Engineering design of spraying systems for horticulturalapplications using computational fluid dynamics

Bij zowel voor- als naoogstbehandelingen van tuinbouwproducten wordt spuittechnologie gebruikt met het oog op een verbeterde productkwaliteit. Het onderzoek richtte zich op twee verschillende spuitsystemen in de productieketen van tuinbouwproducten: dwarsstroom boomgaardspuittoestellen met luchtondersteuning en bevochtingssystemen op basis van microverneveling. In de eerste toepassing leidt onoordeelkundig gebruik van de toepassingtechniek tot drift en milieuschade en fytotoxische effecten ten gevolge van overdosissen. De tweede toepassing beoogt het voorkomen van te sterke uitdroging van product, terwijl verkeerd gebruik leidt tot een afname van de koelefficiëntie en de uitgroei van microörganismen. In dit onderzoek beogen we een beter ontwerp en engineering van spuitsystemen. De hoofddoelstelling is het ontwikkelen van een modelgebaseerde methodologie voor ontwerp en engineering van spuitsystemen. De kern van deze methodologie is een 3-dimensioneel Computational Fluid Dynamics (CFD) model dat de relevante variabelen van het spuitproces in de verschillende toepassingen berekent als functie van de instelparameters en omgevingscondities. Het pad van de vernevelde druppels wordt voorspeld door middel van een Euleriaans-Lagrangiaans deeltjestransportmodel. Dit model brengt de effecten van turbulente dispersie, druppelverdamping, en de volledige koppeling van momentum, warmte- en massaoverdracht tussen de continue luchtfase en de discrete druppelfase in rekening. De berekeningen maken het voor het eerst mogelijk om voor elke specifieke configuratie een gedetailleerde en kwantitatieve evaluatie te maken van de spuitnevelverdeling, de luchtstroming, de depositie van de druppels, de temperatuur en de relatieve vochtigheid, zowel ruimtelijk als in functie van de tijd. Voor boomgaardspuiten werd een gevalideerd CFD model ontwikkeld dat rekening houdt met het profiel van de luchtondersteuning, de tractorsnelheid en de dopkarakteristieken. Zo werd het mogelijk ontwerp en instelling van spuittoestellen te verbeteren en te implementeren in de praktijk, met een verlaagd risico op drift en een uniformere spuitnevel. Dwarsstroom boomgaardspuittoestellen produceren een complex drie-dimensioneel profiel van de luchtondersteuning, dat niet kan beschreven worden met de bestaande theorie van luchtstralen. Het volledige 3-D profiel van de luchtstroming beïnvloedt in grote mate de beweging van de druppels, en is sterk afhankelijk van ventilatorsnelheid en tractorsnelheid. Het verticaal profiel van de spuitnevel wordt tevens sterk beïnvloed door de druppelgrootteverdeling van de spuitdoppen. Voor een reductie van drift, moeten het aandeel van fijnere druppels zo laag mogelijk worden gehouden, en de instellingen van de luchtondersteuning aangepast. Het gebruik van veldspuitdoppen werd aangereikt als een middel om dit te verwezenlijken. Voor bevochtingssystemen in koude bewaarruimten werd een gevalideerd multischaal CFD model ontwikkeld dat rekening houdt met het ontwerp van de bewaarruimte en koelinstallatie, de thermofysische producteigenschappen, de stapelwijze en de dopkarakteristieken. De plaatsing en instelling van bevochtigers en het ontwerp van de bewaarruimte werd aanzienlijk verbeterd om te komen tot een reductie van de condensatie en een verhoogde waarde en uniformere verdeling van de relatieve vochtigheid in de ruimte bij lage temperatuur. Het multischaalmodel bestaat enerzijds, op de kleinste schaal van de individuele box met producten, uit een gecombineerd discrete-elementen (DE) en CFD model en anderzijds, op de schaal van de complete bewaarruimte, uit een CFD model met een poreus-medium model van de productstapel. De anisotrope parameters van het poreus-medium model werden bepaald door het DE-CFD model. Er werd aangetoond dat deze multischaal aanpak resulteerde in nauwkeurigere voorspellingen van luchtsnelheid, temperatuur en relatieve vochtigheid in toepassingen met gestapelde producten. Intervalbevochtiging met hoge-druk doppen werd voorgesteld als oplossing voor het verhogen van de relatieve vochtigheid, reductie van de inkoeltijd en het verkleinen van vochtverlies van de producten in de bewaarruimte. Om te komen tot en reductie van excessieve condensatie, moet deze methode evenwel gecombineerd worden met een geoptimaliseerde plaatsing, druk en debiet van de doppen, een voldoende lang verdampingspad voor de vernevelde druppels en het juiste bevochtingsinterval en duur. De geoptimaliseerde waarden zijn specifiek voor een bepaalde bewaarruimte en toepassing. De resultaten toonden aan dat verbeteringen in de praktijk mogelijk zijn aan de hand van de generieke ontwerpmethodologie die in dit doctoraat werd ontwikkeld.status: publishe

Design, development, and testing of rice-husk fueled mixed-flow rice dryer for small-scale rice producer farmers

In underdeveloped nations, rice is frequently harvested at a relatively high moisture content and then dried under the open sun to a storage moisture content. However, direct UV exposure, rain, dust, premature drying, contamination, and open sun drying are all associated with problems like poor grains, discolorations, and cracking. Commercial mechanical dryer utilization is not practical in remote regions due to the absence of electrical service, high startup costs, and ongoing operating expenses. In this work, a pilot mixed-flow rice drier that ran on rice husk energy and solar energy to power the driving fan was designed, produced, and tested. The major parts of the dryer assembly that were conceived and created were the combustion chamber, heat exchanger, and mixed-flow dryer. The results of the trial revealed that the combustion chamber's average temperature was 347.3 °C, the drying air at the heat exchanger output, where the drying chamber was attached, was 63.3 °C, and the combustion chamber and heat exchanger's respective efficiencies were 52.4% and 14.9%. The mixed-flow dryer powered by rice has a significantly lower operating cost than a comparable dryer powered by electricity, petrol, and diesel. The study makes it evident that such a reasonably priced and effective rice dryer might significantly help small-scale rice producers to extend the storage duration and maintain the quality of their product

Evaluation of water flow in cotton yarn and fabric assemblies for capillary evaporative cooling

AbstractIn cotton yarn bundles and fabric layers, wicking and rate are accounted as crucial indigenous liquid transportation properties, playing a significant role in temperature reduction on their surfaces and being used to extend the food and agricultural storage life. In this article, manual test methods are described to measure water wickability and wicking rate of cotton yarn bundles and plain weave fabric layers. These methods described the water flow through the in-plane surface of yarn bundles and fabric layers oriented in either vertical or horizontal lines without external force. The wicking lengths and wicking growth rates in both untreated and treated cotton yarn bundles and fabric samples in either in-plane vertical or horizontal orientations were compared. The highest to lowest wicking length and rate were found in the treated yarn bundles, treated fabric layers, untreated yarn bundles, and untreated fabric strips, respectively. The wicking height and length obtained in untreated yarn bundles and untreated fabric layers was lower than the Kraft paper. The higher wicking and rate values indicate a considerable potential for liquid water migration. The results indicated that treated yarn bundles and fabric layers that are oriented horizontal direction are the best options for constructing capillary evaporative cooling

Studying the impact characteristics of spray droplets on plant surfaces using a multiphase CFD model

peer reviewedThe impact characteristics of spray droplets on plant surfaces was investigated based on a multiphase computational fluid dynamics (CFD) model using the Volume Of Fluid (VOF) approach. The contact angle of the droplet on different surfaces was measured and included as a model parameter. The model was validated using experimental results that were conducted on different plant surfaces (apple, pear, cabbage and leek) and the model was applied to study the effect of droplet impact velocity, droplet diameter, formulation and surface topology on droplet impact characteristics. For each combination of model parameters, the model was capable of predicting the droplet impact outcome (adherence, rebound, splash and shattering). The results showed that multiphase CFD model has a capacity to predict the behavior of plant protection mixture droplets at impact on target surfaces

A leakage model of postharvest storage facilities

A leakage model to describe gas transport between postharvest storage facilities and their environment was developed. The model assumed the gas flow to be proportional to the pressure difference between the storage facility and the environment. A protocol was developed to perform a standardized leakage test to define a specific value for the leakiness of the storage facility which is independent of storage facility characteristics and allows comparison. The proposed methodology allows not only to estimate the leakage before start of the storage season, but allows to estimate and monitor the leakiness of the facility after loading of the fruit throughout the storage season. The model was experimentally validated in controlled atmosphere conditions in which different kinds of known leaks were induced in an empty gastight storage container. The model was able to predict the measured pressure changes accurately for all induced leakages.status: publishe

The extent of groundnut post-harvest loss in Africa and its implications for food and nutrition security

Reducing post-harvest loss conserves resources such as natural, human, and financial inputs that help reduce poverty, raise household incomes, and improve rural livelihoods. The plant-based protein, higher unsaturated fat content, and higher fiber value of groundnuts make them preferable for nutrition enhancement. Groundnut is also well known for its environmental significance, as it reduces the use of chemical fertilizer by fixing nitrogen from the air and enriching soil fertility. However, there are few published scientific reports on groundnut post-harvest loss assessment in African countries. Moreover, published studies of groundnut post-harvest loss focused primarily on biodeterioration during storage. Hence, this review aimed to assess the underlying causes, extent of post-harvest quality and quantity loss of groundnut in the supply chain, and post-harvest loss mitigating technologies in Africa and their implications for food and nutrition security. This review found that the higher drudgery required in the groundnut supply chain is a limiting factor for smallholder farmers in sub-Saharan African countries. Groundnut qualitative and quantitative post-harvest loss is higher during groundnut pod stripping and shelling and also during on-farm and warehouse storage of groundnut in the supply chain. Post-harvest losses of groundnut in African countries extend from 8.9% (Ghana) to 31% (Uganda). Higher-quality groundnut producers do not receive a higher market price as traders and processing factories do not test for aflatoxin content during purchase, which lets producers not follow labor- and cost-demanding good agricultural practices. In conclusion, adopting and providing improved groundnut varieties, aflatoxin control mechanisms, and post-harvest technologies of higher efficiency, lower cost, and local availability should be carried out. In addition, public awareness of aflatoxin toxicity and mitigation measures should be widely disseminated

Nutritional, Physicochemical, Functional, and Textural Properties of Red Pepper (Capsicum annuum L.), Red Onion (Allium cepa), Ginger (Zingiber officinale), and Garlic (Allium sativum): Main Ingredients for the Preparation of Spicy Foods in Ethiopia

Spices are known to have important benefits in our daily diet, and it is common to see industrial and traditional spicy foods in our households and markets. In the present work, a systematic profiling of the nutritional, physicochemical, and textural properties of red pepper, garlic, red onion, and ginger was conducted. The detailed data of forty eight (48) parameters that consisted of macronutrients, micronutrients, physicochemical properties, functional property, and rheological properties of each of the components were organized. The result showed that red pepper had the highest content of crude protein (14.7%), crude fat (11.3%), crude fiber (38.57%), ash (6.7%), redness (a∗ value) (32.5), CI (37.4%), and porosity (37.43%) compared to garlic, ginger, and red onion. Garlic had the highest content of carbohydrate content (76.42%), energy (346.58 kcal), pH (6.03), total soluble solid (26.76), particle size (D90, 561 µm), and volume weighted mean (238 µm) which is related to the high antimicrobial and antioxidant quality of garlic. Red onion had the highest content of Zn (71.16 mg/100 g), Na (94.5 mg/100 g), and Ca (71.16 mg/100 g) indicating that it is a rich source of minerals. The availability of data about the nutritional, physicochemical, functional, and textural properties of the ingredients is crucial for the production and formulation of industrial and traditional spicy foods with the highest quality and stability

Evaluation of a chicory root cold store humidification system using computational fluid dynamics

Humidification of chicory root cold stores helps in maintaining the quality and extending the postharvest storage time of chicory roots. Low evaporation rate of the sprayed droplets at such sub-zero temperatures (-2 degrees C to -1 degrees C) favours surface deposition that could have an adverse effect on the efficiency of the storage room. A three-dimensional computational fluid dynamics (CFD) model was developed and used to predict the storage room air velocity, temperature and humidity distributions, and fate of the water droplets that were sprayed for humidifying the storage room. The humidification system in a chicory root cold store was then optimized. The efficiency of the humidification system was affected by length of cold air deflector, stack height, number of nozzles and duration of humidification. Elongating the air deflector, reducing the stack height, reducing the number of nozzles and shortening the humidification time increased the amount of droplet evaporated and decreased the amount of droplet deposited on the stack. The following combinations of room design and operating parameters could clearly give the best performance of the humidification system: deflector length of 0.8 m, two nozzles with an interval humidification of 1.5 min on and 2 min off cycle and stack height of 3.4 m. (C) 2009 Elsevier Ltd. All rights reserved.status: publishe

Model based study of parameters that affect the impact behavior of droplets on leaves

Improper spraying of pesticides can cause lower biological efficacy, and can cause damage to the environment and human health. Understanding the interaction between application system, the formulation of the plant protection chemical, the surface morphology of the plant surface and the micro climate conditions can help in minimizing these adverse effects. The dynamic behavior of the droplets during impact on leaves was investigated using a computational fluid dynamics (CFD) model. The study is conducted using the Volume Of Fluid (VOF) approach. The model was developed based on young cabbage and leek (hydrophobic surface), and old apple and pear (hydrophilic surface) leaves. The contact angle of the droplets on the leaves was measured and applied as model parameter. The model was validated using experimental results that were conducted on different leaves. The validated model was applied to study the effect of droplet impact characteristics (velocity, diameter and direction), liquid formulation, surface topology and orientation. For each combination of model parameters, the model was capable of predicting the dynamic impact behavior of the droplet and the outcomes (adherence, rebound and splash) of the impact process The impact process was highly affected by leave surface property, droplet impact characteristics and liquid formulation. For higher surface inclination, even for the highly hydrophobic leaf surfaces due to the effect of gravity the droplets did not rebound rather slid down the surface. The presence of surfactant increased the spread diameter and the adherence tendency of the droplets. The characteristics of impact behavior was expressed using dimensionless number of Weber, Reynolds and Ohnesorge numbers. The result showed the capacity of CFD model to understand the impact characteristics of pesticide droplets on leaves.status: publishe

Model-based design and development of horticultural produce crate from bamboo

AbstractThis study proposes a model-based design and development of ventilated horticultural product crate from bamboo using a validated computational fluid dynamics and finite element analysis models. The models were used to predict the airflow, pressure and temperature distributions, and mechanical integrity of the crate. The model results were validated using experimental results. Results of the newly developed crate were compared to the commonly used conventional wooden crate. The optimal vent area, vent number, and cooling air velocity were found to be 8%, nine vents, and 1.38 m s−1, respectively. Compared to the conventional crate, the improvement in cooling rate, pressure drop, and flow uniformity was 60%, 98%, and 37.9%, respectively. The maximum deformation in the conventional wooden and newly developed crates was 28.483 mm and 0.329 mm, respectively. The results indicate that the newly developed bamboo-based crate has good air ventilation, good cooling, and best in mechanical integrity. We conclude that the improved bamboo crate is a viable alternative to the present post-harvest packaging constraints