Stream Of Uniform Droplets Research Articles

Numerical investigation of nozzle length effects on Rayleigh jet breakup behaviors and droplet formation properties at different modulation amplitudes in liquid droplet radiator

Uniform droplet stream generation is required for a liquid droplet radiator to achieve the efficient heat dissipation of space nuclear power systems. In this study, Rayleigh jets breaking into continuous droplet streams at different modulation amplitudes are numerically simulated to investigate the nozzle length effects on jet breakup behaviors and droplet formation properties. First, simulated results confirm that the growth of secondary instability wave on jet free-surface causes the jet breakup pattern transition from downstream pinching to upstream pinching. As the modulation amplitude is from 0.04 up to 0.16, the nozzle length range where the upstream pinching occurs in the jet breakup is broadened from null to 1–5. The essential reason for the increase of jet breakup length is the reduction of fundamental amplitude and the increase of full velocity relaxation length. Then, a comprehensive prediction model for the velocity-modulated jet breakup length is developed in agreement with the experiments, and the average relative error is below 7.38 %. Finally, two types of satellite droplet formation regimes including rear-merging and forward-merging satellite droplets are identified by the oscillation mode of the jet tip. It is found that the primary droplet generation frequency is equal to the external disturbance frequency and independent of nozzle length and modulation amplitude. Increasing the nozzle length and modulation amplitude can both increase the satellite droplet diameter and primary droplet spacing, while the primary droplet diameter is almost constant at around 1.85.

Study on linear bio-structure print process based on alginate bio-ink in 3D bio-fabrication

Ink-jet printing is a non-impact printing technology in which drops jetted from an orifice onto a designated position. This technology can digitally transport fluids containing cells precisely onto desired substrates to construct three-dimensional organs. In order to obtain the stable uniform droplets, a stream is the key point of this technology. However, there are so many factors that affect the uniform droplet stream construction process: print parameters, material parameters, control method, etc. A good understanding of the various coupled transport processes that occur during bio-ink impact and spreading on bio-structure can improve the success of print-ability. This paper aims to obtain a good linear bio-structure with ink-jet printing technology. First, a typical droplet deposition process model is constructed; including droplet dynamics impact models and droplet diffusion cap models. Second, a model of successive droplet overlap, to form linear bio-structures, is constructed. Third, the finite element method is used to simulate the droplet impact, collision, and fusion process. Finally, the main influencing factors of the continuous injection printing process, namely the time interval between consecutive droplets and the droplet contact angles, are discussed. Sodium alginate is selected as bio-ink to verify the theory, and it is found that a good linear bio-structure could be obtained if the printing parameters are controlled optimally, i.e., if the initial contact angle is set as 60 degrees and the trigger frequency is set as 150 kHz. With a proper printing speed and gel coating, a good survival rate of printed cells could be obtained.

Fully Embedded Flow Control Device for Microfluidic Applications

Microfluidics is a multidisciplinary field that is changing the way how biological research is being performed, enabling new applications and accelerating the existing ones. However, one of its most important drawbacks is the lack of technological tools to facilitate its widespread use. In this paper we present a new pressure and flow control device for the high-performance control of microfluidic applications. The main advantage of our device is that all pneumatic and electronic components, including the communications and control circuitry, are fully embedded inside the apparatus. Therefore, this device can be used as a standalone laboratory equipment and it can also be remotely operated from a personal computer. The microfluidic application used to demonstrate the performance of the proposed tool is the generation of alginate (1% sodium alginate solution) droplets in mineral oil. The generation of a stable stream of uniform droplets validates the good performance of our control device.

Detailed studies on the absorption kinetics of CO2 in aqueous solutions for small superficial liquid loadings

The absorption kinetics of CO2 in aqueous solutions for low superficial loadings have been measured with a droplet train reactor. A well defined stream of uniform droplets was exposed to an atmosphere with exactly known CO2 concentration. Based on the short gas-liquid contact time within the reactor and a sensitive volumetric measurement of the CO2 flux the analysis of CO2 mass transfer in the liquid droplets was performed for small liquid loadings.

Performance of droplet generator and droplet collector in liquid droplet radiator under microgravity

The Liquid Droplet Radiator (LDR) has an advantage over comparable conventional radiators in terms of the rejected heat power-weight ratio. Therefore, the LDR has attracted attention as an advanced radiator for high-power space systems that will be prerequisite for large space structures. The performance of the LDR under microgravity condition has been studied from the viewpoint of operational space use of the LDR in the future. In this study, the performances of a droplet generator and a droplet collector in the LDR are investigated using drop shafts in Japan: MGLAB and JAMIC. As a result, it is considered that (1) the droplet generator can produce uniform droplet streams in the droplet diameter range from 200 to 280 [µm] and the spacing range from 400 to 950 [µm] under microgravity condition, (2) the droplet collector with the incidence angle of 35 degrees can prevent a uniform droplet stream, in which droplet diameter is 250 [µm] and the velocity is 16 [m/s], from splashing under microgravity condition, whereas splashes may occur at the surface of the droplet collector in the event that a nonuniform droplet stream collides against it.

Study of sol–gel processing for fabrication of low density alumina microspheres

A sol–gel process for producing microspheres of low density alumina has been developed. A Dispal alumina sol and aluminum monohydrate were used as starting materials. Microspheres with spherical shape and controllable size have been produced by using a drop generation technique. The technique consists of producing a continuous stream of uniform droplets of alumina sol and then converting the drops into a rigid form by exposing them to an ammonium hydroxide gelation medium. By using this technique, alumina spheres with surface area 351 m 2 g −1 and pore size 10.7 A° have been prepared.

液滴ラジエータにおける液滴回収過程の観察

The first stage of droplet collection in a droplet collector of the Liquid Droplet Radiator is collisions of droplet streams with a liquid film formed in an inner surface of the collector. When the droplet streams are absorbed in this liquid film, no splashes should be formed to achieve high collection efficiency. As specifications of a droplet collector, a miscapture rate of incoming droplets is required to be less than 10-6. The collisions and the splashing phenomena of incoming droplets with a liquid film was observed by using a magnifying CCD camera with synchronized irradiation by a laser diode. When the uniform droplet stream is produced where the droplet diameter is less than 300mm, and the droplet speed less than 20m/s, no splash is observed.

液滴ラジエータ用均一液滴流の生成

The liquid droplet radiator (LDR) uses many streams of droplets to radiate heat to space. A droplet emitter of the liquid droplet radiator produces directed droplets streams from its orifices toward a droplet collector. During the flight, droplets loses heat by radiation. In order to constitute an effectivelly radiative droplet sheat and minimize the working fluid loss at the collector, uniformly formed and spaced droplet streams with a good aiming accuracy are required to be formed. To investigate the formation of such a uniform droplet stream, and develop the droplet emitter, a laboratory model with a single orifice was made. Diffusion pump oil (DC-704) was used as a working fluid, and squirted out from the orifice by applying pressure. In addition, pressure perturbation was caused by the piezoelectric ceramic to produce uniform droplets from the liquid jet coming out from the orifice. The formation characteristics of the liquid droplet stream was tested in a vacuum, and it was confirmed the liquid droplet stream thus produced reached the required level for the liquid droplet radiator.

Generation of controllable monodispersed sprays using impulse jet and charging techniques

A technique for producing a tunable monodispersed spray is developed with a combination of impulsed jet and charging techniques. A single orifice impulse-jet droplet generator, of a unique configuration, was used to produce a single stream of uniform droplets over a wide range of diameters. The single stream of droplets is dispersed with an electrostatic charging technique. Control of drop number density was enhanced by a droplet selection technique, in which a number of drops could be removed from the spray.