet and outlet ports was machined by mechanical milling and drilling and was assembled with a micro-channel plate using a holder to form a liposome synthesizing device. Flow and mixing of solutions in the micro-channels were tested using colored water to check the micro-fluidic characteristics of the device. Finally, a L-α-phosphatidylcholine (SOY PC) liposome was synthesized using EtOH solution of SOY PC (95%) and saline (0.85% NaOH solution) to find that the liposomes were around 230 and 260 nm in diameter, depending on the flow rate of the lipid solution.
ABSTRACT
We report on the application of femtosecond laser micromachining to the fabrication of complex glass microdevices, for high-order harmonic generation in gas. The three-dimensional capabilities and extreme flexibility of femtosecond laser micromachining allow us to achieve accurate control of gas density inside the micrometer interaction channel. This device gives a considerable increase in harmonics' generation efficiency if compared with traditional harmonic generation in gas jets. We propose different chip geometries that allow the control of the gas density and driving field intensity inside the interaction channel to achieve quasi phase-matching conditions in the harmonic generation process. We believe that these glass micro-devices will pave the way to future downscaling of high-order harmonic generation beamlines.
ABSTRACT
A micro droplet generator based on V-shape linear ultrasonic motor was prepared to produce micro droplets with higher accuracy in the field of biochemistry.The device was composed of a micro droplet generator which was driven by the V-shaped linear ultrasonic motor, a three-dimensional displacement platform based on V-shaped linear ultrasonic motor, and a micro droplet separation unit based on the piezoelectric vibrator.The generating part consisted of an ultrasonic motor, a medical syringe, a silica flexible tube and a self-made micro nozzle based on glass.Utilizing the drive controller to drive the linear ultrasonic motor, the slipway pushes forward the syringe and the micro droplet was attached to the glass nozzle.The natural mode of the rod nozzle was excited by the piezoelectric vibrator.The attached droplet was separated from the tip of the nozzle after overcoming the viscous force.The separated droplet fell in a certain range.And the radius of the spherical droplet was calculated.In the experiment, distilled water was used as the initial liquid to investigate the characteristics of the micro droplets produced by the device.The experimental results showed that the droplet was attached to the tip of the micro nozzle which was formed by distilled water under the linear motor.By the vibration of the separation unit, the attached droplets formed the spherical droplets by overcoming the viscous forces in the tip of the nozzle.The radius of spherical droplets generated by this device was less than 40 μm by measuring the size.
ABSTRACT
To improve the jetting performance of liquid metals, an electromagnetic micro-jetting (EMJ) valve that realizes drop-on-demand (DOD) jetting while not involving any valve core or moving parts was designed. The influence of the lead angle of the nozzle on the jetting of liquid metal gallium (Ga) was investigated. It was found that the Lorentz force component parallel to the nozzle that jets the electrified liquid Ga is always larger than its internal friction; thus, jet can be generated with any lead angle but with different kinetic energies. Experimental results show that the mass of the jetting liquid, the jetting distance, the initial velocity of the jet, and the resulting kinetic energy of the jet increase first and then decrease. When the lead angle is 90°, the mass of the jetting liquid and the kinetic energy are at their maximum. When the angle is 80°, the initial velocity achieves its maximum, with a calculated value of 0.042 m/s. Moreover, very close and comparatively high kinetic energies are obtained at 80° and 90°, indicating that angles in between this range can produce a preferable performance. This work provides an important theoretical basis for the design of the EMJ valve, and may promote the development and application of micro electromagnetic jetting technology.
