Instantaneous Deicing of Freezer Ice via Ultrasonic Actuation

A low-power, non-thermal, ultrasonic deicing system is introduced as a potential deicing system for helicopter rotor blades that are currently being used. In this research effort, ultrasonic actuator disks excite isotropic plates and airfoil-shaped structures that are representative of helicopter leading edge protection caps. The system generates delaminating ultrasonic transverse shear stresses at the interface of accreted ice, de-bonding thin ice layers (< 3 mm thick) as they form on the isotropic host structure. A finite element model of the proposed actuator and of the isotropic plates is used to guide the selection of the actuator prototypes. Several actuator-isotropic plate structures are fabricated and tested under freezer ice conditions. Test results demonstrate that radial resonance disk actuators (28 – 32 KHz) create ultrasonic transverse shear stresses capable of instantaneously delaminating ice layers. At environment temperatures of -20o C, the system delaminates 2.5 mm thick ice layers with power input densities as low as 0.07 W/cm 2 (0.5 W/in 2 ). The effects of ice thickness on the instantaneous delamination of accreted ice is studied by modeling the interface stresses on three different ice thickness layers and correlating the predictions with experimental results. The finite element modeling predicts the delamination patterns of the accreted ice layers. Models also predict within 15% the required input voltage to promote instantaneous ice de-bonding. The actuators were selected such that during excitation, the temperature of the PZT material remained well below freezing, hence eliminating heat propagation and melting as the main source of ice delamination.