Second law analysis of thermal systems

Numerical investigations of exergy destroyed by operations of a conventional steam power plant and a solar heating system are computed via exergy cascades. Order of magnitude analyses show that exergy destruction in the power plant is dominated by combustion and heat transfer across temperature differences inside the boiler, and conversion of energy entering the turbine/generator sets from thermal to electrical. Exergy destruction in the solar heating system is dominated by heat transfer across temperature difference, when the incoming insolation is degraded to thermal energy. Analyses are also given to compare the exergy cascade to the energy cascade. Efficiencies based on both the first law and second law of thermodynamics are calculated for a number of components and for the plant and the solar heating system. The results show that high first law efficiency does not necessarily mean high second law efficiency. Therefore, the second law analysis has been proven to be a more powerful tool in pinpointing real energy quality losses. The procedure used to determine total exergy destruction and second law efficiency can be used in a conceptual design and parametric study to evaluate the performance of other thermal systems.; Residential winter thermal energy storage (TES) features water encapsulated into 3 inch (7.6 cm) diameter plastic pipes, mounted into conventional stud wall, floor and ceiling cavities of a house. With an air solar collector, solar heated air can be passed through the stud cavities, heating the water. During the discharge mode, this water passively loses its heat directly to the house, and the radiating walls, floors and ceilings allow the residents to feel warm even at lower interior air temperatures.; Empirical and theoretical component performance data are reported for the waterwall, waterfloor and waterceiling TES unit. The interaction between a large air heating solar collector and the TES is considered for the winter heating mode. The collector-storage thermal integration analysis is detailed for a charging flowrate of 40 CFM per cavity. A simpler but reasonably accurate integration analysis is illustrated for 10 CFM/cavity flowrate. Performance parameters indicate that the waterwall, waterfloor and waterceiling TES approach is very compatible with a solar air heater.