Schlieren imagery and velocimetry of electrohydrodynamic heat transfer enhancement in an organic phase change material

The study proposes and demonstrates a methodology for velocity measurement of electrohydrodynamic (EHD) flows that is totally non-intrusive. By using Schlieren imagery in conjunction with optical flow measurement velocity fields are measured in the liquid phase of a phase change material (PCM) under the application of EHD. The test section applied 8, 10, and 12 kV across a differentially heated cavity containing octadecane, at approximately 50% melt fraction. Velocity fields were measured using the schlieren methodology and showed there was a clear jet/recirculation zone pattern with peak velocities approaching 18 mm/s across a 10 mm gap. The error in the velocity field was considered using a 99.7% confidence interval in the averaged velocity. Within the jet region the corresponding relative error was consistently under 10%. The study demonstrates that schlieren imagery is an effective means to visualize non-isothermal EHD fluid phenomena without the intrusion of any measurement devices (seeding particles, anemometers) in the cavity.