Experimental study of nucleate boiling heat transfer under low gravity conditions using TLCs for high resolution temperature measurements

Heat transfer in nucleate boiling is strongly influenced by a very small circular area in the vicinity of the three phase contact line where a thin liquid film approaches the heated wall. This area is characterised by high evaporation rates which trigger a local temperature drop in the wall. The wall temperature drop can be computed using an existing nucleate boiling model. To verify the complex model and the underlying assumptions, an experiment was designed with an artificial nucleation site in a thin electrically heated wall featuring a two-dimensional, high resolution temperature measurement technique using unencapsulated thermochromic liquid crystals and a high speed colour camera. The shape of the bubble is observed simultaneously with a second high speed camera. Experiments were conducted in a low gravity environment of a parabolic flight, causing larger bubble departure diameters than in normal gravity environments. Thus, it was possible to measure the evolution of the predicted temperature drop in a transient boiling process.