Quiz: Industrial Fans and Application Product Lines¶
Test your understanding of plug, vaneaxial, radial, pressure blower and packaged fan lines, application fans, and lab exhaust flow with these review questions.
1. What feature of a plug fan keeps the motor and drive components out of the process air?¶
- A section of stationary guide vanes behind the impeller
- A gusseted mounting panel fastened to the outside of the plenum wall
- A belt tube that carries the belts across the airstream
- A scroll housing that surrounds the impeller inside the plenum
Show Answer
The correct answer is B. A plug fan is an unhoused centrifugal fan "plugged" into a plenum wall. The mounting panel fastens to the outside of the wall while the impeller sits inside, so the panel separates the motor and drive from the process air and lets the fan be installed and removed as a unit. Guide vanes belong to vaneaxial fans, a belt tube to belt driven tubular fans, and a plug fan has no scroll housing of its own; the plenum does that job.
Concept Tested: Plug Fan
2. Why can a vaneaxial fan reach pressures that a plain tubeaxial fan cannot deliver efficiently?¶
- Its impeller turns faster because it is always direct driven
- It draws air through two inlets, one on each side of the impeller
- Its housing is narrower than a tubeaxial housing of the same size
- Its stationary guide vanes turn part of the swirl's rotational energy into static pressure
Show Answer
The correct answer is D. Air leaving any axial impeller swirls around the axis, and that swirl carries energy that does not appear as useful duct pressure. A vaneaxial fan adds a section of stationary guide vanes that straighten the flow and recover part of that rotational energy as static pressure. That is why the catalog describes vaneaxial fans as moving large volumes at moderate to high pressures in a compact tube. Vaneaxial fans come in both direct and belt driven versions, and double inlets and narrow housings belong to other fan types.
Concept Tested: Vaneaxial Fan
3. A customer wants a direct drive plug fan, but the airstream is hot, so the impeller should not sit on the motor shaft. The plenum wall can carry the fan and there is room for a long assembly. Which arrangement fits?¶
- Arrangement 8
- Arrangement 4
- Arrangement 9P
- Arrangement 4P
Show Answer
The correct answer is A. Work the three questions in order. Direct drive leaves Arrangements 4, 4P, 8 and 8P. A hot airstream may limit Arrangement 4 and 4P, where the impeller is mounted on the motor shaft, so the motor-coupled-to-fan-shaft design, Arrangement 8, is used. The wall is adequate, so the wall-mounted version applies rather than 8P. Arrangement 9P is belt driven and grade mounted, which the customer did not ask for.
Concept Tested: Plug Fan
4. Which statement best describes the trade-off between a radial tip fan and a radial bladed fan?¶
- The radial bladed fan is more efficient at high airflow, while the radial tip fan is more rugged
- Both have identical efficiency, so the choice depends only on the housing material
- The radial tip fan is much more efficient at high airflow, while the radial bladed fan still wins when the material is bulky, sticky or abrasive
- The radial tip fan is meant only for clean air on the clean side of a filter
Show Answer
The correct answer is C. A radial tip impeller is curved forward at the entering edge and radial at the tip, so it suits dirty, particulate-laden air while letting air onto the blade more smoothly. The current catalog states that at high airflows it is much more efficient than a comparable radial blade fan. The radial bladed fan, the industry's "workhorse," remains the choice when durability must outrank efficiency because the material is bulky, sticky or abrasive. Option A reverses the trade-off.
Concept Tested: Radial Tip Fan
See: Radial Tip Fans
5. A process fan must move 20,000 CFM at 10 in. wg total pressure with a total efficiency of 65%. Using BHP = (Q × TP) / (6356 × η), about how much brake horsepower does it draw?¶
- About 31.5 BHP
- About 20.5 BHP
- About 48.4 BHP
- About 74.5 BHP
Show Answer
The correct answer is C. Multiply airflow by total pressure: 20,000 × 10 = 200,000. Multiply the constant by the efficiency: 6356 × 0.65 = 4,131. Then 200,000 / 4,131 ≈ 48.4 BHP. Option A leaves out the efficiency (that is the air power), option B multiplies by the efficiency instead of dividing, and option D divides by the efficiency twice. Lower efficiency always means more brake horsepower for the same duty.
Concept Tested: Radial Tip Fan
See: Radial Tip Fans
6. Which description fits a pressure blower?¶
- A housed centrifugal with a narrower housing and impeller width, built for high pressure at relatively low airflow
- A double-inlet scroll fan mounted inside an enclosure for large volumes at low pressure
- An axial impeller in a flat panel housing with a stack cap or hood
- A forward curved double inlet impeller sold without a housing
Show Answer
The correct answer is A. FanPedia notes that pressure blowers have narrower housings and impeller widths than standard centrifugal fans. The current catalog adds that their performance is stable through the operating range and that they can be turned down to zero flow with a discharge damper. Option B describes a duct fan, option C a roof mounted panel fan, and option D an air kit.
Concept Tested: Pressure Blower
See: Pressure Blowers
7. A customer asks for a fan for a dust collector and says only that the air is "dirty." Which fact should you pin down first to decide between a high-efficiency clean-air fan and a rugged dirty-air fan?¶
- Whether the collector is indoors or outdoors
- Whether the motor will be direct drive or belt driven
- The color and finish the customer wants on the housing
- Whether the fan sits on the clean side of the filter or handles dust-laden air, as on a cyclone
Show Answer
The correct answer is D. The current application page states the split: backward inclined fans are used on the clean side of a filter, where the dust has already been removed, and radial bladed fans are used for cyclone applications, where dust-laden air reaches the fan. The fan's position relative to the filter decides which family survives the airstream. Location, drive type and finish matter to the order, but none of them decides between an efficient clean-air fan and a rugged dirty-air fan.
Concept Tested: Dust Collection Fan
8. A lab's fume hoods exhaust 6,000 CFM of contaminated air, the bypass damper admits 4,000 CFM, and the nozzle entrains another 10,000 CFM. What is the fan flow the fan is selected on, and what is the lab exhaust total flow?¶
- Fan flow 20,000 CFM; total flow 20,000 CFM
- Fan flow 10,000 CFM; total flow 20,000 CFM
- Fan flow 6,000 CFM; total flow 16,000 CFM
- Fan flow 16,000 CFM; total flow 20,000 CFM
Show Answer
The correct answer is B. Contaminated air and bypass air both pass through the impeller, so fan flow is 6,000 + 4,000 = 10,000 CFM. Entrained air joins only after the air leaves the fan, so total flow is 10,000 + 10,000 = 20,000 CFM. Option A sizes the fan to the total flow, which the chapter warns against. Option C leaves out the bypass air, and option D counts the entrained air in the fan flow.
Concept Tested: Lab Exhaust Total Flow
9. Why should a quotation for an air kit state clearly who supplies the enclosure, insulation and supports?¶
- An air kit is supplied without a housing; FanPedia states the enclosure and insulation are provided by others
- Air kits are always shipped with a pedestal that replaces the enclosure
- Air kits are complete roof units that only need a curb
- An air kit's enclosure is welded at the factory, so it cannot be modified on site
Show Answer
The correct answer is A. An air kit is forward curved, double-width, double-inlet impellers on a shaft, sold as a component for someone else's enclosure, such as an oven or plenum. FanPedia shows the enclosure and insulation as provided by others in the field and notes that air kits need support supplied by Twin City Fan or others rather than a pedestal. Quoting an air kit as if it were a finished fan is a common trap, so the scope split belongs on the quote.
Concept Tested: Air Kit
10. At night, fume hood sashes close and contaminated exhaust drops, and the bypass damper opens by the same amount. With entrained flow unchanged, what happens at the stack?¶
- Fan flow drops, so the plume rises less and may return to the building
- Entrained flow falls to zero because the fan flow has changed
- Fan flow and stack velocity stay steady, and the contaminated share of the plume falls
- The bypass damper closes to save energy, so total flow doubles
Show Answer
The correct answer is C. Fan flow is contaminated plus bypass flow, so when bypass rises by exactly as much as contaminated air falls, fan flow and stack velocity hold steady. That is the purpose of bypass flow in common practice. In the chapter's example, contaminated air falls from 8,000 to 5,000 CFM while bypass rises from 2,000 to 5,000 CFM; fan flow stays at 10,000 CFM and the contaminated share of a 20,000 CFM plume falls from 40% to 25%.
Concept Tested: Bypass Flow