Visualization at cryogenic temperatures using a glass fiber bundle

A visualization method is being used to investigate features of nucleate bo iling in narrow channels of liquid nitrogen. The information regarding bubb le size, departure frequency, bubble spacing, and velocity will be used to develop an analytical model for critical heat flux (CHF) - especially its d ependence in narrow channels on inclination angle and gap spacing. We repor t on the use of a glass fiber bundle combined with two different photograph ic and illumination techniques to study the desired bubble characteristics. The special considerations encountered with this approach at liquid nitrog en temperature are highlighted., including the use of submerged light-emitt ing diodes (LEDs) for illumination. (C) 2001 Elsevier Science Ltd. All righ ts reserved.