Thermoacoustic refrigerator driven by a combustion-powered thermoacoustic engine - Demonstrator of device for rural areas of developing countries

This paper presents the design, construction and experimental evaluation of a demonstrator thermoacoustic refrigerator driven by a combustion-powered thermoacoustic engine. The system was developed to be a low-cost device for users based in remote and rural areas of developing countries. It employs a thermoacoustic engine/refrigerator coupling based on a travelling wave looped-tube configuration because of its relatively good thermal performance and construction simplicity. In the present demonstrator, a propane gas burner is used to simulate the thermal input from biomass combustion which is envisaged to be the source of energy for driving the system. Atmospheric air is applied as working fluid, while the operating frequency of the loop is 58.6 Hz. The location of the refrigerator is optimized experimentally to achieve the maximum cooling performance. So far, the lowest temperature achieved at the cold end of the regenerator is -3.6°C, while the maximum COPR achieved is 1.42%

Optimizing Lags and Hidden Layers in Hybrid Models for Forecasting Stock Return

This study aims to minimize the root mean square error for stock return by optimizing lags and hidden layers in a hybrid model. The model combines the autoregressive integrated moving average with the exogenous variables model as linear components. The residuals derived from linear components are used in artificial neural networks and Elman recurrent neural networks as non-linear components. A key feature of this approach is optimizing the selection of hidden layers and lags within the neural network, improving forecasting accuracy. The minimum mean square error forecast expression is derived, and the model is tested on stock price data during the COVID-19 period, marked by significant market shocks. The root mean square error results for the proposed model, traditional hybrid model, and traditional time series model range from 0.0004 to 0.01, 0.0006 to 0.01, and 0.006 to 0.03, respectively. The results show that the proposed model outperforms both traditional models

Optimal design of a thermoacoustic system comprising of a standing-wave engine driving a travelling-wave cooler

This paper presents the design and optimisation of a coupled thermoacoustic system comprising of a standing wave thermoacoustic engine and a coaxial travelling wave thermoacoustic cooler in a linear configuration. The overall aim is to propose an economical design of a prototype system which could be used by people living in remote rural areas of developing countries with no access to the electrical grid. The cooler coaxial configuration provides a feedback inertance and compliance to create the required travelling-wave phasing. Compressed air at 10 bar is used as the working fluid. The operating frequency is around 50 Hz. The geometric parameters of both engine and cooler, affecting the overall efficiency of cooling, have been investigated to evaluate the optimal configuration of the system. The most sensitive parameters are the cross sectional areas of the engine and cooler and the hydraulic radii of stack and regenerator

The Effect of Vibration on Flow Inside a Standing Wave Thermoacoustic Condition

This paper explores the complex relationship between acoustic streaming and vibration in thermoacoustic systems, enhancing the comprehension of these interconnected phenomena in the realm of energy conversion and heat transfer. Thermoacoustic devices are becoming more important for sustainable energy uses. The dynamic interaction between acoustic streaming and vibration is a crucial yet unexplored aspect of the performance of thermoacoustic devices. This research is driven by the necessity of filling current knowledge deficiencies and acknowledging the importance of these factors in the performance of thermoacoustic systems. This study intends to enhance the understanding about acoustic streaming and vibration through the utilisation of numerical simulations and experimental studies. In this paper, a two-dimensional (2D) computational fluid dynamics (CFD) model of standing wave thermoacoustic flow conditions was solved using the SST k-ꞷ turbulence model in ANSYS Fluent to simulate the streaming induced by the vibrational responses within a standing wave thermoacoustic test rig. This numerical prediction is then validated using experimental results from a similar operating condition with a single resonance frequency of 23.6 Hz. Three drive ratios were examined. Disparity between velocity amplitude from CFD simulation and experimental data was observed particularly at the highest drive ratio. As the drive ratio increases, so does the amplitude of the velocity. It was discovered that the model that includes vibration brings the difference in results between the model and the experiment to be smaller and it replicates the closest scenario to the actual condition.

Thermal performance improvement of forced-air cooling system combined with liquid spray for densely packed batteries of electric vehicle

In the electric vehicles (EVs), battery thermal management system (BTMS) serves a key role in addressing the issue of excessive heat generated from chemical reactions and internal resistance which can cause capacity fade, thermal runaway and instability issues. In this study, a novel cooling system that combines liquid spray and forced-air is proposed. The cooling fluid used is Hydrofluoroether (HFE) which is a non-electrically conductive liquid. The study develops a transient heat transfer model of the battery module and investigates the effects of injection rate and injector arrangement on cooling performance. The results demonstrate that increasing the amount of HFE can further decrease the maximum temperature and the temperature non-uniformity of the battery module, but cost benefit considerations must be taken into account. The injector layout also has a significant impact on the temperature distribution of the module. Optimizing the cooling system can reduce the maximum temperature and temperature difference of the module by 5.9 °C and 4.0 °C, respectively, compared to dry air cooling. These findings of the spray-assisted forced-air cooling system provide useful insights for developing a practical thermal management solution for EVs

Vibration-induced flow and streaming in oscillatory flow of thermoacoustics

Induced acoustic streaming flow in thermoacoustic systems occurs due to acoustic vibrations, causing changes to the mean flow in the systems. This phenomenon creates a tendency to generate net fluid flow that can cause energy change within certain areas inside the system. However, the effects of the entire system’s vibrations on the flow streaming are not yet fully understood, yet it is important for a more effective operation. This study experimentally investigated the flow streaming resulting from vibration in a standing-wave thermoacoustic test rig with a flow frequency of 23.6 Hz. The existence of flow streaming due to vibration which was not counted in the theoretical formula is shown and indicated by experimental values. The result shows that there is a correlation between the amplitude of the drive ratio (DR) and the velocity of the oscillation of the flow. Upon examining both the theoretical and the practical evidence, it becomes clear that there exists a marginal flow velocity in directions other than the main flow due to the vibration of resonator’s wall as measured at the intake and outflow areas of the stack. This marginal flow velocity amplifies as the drive ratio of flow increases and it may potentially explain the observed difference between measured flow amplitude and the theoretical value

The effect of porous materials on temperature drop in a standing wave thermoacoustic cooler

Thermoacoustics is a principle of sciences that offers an alternative solution for cooling system with a technology that is green and sustainable. The thermoacoustic energy conversion takes place mostly within the area of the porous structure that forms the core of the system. In this study, the effect of changing the material of the porous structure on the performance of the thermoacoustic refrigerating system is reported. Experiments were performed under standing wave environment with two different resonance frequencies with air at atmospheric pressure. The porous stack was chosen to be with three different materials of polycarbonate, ceramic and stainless steel. The results show that the use of ceramic celcor as the porous material provides the biggest temperature difference which means that thermoacoustic performance is better. The performance is even better when the system is working with higher resonance frequency. At atmospheric pressure condition with air as working medium, the thermoacoustic cooler with ceramic porous material is capable of producing temperature difference of 39.16C when operating at a frequency of 202.1 Hz

Thermoacoustic cooler with different waveform excitations and the noise control test

Many researchers have been devoted into improving the operation of thermoacoustic cooling system as it offers a promising alternative to traditional cooling methods. This study reported potential system’s improvements that can be obtained when it is operated with different excitation of waveforms and resonator’s material. Resonant test was first carried out to identify the frequency for the operation. Temperature drop that can be obtained by the system was then tested for sine wave, square wave and triangle wave excitations. It was found that a change in resonator material alters the resonance frequency for the operation. Resonance was recorded at 186.6 Hz when acrylic resonator was used while a resonance frequency of 170.5 Hz was found when polyvinyl-chloride’s resonator was used. In term of temperature effects, the square wave excitation resulted to the maximum temperature difference of 45.64˚°C in the acrylic resonator, followed by sine wave at 43.46°C and triangle wave came in last at 40.11°C. Then, as the polyvinyl-chloride’s resonator was used, smaller values of maximum temperature was observed with 38.07°C, 35.94°C and 30.05°C for square wave, sine wave and triangle wave, respectively