Characterisation of activation pressure, flowrate and spray angle for hollow-cone nozzles controlled by pulse width modulation

Authors: SALCEDO, RAMON - The Ohio State University; Zhu, Heping; Jeon, Hongyoung; OZKAN, ERDAL - The Ohio State University; WEI, ZHIMING - Shandong Academy Of Agricultural Sciences; GIL, EMILIO - Universitat Politècnica De Catalunya (UPC)

Submitted to: Biosystems Engineering
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/1/2022
Publication Date: 4/20/2022
Citation: Salcedo, R., Zhu, H., Jeon, H., Ozkan, E., Wei, Z., Gil, E. 2022. Characterisation of activation pressure, flowrate and spray angle for hollow-cone nozzles controlled by pulse width modulation. Biosystems Engineering. 218:139-152. https://doi.org/10.1016/j.biosystemseng.2022.04.002.
DOI: https://doi.org/10.1016/j.biosystemseng.2022.04.002

Interpretive Summary: Pulse width modulated (PWM) hollow-cone nozzles are widely used in intelligent spray systems for controlling flow rates to achieve precision spray applications in orchards, vineyards and nurseries. However, spray characteristics of these PWM-controlled nozzles have not been well documented. In this research, nozzle flow rates, activation pressures and times, and spray angles were investigated and documented for disc-core hollow-cone nozzles coupled with two different commercially available PWM valves. Spray operating pressures and PWM duty cycles significantly affected these characteristics. The PWM valve fabrication also affected these spray characteristics except for the spray angle. There were no significant differences in spray angles between the two PWM valve fabrications. Increasing the operating pressure increased both activation pressures and activation times and thereby increasing the flow rates. The measured flow rates proportionally decreased as duty cycles decreased for both PWM valves. As a result, a large digital database of these spray characteristics was established for future improvement of precision air-assisted sprayers.

Technical Abstract: Pulse width modulation (PWM) solenoid valves have been used for controlling flow rates of hollow-cone nozzles on variable-rate air-assisted orchard sprayers. However, little information is available on spray characteristics of these PWM-controlled nozzles. Laboratory tests were performed to evaluate the influences of duty cycles of two different fabricated PWM solenoid valves along with five operating pressures on spray characteristics of five hollow-cone nozzles with different disc-core combinations. Parameters of the spray characteristics investigated were nozzle flow rates, upstream and downstream pressures of the PWM valves, nozzle activation pressures and times, and spray angles of water discharged from nozzles. Test results illustrated that these parameters except for the spray angle were greatly affected by the operating pressure, nozzle selection (disc orifice size and quantity of holes on core), PWM duty cycle and solenoid valve fabrication. Spray angles were affected by the duty cycle but not the PWM valve fabrication. In general, nozzles with larger disc orifice and higher operating pressures resulted in higher flow rates as expected, while the nozzle activation pressure and the spray angle decreased as the duty cycle decreased. Thus, variations in spray characteristics of disc-core type hollow-cone nozzles coupled with PWM solenoid valves should be considered and minimized through established digital database in future designs of orchard sprayers to perform precision variable-rate pesticide applications.