W. E. Muir

REVIEW OF THIN-LAYER DRYING AND WETTING EQUATIONS

ABSTRACT Thin-layer equations contribute to the understanding of the heat and mass transfer phenomena in agricultural products and computer simulations for designing new and improving existing commercial drying processes. Many different equations have been developed to represent thin-layer drying behaviour of the grains. Many thin-layer drying and rewetting equations are reviewed and discussed. Some suggestions for future coordinated research work arc given.

Some physical properties of fababeans

The specific heat of fababeans, tick beans, (Vicia faba L.) was measured at four moisture contents (10·3, 14·5, 19·5 and 25·0% wet weight basis) and four temperature ranges (−32 to 20°C, 0 to 20°C, 0 to 40°C and 0 to 60°C). The specific heat of fababeans varied from 1·35 kJ kg−1 K−1 at 10·3% moisture content in the temperature range −32 to 20°C to 2·25 kJ kg−1 K−1 at 24·6% moisture content in the temperature range 0 to 60°C. The angle of repose of fababeans measured for four moisture contents varied from 0·36 rad at 8·5% moisture content to 0·41 rad at 20·9% moisture content. For the moisture content range of 8·5 to 21·6% the static coefficients of friction of fababeans ranged from 0·28 to 0·46 parallel to the plywood grain, 0·32 to 0·55 perpendicular to the plywood grain and 0·32 to 0·38 on galvanized steel. Bulk density decreased with increasing moisture content from 850 kg m−3 at 8·5% moisture content to 730 kg m−3 at 34·8% moisture content. The 1000-kernel weight was 405 g at 8·5% moisture content, wet weight basis.

Specific heat of wheat

The specific heat of hard red spring wheat is a linear function of both temperature in the range −33·5 to 21·8°C and of moisture content in the range 1 to 19% wet weight basis. The specific heat of wheat containing 23·4 and 29·6% moisture is not a linear function of temperature and moisture content. Latent heat of fusion is released by wheat containing 23·4 and 29·6% moisture in wide ranges of temperature below 0°C. Moisture in wheat containing 19% or less moisture does not appear to undergo a change in phase down to −33·5°C. Above 0°C the heat content of moisture in wheat appears to be greater than free water. Specific heat of wheat is not significantly affected by dockage in the wheat or by year of harvest.

A simulation model of temperatures in stored grain

Abstract Temperature is one of the most crucial factors limiting the distribution and abundance of anthropods and fungi that contaminate stored grain. A mathematical model, based on the finite-difference method of calculating heat transfer, has been developed to simulate the temperatures in a cylindrical bin of grain. The main variables that can be studied using this computer model are: thermal properties of the grain, initial temperature of the grain, ambient air temperature, wind velocity, diameter of the bin, and type of bin-wall material. Simulation results indicated that grain stored on the Canadian Prairies would remain at lower temperatures and so would probably be in better condition than grain stored at the shipping points of Vancouver, Toronto and Montreal. In small bins, pests may not be able to overwinter while in large bins temperatures remain warmer and many pests may survive. Painting galvanized-steel bins white has a considerable effect on the temperatures of grain in the bin.

THREE-DIMENSIONAL, FINITE ELEMENT, HEAT TRANSFER MODEL OF TEMPERATURE DISTRIBUTION IN GRAIN STORAGE BINS

ABSTRACT A three-dimensional, heat conduction problem in cartesian coordinate system was solved using the finite element method for predicting the temperature distribution in grain storage bins. The program can handle linear and quadratic hexahedron elements with 1, 2, or 3 point Gauss quadrature in each plane. The model can simulate the temperatures in filled grain bins of any shape and at any location, if the hourly weather data (solar radiation, wind velocity, and ambient air temperature) for the location and the grain temperatures at the start of simulation are available. Other input data required for the model include the three dimensional grid data of a linear or quadratic hexahedron element, and the thermal properties of grain, bin wall material, soil and air. Temperatures predicted by the model were in very good agreement with the measured temperatures in two 5.56 m diameter bins containing rapeseed and barley, respectively, located near Winnipeg. Temperatures predicted by the model in 3.0 m and 4.0 m tall rapeseed bulks of various diameters were compared with the temperatures predicted by 2D finite difference and 3D finite difference models. The temperatures predicted by the 3D finite element model and the 3D finite difference model were nearly identical for different locations in the grain bulks. Three dimensional finite element model predicted higher temperatures by about 5 K to 15 K towards the south side of the bin than the north side, whereas 2D model predicted equal temperatures at these locations.

Odor volatiles associated with microflora in damp ventilated and non-ventilated bin-stored bulk wheat

Western hard red spring wheat, stored at 20 and 25% moisture contents for 10 months during 1985-86, was monitored for biotic and abiotic variables in 10 unheated bins in Winnipeg, Manitoba. The major odor volatiles identified were 3-methyl-1-butanol, 3-octanone and 1-octen-3-ol. The production of these volatiles was associated and correlated with microfloral infection. Ventilation, used for cooling and drying of grain, disrupted microfloral growth patterns and production of volatiles. The highest levels of 3-methyl-1-butanol occurred in 25% moisture content wheat infected with bacteria, Penicillium spp. and Fusarium spp. In non-ventilated (control) bins with 20% moisture content wheat, 3-methyl-1-butanol was correlated with infection by members of the Aspergillus glaucus group and bacteria. In control bins, 1-octen-3-ol production was correlated with infection of wheat of both moisture contents by Penicillium spp. The fungal species, isolated from damp bin-stored wheat and tested for production of odor volatiles on wheat substrate, included Alternaria alternata (Fr.) Keissler, Aspergillus repens (Corda) Saccardo, A. flavus Link ex Fries, A. versicolor (Vuill.) Tiraboschi, Penicillium chrysogenum Thom, P. cyclopium Westling, Fusarium moniliforme Sheldon, F. semitectum (Cooke) Sacc. In the laboratory, fungus-inoculated wheat produced 3-methyl-1-butanol; 3-octanone and 1-octen-3-ol were also produced, but less frequently. Two unidentified bacterial species isolated from damp wheat and inoculated on agar produced 3-methyl-1-butanol.

Fungal volatiles associated with moldy grain in ventilated and non-ventilated bin-stored wheat.

The fungal odor compounds 3-methyl-l-butanol, l-octen-3-ol and 3-octanone were monitored in nine experimental bins in Winnipeg, Manitoba containing a hard red spring wheat during the autumn, winter and summer seasons of 1984–85. Quality changes were associated with seed-borne microflora and moisture content in both ventilated and non-ventilated bins containing wheat of 15.6 and 18.2% initial moisture content. All three odor compounds occurred in considerably greater amounts in bulk wheat in non-ventilated than in ventilated bins, particularly in those with wheat having 18.2% moisture content. The presence of these compounds usually coincided with infection of the seeds by the fungi Alternaria alternata (Fr.) Keissler, Aspergillus repens DeBarry, A. versicolor (Vuill.) Tiraboschi, Penicillium crustosum Thom, P. oxalicum Currie and Thom, P. aurantiogriseum Dierckx, and P. citrinum Thom. High production of all three odor compounds in damp wheat stored in non-ventilated bins was associated with heavy fungal infection of the seeds and reduction in seed germinability. High initial moisture content of the harvested grain accelerated the production of all three fungal volatiles in non-ventilated bins.

Airflow Requirements Predicted for Drying Grain with Ambient and Solar-Heated Air in Canada

ABSTRACT COMPUTER simulation was used to determine the rate of airflow required to dry wheat at Edmonton, Swift Current and Winnipeg and to dry corn at Winnipeg and London with ambient air and with air heated with two sizes of solar collector. For each crop five initial moisture contents and five harvest dates were con-sidered. Airflow requirements increased from the north-west to the southeast. Airflow requirements decreased by approximately 50 percent for each months delay in harvest and approximately doubled for each increase of two percentage points in initial moisture content.

Temperature and Geotaxis Preference by Cryptolestes ferrugineus (Coleoptera: Laemophloeidae) Adults in Response to 5°C/m Temperature Gradients at Optimum and Hot Temperatures in Stored Wheat and Their Mortality at High Temperature

Abstract Cryptolestes ferrugineus (Stephens) is often found in abundance in association with heating stored grain. Their mortality at high temperature and their distribution at optimum and hot temperatures are important information for insect control and for models of their distribution in grain bins. The lethal exposure times of the adults were determined at 42 ± 0.2–50 ± 0.2°C and 75 ± 5% RH. Insect mortality increased with increasing temperatures and exposure time. For each temperature, there was a cumulative period of thermal stress, and after the critical exposure time an additional few hours or minutes at that temperature would kill all of the adults. The mortality was 100% at 45°C in 78 h, at 47°C in 18 h, at 49°C in 4.5 h, and at 50°C in 3 h. At 50°C, insect mortality determined at 0 h was significantly different than that determined 12 h later after the insects had been moved to room temperature. A regression equation predicted insect mortality better than published models when temperatures were above 45°C. The net displacement of the adults in both vertical and horizontal directions at 27.5–52.5°C was determined in 100 by 100 by 1,000-mm wheat columns at 14.5 ± 0.3% moisture content with or without a 5°C/m temperature gradient. The adults responded to temperature gradients and the preferred temperature was from 30 to 36.5°C. There was no obvious boundary between preference and nonpreference temperatures for the adults. In horizontal wheat columns without a temperature gradient, the adults moved in both directions, and the distribution pattern gradually became more uniform when temperature increased but was under 42°C. At hot temperatures, adults could locate and move to the cooler area in <12 h; however, the adults could not move at 50°C. Geotaxis, temperature gradient, and the interaction between these two factors affected insect distribution and movement direction; and the geotaxis was more influential than temperature gradient at any condition in the vertical columns. A pattern for adult movement was suggested.

DEHYDRATION OF SUGAR-BEET PULP IN SUPERHEATED STEAM AND HOT AIR

The drying characteristics of sugar-beet pulp in superheated steam and hot air at three temperatures (130, 157, and 183°C) and three velocities (0.24, 0.32, and 0.37 m/s) of drying media (air or steam) under atmospheric pressure were studied. The drying rate was higher and the drying time was shorter in superheated steam than in hot air of the same temperature. The drying rate increased and the drying time decreased with increased temperature for both superheated-steam drying and hot-air drying; however, the effect of temperature on superheated-steam drying was greater than on hot-air drying. At 157°C, increasing the velocity of the drying medium did not affect the drying characteristics of the samples dehydrated with hot air, but increased the drying rate at moisture contents greater than 0.5 kg/kg dry basis (d.b.) for superheated-steam drying. Sugar-beet pulp dehydrated with either superheated steam or hot air under the same drying conditions (157°C and 0.32 m/s) had the same water activities.