Shock, shockwave pressure effect

The microchannel geometric characteristics are length (2L) and hydraulic diameter (Dh, equal to four times the area divided by the perimeter of a section), shown in Fig. la. The model relates the efficiency of the compression process to the velocity, pressure, and temperature of the gas at the entrance of the channel (station 1 Mj, pi, Ti) the pressure ratio across the shock 11s the friction coefficient fi and channel dimensicms. fri Fig. la, a shockwave is shown that moves in the opposite direction to the flow and is positioned in the middle of the channel. It can be shown that a snapshot evaluatimi at the mid position is a good representation of the overall results and does not affect the accuracy of the model. Friction is considered along the lengths L before and after the shock. The frictional effect is modeled as shear stress at the wall acting on a fluid with uniform properties over the cross section. 

These IR complex index component spectra were used to calculate the spectral effects that would be observed in a shock compression experiment. Figure 12 shows the time-dependent IR reflectance spectra calculated for normal incidence and p polarization in a 1 pm thick PMMA film during passage of the shockwave, assuming no pressure shift of the band frequencies. The uniaxial shock compression ratio fVE = l/(l-Up/us) was 1.5, as expected for... 

Experiments with a miniature shock tube using low pressures to simulate the effects of small scale have shown qualitative agreement with the proposed model. The effects of scale are even more pronounced than what has been predicted by the model. Experimental and numerical investigations for incident shock Mach number of M = 1.2 have shown significant viscous effects for channel heights below 4 mm even at atmospheric pressure. That shockwaves propagate more slowly at low pressures in a narrow channel has been confirmed, but they may... 

The data trend of the above presented analytical study has been verified by computational fluid dynamics (CFD) analysis. Moreover, some microscale-specific effects could be seen for the initial part of the process, the pressure drop is confined over a short distance (between stations 2 and 3 in Fig. 5a) as the shockwave travels further from the left to the right, the pressure gradient dissipates more and more continuously over a longer range. Instead of a well-defined shockwave, a set of conpres-sion waves can then be seen distributed over more than a half of the length of the channel (Fig. 5b). This effect has already been noted in experiments with microscale shock tubes [9], originating from the stronger influence of the viscous forces at low Reynolds numbers. In the den-... 

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