Behaviors of a Hole-Pattern Seal With Wet-Gas

Hole-pattern (HP) seals are widely used in centrifugal compressors to control leakage. This paper investigates the behaviors of an HP with wet-gas mixtures. The mixture consists of oil and air with inlet liquid volume fraction (LVF) up to 8%. Injecting oil into the air stream increases the leakage mass flowrate. Direct stiffness K is frequency-dependent and increases with increasing excitation frequency Ω. Injecting oil into the airflow makes this stiffening effect more pronounced. At low frequencies, increasing inlet LVF shows no appreciable impact on K; however, as Ω increases, the effects of changing LVF become more pronounced; i.e., at high frequencies, increasing LVF increases K. The effective damping Ceff value at half of the running speed is indicative of the system stability because many compressor rotors frequently show instabilities at ∼50% of the running speed. At 50% of the running speed, Ceff is positive, and it increases with increasing inlet LVF. Predictions based on San Andrés's (2011) homogenous-mixture bulk-flow model show a good agreement with test results for leakage mass flowrate, K, and the Ceff value near 50% of the running speed. When Ω = 0.5ω, the predicted value of Ceff is smaller than the measured value by ∼12.5%, giving a safe margin for the compressor design.

Foam Quality of Foams Formed on Capillaries and Porous Media Systems

Foams are of great importance as a result of their expansive presence in everyday life—they are used in the food, cosmetic, and process industries, and in detergency, oil recovery, and firefighting. There is a little understanding of foam formation using soft porous media in terms of the quality of foam and foam formation. Interaction of foams with porous media has recently been investigated in a study by Arjmandi-Tash et al., where three different regimes of foam drainage in contact with porous media were observed. In this study, the amount of foam generated using porous media with surfactant solutions is investigated. The aim is to understand the quality of foam produced using porous media. The effect of capillary sizes and arrangement of porous in porous media has on the quality of foam is investigated. This is then followed by the use of soft porous media for foam formation to understand how the foam is generated on the surface of the porous media and the effect that different conditions (such as concentration) have on the quality of the foam. The quality of foam is a blanket term for bubble size, liquid volume fraction, and stability of the foam. The liquid volume fraction is calculated using a homemade dynamic foam analyser, which is used to obtain the distribution of liquid volume fraction along with the foam height. Soft porous media does not influence substantially the rate of decay of foam produced, however, it decreases the average diameter of the bubbles, whilst increasing the range of bubble sizes due to the wide range of pore sizes present in the soft porous media. The foam analyser showed the expected behaviour that, as the foam decays and becomes drier, the liquid volume fraction of the foam falls, and therefore the conductivity of foam also decreases, indicating the usefulness of the home-made device for future investigations.

Testing Liquid Distribution in a Vane-Type Propellant Tank under Conditions of Microgravity Using a Drop Tower Test

Propellant management devices (PMDs) are a key component used to manage liquid propellant in a propellant tank under zero gravity conditions. A microgravity drop tower test system was established to investigate the performance of a PMD. A single module was used for the experiments, and the microgravity level was less than 3 × 10 − 3 g . Anhydrous ethanol was used as the simulate liquid. Different volume fractions of liquid were used to study the influence of the PMD on performance management. Experiments were conducted with the position of the container oriented in different directions. Changes in the gas-liquid interface were studied during the test. This kind of vane transports liquid through the rectangular area between the vane and the wall. The velocity flows along the vane of different liquid volume fractions in the tank were different at the beginning ( t < 0.8 s ) compared with the end of the test. The liquid relocation time was less than 0.8 s while the liquid volume fraction was larger than 25%. The liquid relocation time was prolonged when the liquid volume fraction was less than 25%. The liquid climbing height along the vane under microgravity increased as the volume fraction of liquid reduced. The climbing velocity of the liquid is half reduction when the liquid volume fraction is small. The time for the liquid transferred from the top of the tank to the liquid outlet can be obtained by climbing velocity. It shows that the maneuverability of the satellite decreases at the end of its life. The above results are applicable to all propellant tank with vertical vanes. These results provide a favorable reference for further optimized design of vertical vane-type propellant tanks.

The Liquid Maldistribution Analysis of the Trickle Bed Reactor with the CFD Method

The liquid phase maldistribution factor has been investigated in trickle bed reactor, and the results are compared with the previous measurement data from literature by using the Electrical Resistance Tomography. The simulation results are in agreement with the experimental results to some degree. The flow rates and particle sizes have been simulated with the method of multiphase flow. There are two different particles with average diameters of 3.4 mm and 5.3 mm. The flow rate has been studied ranging from 100 ml/min to 1100 ml/min. It has been found that the changes of the particles and liquid flow rates have a significant impact on the distribution of the liquid volume fraction. The internal liquid holdup is more serious, and the wall-flow phenomenon is more obvious in a bigger flow rate. The prediction of the liquid volume fraction distribution is a key research technique. Regression predictions have also been researched on the section near outlet, which can predict the internal flow state of the trickle bed under the condition of high temperature and high pressure. The average liquid volume fraction is linear with flow rates. The maldistribution factor is the index correlation with the flow rates. The results and main conclusions can be used to predict the distributions and get the properties in a trickle bed reactor.

Application of SLIPI-Based Techniques for Droplet Size, Concentration, and Liquid Volume Fraction Mapping in Sprays

Structured laser illumination planar imaging (SLIPI)-based techniques have been employed during the past decade for addressing multiple light scattering issues in spray imaging. In this article, SLIPI droplet sizing based on the intensity ratio of laser-induced fluorescence (LIF) over Mie scattering (SLIPI-LIF/Mie) and SLIPI-Scan for extinction-coefficient (µe) mapping are applied simultaneously. In addition, phase Doppler anemometry (PDA) and numerical calculations based on the Lorenz–Mie theory are also employed in order to extract the droplets Sauter mean diameter (SMD), the droplets number density (N), and the liquid volume fraction (LVF) in a steady asymmetric hollow cone water spray. The SLIPI-LIF/Mie ratio is converted to droplets SMD by means of a calibration procedure based on PDA measurements. The droplet SMD for the investigated spray varies from 20 µm to 60 µm, the N values range from 5 to 60 droplets per mm3, and the LVF varies between 0.05 × 10−4 and 5.5 × 10−4 within the probed region of the spray. To generate a series of two-dimensional images at different planes, the spray scanning procedure is operated in a “bread slicing” manner by moving the spray perpendicularly to the light sheet axis. From the resulting series of images, the procedure described here shows the possibility of obtaining three-dimensional reconstructions of each scalar quantity, allowing a more complete characterization of droplet clouds forming the spray region.

A Study for Rotordynamic and Leakage Characteristics of a Long-Honeycomb Seal With Two-Phase, Mainly Air Mixtures

This paper investigates the impact of the oil (silicone oil PSF-5cSt) presence in the air on the leakage and rotordynamic characteristics of a long-honeycomb seal with length-to-diameter ratio L/D = 0.748 and diameter D = 114.656 mm. Tests are carried out with inlet pressure Pi = 70.7 bars, pressure ratio (PR) = 0.35 and 0.25, inlet liquid volume fraction (LVF) = 0%, 3.5%, and 7%, and shaft speed ω = 10, 15, and 20 krpm. During the tests, the seal is centered. Test results show that leakage mass flow rate m˙ increases (as expected) as inlet LVF increases. Increasing inlet LVF makes direct stiffness K increase more rapidly with increasing excitation frequency Ω. Increasing inlet LVF has a negligible effect on K at low Ω values, but increases K at high Ω values. The value of effective damping Ceff at about 0.5ω is an indicator to the system stability since an unstable centrifugal compressor rotor can precess at about 0.5ω. Increasing inlet LVF increases the value of Ceff at about 0.5ω, reducing the possibility of subsynchronous vibrations (SSVs) at about 0.5ω. San Andrés's model is used to produce predictions. The model assumes that the test fluid in the seal clearance is an isothermal-homogenous mixture. The model adequately predicts m˙, K, and the value of Ceff at about 0.5ω.