ON THE TESTING METHODOLOGY FOR AUXILIARY VENTILATION FANS

Yu. N. Sokolov, V. I. Lvov, A. R. Aizenshtein

(Presented by the scientific seminar of the Department of Mining Mechanics)

The results of tests of axial fans carried out on factory test stands and under laboratory conditions often differ noticeably. Thus, for example, there is a substantial discrepancy between the characteristics of a prototype of the SVM-5m fan, designed and manufactured by the Tomsk Electromechanical Plant (TEMZ), obtained on the factory stand of this plant and in the fan laboratory of TsAGI (Fig. 1).

For the purpose of determining the causes of these discrepancies, the same prototype of the SVM-5m fan was subjected to investigations in the laboratory of hydraulic and air-flow machines of the Tomsk Polytechnic Institute (TPI). The characteristics obtained in this case (Fig. 1) proved to be still lower than those obtained from the TsAGI test results.

As it was possible to establish, the cause of these discrepancies was that the operating conditions of the fan under test in each of the compared cases differed substantially. The factory tests at TEMZ were carried out according to the “Giprouglemash” method on a stand with a suction pipe whose diameter immediately in front of the fan corresponded to the diameter of its casing (Fig. 2). At TsAGI the tests of the same fan were carried out in an installation with a chamber, with the air flow being taken in through a well-profiled

Fig. 1. Results of tests of the SVM-5m fan at TEMZ, at TsAGI, and at TPI.

Fig. 2. Factory TEMZ scheme for testing fans.

Visible labels in the diagram:

• Section \(I_1-I_1\)
• Replaceable diaphragm
• \(H_{\mathrm{st}}\)
• \(t^\circ,\ t_{\mathrm{in}}\)
• \(D/2\)
• \(5D\)
• \(D\)
• \(l\)
• \(d\)
• \(\beta\)

Fig. 3. Diagram of the chamber for testing TsAGI and TEMZ fans.

Visible annotations in the diagram:

• TEMZ collector
• TsAGI collector
• Damper
• Screens
• Booster fan
• Test fan
• Collector
• \(B\)
• \(t^\circ\)
• \(t_{\mathrm{wb}}\)
• \(h_k\)
• \(D_k\)
• \(D_0\)
• \(D_1\)
• \(D_2\)
• \(D_3\)
• \(S_3\)
• \(\alpha\)
• \(\varphi\)

and a carefully made wooden polished collector. The tests in the TPI laboratory were likewise carried out in a chamber; however, here a production collector was used, made by stamping from sheet steel and small in size (callouts in Fig. 3).

The conditions of entry of the flow into the guide apparatus and onto the impeller of the fan being tested were, in the cases being compared, obviously not the same. On the factory test stand the flow entering the fan had already been fully formed in its axial motion through the pipe. On the TsAGI stand the incoming flow was formed by the collector. Judging from the fact that, on the TsAGI stand, the same fan gives a lower pressure, one may suppose that the collector does not provide as good an organization of the flow at entry into the guide apparatus and onto the fan impeller as is achieved by the suction pipe with a straightening grid of the factory stand.

Fig. 4. Test results for the SVM-5m fan in a chamber: without a collector and with the TsAGI and TEMZ collectors.

In the TPI tests, because of the poorer qualities of the collector used, this effect was even more pronounced.

To verify the correctness of the assumption made, strictly speaking, special experiments would have had to be set up. However, the materials presented above are sufficient to recognize that the principal cause of the discrepancies in the compared test results is precisely the different inlet conditions, and not anything else. This is also confirmed by the comparison of test results for the same model of fan, SVM-5m, at TsAGI and at TPI under otherwise identical conditions, but without a collector (Fig. 4). In this case the characteristics in their working portion practically coincide, while certain discrepancies in the zone of unstable operation are evidently explained by the fact that at TsAGI and at TPI different specimens of a fan of one and the same model were tested, i.e., by the individual features of each test specimen.

It is also characteristic that, in chamber tests without a collector, both at TsAGI and at TPI, a practically smooth course of the pressure characteristics over their entire extent was obtained, whereas the presence of a collector already creates a noticeable zone of unstable operation. In tests with a suction pipe the latter is expressed still more clearly. This is connected with the fact that entry without a collector is accompanied by separation of the flow from the inner wall of the fan casing. The peripheral elements of the blades—the separation phenomena on which determine the unstable operation of the fan—are in this case practically excluded from operation. Entry with a collector, however, by ensuring the operation of the peripheral elements of the blades,

is accompanied by separation phenomena, despite the presence in the SVM-5m fan of a special separator intended to straighten the characteristics. Separation phenomena are more noticeable when the flow more fully fills the sections swept by the blades, i.e., when the collector is better, or when the flow has already been fully formed before entering the fan.

In fans of the SVM-5m type all this is manifested especially noticeably because the axial distance from the entrance to the fan suction nozzle to the guide apparatus and the impeller in this model is small, since the electric motor is located at the rear.

Everything noted here is not in itself new, since the influence of the inlet arrangement on the characteristic of an axial fan has been studied sufficiently. In applying this, however, to the question of the methodology for conducting factory and laboratory tests, this circumstance has so far not been given due importance, whereas here it is fundamental and determines the principal operating indicators of the fans being tested.

The testing of axial fans, both factory and laboratory, must be unified and brought into conformity with the conditions under which these fans are used in operation. Only in this case can the test results on factory stands and in laboratories, and the characteristics obtained on their basis, be comparable with one another and truly reflect the quality of the fans under investigation in the course of their operation.

With regard to mine auxiliary ventilation fans, which, as a rule, take air from the main drift and deliver it to the face through a pressure pipeline, both factory and laboratory tests should be carried out in chambers with the installation, alongside them, of the collectors with which these fans will operate in service.