The flow focusing nozzle is a new type of nozzle that performs effective atomization of the discrete phase by means of high-speed motion of the continuous phase.The flow pattern and its morphological changes have a si...The flow focusing nozzle is a new type of nozzle that performs effective atomization of the discrete phase by means of high-speed motion of the continuous phase.The flow pattern and its morphological changes have a significant effect on the atomization, but the influence of different parameters on the morphological change of the flow pattern remains unclear.The flow focusing pattern and morphological changes in the two-phase flow inside the nozzle were simulated numerically, based on the volume of fluid method.The results demonstrate that the ratio of the nozzle-to-capillary distance and capillary diameter, the gas–liquid velocity ratio, and capillary diameter have significant effects on the flow pattern.When the ratio of the nozzle-to-capillary distance H and capillary diameter D increases, or the capillary diameter D increases, the flow pattern tends to transform into a laminar form; however, when the gas–liquid velocity ratio V increases, the flow pattern tends to transform into a turbulence form.Furthermore, we define the cone-shaped expansion rate, cone-shaped focusing rate,and cone angle in order to study the morphological changes in the cone shape inside the nozzle.The results indicate that the morphological change of the cone shape and flow pattern transformation is interrelated.When the cone shape tends to be unstable, the flow pattern changes towards flow blurring, whereas, a stable cone indicates that the flow tends to exhibit a droplet pattern.展开更多
High-intensity focused ultrasound (HIFU) has attracted increasing interests as a promising noninvasive modality for the treatment of deep tumors in the thoracic and abdominal cavity.A 90-element HIFU spherical phased ...High-intensity focused ultrasound (HIFU) has attracted increasing interests as a promising noninvasive modality for the treatment of deep tumors in the thoracic and abdominal cavity.A 90-element HIFU spherical phased array applicator operated at 1 MHz has been developed for deep tissue ablation.The spherical array with a 5 cm wide central hole has a 21 cm diameter and an 18 cm radius of curvature.Annular element distribution with unequal element spacing is used to reduce the number of elements.The array is constructed with piezoelectric lead zirconate titanate (PZT-8) circular elements that are 1.4 cm in diameter and have a wall with thickness of 0.2 cm.The array offers an effective ablating depth of at least 8 cm in the tissue for both simulations and ex vivo experiments.The simulations demonstrate that the developed array can steer the focus with good quality of intensity distributions up to 6 mm off center over ranges from 17 to 21 cm when the water depth is set at 11 cm.We also present the beam focusing capability in deep tissue through a series of ex vivo experiments by measuring discoloration areas after sonications.These results indicate that the developed array is ideal for the ablation of deep-seated tissue.展开更多
基金Supported by the National Natural Science Foundation of China(51776016,51606006)Beijing Natural Science Foundation(3172025,3182030)+2 种基金National Key Research and Development Program(2017YFB0103401)National Engineering Laboratory for Mobile Source Emission Control Technology(NELMS2017A10)the Talents Foundation of Beijing Jiaotong University(2018RC017)
文摘The flow focusing nozzle is a new type of nozzle that performs effective atomization of the discrete phase by means of high-speed motion of the continuous phase.The flow pattern and its morphological changes have a significant effect on the atomization, but the influence of different parameters on the morphological change of the flow pattern remains unclear.The flow focusing pattern and morphological changes in the two-phase flow inside the nozzle were simulated numerically, based on the volume of fluid method.The results demonstrate that the ratio of the nozzle-to-capillary distance and capillary diameter, the gas–liquid velocity ratio, and capillary diameter have significant effects on the flow pattern.When the ratio of the nozzle-to-capillary distance H and capillary diameter D increases, or the capillary diameter D increases, the flow pattern tends to transform into a laminar form; however, when the gas–liquid velocity ratio V increases, the flow pattern tends to transform into a turbulence form.Furthermore, we define the cone-shaped expansion rate, cone-shaped focusing rate,and cone angle in order to study the morphological changes in the cone shape inside the nozzle.The results indicate that the morphological change of the cone shape and flow pattern transformation is interrelated.When the cone shape tends to be unstable, the flow pattern changes towards flow blurring, whereas, a stable cone indicates that the flow tends to exhibit a droplet pattern.
基金the National Natural Science Foundation of China(No. 30800246)the Shanghai Key Technologies R&D Program of China(No. 09441500900)the Med-X Shanghai Engineering Center Foundation(No. 08DZ2211201)
文摘High-intensity focused ultrasound (HIFU) has attracted increasing interests as a promising noninvasive modality for the treatment of deep tumors in the thoracic and abdominal cavity.A 90-element HIFU spherical phased array applicator operated at 1 MHz has been developed for deep tissue ablation.The spherical array with a 5 cm wide central hole has a 21 cm diameter and an 18 cm radius of curvature.Annular element distribution with unequal element spacing is used to reduce the number of elements.The array is constructed with piezoelectric lead zirconate titanate (PZT-8) circular elements that are 1.4 cm in diameter and have a wall with thickness of 0.2 cm.The array offers an effective ablating depth of at least 8 cm in the tissue for both simulations and ex vivo experiments.The simulations demonstrate that the developed array can steer the focus with good quality of intensity distributions up to 6 mm off center over ranges from 17 to 21 cm when the water depth is set at 11 cm.We also present the beam focusing capability in deep tissue through a series of ex vivo experiments by measuring discoloration areas after sonications.These results indicate that the developed array is ideal for the ablation of deep-seated tissue.
