Modeling of Saturated and Superheated N2O Heat Transfer Rates, with Experimental Verification

Nitrous oxide (N2O), a common oxidizer in hybrid rockets, may be used as an effective cooling agent; the potential uses for aerospike nozzles are particularly appealing. So far, there have been little efforts to characterize nitrous oxide as a two-phase flow cooling agent. In order to study nitrous oxide in this context, a Rayleigh tube apparatus developed at Cal Poly was used. Heat transfer coefficient in the nucleate boiling region is investigated by combining experimental and numerical modeling. This included the application of a homogeneous flow model along with a correlation proposed by Shah. The poor agreement obtained, however, has motivated the authors to introduce a modification to the Shah correlation that considers an “effective” Boiling number, defined as 35% of the actual boiling number, Bo. This modification reduces the overall mean absolute deviation between experiment and model from 68.0% to 13.0%, and provides agreement to within 3% at low flow quality, suggesting a lower influence of bubble nucleation on heat transfer in the case of nitrous oxide compared to other two-phase fluids.