Numerical Study of the Influence of Water Evaporation on Radiofrequency Ablation

Radiofrequency (RF) ablation is one of the promising technologies of tumor therapy due to its minimal invasiveness and other advantages. The high frequency alternating electrical current makes movement of the intracellular ions, results in frictional heat inside the tumor tissue and local temperature rising. Temperature of the tissue near the RF electrode increases much faster than the distant part. When it reaches the vapor (boiling) point, excessive evaporation takes place and increases electrical impedance between the electrode and the targeted tissue. This has been a major obstacle for its application. Coolants such as water circulating in the electrodes has been proposed, but as the coolants are only effective on the electrode wall, quick evaporation and correspondent carbonization still exists.

Flow Development and Analysis of MHD Generators and Seawater Thrusters

The flow characteristics inside magnetohydrodynamic (MHD) plasma generators and seawater thrusters are analyzed and are compared using a three-dimensional computer model that solves the governing partial differential equations for fluid flow and electrical fields. Calculations have been performed for a Faraday plasma generator and for a continuous electrode seawater thruster. The results of the calculations show that the effects caused by the interaction of the MHD forces with the fluid flow are strongly manifested in the case of the MHD generator as compared to the flow development in the MHD thruster. The existence of velocity overshoots over the sidewalls confirm previously published results for MHD generators with strong MHD interaction. For MHD thrusters, the velocity profile is found to be slightly flatter over the sidewall as compared to that over the electrode wall. As a result, distinct enhancement of the skin friction exists over the sidewalls of MHD generators in comparison to that of MHD thrusters. Plots of velocity profiles and skin friction distributions are presented to illustrate and compare the flow development in MHD generators and thrusters.