The objective of this research was to equate the standard deviation of the frequency of distribution of tomato seed deaths (sigma) in the probit model using a small number of storage conditions and a relatively short storage period. Four accessions of tomato seeds were taken from the vegetable germoplasm bank of the Federal University of Vicosa, Brazil and were used to obtain data of seed longevity under constant conditions of temperature and moisture content. Seed samples with moisture contents of 10, 12, and 14% on wet basis were sealed in aluminum foil polyethylene storage packets and stored at 31, 41, and 51 degrees C over 208 days. Percentage germination Values obtained during storage were transformed into probit and used in multiple linear regressions for determination of the coefficients of the longevity equation. The equation obtained to express the logarithm of sigma presented an adjusted linear coefficient of determination of 0.924 and a standard error of 0.14. All equation coefficients were significant at a 0.001% probability level. The viability model presented an adjusted linear coefficient of determination of 0.707 and a standard error of 10.2% for all data points and seed survival curves.

The research objectives were to improve the probit model for predicting longevity of orthodox seeds by taking into account the seed composition, and to conduct an error analysis to determine the uncertainties involved in the probit model for three seed species (chickpea, cowpea, and soya bean). Multiple linear regression method was employed to determine the dependency of the viability constants of the probit model on seed composition. Probit equations, already developed for six seed species (barley, chickpea, cowpea, groundnut, sorghum, and soya bean), were used to generate a data set in the ranges of 5–25% moisture content and −20 to 70 °C temperature. The improved model obtained, called a generalised longevity model, can be used to predict seed viability as a function of initial seed viability, time period, and seed temperature, moisture content, and composition (carbohydrate, lipid, and protein fractions). The average error for predicting seed viability by using the proposed model (5·8%) was much lower than the average uncertainty of the probit equations (33·9%). The generalised longevity model could be used for seed species with known composition and unknown viability constants. Further research is recommended to validate the proposed model by using experimental data of different seed species.

The research objective was to determine the best airflow rates and fan control methods for preventingspoilage of aerated wheat stored in round bins and large horizontal storages under tropical and subtropical climaticconditions. The best aeration strategies were determined for eight Brazilian locations based on the simulated results ofover drying costs, deterioration, and electrical energy to operate the fan using 10 years of weather data. The computermodel simulated one-dimensional forced convection using a non-equilibrium model, heat conduction in the direction ofthe airflow for periods without ventilation, and grain deterioration during the storage period. The least cost fan controlmethod for wheat aeration was a differential thermostat that operated the fan according to the difference between theaverage grain temperature and the dry bulb temperature of the outside ambient air. The best aeration conditions withgrain at 13% initial moisture content were a differential thermostat setting between 5 and 7C, a linear airflow ratebetween 1 and 3 L s1 m3, and an air temperature increment between 1 and 5C. The maximum allowable storage timesfor storing aerated wheat at 13% initial moisture content in round bins were Curitiba (12 mo), Porto Alegre (11 mo), SoPaulo (10 mo), Belo Horizonte (9 mo), Goinia (8 mo), Florianpolis (8 mo), Campo Grande (7 mo), and Cuiab (4 mo).These maximum times correlated fairly well with the annual average time that the ambient air temperature was below15C. The maximum allowable storage time was up to 3 mo shorter for horizontal grain storage structures than for roundbins.

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.

Equilibrium and non-equilibrium heat and mass balance models are compared to simulate aeration of stored wheat under tropical and subtropical climates using both linear and non-linear airflow distributions. The approach used was to compare deviations in predicted grain deterioration instead of deviations in grain moisture content and temperature. The results produced by the equilibrium and non-equilibrium models were significantly different (P=0·05)when simulating aeration of wheat stored for 1 yr in Curitiba, Brazil because the deviations in grain deterioration were equal to or greater than the uncertainty in predicting deterioration (±30%) for most test conditions. The non-equilibrium model appears more appropriate than the equilibrium model for simulating aeration of stored wheat because it is based on experimental thin-layer drying and wetting equations and equilibrium moisture content equations for desorption and adsorption. In addition, the equilibrium model over-predicts wheat moisture content and temperature, causing an over-prediction of grain deterioration. It is concluded that a more accurate deterioration model is needed to increase the uncertainty in predicting wheat deterioration for simulated aeration of stored wheat.

The objectives were to compare equilibrium and non-equilibrium heat and mass balance models and to determine the relative importance of several parameters in a non-equilibrium model for simulating stored wheat aeration in Winnipeg, Canada with linear and non-linear airflow distributions. Predicted grain deterioration for each grain layer was compared after 3 months of storage for various input conditions. The relative importance of each parameter was determined by changing it within its expected range of variation and by calculating the effect of this change on the predicted grain deterioration, after 3 months of storage. The equilibrium and non-equilibrium models were not significantly different for most conditions analyzed when ventilating from 0000 to 0600 h. The most important parameter to simulate aeration of wheat stored for 3 months in Winnipeg, Canada was the parameter N in the thin-layer drying equation followed by the EMC desorption equation, fan temperature rise, and parameter K' in the thin-layer wetting equation, which were equally important. The deterioration model must be improved because the uncertainty in the calculation of wheat deterioration is much higher than the uncertainty generated by the equations used in the computer program for simulating aeration of stored wheat; wheat bulk density can be considered constant; the net heat of sorption can be neglected; and the ratio of bin diameter to bin height is not important in the mathematical model.

The sorption of carbon dioxide gas (CO2) by wheat was determined in glass flasks at four temperatures (0, 10, 20 and 30 °C) and four moisture contents (m.c.) (12, 14, 16 and 18% wet basis). The gaseous concentrations were analyzed by gas chromatography and the vacuum developed from the sorption of CO2 by wheat was measured with a mercury manometer. The calculated amount of CO2 sorted at equilibrium was a non-linear function of both temperature and moisture content. Sorption of CO2 by wheat decreased with increasing temperature from 0 to 30 °C at 14% m.c., and the initial rate of sorption increased with increasing m.c. from 12 to 18% at a temperature of 20 °C. Sorption was modelled using non-linear regression at two conditions (0–30 °C at 14% moisture content and 12–18% moisture content at 20 °C). The maximum mass of CO2 sorbed in 60 h was 0.510 g/kg of wheat at 18% m.c. and 0 °C and the lowest was 0.224 g/kg at 18% m.c. and 30 °C. A linear relationship existed between the initial CO2 concentration and the concentration after 60 h when 250 g of wheat of 14% m.c. at 20 °C was exposed in 500 ml flasks.

The research objectives were to determine accurate thin-layer drying and wetting equations for ‘Katepwa’ wheat. Equilibrium moisture content (EMC) equations for adsorption and desorption were also developed based on the experimental drying and wetting data. The modified Chung-Pfost equation predicted reasonably well the EMC for both adsorption and desorption of wheat. The range of test conditions were: temperature 7.6–35.1 °C; relative humidity 28–92%; air velocity 0.04–0.2 m s−1; and initial moisture content 9.2–16.7% (wet mass basis). Thin-layer drying of wheat was affected by air temperature, relative humidity, and initial moisture content while thin-layer wetting also slightly depended on air velocity. The semi-empirical equation of Page was more accurate than the theoretical diffusion equation with the diffusion coefficient dependent on temperature only.

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.

Intermittent forced convection through corn and wheat stored in Sorocaba, Sao Paulo State, Brazil, was mathematically simulated using three years of weather data. The objective was to determine the effect of airflow rate and fan control methods on total fan operating time and on moisture content and deterioration of grains in large storages. Continuous aeration at 1 (L/s)/m3 started on 1 March resulted in predicted spoilage of corn within seven months and wheat within three months. Fan control using a differential thermostat or time-clock resulted in less deterioration than for continuous aeration or for no aeration and less energy consumption than for continuous fan operation.