Search Results (5)

The existence and development of modern society require significant amounts of available energy. Combustion engines are the main sources of heat. Their operation is accompanied by the formation of large volumes of emissions, which have different temperatures and contain harmful substances ejected into the environment. Therefore, the urgent problem today is the reduction in heat emissions. This might be achieved through a reduction in the amount of these pollutants by improving primary heat engines, converting to new, alternative types of fuel, and at the same time, to carbon-free fuel. However, such measures only reduce the temperature level of waste heat but not its volume. Conventional technologies for the utilization of heat emissions are ineffective for using heat with temperatures below 500 K. Thermoacoustic technologies can be used to convert such low-temperature heat emissions into mechanical work or electricity. This article is focused on analyzing the possibilities of improving the thermoacoustic engines of energy-saving systems through the rational organization of thermoacoustic energy conversion processes. An original mathematical model of energy exchange between the internal elements of thermoacoustic engines is developed. It is shown that the use of recuperative heat exchangers in thermoacoustic engines leads to a decrease in their efficiency by 10–30%. From the research results, new methods of increasing the efficiency of low-temperature engines of energy-saving systems are proposed. Full article

In this article, a comprehensive review of the computational fluid dynamics (CFD)-based modeling approach for thermoacoustic energy conversion devices is proposed. Although thermoacoustic phenomena were discovered two centuries ago, only in recent decades have such thermoacoustic devices been spreading for energy conversion. The limited understanding of thermoacoustic nonlinearities is one of the reasons limiting their diffusion. CFD is a powerful tool that allows taking into consideration all the nonlinear phenomena neglected by linear theory, on which standard designs are based, to develop energy devices that are increasingly efficient. Starting from a description of all possible numerical models to highlight the difference from a full CFD method, the nonlinearities (dynamic, fluid dynamic and acoustic) are discussed from a physical and modeling point of view. The articles found in the literature were analyzed according to their setup, with either a single thermoacoustic core (TAC) or a full device. With regard to the full devices, a further distinction was made between those models solved at the microscopic scale and those involving a macroscopic porous media approach to model the thermoacoustic core. This review shows that there is no nonlinear porous media model that can be applied to the stack, regenerator and heat exchangers of all thermoacoustic devices in oscillating flows for each frequency, and that the eventual choice of turbulence model requires further studies. Full article

Electrified aircraft propulsion enables new aircraft designs with fewer emissions. One challenge of electrified architectures is handling the electrical components’ waste heat. This is because batteries and other electrical components are sensitive to high temperatures and accumulate heat within their structure. In this work, we investigate using a thermoacoustic refrigerator to cool the battery of a parallel hybrid single-aisle commercial transport aircraft. This thermoacoustic refrigeration system is powered by waste heat from the turbofan engine core, whereas a conventional refrigerator consumes electricity from the battery or shaft power offtakes. Compared to a conventional vapor cycle refrigerator, the thermoacoustic refrigeration system results in greater mission fuel burn because of pressure losses attributable to the extraction of heat from the turbofan to drive the thermoacoustic refrigerator. Heat exchangers with very low pressure losses may render the thermoacoustic refrigeration system beneficial compared to conventional refrigeration in certain use cases, such as low-altitude missions. Full article

In order to study the influence of streamwise forcing on the formation mechanism of liquid ligaments and droplets in the primary breakup process of liquid circular jet, the VOF interface capturing method-based direct numerical simulation was adopted, and a range of sinusoidal velocity disturbances with different frequencies were considered. The selected disturbance frequency range is 0–3000 kHz. This work analyzes the evolution process of the jet surface waves at different disturbance frequencies, and the coupling effect of the jet tip and liquid core on the overall spray field from overall structure, liquid ligament, and droplet formation. The results show that different disturbance frequencies affect the droplet shape distribution and size distribution in spray field. Current work provides guidance for the control of the thermoacoustic instability of the engine and design of the nozzle. Full article

The thermoacoustic behavior of different typologies of porous cores is studied in this paper with the goal of finding the most suitable solution for small thermoacoustic devices, including solar driven air coolers and generators, which can be used in future buildings. Cores provided with circular pores, with rectangular slits and with arrays of parallel cylindrical pins are investigated. For the type of applications in focus, the main design constraints are represented by the reduced amount of the input heat power and the size limitations of the device. In this paper, a numerical procedure has been implemented to assess the behavior of the different core typologies. For a fixed input heat power, the maximum acoustic power delivered by each core is computed and the corresponding engine configuration (length of the resonator and position of the core) is provided. It has been found that cores with parallel pins provide the largest amount of acoustic power with the smallest resonator length. This conclusion has been confirmed by experiments where additive manufactured cores have been tested in a small, light-driven, thermoacoustic prime mover. Full article