Qi Hang 1, Zhang Xinyue 1, Dai Zeyu 1, Zhang Jianyun 2, Zhu Hailei 2, Lyu Qian 1, Yu Xiaoling 1

(1. School of Chemical Engineering and Technology, Xi 'an Jiaotong University, Xi 'an 710049, Shaanxi; 2. Shenyang Blower Group Co., LTD., Shenyang 100869, Liaoning)

[Abstract] : Aiming at the pressure pulsation problem existing in the pipeline of reciprocating compressors, a method combining numerical simulation and experimental testing was adopted to systematically investigate the influence law of orifice plate parameters on pressure pulsation suppression and pressure drop. A flow field model of the first-stage intake pipeline of the compressor was constructed. According to the direction of the airflow coming through the buffer tank as the front, two installation positions of the perforated plate were set before and after the buffer tank. Under the condition of keeping the total opening area consistent, the effects of structural parameters such as the position of the perforated plate, the number of perforated plates, and the offset of the hole center on the pulsation amplitude and pressure drop were compared. The results show that installing perforated plates before and after the buffer tank can both reduce pressure fluctuations. Installing perforated plates before and after the buffer tank has a good effect on reducing the pulsation of the pipeline and the buffer tank respectively. The three-hole system has a significantly better effect in suppressing pressure pulsation than the single-hole system. Further increasing the number of holes has a relatively small increase in the effect of weakening pressure pulsation. When the distance from the center of the hole to the center of the hole plate increases, the pulsation change is not significant, but the pressure drop is the smallest when the distance is approximately half of the radius of the hole plate. The research results show that the reasonable selection of the installation position, quantity and radial position structure parameters of the orifine plates can effectively suppress pressure pulsation and take into account pressure drop control, providing a reference for the optimization of the compressor pipeline system.

[Key words] : Compressor pipeline Orifice plate parameters; Pressure pulsation Pressure drop Numerical simulation Experiment

Chinese Library Classification Number: TH457 TB535 Document Code: A

Article Number: 1006-2971 (2026) 02-0001-06

1 Introduction

Gas pulsation is the result of the discontinuous characteristics of gas flow in reciprocating compressors [1-2]. Gas pulsation in the compressor pipeline can reduce the performance of the compressor, hinder the normal operation of the compressor valve, and cause pipeline vibration, which can lead to pipeline fatigue failure, loose fasteners, compressor overload, and even serious safety issues [3-4]. In the petrochemical industry, gas pulsation and pipeline vibration are regarded as the most common causes of unplanned shutdowns and accidents in reciprocating compressors. Therefore, controlling gas pulsation and pipeline vibration in the compressor pipeline system is a very important issue. Orifice plates are widely used in suppressing pipeline pulsation, and their effectiveness largely depends on the size and installation position of the orifice plates [5]. Although the theoretical mechanism by which orifices suppress gas pulsation has been relatively clear, its practical application still requires specific exploration, including the optimization of parameter selection and installation position, as well as the resulting pressure loss [6].

RYDLEWICZ et al. [7] confirmed through experiments and model analysis that orifice plates can effectively suppress pressure pulsation in pulsating flow, and the attenuation effect is nonlinearly related to the orifice ratio. JIAX et al. [5] investigated the influence of orifine plate parameters and installation positions on gas pulsation in reciprocating compressor pipeline systems through a systematic approach that combined acoustic theoretical modeling with experimental verification. ZHANG et al. [8] analyzed the pressure pulsation on the orifice plate surface through numerical simulation and found that the gas-liquid two-phase flow could induce wideband excitation, which might cause multi-frequency vibration in the pipeline. CHANG et al. [9] investigated the noise characteristics and hydraulic losses of cavitation flow in perforated plates through experimental measurements and large-scale vortex simulation (LES) combined with the ZGB cavitation model, and established an empirical relationship model between the pressure loss coefficient and the Reynolds number and porosity.

BARROSFILHO et al. [10] investigated the influence of the chamfer geometry of the orifice plate in the fuel pipeline of a nuclear reactor on the hydraulic drop during cold recovery through numerical simulation and scale experiments. MAY et al. [11] experimentally studied the pressure drop characteristics of wet gas flowing through a perforated plate in a low gas phase Fraoud number region, providing a more reliable model support for the measurement of wet gas flow. Li Haoran et al. [12] studied the influence mechanism of the inner Angle on the pressure drop of the orifice plate through CFD simulation and experiments. The research confirmed that the inner Angle of the orifice plate has a significant impact on the pressure drop and proposed an improved calculation formula including the influence of the inner Angle. Ji Mingzhen et al. [13] studied the resistance characteristics of orifice plates suitable for air supply through a combination of numerical simulation and experimental verification. They focused on discussing the influences of orifice shape, orifice plate thickness, orifice diameter and orifice ratio on the local resistance coefficient. WUY et al. [14] studied the influence of the structural parameters of the perforated plate on the pressure drop characteristics of single-phase flow through experimental research methods and reached the following conclusion: The equivalent diameter ratio β has the most significant effect on the pressure drop coefficient ξ in the stable zone, while increasing the relative hole thickness and the number of holes has a limited effect on its pressure drop.

How to strike a balance between suppressing pressure pulsation and reducing resistance loss has become a key issue in the design of compressor piping systems. This paper will explore the influence laws of installing orifoil plates on pipeline pressure pulsation and resistance loss through theoretical analysis and experimental verification, providing a theoretical basis for the optimal design of compressor pipeline systems.

2 Numerical Simulation

The calculated pipeline model is the first-stage intake pipeline of the reciprocating compressor, with an intake pressure of 2.522MPa. The specific parameters of the compressor are shown in Table 1. The medium in the compressor pipeline is shown in Table 2. The end of the intake pipe is simultaneously connected to the shaft side and cover side cylinders of a double-acting compressor, providing intake for the two cylinders. The compressor's rotational speed is 300r/min, meaning the cycle is the same at 0.2 seconds. The intake period of the pipeline is 0.2 seconds. As shown in Table 2.

2.1 Establishment of Computational Model

The fluid domain was extracted according to the shape of the compressor's intake pipe as shown in Figure 1.

The gas flows in from the intake end of the pipeline, passes through the pipeline and then enters the compressor from the intake end of the compressor. A buffer tank is installed in front of the compressor to suppress the pulsation amplitude of the compressor's intake pipe.

2.2 Boundary Conditions

The boundary conditions of the fluid in contact with the pipe wall are set as the boundary conditions of the adiabatic wall, and are set as the velocity outlet and pressure inlet. The intake velocity of the compressor, that is, the calculated model velocity outlet, can be expressed as [15] :

In Equation (1) : α is the crank Angle; b is the ratio of the flow area of the cylinder to that of the pipe. r represents the length of the crank. ω represents the angular velocity of the crank; λ is the ratio of the length of the crank to that of the connecting rod. αx is the opening Angle of the air valve. The overall calculation process of the opening Angle of the air valve is as follows: Calculate the piston displacement based on the crank rotation Angle, and then calculate the air force based on the piston displacement. The calculation of the piston displacement can be expressed as:

In the formula: pi represents the gas pressure inside the cylinder; po is the gas pressure at the beginning of expansion, that is, the exhaust pressure. xi represents the displacement of the piston; m is the inflation index; S0 is the relative clearance volume converted to the relative clearance stroke.

The intake process begins when the gas in the cylinder expands to a point where its pressure reaches equilibrium with that in the intake pipe. At this point, the crank Angle is the opening Angle of the air valve.

The outlet velocity of the calculation model includes the intake velocity of the cylinder on the cover side and the shaft side. The excitation velocity of the pipeline system within one cycle is shown in Figure 2.

3. Results and Discussion

3.1 Test Result Analysis

There are two measurement points arranged on the first-stage intake pipe of the compressor, located on the pipe and the buffer tank respectively. The specific measurement point positions are shown in Figure 3. The time-domain measurement values of pressure pulsation at the measurement points of the pipeline and the buffer tank are shown in Figure 4.

The frequency domain results obtained through Fourier transform are shown in Figure 5, indicating that the pulsating main frequency is 5Hz, corresponding to the compressor's rotational speed of 300r/min, and the frequency domain values are mainly concentrated in the first 60Hz. Therefore, the subsequent analysis will focus on this frequency band.

3.2 Orifice plates are installed before and after the buffer tank

After filtering out the high-frequency components above 60Hz, the pressure pulsation measurement values of the pipeline and buffer tank measurement points are compared with the simulated values as shown in Figure 6. It can be seen from the figure that the simulated value and the measured value of the pipeline pressure pulsation change trend are highly consistent, and the errors of the peak-to-peak values of the two pulsations are 4.90% and 2.93% respectively.

This result indicates that the model established in this study can reliably simulate the pressure pulsation behavior in the pipeline.

The diameter of the orifice plate is D = 154.06mm. Two calculation models were established, namely installing the orifice plate before the buffer tank and installing it after the buffer tank. The positions of the orifice plates are shown in Figure 7. The hole diameters of the orifice plates are all 0.5D.

The time-domain values of the pressure pulsation obtained by installing orifine plates before and after the buffer tank were calculated and compared with the pulsation values obtained by the original orifine plates. As shown in Figures 8 and 9, they are the time-domain values of the pulsation at the pipeline measurement points and the buffer tank measurement points respectively. Compared with the reference working condition without orifine plates, the pulsation attenuation effect at each measurement point after installing orifine plates is as follows At the pipeline measurement points, orifine plates were installed before and after the buffer tank, reducing the peak-to-peak value of pressure pulsation by 10.28% and -3.32% respectively. At the measurement points of the buffer tank, the two installation methods reduced by 6.99% and 10.98% respectively.

The pressure pulsation values were subjected to Fourier transform to obtain the frequency domain values as shown in Figures 10 and 11. It can be seen from the figures that installing a perforated plate before the buffer tank has a better suppression effect on the pressure pulsation of the pipeline, and installing a perforated plate after the buffer tank has a better suppression effect on the pressure pulsation of the buffer tank.

Based on the time-frequency domain values of the two measurement points, it can be known that installing the orifine plate before the buffer tank has a better overall suppression effect on pressure pulsation.

Figure 12 shows the pressure distribution near the buffer tank. When the orifice plate is not installed, the pressure inside the tank and in the connected pipelines is uniform and the flow field is stable. After the orifine plate is installed, a high-pressure area appears upstream of the buffer tank and a low-pressure area forms downstream. Combined with the velocity cloud diagram in Figure 13, it can be seen that the flow velocity in this low-pressure area has significantly increased, presenting typical throttling expansion characteristics.

As shown in Figure 13, it is the velocity distribution of the cross-section near the buffer tank. It is clearly visible from the figure that there is a distinct vortex area inside the buffer tank, and its generation location is significantly affected by the position of the orifice plate. At the same time, a large number of vortex structures will form in the area close to the wall behind the orifice plate. The generation of these vortices will dissipate the kinetic energy of the fluid, thereby causing pressure loss.

3.3 The influence of the number of holes in the orifice plate on pulsation

To study the influence of the number of orifice plates on pressure pulsation, the number of holes n on the orifice plate was changed from 1 to 9. The model parameters are shown in Table 3. Some of the orifice plate cross-sectional models are shown in Figure 14.

The pressure pulsation of the pipelines and buffer tank systems corresponding to each model was calculated and analyzed, and the results are shown in Figure 15. It can be seen from the figure that the pressure pulsation decreases with the increase of the number of holes. Among them, the pressure pulsation decreases significantly from n from 1 to 3, while it decreases less when n increases from 3 to 9.

The pressure drop before and after the orifice plate is calculated as shown in Figure 16. It can be seen from the figure that the pressure drop caused by the orifice plate increases significantly with the increase of the number of holes.

3.4 Influence of the opening position of the orifice plate on Pulsation

For a three-hole plate, a calculation model is established by changing the distance L between the hole center and the center of the plate (the value is shown in Table 4).

The pressure pulsation curves of the monitoring points of the pipeline and the buffer tank under different opening hole orientation positions are shown in Figure 17. It can be seen from the figure that the distance L between the center of the opening and the center of the orifice-plate has no obvious influence on the amplitude of the pressure pulsation.

4 Conclusion

(1) The orifice plate installed before the buffer tank has a significant inhibitory effect on pipeline pulsation, and the orifice plate installed after the buffer tank has an even better inhibitory effect on pulsation inside the buffer tank. Comprehensive analysis shows that the overall buffering effect installed before the buffer tank is better.

(2) As the number of holes in the orifice plate increases, the pressure pulsation shows a downward trend. However, when the number of holes in the orifice plate increases to 3, the pressure pulsation decreases less when the number of holes is further increased. Meanwhile, the pressure drop increases significantly with the increase in the number of holes.

(3) As the distance between the center of the hole and the center of the orifine plate increases, the pressure pulsation does not change significantly, and the pressure drop shows a trend of first decreasing and then increasing. When the distance is approximately half of the radius of the orifine plate, the pressure drop is the smallest.

Author's Profile: Qi Hang (2000-), male, from Shangqiu, holds a master's degree, and his research focuses on reciprocating compressors.

Corresponding author: Yu Xiaoling (1978-), female, professor, currently mainly engaged in research on reciprocating compressor-related technologies.