Jim R. Jones

Synthesizing large-scale pyroclastic flows: Experimental design, scaling, and first results from PELE

Pyroclastic flow eruption large-scale experiment (PELE) is a large-scale facility for experimental studies of pyroclastic density currents (PDCs). It is used to generate high-energy currents involving 500–6500 m3 natural volcanic material and air that achieve velocities of 7–30 m s−1, flow thicknesses of 2–4.5 m, and runouts of >35 m. The experimental PDCs are synthesized by a controlled “eruption column collapse” of ash-lapilli suspensions onto an instrumented channel. The first set of experiments are documented here and used to elucidate the main flow regimes that influence PDC dynamic structure. Four phases are identified: (1) mixture acceleration during eruption column collapse, (2) column-slope impact, (3) PDC generation, and (4) ash cloud diffusion. The currents produced are fully turbulent flows and scale well to natural PDCs including small to large scales of turbulent transport. PELE is capable of generating short, pulsed, and sustained currents over periods of several tens of seconds, and dilute surge-like PDCs through to highly concentrated pyroclastic flow-like currents. The surge-like variants develop a basal <0.05 m thick regime of saltating/rolling particles and shifting sand waves, capped by a 2.5–4.5 m thick, turbulent suspension that grades upward to lower particle concentrations. Resulting deposits include stratified dunes, wavy and planar laminated beds, and thin ash cloud fall layers. Concentrated currents segregate into a dense basal underflow of <0.6 m thickness that remains aerated. This is capped by an upper ash cloud surge (1.5–3 m thick) with 100 to 10−4 vol % particles. Their deposits include stratified, massive, normally and reversely graded beds, lobate fronts, and laterally extensive veneer facies beyond channel margins.

Effect of Fines on Agglomeration in Spray Dryers: An Experimental Study

Agglomeration in spray dryers occurs by overlapping the spray patterns of multiple liquid nozzles and the airstreams containing recycled fine powder. In this work, the role of the recycled fines stream is explored by measuring the extent of agglomeration. Two scales are investigated, a small-scale dryer with nominal capacity of ~ 1 kg/h and a pilot-scale dryer of ~ 75 kg/h. Experiments were designed to investigate a number of parameters at three levels: low, medium and high about midpoints that represent typical operation at each scale. These operating points are representative of those available, or potentially available, to operators of agglomerating spray dryers: spray flow rate, spray solids concentration, spray droplet size, powder flow rate, and powder particle size. Drying conditions were kept as constant as possible and all experiments used skim milk powder. A measure of success, called the agglomeration efficiency, was developed based on examining the agglomerated product size distribution relative to the spray and fines. The efficiency reflects the proportion of particles sizes that disappear from the spray size distribution and then appear in the agglomerated product after the fines have been censored from it. Comparisons were made between the reference case of natural agglomeration when the dryer was run without fines, and later forced agglomeration trials with fines. These confirm that fines addition does promote agglomeration. Trials containing fines show that the extent of agglomeration depends principally on the mass flux ratio of fines to spray followed by the particle size of the fines; this can be linked to the probability of interaction between spray and fines in the turbulent interaction zone. The concentration of the spray liquid has a weaker effect on influencing forced agglomeration, but has a major influence on the final product particle size because high solids concentrations promote natural agglomeration when sprays interact. This relates to the development of surface stickiness which influences the success of collisions. The two scales of dryer have the same trends and approximately scale.

Milks and Milk Concentrates: Surface Tension Measurement

Surface tension is an important property of milk concentrates because it affects atomisation in spray drying. A Krüss tensiometer and Wilhelmy plate were used to measure surface tension. Skim milk and whole milk were tested at a range of solids concentrations and were compared with the surface tension of standard and reconstituted milks. It was found that surface tension was affected more by temperature than by fat content or solids concentration. The surface tensions for concentrates correspond to published values for standard milks below 60°C, but above 60°C, the surface tension increases markedly, which can be attributed to changes in the milk chemistry. The difficulty associated with using the Wilhelmy plate method is the time taken to perform each measurement, which allows a skin to form and reduces the accuracy of the measurements.

The Slip Extrusion Test: A Novel Method to Characterise Bolus Properties

The role of mastication is to prepare a bolus for safe swallowing. The Swallow Safe model defines deformability, slippiness, and cohesiveness as key properties that influence whether a bolus is safe to swallow. Defining these properties numerically is difficult and current instruments used for bolus analysis have limitations. The slip extrusion test (SET) was developed to objectively measure the swallowability of the bolus through determination of its resistance to deformation and slip. The test measures the force needed to extrude a bolus through a bag as it is pulled through a pair of rollers, imitating the swallowing action of a bolus. Three food model systems were used to evaluate the SET: (a) viscous solutions with varying viscosity, (b) gels with varying hardness, and (c) particulate systems of varying cohesion. The test was applied to peanut boluses produced in vivo to demonstrate its potential in characterizing boluses. The deformation and slip resistance measurements correlated well with the hardness and viscosity measurements of the gels and viscous solutions respectively (correlation coefficient r = .94 between deformation resistance and hardness; r = .85 for slip resistance and hardness in gels; r = .98 for deformation resistance and viscosity; r = .93 for slip resistance and viscosity in solutions). The advantage of the SET is it can evaluate the swallowability of a wide range of foods of different structure and composition. It could potentially be used to investigate the properties of boluses throughout oral processing and help in establishing the criteria for a safe to swallow bolus in a quantitative way. PRACTICAL APPLICATIONS The test could be used to measure bolus properties from the initial stages of breakdown to the point of swallow for all types of food. The ability to measure the changes in bolus properties through all stages of breakdown using the same instrument is a significant development. The resistance to deformation and slip are quantitative measurements that could potentially be used to further develop the Swallow Safe model by providing numerical limits to the identified properties. This could be of interest to the development of foods for dysphagia sufferers.

A statistical analysis of international test methods used for analysing spreader performance

Abstract There are a number of tray testing methods used throughout the world to assess the distribution accuracy of fertiliser spreaders, all of which calculate differences in distribution pattern. The main objective of this work was to perform a statistical analysis of the differences between methods. The effect of variations in calculated bout width due to change in distribution pattern was investigated. Six international test methods were compared simultaneously using a matrix of 1400 trays, each 0.5 × 0.5 m. Each test method was able to be extracted from the tray matrix. Urea fertiliser (46% N) was used for all tests at three application rates, 80, 100, and 150 kg ha–1. A simulation model created in @RISK was used to predict certifiable bout widths from each test method using overall spread pattern characteristics and statistics. Results indicated that there were major variations in calculated certifiable bout width using the different methods. Tray layout within ±5 m of the spread line had the biggest effect on calculated bout width. Method designs that incorporated trays in the longitudinal direction were more accurate in predicting the average variation than when a single transverse test was used. In conclusion, if comparison is required between two or more spreaders, the same test method and tray layout should be used. Having a sufficient concentration of trays within ±5 m of the centre of the distribution pattern will describe the behaviour of a spreader with greater accuracy.

Variable–Rate Application Technology for Aerial Topdressing Aircraft.

It has long been recognized that pasture production in New Zealand’s hill country, beef and sheep sector, is highly variable. Annual pasture production on individual farms typically varies between 4,000 to 11,000 kg DM ha-1. The terrain is often difficult to access and travel on with wheeled vehicles, this lead to the use of topdressing aircraft for fertilizer application some 50 years ago. Over the last decade the industry has seen the uptake of GPS technology for guidance assistance for the pilots. This project has taken it one step further by implementing variable rate technology for fertilizer application. The criteria for deciding on the fertilizer application rate are presently the slope and aspect of the terrain. The properties are mapped using existing imagery and a digital elevation model created. Other areas such as native bush and recognized waterways are filtered out in order to avoid fertilizer contamination. The system will shut off flow before the water body is reached and start applying once the water body is crossed. The system does not restrict the jettisoning of fertilizer or lime in an emergency. The system has been tested and meets Civil Aviation Authority (CAA) requirements. The shut off distances and distances to change flow rate have been tested, shut off is achieved within 0.5 of a second, the distance this translates to, in terms of fertilizer landing on the ground, depends on aircraft height, speed, material and rate being spread. The system is presently being used in the North Island of New Zealand to evaluate the technology.

Defining the end‐point of mastication: A conceptual model

The great risks of swallowing are choking and aspiration of food into the lungs. Both are rare in normal functioning humans, which is remarkable given the diversity of foods and the estimated 10 million swallows performed in a lifetime. Nevertheless, it remains a major challenge to define the food properties that are necessary to ensure a safe swallow. Here, the mouth is viewed as a well-controlled processor where mechanical sensory assessment occurs throughout the occlusion-circulation cycle of mastication. Swallowing is a subsequent action. It is proposed here that, during mastication, temporal maps of interfacial property data are generated, which the central nervous system compares against a series of criteria in order to be sure that the bolus is safe to swallow. To determine these criteria, an engineering hazard analysis tool, alongside an understanding of fluid and particle mechanics, is used to deduce the mechanisms by which food may deposit or become stranded during swallowing. These mechanisms define the food properties that must be avoided. By inverting the thinking, from hazards to ensuring safety, six criteria arise which are necessary for a safe-to-swallow bolus. A new conceptual model is proposed to define when food is safe to swallow during mastication. This significantly advances earlier mouth models. PRACTICAL APPLICATIONS The conceptual model proposed in this work provides a framework of decision-making to define when food is safe to swallow. This will be of interest to designers of dietary foods, foods for dysphagia sufferers and will aid the further development of mastication robots for preparation of artificial boluses for digestion research. It enables food designers to influence the swallow-point properties of their products. For example, a product may be designed to satisfy five of the criteria for a safe-to-swallow bolus, which means the sixth criterion and its attendant food properties define the swallow-point. Alongside other organoleptic factors, these properties define the end-point texture and enduring sensory perception of the food.

Technical Note: A Comparison of Shear Tests Using Carr-Walker and Schulze Annular Shear Cells on Commercial Agricultural Crushed Limestone of New Zealand

Crushed agricultural limestone is used extensively throughout New Zealand to raise the pH of the countrys largely acidic soils. The materials used are quarried from areas of varying mineralogy and levels of purity and are measured in calcium carbonate neutralizing equivalence, which must be greater than 65%. About half of the agricultural limestone used in New Zealand is applied by aircraft due to the terrain of the pasture land in production. The flow properties of limestone are of interest, as a number of accidents have occurred as a result of the limestone failing to discharge from the hoppers of the aircraft applying it. A copy of the Carr-Walker annular shear cell was used to measure the strength characteristics of crushed agricultural limestones from New Zealand. Measurements were also made on samples of the same materials using a Schulze RST-XS 200 mL tester, and the results were compared. Five limestones were tested and multipoint loci were produced, from which four point powder flow functions were obtained. In addition, wall yield loci were compared, and hopper opening and half angle were calculated to compare the design differences resulting from the yield loci of each shear cell. The results from the Carr-Walker cell were less conservative for cohesive materials than those obtained from the Schulze cell, which performed more closely to the Jenike shear cell. These results are consistent with earlier findings that the Jenike shear cell did not offer design criteria that provided agreement with engineering practice for some materials.

Resolving the Agricultural Crushed Limestone Flow Problem from Fixed-Wing Aircraft

There are on average 13 aerial topdressing accidents and about four deaths per 100,000 flying hours in New Zealand; currently, one pilot is killed every 215 days. The number of fixed-wing flying hours undertaken each year varies between 30,000 and 55,000. Crushed agricultural limestone is the most cohesive material commonly applied as a bulk solid from fixed-wing agricultural aircraft in New Zealand, and limestone is present in a disproportionate number of these accidents. The failure of limestone to flow out of the aircraft when desired is one probable cause. In addition, unless products are free flowing, controlling the spread is impossible, and they cannot be applied at the desired application rate from an aircraft. Shear tests on ten commercial Fertmark-registered crushed limestones showed them all to be either cohesive or easy-flow materials as rated by the Jenike flow index. Loose bulk densities and tapped densities were measured for each of the limestones. These were much more variable than the particle densities, which were measured using helium pycnometry. Variations in bulk density are caused by the way the particles pack, which largely reflects differences in the particle size distributions. Removing the fines smaller than 325 µm in a sample of Whiterock limestone, thus reducing the span of the particle size distribution, produced a free-flowing bulk solid whose flow rate was consistent with that calculated using an established equation and parameters. In contrast, the as-received material was a borderline cohesive/easy-flow bulk solid. The cohesion problem, therefore, is apparently caused by the packing of fine particles into the void spaces, which occurs as a result of the wide particle size distributions in as-received commercial products.

Modeling the Coarse Fraction of Solid Fertilizer Deposition from a Fixed-Wing Aircraft: 1. A Ballistics Model

A particle ballistics model is proposed to predict the landing position of granular fertilizer particles ejected from fixed-wing agricultural aircraft. The model is a single-particle model that predicts flight trajectory from the particle force balance based on the aircraft ground speed, axial and tangential propeller wash, wind characteristics, and particle properties including sphericity. As an input, the model relies on known exit velocities from the spreader device mounted underneath the aircraft. When simplified, the mathematics for a particle falling vertically in quiescent air is the same as that developed by Grift et al., 1997 [Trans. ASAE 40(1): 13-20]. Without the propeller wash model, comparison is made to the lateral prediction of Bansal et al., 1998 [Trans. ASAE 41(3): 537-544], who used a simpler model for which similar results and similar trends are obtained. Lastly, with the propeller wash model turned on, model predictions are compared to predictions from AGDISP 8.15. Again, results and trends are similar. The model takes the first step in creating a system to evaluate the performance of agricultural aircraft with respect to delivering variable-rate application technology. The next step is to include a gatebox/distributor model so that a transverse spread distribution pattern can be generated by running the model multiple times, and then to validate this against field measurements.