| Author | Teerapol Silakul |
| Call Number | AIT Diss. no.PH-01-1 |
| Subject(s) | Mung bean--Drying--Simulation methods
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| Note | A dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Technical Science, School of Environment, Resources and Development |
| Publisher | Asian Institute of Technology |
| Abstract | Mungbean (Vigna radiata (L.) Wilczek) is an important crop of Thailand. Drying of mungbean is an urgent problem because mungbean is harvested during the rainy season. As a result, drying is required to maintain seed qualities. The objectives of this study were to investigate the drying characteristics of mungbean in a fixed-bed when exposed to the heated and ambient air for the purpose of developing drying simulation models, and to study the effects of experimental drying conditions on the germination and vigor of mungbean seed for practical applications.
Two drying simulation schemes, proposed by Thompson et al. (1968) and Thompson (1972), were followed to predict the changes in moisture content of mungbean due to flow of heated and ambient air in fixed-beds. The development of simulation models required the determination of thin-layer drying characteristic and other properties of mungbean such as the equilibrium moisture content (EMC), latent heat of moisture vaporization, bulk density and specific heat. Subsequently, a number of experimental tests for drying of mungbean in fixed-beds were conducted to verify the applicability of developed simulation models. The drying of mungbean in 0.63 m deep-beds was carried out with initial moisture content ranging from 15.9 to 31.1 % wet basis. The drying air temperature and relative humidity approximately ranged from 38.3 to 56.7°C and 20.8 to 67.5%, respectively. The air velocity in the drying bed was maintained in the range of 0.1 to 0.15 mis. In addition, empirical equations were developed to estimate reductive average germination (RG) and reductive average vigor (RV) as a function of drying air temperature and time, and initial moisture content of mungbean.
A two-parameter empirical equation described the variation in EMC of mungbean adequately as a function of drying air temperature and relative humidity, and was used for calculating the latent heat of vaporization based on Othmer's equation. The bulk density of mungbean decreased with an increase in the moisture content whereas the specific heat increased with increasing moisture content. Thin-layer drying characteristics of mungbean were best described by a quadratic equation with moisture ratio as dependent and drying time as independent variable. The parameters of drying equation were determined to be the function of air temperature and relative humidity, and initial moisture content of mungbean.
Results of simulated test runs showed that the Thompson et al. (1968) model was not sensitive to the choice of grain layer thickness and drying time step in the simulation scheme. In contrast, Thompson (1972) model tended to predict narrower drying zones than Thompson et al. (1968) model basically due to the assumption of complete equilibrium in grain and drying air conditions. The comparison of experimental and simulated moisture profiles in heated air drying of mungbean in fixed-beds showed similar patterns with Thompson (1972) model resulting in slightly better overall performance in predicting the changes in moisture content in the grain bed. Thompson (1972) model indicated a mean root-mean-square-error (RMSE) of 1.84% wet basis as compared to 2. 14% wet basis for the Thompson et al. (1968) model. Also Thompson (1972) model gave much lower values of RMSE for drying tests conducted at near-ambient temperatures.
The quality of mungbean as seed both in terms of RG and RV was influenced by the drying treatments. The RG and RV of mungbean increased with an increased in drying
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air temperature and time as well as the initial moisture content. In case of aeration, high initial moisture content of mungbean resulted in higher moisture gradient across the grain bed as well as higher values of RG and RV. These results may be beneficial in the selection of strategies for minimizing RG and RV of mungbean seed during fixed-bed drying. |
| Year | 2001 |
| Type | Dissertation |
| School | School of Environment, Resources, and Development (SERD) |
| Department | Department of Food, Agriculture and Natural Resources (Former title: Department of Food Agriculture, and BioResources (DFAB)) |
| Academic Program/FoS | Postharvest and Food Process Engineering (PH) |
| Chairperson(s) | Jindal, V. K.; |
| Examination Committee(s) | Athapol Noomhorm ;Ranamukhaarachchi S.L. ;Sokhansanj, Shahab; |
| Scholarship Donor(s) | Royal Thai Government (RTG); |
| Degree | Thesis (Ph.D.) - Asian Institute of Technology, 2001 |