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18 pages, 2468 KiB

Open AccessArticle

Optimization Study of Hydrothermal Liquefaction Sewage Sludge to Biocrude Oil in Continuous Multiphase Plug Flow Reactor

by Artur Wodołażski and Adam Smoliński

Processes 2025, 13(4), 976; https://doi.org/10.3390/pr13040976 - 25 Mar 2025

Viewed by 799

Abstract

This paper provides an optimization analysis of the hydrothermal liquefaction (HTL) process of sewage sludge to biocrude oil in a continuous plug-flow reactor. The increase in flow rate led to enhanced swirling flow, which significantly improved convective heat transfer. The composition and yield [...] Read more.

This paper provides an optimization analysis of the hydrothermal liquefaction (HTL) process of sewage sludge to biocrude oil in a continuous plug-flow reactor. The increase in flow rate led to enhanced swirling flow, which significantly improved convective heat transfer. The composition and yield of biocrude oil produced in the process (HTL) can vary significantly depending on the type of feedstock used. Using process simulation principles and a kinetic model, this study thoroughly evaluated the mass and energy balance of the HTL reaction, considering heat and mass momentum exchange in a multiphase system. Therefore, it is useful to use a transient flow model to determine the influence of process parameters on optimization. A parametric study with multiphase profiles along the reactor axis allowed tracing of interphase flow trajectories for optimal conditions in order to maximize the process efficiency of biocrude oil production. Through optimization of process parameters, there was a significant improvement in the conversion of sewage sludge to biocrude oil in the continuous HTL process. The optimal conditions were where the reaction mass maintained in the liquid phase enabled the stabilization of process parameters, preventing evaporation and heat loss by increasing the energy process efficiency. Full article

(This article belongs to the Section Energy Systems)

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12 pages, 2358 KiB

Open AccessArticle

Transient Phenomena of Dynamic Contact Angle in Micro Capillary Flows

by Young Bae Kim and Jaeyong Sung

Appl. Sci. 2024, 14(8), 3293; https://doi.org/10.3390/app14083293 - 13 Apr 2024

Cited by 1 | Viewed by 1803

Abstract

This study is devoted to investigating the dynamics of liquid driven by capillary force in a circular tube. A microscope was used to visualize the meniscus movement and the contact angle. The experiments were carried out with glycerin–water mixtures with viscosity ranging from [...] Read more.

This study is devoted to investigating the dynamics of liquid driven by capillary force in a circular tube. A microscope was used to visualize the meniscus movement and the contact angle. The experiments were carried out with glycerin–water mixtures with viscosity ranging from 0.21 to 1.36 Pa∙s by filling the test liquid in a borosilicate glass tube with an inner diameter of 200 μm. The wetting distances of the meniscus with time were compared with the theoretical solution by considering the dynamic variation of contact angle. The results show that the theoretical solution agrees well with experimental data due to the reflection of the actual dynamic contact angle for the transient motions in the developing entrance region. In view of momentum balance, variations of dominant force according to the time were determined by separated inertial periods, such as inertial, inertial-viscous, and viscous time stages. Full article

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29 pages, 2445 KiB

Open AccessArticle

Start-Up Multilayer Electro-Osmotic Flow of Maxwell Fluids through an Annular Microchannel under Hydrodynamic Slip Conditions

by Cesar A. Valencia, David A. Torres, Clara G. Hernández, Juan P. Escandón, Juan R. Gómez and René O. Vargas

Mathematics 2023, 11(20), 4231; https://doi.org/10.3390/math11204231 - 10 Oct 2023

Cited by 2 | Viewed by 2126

Abstract

The present investigation analyzes the transient multilayer electro-osmotic flow through an annular microchannel with hydrophobic walls. The fluids are considered immiscible and viscoelastic, following the Maxwell rheological model. In the problem examined, the linearized Poisson–Boltzmann and Cauchy momentum equations are used to determine [...] Read more.

The present investigation analyzes the transient multilayer electro-osmotic flow through an annular microchannel with hydrophobic walls. The fluids are considered immiscible and viscoelastic, following the Maxwell rheological model. In the problem examined, the linearized Poisson–Boltzmann and Cauchy momentum equations are used to determine the electric potential distribution and the flow field, respectively. Here, different interfacial phenomena are studied through the imposed boundary conditions, such as the hydrodynamic slip and specified zeta potentials at solid–liquid interfaces, the velocity continuity, the electroviscous stresses balance, the potential difference, and the continuity of electrical displacements at the interfaces between fluids. The semi-analytic solution uses the Laplace transform theory. In the results, the velocity profiles and velocity tracking show the oscillatory behavior of flow, which strongly depends on the dimensionless relaxation time. Furthermore, the hydrodynamic slip on the channel walls contributes to the release of energy stored in the fluids due to elastic effects at the start-up of the flow. Similarly, other dimensionless parameters are also investigated. This research aims to predict the parallel flow behavior in microfluidic devices under electro-osmotic effects. Full article

(This article belongs to the Special Issue Numerical and Analytical Study of Fluid Dynamics)

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31 pages, 1466 KiB

Open AccessArticle

Prescribed Performance Adaptive Balance Control for Reaction Wheel-Based Inverted Pendulum-Type Cubli Rovers in Asteroid

by He Huang, Zejian Li, Zongyi Guo, Jianguo Guo, Le Suo and Haoliang Wang

Aerospace 2022, 9(11), 728; https://doi.org/10.3390/aerospace9110728 - 18 Nov 2022

Cited by 4 | Viewed by 2471

Abstract

This paper investigates the issue of balance control for reaction-wheeled inverted pendulum-type Cubli Rovers on asteroids, and an adaptive control scheme is proposed via the prescribed performance control technique. The main feature lies in the fact that the transient behavior is satisfied which [...] Read more.

This paper investigates the issue of balance control for reaction-wheeled inverted pendulum-type Cubli Rovers on asteroids, and an adaptive control scheme is proposed via the prescribed performance control technique. The main feature lies in the fact that the transient behavior is satisfied which is required critically in the environment of asteroids. The attitude model of reaction-wheeled inverted pendulum-type Cubli Rovers is first constructed by virtue of the momentum moment theorem and Eulerian kinematics. Based on that, the gravitational field in the asteroid is described and the avoiding jumping condition is analyzed. Then, an adaptive prescribed performance control (APPC) method is proposed to obtain the fine tracking performance of the equilibrium error such that the inverted pendulum-type Cubli Rovers achieve the self-balancing motion. The proposed method is capable of ensuring the tracking errors inside the preset boundary functions, and the asymptotic stability of all states in the closed-loop system is guaranteed via the Lyapunov stability theory. The simulation and comparison results on the environment of asteroids verify the effectiveness and superiority of the presented control law. Full article

(This article belongs to the Special Issue Dynamics and Control Problems on Asteroid Explorations)

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17 pages, 7573 KiB

Open AccessArticle

Dynamic Model of a Transcritical CO₂ Heat Pump for Residential Water Heating

by Hélio A. G. Diniz, Tiago F. Paulino, Juan J. G. Pabon, Antônio A. T. Maia and Raphael N. Oliveira

Sustainability 2021, 13(6), 3464; https://doi.org/10.3390/su13063464 - 21 Mar 2021

Cited by 17 | Viewed by 3031

Abstract

This paper presents a distributed mathematical model for a carbon dioxide direct expansion solar-assisted heat pump used to heat bath water. The main components are a gas cooler, a needle valve, an evaporator/collector, and a compressor. To develop the heat exchange models, mass, [...] Read more.

This paper presents a distributed mathematical model for a carbon dioxide direct expansion solar-assisted heat pump used to heat bath water. The main components are a gas cooler, a needle valve, an evaporator/collector, and a compressor. To develop the heat exchange models, mass, energy, and momentum balances were used. The model was validated for transient as well as steady state conditions using experimental data. A reasonably good agreement was observed between the predicted temperatures and experimental data. The simulations showed that the time step required to demonstrate the behavior of the heat pump in the transient regime is greater than the time step required for the steady state. The results obtained with the mathematical model revealed that a reduction in the water mass flow rate results in an increase in the water outlet temperature. In addition, when the carbon dioxide mass flow rate is reduced, the compressor inlet and outlet temperatures increase as well as the water outlet temperature. Full article

(This article belongs to the Special Issue A Pathway to Renewable Energy Promotion for Achieving Low-Carbon Energy Networks: Electricity, District Heating and District Cooling Networks)

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14 pages, 4522 KiB

Open AccessArticle

Numerical Study of Binary Trickle Flow of Liquid Iron and Molten Slag in Coke Bed by Smoothed Particle Hydrodynamics

by Shungo Natsui, Kazui Tonya, Hiroshi Nogami, Tatsuya Kikuchi, Ryosuke O. Suzuki, Ko-ichiro Ohno, Sohei Sukenaga, Tatsuya Kon, Shingo Ishihara and Shigeru Ueda

Processes 2020, 8(2), 221; https://doi.org/10.3390/pr8020221 - 14 Feb 2020

Cited by 9 | Viewed by 4110

Abstract

In the bottom region of blast furnaces during the ironmaking process, the liquid iron and molten slag drip into the coke bed by the action of gravity. In this study, a practical multi-interfacial smoothed particle hydrodynamics (SPH) simulation is carried out to track [...] Read more.

In the bottom region of blast furnaces during the ironmaking process, the liquid iron and molten slag drip into the coke bed by the action of gravity. In this study, a practical multi-interfacial smoothed particle hydrodynamics (SPH) simulation is carried out to track the complex liquid transient dripping behavior involving two immiscible phases in the coke bed. Numerical simulations were performed for different conditions corresponding to different values of wettability force between molten slag and cokes. The predicted dripping velocity changes and interfacial shape were investigated. The relaxation of the surface force of liquid iron plays a significant role in the dripping rate; i.e., the molten slag on the cokes acts as a lubricant against liquid iron flow. If the attractive force between the coke and slag is smaller than the gravitational force, the slag then drops together with the liquid iron. When the attractive force between the coke and slag becomes dominant, the iron-slag interface will be preferentially detached. These results indicate that transient interface morphology is formed by the balance between the momentum of the melt and the force acting on each interface. Full article

(This article belongs to the Special Issue Process Modeling in Pyrometallurgical Engineering)

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22 pages, 574 KiB

Open AccessArticle

Computational Simulation of PT6A Gas Turbine Engine Operating with Different Blends of Biodiesel—A Transient-Response Analysis

by Camilo Bayona-Roa, J.S. Solís-Chaves, Javier Bonilla, A.G. Rodriguez-Melendez and Diego Castellanos

Energies 2019, 12(22), 4258; https://doi.org/10.3390/en12224258 - 8 Nov 2019

Cited by 11 | Viewed by 8385

Abstract

Instead of simplified steady-state models, with modern computers, one can solve the complete aero-thermodynamics happening in gas turbine engines. In the present article, we describe a mathematical model and numerical procedure to represent the transient response of a PT6A gas turbine engine operating [...] Read more.

Instead of simplified steady-state models, with modern computers, one can solve the complete aero-thermodynamics happening in gas turbine engines. In the present article, we describe a mathematical model and numerical procedure to represent the transient response of a PT6A gas turbine engine operating at off-design conditions. The aero-thermal model consists of a set of algebraic and ordinary differential equations that arise from the application of the mass, linear momentum, angular momentum and energy balances in each engine’s component. The solution code has been developed in Matlab-Simulink^® using a block-oriented approach. Transient simulations of the PT6A engine start-up have been carried out by changing the original Jet-A1 fuel with biodiesel blends. Time plots of the main thermodynamic variables are shown, especially those regarding the structural integrity of the burner. Numerical results have been validated against reported experimental measurements and GasTurb^® simulations. The computer model has been capable to predict acceptable fuel blends, such that the real PT6A engine can be substituted to avoid the risk of damaging it. Full article

(This article belongs to the Special Issue Small-Scale Energy Systems with Gas Turbines and Heat Pumps)

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22 pages, 5235 KiB

Open AccessFeature PaperArticle

Experimental and Theoretical Study on Dynamic Hydraulic Fracture

by Jingnan Dong, Mian Chen, Yuwei Li, Shiyong Wang, Chao Zeng and Musharraf Zaman

Energies 2019, 12(3), 397; https://doi.org/10.3390/en12030397 - 27 Jan 2019

Cited by 28 | Viewed by 4667

Abstract

Hydraulic fracturing is vital in the stimulation of oil and gas reservoirs, whereas the dynamic process during hydraulic fracturing is still unclear due to the difficulty in capturing the behavior of both fluid and fracture in the transient process. For the first time, [...] Read more.

Hydraulic fracturing is vital in the stimulation of oil and gas reservoirs, whereas the dynamic process during hydraulic fracturing is still unclear due to the difficulty in capturing the behavior of both fluid and fracture in the transient process. For the first time, the direct observations and theoretical analyses of the relationship between the crack tip and the fluid front in a dynamic hydraulic fracture are presented. A laboratory-scale hydraulic fracturing device is built. The momentum-balance equation of the fracturing fluid is established and numerically solved. The theoretical predictions conform well to the directly observed relationship between the crack tip and the fluid front. The kinetic energy of the fluid occupies over half of the total input energy. Using dimensionless analyses, the existence of equilibrium state of the driving fluid in this dynamic system is theoretically established and experimentally verified. The dimensionless separation criterion of the crack tip and the fluid front in the dynamic situation is established and conforms well to the experimental data. The dynamic analyses show that the separation of crack tip and fluid front is dominated by the crack profile and the equilibrium fluid velocity. This study provides a better understanding of the dynamic hydraulic fracture. Full article

(This article belongs to the Special Issue Mathematical Modeling of Fluid Flow and Heat Transfer in Petroleum Industries and Geothermal Applications)

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49 pages, 3293 KiB

Open AccessArticle

Implementation and Validation of a Free Open Source 1D Water Hammer Code

by Rune Kjerrumgaard Jensen, Jesper Kær Larsen, Kasper Lindgren Lassen, Matthias Mandø and Anders Andreasen

Fluids 2018, 3(3), 64; https://doi.org/10.3390/fluids3030064 - 3 Sep 2018

Cited by 17 | Viewed by 10617

Abstract

This paper presents a free code for calculating 1D hydraulic transients in liquid-filled piping. The transient of focus is the Water Hammer phenomenon which may arise due to e.g., sudden valve closure, pump start/stop etc. The method of solution of the system of [...] Read more.

This paper presents a free code for calculating 1D hydraulic transients in liquid-filled piping. The transient of focus is the Water Hammer phenomenon which may arise due to e.g., sudden valve closure, pump start/stop etc. The method of solution of the system of partial differential equations given by the continuity and momentum balance is the Method of Characteristics (MOC). Various friction models ranging from steady-state and quasi steady-state to unsteady friction models including Convolution Based models (CB) as well as an Instantaneous Acceleration Based (IAB) model are implemented. Furthermore, two different models for modelling cavitation/column separation are implemented. Column separation may occur during low pressure pulses if the pressure decreases below the vapour pressure of the fluid. The code implementing the various models are compared to experiments from the literature. All experiments consist of an upstream reservoir, a straight pipe and a downstream valve. Full article

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35 pages, 2204 KiB

Open AccessArticle

Transient Momentum Balance—A Method for Improving the Performance of Mean-Value Engine Plant Models

by Tomaž Katrašnik

Energies 2013, 6(6), 2892-2926; https://doi.org/10.3390/en6062892 - 14 Jun 2013

Cited by 8 | Viewed by 6051

Abstract

Mean-value engine models (MVEMs) are frequently applied in system-level simulations of vehicle powertrains. In particular, MVEMs are a common choice in engine simulators, where real-time execution is mandatory. In the case of real-time applications with prescribed, fixed sampling times, the use of explicit [...] Read more.

Mean-value engine models (MVEMs) are frequently applied in system-level simulations of vehicle powertrains. In particular, MVEMs are a common choice in engine simulators, where real-time execution is mandatory. In the case of real-time applications with prescribed, fixed sampling times, the use of explicit integration schemes is almost mandatory. Thus the stability of MVEMs is one of the main limitations when it comes to optimizing their performance. It is limited either by the minimum size of the gas volume elements or by the maximum integration time step. An innovative approach that addresses both constraints arises from the fact that the mass flow through the transfer elements of the MVEM is not modelled considering the quasi-steady assumption, but instead the mass-flow is calculated using a single transient momentum balance (TMB) equation. The proposed approach closely resembles phenomena in the physical model, since it considers both the flow-field history and the inertial effects arising from the time variation of the mass flow. It is shown in this paper that a consideration of the TMB equation improves the stability and/or the computational speed of the MVEMs, whereas it also makes it possible to capture physical phenomena in a more physically plausible manner. Full article

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21 pages, 2100 KiB

Open AccessArticle

Analysis of the Magnetic Field Effect on Entropy Generation at Thermosolutal Convection in a Square Cavity

by Mounir Bouabid, Nejib Hidouri, Mourad Magherbi and Ammar Ben Brahim

Entropy 2011, 13(5), 1034-1054; https://doi.org/10.3390/e13051034 - 23 May 2011

Cited by 22 | Viewed by 7538

Abstract

Thermosolutal convection in a square cavity filled with air and submitted to an inclined magnetic field is investigated numerically. The cavity is heated and cooled along the active walls with a mass gradient whereas the two other walls of the cavity are adiabatic [...] Read more.

Thermosolutal convection in a square cavity filled with air and submitted to an inclined magnetic field is investigated numerically. The cavity is heated and cooled along the active walls with a mass gradient whereas the two other walls of the cavity are adiabatic and insulated. Entropy generation due to heat and mass transfer, fluid friction and magnetic effect has been determined in transient state for laminar flow by solving numerically the continuity, momentum energy and mass balance equations, using a Control Volume Finite—Element Method. The structure of the studied flows depends on four dimensionless parameters which are the Grashof number, the buoyancy ratio, the Hartman number and the inclination angle. The results show that the magnetic field parameter has a retarding effect on the flow in the cavity and this lead to a decrease of entropy generation, Temperature and concentration decrease with increasing value of the magnetic field parameter. Full article

(This article belongs to the Special Issue Entropy Generation Minimization)

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