Fangzhong Guo

Ecological Optimization Performance of An Irreversible Quantum Otto Cycle Working with an Ideal Fermi Gas

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.

Optimal performance of an irreversible quantum Brayton refrigerator with ideal Bose gases

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.

Investigation on the oscillation modes in a thermoacoustic Stirling prime mover: mode stability and mode transition

The purpose of this paper is to investigate the stability of oscillation modes in a thermoacoustic Stirling prime mover, which is a combination of looped tube and resonator. Two modes, with oscillation frequencies of 76 and 528 Hz, have been observed, stabilities of which are widely different. The stability of the high frequency mode (HFM) is affected by low frequency mode (LFM) strongly. Once the LFM is excited when the HFM is present, the HFM will be gradually slaved and suppressed by the LFM. The details of the transition from HFM to LFM have been described. The two stability curves of the two modes have been measured. Mean pressure Pm is an important control parameter influencing the mode stability in the tested system.

Optimization criteria for an irreversible quantum Brayton engine with an ideal Bose gas

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* versus efficiency η for the irreversible quantum Brayton engine with heat leakage and other irreversible losses are derived.

Optimization of a Thermoacoustic Engine with a Complex Heat Transfer Exponent

Abstract: Heat transfer between a thermoacoustic engine and its surrounding heat reservoirs can be out of phase with oscillating working gas temperature. The paper presents a generalized heat transfer model using a complex heat transfer exponent. Both the real part and the imaginary part of the heat transfer exponent change the power versus efficiency relationship quantitatively. When the real part of the heat transfer exponent is fixed, the power output P decreases and the efficiency increases along with increasing of the imaginary part. The Optimization zone on the performance of the thermoacoustic heat engine is obtained. The results obtained will be helpful for the further understanding and the selection of the optimal operating mode of the thermoacoustic heat engine. Keywords: Thermoacoustic engine, Complex heat transfer exponent, Optimization zone __________________________________________________________________________________ Introduction A thermoacoustic engine (prime mover and refrigerator) [1-4] is of the advantages of high reliability, low noise, simple construction, non-parts of motion, non-pollution, ability to self-start etc. It can utilize a wide variety of energy resources: solar, geothermal, industrial waste heat and marsh gas. It has very important significance for environmental protection and moderating the tense petroleum needs in the world. With this great potential, the thermoacoustic engine has captivated many engineers

Flow characteristics of a cyclic flow regenerator

Abstract The results of experimental investigations on the cyclic flow characteristic of the regenerator of a split cycle Stirling cryocooler is presented. A mathematical model has been proposed to describe the action of regenerator and other main components of the cryocooler system on its dynamic response.

Acoustically controlled heat transfer of ferromagnetic fluid

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.

Influence of temperature gradient on acoustic characteristic parameters of stack in TAE

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.

Exergy efficiency optimization of a thermoacoustic engine with a complex heat transfer exponent

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.

Temperature difference generated in thermo-driven thermoacoustic refrigerator

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.