Spatial correlations in bounded nonequilibrium fluid systems

We study the influence of boundaries on the equal-time thermal correlations in a three-dimensional fluid maintained under a constant temperature gradient. Within the confines of the model for an idealized fluid bounded by two infinite, parallel walls, we show that it is crucial to retain the unbounded spatial components in the problem so that the solutions approach meaningful results as we move the walls infinitely far apart. In addition, we consider a composite system by including the dynamics of the {open_quotes}walls,{close_quotes} and we investigate the conditions for the relevant physical parameters under which the details of wall dynamics may be neglected by employing the simple boundary condition {delta}T=0.