近室温热源驱动的气液相变热声发动机

A vapor-liquid phase-change thermoacoustic engine driven by near room-temperature heat source

热声发动机是一种结构简单且运行可靠的新型热机,可直接将热能转化为声波,进而驱动发电或者制冷,具有良好的应用前景.本研究基于对回热器的优化,研制了一台近室温热源驱动的气液相变热声发动机,着重研究了回热器填料的丝网目数和材料对系统起振温度和压比的影响.研究发现,当采用120目的紫铜丝网作为回热器时,以R134a和R1234ze(E)为工质,系统的最低起振温度分别为18.1和26.4°C(对应的冷端温度为11.1和11.3°C);当热端温度为183°C且选用R1234ze(E)作为工质时,采用紫铜丝网的系统输出声波的压比最高可达1.094,与相近热端温度下选用1 MPa的氦气作为工质的单级环路行波型热声发动机相当,而所需的加热功率则明显降低.结果表明,气液相变热声发动机在近室温低品位热源利用方面拥有可观的应用潜力.

Utilization of low-grade heat has attracted considerable attention as an inspiring pathway towards sustainable and lowcarbon energy future.However,low-grade heat,either in the form of natural source or waste heat,is abundantly available but not yet effectively exploited.With the outstanding merits of free maintenance and high reliability,thermoacoustic engine is conceived as one of cost-effective and reliable alternative technologies for low-grade heat recovery.Most recently,two-phase thermoacoustic engine induced increasing interest,thanks to its capability of running across a small temperature difference between heat source and heat sink.In this work,a vapor-liquid phase-change thermoacoustic engine,where the working fluid undergoes periodic condensation and evaporation,is constructed to realize low temperature-differential operation.The engine consists of a looped thermoacoustic unit and a branch resonator,where the former contains a cold heat exchanger,a regenerator,a hot heat exchanger and segments of tubes,while the latter contains a gas reservoir and a load tube.R134 a is adopted as the working fluid in the preliminary study of this thermoacoustic engine,for its boling point near ambient temperature at the operating pressure around 0.5 MPa.Besides,R1234 ze(E)is also used as the working fluid,thanks to its zero ozone depletion potential and low global warming potential.The experiments focus on onset temperature and pressure ratio,since the former determines the lowest grade of usable heat source,while the latter is an essential parameter for evaluating the intensity of pressure oscillation.The results show that an onset temperature of 18.1℃,lowest ever reported,can be achieved with R134 a as working fluid when the regenerator is packed with copper mesh screens.The highest pressure ratio of 1.094 is achieved with R1234 ze(E)as working fluid at a hot temperature of 183℃and a heating power of 200 W,which is comparable to the single-stage looped travelling wave thermoacoustic engine with helium of 1 MPa as working fluid at a similar hot temperature but a much lower heating power.Besides,the onset temperature firstly drops and then rises with the decreasing mesh number of regenerator’s mesh screen,while the pressure ratio always rises.It is also found that regenerator material has marked effect on the engine performance.The engine with copper mesh screen achieves the lowest onset temperature,then stainless steel,and finally nylon.Besides,the cases of pressure ratio are in the increasing order of nylon,stainless steel and copper.The low temperature-differential onset enables the phase-change thermoacoustic engine to harvest the near roomtemperature heat source.Further work on performance optimization of this novel thermoacoustic engine is still necessary and will be our near future work.