OPTIMUM OPERATION FOR DIFFERENT DESIGN CONDITIONS OF A SINGLE PRESSURE HEAT RECOVERY STEAM GENERATOR (HRSG) FOR MINIMUM ENTROPY GENERATION
Heat Recovery Steam Generator (HRSG) is the critical link between the “topping” gas and “bottoming” steam power cycle of a combined power plant. Depending on the mass flow and property of exhaust flue gas from the gas cycle, optimum design and operation, for minimum entropy generation in a single pressure HRSG generating superheated steam is reported in this paper. It shows that an optimum pressure of steam generation exists for minimum entropy generation. The interdependence between the physical size (and hence cost) of different heat transfer components of HRSG with the thermodynamic optimum operation for minimum entropy generation is presented. Optimum pressure of steam generation increases with greater size of super heater, economizer and evaporator up to certain limit, beyond which the increase in optimum saturation pressure is marginal with increase in size of the heat transfer units. However, increasing evaporator size and degree of superheat have the adverse effect of lesser steam generation for a given economizer and super heater for minimum entropy generation.
Second law analysis of a waste heat recovery steam generator
In recent years a great deal of attention is focussed on the efficient utilization of energy resources with minimum heat loss. There is a growing interest on second law analysis to minimize the entropy generation in various thermal units and thereby to improve and optimize the design and performance. In the present work, a waste heat recovery steam generator is considered, which consists of an economizer, an evaporator and a super heater. The unit produces superheated steam by absorbing heat from the hot flue gases. A general equation for the entropy generation has been proposed, which incorporates all the irreversibilities associated with the process. By using suitable non-dimensional operating parameters, an equation for entropy generation number is derived. The effect of various non-dimensional operating parameters, on the entropy generation number are investigated. The role of gas specific heat, non-dimensional inlet gas temperature difference ratio (τ), heat exchanger unit sizes (NTUB, NTUS, NTUE) on entropy generation number are also reported. The results will help to understand the influence of different non-dimensional operating parameters on entropy generation number, which in turn will be useful to optimize the performance of the unit.
Synergistic and antagonistic combinations of drugs in human prostate cancer cell lines in vitro
Microtubulin binding agents such as docetaxel have significant preclinical and clinical activity in the treatment of hormone-refractory prostate cancer. We have previously used median-effect analysis in vitro to define both synergistic and antagonistic drug combinations which may be of value in management of human disease. These studies extend our findings in defined prostate cancer cell lines. A semi-automated microtiter culture system was used. Docetaxel was combined with 18 other agents, incubated with DU 145, LnCaP or PC 3 prostate cancer cell lines for 72 h and the cells then incubated with MTT to determine cytotoxic effect. Both doublet and triplet combinations were examined. Synergy and antagonism as measured by the combination index were determined for each combination. The non-mutually exclusive criterion was applied. Docetaxel demonstrated cytotoxic additive effects or synergy with cis-retinoic acid, cyclosporin A and vinorelbine in all three cell lines. Docetaxel combined with either epirubicin or doxorubicin displayed cytotoxic synergistic effects in hormone-refractory DU 145 and PC 3 cell lines. In contrast, drugs which have been combined clinically to treat hormone-refractory prostate cancer, i.e. cisplatin, carboplatin or etoposide, were antagonistic when combined with docetaxel. We conclude that combinations of docetaxel with either cis-retinoic acid or vinorelbine may offer an enhanced cytotoxic effect in the management of hormone-refractory prostate cancer and need to be evaluated for therapeutic effect. The combination of docetaxel with an anthracycline was also synergistic in the two hormone-refractory cell lines, DU 145 and PC3, thus suggesting a potential role in advanced disease after endocrine failure. Combinations of docetaxel with platinum or etoposide may lead to subadditive effects in treatment.