title: Unified Total Site Heat Integration: Targeting, Optimisation and Network Design

authors: Tarighaleslami, Amir Hossein

subjects: Total Site Heat Integration

abstract: Process industries in New Zealand use 214.3 PJ of process heat, of which approximately 65 % is fossil fuels. Despite increasing energy demands, depleting fossil fuel resources, and pressure to reduce Greenhouse Gas emissions, low grade heat in large-scale processing sites is still not fully utilised. This thesis presents methods to target, optimise and design more practical heat recovery systems for large industrial sites, i.e. Total Sites, and overcome technical limitations of current methods. Original contributions of this thesis to literature include novel developments and applications in six areas: i) a new Total Site Heat Integration (TSHI) targeting method – Unified Total Site Targeting (UTST) –  which sets realistic targets for isothermal and non-isothermal utilities and heat recovery via the utility system; ii) a new TSHI optimisation and utility temperature selection method to optimise Total Cost of the utility system; iii) a new Utility Exchanger Network synthesis and design method based on the targets achieved by the UTST method and optimal temperatures from optimisation method; iv) a new method for calculating assisted heat transfer and shaft work to further improve TSHI cogeneration and performance; v) examination of heat transfer enhancement techniques in TSHI to achieve higher heat recovery and lower required area by substituting conventional utility mediums by nanofluids in the utility system; and vi) a spreadsheet software tool called Unified Total Site Integration to apply the developed methods to real industrial cases. 
The developed methods have been applied to three large industrial case studies. Results confirm that heat recovery and utility targets obtained from the UTST method were lower but more realistic to achieve in practice when compared to conventional TSHI methods. The three industrial case studies represent a wide variety of processing industries. In summary, the over-estimation of TSHI targets for the three case studies from using the conventional method compared to the new method are 0.2 % for the Södra Cell Värö Kraft Pulp Mill, 22 % for a New Zealand Dairy Factory, and 0.1 % for Petrochemical Complex. The Total Annualised Costs (TAC) for the three case studies are minimised using a new derivative based approach. Results show TAC reductions 4.6 % for Kraft Pulp Mill, 0.6 % for Dairy Factory, and 3.4 % for Petrochemical Complex case studies. In addition, sensitivity analysis for the optimisation is undertaken. The UTST method with its modified targeting procedure is demonstrated to generate simpler Utility Exchanger Network designs compared to conventional methods, which confirm the original targets are realistic and achievable. A new method for calculating assisted heat integration targets applied to an example Total Site problem increased heat recovery by 1,737 kW, which is a 21% increase in Total Site heat recovery, and increased shaft work by 80 kW. Lastly, the addition of nanoparticles to create a closed nanofluid heat recovery systems shows heat recovery from liquid-liquid heat exchangers increases of 5 % to 9 % using an intermediate fluid with 1.5 vol. % CuO/water.

text: Unified Total Site Heat Integration: Targeting, Optimisation and Network Design Process industries in New Zealand use 214.3 PJ of process heat, of which approximately 65 % is fossil fuels. Despite increasing energy demands, depleting fossil fuel resources, and pressure to reduce Greenhouse Gas emissions, low grade heat in large-scale processing sites is still not fully utilised. This thesis presents methods to target, optimise and design more practical heat recovery systems for large industrial sites, i.e. Total Sites, and overcome technical limitations of current methods. Original contributions of this thesis to literature include novel developments and applications in six areas: i) a new Total Site Heat Integration (TSHI) targeting method – Unified Total Site Targeting (UTST) –  which sets realistic targets for isothermal and non-isothermal utilities and heat recovery via the utility system; ii) a new TSHI optimisation and utility temperature selection method to optimise Total Cost of the utility system; iii) a new Utility Exchanger Network synthesis and design method based on the targets achieved by the UTST method and optimal temperatures from optimisation method; iv) a new method for calculating assisted heat transfer and shaft work to further improve TSHI cogeneration and performance; v) examination of heat transfer enhancement techniques in TSHI to achieve higher heat recovery and lower required area by substituting conventional utility mediums by nanofluids in the utility system; and vi) a spreadsheet software tool called Unified Total Site Integration to apply the developed methods to real industrial cases. 
The developed methods have been applied to three large industrial case studies. Results confirm that heat recovery and utility targets obtained from the UTST method were lower but more realistic to achieve in practice when compared to conventional TSHI methods. The three industrial case studies represent a wide variety of processing industries. In summary, the over-estimation of TSHI targets for the three case studies from using the conventional method compared to the new method are 0.2 % for the Södra Cell Värö Kraft Pulp Mill, 22 % for a New Zealand Dairy Factory, and 0.1 % for Petrochemical Complex. The Total Annualised Costs (TAC) for the three case studies are minimised using a new derivative based approach. Results show TAC reductions 4.6 % for Kraft Pulp Mill, 0.6 % for Dairy Factory, and 3.4 % for Petrochemical Complex case studies. In addition, sensitivity analysis for the optimisation is undertaken. The UTST method with its modified targeting procedure is demonstrated to generate simpler Utility Exchanger Network designs compared to conventional methods, which confirm the original targets are realistic and achievable. A new method for calculating assisted heat integration targets applied to an example Total Site problem increased heat recovery by 1,737 kW, which is a 21% increase in Total Site heat recovery, and increased shaft work by 80 kW. Lastly, the addition of nanoparticles to create a closed nanofluid heat recovery systems shows heat recovery from liquid-liquid heat exchangers increases of 5 % to 9 % using an intermediate fluid with 1.5 vol. % CuO/water.

year: 2018

title: Dynamic Electroporation Modelling

authors: Talele, Sadhana

subjects: electroporation

abstract: In this thesis, modelling and simulation of the effects of electric fields on a single spherical cell are undertaken. Of interest is the effect that different electric field waveforms have on the induced transmembrane potential of the cell and by consequence the electropermeabilization of the cell membrane in terms of pore density or the fraction of the cell area that the pores occupy. Conventional biotechnology processes of electroporation make use of unipolar electric field pulses, which are known to generate undesirable conditions such as asymmetrical electropermeabilization. These electrical protocols also contribute to lower efficiencies in electroporation based applications (in terms of uptake of molecules in the cell) by being sensitive to cell radii.

Until recently, theoretical models of electroporation have lagged behind the experimental research. In order to optimize the efficiency of electroporation, it is important to consider as many biological and physical aspects as possible and it is a necessity that a variety of electric pulse parameters be tested. Thus a comprehensive model which can predict electropermeabilization as a result of any form of applied electric field and other important electroporation parameters is necessary. None of the existing theoretical modelling studies present simulations of dynamic electroporation modelling as a cell response to bipolar electric field wave-shapes. Developing such a model is the aim of this thesis.

In this thesis two numerical models are developed. These models consider electroporation as a dynamic process and include the non-linear dynamic effects of membrane electropermeabilization. The first model assumes all pores are identical and small (0.76~nm radius) and is capable of simulating transmembrane potential and pore density temporally and spatially, given any form of applied electric field and other important electroporation system parameters such as external medium, membrane, and cytoplasm complex dielectric properties. The piece-wise step response model presented here is used to simulate cell response to several different applied electric field wave-shape pulses.% including a unipolar square wave, bipolar square wave, bipolar sine wave, bipolar rectangular wave (rectangular pulse train), and a bipolar triangular wave.

Additional results from the first model demonstrate how the efficiency of electroporation related applications can be significantly improved by appropriately adjusting the parameters of the applied electric field and the  extracellular conductivity. Emphasis is given on the normalization of the degree of electroporation (in terms of pore density) for  two  cell radii (7.5~$\mu$m and 15~$\mu$m).

Although, these results gave a fair indication of the extent of electroporation in terms of pore density, the approximation that all pores have the same size, and do not change with time, may not be  appropriate. There is a need to model electroporation so as to reflect the growth or shrinkage of pores with time, as well as efficiently handle arbitrary waveshapes of electric fields. The additional information about pore radius evolution  gives a more realistic picture of the extent of electroporation, especially if one is to model for longer time (longer than 1~$\mu$s) or if an application necessarily required existence of larger pores (radius lager than 1~nm) rather than just the total pore area. Pore radius and pore numbers  affect the transmembrane potential, which in turn  affects pore density and pore radius.
Literature includes information on spatial and temporal aspects of pore radius evolution. However, the electric fields used in these models were limited to unipolar DC pulses and details of temporal and spatial evolution of transmembrane potential and pore radius have not been reported.
 
The second model developed in this thesis   simulates  spatial and temporal aspects of pore radius as an effect of  any given form  of applied electric field (including unipolar or bipolar), and other important electroporation system parameters.   The transmembrane potential and pore radii as function of time and angular position about the cell membrane   are presented. The results show that pore  radii    tend to be more normalized when an AC (bipolar)    field is used when compared to a  DC (unipolar) field (pore radii ranging from 1~nm to 8~nm for DC protocol compared with 1~nm to 3.4~nm for AC protocol when  the pulse amplitude used in both  cases is such as to give a similar fractional pore area at the end of 2~$\mu$s).
 
Additional simulation results from this model are  used to  compare the extent of electroporation   in response to sinusoidal AC (bipolar) electric field pulses of two different frequencies in a range of extracellular conductivity for two different cell radii (7.5~$\mu$m and 15~$\mu$m). 
It is   observed that  a higher frequency (1~MHz) bipolar sinusoidal applied electric field pulse reduces the relative difference in fractional pore area   for the two cell sizes compared to a lower frequency  (100~kHz) pulse. Nevertheless for the high frequency, a significantly higher amplitude is required to create the same level of average fractional pore area. Asymmetry of fractional pore area between the two hemispheres of the cell is observed for both field protocols.

text: Dynamic Electroporation Modelling In this thesis, modelling and simulation of the effects of electric fields on a single spherical cell are undertaken. Of interest is the effect that different electric field waveforms have on the induced transmembrane potential of the cell and by consequence the electropermeabilization of the cell membrane in terms of pore density or the fraction of the cell area that the pores occupy. Conventional biotechnology processes of electroporation make use of unipolar electric field pulses, which are known to generate undesirable conditions such as asymmetrical electropermeabilization. These electrical protocols also contribute to lower efficiencies in electroporation based applications (in terms of uptake of molecules in the cell) by being sensitive to cell radii.

Until recently, theoretical models of electroporation have lagged behind the experimental research. In order to optimize the efficiency of electroporation, it is important to consider as many biological and physical aspects as possible and it is a necessity that a variety of electric pulse parameters be tested. Thus a comprehensive model which can predict electropermeabilization as a result of any form of applied electric field and other important electroporation parameters is necessary. None of the existing theoretical modelling studies present simulations of dynamic electroporation modelling as a cell response to bipolar electric field wave-shapes. Developing such a model is the aim of this thesis.

In this thesis two numerical models are developed. These models consider electroporation as a dynamic process and include the non-linear dynamic effects of membrane electropermeabilization. The first model assumes all pores are identical and small (0.76~nm radius) and is capable of simulating transmembrane potential and pore density temporally and spatially, given any form of applied electric field and other important electroporation system parameters such as external medium, membrane, and cytoplasm complex dielectric properties. The piece-wise step response model presented here is used to simulate cell response to several different applied electric field wave-shape pulses.% including a unipolar square wave, bipolar square wave, bipolar sine wave, bipolar rectangular wave (rectangular pulse train), and a bipolar triangular wave.

Additional results from the first model demonstrate how the efficiency of electroporation related applications can be significantly improved by appropriately adjusting the parameters of the applied electric field and the  extracellular conductivity. Emphasis is given on the normalization of the degree of electroporation (in terms of pore density) for  two  cell radii (7.5~$\mu$m and 15~$\mu$m).

Although, these results gave a fair indication of the extent of electroporation in terms of pore density, the approximation that all pores have the same size, and do not change with time, may not be  appropriate. There is a need to model electroporation so as to reflect the growth or shrinkage of pores with time, as well as efficiently handle arbitrary waveshapes of electric fields. The additional information about pore radius evolution  gives a more realistic picture of the extent of electroporation, especially if one is to model for longer time (longer than 1~$\mu$s) or if an application necessarily required existence of larger pores (radius lager than 1~nm) rather than just the total pore area. Pore radius and pore numbers  affect the transmembrane potential, which in turn  affects pore density and pore radius.
Literature includes information on spatial and temporal aspects of pore radius evolution. However, the electric fields used in these models were limited to unipolar DC pulses and details of temporal and spatial evolution of transmembrane potential and pore radius have not been reported.
 
The second model developed in this thesis   simulates  spatial and temporal aspects of pore radius as an effect of  any given form  of applied electric field (including unipolar or bipolar), and other important electroporation system parameters.   The transmembrane potential and pore radii as function of time and angular position about the cell membrane   are presented. The results show that pore  radii    tend to be more normalized when an AC (bipolar)    field is used when compared to a  DC (unipolar) field (pore radii ranging from 1~nm to 8~nm for DC protocol compared with 1~nm to 3.4~nm for AC protocol when  the pulse amplitude used in both  cases is such as to give a similar fractional pore area at the end of 2~$\mu$s).
 
Additional simulation results from this model are  used to  compare the extent of electroporation   in response to sinusoidal AC (bipolar) electric field pulses of two different frequencies in a range of extracellular conductivity for two different cell radii (7.5~$\mu$m and 15~$\mu$m). 
It is   observed that  a higher frequency (1~MHz) bipolar sinusoidal applied electric field pulse reduces the relative difference in fractional pore area   for the two cell sizes compared to a lower frequency  (100~kHz) pulse. Nevertheless for the high frequency, a significantly higher amplitude is required to create the same level of average fractional pore area. Asymmetry of fractional pore area between the two hemispheres of the cell is observed for both field protocols.

year: 2009

title: Collective Indigenous approaches to centring Pacific voices of leadership for our futures

authors: Uasike Allen, JM

abstract: Education systems in western nations are often built on a long history of centralising the western canon of knowledge and colonial norms. These norms are perpetuated and reinforced via western research which amplifies the voices of the dominant, while working to silence the values, practices, and knowledges of minority groups. As a colonial nation, Aotearoa New Zealand continues to be impacted by its colonial histories, where colonial (read white) ways of being, knowing, and understanding dominate initial teacher education, schools, tertiary institutions, research, and our everyday lives. However, within education and research more generally, Indigenous and Pacific researchers and practitioners have been working hard to carve out space in institutions to challenge colonial hierarchies of knowledge and make space for Indigenous ways of being, knowing, seeing, doing, and feeling. This article contributes to the work being done by Indigenous and Pacific scholars in Aotearoa New Zealand by detailing our collective, relational approach to convening the special issue of Shifting the System for the Ethnographic Edge journal. Convening a special issue is not unique and groups of academics do it regularly across a range of academic journals and fields. However, our experiences of convening this special issue were quite different. Here we share the journey and reflect on how our focus on privileging the often-marginalised voices of Pacific school leaders was underpinned by an Indigenous, collective approach embedded in the pedagogical practice of Indigenous Storywork. Employing collaborative critical autoethnography, we articulate the ways in which our engagement with each other and the authors within this special issue disrupted western power relations often present in interactions between ‘researchers’ within the university and ‘practitioners’ at the coalface. Furthermore, we demonstrate how engaging in relational practices builds a space that encourages the principles of respect, responsibility, reverence, reciprocity, holism, interrelatedness, and synergy.

text: Collective Indigenous approaches to centring Pacific voices of leadership for our futures Education systems in western nations are often built on a long history of centralising the western canon of knowledge and colonial norms. These norms are perpetuated and reinforced via western research which amplifies the voices of the dominant, while working to silence the values, practices, and knowledges of minority groups. As a colonial nation, Aotearoa New Zealand continues to be impacted by its colonial histories, where colonial (read white) ways of being, knowing, and understanding dominate initial teacher education, schools, tertiary institutions, research, and our everyday lives. However, within education and research more generally, Indigenous and Pacific researchers and practitioners have been working hard to carve out space in institutions to challenge colonial hierarchies of knowledge and make space for Indigenous ways of being, knowing, seeing, doing, and feeling. This article contributes to the work being done by Indigenous and Pacific scholars in Aotearoa New Zealand by detailing our collective, relational approach to convening the special issue of Shifting the System for the Ethnographic Edge journal. Convening a special issue is not unique and groups of academics do it regularly across a range of academic journals and fields. However, our experiences of convening this special issue were quite different. Here we share the journey and reflect on how our focus on privileging the often-marginalised voices of Pacific school leaders was underpinned by an Indigenous, collective approach embedded in the pedagogical practice of Indigenous Storywork. Employing collaborative critical autoethnography, we articulate the ways in which our engagement with each other and the authors within this special issue disrupted western power relations often present in interactions between ‘researchers’ within the university and ‘practitioners’ at the coalface. Furthermore, we demonstrate how engaging in relational practices builds a space that encourages the principles of respect, responsibility, reverence, reciprocity, holism, interrelatedness, and synergy.

year: 2022