S. R. Murrell
Ford Motor Co. Res. Lab., Maildrop 3028 SRL, P.O. Box 2053, Dearborn, MI 48121-2053
Among the critical components of an efficient thermoacoustic device are its heat exchangers. This investigation was undertaken to determine whether it is reasonable to apply values of heat-exchange coefficients, h, estimated from well-known forced-convection correlations obtained in steady flow. The method involves suspending an element of the heat exchanger at a velocity antinode in a standing acoustic wave. Using Joule heating, the element is heated several degrees above the surrounding gas. Upon switching off the heating current, the element's temperature (deduced from its electrical resistance) decays toward ambient. The value of h is extracted both from the amplitude and from the decay time. Measurement of h of single wires was chosen for the initial application of this method. Preliminary results have shown that the coefficient h decreases with increasing frequency to values substantially smaller than those estimated from steady-flow forced-convection correlations.