PLIF measurement of instantaneous temperature field within thermoacoustic heat exchangers

A typical standing-wave thermoacoustic device consists of a stack of parallel plates sandwiched between the cold and hot heat exchangers, which are placed in an appropriately designed acoustic resonator. The cold and hot heat exchangers work as a heat sink and heat source, respectively, which allows the thermoacoustic energy conversion to take place in the stack. Unfortunately, the performance of heat exchangers in the oscillatory flow is difficult to predict, as most of the available handbook data relate to steady flows, while the experimental studies are very limited. This paper investigates the temperature field around the fins of a pair of model heat exchangers placed in an acoustic resonator, using acetone-based Planar Laser Induced Fluorescence (PLIF). The fins are kept at constant temperatures by virtue of resistive heating and water cooling, respectively. The overall objective of the work is to develop reliable measurement methods to obtain the time-dependent local convection heat transfer coefficients and ultimately the corresponding Nusselt numbers estimated from the temperature gradients in the thermal boundary layer. Some preliminary results comprising the instantaneous temperature distributions within the flow field are presented together with estimates of heat flux calculations to illustrate the methodology. A discussion of measurement accuracy and future work to improve the measurement technique proposed is provided.