CFD-DEM Simulation of Reverse Circulation Pneumatic Cuttings Removal during Coal Seam Drilling

To solve the problems that the borehole depth is shallow and the borehole formation rate is low during the gas drainage drilling in soft coal seam with current cuttings removal method, a new technology of reverse circulation pneumatic cuttings removal is put forward. The CFD-DEM coupling method is used to establish the simulation model of cuttings-air two-phase flow in drill pipe. The effects of the air velocity for cuttings removal and the mass flow rate of cuttings on the flow characteristics, cuttings removal effect and pressure drop of cuttings-gas two-phase flow are analysed. The results show that the drag force of drilling cuttings becomes larger with the increase of air velocity and the stratified flow characteristic is obvious. The drill cuttings migration ratio is positively correlated with the air velocity for cuttings removal and negatively correlated with the mass flow rate of cuttings. When the mass flow rate of cuttings is constant, the increase of air velocity for cuttings removal leads to the increase of pressure drop in the inner hole of drill pipe. When the air velocity of cuttings removal is constant, the mass flow rate of cuttings and the pressure drop in the inner hole of drill pipe increases. Therefore, the appropriate air velocity should be selected considering the energy consumption during cuttings removal.

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Pressure drop characteristics of reverse circulation pneumatic cuttings removal during coal seam drilling

Science Progress ◽

10.1177/0036850420925235 ◽

2020 ◽

Vol 103 (2) ◽

pp. 003685042092523 ◽

Cited By ~ 1

Author(s):

Xiaoming Han ◽

Songnan Song ◽

Jialiang Li

Keyword(s):

Particle Size ◽

Pressure Drop ◽

Coal Seam ◽

Mass Flow Rate ◽

Mass Flow ◽

Flow Rate ◽

New Technology ◽

Drill Pipe ◽

Air Velocity ◽

Reverse Circulation

To solve the problems that the borehole depth is shallow and the drilling efficiency is low during the gas drainage drilling in soft coal seam with current cuttings removal method, a new technology of reverse circulation pneumatic cuttings removal is proposed. The working principle of reverse circulation pneumatic cuttings removal is analyzed, and the kinetic equation of cuttings in the inner hole of the drill pipe is established. Through experiments, the pressure drop in the drill pipe is measured to reveal the effects of air velocity, cuttings mass flow rate, and cuttings particle size on the pressure drop in inner hole of the drill pipe. When the cuttings mass flow rate is constant, the pressure drop increases with the increase in air velocity. When the air velocity is constant, the pressure drop increases with the increase in cuttings mass flow rate. At low air velocity, the pressure drop of cuttings is primary. As the air velocity increases, the pressure drop ratio of cuttings decreases. Under the same conditions, the order of pressure drop with different particle size cuttings is coarse cuttings > medium cuttings > fine cuttings. Empirical equation of pressure drop coefficient of cuttings is established, which is in good agreement with the actual data.

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Research on Two-Phase Flow Instability in Evaporator of Refrigeration System

ASME 2010 3rd Joint US-European Fluids Engineering Summer Meeting: Volume 1, Symposia – Parts A, B, and C ◽

10.1115/fedsm-icnmm2010-30487 ◽

2010 ◽

Author(s):

Nan Liang ◽

Changqing Tian ◽

Shuangquan Shao

Keyword(s):

Pressure Drop ◽

Mass Flow Rate ◽

Mass Flow ◽

Flow Rate ◽

Two Phase Flow ◽

Density Wave ◽

Phase Flow ◽

Constant Mass ◽

Refrigeration System ◽

Two Phase

As one kind of fluid machinery related to the two-phase flow, the refrigeration system encounters more problems of instability. It is essential to ensure the stability of the refrigeration systems for the operation and efficiency. This paper presents the experimental investigation on the static and dynamic instability in an evaporator of refrigeration system. The static instability experiments showed that the oscillatory period and swing of the mixture-vapor transition point by observation with a camera through the transparent quartz glass tube at the outlet of the evaporator. The pressure drop versus mass flow rate curves of refrigerant two phase flow in the evaporator were obtained with a negative slope region in addition to two positive slope regions, thus making the flow rate a multi-valued function of the pressure drop. For dynamic instabilities in the evaporation process, three types of oscillations (density wave type, pressure drop type and thermal type) were observed at different mass flow rates and heat fluxes, which can be represented in the pressure drop versus mass flow rate curves. For the dynamic instabilities, density wave oscillations happen when the heat flux is high with the constant mass flow rate. Thermal oscillations happen when the heat flux is correspondingly low with constant mass flow rate. Though the refrigeration system do not have special tank, the accumulator and receiver provide enough compressible volume to induce the pressure drop oscillations. The representation and characteristic of each oscillation type were also analyzed in the paper.

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Experimental Research on Pulsating Two-Phase Flow Pressure Drop Characteristics in Horizontal Rectangular Channel

Volume 2A: Thermal Hydraulics ◽

10.1115/icone22-30392 ◽

2014 ◽

Author(s):

Siqi Zhang ◽

Puzhen Gao

Keyword(s):

Pressure Drop ◽

Mass Flow Rate ◽

Mass Flow ◽

Flow Rate ◽

Two Phase Flow ◽

Rectangular Channel ◽

Phase Flow ◽

Two Phase ◽

Mean Values ◽

Water Mass Flow Rate

In spite of most previous studies since 1970, the theory of pulsating pipe flows supported by experimental investigations has not yet completed in comparison with the well-defined theory of steady pipe flows. Therefore, it seems that there is much to be done about experimental research in this field. In order to determine the resistance characteristics of two-phase flow under pulsatile conditions, an experimental investigation on two-phase flow with periodically fluctuating flow rates in a narrow rectangular channel is carried out. A frequency inverter is used to obtain experimental conditions with different fluctuating frequencies, amplitudes and mean values of water mass flow rate. After obtaining experimental results, comparisons between experimental frictional pressure drop values and theoretical calculations have been done. Two-phase flow on pulsating conditions is far more complicated than that on steady conditions because pulsating flow is composed of two parts: a steady component and a superimposed periodical time varying component called oscillation. In this paper, the influence of different fluctuating frequencies, amplitudes and mean values of liquid and gas mass flow rate on two-phase flow pressure drop characteristics is also discussed. The results show that the total pressure drop and water mass flow rate change with the same fluctuating period except for a phase difference. The phase lag also changes with the fluctuating frequencies and amplitude. The accelerating pressure drop changes dramatically in a fluctuating period, especially at the end of acceleration. Also, the time when the acceleration pressure drop has its maximum value lags the time when the acceleration reaches its peak, mainly because of the inertial of the fluid.

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Numerical Simulation of Flow Behavior within a Venturi Scrubber

Mathematical Problems in Engineering ◽

10.1155/2014/106329 ◽

2014 ◽

Vol 2014 ◽

pp. 1-7

Author(s):

M. M. Toledo-Melchor ◽

C. del C. Gutiérrez-Torres ◽

J. A. Jiménez-Bernal ◽

J. G. Barbosa-Saldaña ◽

S. A. Martínez-Delgadillo ◽

...

Keyword(s):

Numerical Simulation ◽

Pressure Drop ◽

Mass Flow Rate ◽

Mass Flow ◽

Flow Rate ◽

Gas Flow ◽

Two Phase Flow ◽

Phase Flow ◽

Two Phase ◽

Venturi Scrubber

The present work details the three-dimensional numerical simulation of single-phase and two-phase flow (air-water) in a venturi scrubber with an inlet and throat diameters of 250 and 122.5 mm, respectively. The dimensions and operating parameters correspond to industrial applications. The mass flow rate conditions were 0.483 kg/s, 0.736 kg/s, 0.861 kg/s, and 0.987 kg/s for the gas only simulation; the mass flow rate for the liquid was 0.013 kg/s and 0.038 kg/s. The gas flow was simulated in five geometries with different converging and diverging angles while the two-phase flow was only simulated for one geometry. The results obtained were validated with experimental data obtained by other researchers. The results show that the pressure drop depends significantly on the gas flow rate and that water flow rate does not have significant effects neither on the pressure drop nor on the fluid maximum velocity within the scrubber.

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Pressure Drop Oscillations with Symmetry Breakdown in Two-Phase Flow Parallel Channels

Journal of Heat Transfer ◽

10.1115/1.4049032 ◽

2020 ◽

Author(s):

Md Emadur Rahman ◽

Suneet Singh

Keyword(s):

Pressure Drop ◽

Mass Flow Rate ◽

Mass Flow ◽

Flow Rate ◽

Two Phase Flow ◽

Phase Flow ◽

Two Phase ◽

Symmetry Breakdown ◽

Flow Maldistribution ◽

Parameter Values

Abstract Two-phase flow in parallel heated channels is prone to symmetry breakdown resulting in mass flow maldistribution. Moreover, in the presence of compressible volume, such systems also undergo pressure drop oscillations (PDO). The performances of such systems depend on the effect of these flow instabilities. However, the simultaneous occurrence of these two- phenomena has been rarely reported in the literature. In the present work, an approach is applied in a two channels system to demarcate the parameter space of mass flow rate and inlet temperature into several areas, where these two phenomena take place. The loss in the symmetry in the flow rate is observed as the mass flow rate is varied, which leads to flow maldistribution. The PDO are also observed for specific values of mass flow rate in the system. One unique feature of the parallel channel system is the existence of the oscillatory and stable (albeit asymmetric) states at the same parameter values. For these parameter values, the final state of the system is dependent on the type of initial disturbance. The flow maldistribution due to symmetry breakdown is identified by the pitchfork bifurcation, and oscillations of mass flow rate are identified by the presence of Hopf bifurcation. Moreover, the physical interpretation of the different phenomena in the system is carried out using internal and external pressure drop characteristics curves.

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