[Show abstract][Hide abstract]ABSTRACT: On the basis of exergetic analysis, the performance analysis and optimization of a generalized irreversible thermoacoustic engine with heat resistance, heat leakage, thermal relaxation and internal dissipation, in which heat transfer between the working fluid and heat reservoirs obeys a complex generalized heat transfer law , where n is a complex, is investigated by taking exergetic efficiency as the optimization objective using finite-time thermodynamics. Both the real part and the imaginary part of the complex heat transfer exponent change the optimal exergy efficiency versus power output relationship. Analytical formulas for the exergy efficiency, power output and thermal efficiency of the thermoacoustic engine are derived. Furthermore, comparative analyses of the influences of various factors on optimal performance of the generalized irreversible thermoacoustic engine are carried out with detailed numerical examples. The optimal zone on the performance of the thermoacoustic engine is obtained by numerical analysis. The results obtained herein can provide some theoretical guidelines for the design of a real thermoacoustic engine.
Full-text · Article · Dec 2010 · International Journal of Sustainable Energy
[Show abstract][Hide abstract]ABSTRACT: A thermoacoustic refrigeration device (TAR) includes an acoustic wave generation device arranged directed to the channel of a hollow tube, and a regenerator provided at a predetermined position in the channel of the tube. A temperature gradient is obtained across the regenerator by an acoustic wave emitted from the acoustic wave generation device. Therefore, a TAR realizing a gas Stirling cycle approximating the Carnot cycle which is an ideal gas cycle, and realizing simplification of the structure and high efficiency of the device is provided.
[Show abstract][Hide abstract]ABSTRACT: This article has been retracted. Please see Elsevier Policy on Article Withdrawal (http://www.elsevier.com/locate/withdrawalpolicy).
Reason: The Editors would like to confirm the retraction of this paper at the request of the Authors. This article was a duplication of a paper that had already appeared in Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science, Vol. 221, 1339-1343 (2007) doi: 10.1243/09544062JMES739. The authors would like to apologize for this administrative error on their part.
[Show abstract][Hide abstract]ABSTRACT: An Otto cycle working with an ideal Bose gas is called a Bose Otto cycle. The internal irreversibility of the cycle is included in the factors of internal irreversibility degree. The quantum degeneracy effect on the performance of the cycle is investigated based on quantum statistical mechanics and thermodynamics. Variations of the maximum work output ratio RW and the efficiency ratio y with temperature ratio τ are examined, which reveal the influence of the quantum degeneracy of the working substance on the performance of a Bose Otto cycle. It is shown that the results obtained herein are valid under both classical and quantum ideal gas conditions.
Full-text · Article · Nov 2006 · Energy Conversion and Management
[Show abstract][Hide abstract]ABSTRACT: The purpose of this paper is to study the optimal performance for an irreversible quantum Brayton engine consisting of two constant-frequency branches connected by two irreversible adiabatic branches. The solution of the generalized quantum master equation of a thermal system is obtained in the Heisenberg picture. The optimization region (or criteria) for an irreversible quantum Brayton engine is obtained. The relationship between the dimensionless power output P<sup>*</sup> versus efficiency η for the irreversible quantum Brayton engine with heat leakage and other irreversible losses are derived.
[Show abstract][Hide abstract]ABSTRACT: This paper presents a model of an irreversible quantum Brayton refrigerator (IQBR) using ideal Bose gases as working fluid. The optimal relationship between the dimensionless cooling rate and the coefficient of performance, and the optimization region (or criteria) for an IQBR is obtained. The effects of heat leakage, irreversibility in two adiabatic processes and the quantum characteristic of the working fluid are discussed.
[Show abstract][Hide abstract]ABSTRACT: The model of an irreversible Otto cycle using an ideal Fermi gas as the working fluid, which is called as the irreversible
Fermi Otto cycle, is established in this paper. Based on the equation of state of an ideal Fermi gas, the ecological optimization
performance of an irreversible Fermi Otto cycle is examined by taking an ecological optimization criterion as the objective,
which consists of maximizing a function representing the best compromise between the exergy output and exergy loss (entropy
production) of the cycle. The relationship between the ecological function E and the efficiency η is studied. Three special
cases are discussed in detail. The results obtained herein may reveal the general performance characteristics of the irreversible
Fermi Otto cycle.
Full-text · Article · Feb 2006 · Open Systems & Information Dynamics
[Show abstract][Hide abstract]ABSTRACT: As a novel refrigerator, piezoelectricity-driven miniature thermoacoustic refrigerator can be miniaturized and used in miniature electric components. Design method of the miniature refrigerator is presented in this paper. The design calculation model is first built in order to design the refrigerator. The active network model of thermoacoustic refrigerator is given and used in design calculation. In design, the pin-array stack is chosen as the heat-pump stack. Its pin spacing is optimized in terms of maximum cool power factor and minimal dissipation power factor. The length and the position are designed by the network model on the basis of the coefficient of performance (COP). Then the heat exchangers between the two ends of the stack can be designed by the same method. The design method considers the influence of the stack and heat exchanger on the acoustic field.
No preview · Article · Dec 2005 · Acta Acustica united with Acustica
[Show abstract][Hide abstract]ABSTRACT: In this paper, the frequency characteristic of loudspeaker-driven thermoacoustic refrigerator (TAR) and the influence factors were investigated theoretically and experimentally. Experimental results under different conditions show that a narrow transmission frequency band of TAR exists to generate strong oscillation and cause significant thermoacoustic effect, and TAR achieves optimum performance at the resonance frequency. The frequency characteristic is determined by combined network elements of TAR. Then the analytical model was built to validate the experimental results. It provides a coupling method for design of loudspeaker-driven TAR system.
[Show abstract][Hide abstract]ABSTRACT: The phase space method is used in studying a thermo-acoustic heat engine in this paper. The maximum Lyapunov exponent is used to quantify the phase space that is reconstructed from the pressure signal of the thermo-acoustic heat engine. For quantifying the system change, the maximum Lyapunov exponents of the reconstructed pressure phase space trails are calculated. The plot of the maximum Lyapunov exponents versus time is attained. Good agreement between the plot and the evolving process of the real physical phenomenum indicates that the maximum Lyapunov exponents can reflect the state changes of the thermo-acoustic heat engine.
No preview · Article · Aug 2004 · Energy Conversion and Management
[Show abstract][Hide abstract]ABSTRACT: Thermodynamic mechanism of thermoacoustic self-excited oscillation is analyzed in this paper. The law of minimizing entropy flow is obtained basing on the fundamentals of finite-time thermodynamics. The results obtained here show that the thermoacoustic self-excited oscillation, which is a non-isentropic oscillation with power output corresponding to a limit cycle in the phase space takes place when hot temperature T
h exceeds a threshold value T
*. The effect of nonlinear terms on the system will lead to the second harmonic wave.
No preview · Article · Nov 2003 · Open Systems & Information Dynamics
[Show abstract][Hide abstract]ABSTRACT: The work proposes a simple and feasible calculation method––network model method to calculate temperature differences generated in thermo-driven thermoacoustic refrigerator (TAR). The theoretical calculation model is first built. The network model is given and used to make numerical calculations under different conditions including heat-pump stack positions in TAR, different oscillating pressure ratios (PR), plate spacings and different stack geometries. Theoretically calculated results show that the former two factors make significant influence on temperature differences, the influence of stack spacing on temperature difference has relation with PR, and cooling effect of pin-array stack is superior to that of parallel plate stack under other same conditions. Furthermore, theoretically calculated results and experimentally measured data are in good agreement at small acoustic pressure amplitude.
[Show abstract][Hide abstract]ABSTRACT: Acoustic characteristic parameters, i.e. propagation constants, characteristic impedance, and transmission loss are used to describe acoustic characteristics of the stack in a thermo-acoustic engine. The transfer-matrix equations of the thermo-acoustic stack and additional stacks are established. Then the expressions of their important acoustic characteristic parameters are derived. Theoretical calculation results show that the imposed temperature gradients have an influence on the acoustic characteristic parameters of the two kinds of stacks. For additional stacks, due to no longitudinal temperature gradients, thermo-acoustic source α is zero. The expressions for the propagation constant and characteristic impedance are specialized to the thermo-acoustic stack. Theoretical calculation results of the acoustic characteristic parameters of the thermo-acoustic stack are presented to verify the application of the model built in this paper.
No preview · Article · Jul 2003 · International Journal of Engineering Science
[Show abstract][Hide abstract]ABSTRACT: A traveling wave thermoacoustic engine consisting of a loop tube with a resonator has been tested. The onset characteristic
together with the transition of oscillation mode from traveling wave to standing wave and the periodic shifting between modes
in this system are investigated experimentally. The process of self-sustained thermoacoustic oscillation in this heat engine
is described and analyzed through phase space distribution reconstructed from the time series of acoustic signal.
No preview · Article · Jan 2003 · Journal of Thermal Science
[Show abstract][Hide abstract]ABSTRACT: The purpose of this paper is to study the optimal performance for an irreversible quantum Stirling cooler with heat leak and
other irreversible losses. The relationship between the optimal cooling load and the coefficient of performance (COP) for
the quantum Stirling cooler is derived. The maximum cooling load and the corresponding COP, as well as the maximum coefficient
of performance and the corresponding cooling load are obtained. The experimental observation for the optimal region is provided.
No preview · Article · Jul 2002 · Journal of Thermal Science
[Show abstract][Hide abstract]ABSTRACT: The network model consisting of series impedance, shunted admittance, current controllable current source and magnet controllable pressure source for two-phase oscillating flow by magnet control is established. The relationship between the output and input of the network is obtained by means of the transmission matrix of the network. The physical significance of the network parameters are revealed.
Full-text · Article · Jun 2002 · Open Systems & Information Dynamics
[Show abstract][Hide abstract]ABSTRACT: The temperature field of a traveling wave in a system is analyzed. The system consists of a rapidly moving small specimen tube and sub-cooled liquid nitrogen (SLN2). The temporal and spatial temperature distribution of the subsonic wave is investigated. The relationship between a dimensionless cooling rate and the thermal Mach number (M) is derived. When the quenching speed of sample tube in the sub-cooled liquid nitrogen is equal to or faster than that of the thermal wave propagated, a shock wave is expected.
No preview · Article · Mar 2002 · International Journal of Engineering Science
[Show abstract][Hide abstract]ABSTRACT: A traveling wave thermoacoustic-driven system with a designed resonant frequency of 200 Hz has been established. Nonlinear
thermoacoustic phenomena, such as the oscillation onset temperature and shifts of the resonant frequency, are presented. Experimental
investigations have been conducted by changing wire-screen mesh size, working gases, and mean pressures, and the effects have
been noted on temperature profiles, oscillation modes, frequency jumps, and pressure amplitudes. The analysis indicates that
the relative penetration depth ratio (δv/rh) plays an important role with these nonlinear phenomena.
[Show abstract][Hide abstract]ABSTRACT: The acoustically controlled heat transfer enhancement of a ferromagnetic fluid in an external magnetic field is studied in this paper. The analytical expression for the effective thermal diffusivity is obtained. The numerical analysis and experimental results are discussed.
Preview · Article · Dec 2001 · International Journal of Heat and Mass Transfer