SOME ELEMENTS OF PHISICS USED AT THE CALCULATION OF THE INDUSTRIAL FANS’ MAIN PARAMETERS. RELATIONS. DIAGRAMS. CHARACTERISTIC CURVES.
As I mentioned in one of the previous articles, the operation general principle of all fans is that they transfer to the environment some of the energy used. The difference between the energy used to drive the fluid and the useful energy delivered at a certain flow and a certain pressure represents the loss of the ventilation functioning, i.e. its yield, respectively its return (η %). This is as lower as the yield of the fan is higher.
As we have seen, the predominant relationship when calculating any industrial fan is between pressure and flow. Always when the flow rate Q increases, the pressure Δp (or H, under other encodings) decreases. Depending on the values obtained by simultaneous measurements, it is then drawn for each industrial fan, the working diagram. The characteristic of the pipes network is given, as known already, by the sum of the local losses and of those distributed and can be written as follows:
where C and K are two constant calculation units, specific to each ventilation installation; they are either calculated or measured.
Therefore their graphic representation is like in the following diagrams, where the curves show the trend of Q and Δp (or H).
Natural Numbers Representation
As a result, if it is known the flow Q1 and the pressure H1, for an each and every given functioning point of the network, its characteristics can be written according to the following relation:
Also on this chart, according to the same parameters, is calculated and represented Nef, which represents the absorbed power in each measured point and which, naturally, is as higher as the flow rate increases during work. Consequently, the question which always arises when calculating the energetic efficiency is actually the rising slope of Nef. The flatter it is, angled slightly, in a lower growth, with the horizontal line o-x, the lower the energy consumption is. And the difference of energy ceased to the environment is therefore significantly reduced. It results thereof that the efficiency of the use of the industrial fan will be subsequently greater. The following diagrams exemplify the way Nef is represented on the charts and how it is influenced by the parameters changed once the impeller’s dimensions are changed, at the different fans of the same family. In the given example, the chosen family is V20, high pressure radial fans.
Increasing efficiency leads directly to significant energy savings, which stands out strongly especially to the big industrial fans, located in medium and large industrial units, with numerous machinery and extreme power consumption, or used in cooling large machinery or production lines working at high temperatures (hot-rolling mills, coking plants, steel making shops, furnaces or heating ovens, galvanizing baths etc.), or transformers and electric motors power cooling, where the consumptions for providing constant flow and working pressure to these industrial fans also have significant values, directly proportional to the needs of the machines they serve.
Thank you and wait to meeting you in the next pages. Or, even better, in our factory …
Lucian GOJ, Research & Development Director,
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