Static Energy Conversion Research Articles

Modeling and thermodynamic analysis of a novel combined cooling and power system composed of alkali metal thermal electric converter and looped multistage thermoacoustically-driven refrigerator

A large amount of high-quality heat from alkali metal thermal electric converter (AMTEC) is wasted, which greatly degrades its thermodynamic performance and causes serious thermal pollution. For solving this issue, a novel combined cooling and power (CCP) distributed system including two static energy conversion units, i.e., the AMTEC unit and looped multistage thermoacoustic-driven refrigerator (LMTADR) unit, is proposed. The general performance for the proposed system is analyzed via establishing the mathematical model, and the optimal region is obtained by considering both equivalent power density and exergy efficiency. Then, the parameter sensitive analysis is represented to provide some theoretical guidance for design of the proposed system. The results reveal that compared with a sole AMTEC system, the maximum equivalent power density and exergy efficiency of the combined system are improved by 42.4% and 22.5%, respectively. When the performance improvement rate reaches the maximum, the combined system achieves an equivalent power density of 9203.3 W m−2, a cooling rate density of 3190.2 W m−2 and an exergy efficiency of 25.8%. This study not only proves the superiority of AMTEC-LMTADR combined system, but also implies the extensive possibility of recovering medium and high-grade heat through LMTADR for refrigeration.

Performance enhancement in hybrid static power generation by AMTEC–TEG systems: Energy, exergy, and interactions analyses and optimizations

Alkali metal thermal electric converter (AMTEC) and thermoelectric generator (TEG) are two static energy conversion devices with attractive attributes including high scalability and the ability to utilize renewable energy sources. The present study analytically simulates and optimizes the performance of a novel hybrid AMTEC–TEG system from energy and exergy perspectives. The study scrutinizes interactions between the two devices, exergy destruction sources, solutions toward enhancing exergy efficiency, and the impacts of the heat sink, not accomplished in the open literature. The results reveal that exergy loss within the AMTEC condenser is the main source of exergy destruction; nonetheless, there exists a number of optimal designs by which the TEG can effectively recover this lost exergy. Also, the results show that a simple fin-fan or a passive heat exchanger can be sufficient for cooling the hybrid system while protecting the hybrid system’s valuable features like static and maintenance-free operation. The maximum values of energy and exergy efficiencies and generated power, attained within an improved load-following range for the hybrid system, are respectively 35.6%, 47.8%, and 8136 W. Furthermore, comparisons with similar systems acknowledge the superiority of the proposed hybrid system. Overall, the hybrid system is seen to be of high potential as a flexible, modular, static power generation system whose advantages are thoroughly discussed alongside its weaknesses, providing beneficial information for future studies.

2.79 [formula omitted]m LGS electro-optical Q-switched Er, Cr: YSGG laser

2.79 μm-band pulsed laser has important application prospects in medicine, military, etc. In this paper, the pulse operation of Er, Cr: YSGG laser Q-switched by piezoelectric crystal La3Ga5SIO14(LGS) is realized, and high-energy output under nanosecond pulse is obtained. In the experiment, LGS crystal was used as the de-voltage Q-switching element. At a repetition frequency of 10 Hz, the obtained pulse width was 27.4 ns, the corresponding single pulse maximum output energy was 136 mJ, and the dynamic–static energy conversion efficiency was 75.6%; The output beam quality factor M2 obtained by self-made spot analysis software in the x and y directions are 1.34 and 1.40, respectively.

Thermoelectric performance study on a heat pipe thermoelectric generator for micro nuclear reactor application

Heat pipe cooled reactor is designed to meet the future energy demands with many unique advantages such as modularization, solid and static state, high reliability and passive safety. In the innovative nuclear reactor design, heat pipes are used to cool the reactor core and transfer the fission heat passively, thermoelectric generators (TEGs) are utilized to achieve static energy conversion. In this article, a finite element model is established to investigate the detailed TEG thermoelectric performance coupled with heat pipes. A temperature field and flow field coupling model is used to simulate the heat transfer performance of the potassium heat pipe including a heat pipe wall, wick and vapor region. A heat pipe TEG experimental setup is established and the steady-state experiment is conducted. The experimental setup is selected as the numerical simulation object and the simulated results are compared with the experimental data to verify the numerical model. The maximum simulation error is within 5%. Based on the verification and validation, the steady-state thermoelectric performances, the effect of contact thermal resistance and external load on the skutterudite TEG thermoelectric performances are investigated. The detailed heat flux distributions, temperature distributions and potential distributions are researched in the steady-state simulation. The temperature distributions of the TEG cross section are centrally symmetrical and the horizontal temperature difference is 26°C. The temperature difference introduced by thermal resistance at the TEG hot side increases from 33°C to 94°C with the increasing heat flux through TEG module. The influence of thermal resistance on TEG hot side is more significant than that on TEG cold side. The effect of external load on TEG output characteristics is investigated under different heat flux conditions. With the increase of heat flux from 60 to 166 kW/m2, the temperature difference of TEG module and p-n unit increase by 432°C and 348°C, the thermoelectric conversion efficiency is improved from 3.6% to 8.5%, and output power increases by 20 W, respectively. The research results are of guiding significance for exploring the application potential of TEGs in the static heat pipe cooled reactor. This work provides research foundations for the multiphysics coupling analysis of the micro heat pipe cooled reactor.

Experimental investigation of a novel heat pipe thermoelectric generator for waste heat recovery and electricity generation

Waste heat recovery helps reduce energy consumption, decreases carbon emissions, and enhances sustainable energy development. In China, energy-intensive industries dominate the industrial sector and have significant potential for waste heat recovery. We propose a novel waste heat recovery system assisted by a heat pipe and thermoelectric generator (TEG) namely, heat pipe TEG (HPTEG)，to simultaneously recover waste heat and achieve electricity generation. Moreover, the HPTEG provides a good approach to bridging the mismatch between energy supply and demand. Based on the technical reserve on high-temperature heat pipe manufacturing and TEG device integration, a laboratory-scale HPTEG prototype was established to investigate the coupling performances of the heat pipes and TEGs. Static energy conversion and passive thermal transport were achieved with the assistance of skutterudite TEGs and potassium heat pipes. Based on the HPTEG prototype, the heat transfer and the thermoelectric conversion performances were investigated. Potassium heat pipes exhibited excellent heat transfer performance with 95% thermal efficiency. The isothermality of such a heat pipe was excellent, and the heat pipe temperature gradient was within 15°C. The TEG's thermoelectric conversion efficiency of 7.5% and HPTEG's prototype system thermoelectric conversion efficiency of 6.2% were achieved. When the TEG hot surface temperature reached 625°C, the maximum electrical output power of the TEG peaked at 183.2 W, and the open-circuit voltage reached 42.2 V. The high performances of the HPTEG prototype demonstrated the potential of the HPTEG for use in engineering applications.

Fuel cells and load transients

Fuel cells are static energy conversion devices that convert the chemical energy of fuel into electrical energy directly. Compared with conventional power generation systems, they have many advantages, such as high efficiency, zero or low emission (of pollutant gases), and flexible modular structure. Fuel cells are expected to play an important role in future distributed generation (DG) applications. Fuel cell DGs (FCDGs) can either be connected to a utility grid for network reinforcement or installed in a remote area to supply stand-alone power. In this article, a load transient mitigation controller is described for hybrid PEMFC-battery power generation systems. The hybrid FCDG is controlled in a way that during a load transient, the fuel cell provides the steady-state part of the load, and the battery will supply the transient part of the load. The proposed technique can be especially useful in fuel cell vehicles (motor starting and accelerating) as well as in stationary applications, where load transients are unavoidable. The load transient mitigation controller is applicable to other types of FCDGs

A Unified Dynamic Model and Control for the Voltage-Sourced Converter Under Unbalanced Grid Conditions

This paper introduces and develops i) a novel unified dynamic model, and ii) new control schemes for a grid-connected static energy conversion system that is based on the voltage-sourced converter (VSC) configuration. The model and the controls are applicable to both the conventional two-level and the three-level neutral point diode clamped (NPC) VSCs. The model is unified since it represents the dynamic behavior of the with respect to both positiveand negative-sequence components, due to unbalanced grid conditions and disturbances. To develop the unified model, the concepts of generalized sinusoidal pulse-width modulation (SPWM) and VSC sequence subsystems are presented. Based on the negative-sequence subsystem control, a new control strategy, to either balance the ac line currents or to mitigate dc-bus voltage ripples, is introduced. Application of the developed model and the controls to a variable-speed wind-power unit is presented in the paper.

04/01279 Analyses of static energy conversion systems for small nuclear power plants: El-Genk, M. S. and Tournier, J.-M. P. Progress in Nuclear Energy, 2003, 42, (3), 283–310

04/01279 Analyses of static energy conversion systems for small nuclear power plants: El-Genk, M. S. and Tournier, J.-M. P. Progress in Nuclear Energy, 2003, 42, (3), 283–310

Analyses of static energy conversion systems for small nuclear power plants

Small, Gas Cooled Reactor (GCR) nuclear power plants with static energy conversion could meet the energy mix in underdeveloped countries, including electricity, residential and industrial space heating, seawater desalination, and/or high temperature process heat or steam for industrial uses. Analyses are performed of one high-temperature GCR and three intermediate-temperature GCR power plants with co-generation options to calculate and compare the total energy utilizations of the plants. Conversion of the reactor thermal power to electricity is accomplished using static energy conversion units comprised of an Alkali Metal Thermal-To-Electric topping cycle and a Thermoelectric bottom cycle, as well as segmented thermoelectric converters. The calculated total energy utilization of these plants of 95% includes low-voltage (∼ 400 V) DC electrical power at a net plant efficiency of up to 32.7%, and co-generation for residential and industrial space heating at < 400 K, desalination at 365 K, and/or high temperature process heat or steam at > 500 K. Results indicate that the intermediate-temperature GCR plants with a small coolant temperature rise of 100 – 160 K in the reactor core could deliver 2–3 times the electricity of a GCR plant with a higher temperature rise of 340 K, and that all plants could provide for both seawater desalination and high temperature process heat/steam concurrently. In addition, depending on the number of co-generation options employed, the fraction of the reactor thermal power used for co-generation in the high-temperature GCR plant is ∼ 10–30% higher than in the intermediate-temperature GCR plants with a smaller temperature rise in the reactor.

Scaling and dimensioning of switched reluctance machines

AbstractA scaling law applying to a geometrically analogous series of switched reluctance machines (SRM), based on two‐dimensional non‐linear field analysis is presented in the paper. It highlights the fact that both linear and saturated permeances per unit axial length at different rotor positions are invariant under scaling. Based on a normalized static energy conversion loop in the electric/magnetic loading plane a quality factor is defined which serves to calculate the average specific torque. A simple analytic expression for predicting the quality factor of a SRM is derived which depends only on the linear permeances at two extreme rotor positions and the electric and magnetic loadings at the top point of the static energy conversion loop. This simplifies greatly the prediction of specific torque at an early design stage. Finally, the effects of air‐gap dimension ratios, electric loading, magnetic gear ratio and leakage flux on the quality factor and the specific torque in designing SRM having different magnetic gear ratios are discussed.

Inverter for use with very low input voltages

A CONTINUING impetus to advance the technology of static energy-conversion methods is being provided by the demands of our and other nations' rapidly expanding programs of space exploration. Not only the various environmental considerations, but more particularly, the stringent reliability requirements serve to justify the considerable research effort being direct toward the development of static methods for the generation and processing of electric energy for spacecraft.

Chemical-thermionic auxiliary power systems

An analysis of the problems of matching the performance of a high-temperature plasma-thermionic static-energy conversion device to a heat source consisting of the combustion products of chemical fuels is presented. The thermodynamic relationships governing the efficiency and power densities of the thermionic converter as a function of cathode temperature and work function are established and the limitations imposed by positive ion space charge neutralization are pointed out. The temperature and heat flux limits set by the heat source are compared to the converter requirements and various matching problems are discussed.