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Lab Exhaust Flow Calculator

Run the Lab Exhaust Flow Calculator MicroSim Fullscreen

This p5.js sketch is built on the shared FanPedia MicroSim kit. To run it in the p5.js editor, add the kit files (fanpedia-sim.css, fanpedia-core.js, fanpedia-p5.js, fan-models.js and fan-drawings.js from ../shared-libs/, or their published URLs) to the editor's index.html before pasting the sketch.

About This MicroSim

A laboratory exhaust fan dilutes contaminated fume hood air with outside air and throws the mixture high above the roof. Two streams of outside air do the diluting, and they join at different places (FanPedia pp. 4 and 6):

  • Bypass flow enters through the bypass air plenum, controlled by a bypass damper, before the impeller, so it passes through the fan.
  • Entrained flow is pulled into the jet at the nozzle or windband after the fan; it never passes through the impeller.

The sim uses the chapter's flow bookkeeping:

  • Fan flow = contaminated + bypass (CFM)
  • Total flow = fan flow + entrained (CFM)
  • Contaminated share = contaminated ÷ total × 100, to the nearest whole percent ("not defined" when the total is 0, and no plume is drawn)

Three challenges, in a fixed order, give the contaminated, bypass and entrained flows. For each you type the fan flow, the total flow and the contaminated share before the diagram fills in.

# Contaminated Bypass Entrained Fan flow Total flow Share
1 6,000 0 9,000 6,000 15,000 40%
2 5,000 5,000 10,000 10,000 20,000 25%
3 12,000 3,000 15,000 15,000 30,000 40%

Flows must match the model exactly; the share is correct within ±1 percentage point. Each value is marked ✓ or ✗ after a check. You get two attempts; a wrong answer shows the challenge's worked explanation, and a second wrong answer shows the model values and the challenge counts as missed. When a challenge resolves, the stack diagram shows the value on every stream, and the arrow weights grow with flow. Mastery is 3 of 3 challenges with all three values right on the first attempt.

After challenge 3, Explore mode unlocks three sliders (contaminated air 0–20,000, bypass flow 0–10,000, entrained flow 0–30,000 CFM, in 500 CFM steps). The diagram and the worked sums update at once. The first time you lower contaminated air and raise bypass by the same amount, the sim points out that the fan flow stayed constant, which is what the bypass damper does as fume hood sashes close. In a real fan, entrained flow depends on the fan flow and the nozzle design and comes from the manufacturer's rating; the sim treats it as an independent input for practice and says so on screen. Explore mode is never scored.

How to Use

  1. Read the given flows, then type the fan flow, the total flow (CFM) and the contaminated share (%) and press Check (or Enter in any box). Commas and a trailing % are accepted.
  2. Read the ✓/✗ marks for each value and the feedback. "✓ Correct: fan flow …, total flow …, contaminated share …%." appears in a solid green box; a wrong answer shows the worked explanation in a dashed red box. Fix the boxes and check again if an attempt is left.
  3. Press Next challenge (or Enter). After challenge 3 press Start exploring to read the first-attempt score and mastery line and unlock the sliders.
  4. In Explore mode, try the night setback: lower contaminated air and raise bypass by the same amount, and watch the fan flow. Start over clears the score and returns to challenge 1.

Keyboard: Tab moves between the three answer boxes and the buttons; Enter checks the answer, then goes to the next challenge. In Explore mode the arrow keys move a focused slider.

Data label: "Illustrative values · Stream names: FanPedia pp. 4, 6, 138", at the bottom left of the drawing.

Iframe Embed Code

You can add this MicroSim to any web page by adding this to your HTML:

<iframe src="https://moroshek.github.io/FanTASTIC-textbook/sims/ch06-lab-exhaust-flow-calculator/main.html"
        height="642px"
        width="100%"
        scrolling="no"></iframe>

Lesson Plan

Learning Objective

The learner will calculate the fan flow, the lab exhaust total flow and the contaminated share of the plume from given contaminated, bypass and entrained flows, matching the model values exactly on at least 3 of 3 challenges (Bloom: Apply, verb: calculate).

Audience

Adult professional development: new application engineers, sales staff, representatives and facilities staff.

Duration

10-15 minutes

Prerequisites

  • Contaminated air, bypass flow, bypass air plenum, entrained flow, fan flow, lab exhaust total flow and plume dilution (Chapter 6, "Laboratory Exhaust: Dilute, Then Throw It High")
  • Entrained flow (Chapter 5)

Activities

  1. Challenges (5-7 min): Work each challenge on paper before typing. Say where each stream joins: before or after the impeller.
  2. Explore (4-6 min): Reproduce the chapter's worked example (8,000 contaminated, 2,000 bypass, 10,000 entrained: 20,000 CFM total, 40%), then the night case (5,000 and 5,000: 25%).
  3. Discussion (2 min): Why is the fan selected on contaminated plus bypass flow, and not on the total flow?

Common Misconceptions Addressed

  • Entrained air passes through the fan, so the fan must be sized for total flow: the diagram shows entrained air joining at the windband, after the fan.
  • Bypass air is wasted air that does not help dilution: the share falls when bypass rises.
  • When fume hood exhaust drops, the fan flow must drop too: the constant-fan-flow note in Explore mode shows the bypass damper making up the difference.

Assessment

  • The running line "Challenges correct: n of 3" counts challenges solved on either attempt; the summary shows "First-attempt score: n of 3" and the mastery line. Mastery is 3 of 3 with all three values right on the first attempt.
  • Explore mode is not evidence. Follow-up: a lab drops from 9,000 to 6,000 CFM of hood exhaust at night; what bypass keeps a 10,000 CFM fan flow, and what happens to the contaminated share?

References

  1. FanPedia: The Fan & Blower Encyclopedia (PDF) - lab exhaust diagrams naming contaminated air, bypass flow, fan flow, entrained flow and total flow (pp. 4, 6) and bypass dampers (p. 138).
  2. Twin City Fan - current laboratory and fume exhaust fan catalog pages (TVIFE, QIFE, QFE, TFE, BAIFE, BCIFE).
  3. Fume hood - Wikipedia overview of fume hoods, sash operation and variable-air-volume exhaust.