Abstract
For the development of high performance and small sized carbon dioxide (CO_2) heat pump water heater, high performance heat transfer tube is very important. In the previous studies, parts of the authors experimentally clarified average boiling heat transfer coefficient of CO_2 in horizontally located smooth tubes takes a maximum against mass velocity but not in grooved tubes. In this study, the experimental data are compared with conventional correlations based on local coefficients to clarify the phenomena, and also predicting performance of the correlations is examined. It is concluded that more experimental data in dryout and post-dryout region should be obtained.
