A detailed transient model of an OTEC evaporator

Ocean thermal energy conversion (OTEC) is a process in which a working fluid is alternately evaporated and condensed in heat exchangers fed by shallow and deep ocean water, respectively. The expansion of the working fluid permits extraction of useful work in a low pressure turbine. Models of the OTEC cycle often consider the evaporator and condenser units simply as having sufficient capacity (steady-state model) or with simple linear low-order models. In this paper, the evaporator is modeled in detail including the nonlinearities of two phase boiling, enthalpy-temperature relationship, and mixed phase fluid flow and heat exchange. The evaporator considered is of the cross-flow type using propane as the working fluid, however, the technique is valid for any channel configuration and working fluid provided that vertical flow exists in the working fluid. The model is used for transient studies in a wide range of working states.