Numerical analysis of a cross-flow fan with two outlets

Paper presented at the 5th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, South Africa, 1-4 July, 2007.Cross Flow Fans (CFFs) are used in air conditioning and ventilation technology because of their compact design and low noise. In addition, CFFs can provide a uniform velocity profile along the width of the fan. This offers an enormous advantage in applications with large width to diameter ratios as needed. However, as the flow pattern inside a CFF is very complex, classical fan design is not applicable. At present, the design of CFFs is most often based on experimental investigation and empirical experience. In order to investigate the behaviour of these type of fans and its relation to the complex flow structure inside casing and rotor, CFD-simulations are carried out. In this study, transient solutions for a two dimensional viscous and incompressible model of the fan are used to assess the cross flow fan with two parallel outlets. The impact of the outlet configuration on the flow patterns is thereby numerically investigated. It is shown that both the diffuser and the position of the vortex wall play a crucial role to achieve stable and balanced volumetric flows through the two outlets.cs201

Analysis of load displacement in grape harvesters and corresponding effect on dynamic weighing system under laboratory conditions

Harvester bin dynamic weighing systems are affected by a number of sources of variation such as field slopes and load displacement. In grape harvesters, the nature of the material (wine grapes and wine grape juice) and its relative composition can vary significantly. Laboratory tests were carried out using hydrogel spheres and water to simulate field dynamic conditions during harvest. This paper quantifies the sources of variation, submitting an instrumented grape harvester to graduated inclination under shaking conditions. Load displacement is characterized using image analysis from recorded movies on four different pitch axis motions of the machine: front to horizontal, horizontal to rear, rear to horizontal and horizontal to front. Differences in the displacement of the load in relation to the machine inclination and to the load composition have been addressed

A mathematical model for the development of mealiness in apples

Mealiness in apples (Malus domestica Borkh.) is an internal quality defect which is characterised by a dry and crumbly texture. It is related to the relative strength of the cell wall and the middle lamella. A mathematical model has been built to relate changes in the texture attributes juiciness, tensile strength and hardness, which are associated with mealiness, to the development of the turgor pressure of the tissue and the degree of hydrolysis of the middle lamella. The latter, in turn, are described in terms of properties which are meaningful from the physiological point of view, such as starch content, soluble solids content, non-hydrolysed and hydrolysed middle lamella, water in the symplast, and water in the apoplast. Biochemical reactions as well as water transfer processes are incorporated in the model. The parameter values of the model are estimated using experimental data from a storage experiment. The model fits the three texture characteristics adequately. The correlation coefficients between the parameters were below 0.96, which indicates that the model does not overfit the data

Reliability of vibration measurements and impact response characteristics for the quality assessment of tomatoes

The applicability of the acoustic impulse-response and the impact response devices for t he measurement of fresh table tomato firmness states with both instruments. A high positive correlation wasfound between the maximal acceleration, measured with the impact response device, and the stiffness measured with the acoustic tester. For the impact tester, the ratio between the maximal acceleration and the impact duration was the most segregating parameter when classifying tomatoes into different firmness classes. For the acoustic tester, the repeatability of the measurements was significantly higher at the equator than at the bottom of the tomato. This was not the case for the impact tester, which gave similar results at both positions. The overall discrimant power of both methods was found to be very similar. For the acoustic tester, discrimination between different firmness states was much better when measuring at the bottom. For the impact tester, it makes not too much difference in discriminat power where to measure

Controlling moisture loss as a tool to reduce bruise susceptibility.

A method to reduce the bruise susceptibility of apples by controlling the moisture loss of the fruit was evaluated. Previous research indicates that reduction of the relative humidity of the storage air leads to an immediate effect on the weight loss and on skin properties and to a lower bruise susceptibility of apples. The diffusion equation is used to determine the waterpotential profile inside the fruit during storage. Characteristics of the waterpotential distribution in the fruit are related to measured bruise volumes. The results indicate how /this model can be used to control bruise susceptibility

A mobile, in-situ soil bin test facility to investigate the performance of maresha plough

Ethiopia is well known for its use of an ard plough dating from antiquity – maresha – which fractures and disturbs the soil. However, hardly any notable progress of experimental research on this animal drawn tillage tool in the field has been made. The attendant problems in current practise are soil-maresha interaction, viz., uneven oxen strength along with different pace of walking, uncontrolled implement behaviour, and field conditions. Taking stock of the experimental research on animal drawn tillage tools in general, most of the documented works on the dynamics of the interaction between soil and animal drawn tillage tools tend to rely on trial-and-error based on factors mainly based on experience and cultural context. As such, no research tailored to systematically handle the link between maresha plough and soil bin experiments exists. To this aim, this study developed a mobile in-situ soil bin facility in which the system was calibrated, tested, and evaluated under outdoor experimental conditions, wherein online measurements of draught, speed, and depth of tillage were carried out. The insights and observations gained from the experimentation were discussed and reported in terms of smooth run, overload, cyclic forces, zero speed with minimal force, stoppage, speed measurement with no force, force measurement with no speed, and low speed with low force

Effect of side-wings on draught: The case of Ethiopian Ard plough (maresha)

Ethiopian farmers have been using an ox-drawn breaking plough, known as ard plough – maresha, for thousands of years. Maresha is a pointed, steel-tipped tine attached to a draught pole at an adjustable shallow angle. It has narrow side-wings, attached to the left and right side of it, to push soil to either side without inverting. The aim of this paper is to explore the effect of side-wings on draught using a field soil bin test facility. To this end, a mobile and an in-situ soil bin test system, for online measurements of draught, was designed and developed. This research considered tool geometry (maresha plough with and without side-wings) and rake angle (shallow – 8°, medium deep – 15°, and deep – 24°, representing primary, secondary and tertiary tillage processes in Ethiopia, respectively). Maresha plough with side-wings has greater contact area, between the moving soil and tool, than its wingless counterpart. When the ploughshare surface and soil slide relative to one another, the draught expected to increase with contact area, as adhesion and friction resistance increases with area. However, experimental analysis indicated that the maresha with side-wings required less draught compared to maresha without side-wings (ρ < 0.001). This might be attributed to the effect of side-wings on crack propagation by a wedging effect to enhance and facilitate subsequent ploughing. This paper also dealt with the effect of rake angle on draught. Though the depth setup was getting smaller d1 < d2 < d3 for the successive tillage runs, analysis showed increment in draught force (ρ < 0.001) with rake angle. This might be attributed to higher soil compaction that comes with depth and downward force resulting from repeated use of maresha every season to the same depth for thousand years. Although more and rigorous studies should be undertaken considering soil, tool, and operational parameters to arrive at conclusive results, this paper gave some insights regarding effect of side-wings on maresha plough and rake angle on draught. This shows that there is still room for improvement of maresha plough geometry for minimum draught requirement and optimum soil manipulation

Discrete element modelling for process simulation in agriculture

This paper presents an overview of discrete element modelling (DEM) as a modelling technique for granular assemblies. It focusses on DEM for agricultural products and processes and discusses important algorithmic and physical issues connected to this domain. Existing applications in the literature are reviewed and an overview of ongoing DEM applications in the Laboratory for Agro-Machinery and Processing is presented. (C) 2003 Elsevier Ltd. All rights reserved.status: publishe

Detection of hollow pears by tree based modelling on non-destructive acoustic respons spectra

After CA storage, some pears show internal breakdown and brown discoloration. This can be caused by a combination of picking time and storage conditions. There is no visual evidence on the outside of the fruit that there is an internal defect. When the quality of horticultural products is a major issue, it becomes a problem for marketing strategies when the consumer finds hollow pears. Acoustic response spectra have already proven to be a valuable tool in the determination of some internal characteristics of fruits, like the stiflhess of tomatoes. The acoustic response spectra show some abnormalities for pears with internal cavities. Classical numerical values (second moment, damping, frequency etc.) based on these spectra, were used to identify non-marketable fruits. An additional Fourier series algorithm of the spectrum and the use of "tree based modelling" on the coefficients yielded satisfactory results. This made it possible to identify the hollow pears quite adequately. Since the protocol is based on nondestructive methods, it is possible to incorporate it in a sorting line. In this way a substantial amount of affected pears can be removed, resulting in better overall quality. © ISHS 1998.status: publishe