Refrigeration system holds an important role in process industries. The optimal synthesis cannot only reduce the energy consumption, but also save the production costs. In this study, a general methodology is develope...Refrigeration system holds an important role in process industries. The optimal synthesis cannot only reduce the energy consumption, but also save the production costs. In this study, a general methodology is developed for the optimal design of refrigeration cycle and heat exchanger network(HEN) simultaneously. Taking the heat integration between the external heat sources/sinks and the refrigeration cycle into consideration, a superstructure with sub-coolers is developed. Through defining logical variables that indicate the relative temperature positions of refrigerant streams after sub-coolers, the synthesis is formulated as a Generalized Disjunctive Programming(GDP) problem based on LP transshipment model, with the target of minimizing the total compressor shaft work in the refrigeration system. The GDP model is then reformulated as a Mixed Integer Nonlinear Programming(MINLP) problem with the aid of binary variables and Big-M Constraint Method. The efficacy of the process synthesis model is demonstrated by a case study of ethylene refrigeration system. The result shows that the optimization can significantly reduce the exergy loss as well as the total compression shaft work.展开更多
Surplus production models are the simplest analytical methods effective for fish stock assessment and fisheries management. In this paper, eight surplus production estimators(three estimation procedures) were tested o...Surplus production models are the simplest analytical methods effective for fish stock assessment and fisheries management. In this paper, eight surplus production estimators(three estimation procedures) were tested on Schaefer and Fox type simulated data in three simulated fisheries(declining, well-managed, and restoring fisheries) at two white noise levels. Monte Carlo simulation was conducted to verify the utility of moving averaging(MA), which was an important technique for reducing the effect of noise in data in these models. The relative estimation error(REE) of maximum sustainable yield(MSY) was used as an indicator for the analysis, and one-way ANOVA was applied to test the significance of the REE calculated at four levels of MA. Simulation results suggested that increasing the value of MA could significantly improve the performance of the surplus production model(low REE) in all cases when the white noise level was low(coefficient of variation(CV) = 0.02). However, when the white noise level increased(CV= 0.25), adding the value of MA could still significantly enhance the performance of most models. Our results indicated that the best model performance occurred frequently when MA was equal to 3; however, some exceptions were observed when MA was higher.展开更多
The objective of this study was to determine the influence of production and consumption characteristics of improved sorghum varieties on farmers＇ adoption decisions. Thirty-four farmers and 231 consumers evaluated f...The objective of this study was to determine the influence of production and consumption characteristics of improved sorghum varieties on farmers＇ adoption decisions. Thirty-four farmers and 231 consumers evaluated five sorghum varieties to determine their preferences. The perceptions of the farmers and consumers were summarized and presented to 100 sorghum farmers to help them choose the best varieties, based on results obtained earlier. Ordered probit models were used to predict their adoption decisions. Results indicated that when adoption is predicted on production characteristics alone the adoption rate was lower than when prediction incorporated both production and consumption characteristics of the sorghum varieties. Therefore, when disseminating new technologies farmers need to be informed about the production as well as the consumption characteristics of the new technologies. The outcomes of this study imply that involving producers and consumers in the generation of new agricultural technologies would potentially increase their adoption rates when they are disseminated. Thus a subsector analytical approach is recommended.展开更多
基金Supported by the National Natural Science Foundation of China(21676183)
文摘Refrigeration system holds an important role in process industries. The optimal synthesis cannot only reduce the energy consumption, but also save the production costs. In this study, a general methodology is developed for the optimal design of refrigeration cycle and heat exchanger network(HEN) simultaneously. Taking the heat integration between the external heat sources/sinks and the refrigeration cycle into consideration, a superstructure with sub-coolers is developed. Through defining logical variables that indicate the relative temperature positions of refrigerant streams after sub-coolers, the synthesis is formulated as a Generalized Disjunctive Programming(GDP) problem based on LP transshipment model, with the target of minimizing the total compressor shaft work in the refrigeration system. The GDP model is then reformulated as a Mixed Integer Nonlinear Programming(MINLP) problem with the aid of binary variables and Big-M Constraint Method. The efficacy of the process synthesis model is demonstrated by a case study of ethylene refrigeration system. The result shows that the optimization can significantly reduce the exergy loss as well as the total compression shaft work.
基金supported by the special research fund of Ocean University of China (201022001)
文摘Surplus production models are the simplest analytical methods effective for fish stock assessment and fisheries management. In this paper, eight surplus production estimators(three estimation procedures) were tested on Schaefer and Fox type simulated data in three simulated fisheries(declining, well-managed, and restoring fisheries) at two white noise levels. Monte Carlo simulation was conducted to verify the utility of moving averaging(MA), which was an important technique for reducing the effect of noise in data in these models. The relative estimation error(REE) of maximum sustainable yield(MSY) was used as an indicator for the analysis, and one-way ANOVA was applied to test the significance of the REE calculated at four levels of MA. Simulation results suggested that increasing the value of MA could significantly improve the performance of the surplus production model(low REE) in all cases when the white noise level was low(coefficient of variation(CV) = 0.02). However, when the white noise level increased(CV= 0.25), adding the value of MA could still significantly enhance the performance of most models. Our results indicated that the best model performance occurred frequently when MA was equal to 3; however, some exceptions were observed when MA was higher.
文摘The objective of this study was to determine the influence of production and consumption characteristics of improved sorghum varieties on farmers＇ adoption decisions. Thirty-four farmers and 231 consumers evaluated five sorghum varieties to determine their preferences. The perceptions of the farmers and consumers were summarized and presented to 100 sorghum farmers to help them choose the best varieties, based on results obtained earlier. Ordered probit models were used to predict their adoption decisions. Results indicated that when adoption is predicted on production characteristics alone the adoption rate was lower than when prediction incorporated both production and consumption characteristics of the sorghum varieties. Therefore, when disseminating new technologies farmers need to be informed about the production as well as the consumption characteristics of the new technologies. The outcomes of this study imply that involving producers and consumers in the generation of new agricultural technologies would potentially increase their adoption rates when they are disseminated. Thus a subsector analytical approach is recommended.
