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Fan Curve Explorer

Run the Fan Curve Explorer MicroSim Fullscreen

About This MicroSim

Two illustrative centrifugal fans, labeled Curve A and Curve B, are drawn at one fixed speed each and at standard air. The top plot shows fan static pressure (in. wg) against airflow (CFM); the bottom plot shows brake horsepower (BHP) against the same airflow axis. Hovering any data point shows its airflow, fan static pressure and BHP.

Six questions, asked in a fixed order, ask the learner to decide whether four duty points sit in the stall region, which fan has a non-overloading power curve, and how large a motor Curve A needs so that it cannot be overloaded at this speed. Each question has one scored attempt. Each answer marks the point or curve it is about on the chart: a round marker with a solid green ring and ✓ for a correct answer, a square marker with a red ring and ✗ for an incorrect one. The feedback shows the reason, and after a miss it also shows the correct answer. After the last question the stall region of each fan is shaded so the two can be compared, and the score is shown as "n of 6 correct". Mastery is 5 of 6 on the first attempt.

Both curves are illustrative. They are shaped after typical backward inclined (Curve A) and forward curved (Curve B) fan behavior described in standard fan engineering texts and are not Twin City Fan published ratings. Curve A is the same illustrative fan curve tabulated in Chapter 10.

How to Use

  1. Hover along both pressure curves and both BHP curves to read values. Find the airflow at which each pressure curve reaches its peak (for Curve B, the right-hand peak after the dip).
  2. Answer each question by pressing Yes / No or Curve A / Curve B. Question 6 needs a typed number of BHP; press Submit or Enter. Each question has one attempt.
  3. Read the feedback, look at the point the sim just marked, then press Next question.
  4. After question 6, press See score. The score reads "n of 6 correct", followed by "Mastery reached" at 5 or more, or by what to review. Start over clears the marks and starts again at question 1; it is available at any time.

Keyboard: keys 1 and 2 choose the first or second answer; Enter submits a typed value, goes to the next question, and starts over from the score screen. Tab and Space or Enter work on every button.

Data label: "Illustrative data, standard air, one fixed speed per fan", shown at the bottom left of the chart.

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/ch10-fan-curve-explorer/main.html"
        height="802px"
        width="100%"
        scrolling="no"></iframe>

Lesson Plan

Learning Objective

The learner will differentiate stable from stall-region operating points, and overloading from non-overloading power curves, by reading the pressure and BHP curves of two illustrative fans (Bloom: Analyze, verb: differentiate).

Audience

New application engineers, inside and outside sales staff, manufacturer's representatives and specifying engineers who read fan curves to judge a selection.

Duration

10-15 minutes

Prerequisites

Fan curve, fan static pressure, brake horsepower, stall region, overloading power curve and non-overloading power curve, as defined in the section "The Fan Curve" of Chapter 10.

Activities

  1. Exploration (4 min): Hover along Curve A and find the airflow of peak pressure (4,000 CFM, 4.9 in. wg). Then find Curve B's right-hand peak. Ask: which fan has more of its airflow range to the left of its peak?
  2. Committed answers (6 min): Work through the six questions without looking back at the chapter tables. Before pressing an answer, say out loud which side of the peak the point is on.
  3. Debrief (5 min): With the stall regions shaded, compare their extent. Discuss why the highest-pressure point is the edge of the stall region rather than the best place to select a fan, and why a 10 hp motor protects Curve A at this speed while Curve B's motor must be sized for the highest airflow the fan could realistically see.

Common Misconceptions Addressed

  • Any point the pressure curve passes through is a safe operating point, including points left of the peak (questions 1-4).
  • A fan's BHP always rises with airflow (question 5).
  • The highest-pressure point is the best place to select a fan (debrief and final summary).

Assessment

  • The running score reads "Questions correct: n of 6"; the final score reads "n of 6 correct". Mastery is 5 of 6 correct on the first attempt (one scored attempt per question).
  • Hovering to read values is exploration and does not count as evidence. Question 6 accepts any value within 0.1 of 9.5 BHP.

References

  1. Chapter 10: Fan Performance, Curves and Ratings - the fan curve, stall region and power curve sections this MicroSim exercises.
  2. FanPedia: The Fan & Blower Encyclopedia (PDF) - Twin City Fan's reference on fan types, performance and selection.
  3. FanPedia online - Twin City Fan's online fan and blower encyclopedia.
  4. Plotly JavaScript Open Source Graphing Library - the charting library used to draw the curves.