Pressure-drop characteristics of CO2 boiling flow in the regenerative-cooling channel of an Mg/CO2 powder rocket engine for Mars missions

To solve the problem of the thermal protection of Mg/CO2 powder rocket engines, how different working conditions in the regenerative-cooling channel influence the pressure drop of CO2 coolant is investigated. It is found that the proportion of two-phase acceleration pressure drop increases with increasing CO2 mass flux, inlet temperature, and heat flux and decreases with increasing backpressure. The ratio of acceleration pressure drop to total pressure drop is ∼0.3. With increasing mass flux, incoming flow temperature, and heat flux, the two-phase frictional pressure drop increases, and the increase of backpressure decreases the two-phase frictional pressure gradient. The factor flp is introduced to correct for the local pressure drop of the experimental system, and flp = 1.9819 when the two-phase coolant Reynolds number is between 20 000 and 50 000. For the unidirectionally heated cooling channel, the coolant is heated unevenly therein, so the heat-transfer mode has an important influence on the frictional pressure gradient of the coolant. It is found that μl can be used to predict the frictional pressure drop of μtp, but the deviation is still more than 20%. Based on experimental data, a new correlation for predicting the two-phase frictional pressure gradient is proposed. The relative deviation of the predicted data is only −7.02%, and 96.12% of the predicted data fall within the ±15% deviation band, so the prediction accuracy is greatly improved. The present research provides a theoretical basis for designing a regenerative-cooling scheme for an Mg/CO2 powder rocket engine.