Characterizing heat transfer coefficients for heat exchangers in standing wave thermoacoustic coolers

The thermal performance of heat exchangers within a thermoacoustic cooler was investigated. Experimental procedures and calculation methods to evaluate the oscillating flow heat transfer coefficients were developed. Dimension less heat transfer coefficients, or Colburn-j factors, were estimated based on the oscillating-flow variables and compared with results from steady-flow measurements. The results were also compared with heat transfer coefficients predicted from a boundary-layer conduction model, and methods that utilize steady-flow correlations with Reynolds numbers that characterize oscillating flow conditions. Although the boundary layer model is commonly employed for thermoacoustic calculations, it did not accurately predict heat transfer coefficients and the influence of Reynolds number on heat transfer performance. However, accurate predictions were obtained using a steady-flow con-elation and a modified Reynolds number that accounts for the oscillating flow field, assuming a half-cycle Reynolds number correction value of 0.109. (c) 2005 Acoustical Society of America.