DESIGN AND DEVELOPMENT OF RECIPROCATING PERFORATED CYLINDRICAL TYPE RAINFALL SIMULATOR
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Date
2004
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Indira Gandhi Krishi Vishwavidyalaya, Raipur
Abstract
Rainfall and its characteristics are the key factors in the process of soil erosion. These characteristics viz. intensity, duration, timing and distribution are beyond human control. The alternative available could be to fabricate a unit of rainfall simulator, which can reproduce desirable range of natural rainfall characteristics. In this study mainly two important criteria were considered, the mobility and the simulation of erosive rainfall comparable to that of the natural rainfall for the region. The simulator unit was fabricated using PVC pipe, with reciprocating motion provided manually. It consisted of stand, fitted with four stage telescopic tubes for height adjustment, set of cylindrical simulator pipes fitted in a frame, water tank, mono block pump and various water and pressure control units. Several combinations of holes placement and arrangement at varying pressures in the form of various setups were attempted to produce artificial rainfall similar to the natural rainfall. These artificially produced rainfall were subjected to various hydraulic testing with selected evaluation parameters viz. rainfall intensity, uniformity coefficient and water drop size, in order to simulate it with the natural rainfall. The desired range of average rainfall intensity was 25 to 75 mm/h, as observed for Raipur. Similarly the value of uniformity coefficient considered was 85 per cent or more for evaluating the simulator performance. The simulator was operated at a fixed height of 2 m, with two cylinders (hole spacing 10 cm,15 cm or its combinations). It was fitted on the triangular frame and reciprocationg motions were produced manually. The acceptable range of rainfall intensities (25-75 mm/h) were obtained in various setups. The rainfall intensity of 52.38 mm/h was obtained at operating pressure of 0.15 kg/cm2 when both cylinders had hole spacing of 10 cm. The rainfall intensities of 38.66 and 43.23 mm/h were obtained at operating pressures of 0.15 and 0.20 kg/cm2 respectively when both cylinders had hole spacing of 15 cm. The rainfall intensities of 33.42, 56.28 and 64.31 mm/h were obtained at operating pressures of 0.15, 0.20 and 0.25 kg/cm2 respectively, when combination of hole spacing of 10 and 15 cm was used. The cumulative percent volume of the simulated raindrops matched closely with the cumulative percent volume of natural rainfall. The median drop diameter of simulated rainfall was found to be 2.67 mm at 0.15 kg/cm2 pressure in case when both cylinders had hole spacing of 10 cm. It was 2.54 and 2.67 mm at pressures of 0.15 and 0.20 kg/cm2 respectively, when both cylinders had hole spacing of 15 cm. But in case of combination of 10 and 15 cm hole spacing, the median drop diameter was tend to be 2.88, 2.67 and 2.54 mm, at pressures of 0.25, 0.20 and 0.15 kg/cm2, respectively. The designed and developed rainfall simulator was found to be light in weight, easy in operation and simple in construction. The output range of the designed and developed simulator was within the acceptable range of rainfall intensity observed at Raipur. The coefficient of uniformity was also 85% and above.