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Moisture Sorption Isotherms of Gram

M. M. I. Chowdhury
Department of Farm Mechanics, Patuakhali Agricultural College, Dumki, Patuakhali

R. I. Sarker
Department of Farm Power and Machinery, Bangladesh Agricultural University, Mymensingh

B. K. Bala
Department of Farm Power and Machinery, Bangladesh Agricultural University, Mymensingh

M.A. Hossa in
M.R.M. Division, Bangladesh Agricultural Research Institute, Joydebpur, Gazipur, Bangladesh

Abstract/ Executive Summary:

The adsorption and desorption isotherms of gram 'AC re determined experimentally in relative humidity range of 11 to 93 per cent and at the temperatures of 20, 3 0. 40 and 50° C . The experimental procedure used was the dynamic method with periodically recording of sample mass. The effect of temperature on adsorption and desorption isotherms was found to be significant. Hystereses were observed for the relative humidity range of 1 1 to 97 per cent and hysteresis loops decreased with the increase of temperature. The adsorption and desorption isotherm data were fitted to six isotherm models. The Smith equation was found to be the best fit equation to the experimental data for relative humidity range of II to 93 per cent and at the temperatures of 20^0, 30^0, 40⁰ and 50⁰ C. So the Smith equation is recommended for predicting the adsorption and desorption isotherms of gram.

Keywords: Moisture, Sorption, Isotherms, Gram.

Location: Engineering Laboratory, in the Department of Farm Power and Machinery, Bangladesh Agricultural University, Mymensingh

Start Date: 01-12-1999

End Date: 30-06-2000

Program Area: Crop-Soil-Water Management

Non-commodity: Performance

Objectives:

To determine the sorption isotherms of gram at different temperatures and relative humidity and to fit the experimental data to different isotherm models.

Methodology:

The experiment was conducted at the Process Engineering Laboratory, in the Department of Farm Power and Machinery, Bangladesh Agricultural University, Mymensingh, Bangladesh, during the period from December 1999 to June 2000. The dynamic method was used to measure the adsorption and desorption isotherms of gram. Air tight cylindrical plastic container, 115 mm diameter and 135 mm height. containing saturated salt solutions were placed in an electric oven to provide constant temperature and relative humidity environments. The digital temperature controller provided the desired temperature (accuracy ±1o C). A mini fan of 60 mm (3 V, 0.25 A) was fitted inside the plastic container to provide continuo us stirring of the air inside the container. The values for relative humidity of the saturated salt solutions were obtained .The gram sample of variety BARI-l was dried in the sun from the initial moisture content of about 30 per cent to the final moisture content of about 5 per cent (dry basis). About 20 g of dried sample was put in a nylon box (50 mm diameter and 40 mm height) which was suspended over the saturated salt solutions in a plastic container that was made air tight with a plastic cover. The container was then placed in an oven at a desired constant temperature and allowed to equilibrate with the environment inside the containers. After adsorption or desorption of moisture from the environment in the container, when the mass of sample reached constant, it is assumed that the sample reached the equilibrium condition.

Source of Information: Journal of the Institution of Engineers, Bangladesh Agricultural Engineering Division, Vol. 27/AE, No. 1. Dec. 2000

Article Link (Online Journal):

Funding Source:

Total Budget (Tk.) :

Achievement/Findings:

Equilibrium moisture contents registered high values with the decreasing temperatures. The experimental data was fitted to six isotherm models. The Smith model was found to be the best fit model to describe the adsorption and desorptin isotherms of gram in the temperature range of 20 to 50°C and relative humidity range of 11 to 93 per cent. So the Smith equation is recommended for predicting the adsorption and desorption isotherms of gram.

Knowledge Management: Journal