  This paper is concerned with the stabilization of parallel-flow heat
exchangers equation with boundary control and arbitrarily delayed observation.
The observer and predictor-based method, developed by [B.Z. Guo, K.Y. Yang,
Automatica, 2009, 45(6): 1468-1475], is used to stabilize equation. The
exponentially stabilization of such system by estimated state feedback control
law is proved.
