On Some Terms in the Literature on Mine Ventilation
Abstract Generated abstract
This article examines several entrenched terms in mine ventilation literature, especially “depression,” and argues that they obscure rather than clarify the physical processes involved. Using Bernoulli’s equation and pressure diagrams for fans operating in suction and blowing modes, it shows that measured depression is not necessarily equal to either the static or total fan head, and may be greater than, equal to, or less than total head depending on measurement conditions. The paper proposes replacing ambiguous or physically imprecise mining terminology with terms aligned with general industrial ventilation, such as head, pressure loss, capacity, air meter, dead-end working, and local ventilation. It also calls for clearer distinction among relative weight, specific weight, and density, and for standardized terminology across mining and non-mining ventilation practice.
Full Text
On Some Terms in the Literature on Mine Ventilation
B. M. Titov
“For the flourishing of science, of that science whose people, while understanding the force and significance of the traditions established in science and skillfully using them in the interests of science, nevertheless do not wish to be slaves of these traditions; which has the courage and determination to break old traditions, norms, and precepts when they become obsolete, when they turn into a brake on forward movement; and which knows how to create new traditions, new norms, new precepts.” (From Comrade Stalin’s speech at the reception in the Kremlin for workers of higher education, May 17, 1938.)
In the mining literature dealing with mine ventilation, the terms depression, debit, volumometer, blind working, partial ventilation, and a number of derivatives from them—for example, depression survey, gas debit, etc.—have become historically entrenched.
At the same time, these terms (one might say, this jargon) are entirely absent from the analogous modern literature dealing with the ventilation of industrial and residential buildings, as well as from the terminology used by TsAGI.
The question involuntarily arises: do the indicated terms help mining engineers better explain and understand questions connected with mine ventilation, or is their use explained only by a peculiar conservatism among workers in mining science?
In order to clarify the expediency of retaining the term depression in the mining literature, let us consider the operation of a fan under suction and pressure methods of ventilating workings.
When a fan operates in suction (Fig. 1), for sections I—I and II—II, according to Bernoulli’s equation, one may write:
\[ p_{cm_1} + \rho \frac{v_1^2}{2} = p_{cm_2} + \rho \frac{v_2^2}{2} - H, \]
where \(p_{cm_1}\) and \(p_{cm_2}\) are the absolute static pressure before and after the fan, kg/m²;
\[ \rho \]
is the air density, kg·sec²/m⁴;
\(v_1\) and \(v_2\) are the air velocities, m/sec;
\(H\) is the total pressure of the fan, kg/m².
Substituting the values \(p_{c m_2}=p_{a m}\), \(v_2=v_{\text{out}}\) and carrying out the transformation, we obtain
\[ H=\left(p_{a m}-p_{c m_1}-\rho \frac{v_1^2}{2}\right)+\rho \frac{v_{\text{out}}^2}{2}, \]
where
\[ \begin{aligned} p_{a m} &\text{ is atmospheric pressure, } \mathrm{kg}/\mathrm{m}^2;\\ v_{\text{out}} &\text{ is the air velocity in the outlet section, } \mathrm{m}/\mathrm{sec}. \end{aligned} \]
It is known that the total pressure of a fan is equal to:
\[ H=H_{c m}+\rho \frac{v_{\text{out}}^2}{2}, \]
where \(H_{c m}\) is the static pressure of the fan, i.e., the part of the total pressure used to overcome resistances in the pipeline, \(\mathrm{kg}/\mathrm{m}^2\);
Fig. 1
In the figure: “pipeline resistance”; \(h=p_{a m}-p_{c m_1}\); \(p_{c m_1}<p_{a m}\); \(v_1>0\); \(p_{c m_2}=p_{a m}\); \(v_2=v_{\text{out}}\).
\[ \rho \frac{v_{\text{out}}^2}{2} \]
is the dynamic pressure at the fan or pipeline outlet \(\left(H_{\text{dyn., out}}\right)\), i.e., the part of the total pressure (energy) lost with the outgoing air jet, \(\mathrm{kg}/\mathrm{m}^2\).
Solving the last two equations simultaneously, we have
\[ H_{c m}=p_{a m}-p_{c m_1}-\rho \frac{v_1^2}{2}. \]
In this expression the difference of the static pressures is equal to the depression measured by a water manometer (Fig. 1), \(h=p_{a m}-p_{c m_1}\), therefore:
\[ H_{c m}=h-\rho \frac{v_1^2}{2}. \]
Consequently, when a fan operates in suction, in order to determine the static pressure it is necessary to subtract from the measured depression the dynamic pressure calculated for the section in which the depression was measured:
\[ H_{c m}=h-H_{\text{dyn. depr}}=h-\frac{\rho}{2}\left(\frac{Q}{F_h}\right)^2, \]
where \(Q\) is the capacity of the fan, \(\mathrm{m}^3/\mathrm{sec}\);
\(F_h\) is the cross-sectional area of the duct at the place where the depression (static pressure) is measured, \(\mathrm{m}^2\).
Thus, one must not confuse depression (or the difference of static pressures) with the static head produced by the fan.
To illustrate the uncertainty introduced into mining literature by the term “depression,” let us construct the pressure diagram of a fan operating on suction, remembering that the dynamic head always has a positive sign. The construction (Fig. 2) is made in absolute pressure units and under the assumption that the cross section of the duct at the point where the depression is measured is smaller than the outlet cross section of the fan:
\[ F_h < F_{\text{out}}, \qquad v_h > v_{\text{out}}, \qquad H_{\text{dyn. depr.}} > H_{\text{dyn. out.}} . \]
Fig. 2
Fig. 3
From Fig. 2 it is seen that the measured depression is not equal to the static head and will be greater than the total head produced by the fan, i.e.
\[ h > H. \]
If \(F_h = F_{\text{out}}\), then \(H_{\text{dyn. depr.}} = H_{\text{dyn. out.}}\) and \(h = H\).
For \(F_h > F_{\text{out}}\) we have: \(H_{\text{dyn. depr.}} < H_{\text{dyn. out.}}\) and \(h < H\).
Thus, the depression may be greater than, equal to, or less than the total head of the fan.
In the case of a fan operating on blowing (Fig. 3), for sections I—I and II—II one may write:
\[ p_{\text{st}_1} + 0 = p_{\text{st}_2} + \rho \frac{v_2^2}{2} - H . \]
Substituting \(p_{\text{st}_1} = p_{\text{atm}}\) and taking into account that \(p_{\text{st}_2} - p_{\text{atm}} = h\) and \(F_2 = F_{\text{out}}\), we obtain:
\[ h = H - \rho \frac{v_2^2}{2} = H - H_{\text{dyn. out.}} = H_{\text{st}} . \]
Consequently, when the fan operates on blowing and \(F_h = F_{\text{out}}\), the depression is, in magnitude, equal to the static head of the fan, and therefore the total head of the fan must be calculated by the formula:
\[ H = h + H_{\text{dyn. depr.}} = h + \frac{\rho}{2}\left(\frac{Q}{F_h}\right)^2 . \]
For the construction of the pressure diagram of a fan operating on blowing, see Fig. 4.
The diagrams in Figs. 3 and 4 do not contradict the definition of the total head of a fan as the difference of the total pressures before and after the fan:
\[ H = p_2 - p_1 = \left(p_{cm_2} + \rho \frac{v_2^2}{2}\right) - \left(p_{cm_1} + \rho \frac{v_1^2}{2}\right). \]
It follows from the foregoing that the term “depression” may be understood differently by the author and by the reader, and therefore it is not a felicitous term and merely introduces confusion into the literature on mine ventilation. The use of the term depression (and not compression) in forced ventilation does not even correspond to the physical meaning of the word itself.
The terms: delivery, volumometer, blind working, partial ventilation, although they do not disorient the reader, also do not correspond precisely to the physical meaning of the concepts they denote.
Fig. 4
In addition, it must be noted that in the Russian language there are more suitable words for expressing the physical meaning of the phenomena denoted by the terms depression, delivery, volumometer, and derivatives of them.
V. I. Lenin, as early as 1924, wrote in the article “On the Purification of the Russian Language”: “If it is pardonable for someone who has only recently learned to read to use foreign words as a novelty, then writers cannot be forgiven for this. Is it not time for us to declare war on the use of foreign words without necessity?” (V. I. Lenin, Works, vol. 30, 4th ed., p. 274, 1950).
From our point of view, the terms indicated above, as not corresponding to the physical meaning of the phenomena, should not be used in the future, and they must be replaced by analogous concepts in Russian from the course of general industrial ventilation.
For example, the term “depression” should be replaced by the term “head” or “pressure loss” (with the corresponding division into static and total pressure); instead of “delivery,” the terms “capacity” and “quantity of air supplied” should be used, depending on whether the fan or the ventilation network is being discussed. A volumometer should be called an air meter. A “blind” working is more properly called a “dead-end” working. The term “partial” ventilation should be replaced by “local” ventilation. The same applies to derivatives of them; for example, “depression survey” may be called “measurement of pressure loss,” “gas delivery” — “gas emission,” etc.
In addition to the use of the above-mentioned unsuccessful terms, it must be noted that many authors (and not only mining engineers) incorrectly use and fail to distinguish such concepts as specific weight, relative weight, and density, although these are three entirely different quantities.
Relative weight is the ratio of the weight of a body to the weight of distilled water of the same volume at \(4^\circ\mathrm{C}\) [1].
The relative weight \(d\) is a dimensionless quantity and for water is equal to unity.
Specific weight is the ratio of the weight of a body to its volume. The specific weight \(\gamma\) has dimensions and, for water, in the practical system of units is equal to \(1000\ \mathrm{kg}/\mathrm{m}^3\).
Density is the ratio of the mass of a body to its volume. For water the density is equal to:
\[ \rho = \frac{m}{V} = \frac{\gamma}{g} = \frac{1000}{9.81} = 102\ \frac{\mathrm{kg}\cdot \mathrm{sec}^2}{\mathrm{m}^4}, \]
\(g = 9.81\)—the acceleration of gravity, \(\mathrm{m}/\mathrm{sec}^2\).
The term “volumetric weight” is not recommended for use [2].
For air under normal atmospheric conditions \(p_{am}=760\ \mathrm{mm}\) Hg, \(t=20^\circ\mathrm{C}\), and humidity \(\varphi=50\%\), respectively, we have:
\[ d = 0.0012;\quad \gamma = 1.2\ \frac{\mathrm{kg}}{\mathrm{m}^3};\quad \rho = 0.122\ \frac{\mathrm{kg}\cdot \mathrm{sec}^2}{\mathrm{m}^4}. \]
It seems to us that in the future the Committee on Technical Terminology of the Academy of Sciences of the USSR should develop unified terms for the course of ventilation, mandatory for use both in mining and in non-mining industry, and that Ugletekhizdat and Metallurgizdat should adhere to them strictly when editing literature.
REFERENCES
- Terminology of Hydromechanics. Publishing House of the Academy of Sciences of the USSR, Moscow–Leningrad, 1947.
- Terminology of Fluid Mechanics (Hydromechanics). Publishing House of the Academy of Sciences of the USSR, Moscow, 1952.