| Thermoacoustic heat engine is a new type of energy conversion equipment.Because of its simple structure,high reliability,no-pollution,no moving parts and so on,which attracted many researchers.Thermoacoustic engine mainly make up of cold heat exchanger,hot heat exchanger,regenerator and resonant tube.The role of cold and hot heat exchanger is to make both ends of the regenerator form a temperature gradient,which is the fundamental reason of the thermoacoustic effect.Therefore,thermoacoustic heat exchangers are the focus and difficultly of thermoacoustic conversion.At present,there are few researches on the theoretical analysis and numerical calculation of thermoacoustic heat exchangers.However,compared with most of heat exchangers,most of which are according to the correlation equation of steady flow,which is not applicable to oscillatory fluid heat exchanger this paper is based on the study of previous research results and continue the study in thermoacoustic heat exchanger on following aspects:Using the method of finite-time thermodynamics,the circulatory system of the irreversible thermoacoustic heat engine under the complex heat transfer discipline is established.Analysis of the entropy generation and the entransy dissipation theory in the heat exchanger is carried out and theoretical analysis and numerical simulation to study the oscillating flow heat exchanger related characteristics.The results show that the characteristic parameters,geometry structure and operating conditions of the thermoacoustic heat exchanger have effects on the entransy dissipation number and entropy generation.With the increase of the NTU and the effective degree,the entransy dissipation number decreases,the simulation shows that the counter flow heat exchange method is smaller than that of the parallel flow heat exchange method.From the perspective of flow field and temperature field,the optimization of convective heat transfer is studied.On the basis of this,the field synergistic principle of heat exchange enhancement is put forward,which can better understand the nature of the current convection heat transfer and heat transfer enhancement and provide a new kind of the heat transfer enhancement technology.At the same time,this paper proposes the concept of field synergy number and studies the influence of each parameter on field synergy number,so as to optimize the heat exchange performance.The results show that: the cosine of included angle between temperature gradient vector and velocity vector is increased,and the included angle of the vector is far away from 90℃.When the temperature and velocity are constant,the fluid velocity and temperature are distributed as uniformly as possible.Based on the existing experimental bench of the research group,the influence of the heating temperature on pressure wave amplitude,the resonant frequency and dimensionless oscillation temperature were studied.The experimental results show that the higher the heating temperature,the higher the resonance frequency,the amplitude of the pressure wave and the dimensionless oscillation temperature increase,and the improvement of the parameters can improve the overall performance of the thermoacoustic device.At the same time,the numerical calculation of the temperature in the thermoacoustic heater exchanger was verified. |
