local exhaust ventilation 4
1-At the hood, if all of the available static pressure can be converted to velocity pressure (that is, 100%), please determine the value and relationship for the following parameter: SPh _________ VP (<, = or >); Hood entry loss (he) = _______” w.g.; Hood loss factor K (or Fh) = __________; Hood’s efficiency (Ce) = __________.
2-How many duct diameters away from the hood (or from the beginning of the duct), should you take SP measurement in the duct?
3-Please give at least two specific hood examples for the following types of hood: 1) Enclosing hood; 2) Capture hood; 3) Receiving hood. Look at page 6-10.
4-To allow LEV to remove airborne contaminates from the working environment, the SP in the hood should be positive or negative? Briefly explain the reason.
5-Look at ABIH sheet 9-a, compare the bell mouth entry to the plain duct end, and determine the percentage of SP converted into VP (or calculate VP/SP*100%) between the two hoods. Remember, you can use Ce equation to solve this question. This question will help you understand why adding flange is important.
6-Modified Exercise 6-6: What is the estimated flow rate through a hood if K = 0.1, SPh = -2.0 inch w.g., and the duct diameter is D = 24 inches? (Assume STP, d = 1).
7-Use your own words to explain why hood is one of the most important components for LEV system?
8-At the hood with df = 1, if only 90% of the available static pressure can be converted to velocity Pressure (that is, VP = – 90% SPh or 90% absolute value of SPh), please determine the value and relationship for the following parameter: Hood’s efficiency (Ce) = __________; Hood loss factor K (or Fh) = __________ ; Hood entry loss (he) = _______% of SPh. You should include appropriate unit and keep three decimals.
9-Use your own words to explain why you will not take pressure measurement within hood or at the entrance to the duct?
