Steam condensation in mini-channels: A benchmark of available correlations
Résumé
This study takes place in the framework of the development of innovative heat exchangers. We consider a heat exchanger with vertical mini-channels (hydraulic diameter <3mm) operating in forced circulation, with pure steam at the inlet of the primary side. In such conditions, gravity and surface tension drive the condensation mechanism, but the latter effect is generally neglected in the modeling of the heat transfer coefficient. Indeed, condensation at mini-channel scale exhibits specific flow regimes that require dedicated modeling. Considerable effort has been done in the last two decades in order to model friction coefficients and heat transfer coefficients. Nevertheless, all the experimental studies took place with refrigerant fluids, whose properties significantly differ from those of steam. Therefore, transposition of previous work is delicate. A 1-dimensional model is used to investigate the effect of the closure laws on condensation and the results are compared with the results of the system-scale code CATHARE. In the latter model, surface tension effects are not taken into account. The results show that the decrease in hydraulic diameter favors quicker condensation, despite the increase in wall friction. Operating conditions are also explored. The results show a major influence of the heat transfer closure law on the results, e.g. the condensation length. This work highlights the lack of unicity in the available literature regarding steam condensation in innovative heat exchangers. Dedicated experimental work on steam is needed in the future.
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