Size effect on gas flow in micro nozzles

Abstract

The performance of a micro propulsion system is determined primarily by the performance of the micro nozzles. A rectangular cross-section convergent–divergent micro nozzle, with a throat width of 20 µm and an expansion area ratio of 1.7, is fabricated and studied using experiment and numerical simulation. Experiments are conducted to measure the mass flow rates and pressure distributions near the nozzle's throat under various outlet pressures. The results of the numerical simulations accord with the experimental data. Moreover, differences between the micro scale flow and the conventional scale flow are discovered from the simulation results. The Mach number near the downstream position of the micro nozzle's throat is lower than that in the conventional nozzle. In the divergent region of the micro nozzle, there is a supersonic area instead of the shock wave that usually occurs in the conventional scale nozzles. The results of the numerical simulation also show that the position of the sonic point moves away from the throat towards the outlet with the decrease in the size of the nozzle. This particular behavior is attributed to the higher viscous dissipation in micro nozzles as compared to that in the conventional scale nozzles.

Large eddy simulation of highly turbulent under-expanded hydrogen and methane jets for gaseous-fuelled internal combustion engines

“…The distance of this normal shock from the nozzle exit increased quickly and at t10t 0 (t=18 μs) the shock can be considered as a Mach disk which in conjunction with the intercepting shock form the first shock cell (barrel-shape shock). The larger scale counterparts [69][70][71][72]. For instance, in a micro-size convergent-divergent nozzle Hao et al [72] noticed that, by scaling down the nozzle size, the Mach number at the throat and the nozzle exit decreased and the choked condition moved away from the throat towards the exit.…”

“…The larger scale counterparts [69][70][71][72]. For instance, in a micro-size convergent-divergent nozzle Hao et al [72] noticed that, by scaling down the nozzle size, the Mach number at the throat and the nozzle exit decreased and the choked condition moved away from the throat towards the exit. The nozzle used in the current study had two sections, a converging part and constant area section with length of 0.6D ( Figure 2).…”

“…As mentioned earlier, for all jets of the current at semi-steady conditions, Ma=1 occurred at about 0.1D downstream of the beginning of the constant area section. This can be explained by high compressibility effects [70] and high viscosity dissipation due to increased surface-to-volume ratio [72]. Just after the sonic line, expansion fans started forming and caused the flow to accelerate and reach a maximum Mach number of about 1.3 at about 0.2D upstream of the nozzle exit where the reflected fans (from the nozzle wall) produced normal-shape shock which changed the flow condition to subsonic.…”

Fabrication of Microglass Nozzle for Microdroplet Jetting

“…The diameter size, the flow channel geometry, and fluid impedance are the key factors affecting the ejection capacity [1][2][3][4][5][6][7][8]. Each application requires an optimal shape and size for micronozzles; hence a controllable fabrication process is extremely desirable [9][10][11][12][13]. Currently, micronozzles have been made by several methods including micromechanical drilling, laser drilling, electroforming over a sacrificial post, electron beam machining, electrodischarge machining, lithography and etching, deep reactive ion etching (DRIE), LIGA process, and bulk-silicon etching [14].…”

A computational study of gas flow in a De‐Laval micronozzle at different throat diameters

“…Although the geometric effect has got the attention of many researchers in the past, the available data are within very limited ranges of Reynolds number and throat diameter for micronozzles [20].…”