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An example of the TA-MHD generator using solar energy.
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The thermo-acoustic generators offer a unique means of converting thermal energy into mechanical energy without any moving parts and without fluid circulation. They are comparable to the Stirling engine with the advantage of much greater simplicity. They are therefore natural candidates for special uses where interventions are limited. The problem...
Citations
... While traditional electromagnetic devices [8,9,10], like loudspeakers and linear alternators, have been used for acoustic-to-mechanical conversion, their effectiveness decreases at larger scales. Therefore, researchers are exploring alternative methods such as piezoelectric materials [5,11], magneto-hydro-dynamic devices [9,12], and bi-directional turbines [13,14,15] as potential solutions for this crucial conversion process. ...
This paper explores the emerging field of thermo-acoustic devices, specifically focusing on developing robust bidirectional turbines. Amidst growing concerns about climate change, rising energy demands, and the urgent need for alternative solutions, the study highlights the underexplored domain of bidirectional turbines within thermo-acoustic systems, offering a crucial pathway toward cleaner and more sustainable technologies, thereby providing commercialization potential. It identifies a significant gap in dedicated investigations regarding the interaction, efficiency, and challenges associated with bidirectional turbines and adopts a comprehensive methodology integrating analytical modelling, computational fluid dynamics simulations, and practical experimentation. An axial bidirectional turbine is carefully selected, designed, and optimized using advanced tools such as MATLAB R2016a and CAD software, including PTC Creo 5.0 and Solidworks 2023. The validity of the CAD model is verified through ANSYS 16.2 CFX simulations, followed by experimental validation to corroborate and enhance theoretical insights. The conclusions drawn from this study offer valuable recommendations for further research and practical implementations.
... The main principle is conceptualized as electromagnetic pumps working in generators. But here the pumps transform the electromagnetic energy into mechanical energy which is exactly opposite to the transfer that occurs in generators [41,43,44]. ...
A layout of urban waste fired zero emission power plant is described in this paper. The principle of layout, which comes from similar coal-fired plants retrieved from the literature, integrates gasification with a power generation section, and implements two parallel conversion processes, one supplied by the heat of the gasifier consisting of a thermoacousticmagnetohydrodynamic (TAMHD) generator, while in the second one the syngas is treated in order to obtain almost pure hydrogen, which is fed to fuel cells. The CO2 deriving from the oxidation of Carbon base is stocked in liquid form. The novelty of the proposed layout lies in the fact that the entire conversion is performed without solid moving parts. The resulting plant avoids any type of emissions in the atmosphere, increases mechanical efficiency as compared to traditional plants, thanks to the absence of moving parts, nonetheless, resolving at its root the ever-increasing waste-related pollution problems.
... Beyond noise, further problems are the huge values of the magnetic field (≈ O(1) T -see Table 1 of [4]) and of the working pressure involved (≈ 5 bar -see Sec. 7.2 of [5]), which may lead to significant (magneto)mechanical stress; moreover, magnets may require a dedicated power supply. The efficiency is the product of the heat-to-mechanical conversion energy (sound) efficiency and of sound-electric conversion efficiency; typical optimum values are 0.28 times the Carnot efficiency and 40% respectively so that η = 0.11 times the Carnot efficiency. ...
Conventional waste heat recovery systems usually require water (e.g. to supply steam for a turbine) and imply the wearing of moving parts, to the detriment of usability in case of drought and/or in the long term. Unconventional approaches (thermoacoustic and thermoelectric conversion of heat into electricity) overcome these obstacles, but their utilization for multi Kilowatt (KW) electric power in an industrial environment is jeopardized either by large working pressure, excessive noise, the need for cooling systems or huge magnetic fields. Welander and Erhard et al. discuss the existence and the stability of steady-state convection driven by an applied temperature gradient of a fluid circulating in a tube that forms a vertical, closed loop. Convection ensures the spontaneous conversion of heat into mechanical energy through competing buoyancy, drag and heat conduction between the fluid and the walls of the tube. Crucially, their results do not depend on the nature of the drag. If the working is an electrical conductor and a magnetic field is applied, the impact of the resulting Lorenz force acts as a drag on the motion of the fluid just like viscosity; the viscous and the magnetic drag are dealt with on an equal basis. The magnetic drag transforms the mechanical energy of the convective motion of the fluid into electric energy. Since convection is driven by a temperature gradient, spontaneous, water-free conversion of heat into electricity occurs with no moving part at atmospheric pressure. Such conversion is suitable for the purposes of waste heat recovery. As an example, let a 1-cm-radius tube filled GalinstanTM (a commercially available, atoxic liquid metal alloy) be rolled up in a double helix wrapped around a 30-m-tall, 3-m-radius chimney located above a furnace. If there is a 350 K temperature difference between the bottom of the tube (near the furnace) and the top, and if permanent magnets located on the tube provide a 0.017 T magnetic field, then conservative estimates show that we obtain 2 KW DC electric power with efficiency > 2.1%. This lower bound suggests that our system is competitive with thermoacoustic and thermoelectric conversion.
... Hence the feasibility of a thermoacoustic MHD generator was not verified till 2006 by Castrejon-Pita and Huelsz [30], who used a thermoacoustic prime mover coupled with an electrolyte-based MHD transducer and achieved an output of a few millivolts. Later, some theoretical works on thermoacoustic engines coupled with LMMHD generators have been performed by Alemany et al. [31,32]. Based on these works, they developed a thermoacoustic LMMHD generator prototype that could be used for radioisotopic power supply in space under the support of the European "Space TRIP" project [33]. ...
Combining a thermoacoustic cycle engine with a liquid metal magnetohydrodynamic (LMMHD) generator will result in a thermal power generation system with no mechanical moving parts and high reliability. This disruptive technology has drawn much attention in space nuclear power generation, especially in recent years. It requires an LMMHD generator to work at a higher frequency than conventional LMMHD generators targeted for ocean wave energy conversion. However, the operating characteristics and loss mechanisms of LMMHD generators at high operating frequencies remain poorly understood, and experimental characterization of such a generator is lacking. In this work, a three-dimensional transient numerical analysis of a high-frequency LMMHD generator is performed based on multi-physics field simulation software COMSOL, to understand the operating characteristics of the generator, and the effects of inlet velocity, load resistance, and operating frequency on the generator's performance. Furthermore, an LMMHD generator prototype was designed, constructed, and tested under different inlet velocities, load resistances, and frequencies by using a linear compressor for the first time. When the operating frequency and inlet velocity are 15 Hz and 4.3 m/s, the output voltage and current of the generator prototype reached 113 mV and 1720 A, with an output power of 68 W at a corresponding acoustic-to-electric efficiency of 24 %. A discrepancy between the numerical predictions and the experimental results was found, which gave insight into where further improvements can be made. This work reveals the operating characteristics and losses mechanism of LMMHD generators operating at higher frequencies and contributes to the development of high-efficiency generators for thermoacoustic power generation. Nomenclature v velocity of liquid metal (m/s) V voltage (V); volume (m 3) Symbols V0 initial volume (m 3) A magnetic vector potential (Wb/m) γ adiabatic index B magnetic flux density (T) η generator efficiency B0 externally applied magnetic field (T) dynamic viscosity (kg/m s) Bm amplitude of time-varying magnetic flux density (T) μ0 vacuum magnetic permeability (N/A 2) Bi induced magnetic field (T) μr relative permeability (N/A 2) Br remanent magnetic flux density (T) ρ density (kg/m 3) D electric displacement vector (C/m 2) electrical conductivity (S/m) E electric field strength (V/m)
... To overcome these drawbacks, several studies have been made, with the aim of exploiting magnetic induction to transfer energy from plasma to armature, without the need for electrodes [4][5][6][7][8]. ...
... More recently, an alternate MHD induction generator has been proposed [8], combined with a thermoacoustic machine, which converts thermal energy into mechanical vibration. The plasma consists of a liquid metal and the magnetic field is generated by a permanent magnet. ...
In this paper, the problem of optimizing the design of an inductive Magneto-Hydro-Dynamic (MHD) electric generator is formalized as a multi-objective optimization problem where the conflicting objectives consist of maximizing the output power while minimizing the hydraulic losses and the mass of the apparatus. In the proposal, the working fluid is ionized with periodical pulsed discharges and the resulting neutral plasma is unbalanced by means of an intense DC electrical field. The gas is thus split into two charged streams, which induce an electromotive force into a magnetically coupled coil. The resulting generator layout does not require the use of superconducting coils and allows you to manage the issues related to the conductivity of the gas and the corrosion of the electrodes, which are typical limits of the MHD generators. A tailored multi-objective optimization algorithm, based on the Tabu Search meta-heuristics, has been implemented, which returns a set of Pareto optimal solutions from which it is possible to choose the optimal solution according to further applicative or performance constraints.
... In 2006, Castrejon-Pita and Huelsz demonstrated the feasibility of thermoacoustic magnetohydrodynamic (MHD) generator by using a thermoacoustic prime mover coupled with an electrolyte-based MHD transducer [39]. Later, Alemany et al. performed a series of theoretical works on thermoacoustic engines coupled with both conductive [40] and inductive [41] LMMHD generators, respectively; and promising performance results have been obtained on the two types of system. In 2013, a project entitled 'Space Thermoacoustic Radio-Isotopic Power System' was funded by the European Commission, which aims to raise the technology readiness level of thermoacoustic LMMHD generators and show that this technology is feasible for European radioisotopic power systems [42]. ...
The generation of electricity in space is a major issue for space exploration, and among the viable alternatives, nuclear power systems appear to present a particularly suitable solution, especially for deep space exploration. Recent developments in thermoacoustic engine and liquid metal magnetohydrodynamic (LMMHD) generator technologies have shown that thermoacoustically-driven LMMHD generators are a promising thermal-to-electrical converter option for space nuclear reactors. In order to improve the power density and capacity of current thermoacoustically-driven LMMHD generators, a novel three-stage looped thermoacoustically-driven LMMHD generator is proposed and investigated in this work. A numerical model of the integrated system including a lumped parameter sub-model for the LMMHD generator is developed and validated. Using this model, the effect of key geometric and operating parameters on the operation and performance of the proposed system are investigated numerically, and acoustic field distributions are presented. The results indicate that when the heat source and sink temperatures are 900 K and 300 K, respectively, a thermal-to-electric efficiency of 27.7% with a total electric power of 4750 W can be obtained at a load factor of 0.92. This work provides guidance for the design of similar systems and contributes to the development of a new thermal-to-electrical conversion technology for space applications.
... and in deep-ocean applications. Since the first attempt byMigliori and Swift in 1988 to completely remove oscillating components through MHD transduction, with a resultant efficiency of less than 2%,43 certain ambitious projects have produced electric power from a thermoacoustic engine operating with an MHD transducer.[44][45][46][47][48] 3. Classification of TA-SLiCE electric generatorsFor successful adoption of this technology, it is crucial to understand and determine scalability to provide electric power in the range of a few milliwatts up to kilowatts. The electric power achieved by the TA-SLiCE generators described in Sections 3.1 and 3.2 could be used to power other low power devices (milliwatts to tens of watts) via loudspeakers and piezoelectric transducers. ...
The proliferation of environmentally friendly electricity-generating technologies has fostered a growing interest in travelling-wave thermoacoustic electric-generator technology and its potential applications. Although reviews exist that focus generally on Stirling engines and thermoacoustic engines, no specific and complete review has addressed the generation of electrical energy through a thermoacoustic Stirling-like cycle engine (TA-SLiCE), which has undergone extensive development in recent years. The present review covers this gap and focuses on the analysis of electric power generation through the TA-SLiCE over different temperature ranges. Therefore, in this review, the general status of travelling-wave thermoacoustic energy generation and the evaluation of the TA-SLiCE types that represent current travelling-wave thermoacoustic generator technologies are presented. In addition, the agents involved in the development of this technology are reviewed, and selected examples of prototypes and promising products currently in a research and testing phase using this technology are presented. In closing the difficulties in this field, the novelties and current research are presented concluding with the main ideas and recommendations.
... In this manner, the inductive MHD generator creates an alternating electric current with adjustable strength and voltage. 89,90 The conductive MHD generators work similar to the inductive devices depicted in Fig. 5. The main difference is that there is no coil, but a pair of electrodes that directly collects the alternating current from the working fluid. ...
... The electrode pair is placed perpendicular to both the magnetic field lines and the oscillating working fluid, which is in and out of the plane of Fig. 5. The conductive MHD generators produce a strong electric current at a low voltage, 89,90 which is generally not preferred over the adjustable strength and voltage of the inductive MHD transducers. 91 Furthermore, at high mean pressures of the working fluid, sealing the electrode connections from leaks might be troublesome. ...
... 91 Furthermore, at high mean pressures of the working fluid, sealing the electrode connections from leaks might be troublesome. 90 These disadvantages have caused the focus in thermoacoustics to shift from the conductive devices of the early days 86,92,93 towards inductive MHD generators in most of the recent work. 85,89,90 Independent of the configuration, the electrically conducting working fluid mostly used is liquid sodium. ...
Thermoacoustic engines convert heat energy into high amplitude acoustic waves and subsequently into electric power. This article provides a review of the four main methods to convert the (thermo)acoustic power into electricity. First, loudspeakers and linear alternators are discussed in a section on electromagnetic devices. This is followed by sections on piezoelectric transducers, magnetohydrodynamic generators, and bidirectional turbines. Each segment provides a literature review of the given technology for the field of thermoacoustics, focusing on possible configurations, operating characteristics, output performance, and analytical and numerical methods to study the devices. This information is used as an input to discuss the performance and feasibility of each method, and to identify challenges that should be overcome for a more successful implementation in thermoacoustic engines. The work is concluded by a comparison of the four technologies, concentrating on the possible areas of application, the conversion efficiency, maximum electrical power output and more generally the suggested focus for future work in the field.
... Coupling this system with a MHD energy conversion stage, a totally static electric generator powered by the heat can be suitably built, e.g., for space applications [11,16]. MHD power generation systems can make the best with the available enthalpy gradient because the interaction of plasma with a magnetic field must take place at much higher temperatures than in a classic mechanical turbine. ...
The aim of the proposed work is to study the optimal design of an innovative Thermo-Acoustic-Magneto-Hydro-Dynamic electric generator, with particular reference to the Magneto-Hydro-Dynamic section. A multi-objective optimization algorithm, which makes use of a Tabu Search meta-heuristic, has been developed to this purpose. Thermo-Acoustic and Magneto-Hydro-Dynamic energy conversion processes give a great advantage by converting energy without solid moving components. This makes the cited technologies very interesting for the low weight, the low maintenance costs, and the high conversion efficiency. The design of the generator has to be optimized by considering conflicting objectives, i.e., maximizing the output power, minimizing the applied electrical voltage, and minimizing mass and size of the device. Therefore, a multi-objective vectorial optimization approach is mandatory. A fully vector scheme has been implemented that takes under control both the Pareto optimality of the solutions, and the uniformity in the Pareto front sampling.
... They have a controlled mass and promise to be highly reliable. Coupling this system with an MHD generator will create an electric generator powered by the heat suitable for space applications [2][3][4]. ...
... In order to simulate the thermoacoustic effect, a vibration with previously assigned values of amplitude and frequency was applied to the gas. In agreement with the typical values from the literature [2], a value of 30 m/s for the velocity was chosen and consequently the inlet acoustic pressure was imposed. On the other hand, by assuming an ideal energy conversion process, the relative pressure at the outlet was set to zero, thus, also the outlet velocity resulted to be null. ...
This paper pertains to the feasibility analysis of a magnetohydrodynamic (MHD) inductive generator coupled with a Thermo Acoustic (TA) resonator. The MHD and TA processes have the great advantage to convert energy without mechanical moving components. In this work, first, the design criteria are given, then the order of magnitude of the obtained parameters is used to model the system by using the finite element method (FEM) to confirm the theoretical results. The conceptual idea and the FEM model are described.
