# Dyson fan efficiency

T C
TL;DR Summary
I just want to know whether market available blowers (whether positive displacement, centrifugal or any other kind of market available blower that uses blades) has better efficiency or a dyson fan/air multiplier in terms of power consumption.
We all know about various kinds of market available blowers and their efficiency is well known more or less. I recently came to know about dyson fan/air multiplier I want to know which one, whether market available blowers or the Dyson fan is efficient in terms of creating mass flow rate at ambient pressure. In short, if I use an air multiplier instead of a market available table/stand/ceiling fan, whether that will be help me to reduce my electric bill or increase it.

T C
four or five times the air for the same running costs

Mentor
The Dyson moves four or five times the air for the same running costs, but the initial purchase price is higher. The last two graphs on this page give you some idea of the benefits.
I haven't read the article yet, but that conclusion would go against what other tests have found and fluid dynamics tells us should be true. There is an energy penalty associated with the higher velocity and static pressure creating the jets. There's also a corellation between fan size and efficiency (bigger is better for the same cfm).

We've discussed this topic before. I'll dig into it and see what's going on...

Baluncore
T C
I am also curious to know what others are saying regarding this matter.

Maybe the velocity distribution across the aperture was ignored. The airspeed could have been measured at one point on the periphery, but then extrapolated across the entire entrained airflow, on the assumption that all air was moving at that speed, when it was actually slower.

anorlunda
Mentor
Maybe the velocity distribution across the aperture was ignored. The airspeed could have been measured at one point on the periphery, but then extrapolated across the entire entrained airflow, on the assumption that all air was moving at that speed, when it was actually slower.
Could be. I'm also having trouble with his math. The Vornado 6304 is 9.4" diameter and the Dyson AM06 is 10". The Vornado velocity was measured at 644 fpm and the Dyson at 548 fpm. Airflows listed: 1250 and 1150 CFM. I get 310 and 299 CFM. I think he may have divided by cross sectional area instead of multiplying. He doesn't list the Honeywell size, but I think it's a 12". That would fit with why he got 750 CFM instead of 392 CFM.

That gives corrected efficiencies of:
Dyson: 14.95 CFM/Watt
Honeywell: 9.8 CFM/Watt

In this test the Dyson is more efficient due to its much lower power input than the other fans. It's also much lower than in the other test I linked whereas the Honeywell is identical. They are likely not the same model Dyson but the Honeywell probably is.

The test I linked measured velocity profiles, and it does indeed show a very uneven velocity for the Dyson vs the conventional fan:

So if I had to speculate, I think the claimed airflow for the DAM in the other test is probably high by a factor of 3-4 due to the improper usage of a single point velocity measurement.

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Baluncore and berkeman
Mentor
T C
There is no photo in the link.

T C
At least it proves that the flow from DAM is much more laminar than the flow produced by conventional fan.

Mentor
At least it proves that the flow from DAM is much more laminar than the flow produced by conventional fan.
Ehh k.

hutchphd
T C
If, instead of a simply hole at the body, the compressed air is blown out through a properly designed convergent-divergent nozzle at supersonic velocity, can that improve the performance of the machine or it will remain the same?

Mentor
If, instead of a simply hole at the body, the compressed air is blown out through a properly designed convergent-divergent nozzle at supersonic velocity, can that improve the performance of the machine or it will remain the same?
The Dyson's blower doesn't create anywhere near enough pressure for choked flow through a nozzle. I suppose you could replace the blower with a much more powerful one that could, but that would just make the problems previously described worse.

And it would be exceptionally loud.

FluidDroog