The Effect Of Rolling Motion On Flow And Heat Transfer Characteristics Of Natural Circulation

Narrow rectangular channels are widely used in marine compact heat exchangers.But the additional inertia force has a great influence on the flow and heat transfer characteristics due to the change of spatial position of equipment caused by rolling motion.In this experiment,the flow and heat transfer characteristics of natural circulation in a narrow rectangular channel under vertical,inclined and rolling condition were studied.The deionized water is chosen to be the working fluid.The rolling angle is from 10°to 20°and the rolling period is from 10s to 20s.The test section is a stainless steel rectangular channel with the cross section of 40mm×2mm and 1100mm long.It's found that the change in flowrate can be divided into three sections,single-phase flow,subcooled boiling flow and saturated boiling flow.In the single-phase flow,the flowrate is increased linearly with heat flux.In the subcooled boiling flow,the fluctuation of the flowrate is small.For saturated boiling flow,the flowtate incerses rapidy.But when the quality exceeds a certain value,the flowrate decreases with the heat flux.The maximal flowrate is related to the true quality at the outlet.With higher system pressure and angle of inclination,the true quality of the maximal flow is higher.Temperature at the inlet has no influence on the quality at the outlet.The influence of incline angle is determined by the spatial arrangement of equipment.In static condition,tilt angle has no effect on the flow and heat transfer characteristics of natural circulation.For single-phase flow,the effect of the heated wall should be considered for the coefficient of friction resistance.The way of the heat added to the test section does not affect the friction.The Nusselt numbers are lower than the values predicted by Gnielinski correlation.And the Rayleigh number Ra can be used to modify the Gnielinski correlation to predict the averaged Nu.For two-phase flow,Hsu correlation can predict the position of ONB.The subcooling is small.And when the net vapor generated,it means the saturated boiling happened.Chen correlation and the Schrock-Grossman correlation can be used to predict the heat transfer coefficient of saturated boiling.There are fine beam annular flow for natural circulation after saturated boiling.And the homogeneous model can be used to predict the pressure drop.In rolling condition,there is no obvious phase-lag between flow rate and pressure drop.The critical Reynolds number Re_c is different in different movements.Increasing the amplitude,frequency,and reducing the heated power will promote the transition.Rolling motion has different effect on heat transfer.For low flow rate,it will reduce the flow and the heat transfer coefficient which is lower than theoretical data.For high flow rate,rolling will enhance the heat transfer.It has little effect on boiling heat transfer.Chen correlation and the Schrock-Grossman correlation can be also used to predict the saturated boiling heat transfer coefficient.