SUMMARY: The application of chemical products is nowadays an extended technique in pressurized irrigation systems that present evident advantages. This operation, called chemigation, is used in sprinkler irrigation and drip irrigation Systems.The Venturi injector is a very used chemigation system, in small and medium size farms.
      The usual connection of a Venturi injector in irrigation systems is in by-pass from the main pipe. This system produces high velocities which originate negative pressures in the nozzle that pump the flow from the injection solution. This system is cheap, robust and its operation uses hydraulic energy, without needing any external contribution. Nevertheless the head losses introduced by this injector type are over 30 % of the pressure of entry. Besides it presents problems of regulation, air injection or cavitation.
      First of all, in this thesis is shown that the main problems can be mitigated modifying the typical installation. The proposed system locates the injector directly in the main pipe and the relative position of the solution is inverted and now is above the throat of the Venturi. For this reason, a semiautomatic functioning of the injection is achieved. A minimal level is established in the tank of the injected solution, determined by the pressure needed in the throat, being now higher than the atmospheric one.
      Four prototypes of Venturi injector with different dimensions in their principal sections have been tested in the laboratory, registering operation data for each one in three different situations: without injection, with injection and negative pressures in the throat and with injection and positive pressures in the throat.
      Simultaneously it is checked the suitability of the Computational Fluid Dynamics techniques in the analysis of the hydraulic behaviour of the Venturi, and if they are appropriate enough for the design of new injectors, the prediction of the operation of commercial models and the grade of reliability of the theoretical current formulation. The techniques of CFD are an engineering tool that allows simulating any system or equipment in which fluids intervene by means a computer application.
      For every situation tested in laboratory there have been obtained the expressions that relate the injected flow rate, the difference of pressures and the head loss with the principal flow rate or the existing pressures in the principal sections of the Venturi.
      These cases have been reproduced with CFD techniques and their results have been compared with the experimental ones. Likewise it has been analyzed the geometrical influence of the injector in the head losses.
      After the analysis of the tests it can be affirmed that the head losses, for the same injected flow, are lower if the operation is carried out with positive pressures instead of negative pressures. 
      The relationship of flow rates or the efficiency also provide higher values under the form of the proposed installation. It can be concluded that the behaviour improves if the level of the solution is located above the Venturi.
      Also its shown that the relation of flows and the efficiency are better when the diameter of the aspiration increases and are worse when decreases the diameter of the throat, these dimensions are the more important in the injection.
      Finally, it can be said that numerical results and this methodology will provide acceptable values of injected flows and pressures, comparing them the experimental results. The CFD techniques appear as a suitable tool for the analysis of the injector operation, but it is indispensable their validation with experimental results.