• cristalli liquidi
• electrohydrodynamics
• elettroidrodinamica
• liquid crystals
• microgravità
• microgravity
• mixed convection
• thermal control

The aim of the present work is to investigate the effect of the electrical and gravitational force fields on laminar to weakly turbulent convection in a square duct heated from the bottom side. Results in microgravity conditions were obtained during a European Space Agency parabolic flight campaign. The working fluid is the dielectric liquid HFE-7100. The tests are conducted in a Reynolds number range from 430 to 5640. Local temperatures on the heated wall are misured by liquid crystal thermography. Being in a regime of mixed convection, heat transfer coefficients are influenced by the gravity level in the various phases of the flight parabolas, particularly at the low flow rates. At the application of a sufficiently high DC electric field, heat transfer is dramatically augmented – almost independently from the flow rate – by the mechanism of ion injection from an array of high-voltage points opposite to the heated strip. Enhanced heat transfer rates are no longer gravity-dependent, showing that the resulting convection is dominated by the electrohydrodynamic phenomenon, conveniently controllable by the applied high voltage. Relatively small pressure drop increases caused by the induced flow are also measured. Profitable implementation of electrohydrodynamics in the design of compact heat exchangers and heat sinks such as cold plates is foreseen; possible benefits are pumping power reduction, size and weight reduction, and heat exchange capability augmentation. Having shown that – in the presence of the electric field – the gravity level is immaterial in terms of resulting heat transfer rates, the main technological application of the technique is possibly thermal control in space.