Inlet-outlet Conditions Research Articles

Thermally efficient gas turbine with pressure drop-based automated filter cleaning and optimized fuel control system

Optimizing elements like fuel specifications and inlet–outlet conditions is essential for enhancing gas turbine performance. Prior research optimized filter house pressure drop using statistical methods, but these methods had drawbacks related to measurement errors. Additionally, with changing air conditions, periodic-based cleaning for self-cleaning pulse filters at the turbine inlet proved unsuccessful, making the procedure difficult and time-consuming. A novel “Thermally Efficient Gas Turbine with Pressure Drop-Based Automated Filter Cleaning and Optimized Fuel Control System” has been suggested to improve gas turbine performance. To handle pressure drop effectively, this cutting-edge system adds a predictive Apriori-based parallel auto-cleaning pulse filter, with automatic cleaning activated at a predetermined pressure difference. An adaptive neuro-fuzzy inference system-multi-layer perceptron integrated simulated annealing-Levenberg Marquardt algorithm has been created to handle mistakes in prediction and improve turbine parameters for greater energy efficiency. This complete strategy considerably increases energy efficiency while also improving air pressure drop prediction. A 200 MW power output, 70 % energy efficiency, 1.3 kg/kW-h fuel consumption, a small residual error (−0.4 mbar), and a pressure difference of only 3 mbar are just a few of the model's excellent performance indicators.

A Preliminary CFD and Tritium Transport Analysis for ARC Blanket

The Affordable, Robust, Compact (ARC) fusion reactor is a preconceptual design proposed by the Plasma Science and Fusion Center at the Massachusetts Institute of Technology that will be developed by Commonwealth Fusion Systems. ARC features a Li2BeF4 (FLiBe) molten salt liquid blanket that provides reactor cooling, neutron shielding, and tritium breeding. This work aims to develop a preliminary coupled computational fluid dynamics (CFD) and tritium transport model to describe FLiBe flow inside the tank and to assess ARC tritium inventory in the vacuum vessel and blanket. Both models are built by taking advantage of COMSOL® Multiphysics. FLiBe velocity and temperature fields are evaluated by the CFD models, and they are passed as input to the tritium transport model. The tritium transport model computes tritium concentration inside solid materials and FLiBe. An auxiliary FLiBe inlet has been moved from the original position in the ARC preconceptual design to improve blanket cooling and to reduce the size of flow eddies. Results show that many recirculation zones generate inside the tank for the chosen tank geometry, size, and inlet-outlet conditions. Larger FLiBe temperature and tritium concentration are found in these zones. The high FLiBe temperature in recirculation areas may not allow for effective cooling, and Inconel 718 reaches critical temperatures. The largest tritium concentration for a steady-state model with continuity of tritium partial pressure at the interfaces is found in Inconel 718 while the second-highest concentration is reached in FLiBe. The total tritium inventory in the ARC blanket with the assumed model is quantified as 3.16 g.

A Probablisitic Approach for Optimal Operation of Gas Processing Plant under Uncertain inlet-outlet Conditions

Natural gas plant operations contribute hugely to the economies of many developed nations that depend on hydrocarbon resources. The plant operation is usually subjected to continuous variations in upstream conditions, such as flow rate, composition, temperature and pressure, which propagate through the plant and affect its stable operations. As a result, decision making for optimal operating conditions of an in-operation plant is a complex problem and it is exacerbated with the changing product specifications and variations in energy supplies. This work presents a new solution method to the problem, which is based on chance constrained optimization. A deterministic model is initially developed from process simulation using Aspen HYSYS and later converted to a chance constrained model. The probabilistic model is then relaxed to its equivalent deterministic form and solved for optimum solution using GAMS. The optimum solution is determined probabilistically using chance constraints that are held at a user-defined confidence level. Optimal solution is represented graphically as a trade-off between reliability of holding the process constraints and profitability of the plant. Two case studies are presented to demonstrate the new method. Optimization results show that uncertainty of plant parameters significantly affect the economic performance of the plant operation. The solution approach developed in this work is able to increase the reliability of maintaining the profit by more than 95% confidence level. As a result, the risk of constraints violation is reduced from more than 50% using the typical deterministic optimization to less than 5% with the developed chance constrained optimization model. In addition, the results from this study indicate that the variation of material flow from the plant inlet has greater impact by more than 86% on profit change compared to variation from the plant outlet, which is less than 2%. Sensitivity analysis results show on how to reduce the effect of N2, CO2 and C5+ by holding the corresponding constraint at a certain confidence level. The developed solution method can aid as guidelines to flexible plant operation decision making for the in-operating plant by satisfying all the process constraints at certain confidence level.

Dynamics of a perturbed solid-body rotation flow in a finite-length straight rotating pipe

Direct numerical simulations are used to study the three-dimensional, incompressible and viscous flow dynamics of a base solid-body rotation flow with a uniform axial velocity entering a rotating, finite-length, straight circular pipe. Steady in time profiles of the axial, radial and circumferential velocities are prescribed along the pipe inlet. The convective boundary conditions for each velocity flux component is set at the pipe outlet. The simulation results describe the neutral stability line in response to either axisymmetric or three-dimensional perturbations in a diagram of Reynolds number ($Re$, based on inlet axial velocity and pipe radius) versus the incoming flow swirl ratio ($\unicode[STIX]{x1D714}$). This line is in good agreement with the neutral stability line recently predicted by the linear stability theory of Wang et al. (J. Fluid Mech., vol. 797, 2016, pp. 284–321). The computed time history of the velocity components at a certain point in the flow is used to describe three-dimensional phase portraits of the flow global dynamics and its long-term behaviour. They show three types of flow evolution scenarios. First, the Wang & Rusak (Phys. Fluids, vol. 8 (4), 1996, pp. 1007–1016) axisymmetric instability mechanism and evolution to a stable axisymmetric breakdown state is recovered at certain operational conditions in terms of $Re$ and $\unicode[STIX]{x1D714}$. However, at other operational conditions with same $\unicode[STIX]{x1D714}$ but with a higher $Re$, a second scenario is found. The axisymmetric breakdown state continues to evolve and a spiral instability mode appears on it and grows to a rotating spiral breakdown state. Moreover, at higher levels of $\unicode[STIX]{x1D714}$ a third scenario is found where there exists a dominant three-dimensional spiral type of instability mode that agrees with the linear stability theory of Wang et al. (J. Fluid Mech., vol. 797, 2016, pp. 284–321). The growth of this mode leads directly to a spiral type of flow roll-up and nonlinearly saturates on a rotating spiral type of vortex breakdown. The Reynolds–Orr equation is used to reveal the mechanism that drives all the instabilities as well as the nonlinear global flow evolution. At high swirl ratios, the confined kinetic energy in the swirling flow can be triggered to be released through various physical agents, such as the asymmetric inlet–outlet conditions, that eliminate axial homogeneity along the pipe and induce flow instabilities and evolution to breakdown states. It is also shown that local instability analysis or its extension using the assumption of a weakly non-parallel flow to conduct convective instability–absolute instability analyses is definitely not related to any of the instability modes found in the present study. Moreover, a stability study based on the strongly non-parallel flow character, including axial inhomogeneity due to a finite-domain boundary conditions, must be conducted to reveal instabilities in such flows.

Reynolds 応力のコレスキー分解に基づく人工的なLES流入変動風生成手法の検討

For merging of mesoscale/regional meteorological models and engineering large-eddy simulation (LES) models seamlessly, to generate appropriate velocity fluctuations at the inflow boundary (inflow turbulence) for engineering LES models is a very essential issue. In this study, we introduced three artificial generation methods of inflow turbulence based on the Cholesky decomposition of Reynolds stresses in the LES analysis of a plane boundary layer flow, and assessed the performance of those methods by comparing their results with those froma LES computation with periodic inlet-outlet conditions. In particular, we investigated the effects of space and/or time correlations of the generated inflow turbulence on the downstream turbulence characteristics.

Energy transfer mechanism of the instability of an axisymmetric swirling flow in a finite-length pipe

The rate of change of the perturbation's kinetic energy E of a perturbed inviscid, incompressible, axisymmetric, columnar and near-critical swirling flow in a finite-length, straight, circular pipe with periodic and non-periodic inlet–outlet conditions is studied using the Reynolds–Orr equation. The perturbation's mode shape and growth rate are computed from the linear-stability eigenvalue problem using a novel asymptotic solution in the case of a flow in a long pipe. This solution technique is general and can be applied to any vortex flow profile, in a range of swirl levels around the critical level, and for various boundary conditions. The solutions are used to analytically estimate the production (or loss) of E at the pipe boundaries and inside the domain and to shed new light on the Wang–Rusak mechanism of exchange of global stability around the critical swirl, that is leading to the vortex breakdown process. It is shown that the production of E inside the domain is modulated by the base flow strain-rate tensor. For the special case of a solid-body rotating flow, this term vanishes and the stability is determined only by the asymmetric transfer of E at the boundaries. For a general base flow, the dominant perturbation's mode shape develops deviations in response to the non-periodic inlet–outlet conditions. These deviations couple with the base flow strain-rate tensor to generate production or loss of E in the bulk. Together with the asymmetric transfer of E at the boundaries, they form a critical balance of production of E and determine the flow stability around the critical state. This behaviour is demonstrated for the Lamb–Oseen and Q vortex models. This analysis reveals a more complicated, as well more realistic, interaction between the perturbed flow in the domain and at the boundaries that dominates vortex flow dynamics.

Effect of the days scrolling on the natural convection in an open ended storage silo

The problem of unsteady natural convection heat transfer in a vertical, open ended, porous cylinder heated laterally with a sinusoidal time variation of the temperature has been investigated numerically. The model considered is the classical Darcian flow coupled with the energy equation. In the case of constant wall temperature, two types of chimney flows take place, with and without fluid recirculation. The present problem depends on the filtration Rayleigh number ( Ra), the aspect ratio ( A) and the inlet–outlet conditions ( Bi). For low dimensionless temperature amplitudes ( XA < 0.5) in the sinusoidal time variation, the resulting heat transfer is found to be globally equivalent to the case of constant wall temperature. The observed relative difference between sinusoidal and constant wall temperature is less than 5%. This difference decreases as the Ra is reduced.

Optimal design of a micro evaporator with lateral gaps

This paper presents an optimal design of a micro evaporator, to maximize the heat transfer coefficient (HTC) and it forms the starting point in developing miniaturized vapor–compression refrigeration system. The experimental design is adopted to determine the optimal parameters of the evaporator for realizing the inlet–outlet conditions of the refrigerating cycle, and for increasing the HTC. The number of lateral gaps, channel width, and lateral gap size were optimized to maximize HTCs of 2062, 2029, and 1895 W/m 2K for heating powers of 40, 60, and 80 W, respectively. The refrigerant and the mass flow rate were fixed as R-123 and 0.72 g/s, respectively. Among the three design parameters, the channel width is the most sensitive parameter influencing the HTC. A periodic change of flow pattern was observed in the evaporator with high HTCs, and a dryout was observed in the evaporator with low HTCs.

Analysis of the Chimney Natural Convection in a Vertical Porous Cylinder

The problem of natural convection in a vertical opened porous cylinder, with a constant wall temperature, has been investigated numerically. Two types of flows behavior, with and without fluid recirculation, have been considered. The conditions of getting one or the other flow depends on the filtration Rayleigh number (Ra), the aspect ratio (A), and the Biot number (Bi). The thermal field obtained depends mainly on the inlet–outlet conditions (Biot number) in the conductive regime. On the other hand, in the convective regime, the heat transfer is a weak function of the Biot number and the aspect ratio.

On longitudinal vortices in curved channel flow

The laminar flow in a curved channel is studied numerically to analyse the initial formation, development and interaction phenomena of an array of centrifugally induced longitudinal vortices arranged across the span of the channel. Simulations employing streamwise periodic boundary conditions (temporal model) as well as inlet-outlet conditions (spatial model) are carried out. In the temporal approach the interactions (pairing of vortices and growth of new vortex pairs) of fully developed vortex pairs are time-dependent, whereas in the spatial approach these events are inherently steady and concern vortices not in their fully developed state. The initial spatial development of the vortices is in excellent agreement with results of a linear stability analysis up to fairly large disturbance amplitudes. In the nonlinear regime a good agreement with experimental results has also been found. The receptivity of the flow is very important in a convectively unstable situation such as the present one and different behaviour is found at fixed Reynolds number (equal to 2.43 times the critical value for the onset of Dean vortices): the flow can be either steady or undergo a continuous sequence of merging and splitting events, depending on the inlet conditions. In the latter situation decorrelated patterns of low- and high-speed streaks are produced in streamwise-spanwise planes and they bear several similarities to near-wall coherent structures of turbulent boundary layers.