Theoretical performance simulation of a high pressure agro-forestry swirl nozzle

Equations of dynamic systems in droplet distribution at high pressure and boundary value flows in the swirl chamber of a swirl nozzle were used in conjunction with momentum equations of forces on moving curved vanes to develop mathematical models. A computer program in C++ language was developed and used to simulate the effect of some flow and geometric parameters, including flow rate, pressure and swirl chamber diameter, on the spray performance of a high pressure agro-forestry swirl nozzle. Each of the three performance parameters of axial flow rate, spray cone angle and output discharge (or performance) coefficient were studied as a function of any two combinations of the nozzle supply pressure, exit orifice diameter and swirl chamber diameter. The study established that the spray cone angle of the discharge flow pattern varied from the minimum value of 40 degree for a swirl chamber diameter of 90 mm to 220 degree for 40 mm as the exit orifice diameter varied from the minimum value of 0.5 mm to 4.0 mm. The simulated nozzle output discharge coefficient could be varied from 0.98, when the nozzle supply pressure was 400 kPa to the minimum value of 0.001 at any of the other six simulated nozzle supply pressure values of 200, 250, 300, 350, 450 and 500 kPa by varying the exit orifice diameter from 0.5 mm to 4.0 mm. The pattern of variation of the simulated nozzle discharge coefficient values were similar to those obtained by measurement during the validation exercise in the laboratory although their sensitivities to the independent variables were different. The results indicated that the range of nozzle discharge coefficient of 0.80 to 0.98 required for a well designed high pressure agro-forestry swirl nozzle has been simulated. With the successful development of the C++ computer program, a useful tool that will cut down on the rigor encountered and time spent by nozzle designers and evaluators during nozzle development process has been developed in the study.