The Influence of Rainfall Simulators Dripper size, Type and Dripping Speed on Generated Drop Size

Abstract

The choice of drippers for dripping rainfall simulators (DRS) is often based on the experience of previous research or personal empirical knowledge, under the assumption that drippers in form of tubes and holes with a smaller internal diameter (ID) generate water drops of a smaller diameter and vice versa, neglecting other factors that affect the size of the drops. The aim of research is to provide insight into the influence of DRS dripper size, type and dripping speed (i.e., the number of water drops dripped out from a dripper per unit of time) on generating different water drop size. A search was conducted for all available scientific papers describing DRS and papers that include a wide range of thematically related papers to soil research in which DRS are used starting from 1941 until today. Out of a total of 188 scientific papers included in the analysis, 76 different types and 31 subtypes of DRS have been singled out. The analyses of DRS drippers design and performance was conducted in terms of the drops’ sizes that they are able to generate. The analysis was conducted integrally, for simulators with more than one dripper and with one dripper. Metal and plastic tubes (MT and PT), which are the most common drippers’ type, showed a strong relationship between the outer diameter (OD) with the drop size, while the ID relationship was moderate to weak. However, when increasing the range of MT drippers’ diameter size, the relationship significance became very strong for both ID and OD. It is observed that with the increase of the ID of PT the relationship deviates from the logarithmic curve that represents all dripper types together. Although the applied dripping intensity difference is quite big for MT, drop size does not differ much. On the other hand, PT generate much bigger difference in drop size for a less drastic change in intensity. It is suggested that a possible reason for such a deviation and difference in the functional forms that describes drop and drippers size relations could be the dripper material, but considering that MT drippers generally have a thinner wall than PT or glass tubes (GT), drippers material type rather determines the thickness of the tube wall.