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I’ve purchased the “Fan Design Calculator v1” of the CalQlata suite this week. Actually, I’ve encountered some problems in interpreting the results got from the “Fan calculator”. For example, in EXCEL file attached to this email you can find 7 sets of input/output parameters for a centrifugal fan calculated by “Fan calculator”. My first problem is about the torque. I calculated the required torque based on Euler turbomachine equation and got totally different values for each case. It is worth mentioning that I’ve calculated the torque based on fluid rotational velocities given by the “Fan Calculator” itself. Furthermore, I had similar problems with power and head calculations. It would be grateful if you can help me understand the cause of these discrepancies. |
Fans is simply a theoretical calculator designed to take the drudgery out of impeller calculations for fan (casing and equipment) designers. It has most probably become CalQlata's most verified calculator due to the number of customers that appear to have difficulty with the theoretical concept and therefore question its output. As stated in the technical help page for this calculator, Fans calculates the movement of air through an impeller (not through a fan) according to Charles Innes, which may or may not be better than any other related theory. However, whilst his theory has been around for more than a hundred years and is well known in the industry, as we all know, there is more than one way to 'skin-a-cat'. I suggest therefore that if your client already has access to software with which he is happy, he may be well advised to continue with it. Charles Innes' theory dealt with air-flow only and does not address torque (and therefore power). CalQlata has incorporated its own torque formulas in Fans, which have been used for many years and appear to work reasonably well. Comparison (with a proprietary manufacturer's product) calculation is provided at the bottom of calculator's technical help page, the relevant results from which are thus: Whilst CalQlata is not prepared to divulge personal copyright data, we can offer the following advice with his Excel calculations: As we all know, equipment efficiency is defined as a ratio of output to input of a given parameter. The efficiency of any process will therefore vary according to the parameter(s) selected. The efficiencies calculated in Fans are as defined by Charles Innes. Your efficiency calculation is unlikely, therefore, to match that of Fans unless it is based upon the same parameter(s) and using the same theory. Both efficiencies may therefore be different and yet correct according to their relative parameter(s). Whilst CalQlata cannot comment on the accuracy or appropriateness of third-party software, perhaps your results apply only to the movement of air, and may not include the requirements for actually achieving this movement, which will vary with impeller design and air velocities. For example; It is possible that you may be comparing a practical calculation method that considers the means needed to achieve actual performance with a theoretical calculation method that only addresses the movement of air. If this is the case, it is not surprising that your results are incompatible. |

We need some centrifugal fan design software. will this calculator helps to design the fan? |
The answer to your question is yes. But a fan comprises two fundamental components; the |

Recently I bought and downloaded "Centrifugal and Axial Fan Calculator", and I guess it is going to be very useful for me. I have some questions regarding the output values that I wasn't able to find in the documentation or Q&A. The objective of my fan configuration is to maximize pressure at the expense of the air flow, using as little power as possible. |
To answer your questions; Have you read the technical help pages for the calculator: https://www.calqlata.com/productpages/00060-help.html & https://www.calqlata.com/productpages/00060-QandA.html You must understand that this calculator is based upon the theory of Charles Innes - the original theorist for impeller design. All designs and theories today are based upon his work. But they apply only to the impeller, not the fan – as explained in the above technical help page. The bottom of that page provides a calculation result from this calculator, which compares favourably with a proprietary design, as it should. This is the least understood by our customers of all theories, and usually takes a while to get used to the input-output data relationships. But you will get to understand it as you play. Due to the difficulties our customers have understanding Innes’ theories, this has become our most verified and modified (input vs output) calculator, but it is exactly as Innes designed it. It works. There are a number of reasons why any efficiency can be greater than 100%: Please note: We only provide the calculator, which applies only to the impeller and is correct according the most recognised associated theory. It is up to its users to get the design configuration needed. That is the purpose of all of our calculators, you play with the input values until you get the output value you are happy with. I would, however, advise you to read the above links carefully, they are very helpful. |

I am using fans to calculate the performance of a centrifugal impeller. I have built the casing to be constant cross sectional area with the inlet blade length approx 3cm. Can you help me understand the data, please? |
First I must point out that vi is the overall (theoretical) velocity generated in the air as it passes the inlet tip of the blade. When efficiencies and casing design are included in the calculation, actual [fan assembly] output data is usually very different. Fans' calculations are correct and accurate (according to the theory) for the impeller. The casing figures (pc, vc, ρc, Hc, Pc) are only as expected based upon relative [inlet and outlet - impeller and casing] areas. Due to his use of 90° straight blades, your Client's design shows a low efficiency (head loss efficiency (%) {air or mechanical efficiency}: εᴴ = -236.095011), which will significantly affect performance. The purpose of Fans was originally to provide the fan designer with a calculator for the impeller only. It is the only part of the fan design that can be accurately predicted with good reliability. |

Is it correct to say that if the discharge were completely blocked off that the static pressure would be equal to the calculation of the pressure increase across the impeller?? |
Yes |

A common problem with this calculator appears to be the use of the gas constant (Ra) in Imperial units |
Your client appears to be using lb, ft & R Imperial units in his calculation, together with an input value for Ra of 0.07666666 Metric: Convert: Imperial: I would normally expect therefore, that his input value for Ra should be 52.28999061 for air |

I have purchased your Fan calculator and am puzzled about something. We wish to design a fan that we cannot buy. We are looking for 0.25 PSI outlet pressure and a minimum flow rate of 1.5 SCFM. We expect to have to use more than one stage on a centrifugal style fan. In order to reduce the number of stages we think we should use the backward facing blade as that gives us the greatest pressure increase. But, when we adjust the inlet and outlet angles the calculator suggests the highest pressures are at inlet angle of small like 10 and outlet angle big like 90. That doesn’t make sense with your chart saying that backward facing blades give the highest pressures. To get a backward facing blade, I would expect to use a small outlet angle to increase pressure, not a large one. We look at the “pressure increase across the impeller” output as we adjust the angles. What are we doing wrong?? |
The problem is the requirement for a high outlet pressure relative to the desired flow rate. A high (reversed) inlet angle (θᵢ) will artificially increase pressure for best results. You can play with the input and output diameters and the impeller width to achieve the desired flow rate. You should remember, however, that the Fans calculator only provides the performance characteristics of the impeller. We should point out that a casing outlet with cross-sectional area no smaller than the impeller outlet area will result in the lowest noise-level. |

I want build centrifical fans. Can your calculator do the design if I give static pressure and volume plus suggest some sizes? |
Our Fans calculator calculates the airflow and power consumption for an impeller. |

We have had one customer complaining that the fan calculator doesn't work. But on sight of his input data his blade angles are completely incorrect, and he refuses to accept this fact. We have therefore decided to provide a general response to ensure that future customers with no experience or knowledge of the subject are aware of the parameters required for an impeller before trying to design one. |
Fan technology is well established and proven to work for all blade angles that comply with Charles Innes' theory, which has been the industry standard since 1916 The customer concerned set his blade outlet angle such that it is driving air back into the impeller with greater energy than his inlet angles are able to overcome. He has completely misunderstood the basic principles of driving air through an impeller and refuses to accept the fact. Inlet blade angles greater than 90° will not drive air out through an impeller, they will drive it back into the inlet cavity. Moreover, if you do not set your inlet blade angles shallow enough to provide sufficient positive outward drive to overcome inward drive from outlet blade angles greater than 90° the theory will become unstable, as would be such an impeller. It is important you try to understand the behaviour of air as it passes through the fan. Whilst it is largely based on common-sense, if you ignore basic flow characetristics you will never get your impeller to work, theoretically or practically. Please take look at the tips we provide in our technical help page |

The rule of thumb "one impeller volume per revolution" has been called in to question ... |
As a result of this question, CalQlata successfully carried out an internal verification based upon the energy required to shift such a mass. Whilst it was considered prudent to re-issue the 'Fans' calculator now calculating the impeller speed (RPM) required to generate an entered value for volumetric flow rate based upon the required energy; |

Unfortunately, I am not a fan expert either! The power and pressure seem OK, but the flow rate is the problem. We have measured directly the flow rate and although there are obviously some errors in measurement, we seem to have broadly similar practical results of less than 1m3/s. What I really would like to know is the accuracy of the 'rule of thumb' (effective rotor volume x rpm), which I cannot seem to corroborate on a google search. Does the calculator just produce this value regardless of any other input values? |
The standard theory on centrifugal fans was generated by Charles H Innes in 1916 ("The Fan"), and it appears to have stood the test of time. Twelve blades, however, may not be suitable for very large diameter impellers of high aspect ratios. I (personally) have never seen a fan deliver more than its impeller volume per revolution unless the atmospheric outlet pressure is less than the inlet pressure (an effective vacuum). Therefore, I am unable to refute Innes' theory. I am happy, however, to leave this debate open to anybody that can show Innes' theory to be incorrect. Please let us know if you can do this mathematically and supported with practical evidence. |

Can you comment on the limitations of the equations that were implemented in this software? Specifically with regards to impeller size. I’m investigating design changes on a relatively small impeller (3-4”), and so far this software is predicting an output flow that is much higher than has been empirically captured. Any feedback would be appreciated. |
The theories in the calculator are correct for all sizes, i.e. for fans with impellers smaller than a millimetre to greater than 10m. As your fan gets smaller the ratio of surface area with volume increases, and the smaller it gets the greater this ratio becomes. In this case ‘δε' represents the increase in inefficiency over the previous size Surface friction has a far greater effect on efficiency in a fan than it does in a pipe because the ratio of surface area (contact surface) is greater than in a pipe. Therefore, a similar table to that above for fans would show an even more marked increase at smaller diameters. Centrifugal fans are less suited to smaller diameter for a number of reasons. This is why centrifugal fans tend to be targeted for larger fans and axial configurations for smaller diameters For what it’s worth, if I were designing a very small high-performance fan, I would start with a multistage axial configuration (along with suitable venturies if I was looking for pressure as opposed to flow).
I believe that your input/output data is based upon the following units: With regard to your concerns about flow rate: May I venture a couple of comments on the input data? The recommended angle for the blade inlet should be used where possible as you will see improvements in efficiency, outlet pressure, outlet velocity and power consumption. Whilst I agree that such improvements are very small between 45° to 46.109°, every little helps when attempting to minimise defects (for such small fans). I notice that the outlet angle (120°) has turned the blades from backward facing to forward facing (see https://www.calqlata.com/productpages/00060-help.html Fig 3). I am not sure if this was intentional (special requirements) but the smaller the outlet angle for a backward facing blade, the better its efficiency. # Note: the efficiency quoted (ε {%}) is for blade design only |