For the design of a venturi type scrubber, the throat velocity is 100 m/s, particles to be collected have 2-m diameter, and water droplet diameter is 200 m. Liquid to gas flow ratio is given as 10^-4. Calculate the total throat length (in mm) to reach 99.99% of collection efficiency (V_rel = 0.8 V_g, _p = 2,500 kg/m³, _air = 1.8x10^-5 kg/m.s) ????