Hungarian Institute of Agricultural Engineering (FVMMI)

Phone: 36-(28)-511-611; E-mail: fmmi@elender.hu

During operation tests heat and material transport processes were determined and fairly accurate mathematical relationships were elaborated to describe the drying characteristics of corn as well as the changes of seed temperature and density.

Aims of the research

Aims of the research were the determination of the processes of heat and material transport of the widely used grain drying systems and analysing and comparison of the drying processes of the traditional thin layer driers with cross-flow system (B1-15) and the thick layer driers with intermittent operation and material circulating system (MECMAR; STELA-MUF)

Material and method

Examinations were carried out under operative conditions. Moisture content of corn varied between 21.3-29.5 %. Types of driers were MECMAR 34/90 and STELA-MUF 70/2 of intermittent running thick layer and material circulating systems. Type of measuring instrument was ALMEMO-5590 heat and airtechnical measuring and data logging system.

Results

Test results and measuring connections of corn drying at different type of driers are shown on Fig. 3; 4; 5; 6; 7.

Drying process can be seen on Fig. 3. While characteristics of the drying speed on Fig. 4. Changing of bulk density of corn are shown on Fig. 5 and Fig. 6. On Fig. 7 laboratory and operational measurings are presented plotted against the moisture content. It serves for verification that maximum value of the bulk density can be measured near the equalibrium moisture content.

Evaluation of results and conclusions

During the tests of heat and material transport of grain drying it has been found as follows.

• Drying process of corn in the range of the examined moisture content
  (29.5 ® 12.0 %) can be described by exponential functions (see on Fig.3.) fairly accuratelly.
• Velocity of drying was 3.00 - 3.10 moisture %/h in the case of thin layer continuous running and cross-flow system and 2.10 - 2.20 moisture %/h in the case of thick layer intermittent running and recirculating type of driers at 110 ^oC pre-setted material temperature. (Fig.4)

• Raising of seed temperature of corn can be described well by a quadratic polynome and in the test conditions did not reach the 50 ^oC that meant a quality drying.

• Owing to the contraction of corn and the abstraction of moisture content density of corn increased by 10.5 – 12.5 % during the drying process. Quadratic equation that described the process had a maximum value around 720 kg/m³ of density, close to the equilibrium moisture content of 14.0 – 15.5 %. In the case of over-drying, between 12.0 – 13.8 % water content, density decreased to about 710 kg/m³.(Fig. 5, 6)

For verifying this theory examinations were carried out with different kind of hybrids in exsiccator. Corn seed with original moisture content of 12-14 % and density of 700-740 kg/m³ were dried under the constant moisture content to 0.04 – 3.60 % value. In this case density decreased to 669-696 kg/m³ while the inner structure of corn was lost. (Fig. 7)

It is worth examinig the diagram of changing of the drying speed in detail (Fig.4) According to the classical theory the speed curve has three stages that differ well from each other. These stages are the steep elevation, the equalibrium condition and the decreasing tendency. In this case all the three curves have maximum values while the stage of constant speed cannot be shown. Our intention is to prove this theory by further investigations.

References

Beke J.: Terményszárítás. Agroinform Budapest, 1997.