The current investigation examines the combined impacts of ultrasonic radiation and hydrogen donors on the viscosity of heavy crude oil. The impact of exposure time, power, duty cycle, and temperature on the viscosity of Iraqi heavy crude oil with 20.32 API was studied. Also, the viscosity of the oil samples, which were mixed with a hydrogen donor (decalin) and subjected to ultrasonic treatment under optimal conditions, was examined to evaluate the combined impact of ultrasonic radiation and hydrogen donor on the viscosity of crude oil. The viscosity experienced a decrease of 52.34% at 2 min of irradiation, 360 W ultrasonic power, 0.8 duty cycle, 35 ⁰C, and 8vol% decalin. To validate the outcomes of the experiments, asphaltene content, sulfur content, API gravity, and distillation tests were conducted on both the original and final samples (under optimal conditions). The concentrations of asphaltene and sulfur exhibited a drop of 37.51% and 35.04%, respectively. The results show that cavitation, a heat phenomenon, and the mechanical impact of ultrasound may help break up long carbon chains and reduce the size of asphaltene aggregates, which causes the crude oil's viscosity to drop. Moreover, the findings demonstrated that the simultaneous application of ultrasound and hydrogen donor yielded the most significant decrease in oil viscosity compared with untreated crude oil or treated just with ultrasonic waves.
