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Follow the Airflow Through a Centrifugal Fan

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About This MicroSim

The drawing is a side view of a ducted, belt-driven SWSI centrifugal fan in Arrangement 9, the fan in the FanPedia exploded view on page 10. Air enters from the duct on the left and leaves through the duct at the top. Eight numbered slot buttons sit along the air path, and a bin at the top right is labeled "Not in the air path".

Eleven part cards start in a shuffled pile. Eight of them are stages the air passes through, in this order:

Slot Part Why
1 Inlet ductwork Air arrives from the upstream duct.
2 Inlet flange (with companion flange) The bolted joint where the duct meets the fan inlet.
3 Inlet funnel Funnels the air smoothly into the eye of the impeller.
4 Impeller The only part that adds energy to the air; air enters at the center and is thrown outward between the blades.
5 Housing scroll Collects the air leaving the impeller and guides it toward the outlet.
6 Cutoff The point of the scroll closest to the impeller, just before the outlet.
7 Outlet flange The bolted joint where the fan outlet meets the downstream duct.
8 Outlet ductwork Air leaves the fan system through the downstream duct.

The other three, the shaft, the bearings and the motor, belong in "Not in the air path": in an Arrangement 9 fan the bearings sit on the pedestal and the motor beside it, outside the airstream, and the shaft only passes through the housing side.

Each slot holds one card; the bin holds any number. A submission counts only when all 11 cards are placed. You get two submissions. Correct cards lock with a ✓. On the first submission, wrong cards go back to the pile marked ✗, with their Why text and the misconception the placement suggests (for example, that air enters the impeller at the blade tips, or that the cutoff is at the inlet). After the second submission every card is shown in its correct place, missed cards are marked ✗, and the air animates once from slot 1 to slot 8, naming each part as it arrives. Mastery is all 11 cards correct within two submissions.

How to Use

  1. Select a card in the pile, then select a numbered slot or Not in the air path. The card shows where it went ("3 · Inlet funnel", or "Out · Motor" for the bin). Placing a card in an occupied slot sends the card that was there back to the pile.
  2. To move a placed card, select it (or its slot) and choose a new place, or press Back to pile.
  3. When all 11 cards are placed, press Submit. The status line shows "Cards correct: n of 11". Select any card marked ✗ to read why, place it again and press Submit (2 of 2).
  4. After the final submission, watch the air path, select any card to read its feedback, press Replay airflow to see it again, or Start over for a new shuffle.

Keyboard: Tab moves through the cards, the slots and the buttons; Enter or Space selects. With a card selected, keys 1-8 place it in that slot, 0 (or N) puts it in "Not in the air path", P returns it to the pile and Escape deselects.

Data label: "Belt-driven SWSI fan, Arrangement 9 (FanPedia p. 10)", 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/ch03-follow-the-airflow/main.html"
        height="822px"
        width="100%"
        scrolling="no"></iframe>

Lesson Plan

Learning Objective

The learner will list, in airflow order, the eight parts that air passes through in a ducted, belt-driven SWSI centrifugal fan, and set aside the three parts that stay out of the air path (Bloom: Remember, verb: list).

Audience

Adult professional development: new application engineers, sales staff, representatives and facilities staff who have read "The Fan Housing" through "The Fan Outlet" in Chapter 3.

Duration

10 minutes

Prerequisites

  • Fan housing, housing scroll and cutoff (Chapter 3)
  • Impeller, inlet funnel, inlet flange and outlet flange (Chapter 3)
  • Shaft, bearing and motor, as named in the chapter introduction

Activities

  1. Placement (5 min): Place all 11 cards from memory and submit. Do not look back at the chapter before the first submission.
  2. Correction (3 min): Read the feedback on every ✗ card, place them again and submit.
  3. Recall (2 min): Watch the airflow animation and say each part's name out loud as the air reaches it, as the chapter's mascot tip suggests.

Common Misconceptions Addressed

  • Air enters the impeller at the blade tips: placing the impeller before the inlet funnel brings the reminder that air enters at the center, through the funnel.
  • The cutoff is at the inlet: placing the cutoff in slots 1 to 3 brings the reminder that it is just upstream of the outlet.
  • Every part of a fan touches the air: placing the shaft, bearings or motor in the air path brings the reminder that they sit outside the airstream in an Arrangement 9 fan.

Assessment

  • "Cards correct: n of 11" after each submission; mastery is all 11 cards correct within two submissions.
  • Moving cards around before a submission is exploration, not evidence. Follow up by asking the learner to name the slot just before and just after the impeller without the drawing.

References

  1. Centrifugal fan - Wikipedia article on centrifugal fans, their impellers, housings and the path the air takes.
  2. FanPedia: The Fan & Blower Encyclopedia - Twin City Fan's reference; page 10 shows the exploded view of a belt-driven Arrangement 9 centrifugal fan used here.
  3. Duct (flow) - Wikipedia overview of the ductwork that carries air to and from a fan.