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UTC Fuel Cells recently developed a freeze capable fuel cell power plant for automotive applications. Steady state and dynamic system models were developed for design and performance characterization. The results of the power plant performance testing indicate very good agreement with these models. Testing showed that the power plant achieves stable performance at all power levels including low power holds. UTC Fuel Cells’ cell stack technology enables operation of the power plant at near-ambient pressure. Additionally the low system pressure drop allows the power plant to achieve very high electrical efficiencies at all power levels. The peak efficiency is about 58% at approximately 20% of rated power. Since the power plant does not require compressors, the auxiliary power requirement and acoustic noise level for the system are also low. The cell stack’s capability of internal water management and ability to operate at low reactant stoichiometric ratio result in a very stable and predictable transient capability to ramp up from low power to rated power in < 2 sec and also to step down from rated power to low power levels instantaneously in a stable manner.

A method for finding the best (optimal) operating layout of heat exchangers in complicated thermal networks is developed in this paper. Computer algorithms are developed that take advantage of pinch technology and economic considerations, and exergetic constraints as well as conventional heat and mass balances. Our goals were to achieve minimum loss of exergy between hot and cold streams subject to practical system constraints. Furthermore, resulting networks should be limited to no more units than the theoretical minimum. The ultimate goal was to minimize investment and operating costs for a set of fixed overall system constaints. These goals were realized by developing a computer-based nonlinear multiple objective optimization algorithm that included the elements discussed above. The final solution is a synthesis of the best system using the above-described mathematical formulation. Results for a 4-stream heat exchanger network are presented in terms of the minimum temperature difference at the pinch point. The influence of the minimum temperature difference on capital cost, heat transfer area, exergetic losses and second law efficiency of various heat exchangers in the network is presented.

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