Since the intake aperture is fixed, a larger but still duct {HEAD ~ wall} defined and confined air mass must undergo a velocity step up when moving into a larger volume exhaust terminated aperture, according to {TAIL ~ the Bernoulli or venturi principle} 
Since the intake aperture is fixed , a larger but still duct { HEAD ~ wall } defined and confined air mass must undergo a velocity step up when moving into a larger volume exhaust terminated aperture , according to { TAIL ~ the Bernoulli or venturi principle }
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