The open homogeneous reactor models (Reactors 4 and 5) also includes an option to represent multiple PSRs that are connected in reactor network. In this case, a very special type of reactor network is formed, which we refer to as a reactor " cluster." The difference is that the reactor "cluster" solution algorithm allows all reactor properties to be solved simultaneously. In this way recycling streams and heat flows between reactors can be included and resolved without external iteration in a computationally efficient manner. In contrast, other reactor networks (between different types of reactor models) involve series simulation of one reactor at time. For the reactor cluster, we assume that the effluent of the preceding reactor is the input to the next PSR by default. The user may add recycling streams and heat flow streams between any two reactors and additional inlets to each reactor. Each PSR in the cluster can have different temperatures, heating rates, volumes, and surface areas, for example. Clusters can be solved in both transient and dynamic modes.