Thermoacoustic Cooler Research Articles

Acoustic field and power matching mechanism in looped heat-driven thermoacoustic refrigerators

Heat-driven thermoacoustic refrigerators (HDTRs) offer great potential for the sustainable energy development due to their environmental friendliness, high reliability, and promising efficiency. However, there remains a gap in the comprehensive study and understanding of their acoustic matching and energy conversion mechanisms, the resolution of which would facilitate the development of more efficient HDTRs. This work employs Sage to model fundamental thermoacoustic engines and coolers, aiming to explore the effects of temperature and acoustic fields on their performance. It highlights the acoustic and temperature-matching patterns of looped HDTRs operating at room temperature range. The optimal impedance phase for the thermoacoustic engine and cooler is located on the negative and positive sides, respectively, of the pure traveling wave zero-phase point. The thermal buffer tube provides better phase matching between the engine outlet and cooler inlet compared to the resonator tube. Focusing on a single-unit HDTR system, the present study evaluates the steady-state performance and acoustic distribution analysis for systems different connections and couplings. Additionally, it compares looped HDTRs with various coupling configurations from the literature, further confirming the superior refrigeration performance of directly coupled systems. These findings provide valuable insights for developing more efficient thermoacoustic refrigerators, contributing to sustainable energy advancement.

Numerical calculation of a heat-driven thermoacoustic cooler with multiple pair of the cooler and engine cores (Study on cores where the cold side of the cooler and the ambient side of the engine are adjacent)

Numerical calculation of a heat-driven thermoacoustic cooler with multiple pair of the cooler and engine cores (Study on cores where the cold side of the cooler and the ambient side of the engine are adjacent)

A displacer coupled thermoacoustic cooler driven by heat and electricity

A small-scale, heat-driven cooling system is required for the on-site liquefaction of unconventional natural gas in a distributed station. The thermoacoustic cooler has been considered a promising candidate for meeting such demands due to its high reliability and environmental friendliness. However, conventional thermoacoustic systems use a resonance tube to couple the thermoacoustic engine and cooler, which degrades cooling performancedue to poor phase-shifting capability and significant power dissipation of the resonance tube. To overcome the limitation, this paper introduces a novel driven by heat and electricity thermoacoustic cooler using displacers to replace the resonance tube, which enables better phase-shifting capability and less power dissipation, thus allowing better cooling performance. Numerical investigation and experimental study are performed on the displacer-coupled thermoacoustic cooler driven by heat and electricity. Firstly, the design method of the displacers is presented based on the acoustic impedance matching principle. Numerical investigations are then conducted to understand the operational characteristics better to explore the axial distribution of critical parameters. The effects of the displacer damping coefficient, operating frequency, and mean pressure are further studied. Experimental investigations are then carried out to understand the impact of operating temperatures on system performance. Experimental results show that the system achieves a record thermal-to-cooling exergy efficiency of 13.4 % and cooling power of 117 W at heating and cooling temperatures of 773 K and 110 K. This represents an over 34 % improvement in efficiency when compared to the previous record-holder thermoacoustic cooler.

A thermoacoustic cooler with a bypass expansion for distributed-temperature heat loads

In the context of the current energy crisis, a compact, simple, and reliable cooler is required at small-scale natural gas liquefaction stations. In this paper, a thermoacoustic cooler with a bypass expansion cooling for distributed-temperature heat loads is proposed. The bypass expansion configuration is used to carry out multiple refrigeration processes to achieve distributed cooling temperatures, thus realizing the cascade processes of natural gas liquefaction and improving the liquefaction efficiency. Simulations were carried out to investigate the effect of cooling-stage numbers on relative power consumption efficiency, exergy losses of components as well as axial distributions of key parameters. A proof-of-concept porotype of a two-stage thermoacoustic cooler was built, and the feasibility of the distributed heat loads was experimentally tested. Comparisons with a conventional single-stage thermoacoustic cooler without bypass expansion indicate that the proposed bypass expansion system improves the liquefaction cooling efficiency by a factor of 3.28 at 120 K. Experiments were also carried out to investigate the effect of the bypass expansion, an important factor, by verifying the total number of bypass orifices. Results show that increasing the number of bypass orifices with a more uniform gas distribution can improve the cooling performance of the system. The findings demonstrate the promising prospects of the proposed thermoacoustic cooler in the field of natural gas liquefaction.

Test-bench for the experimental characterization of porous material used in thermoacoustic refrigerators.

The design of thermoacoustic coolers involves an adequate modeling of the thermoacoustic core's performance, which requires, in particular, a precise knowledge of their thermo-physical properties. Materials such as wire mesh stacks, foams, or compressed fibrous media are hard to describe, and their thermo-physical properties are rarely well enough quantified. Moreover, the classical linear thermoacoustic theory is not sufficient to accurately describe the performance of these materials. This paper deals with the experimental performance characterization of various materials for thermoacoustic heat pumping. A dedicated experimental test-bench has been specially developed, which is composed of two loudspeakers placed at opposite ends of a waveguide containing the porous material and a feedback loop to control the acoustic field in the porous material. Its originality is attributable to the possibility of identifying the optimal acoustic field, specific to each material, that maximizes the temperature difference at the ends of the material. Moreover, a specific protocol is implemented to access and compare the thermoacoustic heat flux through various materials at these optimal acoustic fields. Comparison of the experimental and theoretical results shows a reasonable agreement.

Development of a small-scale piezoelectric-driven thermoacoustic cooler

With the continuous increase of system power and shrinkage of size, heat removal from central processing units in electronic devices becomes more challenging. In this study, a small-scale piezoelectric-driven thermoacoustic cooler (TAC) is proposed as a novel method for electronic cooling. A prototype of the TAC that is merely 7.5 cm long, 2.3 cm in diameter, and uses ambient air as working fluid, has been built and tested. Theoretical models based on linear acoustics and thermoacoustics are established to predict the acoustical and thermal characteristics of the TAC. Results show that the piezoelectric-driven TAC achieves high pressure amplitudes at 1743 Hz (i.e., the acoustic resonance frequency of the acoustic cavity) and 2717 Hz (i.e., the mechanical resonance frequency of the piezoelectric actuator). A maximum temperature difference of 4.4 ℃ is obtained when the TAC operates at 2717 Hz with an electric power input of around 0.4 W. Approaches to further improve the cooling performance of the TAC are suggested. This work demonstrates the great potential of TACs, extending the application of thermoacoustic technology in thermal management of miniature electronics.

A heat-driven combined cooling and heating system based on thermoacoustic technology

Energy crisis and environmental pollution have become global issues. This study reported a heat-driven combined cooling and heating system based on thermoacoustic technology, which adopted two units of thermoacoustic engine and cooler cores to improve the efficiency. This system can be used as a refrigerator and a heat pump at the same time. Experimental results showed that with a charging pressure of 10 MPa, a high temperature of 300 °C, and a medium temperature of 45 °C, cooling power ranging from 0.61 to 3.89 kW and coefficient of performance varying from 0.08 to 0.30 with low temperature changing from −30 to −5 °C were achieved when the system was working as a refrigerator. Meanwhile, under a low temperature of −30 and −10 °C, a heating power of 7.85 and 14.3 kW with a medium temperature of 45 °C could be achieved corresponding to a coefficient of performance of 1.08 and 1.24 when the system was working as a heat pump. These experimental performances show remarkable advantages and a promising prospect for thermal energy utilization in the future.

Combined thermoacoustic cooling and ortho-para conversion of cryogenic hydrogen

Hydrogen is a promising fuel for our future, as it can be produced with renewable energy sources and it does not emit harmful emissions when reacting with oxygen. To make the hydrogen economy viable, hydrogen needs to be transported as a dense cryogenic liquid. Since efficiencies of current cryocoolers are relatively low, improvements of the cooling technologies are required. In this study, an innovative solution involving thermoacoustic flow-through cooler is considered. Acoustic waves passing through porous medium can pump heat and cool hydrogen flowing through the system. An important feature of cryogenic hydrogen is the shift between its equilibrium ortho and para isomer fractions, which requires additional removal of heat. Since the natural conversion is slow, it must be augmented by catalysts for fast transition. The advantage of using the flow-through thermoacoustic system to cool hydrogen is that a catalyst can be placed in the porous matrix where hydrogen flows, so it can be cooled and undergo conversion at the same time. A mathematical model describing this process has been developed. Results showing achievable coefficients of performance, temperature drops, and flow rates of hydrogen are presented for both standing-wave and travelling-wave systems.

The impact of stack parameters on the temperature difference of a thermoacoustic cooler

Thermoacoustics offer alternative solution for cooling needs where a method that is safer to environment is used. The thermodynamic process that needs to be completed by using interaction between inert gaseous and porous material must be made efficient so that the system works properly. This paper reports numerical and experimental investigations of the use of several porous material in air at atmospheric pressure to provide cooling effect. Experimental investigation was also conducted by using cheap and abundant materials as the porous media. Results were collected at two different frequencies and with two different stack lengths. The study showed that thin-walled honeycomb porous structure made of polycarbonate offers the best temperature for thermoacoustic cooler with air at atmospheric pressure. The best COP of 4.73 was recorded. Disparity between numerical and experimental results is expected to be the result of losses that need to be carefully addressed in the future especially when long stack is used in the system.

Numerical study on a heat-driven piston-coupled multi-stage thermoacoustic-Stirling cooler

This work investigates a novel heat-driven multi-stage thermoacoustic cooler that can satisfy cooling requirements in the applications of natural gas liquefaction and high-temperature superconductivity. The proposed system consists of a compressor, multiple thermoacoustic units (engines and coolers) coupled by piston-cylinder assemblies. The acoustic power input by the compressor is successively multiplied in the thermoacoustic engine units, and the amplified acoustic power is then consumed to produce cooling power in the thermoacoustic cooler units. The proposed system overcomes the limitations of the traditional thermoacoustic systems owing to high efficiency, compact size, and ease of control. Analyses are first performed to explore the influence of the number of stages. The design method of the pistons is presented based on acoustic impedance matching principle.Based on the optimized system, simulations are then conducted to investigate the axial distribution of the key parameters, which can explain the reason for improved thermodynamic performance. At heating and cooling temperatures of 873 K and 130 K, the system achieves a cooling power of 2.1 kW and a thermal-to-cooling relative Carnot efficiency of 23%. This represents significant increases by over 60% in efficiency and 80% in cooling capacity when compared to existing systems. Simulations further demonstrate how controlling the input acoustic power and frequency via the compressor enables control of the system under various conditions. Further discussions are made considering a potential combined cooling and power system, indicating an overall thermal-cooling-electricity efficiency of 34% without any external electric power required for the compressor.

Effects of Edge Shapes on Thermal-Fluid Processes in Oscillatory Flows

Thermoacoustic machines, Stirling engines or coolers, and pulse tube coolers are examples of energy systems that operate based on oscillatory flow principles. This class of technology would achieve an improved efficiency from appropriately designed heat exchangers, stacks, regenerators and thermal buffer tubes. In this paper, heat transfer and oscillatory flow behaviour in three identical parallel-plate heat exchangers, one ‘heat source’ positioned between two ‘heat sinks’, are investigated using numerical method. The effect of different plate edge shapes on heat transfer, flow structures and acoustic pressure drop are examined at a selected drive ratio of 0.3 – 2.0%. Flow parameters show a strong dependency on drive ratio and flow direction, especially at low excitation where gas displacements are below or comparable to the heat exchanger length. Cone edge shape minimises the flow complexity better than other shapes with a negligible effect on the heat transfer. The result of this study will benefit the design and development of compact and high-efficiency heat exchangers for the next generation of oscillatory-flow energy and thermal management systems.

Experimental investigation of the effect of different waveforms on heat transfer in a thermoacoustic cooler

Thermoacoustic cooling systems are insufficiently compared to compressor compression cooling systems. The reasons for this should be investigated and solved. The performance of a thermoacoustic cooling system depends on many factors. The cooling system's success is possible by precisely determining the contributions of these factors to thermoacoustic cooling. However, both numerical and experimental studies in the literature on the subject contain certain limitations. One of the most important of these is that the studies were carried out with constant frequency and only a sine wave. This study examined the effect of this approach on thermoacoustic cooling. Thus, a polypropylene stack is placed in the resonance tube, and experiments were carried out. Air is used as a refrigerant. Five different wave types (sine, square, triangle, sawtooth, and trapeze) were used as wave types; resonance tube diameters were also selected as 50, 70, and 100 mm. The study determined that the resonance tube's diameter to be selected and the wave type were related. For the highest ΔT value, it turned out that the use of a 50 mm tube diameter sine wave, 70 mm tube diameter sawtooth wave, and 100 mm tube diameter trapezoidal wave were more appropriate than the other waveforms. the use of a sawtooth wave instead of a sine wave for the 70 mm tube diameter increased the cooling capacity by 2.61%, and trapezoidal wave usage for 100 mm tube diameter increased by 5.91%.

Design Optimization and Analysis of Thermoacoustic Refrigerators

Thermoacoustic refrigeration, a novel technology, uses eco-friendly gases like helium, air or the mixture of noble gases as working substances in the absence of moving parts. The design, optimization and analysis of thermoacoustic refrigerators using helium and air as oscillating gases are discussed. Pure helium is chosen since it is proven as the best and economical working gas compared to the alternate pure or the mixture of noble gases. Air is chosen since it is abundant in nature and the least cost of the pressurized dry air cylinders. The design optimization strategies discussed in this paper serve as a guide for aspiring researchers in the design and development of thermoacoustic coolers. Cooling power as a function of stack diameter is discussed. Theoretical results of the optimized coolers are compared with DeltaEC simulation results for validation and are in agreement with each other.

The effect of mean pressure on the performance of a single-stage heat-driven thermoacoustic cooler

Abstract Waste heat is an environmental issue in the world. There are some technologies that can be used to recovery the waste heat, one of which is thermoacoustic cooler technology. Thermoacoustic technology can be divided into two parts: one is thermoacoustic engine and cooler. To design the cooler system having high efficiency and lower onset heating temperature, the effect of mean pressure is investigated. By increasing mean pressure from 0.5 to 3 MPa, the heating temperature generating acoustic power can be decreased from 831 to 580 K. Moreover, 15% of Thermodynamic upper limit value of the whole cooler system is achieved.

KIERUNKI ROZWOJU I BADAŃ TERMOAKUSTYCZNYCH URZĄDZEŃ CHŁODNICZYCH Z FALĄ STOJĄCĄ

Chłodzenie termoakustyczne to perspektywiczna technologia, która wykorzystuje energię fali akustycznej do transportu ciepła z ośrodka o niskiej do ośrodka o wysokiej temperaturze. Do głównych zalet tej technologii zalicza się dużą niezawodność, prostą konstrukcję urządzeń, a przede wszystkim brak szkodliwych dla środowiska czynników chłodniczych. Z drugiej strony wadą tej technologii jest relatywnie niska sprawność w porównaniu do współczesnych rozwiązań konwencjonalnych. Głównie z tej przyczyny urządzenia termoakustyczne wciąż pozostają w fazie szerokich badań mających na celu poprawę ich wydajności. W artykule tym przedstawiono kierunki obecnie prowadzanych prac. Uwagę zwrócono zwłaszcza na badania eksperymentalne z zakresu wyboru optymalnych parametrów konstrukcyjnych i eksploatacyjnych termoakustycznych urządzeń chłodniczych z falą stojącą. Omówiono również budowę oraz podstawową zasadę działania takich urządzeń.

Experimental Study of Condensation in a Thermoacoustic Cooler With Various 3D-Printed Regenerators Using Water Vapor as the Working Fluid

Abstract Thermoacoustics (TA) deals with the conversion of heat into sound and vice versa. The device that transfers energy from a low-temperature reservoir to a high-temperature one by utilizing acoustic work is called TA cooler (TAC). The main components of a typical TAC are a resonator, a porous regenerator (e.g., stack of parallel plates), and two heat exchangers. The thermoacoustic phenomenon takes place in the regenerator where a nonzero temperature gradient is imposed and interacts with the sound wave. The low temperature at the cold end of TAC can be used to condense water from the humid air and also reduce the moisture. In the current study, the sound wave with high intensity was produced to drive a TAC to produce cooling power at a cold temperature around 18 °C, using saturated water vapor as the working fluid. The drainage of condensate in the regenerator is the key to the system’s performance. This work is dedicated to investigate the effect from temperature gradient created in TAC on the condensation enhancement, by adopting three different designs of regenerators. A 3D printer was used to design and fabricate different structures of regenerator, and then, the systematic cooling capacity was tested and compared with different regenerators. This work can be extended to evaluate how the TA effect can be affected by the condensation if humid air is directly used as the working fluid. The potential application of this investigation can be an autonomous TAC system for water harvesting in arid areas.

Design of simple refrigerating device for multiparametric analysis of the thermoacoustic cooling phenomenon

Although the widespread introduction of numerical tools and the CFD models have improved the design methodology of thermoacoustic coolers and eased optimization of such units, high computational costs vitally limit their application in parametric analyses of thermoacoustic devices. Thus, experimental investigation remains essential field of research, considering design of such units. In the paper, the design and construction of an experimental setup, dedicated to perform an extensive multiparametric analyses on compact thermoacoustic devices with varying characteristic parameters, is discussed in detail. A complete design path, beginning with general consideration, with further detailed dimensioning and selection of market-available parts, ending with installation of control and data acquisition equipment, is described. Initial testing of the device, performed both computationally at the design stage and experimentally after the final setup assembling, is discussed as well. The results of the tests demonstrated ability to observe the variability in the operational parameters of the cooler following change in number of environmental and constructional parameters. The data acquired indicated vital importance of the stack porosity and frequency of the acoustic wave on performance of the thermoacoustic device, which corresponds to the data presented in the literature.

Working gases based scaling-down limitations for thermoacoustic coolers: Miniaturization approach

Regarding miniaturization of thermoacoustic coolers for thermal management purposes, working gases play a key role as the primary media responsible for producing the so-called “thermoacoustic effect” with their interaction with solid media (i.e., secondary media) within stacks or regenerators. However, the role of working gases in limiting scaling-down of thermoacoustic coolers still needs more investigations compared to addressed operational parameters (i.e., mean pressure, temperature difference across stack, etc.). In the present study, a theoretical computational analysis, based on published literature work, would be conducted to investigate allowable minimum sizes of standing-wave thermoacoustic coolers under the effects of working gases thermo-physical properties with considering adverse effects limitation of thermal conduction losses. Different working gases including air and either pure or mixture noble gases have been used for such geometrical scaling-down analysis under specific operating conditions. Moreover, cooling power was focused here as the more desirable performance indicator rather than the efficiency. The results had revealed the cooling capability at different scale levels based on different working gases, which make gases properties significantly contribute to scalability of thermoacoustic coolers to meet the cooling needs for micro-electronics. In addition, more research work will be devoted to other scaling-down issues of thermoacoustic systems.Regarding miniaturization of thermoacoustic coolers for thermal management purposes, working gases play a key role as the primary media responsible for producing the so-called “thermoacoustic effect” with their interaction with solid media (i.e., secondary media) within stacks or regenerators. However, the role of working gases in limiting scaling-down of thermoacoustic coolers still needs more investigations compared to addressed operational parameters (i.e., mean pressure, temperature difference across stack, etc.). In the present study, a theoretical computational analysis, based on published literature work, would be conducted to investigate allowable minimum sizes of standing-wave thermoacoustic coolers under the effects of working gases thermo-physical properties with considering adverse effects limitation of thermal conduction losses. Different working gases including air and either pure or mixture noble gases have been used for such geometrical scaling-down analysis under specific operating condit...

Design and Analysis of Thermoacoustic Refrigerators Using Air as Working Substance

In this paper, the design of 50 W thermoacoustic refrigerators operating with air as working substance at 10 bar pressure and 3% drive ratio for a temperature difference of 28 K is described. The design strategies discussed in this paper help in design and development of low cost thermoacoustic coolers compared to helium as the working substance. The design and optimization of spiral stack and heat exchangers, and the promising 0.2[Formula: see text] and 0.15[Formula: see text] resonator design with taper and divergent section with hemispherical end are discussed. The surface area, volume, length and power density of the hemispherical end design with air as working substance is found better compared to the published 10 and 50 W coolers using helium as the working substance. The theoretical design results are validated using DeltaEC software simulation results. The DeltaEC predicts 51.4% improvement in COP (1.273) at the cold heat exchanger temperature of [Formula: see text]C with air as working substance for the 50[Formula: see text]W 0.15[Formula: see text]TDH resonator design compared to the published 50[Formula: see text]W 0.25[Formula: see text]TDH resonator design with helium as working substance.

Numerical studies of co-axial travelling-wave thermoacoustic cooler powered by standing-wave thermoacoustic engine

Design and optimisation of a co-axial travelling-wave thermoacoustic cooler (TWTC) powered by a standing-wave thermoacoustic engine (SWTE) is conducted based on the linear thermoacoustic theory. The target application is storage of medical supplies in rural communities of developing countries with no access to electricity grid, where waste heat from cooking can be used as energy input. The design is guided by construction simplicity and low cost. Thus the SWTE/TWTC coupling is enclosed in a constant-diameter resonator which accommodates a compact co-axial configuration of the TWTC. Following earlier experiments, working fluid is air at 10 bar, and operating frequency is 50 Hz. Parameters such as the ratio of the cross-sectional area of the cooler to feedback inertance and stack and regenerator geometries, have been optimised for maximum system efficiency. Here, at the target input power of 600 W a drive ratio of 7.75% can be obtained, leading to the cooling load of 133 W at 250 K. This corresponds to the SWTE thermal-to-acoustic efficiency of 17% and TWTC COP of 1.9, and the combined efficiency of 22.2%. The simulations are to inform the build of an enhanced prototype of the proposed device. A detailed discussion and guidelines for practical builds are provided.