Study Of Flow And Heat Transfer In Rectangular Channel In Periodic Force Field

The thermal-hydraulic characteristics of nuclear reactor system are influenced bythe periodic force field under rolling motion conditions, and then the performancecharacteristic of nuclear reactor will be affected. In this paper, the flow and heat transfercharacteristics of rectangular channel in both static state and periodic force field thatinduced by rolling motion are investigated through theoretical, numerical andexperimental methods.Experimental studies of the thermal hydraulics for rectangular channel in static stateshow that the laminar to turbulent transition Reynolds number decreases with theincrease of channel aspect ratio, whereas the wall heating leads to the delay of thetransition. In addition, the experimental results also indicate that the subcooled boilingheat transfer in rectangular channel is different from that in large channels, thus a modifyfactor based on the ratio of bubble departure diameter in flow boiling and pool boiling isintroduced to develop the subcooled boiling heat transfer model in rectangular channel.Furthermore, a series of prediction correlations are developed to calculate the single andtwo-phase flow friction and heat transfer characteristics.Theoretical studies show that the single-phase flow rate pulsation characteristics inperiodic force field are influenced by driving force, additional periodic force andresistance characteristics. The flow rate will not affect by the periodic force field whenthe amplitude of the driven force is10times larger than the periodic force field. However,as the periodic force is large enough to make flow rate pulsate fiercely, the amplitude offlow rate pulsation decreases with the decrease of average flow rate if the flow rate isrestricted through increasing the loop’s resistance, furthermore, the tendency is oppositeif the flow rate is adjusted by decreasing the driving force. As the flow rate does notpulsate notably, the effect of the radial periodic force field on secondary flow andtemperature field increases with the increase of the size of narrow side. In addition, bothnumerical analysis and experimental study indicate that the variation of secondary flowand temperature field induced by the radial periodic force field will not change themacroscope friction and heat transfer characteristics of the narrow rectangular channelwith a cross section of2×40mm. Experimental results also show that the thermal hydraulic characteristics of pulsation flow that induced by rolling motion and periodicdriving force are the same as the influence of radical periodic force can be neglected. Therelationship among flow rate pulsation amplitude, average flow rate and rollingparameters are derived as the flow rate adjusted by changing the driving force, then thefriction and heat transfer calculation correlations are obtained in periodic force fieldcondition.The flow boiling heat transfer experiments in periodic force field indicate that thevariation of mass flow rate relates closely to the outlet mass quality. In low mass qualityexit region, the boiling pressure drop and heat transfer characteristics are not influencedby the periodic force field and the calculation correlations are the same as that in staticcondition. However, as the mass quality reaches a certain value, the variation ofbouyancy force quantity and operating direction which induced by the rolling motionwill introduce the bubble coalescence periodically at the condenser’s exit and then resultin the loop blocking. Therefore the pressure, the boiling intensity and the flow rate in thechannel also varies accordingly. The correlations for friction pressure drop applied to thesteady state are also valid for that under rolling motion conditions for it mainlydepending on the mass quality. However, the saturation boiling heat transfercharacteristics in periodic force field show notable difference with that in steady stateowing to the flow rate fluctuations.