Agricultural Research Management Information System

Home
Research Summary
Search
About Us
- ARMIS
- Brochure
Contact Us
Report
User Request
Data Input
Help
- Operation Manual
  - PDF
  - Video
- Program Area & Commodity
We have reached 37600 number of research entries at this moment.

- Logout

Research Detail

Home
Research
Detail

Thin Layer Solar Drying of Rough Rice

M. A. Zaman
Department of Farm Power and Machinery, Bangladesh Agricultural University,Mymensingh, Bangladesh.

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

Abstract/ Executive Summary:

This paper presents a set of simple empirical equations for natural air flow solar drying of rough rice in mixed-mode type dryer, box-type dryer and open floor drying system. The moisture con-tents predicted by the equations were in good agreement with the observed values. The effect of dry me air temperature on the drying rate constants for these three cases were found to be insignificant. The equilibrium moisture content appeared to be the most important variable controlling the drying rate. The highest drying rate was observed in case of mixed-mode dryer. The drying rate of box dryer was next to that of mixed-mode dryer. This study shows that the introduction of solar dryer for drying of rough rice is highly recommendable in Bangladesh.

Keywords: Solar Energy, Farm Power and Machinery, Solar Drying, Rough Rice

Location: BAU farm, Mymensingh, Bangladesh.

Start Date: 00-06-1984

End Date: 00-12-1984

Program Area: Farm Mechanization

Commodity: Drier

Objectives:

To concern for the development of thin layer solar drying of rough rice in Bangladesh

Methodology:

The three main categories of rice grown in Bang-ladesh are Aus. Aman and Boro. These crops are usually harvested during the period of July to mid-August, mid-November to mid-January and mid-April to June, respectively. The solar drying experiments of rough rice were performed simultaneously in mixed-mode type dryer and box-type dryer in June, August and December of 1984. The ranges of solar radiation, initial moisture content and temperatures inside the dryers during drying shows the ambient and temperatures inside the dryers in a typical day of December 1984. The grains used in these experiments were obtained from the BAU farm and were re-moistened before drying. The moisture contents were determined by air oven method. The grains in each of the test dryers and open concrete floor were about 80 mm thick. Each test run started at 9 a.m. and continued until 4 p.m. For each test three samples of about 300 g of rough rice were placed in a wire mesh tray in each drying unit. During each test the weights of the trays were measured at a regular interval of 1 hour by removing them from the units for approximately 15 - 20 seconds. The ambient dry bulb and wet bulb temperatures, and temperatures inside the dryers, were measured by copper thermocouples connected to digital thermometer (Micromite) at regular interval of 1 hour. Dryer temperatures were measured at 18 positions and the average value was considered as the temperature of drying air. The thermocouples were suspended They were equally spaced in the dryer box. In all, 18 experiments were conducted. The moisture content at any time t was computed from the weight of sample at time t and initial weight and moisture content using the following relationship. M_t= (W_t/W_o)(1 + M_o) - 1 (1) The average drying rate over the time interval t_i to t_i₊₁ was computed as dM/dt = (M_i+1— M_i)/(t_i₊₁ – t_i ), (2) The average moisture content and average temperatures were calculated as (M_av)_i = (M_i + M_i+1)/2, (3) (T_av)_i = (T_i + T_i+1)/2, (4) The ambient relative humidity was computed using the eqns (5), (6), and (7). rh = (P_w/_Ps)(T_d), (5) The saturated vapour pressure, (P_sT_d), at dry bulb temperature, Td, in absolute scale is given by [7] Ps = exp[52.576 – 6790.5/T_d – 5.0281 ln (T_d)], (6) The vapour pressure, P,,, at wet bulb temperature, T , in absolute scale is given by Pw = P_s (T_w) – γ (T_d – T_w), (7) where γ = 0.063 and Ps(T_w) in eqn (7) is calculated using T_w in eqn (6).The humidity of air was calculated from the fol-lowing relationship. H = 0.622 P_w /(P – P_w), (8) For any time interval the ambient air was assumed to be heated to the average temperature inside the dryer without any change in humidity during that interval.

Source of Information: Solar Energy Vol 42. No 2, pp. 167—171, 1989 (Printed in the U.S.A.)

Article Link (Online Journal):

Funding Source:

Total Budget (Tk.) :

Achievement/Findings:

Simple empirical equations have been developed for thin layer natural air flow solar drying of rough rice for mixed-mode dryer, box dryer, and open floor drying system. The predicted and observed moisture contents were in good agreement. The effect of drying air temperature on the drying constants were found to be insignificant. The relative humidity of drying air was found to be the most important variable controlling the drying rate of rough rice. The mixed-mode dryer had the best performance whereas the box dryer had moderate performance. This study indicates that the solar dryer promises the efficient use of solar energy and reduces the risk of damage during rainy season due to improper drying in Bangladesh. Thus the introduction of solar grain dryer is highly recommendable for tropical countries like Bangladesh.

Knowledge Management: Journal