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Determination of Thermal Diffusivity of a Maize Cob

MT Islam
Principal Scientific Officer
FMPHT Division, Bangladesh Rice Research Institute, Gazipur-1701

MA Zami
Senior Scientific Officer
FMPHT Division, Bangladesh Rice Research Institute, Gazipur-1701

MA Islam
Senior Scientific Officer
FMPHT Division, Bangladesh Rice Research Institute, Gazipur-1701

Abstract/ Executive Summary:

This study is concerned with the development of temperature profile inside a maize cob. There was no significant difference in the temperature distribution through the central region during heating or cooling. A faster temperature response was noticed in the germ part. The resistance to heat flow seems to be considerable in a region between the germ and the root of the kernels. Airflow has no significant effect on the temperature distribution, at least within the velocity range of 1.1 m/s to 2.33m/s. Thermal diffusivities wee calculated by graphical method and found to be in close agreement with the results for other cereals.

Keywords: Maize cob, Thermal diffusivity, Temperature distribution, Finite difference method

Location: Nairobi, Kenya

Start Date: 14-05-1994

End Date:

Program Area: Farm Mechanization

Non-commodity: Performance

Objectives:

Objectives:To determine the thermal diffusivity of a maize cob

Methodology:

The cob used in this study was collected from the experimental farm of the University of Nairobi, Kenya. It had been stored in a refrigerator for 9 months. The cob from the lot was randomly selected. Its dimensions were measured by outside calipers. The cob was marked in three positions along its length, two positions at 40 mm inward from each end and one in the middle. Five readings were taken at each position and the average of those readings was considered as the diameter of the cob. The cob selected was 140 mm in diameter.

The cobs were placed inside a cylindrical box with about 300 ml of distilled water and then the box was kept on rolling for 48 hours. The conditioned cob was then kept in the atmosphere to allow the removal of gravitational water. Then four thermo-couple were inserted axially in the cob at the center of the pith, at the periphery of the pithy, at the root of the kernel, and within the germ part of the kernel. These four positions were selected in order to determine the temperature throughout the cob.

Three air-flow rates (1.14, 1.57, 2.33 m/s) were chosen to determine their effect on transfer of heat to the center. The heating temperature of the air has been maintained at 42.5 C+0.5 C during the experimental run.

Two experiments were conducted with each cob. In each of the experiments, one thermocouple was always kept for recording the air temperature. Experiment 1 consisted of heating with subsequent cooling and conducted with a view to establish the nature and rate of heat transfer in a maize cob. Experiment 2 was performed at lower temperatures to minimize the effect of drying and evaporation on temperature change.

Source of Information: Journal of Agricultural Machinery and Mechanization, Vol.3 No.1 &2, 1996

Article Link (Online Journal):

Funding Source:

Total Budget (Tk.) :

Achievement/Findings:

The increase in air velocity slightly increases the rate of change of center temperature, but the effect is small. This suggests that the resistance to heat transfer is largely within the maize cob.

Temperatures are largely uniform during heating or cooling in the central region but the germ pert of the kernel shows a rapid temperature response. These results suggest that the resistance to heat transfer is in a layer between the germ and the root of the kernels. Ambient heating for the cob shows a similar effect.

The shapes of the cooling curves are in better agreement with theory than the heating curves during the final stages. This might be due to evaporative cooling.

Knowledge Management: Journal