## Abstract

The research effort is focused on (1) the development of carefully designed experimentation for investigating on the thermal-fluid processes controlling heat transfer in thermoacoustic heat exchangers on the micro-scale of the individual plates/pores/channels and on (2) the implementation of CFD modeling capabilities to capture the physics of thermal-fluid processes in the micro-scale and to validate the models against the experimental data. Planar Laser Induced Fluorescence (PLIF) and Particle Image Velocimetry (PIV) techniques are applied to obtain spatially and temporally resolved temperature

and velocity fields within the thermoacoustic HX samples. On the basis of recorded temperature fields, the experimental data are processed to obtain the local and global, phase-dependent heat transfer rates and Nusselt numbers, and their dependence on the Reynolds number of the oscillating flow. A two-dimensional low Mach number computational model is implemented to

analyze the time-averaged temperature field and heat transfer rates in a representative domain of the HXs. These last are generated by integrating the thermoacoustic equations of the standard linear theory into an energy balance-based numerical calculus scheme. The comparative analysis of the experimental and numerical temperature and heat transfer distributions suggests that the optimal performance of heat exchangers can be achieved when the gas displacement amplitude is close to the length of hot and cold heat exchanger. Heat transfer coefficients from the gas-side can be predicted with a confidence of about 41% at moderate acoustic Reynolds numbers. Better estimates could be achieved if entrance/exit effects localized at the resonator-HX cross section interfaces and giving rise to complex non-linear temperature and flow patterns (turbulent and vorticity flows) are taken into account. These effects are responsible for considerable heat losses from the couple of HXs to the

surrounding environment (hot and cold ducts).

and velocity fields within the thermoacoustic HX samples. On the basis of recorded temperature fields, the experimental data are processed to obtain the local and global, phase-dependent heat transfer rates and Nusselt numbers, and their dependence on the Reynolds number of the oscillating flow. A two-dimensional low Mach number computational model is implemented to

analyze the time-averaged temperature field and heat transfer rates in a representative domain of the HXs. These last are generated by integrating the thermoacoustic equations of the standard linear theory into an energy balance-based numerical calculus scheme. The comparative analysis of the experimental and numerical temperature and heat transfer distributions suggests that the optimal performance of heat exchangers can be achieved when the gas displacement amplitude is close to the length of hot and cold heat exchanger. Heat transfer coefficients from the gas-side can be predicted with a confidence of about 41% at moderate acoustic Reynolds numbers. Better estimates could be achieved if entrance/exit effects localized at the resonator-HX cross section interfaces and giving rise to complex non-linear temperature and flow patterns (turbulent and vorticity flows) are taken into account. These effects are responsible for considerable heat losses from the couple of HXs to the

surrounding environment (hot and cold ducts).

Original language | English |
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Title of host publication | Proceedings of 66th National Congress of Associazione Termotecnica Italiana (ATI) |

Number of pages | 9 |

Publication status | Published - 5 Sep 2011 |

Externally published | Yes |