Evaluation of the Erosion Characteristics for a Marine Pump Using 3D RANS Simulations

In the present study, an erosion analysis of an industrial pump’s casing and impeller blades has been performed computationally. Effects of various critical parameters, i.e., the concentration and size of solid particles, exit pressure head, and cavitation on the erosion rate density of the casing and blade have been investigated. Commercial codes CFX, ICEM-CFD, and ANSYS Turbogrid are employed to solve the model, mesh generation for the casing, and mesh generation of the impeller, respectively. The Eulerian-Eulerian method is employed to model the pump domain’s flow to solve the two phases (water and solid particles) and the interaction between the phases. Published experimental data was utilized to validate the employed computational model. Later, a parametric study was conducted to evaluate the effects of the parameters mentioned above on the erosion characteristics of the pump’s casing and impeller’s blade. The results show that the concentration of the solid particles significantly affects the pump’s erosion characteristics, followed by the particle size and distribution of the particle size. On the other hand, the exit pressure head and cavitation do not affect the erosion rates considerably but significantly influence the regions of high erosion rate densities.

Perbandingan Performansi Sistem ORC Dengan Varian R-216CA, R-112a, R-141b dan n-Pentane Menggunakan Aspen HYSYS

One of the generation systems that are widely used in various power generation industries is the Organic Rankine Cycle. This cycle has the advantage of a low evaporation point compared to the ordinary steam turbine cycle. The use of refrigerants is the key to the ORC system. Refrigerant is a fluid with quite unique characteristics and many types. This study discusses the use of various types of refrigerants used in the ORC system, namely R-216CA, R-112a, R-141b and n-pentane. By using the Aspen Hysys luna device, we can compare the performance of each Refrigerant Variant of the ORC system. With the same input parameters in each variant, namely for the incoming refrigerant temperature is 600C with a pressure of 450 Kpa, the pump exit pressure is 4000 Kpa, the results are obtained from the Pump Work, Q Condenser, Q Boiler and the resulting turbine power. The result is that the ORC system with refrigerant n-Pantene has a high value for Pump Work, Q Condenser, Q Boiler and Turbine Power produced, but when compared to performance, the System with Refrigerant with R-112a has a higher efficiency value when assessed from its performance.

Cavitating Flow through a Micro-Orifice

Microfluidic systems have witnessed rapid development in recent years. As one of the most common structures, the micro-orifice is always included inside microfluidic systems. Hydrodynamic cavitation in the micro-orifice has been experimentally discovered and is harmful to microfluidic systems. This paper investigates cavitating flow through a micro-orifice. A rectangular micro-orifice with a l/d ratio varying from 0.25 to 4 was selected and the pressure difference between the inlet and outlet varied from 50 to 300 kPa. Results show that cavitation intensity increased with an increase in pressure difference. Decreasing exit pressure led to a decrease in cavitation number and cavitation could be prevented by increasing the exit pressure. In addition, the vapor cavity also increased with an increase in pressure difference and l/d ratio. Results also show the pressure ratio at cavitation inception was 1.8 when l/d was above 0.5 and the cavitation number almost remained constant when l/d was larger than 2. Moreover, there was an apparent difference in cavitation number depending on whether l/d was larger than 1.

Exit, Voice, and Public Reason

Public reason liberals appeal to public deliberation to ensure that a legal order can be publicly justified to its citizens. I argue that thisvoicemechanism should be supplemented byexitmechanisms. By allowing citizens to exit legal orders they believe cannot be publicly justified, citizens can pressure states to change their laws. This exit pressure is sometimes more effective than deliberation. I explore federalism as an exit mechanism that can help public deliberation establish a publicly justified polity.

Leakage and Dynamic Force Coefficients for Two Labyrinth Gas Seals: Teeth-on-Stator and Interlocking Teeth Configurations — A CFD Approach to Their Performance

Labyrinth gas seals (LS) commonly used in turbomachines reduce secondary flow leakage. Conventional see-through labyrinth seal designs include either all Teeth-On-Stator (TOS) or all Teeth-On-Rotor (TOR). Experience shows that an interlocking labyrinth seal (ILS), with teeth on both stator and rotor, reduces gas leakage by up to 30% compared to the conventional see-through designs. However, field data for ILS rotordynamic characteristics is still vague and scarce in the literature. This work presents flow predictions for an ILS and a TOS LS, both seals share identical design features, namely radial clearance Cr = 0.2 mm, rotor diameter D = 150 mm, tooth pitch Li = 3.75 mm, and tooth height B = 3 mm. Air enters the seal at supply pressure Pin = 3.8, 6.9 bar (absolute) and temperature of 25 °C. The ratio of gas exit pressure to supply pressure ranges from 0.5 to 0.8, and the rotor speed is fixed at 10 krpm (surface speed of 79 m/s). The analysis implements a computational fluid dynamics (CFD) method with a multi-frequency-orbit rotor whirl model. The CFD predicted mass flow rate for the ILS is ∼21% lower than that of the TOS LS, thus making the ILS a more efficient choice. Integration of the dynamic pressure fields in the seal cavities, obtained for excitation frequency (ω) ranging from 12% to 168% of rotor speed (sub and super synchronous whirl), allows an accurate estimation of the seal dynamic force coefficients. For all the considered operating conditions, at low frequency range the TOS LS shows a negative direct stiffness (K < 0), frequency independent; whereas the ILS has K > 0 that increases with both frequency and supply pressure. For both seals, the magnitude of K decreases when the exit pressure/inlet pressure ratio increases. On the other hand, the cross-coupled stiffness (k) from both seals is frequency dependent, its magnitude increases with gas supply pressure, and the k for the ILS is more sensitive to a change in the exit/inlet pressure ratio. Notably, k turns negative for subsynchronous frequencies below rotor speed (Ω) for both the TOS LS and ILS. The direct damping (C) for the TOS LS remains constant for ω > ½ Ω and has a larger magnitude than the damping for the ILS over the frequency range up to 1.5Ω. An increase in exit/inlet pressure ratio decreases the direct damping for both seals. The effective damping coefficient, Ceff = (C-k/ω) whenever positive aids to damp vibrations, whereas Ceff < 0 is a potential source for an instability. For frequencies ω /Ω < 1.3, Ceff for the TOS LS is higher in magnitude than that for the ILS. From a rotordynamics point of view, the ILS is not a sound selection albeit it reduces leakage. Comparison of the CFD predicted force coefficients against those from a bulk flow model demonstrate the later simple model delivers poor results, often contradictory and largely indifferent to the type of seal, ILS or TOS LS. In addition, CFD model predictions are benchmarked against experimental dynamic force coefficients for two TOS LSs published by Ertas et al. (2012) and Vannini et al. (2014).

Unsteady Measurement of Core Penetration Flow in a Turbine Rotor-Stator Disc Cavity

The existence and causes of the deep ingress of the annulus flow into the core region of a turbine rotor-stator disc cavity, or core penetration flow, have been investigated experimentally. In addition, the effects of annulus flow coefficient, rotational Reynolds number, and non-dimensional purge air flow rate on the core penetration flow have been examined. Using the low–speed, low expansion ratio single-stage cold turbine test facility at Seoul National University (SNU), time-resolved tangential and radial velocities in the cavity have been measured with 2-D hot-wire anemometers. In addition, time-resolved static pressures on the stator disc have been measured with fast response pressure transducers, and the unsteady cavity velocity field in the absolute frame has been measured using Particle Image Velocimetry (PIV). Geometric non-axisymmetry (e.g. eccentricity of a rotor disc cover in this study) can change the cavity exit pressure, and thus the radial pressure gradient in the cavity. A time lag in the tangential velocity adjustment to the variation in the radial pressure gradient results in a net radial force, leading to core penetration flow. The core penetration flow occurs twice when the cavity exit pressure increases, and once when the cavity exit pressure decreases. In this study, with a once per revolution geometric non-axisymmetry, the core penetration flow occurs three times per revolution, revolving at the disc’s rotational speed. Variations in the annulus flow coefficient or rotational Reynolds number do not affect the core penetration flow, but increasing the purge air flow rate weakens the core penetration flow.

Nuclear coupled thermal hydraulic analysis of fast transient depressurization in supercritical channels

Purpose The objective of the present work is to simulate the nuclear coupled thermal–hydraulic fast transient case studies for a vertically up-flowing supercritical pressure water channel of circular cross section. The emphasis is on analyzing the phenomenon of the deterioration in heat transfer (DHT) inside the channel subjected to sharp pressure variations. Design/methodology/approach The thermal–hydraulic model, THRUST, is integrated with the neutron point kinetic (NPK) solver to account for the non-linear interactions between the thermal–hydraulic and neutronic temperature and density reactivity feedback effects. The model implemented and studied accounts for the time-dependent reactor power and is used to analyze various steady-state and flow-induced transient case studies (time-dependent and step change in exit pressure). Findings There is good agreement in the predicted behavior of the supercritical water pressure system with that of the available experimental data for the steady-state case. The event of DHT in the second transient case (step decrease in exit pressure) is found to be more severe than that of exponential pressure decrease. Originality/value This study evaluated a novel implementation of the thermal–hydraulic model, THRUST, integrated with NPKs applied to supercritical pressure water systems for predicting DHT.