Non-uniform Airflow Research Articles

Sensitivity analysis of a mathematical model to simulate aeration of wheat stored in Brazil

Abstract The research objective was to determine the relative importance of several variables in a non-equilibrium mathematical model for simulating aeration of stored wheat with uniform and non-uniform airflow distributions. The relative importance of each variable was determined by adding or subtracting fixed uncertainties from that variable and by calculating the effect of these changes on the predicted grain deterioration, after 1 year of storage. Results of simulations using weather data from Curitiba, Brazil, ventilation time of 06:00–12:00, fan temperature rises of 1 and 3 °C, and linear airflows of 0.0056 and 0.0278 m3/s per m2 indicated that the most important variables, in decreasing order, were the fan temperature rise, thin-layer wetting equation, and thin-layer drying equation. Wheat bulk density can be a constant and the net heat of sorption can be neglected. The ratio of bin diameter to bin height and the accuracy of the equations to describe wheat specific heat, air resistance to airflow, and equilibrium moisture content for adsorption and desorption were not important in the mathematical model. The deterioration model must be improved because the uncertainty in the calculation of wheat deterioration was much higher than the uncertainty generated by many of the other variables for the Brazilian climate.

MODELING AND ANALYSIS OF MIXED-FLOW GRAIN DRYER

The nature of the mixed-flow drying process was investigated experimentally and by simulation. Experimentsproved that non-uniform drying occurs among the grain kernels; they pass through the dryer along different pathsbecause of the non-uniform airflow and grainflow patterns in mixed-flow dryers. A two-dimensional drying model wasdeveloped to simulate the drying process. The model confirms the non-uniform drying characteristics of the mixed-flowdryer.

Some effects of air flow maldistribution on performance of a compact evaporator with R134a

An experimental facility has been constructed to enable the effects of air flow non-uniformity on the transfer performance of refrigerant evaporators to be investigated. This is based on an open-circuit wind tunnel, which is equipped with a single component traversing LDA system, capable of determining local mean velocities and turbulence levels. The refrigerant circuit uses R134a and has been designed to allow maximum flexibility in setting test conditions. Preliminary results are presented from tests on a single circuit finned-tube evaporator with 33 tubes, 300 mm long, arranged in an in-line matrix 4 rows deep, with 25 mm spacing. The height of the fin block was 225 mm, the fin spacing and tube external diameter were 4 mm and 9.5 mm respectively. Contrary to expectations, increases in heat transfer duty and overall heat transfer coefficients were recorded as air flow non-uniformities were artificially introduced, whilst a constant mean air velocity was maintained.

Nonuniform Air Flow in Inlets: the Effect on Filter Deposits in the Fiber Sampling Cassette

Smoke stream studies were combined with a new technique for visualizing a filter deposit from samples used to monitor asbestos or other fibers. Results clearly show the effect of secondary flow vortices within the sampler under anisoaxial sampling conditions. The vortices observed at low wind velocities occur when the inlet axis is situated at angles between 45 degrees and 180 degrees to the motion of the surrounding air. It is demonstrated that the vortices can create a complex nonuniform pattern in the filter deposit, especially when combined with particle settling or electrostatic interactions between the particles and the sampler. Inertial effects also may play a role in the deposit nonuniformity, as well as causing deposition on the cowl surfaces. Changes in the sampler, such as its placement, may reduce these biases. The effects noted are not likely to occur in all sampling situations, but may explain some reports of high variability on asbestos fiber filter samples. The flow patterns observed in this study are applicable to straight, thin-walled inlets. Although only compact particles were used, the air flow patterns and forces involved will have similar effects on fibers of the same aerodynamic diameter.

Nonuniform Air Flow in Inlets: the Effect on Filter Deposits in the Fiber Sampling Cassette

Nonuniform Air Flow in Inlets: the Effect on Filter Deposits in the Fiber Sampling Cassette

Finite-element prediction of non-uniform airflow in fixed beds of wheat

Resistances to horizontal and vertical airflow through clean, dry wheat ( Triticum aestivum L. ) were determined. Airflow resistance data, expressed in a functional relationship, were used in a mathematical model describing non-uniform flow of air in stored grain. The mathematical model was solved using the finite-element method to predict static pressure patterns in six laboratory-scale configurations. Predicted pressures compared well with the pressures measured in 47 tests, except for points near the grain surfaces.

Improving the Air Flow Distribution in a Batch Walnut Dryer

ABSTRACT ENGLISH walnuts are usually dried on farm in batch dryers. Field measurements have shown that non-uniform air flow patterns exist in one common type of bulk dryer. These non-uniform air flows are the suspected cause of non-uniform drying that has been observed by some walnut growers. A two-dimensional finite element model has been used to evaluate modifications to improve the air flow distribution within the drying bins.

Experience in production of polymetallic reforming catalysts

Attempts to determine the effect of nonuniformity of air flow on the activity and selectivity of the series KR polymetallic reforming catalyst. Reports that a number of modified KR catalysts have been developed and are being used successfully in the petroleum industry. Discusses the manufacturing technology for the new and more efficient compositions, and emphasizes the importance of calcination. Suggests the following measures to further improve the reforming catalysts: production of new catalyst KR-110, which is an improved analog of the KR-104A with a modified support; production of new versions of the support (A-70 and A-75); production of highpurity aluminium oxide; and preparation of catalysts based on such supports. Points out that a large part of the present reforming capacity is scheduled for changeover to polymetallic catalysts in the eleventh Five-Year Plan.

Pressure and Velocity Field in Airflow Through Packed Bed of Corn Mixed with Fines Under Non-Darcy Flow Conditions

ABSTRACT EXPERIMENTS were conducted for non-Darcy air-flow conditions through a bed of corn with nonuniform fines distribution (porosites). A numerical technique was used to solve for pressure, velocity, and direction of air movement at any point in a conical-top cylindrical grain bed. The basic general equation relating pressure drop with air velocity and fine material is: AP = f(Vn,fm) [a] where fm = f(r,z) for a centrally filled bin [b] Continuity equation was also applied with equations [a] and [b] to solve for the pressure field from which velocity and air direction were obtained. Observed pressures and pressures calculated numerically had a correlation coefficient of 0.94 or more. Numerical method presented here should help in studies of nonuniform airflow through grains and in selecting fans for aeration and drying.