Fans And Ventilation Flashcards
What instrument is used to measure fan pressure?
Manometer
Reads Three types of pressure developed by fans: static, velocity, and total pressure depending on which way it is connected to the outlet duct
What is static pressure?
The pressure the air exerts on the inside of the duct walls or piping and is what overcomes the resistance of ducts, fuel beds and grates.
What is velocity pressure?
The pressure over and above static pressure. It is created by the impact of air flowing through a duct and is felt only by the surfaces that the air actually strikes
What is total pressure?
When you add velocity pressure and static pressure
What are the two types of fans?
Centrifugal
Axial flow
What are the tree types of axial fans?
Tube axial
Vane axial
Propeller
What are the three variations of mechanical draft?
Induced draft - pressure in the furnace is below atmospheric pressure. Locate fan between boiler and chimney.
Forced draft - boiler is cooled
Balanced draft - has forced draft fan and induced draft fan.
Where is the fan placed on a furnace to create induced draft?
Between the boiler and the chimney
What are the four general approaches to pollution control?
Intermittent reduction
Wider dispersion
Reduction of pollutants
Change the industrial process
What is the preferred approach of pollution control?
Change the process
What organization sets the rules for Handling of dangerous materials?
WCB
What types of equipment are used to control pollutants?
Filters
Electrostatic precipitators
Cyclones
Mechanical collectors
Scrubbers
Absorbers
Burners
Ultraviolet
Describe the primary treatment of wastewater?
Screen out large debris
Skim off floating debris
Settle out suspended material
What is secondary treatment of wastewater?
Biological treatment is used to breakdown organic matter then skimmed off
What does advanced treatment remove?
Nutrients that promote algae growth
Industrial pollutants (heavy metals and non biodegradable organic materials
Why are small particles so dangerous?
They can imbed deep into the lungs
What are the four techniques to remove particles from the air?
Cyclone separator
Wet scrubber
Electrostatic precipitator
Bag-house
What size particulates in oil smoke?
.01-1
What mechanisms are used to collect solid pollutants from the air?
Wet and dry collectors
Gravity settling chambers
Gravity spray towers
Cyclones
Muti clone collectors
Centrifugal spray scrubbers
Why special problems are present with wet particulate collectors?
Create water pollution
Subject to corrosion
Can freeze
What are the advantages/ disadvantages of gravity settling chambers?
Very low energy cost
Low maintenance cost
Low installation cost
Excellent reliability
High efficiency
Very large
Only used for course particulate
What is the advantage of a multi clone collector?
Collect more efficiently without using more power
Is a bag house a primary or secondary filter?
Secondary small particles will always escape
What is an advantage and disadvantages of bag houses?
Can remove 100percent of particles as fine as .4microna
Can be combustible
Bags are effected by humidity and chemicals
Expensive
Industrial plant and building require efficient air and gas movement through fans. From shop ventilation to material handling to boiler applications, fans are necessary for process support and?
Human health
How is static pressure converted to velocity pressure?
How is velocity pressure converted to Static pressure?
By gradually decreasing the cross sectional area of the duct(converging)
By increasing the cross sectional area of the duct (diverging)
Fans can be used in series or parallel. Series fans are used to?
Parallel fans are used to?
Fans in series are used to increase outlet pressures
Parallel fan arrangements are used where a spare or backup fan is needed
What are some advantages of mechanical draft fans?
- independent of atmospheric air temperatures
- they are independent of chimney temperature. Natural draft this is a very important factor
- can be regulated more accurately than natural draft.
- they have better draft regulation, which increases efficiency of combustion
Three types of backward inclined blade fans?
Flat blade - most robust
Curved blade - more efficient than flat blade
Air foil - most efficient of all. Can exceed efficiency’s of 85%.
All backward inclined fans require less HP to driver specific air volume and are more efficient than forward curved fans.
Forward blade fans (squirrel cage) are typically used in _______ fans?
Small fans
Residential heating, ventilation, HVAC applications
Ideal fan blade for high pressure service?
Radial blade fans
- easy to maintain
- flat blade shape limits material build up and are capable of handling high particulate airstreams such as dust, wood chips and metal scrap.
Open wheeled radial blade is meant for?
Handling air containing small wood blocks, silage(paper trim), or similar materials.
Open wheel and backplate radial fan blades can handle air containing small wood blocks, silage(paper trim) and similar materials. What advantage does the back plate wheel have?
- adds strength and rigidity
- prevents long, fibrous, or stringy materials from wrapping around the wheel
Open wheel and backplate radial fan blades can handle air containing small wood blocks, silage(paper trim) and similar materials. What advantage does the back plate wheel have?
- adds strength and rigidity
- prevents long, fibrous, or stringy materials from wrapping around the wheel
Air flow in axial fans is parallel to the shaft axis. What are the three main groups?
Propeller fan - typically used in air-cooled condenser, unit heaters, exhaust fans for ventilation purposes
Tube axial fan - heavier duty can be mounted within ducting. Loose energy due to friction because of air swirl.
Vane axial fan - similar to tube axial fan but outlet guide games to eliminate most of the airflow swirl making it much more efficient
How come induced fans require more maintenance then forced draft fans?
Induced fans run at significantly higher temperatures and are subjected to boiler ash that builds up on the blades, creating cracks and imbalance problems.
Correct outlet duct length creates good _________ flow. Achieving good laminar flow is important before putting any bends in.
Laminar flow
When performing maintenance on fans you would shut the fan down then ____ and lock it out electronically. Sometimes the inspection cover is removed and the fan wheel is blocked to prevent what?
Isolate
Prevent backward rotation due to reverse flow through ducts and dampers
