Recent advances and applications of solar photovoltaics and thermal technologies

Clean, efficient and affordable energy for a sustainable future

Modeling and experimental investigation of a free-piston Stirling engine-based micro-combined heat and power system

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.

Review on the conversion of thermoacoustic power into electricity

Latest developments in thermoacoustic devices have demonstrated comparable power output and efficiency, but higher reliability and lower cost when compared to conventional low-grade heat recovery technologies. A good coupling between multiple physical fields plays a pivotal role in realizing these potentials. This article provides a comprehensive review of the multi-physics coupling effects, namely, thermal-acoustic coupling, acoustic-mechanical coupling and mechanical-electric coupling, inside thermoacoustic devices including thermoacoustic engines, thermoacoustic electric generators, thermoacoustically-driven refrigerators, etc. The basic principles, operating characteristics, design strategies and future prospects are discussed individually for each coupling effect. System-level design techniques and synthetic optimization methodologies in consideration of the multi-physics coupling effects are presented. This review work gives insights into the underlying mechanisms of various coupling effects in thermoacoustic devices and provides guidelines for improvements of modern thermoacoustic technologies for low-grade thermal energy recovery, refrigeration and electric power generation purposes.

Multi-physics coupling in thermoacoustic devices: A review

As a high energy density hydrogen-rich carrier, ammonia (NH3) is a highly
 promising carbon-free fuel. The large-scale industrial application of NH3 is
 limited by its low reactivity and high nitrogen oxide (NOX) emission. In
 this work, the flame and emission characteristics of ammonia/methane
 (NH3/CH4) non-premixed combustion were investigated under ultrasonic
 excitation. An experimental system was designed and built, including
 non-premixed combustion system, loading ultrasonic system, deflection
 tomography temperature measurement system and flue gas measurement system.
 Combustion and measurement experiments at different ultrasonic frequencies
 and NH3/CH4 blending ratios were carried out. Flame images and flue gas
 species concentrations under ultrasonic excitation were acquired. The 3D
 temperature field was reconstructed. The influence of ultrasonic excitation
 at different frequencies on flame characteristics, flame temperature field
 and emission characteristics of the combustion process was analysed. The
 mechanism of NH3/CH4 combustion enhancement and emission reduction was
 revealed when the flame was excited by ultrasonic waves. Results showed that
 part of the hydrocarbon fuels was replaced by NH3 to reduce carbon dioxide
 (CO2) emission. The height and colour of the NH3/CH4 flame were changed and
 the high-temperature area of the flame gradually expanded as ultrasonic
 acted on the flame. As ultrasonic frequency increased, the emission
 concentrations of unburned CH4, unburned NH3 and NO decreased significantly.
 The flame was excited by ultrasonic waves, which reduced its local
 equivalent ratio, improved combustion efficiency and suppressed NOX
 generation.

http://www.doiserbia.nb.rs/ft.aspx?id=0354-98362300029S

Tianjiao Bi

Papers

Flame and emission characteristics from NH3/CH4 combustion under ultrasonic excitation