The purpose of this paper is to present results of numerical simulations of thermoacoustic effects on isothermal plates that are "short" and "long" compared with the particle displacement lengths of the acoustic standing waves. As well as varying the plate length, the plate spacing was varied. Results are presented mainly in the form of energy density flux distributions, instantaneous velocity fields, particle paths and overall entropy generation rates. The results indicate that thermoacoustic effects diminish on long plates as the plate spacing is reduced while for short plates, thermoacoustic effects occur even with plate spacing is as small as the thermal penetration depth. The results from this study provide a useful insight into the energy flow in thermoacoustic devices and will be of interest to designers of heat exchangers in thermoacoustic engines.