Flow boiling intensification in minichannels by means of mechanical flow turbulising inserts

The work presents the results of experimental investigation on heat transfer in minichannels. Refrigerant R123 was used as a test fluid. Single vertical silver tubes of 380 mm length and 2.3 mm diameter were examined with two variants of turbulising inserts. A wide range of parameters was considered, namely mass flux G = 534 divided by 3011 kg/(m(2) s), heat flux q(w) = 28.5 divided by 68.4 kW/m(2), saturation temperature MAT = 23 divided by 86 degrees C and the full range of vapour quality variation (x = 0 divided by 1). The effect of mass flux and heat flux on heat transfer coefficient was analysed both for the smooth tube and for two turbulisation variants. The results were compared with popular smooth tube correlations. For the case of a smooth tube the M-shape of heat transfer coefficient curve as a function of quality was observed, which is a completely new finding confirmed in the literature only recently. There are some circumstances of similar existence of two heat transfer coefficient maxima also for the tubes with turbulising inserts. The discussion of flow boiling intensification possibilities in minichannels with the use of this method was based on the number of comparisons of the smooth tube and two turbulisation variants for various established parameters. (C) 2012 Elsevier Masson SAS. All rights reserved.