Investigation of an annular thermoacoustic prime mover

The Journal of the Acoustical Society of America, 2000

The theory of acoustic streaming in an annular thermoacoustic prime-mover is developed. It is predicted that above the threshold for traveling wave excitation the device considered ͑which does not contain any moving parts or externally imposed pressure gradients͒ produces circulation of fluid. The heat flux carried by this directional mass flow inside the thermoacoustic stack exceeds ͑or is comparable with͒ the heat flux associated with the acoustically induced increase of thermal diffusivity of the gas. The effects investigated are important for optimization of the performance of thermoacoustic devices.

Physics Letters A, 2006

The nonlinear processes controlling the time-dependent evolution of sound in annular thermoacoustic prime movers are studied. It is demonstrated that, under some heating conditions, the evolution of the temperature field induced by the excitation of acoustic streaming provides an additional amplification of sound which results in a complicated periodic onset and damping of thermoacoustic instability. The study of this particular example provides the opportunity to demonstrate that the excitation of acoustic streaming does not necessarily imply a decrease in the engine's efficiency.

Cryogenics, 2002

Thermoacoustic engines have been subjected to numerous studies for the past ten years. Our current research focus on the transient regime in an annular thermoacoustic primemover. It appears that several phenomena can play a role in the amplification and saturation regimes. Indeed, we can quote acoustically induced conductivity, forced convection due to acoustic streaming, heat conduction in different parts of the thermoacoustic prime-mover, and saturation due to harmonic generation. The experiments presented here show for the first time a double-threshold phenomenon during the amplification regime. The first threshold, which corresponds to the setting of the thermoacoustic instability, is followed by a saturation regime. Then without any changes in the control parameters, a second threshold has been observed after a time delay, corresponding to an additional amplification. Other interesting results are also presented.

2016

The standing-wave thermoacoustic prime mover is a device to convert heat into work in the form of sound. It is one of the most potential applications for a thermoacoustic prime mover to utilize low-grade heat source to drive a refrigerator or electrodynamic linear alternator. Low efficiency of the device becomes interesting to be studied; it is because of no optimum heat exchange between the channel wall and the working gas that occur in the stack. The stack is the main part of the thermoacoustic prime mover in where the thermoacoustic energy conversion process takes place. The ωτ parameter is regarded as a nondimensional parameter determining the efficiency of the heat exchange in the stack and it depends on the hydraulic radius of the stack. This experiment was carried out by changing the hydraulic radius of the stack to control the value of ωτ. The stack was made of a pile stainless steel wire mesh because it is easier to vary the hydraulic radius than another kind of stack. The length of the resonator is 1.28 m and air at atmospheric pressure is used to fill the resonator as the working gas. Experimental results show that ωτ affecting the onset temperature difference, frequency, pressure amplitude, and acoustic power. Finally, ωτ parameter is a useful property which is needed to be considered to enhance the performance of thermoacoustic prime mover.

Thermoacoustic is a field of science and technology that studies heat and sound interactions. It deals with the conversion of thermal energy into acoustical energy and vice-versa. Thermoacoustic prime mover is an attractive alternative for a conventional pressure wave generator to drive cryocooler which attains cryogenic temperature below 123K to liquefy gases, to produce ultra-vacuum, etc. Also, it can be used to produce electricity with the help of thermoacoustic electric generator. The cooling effect generated by thermoacoustic refrigerator can be used in areas where there is no supply of electricity. The advantages of thermoacoustic prime mover lie in its less complicated construction, absence of any moving part and use of environmental friendly gases as a working medium. Number of simulations using gases such as He, Ar, N 2 and He-Ar mixture were carried out in DeltaEC to investigate the performance of the prime mover in terms of pressure amplitude, onset temperature and resonating frequency. Input parameters like working pressure and heat input was varied to observe the effect on the performance of the prime mover. The results showed that as the working pressure increased, the pressure amplitude and onset temperature also increased. Similar effect was observed in case of heat input. Unlike pressure amplitude and onset temperature, resonating frequency does not depend on working pressure and heat input. It is controlled by the working gas and the geometry of the prime mover. Also the type of the working gas has a profound impact on the performance of the prime mover. Simulations also demonstrated that a mixture of He-Ar can be used to get the optimum output from the prime mover.

International Journal of Heat and Mass Transfer, 2018

This paper proposes the experimental and theoretical study of nonlinear heat transport processes generated by large amplitude acoustic oscillations at the ends of a stack of plates in the presence of a temperature gradient. These processes are notably involved in the operation of thermoacoustic engines. The measurement method, a time-resolved and full-field digital holography interferometry technique, enables to measure the density fluctuations from the optical phase difference between two laser beams. This technique is applied to the analysis of density fluctuations in the vicinity of a stack submitted to a temperature gradient, firstly for the case of (uncontrolled) self-sustained acoustic oscillations generated spontaneously in a standing wave thermoacoustic prime mover, and secondly for the case of an assigned acoustic field whose amplitude is controlled by an external sound source. A theoretical model describing the advective heat transport by sound at the ends of the heated stack is also presented, and numerical simulations are then carried out. The comparison between experimental data and numerical simulations is provided for several stack positions, several sound pressure levels, and several amounts of heat supplied to the stack, and the results show good agreement between the experiments and the model.

The Journal of the Acoustical Society of America, 1999

The purpose of this research is to branch out from thermoacoustics in the plane wave geometry to study radial wave thermoacoustic engines. The radial wave prime mover is described. Experimental results for the temperature difference at which oscillations begin are compared with theoretical predictions. Predictive models often assume a uniform pore size and temperature continuity between the stack and heat exchangers; however, stacks of nonuniform pore size and temperature discontinuities between the stack and heat exchangers are common imperfections in experimental devices. The radial engine results are explained using a theoretical model which takes into account these prevalent construction flaws. Theory and experiment are shown to be in agreement after the complications are included. Spectral measurements show that an additional feature of the radial geometry is the anharmonicity of the resonant modes which significantly reduces nonlinear harmonic generation.

Cryogenics, 1998

Measurements of thermoacoustic prime movers with stacks made of copper wire mesh are presented. The resonance frequencies are below 100 Hz, which are useful to drive pulse tube refrigerators. Onset temperature and resonance frequency were studied. It is found that under certain conditions the second harmonic component becomes dominant and the prime mover essentially works on the second mode, which should be avoided. The influence of gas properties, frequency, mean pressure, mesh size and stack length on the overall performance were measured and expressed in terms of normalized input power, heater temperature and pressure amplitude. A maximum output of 26 W from the thermoacoustic prime mover was achieved with the frequency, input power and heater temperature 73 Hz, 833 W and 700 K respectively.

Journal of Physics: Theories and Applications

Thermoacoustic prime movers work by using thermal energy to produce acoustic energy in the form of sound wave through thermoacoustic effect which occurs in a porous medium called stack. This paper describes an experimental study on the relation between the order of resonance frequencies generated by a thermoacoustic prime mover and the length of the resonator and the viscous penetration depth. Extending the resonator length will decreasing the resonance frequency which result in the increasing in the viscous penetration depth. Generally, the generated sound consists of only one frequency, that is the first-order one. However, under certain conditions, the sound has only the second-order frequency or comprises two frequencies of the first-order and second-order resonance frequencies. This phenomenon can be explained by considering the comparison between the effective hydraulic radius of stack () and the viscous penetration depth (). It is found that the first-order frequency appears ...

AIP Conference Proceedings, 2014

Thermoacoustic systems have been a focus of recent research due to its structural simplicity, high reliability due to absence of moving parts, and can be driven by low grade energy such as fuel, gas, solar energy, waste heat etc. There has been extensive research on both standing wave and traveling wave systems. Towards the development of such systems, simulations can be carried out by several methods such as (a) solving the energy equation, (b) enthalpy flow model, (c) DeltaEC, a free software available from LANL, USA (d) Computational Fluid Dynamics (CFD) etc. We present here the simulation studies of standing wave and traveling wave thermoacoustic prime movers using CFD and DeltaEC. The CFD analysis is carried out using Fluent 6.3.26, incorporating the necessary boundary conditions with different working fluids at different operating pressures. The results obtained by CFD are compared with those obtained using DeltaEC. Also, the CFD simulation of the thermoacoustically driven refrigerator is presented.