Conference Agenda

This paper presents analysis of twin-screw vacuum pumps, encompassing both geometrical calculations and numerical simulations. The geometrical calculations include key parameters such as chamber volume, leakage area, suction port area, and discharge port area. These parameters are studied across rotational angles for constant pitch, and stepped pitch configurations. The leakage areas include radial, axial, and interlobe leakage paths. Computational Fluid Dynamics (CFD) is employed to investigate the axial leakage paths. Additionally, the study utilizes the SCORG software package, an in-house simulation tool to calculate thermodynamic processes and integral parameters. By integrating the geometric calculations into SCORG, this approach enables extensive calculation and design optimization of twin-screw vacuum pumps. Five different combinations of pitch were analyzed to assess their impact on both volume flow rate and efficiency. The analysis revealed that reducing the pitch of the second stage resulted in a decrease of approximately 2% in volumetric efficiency, while adiabatic efficiency increased by around 4%. The findings contribute to a more comprehensive understanding of the performance characteristics and design considerations for twin screw vacuum pumps.

The generation of boil-off gas (BOG) is a problem that must be solved during liquid natural gas (LNG) transportation. The dry twin-screw compressor is used for BOG recovery to ensure the purity of the gas, but the efficiency of the dry compressor is more sensitive to leakage clearance. To investigate the effect of rotor deformation on clearance and efficiency under low-temperature working conditions. This paper simulated the working process of the BOG twin-screw compressor based on the thermal-fluid-structure coupling method so that the rotor deformation could be fully considered. It found a temperature difference between the rotors, and the temperature of the male rotor was higher. Besides, when the suction temperature is -30℃, the rotors contract near the suction while expanding on the discharge side, which makes the efficiency of the compressor not significantly change. The volumetric efficiency of the operating model is 1.26% lower, while the isentropic efficiency of the operating model is 0.41% smaller than the start-up model. When the suction temperature of the compressor is -10℃, the volumetric efficiency of the compressor after stable operation increases by 3.77% compared with that at start-up, and the isentropic efficiency is increased by 5%. When the suction temperature is reduced to -50℃, the volumetric efficiency and isentropic efficiency are reduced by 9.25% and 8.25% after stable operation, respectively.

Pressure pulsation within the discharge system of oil-free twin-screw compressors used in Vapor Recovery Units (VRUs) significantly impacts their reliability and the integrity of connected piping. This study investigates the dynamics of pressure pulsations in such compressors within the oil and gas industry, where reliable and robust operation is crucial. A Computational Fluid Dynamics (CFD) model was developed using ANSYS CFX coupled with SCORG mesh generation. Different discharge system configurations were investigated, including scenarios with the discharge port only, discharge port with a venturi pipe and a discharge port with a constant diameter pipe. Non-Reflective Boundary Conditions (NRBC) were adopted at the discharge outlet to minimize wave reflection. Findings revealed minor variations in both the P-𝛼 diagram and pulsation profiles among the configurations. Specifically, the use of a venturi pipe slightly elevated the peak pressure in the P-α diagram and increased the amplitude of discharge pressure pulsations. Additionally, the mass flow rate and indicated power showed negligible variation across the configurations, highlighting the limited impact of discharge system design on these performance metrics. Finally, a frequency domain analysis revealed the presence of the pocket passing frequency and no resonance effects due to different discharge configurations.

To evaluate the performance of oil-injected twin-screw compressors, it is important to understand and model the advanced physical phenomena occurring during the compression process (e.g., mass and heat transfer mechanisms, leakage flows) as well as analyze the mechanical behavior of the compressor (e.g., rotordynamics, bearing loads, deformations). However, comprehensive experimental data is needed to validate the various modeling aspects.

This paper presents a numerical approach to perform a thorough computation of the pressure and volume curves, torque and bearing loads to estimate bearing losses. A 4/6 oil-injected twin-screw compressor with slide-valve part-load modulation and economization is used as the case study. Using data from a previously established experimental setup, the model has been verified and validated with the platform PDSim and numerically checked with SCORG. Indicated diagrams and mechanistic analyses were developed and have been analyzed to experimentally quantify the various losses and to validate the models. The validated model is used to analyze the performance of the compressor.