Page 312 - Теория кавитации

Types of active VHG differ in the designs of activators and braking devices. Activators can also be made
in the form of turbines, bodies of rotation with longitudinally profiled surfaces, perforated cylindrical or conical
drums, unidirectional or oppositely rotating perforated disks, etc.
In each of the three types of military equipment, special modes of operation can be additionally created
to facilitate the activation of the liquid, as a consequence, heat generation increases. For this purpose, pressure
in homogeneities in the working chamber are set, self-oscillations are excited in the liquid, additional vortex
flows are formed, shock braking of oncoming jets is provided, ultrasonic treatment of the liquid is performed,
etc.
In addition, each VHG can be used in various heat schemes of heat supply and heating systems. And often
it is the poorly chosen thermal circuit that can lead to inefficient operation of the VHG.
Despite the absence of moving parts and high operational reliability of passive heat generators, active-
type VHG are more appropriate for practical use, since they provide more efficient heating of the fluid and allow
to reduce noise specifications for pressure and performance, which are installed on electric motors with a speed
of 3000 rpm. The design of the same active type VHG allows the use of low-noise electric motors with a speed
of 1500 rev/min.
Two important conclusions can be made that should be taken into account in the practice of heat supply
systems based on VHGD based on the design features of various VHG, and on the basis of an analysis of
practical experience using some passive heat generators.
Firstly, the heat-generating effect of cavitation in fluid flows is usually manifested under conditions
differing from the conditions of its occurrence. It is especially important to take into account this phenomenon
when measuring flow rates of a liquid and temperature difference, since Measurement errors will be significant.
Secondly, heat generation is associated with a collapse zone, which must be created and maintained (as it
is necessary to set up, for example, a burner on a hot-water boiler).
Both of these conclusions lead to the opinion in studying deeply of this phenomenon on the basis of a
wide practical application of VHG with the aim of explaining a plausible mechanism for the onset of cavitation
with heat generation.
The constructive-technological scheme of the experimental computational technology developed within
the framework of this scientific and research works was carried out taking into account the specific preliminary
theoretical calculations performed in the first stage of the Report under this topic [10]-[12]. The main preliminary
(initial) parameters of the developed VHG are given in Table 1.

Table 1 - Constructive and technological parameters of the experienced VHG
Constructive-technological parameters The value Note
of experimental VHG

1 2 3
Pipe length, m 0,7

Pipe diameter, m 0,12

Pipe material (Plexiglas): Plexiglas XT
density, g/sm 3 1,19
2
impact resistance, kDj/m 10-12
0
recommended heating, C 70-90
The pressure in the pipe, ATM. 4-5

Pump (Grandfos): NS BASIC 5-60
Type
F
Class Power, kW 1,27
Source of nutrition, В
Max. working pressure, kPA 220-240
800
Noise level (at a distance of 2 m) in DB. 75,5

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