Design of thermoacoustic refrigerators
TL;DR: The design strategy described in this paper is a guide for the design and development of thermoacoustic coolers and the optimization of the different parts of the refrigerator will be discussed.
About: This article is published in Cryogenics.The article was published on 2002-01-01 and is currently open access. It has received 165 citations till now. The article focuses on the topics: Refrigeration.
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TL;DR: In this paper, the authors describe the construction and performance of a thermoacoustic refrigerator, which consists of three major parts: the refrigerator, the electronic apparatus necessary for the measurements and acquisition of the experimental data, and the gas-control panel which is used to fill and purge the system and to prepare gas mixtures.
100 citations
TL;DR: A quantitative experimental investigation into the effect of the pore dimensions on the performance of thermoacoustic devices is reported and it is concluded that a plate spacing in the stack of about three times the penetration depth should be optimal for thermoACoustic refrigeration.
Abstract: The characteristic pore dimension in the stack is an important parameter in the design of thermoacoustic refrigerators. A quantitative experimental investigation into the effect of the pore dimensions on the performance of thermoacoustic devices is reported. Parallel-plate stacks with a plate spacing varying between 0.15 and 0.7 mm are manufactured and measured. The performance measurements show that a plate spacing in the stack of 0.25 mm (2.5 deltak) is optimum for the cooling power. A spacing of 0.4 mm (4 deltak) leads to the lowest temperature. The optimum spacing for the performance is about 0.3 mm (3 deltak). It is concluded that a plate spacing in the stack of about three times the penetration depth should be optimal (3 deltak) for thermoacoustic refrigeration.
96 citations
TL;DR: In this article, a comprehensive design and optimization algorithm is developed for designing thermoacoustic devices that can serve as sustainable refrigeration systems, and new features based on the energy balance are also included to design individual thermo-acoustic engines and acoustically-driven thermoACoustic refrigerators.
89 citations
TL;DR: In this paper, the feasibility of using thermoelectric coolers (TECs) in a dehumidification system to condense atmospheric moisture and generate renewable freshwater was investigated.
80 citations
TL;DR: In this article, a two-dimensional computational fluid dynamics (CFD) simulation study of a traveling-wave thermo-acoustic engine is presented, which shows an increase of the dynamic pressure when a linear temperature difference is applied across the regenerator.
Abstract: A two-dimensional computational fluid dynamics (CFD) simulation study of a traveling-wave thermoacoustic engine is presented. The computations show an increase of the dynamic pressure when a linear temperature difference is applied across the regenerator. An amplification of the acoustic power through the engine is also illustrated. A satisfactory agreement between the calculated and expected gains of the traveling-wave thermoacoustic engine is obtained. The expected gain is defined as the ratio of the absolute temperatures at the ends of the regenerator. Nonlinear phenomena that cannot be captured by existing linear theory, like streaming mass flows and vortices formation, are also visualized. It is concluded that CFD codes could be used in the future to predict and optimize thermoacoustic systems. This is an important step towards the development of nonlinear simulation tools for the high-amplitude thermoacoustic systems that are needed for practical use.
78 citations
Cites background from "Design of thermoacoustic refrigerat..."
...R R dy dp = − = B + ( 4 ) where u and v are the gas velocities in the x- and y-directions respectively....
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References
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Proceedings Article•
01 Jan 1991TL;DR: In this paper, an approximate analysis of energy flow and acoustical measurements of a thermoacoustic prime mover with arbitrary cross-sectional geometry is given. But this analysis is restricted to the case of TAEs with circular or parallel slit pore geometry.
Abstract: Thermoacoustic engines (TAEs) can be used to pump heat using a sound wave or pump a sound wave using a temperature gradient. The basic arrangement is a gas-filled acoustic resonator with appropriately positioned thermoacoustic elements. Two types of thermoacoustic elements are used in these engines: (1) heat exchangers used to communicate heat between the gas and external heat reservoirs; and (2) the TAE, also known as a stack. The TAEs are sections of porous media that support the temperature gradient, transport heat on the acoustic wave between the exchangers, and produce or absorb acoustic power. Previous results have been developed for TAEs with circular or parallel slit pore geometries. The theory is extended for gas-filled TAEs to include pores of arbitrary cross-sectional geometry. An approximate analysis of energy flow and acoustical measurements of a thermoacoustic prime mover are given. >
821 citations
"Design of thermoacoustic refrigerat..." refers background in this paper
...Olson and Swift [5] wrote a paper about similitude and dimensionless parameters for thermoacoustic devices....
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...The exact theoretical expressions of the acoustic power and cooling power in the stack are complicated, so one can try to use the simplified expressions deduced from the short stack, and boundary-layer approximations [1,3]....
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...The boundary-layer and short-stack approximations assume the following [1,3]:...
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...In practice the stack material can be chosen so that the thermal conductive term in the heat flow expression can be neglected [1]....
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...As the power density in the thermoacoustic devices is a linear function of the acoustic resonance frequency [1] an obvious choice is thus a high resonance frequency....
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TL;DR: In this paper, the authors used hot wires and flow visualization by means of smoke, and provided new details on turbulence in a Stokes layer, showing that turbulence occurs in the form of periodic bursts which are followed by relaminarimtion in the same cycle and do not lead to turbulent flow during the whole cycle.
Abstract: Published results on transition in a Stokes layer indicate a wide range of transition Reynolds numbers. As thermal effects in a resonance tube (Merkli & Thomann 1975) depend on the state of the boundary layer, the transition Reynolds number was determined, and a critical Reynolds number Ac ≈ 400 was found. The observations were made with hot wires and with flow visualization by means of smoke, and provide new details on turbulence in a Stokes layer. With this knowledge an explanation of the large discrepancies between some stability theories and the experiments is suggested. The main point is that turbulence occurs in the form of periodic bursts which are followed by relaminarimtion in the same cycle and do not lead to turbulent flow during the whole cycle.A further, unexpected result of the present investigation is the discovery of vortex patterns superimposed on the normal laminar acoustic motion.
282 citations
TL;DR: In this paper, a reciprocating oscillatory turbulent flow in a rectangular duct is investigated experimentally by making use of a laser-Doppler velocimeter, hot-wire anemometers as well as electronic digital sampling and processing equipments.
Abstract: A reciprocating oscillatory turbulent flow in a rectangular duct is investigated experimentally by making use of a laser-Doppler velocimeter, hot-wire anemometers as well as electronic digital sampling and processing equipments.The profiles of the mean velocity, the turbulence intensities, the Reynolds stress and the turbulent-energy production rate are compared for the accelerating and decelerating phases.The characteristics of such a flow are quite different from wall turbulence which is steady in the mean. In the accelerating phase, turbulence is triggered by the shear instability at a slight distance from the wall but is suppressed and cannot develop. However, with the beginning of flow deceleration, turbulence grows explosively and violently and is maintained by the bursting type of motion.The turbulent-energy production becomes exceedingly high in the decelerating phase, but the turbulence is reduced to a very low level at the end of the decelerating phase and in the accelerating stage of reversal flow. Spectra and spatial correlations for the various phases are compared. The spectral decay in the high-frequency range for the decelerating phase with high turbulence is far steeper than that of Kolmogorov's −5/3 power law, indicating remarkably high energy dissipation by high-frequency turbulence.Notwithstanding the great difference between the ensemble-averaged characteristics of the oscillatory flow and those of steady wall turbulence, its basic processes such as ejection, sweep and interactions directed towards and away from the wall are the same as those of ‘steady’ wall turbulence.
264 citations
TL;DR: In this paper, the authors used a two-colour laser-Doppler anemometer to measure Axial and radial velocity components of turbulent flow in a circular pipe for the range of Reynolds numbers Reδ = U0δ/ν (U0 = amplitude of cross-sectional mean velocity, δ = (2ν/ω)½) = Stokes layer thickness) from 550 to 2000 and Stokes parameters Λ = R/δ (R = radius of the pipe) from 5 to 10.
Abstract: Experimental results on flow-field statistics are presented for turbulent oscillatory flow in a circular pipe for the range of Reynolds numbers Reδ = U0δ/ν (U0 = amplitude of cross-sectional mean velocity, δ = (2ν/ω)½) = Stokes layer thickness) from 550 to 2000 and Stokes parameters Λ = R/δ (R = radius of the pipe) from 5 to 10. Axial and radial velocity components were measured simultaneously using a two-colour laser-Doppler anemometer, providing information on ensemble-averaged velocity profiles as well as various turbulence statistics for different phases during the cycle. In all flows studied, turbulence appeared explosively towards the end of the acceleration phase of the cycle and was sustained throughout the deceleration phase. During the turbulent portion of the cycle, production of turbulence was restricted to the wall region of the pipe and was the result of turbulent bursts. The statistics of the resulting turbulent flow showed a great deal of similarity to results for steady turbulent pipe flows; in particular the three-layer description of the flow consisting of a viscous sublayer, a logarithmic layer (with von Karman constant = 0.4) and an outer wake could be identified at each phase if the corresponding ensemble-averaged wall-friction velocities were used for normalization. Consideration of similarity laws for these flows reveals that the existence of a logarithmic layer is a dimensional necessity whenever at least two of the scales R, u*/ω and ν/u* are widely separated; with the exact structure of the flow being dependent upon the parameters u*/Rω and u2*/ων. During the initial part of the acceleration phase, production of turbulence as well as turbulent Reynolds stresses were reduced to very low levels and the velocity profiles were in agreement with laminar theory. Nevertheless, the fluctuations retained a small but finite energy. In Part 2 of this paper, the major features observed in these experiments are used as a guideline, in conjunction with direct numerical simulations of the ‘perturbed’ Navier–Stokes equations for oscillatory flow in a channel, to identify the nature of the instability that is most likely to be responsible for transition in this class of flows.
237 citations
219 citations
"Design of thermoacoustic refrigerat..." refers methods in this paper
...DeltaE solves the exact thermoacoustic equations in a geometry given by the user, using the boundary conditions for the different variables....
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...The computer program DeltaE [19] can be used to predict the performance of our refrigerator....
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