JOURNAL OF AGRICULTURAL ENGINEERING RESEARCH
Year:2002 | Volume:3 | Issue:10|Papers Count:7

Artificial drying of rough rice products is one of the common method of the preservation. Rapid drying can cause brittleness and induce internal cracks which predispose the product to breakage during subsequent operation. The drying process must be understood and controlled so that design guidelines which reduce or minimize drying damage to rough rice products should be established and improved. This requires an accurate description of the drying mechanism and phenomenon. Finite element with setting of linear and nonlinear coupled conductive heat and diffusive moisture transfer equations to improve grain drying simulation of axisymmetric bodies were presented. Axisymmetric linear triangular elements with two degree of freedom per node were used to discretize the rice grain in both models. One medium grain, Binam, was used. During the thin layer drying, temperature was measured every five seconds. Fair agreement was observed when the output of nonlinear model compared to experimental data by others. This comparison showed a nonsignificant statistical difference. The simulated temperature profile and gradient were directly usable for stress cracking analyses of rough rice. The results of the finite element analysis would be used for rough rice quality evaluation and drying simulation studies.

Life pollution as a result of chemical materials is the most problem of human. In order to produce qualitative agriculture crops, human health and protection of environmental resources, several alternative non-chemical treatments have been studied. In this study, the effects of combined treatments of fungicide, Iranian (type B) and foreign (type A) polyethylene and curing on the storage life of Thomson Navel oranges were investigated. The results showed that shrink-wrapping with curing could control penicillium rots and reduce weight losses. Shrink wrapping treatments significantly controlled weight losses, whereas curing increased weight losses in compare to the other treatments. Total soluble solids (TSS) in most of treatments were reduced. Titratable acidity (TA) significantly (P<0.01) increased in combined treatments accompanied with shrink wrapping, but it decreased in combined treatments with curing. The ratio of TSS/TA was increased in curing alone or with shrink wrapping treatments. Vitamin C increased in all treatments except in control fruits during storage. The fruits under curing or curing with shrink wrapping treatments significantly changed to pale in skin colour. Shrink wrapping delayed fruit softness. The lowest flavour scores in sensory evaluation were observed in combined treatments with shrink wrapping, fungicide and curing. Shrink wrapping with polyethylene type A found the best score in respect to flavour and overall acceptability. On the other hand, polyethylene of type B showed more deterioration of fruit than polyethylene type A. Therefore within the treatments, polyethylene of type A can be recommended in respect to economic evaluation.

Soil water retention curve is needed for many applications in characterizing the unsaturated subsurface flow. Direct measurement of this curve, due to its high non-linearity, is time consuming and costly. In recent years, many attempts have been made to indirectly predict the retention curve from readily/easily obtainable soil parameters. The so-called Pedo Transfer Functions (PTF) have been proven to be a valuable indirect tool to estimate the soil moisture characteristics with reasonable accuracy. The objective of this study was to derive PTFs to predict the parameters of the closed form equation of Van Genuchten (dependent variables) from particle size distribution, calcium carbonate, geometric mean diameter, geometric standard deviation and soil bulk density. Consequently, twenty seven loamy soil samples with different particle size distributions and calcium carbonate contents (independent variables) were used to establish the PTFs at tensions of 0, 10,33, 100, 300, 500 and 1500 kpa. The undisturbed samples were delivered to the laboratory to determine the particle size distribution, equivalent calcium carbonate and the retention curve. These were obtained using hydrometery, calcimetery and pressure membrane methods, respectively. The bulk densities with paraffin method were determined in the field. The least square optimizer program RETC was used to obtain the Van Genuchten parameters. The best combination of independent variables for prediction of the dependent variables was selected by best subset regression command. The regression equations were obtained, using multiple linear regression method. The results indicated that the water retention at the range of interest could be predicted reasonably well with the derived PTFs. Comparison of retention curves with those measured and estimated provided a significant correlation (p=0.001). The point estimation of water retention at filed capacity and permanent wilting point provided an excellent correlation with measured values. These observations suggest the use of PTFs in calcareous soils when the equivalent calcium carbonate inserted as an input parameter in these functions.

Drying is one of the most important operations in the paddy processing. In general, the method of drying and its precision level has a profound impact on product quality and amount of losses. For this reason, various methods were suggested to dry paddy. Developing and using important factor in processing of rice. The control of the grain final moisture content is not necessarily implemented, excessive moisture extraction may cause in an increase of losses and reduction of quality. Lack of control in the drying process causes fissuring of rice in the dryer which results in rice breakage and loss of quality during the subsequent hulling and polishing operations. Hence, controlling the graing moisture content is a key factor in the drying process. Determination of the relationships between grain moisture content with temperature and relative humidity of the exhaust air from the dryer through the drying process is critical. The investigation was conducted in order to determine the relationships between the effective parameters in the intermittent drying process. In this study, grain moisture content as well as temperature and relative humidity of the exhaust air were measured. Analysing of the data enabled to develop a mathematical relationship between the parameters. Based on the results, temperature and relative humidity (RH) of the exhaust air had linear relationship with time, while the relationship between grain moisture content (M.C.) and time was a second order polynomial. Similarly, grain M. C. with exhaust air temperature and grain M. C. with RH relationships were second order polynomials. Using these equations and utilizing Lagranges polynomial interpolation method, a two-tier mathematical model was estimated to relate grain M.C. with temperature and relative humidity of the exhaust air. Based on the relationship, between the effective parameters, grain moisture content could be estimated at any time during drying by simply measuring temperature or relative humidity of the dryer exhaust air.

The soil leaching efficiency coefficient is one of the important factors in order to determine the potential and reaction of soil to leaching of soluble salts. This coefficient is one of the major and unknown components of salt balance and empirical equations use for determining leaching requirement and planning for preventing re-salinization of soil. In this study using the NPLEC model, values of leaching efficiency coefficient of the soil profile (f) in different layers of soil (f1-f5) were determined. The model was applied to the observed leaching data obtained by conducting leaching experiments in the field. Based on the results all the submodels showed a fairly good performance in determining (f) values. The NPLEC3 sub-model results showed the best agreement between observed and calculated values of soil salinity due to more realistic assumptions in its development. For soil profile (0-125cm), and consequent layers (0-25, 25-50, 50-75, 75-100, 100-125cm) the coefficients were determined as f = 0.7, f1= 0.8, f2= 0.2, f3= 0.05, f4= 0.05, f5= 0.05, respectively.

Since beginning application of mechanical method for paddy threshing, until now only one type of thresher has been used that requires much labor. No effort has been made for their technological improvement. These threshers are hold-on type and because of their design, paddy clusters are inserted into the threshing unit and paddy straw is held stationery while threshing is done by impact on panicle from tooth. In the hold-on threshing method, keeping the paddy stems by hand, is difficult and has risks some times. To eliminate these difficulties a thresher with mechanical feeding system has been designed and manufactured. It has relative advantages. It is able to thresh high moisture paddy continuously (fresh harvested add with rain and stem moisture content equal to 23% an 5% respectively). Mean while, there is no human contact with the thresher thus, thresher has high security. Different parts of the machine are designed based on 300 kg/h threshing capacity (grain) and its estimated power is 2.65kW.