title: An association between Waitaki River winter headwater flows and the Interdecadal Pacific Oscillation (IPO)

authors: Vetrova, V. V.

subjects: Interdecal Pacific Oscillation, Waitaki catchment

abstract: Expressed as 11-year running means (1945- 2008), winter headwater flows in the Waitaki River (New Zealand) and the IPO index show similar patterns in the way they vary over time. However, this effect is not evident in the other seasons. A possible explanation is the IPO in its positive phase is associated with warmer air temperatures in winter, but not in other seasons. Analysis of Mt Cook (Hermitage station) daily rainfalls suggests that warmer winter air temperatures on precipitation days are associated with higher mean daily precipitation, so the positive IPO may result in greater amounts of winter precipitation falling as rain rather than snow. This could provide the link between the winter IPO and headwater discharge. On the other hand, temperature is only weakly associated with precipitation magnitudes in other seasons, when higher average temperatures do not provide the same restricting effect on precipitation as in winter.

text: An association between Waitaki River winter headwater flows and the Interdecadal Pacific Oscillation (IPO) Expressed as 11-year running means (1945- 2008), winter headwater flows in the Waitaki River (New Zealand) and the IPO index show similar patterns in the way they vary over time. However, this effect is not evident in the other seasons. A possible explanation is the IPO in its positive phase is associated with warmer air temperatures in winter, but not in other seasons. Analysis of Mt Cook (Hermitage station) daily rainfalls suggests that warmer winter air temperatures on precipitation days are associated with higher mean daily precipitation, so the positive IPO may result in greater amounts of winter precipitation falling as rain rather than snow. This could provide the link between the winter IPO and headwater discharge. On the other hand, temperature is only weakly associated with precipitation magnitudes in other seasons, when higher average temperatures do not provide the same restricting effect on precipitation as in winter.

year: 2015

title: Experimental and Numerical Investigations of Skim Milk Powder Stickiness and Deposition Mechanisms

authors: Zhao, SongXin

subjects: Deposition

abstract: The particle gun method and Computational Fluid Dynamics (CFD) modelling was used to study stickiness and deposition mechanisms of skim milk powder in an impingement jet hitting a stainless steel plate. The particular focus was on the effect of jet velocity and particle size distribution on deposition. Low jet velocities of 10.3, 14.8 and 19.4 m/s were studied at fine particle size levels of 30, 51, and 61 mm, using a jet-plate height to jet diameter ratio of 4. For skim milk powder with a bulk particle size (d(0.5) = 61 μm), lowering the air velocity from 19.4 m/s to 10.3 m/s increased the level of deposition and decreased the point at which deposition first occur as measured by the temperature difference between the glass transition temperature (Tg) of amorphous lactose and the air jet temperature of the particle gun. This point is called (T-Tg)critical. The critical point decreased from 39.0 °C to 18.6 °C as the velocity decreased from 19.4 to 10.3 m/s and the (T-Tg)critical obtained at the lower velocity is in closer agreement with previously reported fluid bed rig results. The (T-Tg)critical point and level of deposition was also found to be highly dependent on particle size. Increasing the average particle size from 30 μm to 61μm increased the (T-Tg)critical from 8.2 °C to 18.6 °C and 14.8 °C to 39.0 °C for jet velocities of 10.3 m/s and 19.4 m/s respectively. Levels of particle deposition also dramatically decreased for both velocity ranges. Ring shaped deposit morphologies were observed with increasing particle stickiness. Beyond (T-Tg)critical powder deposits formed at the periphery of the plate creating a large round clear zone which decreased until a striped deposit ring formed and finally deposits formed only at the centre. Particles were observed to bounce radially from the centre of the plate before sticking. Milk powder deposits are therefore governed by the kinetic energy of the impinging particle in addition to particle surface stickiness. The particle gun method was modelled using Fluent CFD software as an adhesion phenomenon arising from the particle-surface contact dynamics of a particle laden impingement jet contacting a vertical collection plate. The development of a wall boundary condition for specifying the particle-surface interaction has been the focus. A particle is captured by the wall if the impinging kinetic energy is below the prescribed critical normal kinetic energy; otherwise the particle rebounds with reduced kinetic energy. The model was developed through the User Define Function option of Fluent. The CFD model confirmed that particles rebound radially from the collection plate several times before sticking. Circular deposit morphology results from such modelled contact dynamics which are similar to the observed experimental deposits. The level of deposition predicted by CFD increased with increasing levels of critical normal kinetic energy, in the same way experimental deposits increased with increasing particle stickiness. The current model did not considered the contribution from the tangential velocity component to particle stick/rebound behaviour, but it is expected the tangential velocity may also play a significant role and should be included in future CFD models. It is recommended that the particle-surface interaction needs to be studied in more detail, preferably with imaging systems such as Particle Image Velocimetry (PIV), so that individual particle trajectory and deposition behaviour can be followed and analysed.

text: Experimental and Numerical Investigations of Skim Milk Powder Stickiness and Deposition Mechanisms The particle gun method and Computational Fluid Dynamics (CFD) modelling was used to study stickiness and deposition mechanisms of skim milk powder in an impingement jet hitting a stainless steel plate. The particular focus was on the effect of jet velocity and particle size distribution on deposition. Low jet velocities of 10.3, 14.8 and 19.4 m/s were studied at fine particle size levels of 30, 51, and 61 mm, using a jet-plate height to jet diameter ratio of 4. For skim milk powder with a bulk particle size (d(0.5) = 61 μm), lowering the air velocity from 19.4 m/s to 10.3 m/s increased the level of deposition and decreased the point at which deposition first occur as measured by the temperature difference between the glass transition temperature (Tg) of amorphous lactose and the air jet temperature of the particle gun. This point is called (T-Tg)critical. The critical point decreased from 39.0 °C to 18.6 °C as the velocity decreased from 19.4 to 10.3 m/s and the (T-Tg)critical obtained at the lower velocity is in closer agreement with previously reported fluid bed rig results. The (T-Tg)critical point and level of deposition was also found to be highly dependent on particle size. Increasing the average particle size from 30 μm to 61μm increased the (T-Tg)critical from 8.2 °C to 18.6 °C and 14.8 °C to 39.0 °C for jet velocities of 10.3 m/s and 19.4 m/s respectively. Levels of particle deposition also dramatically decreased for both velocity ranges. Ring shaped deposit morphologies were observed with increasing particle stickiness. Beyond (T-Tg)critical powder deposits formed at the periphery of the plate creating a large round clear zone which decreased until a striped deposit ring formed and finally deposits formed only at the centre. Particles were observed to bounce radially from the centre of the plate before sticking. Milk powder deposits are therefore governed by the kinetic energy of the impinging particle in addition to particle surface stickiness. The particle gun method was modelled using Fluent CFD software as an adhesion phenomenon arising from the particle-surface contact dynamics of a particle laden impingement jet contacting a vertical collection plate. The development of a wall boundary condition for specifying the particle-surface interaction has been the focus. A particle is captured by the wall if the impinging kinetic energy is below the prescribed critical normal kinetic energy; otherwise the particle rebounds with reduced kinetic energy. The model was developed through the User Define Function option of Fluent. The CFD model confirmed that particles rebound radially from the collection plate several times before sticking. Circular deposit morphology results from such modelled contact dynamics which are similar to the observed experimental deposits. The level of deposition predicted by CFD increased with increasing levels of critical normal kinetic energy, in the same way experimental deposits increased with increasing particle stickiness. The current model did not considered the contribution from the tangential velocity component to particle stick/rebound behaviour, but it is expected the tangential velocity may also play a significant role and should be included in future CFD models. It is recommended that the particle-surface interaction needs to be studied in more detail, preferably with imaging systems such as Particle Image Velocimetry (PIV), so that individual particle trajectory and deposition behaviour can be followed and analysed.

year: 2009

title: Mahi Toi Skills in Contemporary Education, Training and Maori Development

authors: Joseph, Makarita Ngapine Tangitu

subjects: Kia mau ki nga taonga tuku iho o nga tupuna

abstract: Since the 1980’s, national investment in human capital and skill formation policy in education has been promoted as key to economic success and social inclusion. Social inclusion, however, is often expressed as helping citizens to become employable. Although employability is a key focus of skills formation and education policy, the context of the western ideologies that it derives from and caters to perpetuates the exclusion of mahi toi (arts and crafts) skills in education. Using a kaupapa Māori approach, two key informants who specialise and teach mahi toi skills, either rāranga (weaving) or pounamu (jade/greenstone), were interviewed. The aim was to get a better understanding of how these skills can contribute to personal, professional and Māori development in the 21st century, and to provide information indicating where and how these skills can be learnt, either through private training enterprises (PTE) or public tertiary educational institutions (TEI), thereby highlighting the value of teaching and learning rāranga and pounamu skills. Findings from analysing their pūrākau indicate that learning rāranga or pounamu skills can provide a foundation for believing in your potential, contribute to cultural identity, improve confidence and communication skills, help an individual be bestowed or acquire mana, offer a type of therapy, enhance career progression and professional identity, provide financial rewards and stability, and help with the revitalisation and transfer of cultural knowledge. Ultimately, it is concluded that mahi toi skills such as rāranga and pounamu can contribute to the development of an individual’s personal and professional lives, but also has benefits for the organisation where they become employed as well as extended whānau, hapū and iwi.

text: Mahi Toi Skills in Contemporary Education, Training and Maori Development Since the 1980’s, national investment in human capital and skill formation policy in education has been promoted as key to economic success and social inclusion. Social inclusion, however, is often expressed as helping citizens to become employable. Although employability is a key focus of skills formation and education policy, the context of the western ideologies that it derives from and caters to perpetuates the exclusion of mahi toi (arts and crafts) skills in education. Using a kaupapa Māori approach, two key informants who specialise and teach mahi toi skills, either rāranga (weaving) or pounamu (jade/greenstone), were interviewed. The aim was to get a better understanding of how these skills can contribute to personal, professional and Māori development in the 21st century, and to provide information indicating where and how these skills can be learnt, either through private training enterprises (PTE) or public tertiary educational institutions (TEI), thereby highlighting the value of teaching and learning rāranga and pounamu skills. Findings from analysing their pūrākau indicate that learning rāranga or pounamu skills can provide a foundation for believing in your potential, contribute to cultural identity, improve confidence and communication skills, help an individual be bestowed or acquire mana, offer a type of therapy, enhance career progression and professional identity, provide financial rewards and stability, and help with the revitalisation and transfer of cultural knowledge. Ultimately, it is concluded that mahi toi skills such as rāranga and pounamu can contribute to the development of an individual’s personal and professional lives, but also has benefits for the organisation where they become employed as well as extended whānau, hapū and iwi.

year: 2018