title: A derivative method for minimising total cost in heat exchanger networks through optimal area allocation

authors: Walmsley, Timothy Gordon

subjects: Cost Derivative Method

abstract: This paper presents a novel Cost Derivative Method (CDM) for finding the optimal area allocation for a defined Heat Exchanger Network (HEN) structure and stream data, without any stream splits to achieve minimum total cost. Using the Pinch Design Method (PDM) to determine the HEN structure, the approach attempts to add, remove and shift area to exchangers where economic benefits are returned. From the derivation of the method, it is found that the slope of the ε-NTU relationship for the specific heat exchanger type, in combination with the difference in exchanger inlet temperatures and the overall heat transfer coefficient, are critical to calculating the extra overall duty each incremental area element returns. The approach is able to account for differences in film coefficients, heat exchanger types, flow arrangements, exchanger cost functions, and utility pricing. Incorporated into the method is the newly defined “utility cost savings flow-on” factor, θ, which evaluates downstream effects on utility use and cost that are caused by changing the area of one exchanger. To illustrate the method, the CDM is applied to the distillation example of Gundersen (2000). After applying the new CDM, the total annual cost was reduced by 7.1 % mainly due to 24 % less HEN area for similar heat recovery. Area reduction resulted from one exchanger having a minimum approach temperature (ΔTmin) of 7.7 °C while the other recovery exchangers had larger ΔTmin values. The optimum ΔTmin for the PDM was 12.5 °C. The CDM solution was found to give a comparable minimum total area and cost to two recently published programming HEN synthesis solutions for the same problem without requiring the increased network complexity through multiple stream splits.

text: A derivative method for minimising total cost in heat exchanger networks through optimal area allocation This paper presents a novel Cost Derivative Method (CDM) for finding the optimal area allocation for a defined Heat Exchanger Network (HEN) structure and stream data, without any stream splits to achieve minimum total cost. Using the Pinch Design Method (PDM) to determine the HEN structure, the approach attempts to add, remove and shift area to exchangers where economic benefits are returned. From the derivation of the method, it is found that the slope of the ε-NTU relationship for the specific heat exchanger type, in combination with the difference in exchanger inlet temperatures and the overall heat transfer coefficient, are critical to calculating the extra overall duty each incremental area element returns. The approach is able to account for differences in film coefficients, heat exchanger types, flow arrangements, exchanger cost functions, and utility pricing. Incorporated into the method is the newly defined “utility cost savings flow-on” factor, θ, which evaluates downstream effects on utility use and cost that are caused by changing the area of one exchanger. To illustrate the method, the CDM is applied to the distillation example of Gundersen (2000). After applying the new CDM, the total annual cost was reduced by 7.1 % mainly due to 24 % less HEN area for similar heat recovery. Area reduction resulted from one exchanger having a minimum approach temperature (ΔTmin) of 7.7 °C while the other recovery exchangers had larger ΔTmin values. The optimum ΔTmin for the PDM was 12.5 °C. The CDM solution was found to give a comparable minimum total area and cost to two recently published programming HEN synthesis solutions for the same problem without requiring the increased network complexity through multiple stream splits.

year: 2013

title: Understanding stakeholder values using cluster analysis

authors: Kaval, Pamela

subjects: Cluster analysis

abstract: The K-Means and Ward’s Clustering procedures were used to categorize value similarities among respondents of a public land management survey. The clustering procedures resulted in two respondent groupings: an anthropocentrically focused group and an ecocentrically focused group. While previous studies have suggested that anthropocentric and ecocentric groups are very different, this study revealed many similarities. Similarities between groups included a strong feeling towards public land and national forest existence as well as the importance of considering both current and future generations when making management decisions for public land. It is recommended that land managers take these similarities into account when making management decisions. It is important to note that using the Ward’s procedure for clustering produced more consistent groupings than the K-Means procedure and is therefore recommended when clustering survey data. K-Means only showed consistency with datasets of over 500 observations.

text: Understanding stakeholder values using cluster analysis The K-Means and Ward’s Clustering procedures were used to categorize value similarities among respondents of a public land management survey. The clustering procedures resulted in two respondent groupings: an anthropocentrically focused group and an ecocentrically focused group. While previous studies have suggested that anthropocentric and ecocentric groups are very different, this study revealed many similarities. Similarities between groups included a strong feeling towards public land and national forest existence as well as the importance of considering both current and future generations when making management decisions for public land. It is recommended that land managers take these similarities into account when making management decisions. It is important to note that using the Ward’s procedure for clustering produced more consistent groupings than the K-Means procedure and is therefore recommended when clustering survey data. K-Means only showed consistency with datasets of over 500 observations.

year: 2007-08

title: Searching for synergy: Māori/indigenous and scientific conservatory values - the affinity propositon

authors: Simon, Katerina Heremoana

subjects: Development studies

abstract: "Reconciling similarity/ affinity and difference/ distinction is one of the most important development issues of our contemporary period. Yet much effort aimed at gaining support for the plight of Māori/ indigenous peoples remains locked into the assertion of difference and distinction alone, those points of cultural affinity that could play an important role in processes of reconciliation and movement forward being largely ignored. What is proposed here is what is referred to as the ‘affinity proposition’, that is, it is argued that Māori/ indigenous development requires, for its further advancement, a focus not only on difference and divergence, but also on similarity and affinity. At the very heart of Māori/ indigenous development are issues relating to social justice, economic equity, freedom, ecological sustainability and cultural diversity, concepts which are equally highly valued in many sectors of mainstream (non-indigenous) society. Certainly, there are important differences in the ways in which these values are perceived and articulated in the context of different cultures, and these differences have recently been the focus of considerable attention and debate. However, there are also similarities which have received less attention in spite of the fact that they may hold the key to achieving a sufficient level of mutual understanding to underpin effective Māori/ indigenous development.

This paper explores the development of a synergistic process of reconciliation between Māori/ indigenous values and scientific conservatory values. It reports on the preliminary findings of a research project whose focus is a cross-cultural study of environmental governance and management regimes under the New Zealand Resource Management Act 1991. The central questions addressed here are: Can reconciliation be achieved through recognition of both affinity and difference? Could such reconciliation underpin effective Māori/ indigenous development? It is argued here that a process of synergy is already under way, a process that can best be understood in terms of a theoretical framework that encompasses both the concept of modernity and the sustainable development paradigm."

text: Searching for synergy: Māori/indigenous and scientific conservatory values - the affinity propositon "Reconciling similarity/ affinity and difference/ distinction is one of the most important development issues of our contemporary period. Yet much effort aimed at gaining support for the plight of Māori/ indigenous peoples remains locked into the assertion of difference and distinction alone, those points of cultural affinity that could play an important role in processes of reconciliation and movement forward being largely ignored. What is proposed here is what is referred to as the ‘affinity proposition’, that is, it is argued that Māori/ indigenous development requires, for its further advancement, a focus not only on difference and divergence, but also on similarity and affinity. At the very heart of Māori/ indigenous development are issues relating to social justice, economic equity, freedom, ecological sustainability and cultural diversity, concepts which are equally highly valued in many sectors of mainstream (non-indigenous) society. Certainly, there are important differences in the ways in which these values are perceived and articulated in the context of different cultures, and these differences have recently been the focus of considerable attention and debate. However, there are also similarities which have received less attention in spite of the fact that they may hold the key to achieving a sufficient level of mutual understanding to underpin effective Māori/ indigenous development.

This paper explores the development of a synergistic process of reconciliation between Māori/ indigenous values and scientific conservatory values. It reports on the preliminary findings of a research project whose focus is a cross-cultural study of environmental governance and management regimes under the New Zealand Resource Management Act 1991. The central questions addressed here are: Can reconciliation be achieved through recognition of both affinity and difference? Could such reconciliation underpin effective Māori/ indigenous development? It is argued here that a process of synergy is already under way, a process that can best be understood in terms of a theoretical framework that encompasses both the concept of modernity and the sustainable development paradigm."

year: 2003-05