Skip to content

Lab Exhaust Entrained Flow Calculator

Run the Lab Exhaust Entrained 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 fume hood air twice. Bypass air enters through the bypass air plenum and mixes with the contaminated air before the fan, so it passes through the impeller. Entrained air is pulled into the plume by the jet leaving the nozzle, so it never passes through the impeller. The flow diagram shows all four flows; the MicroSim uses the chapter's three equations:

  • Fan flow = contaminated air + bypass flow
  • Total flow = fan flow + entrained flow
  • Plume concentration = hood concentration × contaminated air ÷ total flow

Three illustrative cases come in a fixed order, all at a hood concentration of 100 ppm:

Case Contaminated (CFM) Bypass (CFM) Entrained (CFM) Fan flow (CFM) Total flow (CFM) Plume (ppm)
1 8,000 2,000 7,000 10,000 17,000 47.1
2 6,000 0 9,000 6,000 15,000 40.0
3 12,000 4,000 0 16,000 16,000 75.0

For each case you type all three values and press Check. Flows must equal the model value exactly; the plume concentration (rounded to 0.1 ppm) is correct within ±0.5 ppm. Each value has two attempts. A correct value reads "✓ Correct: ."; a first wrong attempt reads "✗ Not yet. Check which air passes through the impeller."; a second wrong attempt shows the case's explanation, reveals the value and counts it as missed. As each value is settled, the diagram fills it in. The running count reads "Values correct: n of 9"; mastery is all nine values correct with at most two attempts each.

After case 3, Explore mode unlocks four sliders (contaminated air, bypass flow, entrained flow and hood concentration). Fan flow, total flow and plume concentration update at once. The first time you double the entrained flow, the sim shows the plume concentration before and after, and that it does not halve.

How to Use

  1. Read the givens on the diagram: hood air and its concentration, bypass air and entrained air.
  2. Type fan flow, total flow and plume concentration in the three boxes, then press Check (or Enter).
  3. Fix any value marked ✗ and check again; a value missed twice is revealed with the explanation.
  4. Press Next case. After case 3, press Start exploring.
  5. In Explore mode, move the sliders. Try doubling the entrained flow, then setting bypass or entrained flow to zero. Case 1 values resets the sliders; Start over clears the score.

Keyboard: Tab moves between the boxes, buttons and sliders. Enter in an answer box checks all three values; Enter again goes to the next case. Arrow keys move a focused slider.

Data label: "Illustrative values · Flow definitions: FanPedia pp. 4, 6", shown 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/ch05-lab-exhaust-entrained-flow-calculator/main.html"
        height="707px"
        width="100%"
        scrolling="no"></iframe>

Lesson Plan

Learning Objective

The learner will calculate the fan flow, total flow and plume concentration of a laboratory exhaust fan from its contaminated, bypass and entrained flows, with flows exact and concentration within 0.5 ppm (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, fan flow, entrained flow and total flow
  • Concentration in ppm
  • The three equations in "Entrained Flow in Laboratory Exhaust" in Chapter 5

Activities

  1. Calculate (8 min): Work the three cases. Before typing, point to the air that passes through the impeller.
  2. Compare (2 min): Note that case 2 has fan flow equal to the hood air (no bypass) and case 3 has total flow equal to fan flow (no entrainment).
  3. Explore (5 min): Double the entrained flow and read the before and after concentrations. Then trade entrained air for bypass air at the same total and compare the fan flow.

Discussion Questions

  1. Why is the fan selected for the fan flow and not for the total flow?
  2. Bypass air and entrained air both dilute the plume. What does each cost the owner?
  3. Why does doubling the entrained flow not halve the plume concentration?

Common Misconceptions Addressed

  • The fan must be sized for the total flow, including entrained air: every case asks for fan flow and total flow separately.
  • Entrained air passes through the impeller: the diagram joins entrained air above the nozzle, and case 2 shows fan flow equal to the hood air.
  • Only one of bypass and entrained air reduces the plume concentration: case 3 shows bypass air alone diluting the plume, and the plume equation uses the total flow.
  • Doubling the entrained flow halves the plume concentration: Explore mode shows the before and after values the first time you double it.

Assessment

  • Running count shown as "Values correct: n of 9"; mastery is all nine values correct with at most two attempts each.
  • Explore mode is not scored.
  • Follow-up: a lab adds a second fume hood; ask learners which of the three results changes first and why.

References

  1. Twin City Fan & Blower. FanPedia: The Fan & Blower Encyclopedia, pp. 4 and 6 (bypass air plenum, entrained flow through the nozzle or windband, lab exhaust fans). PDF
  2. Twin City Fan & Blower. FanPedia online - the same encyclopedia in web form.
  3. Twin City Fan. Laboratory exhaust fans (TVIFE, QIFE, BAIFE, BCIFE induced flow fans; QFE and TFE venturi nozzle fans) - current catalog lines and their discharge velocity and plume height ratings.
  4. Chapter 5: Roof, Wall and Specialty Exhaust Fans, "Entrained Flow in Laboratory Exhaust" - the worked example that case 1 repeats.