Investigation of wall temperature and heat flux distribution during nucleate boiling in the presence of an electric field and in variable gravity

Abstract

Heating wall temperature distribution and bubble shapes were measured during nucleate boiling of FC-72 in microgravity in the presence of an electric field. The presented results are part of the results obtained during the 50th ESA parabolic flight campaign and focused on the electric field experiments. A 25μm stainless steel foil served as heated wall for the boiling process. The temperature distribution of the foil was measured via infrared thermography at a frame rate of 1000Hz and with a resolution of 30μm/pixel. The bubbles were observed by a synchronized high speed camera. A washer shaped electrode was located parallel to the heated wall. The electrode was charged to up to +10kV while the heating foil served as ground potential. The effect of the electric field created by this configuration on the boiling process was investigated for different boiling states. Due to the absence of buoyancy in microgravity the bubbles generally do not detach from the heating foil with the given heat fluxes. The electric force on the bubbles generated by the field gradient sucked the vapor through the center hole of the electrode. Thereby, a reliable bubble detachment and re-wetting mechanism could be established and allowed the implementation of a nucleate boiling process in microgravity.