11.4.2 Theoretical Model of Large Diameter
Pneumatic DTH Hammer
11.4.2.1 Hypothesis of Internal Dynamic Process of Pneumatic DTH
Hammer
Figure 11.16 is a simplified model of pneumatic DTH hammer. The piston mass is
M. The pressure, volume, and temperature in the front and rear chambers are p 1 , V 1 ,
T 1 , p 2 , V 2 ; and T 2 , respectively. Each chamber has an inlet and an exhaust port. G 1
and G 3 represent the unit time flow of the inlet and exhaust of the front chamber,
while G 2 and G 4 represent the unit time flow of the inlet and exhaust of the rear
chamber. The internal dynamic process of pneumatic DTH hammer is complex, and
the following assumptions can be made:
(1) Gases are ideal gases
Ideal gas is a hypothetical gas. Gas molecules are elastic particles that do not
occupy volume, and there is no interaction between molecules. The pneumatic
impactor uses compressed air as the medium and the medium is far away from the
liquid phase, so the distance between molecules is very large, the interaction force
between molecules is very small, and the space occupied by the volume of molecules relative to the movement of gas molecules is extremely small. In this case,
neglecting the volume of the molecule itself and the interaction force between the
molecules will not cause great errors. Therefore, the medium in the pneumatic
impactor can be regarded as an ideal gas.
(2) Thermal process in air chamber is quasi-static
Thermodynamic process refers to the whole process that the system changes from
one equilibrium state to another through continuous intermediate state due to its
interaction with the outside world. Thermodynamic process is the result of the
destroyed equilibrium of the system. If the system transits from one equilibrium
state to another through innumerable intermediate equilibrium states, that is, the
system deviates from the equilibrium state infinitely small and restores the
Exhaust
Exhaust
Drilling bit
Front chamber
Intake
Piston
Intake
Rear chamber
Fig. 11.16 Simplified model
of pneumatic DTH hammer
11.4 Dynamic Process and Theoretical Model of Large Diameter …
227
Pneumatic DTH Hammer
11.4.2.1 Hypothesis of Internal Dynamic Process of Pneumatic DTH
Hammer
Figure 11.16 is a simplified model of pneumatic DTH hammer. The piston mass is
M. The pressure, volume, and temperature in the front and rear chambers are p 1 , V 1 ,
T 1 , p 2 , V 2 ; and T 2 , respectively. Each chamber has an inlet and an exhaust port. G 1
and G 3 represent the unit time flow of the inlet and exhaust of the front chamber,
while G 2 and G 4 represent the unit time flow of the inlet and exhaust of the rear
chamber. The internal dynamic process of pneumatic DTH hammer is complex, and
the following assumptions can be made:
(1) Gases are ideal gases
Ideal gas is a hypothetical gas. Gas molecules are elastic particles that do not
occupy volume, and there is no interaction between molecules. The pneumatic
impactor uses compressed air as the medium and the medium is far away from the
liquid phase, so the distance between molecules is very large, the interaction force
between molecules is very small, and the space occupied by the volume of molecules relative to the movement of gas molecules is extremely small. In this case,
neglecting the volume of the molecule itself and the interaction force between the
molecules will not cause great errors. Therefore, the medium in the pneumatic
impactor can be regarded as an ideal gas.
(2) Thermal process in air chamber is quasi-static
Thermodynamic process refers to the whole process that the system changes from
one equilibrium state to another through continuous intermediate state due to its
interaction with the outside world. Thermodynamic process is the result of the
destroyed equilibrium of the system. If the system transits from one equilibrium
state to another through innumerable intermediate equilibrium states, that is, the
system deviates from the equilibrium state infinitely small and restores the
Exhaust
Exhaust
Drilling bit
Front chamber
Intake
Piston
Intake
Rear chamber
Fig. 11.16 Simplified model
of pneumatic DTH hammer
11.4 Dynamic Process and Theoretical Model of Large Diameter …
227