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: Evaluating remote sensing data classification techniques for mapping freshwater habitats: Trial application in the Tongariro River delta, Lake Taupo

authors: Ashraf, Muhammad Salman

subjects: remote sensing data

abstract: The overall goal of this study is to evaluate different classification techniques that can be applied to multi-source satellite remote sensing data to map different freshwater habitat zones.  The Tongariro River delta at the southern side of the Lake Taupo was used as a test site to evaluate these techniques.

text: Evaluating remote sensing data classification techniques for mapping freshwater habitats: Trial application in the Tongariro River delta, Lake Taupo The overall goal of this study is to evaluate different classification techniques that can be applied to multi-source satellite remote sensing data to map different freshwater habitat zones.  The Tongariro River delta at the southern side of the Lake Taupo was used as a test site to evaluate these techniques.

year: 2008-07

title: Te manemanerau a te kāwanatanga: A history of the confiscation of Tūhoe lands in the Bay of Plenty

authors: Melbourne, Sydney

subjects: Ngāi Tūhoe

abstract: This thesis endeavours to show that Tūhoe lands should never have been confiscated and that Tūhoe efforts to gain compensation have been totally unsuccessful to date. When certain lands within the confiscated district of the Bay of Plenty were returned to the tribes there, Tūhoe were not granted any. Furthermore, lands which actually belonged to Tūhoe were granted to other tribes.
Although the major focus is on issues specific to Tūhoe, these are viewed within the wider context of nineteenth century land acquisition in New Zealand. This study looks at Tūhoe historical claims to disputed lands included in the confiscation district of the Bay of Plenty. Chapter One traces the extent of Tūhoe territories within the confiscation district and describes how Tūhoe came to occupy them and the duration of their occupation. Information about these claims came from tribal oral sources and original manuscripts, as well as from more generally accessible sources.
The development of colonial expansion patterns is discussed in Chapter Two. The contention is that they were based on materialistic considerations and legal pretexts to justify the acquisition of Māori lands. Hostilities between Māori and Government in the Bay of Plenty are dealt with in Chapter Three. Particular attention is paid to the causes of the hostilities and the complex racial and political misunderstandings which contributed to the inevitability of war. As a result of these encounters, the New Zealand Settlements Act was imposed.
Chapter Four covers the implementation of its provisions through the Compensation Court. The failings of this Court and its commissioners and field officials are exposed.
Chapter Five examines the settlement of Tūhoe lands in Ōpouriao and Waimana, as well as the changing fortunes of some of the settlers who took advantage of the settlement scheme. After placing the experiences of Tūhoe people within the wider context of what had taken place in New Zealand, Chapter Six focuses on Tūhoe attempts to bring the wrongs they had suffered to the attention of Government. In retrospect these early Tūhoe attempts at redress show that much has to be learnt about presenting substantial submissions. It was obvious that much of what was known by the elders then, though recorded, was never used in evidence to support their petitions. Nonetheless, without the existence of these manuscripts, present attempts would not be possible.
Chapter Seven gives a basis for a proposed just settlement for the confiscation of Tūhoe lands. In order to provide a guide for monetary compensation, details of values of Tūhoe confiscated land have been sought from official records. Compensation for the denial of justice, the loss of human life, land and property, remain open for negotiation.
Finally, while certain conclusions can be and are drawn from these investigations, the end of the story remains unwritten. It will depend on the outcome of new Tūhoe attempts to gain redress from the appropriate statutory body.

text: Te manemanerau a te kāwanatanga: A history of the confiscation of Tūhoe lands in the Bay of Plenty This thesis endeavours to show that Tūhoe lands should never have been confiscated and that Tūhoe efforts to gain compensation have been totally unsuccessful to date. When certain lands within the confiscated district of the Bay of Plenty were returned to the tribes there, Tūhoe were not granted any. Furthermore, lands which actually belonged to Tūhoe were granted to other tribes.
Although the major focus is on issues specific to Tūhoe, these are viewed within the wider context of nineteenth century land acquisition in New Zealand. This study looks at Tūhoe historical claims to disputed lands included in the confiscation district of the Bay of Plenty. Chapter One traces the extent of Tūhoe territories within the confiscation district and describes how Tūhoe came to occupy them and the duration of their occupation. Information about these claims came from tribal oral sources and original manuscripts, as well as from more generally accessible sources.
The development of colonial expansion patterns is discussed in Chapter Two. The contention is that they were based on materialistic considerations and legal pretexts to justify the acquisition of Māori lands. Hostilities between Māori and Government in the Bay of Plenty are dealt with in Chapter Three. Particular attention is paid to the causes of the hostilities and the complex racial and political misunderstandings which contributed to the inevitability of war. As a result of these encounters, the New Zealand Settlements Act was imposed.
Chapter Four covers the implementation of its provisions through the Compensation Court. The failings of this Court and its commissioners and field officials are exposed.
Chapter Five examines the settlement of Tūhoe lands in Ōpouriao and Waimana, as well as the changing fortunes of some of the settlers who took advantage of the settlement scheme. After placing the experiences of Tūhoe people within the wider context of what had taken place in New Zealand, Chapter Six focuses on Tūhoe attempts to bring the wrongs they had suffered to the attention of Government. In retrospect these early Tūhoe attempts at redress show that much has to be learnt about presenting substantial submissions. It was obvious that much of what was known by the elders then, though recorded, was never used in evidence to support their petitions. Nonetheless, without the existence of these manuscripts, present attempts would not be possible.
Chapter Seven gives a basis for a proposed just settlement for the confiscation of Tūhoe lands. In order to provide a guide for monetary compensation, details of values of Tūhoe confiscated land have been sought from official records. Compensation for the denial of justice, the loss of human life, land and property, remain open for negotiation.
Finally, while certain conclusions can be and are drawn from these investigations, the end of the story remains unwritten. It will depend on the outcome of new Tūhoe attempts to gain redress from the appropriate statutory body.

year: 1987