Hood Design

Posted in: , on 7. Sep. 2011 - 23:49

please advise me,

I am try design canopy hood for our SIGMA Mixer , we are Mixing soda ash . calcite and sodium salphate by using sigma mixer , ingredients load by manually through 400 mm opening hole at SIGMAS MIXER.

for loading condition there is huge dust is generating , we are planning to design enclose ( 3 sides and top ) extraction hood ,only openning area is 4ft X 2ft . please refer drawing.

sigma mixer

then I was calculate CFM required by using Q=0.75V(10x^2 + A)

where v = 350 ft/min - capture velocity

x = 1.5 ft

A = 2ft X 3 ft

Q= 7481 cfm , duct size is around 440 mm ? I am not confidence for my calculation , I think it is too much what is yours suggestions

uditha kohowala

53/46 , Eksath mawatha


Sri Lanka




Hood Design

Posted on 10. Sep. 2011 - 01:12

Your calculation is correct if you follow the guidelines in the handbooks. The selection of capture velocity is a highly subjective business and depends on how well you can enclose the process. The more complete the enclosure, the lower the capture velocity.

If the materials can be loaded from paper bags opened inside the hood, then a hood face velocity of 200 fpm (maybe even 100 fpm) is adequate. As you already know, the airflow rate increases as the square of the distance from the source and the capture velocity must be higher (and take into account the disturbing influence of external drafts etc).

If the material is scooped from a drum, there will be fugitive dust released between the drum top and the hood. Try to keep the drum as close to the hood face as possible.

Michael Reid.


Posted on 11. Sep. 2011 - 06:28

Thanks Michel , you are always help me

as my concern , last 2 ~ 3 years more experts , specialist , engineers reply in this forum ,but unfortunately today this expertise knowledge is in very limited in this forum, there for same time , thank you very much for your cooperation .

uditha kohowala