Patent ID: 7819727

Claim:
A computer-based method of manufacturing a push-pull type ventilation hood having a push device to obtain a push air flow and a pull device to exhaust contaminant flow with an exhaust opening, when the push flow flows through a contaminant source, a contaminated flow of the push flow is exhausted through the exhaust opening, a pull hood flange is set vertically to the direction of the push flow and the pull device, which comprises the steps of: a) determining a liquid-surface rising velocity (vg) and a ratio of a chemical tank length (H) to a pull hood opening height (D) (H/D); b) determining a smallest pull velocity (v s * ) according to a smallest pull velocity definition being: ( v s * /v g )=(−1718.285 v g 3 +981.659 v g 2 −215.819 v g +29.003)×exp[(−7.264 v g 3 +2.881 v g 2 −0.305 v g +0.062)( H/D )]; c) determining a smallest push velocity (v b * ) for the smallest pull velocity (v s * ) by referring to a figure showing boundaries of four characteristic flow regimes for a simulated chemical tank having a predetermined length, wherein the four characteristic flow regimes are regimes of dispersion, transition, encapsulation and strong suction; d) determining a corresponding slope (S) utilizing a corresponding slope-definition; e) selecting a push velocity (v b ) having a value between the smallest push velocity and 1 m/s (meter per second); f) determining and outputting a pull velocity (v s ) utilizing a pull velocity definition defined as: v s >=v s * +S ×( v b −v b * ); and g) outputting push-pull type ventilation hood design parameters on a computer based on computer calculations performed in steps a-f.