Experimental Study On PM-CHF In A Narrow Rectangular Channel

Due to higher power density,larger heat transfer area than conventional channels,narrow rectangular channels are widely used in miniaturization reactors,research reactors,aerospace compact heat exchangers and microelectronics,etc.CHF?critical heat flux?is the limit of boiling heat transfer.Therefore,accurately predicting the critical heat flux is particularly important for safe operation of the reactor and increasing output power.Due to the difference in geometry and the scale effect that the narrow side may bring,the narrow rectangular channel is quite different from the the circular tube with large gap in the two-phase flow and heat transfer characteristics.The existing study results for the round tube can not be simply analogized to narrow rectangular channels.Therefore,it has far-reaching significance to perform CHF experiment in narrow rectangular channel.In this study,the deionized water was used to perform the CHF visualization experiment in a narrow rectangular channel heated from one-side under low pressure forced circulation conditions.It was found that the flow drift instability occurs in the process of gradually increasing power.This instability causes the flow to violently oscillate,which induces the occurrence of premature CHF,namely PM-CHF.In this paper,the thermodynamic quality just before the flow oscillation is referred to as critical quality(x_e,c).On the x_e,c-G curve there exists an apparent turning point,at which the mass flux is approximately 400 kg/?m²·s?under the geometry configuration and operating conditions of this experiment.According to this turning point,the PM-CHF can be divided into PM-CHF under low flow rate and PM-CHF under high flow rate.?1?Under low mass flow rate,the flow pattern transition from diffuse bubbly flow to coalesced bubble flow causes the occurrence of PM-CHF.The value of PM-CHF increases with the increase of inlet subcooling,flow rate,and the system pressure.The critical quality decreases with the increase of inlet subcooling and flow rate.The correlation of onset of flow instability can be used to predict the PM-CHF.The modified Stelling correlation can accurately predict the experimental PM-CHF value,and the prediction error is within±17%.?2?Under high mass flow rate,the corner effect in rectangular channel causes the occurence of PM-CHF.The value of PM-CHF increases with the increase of inlet subcooling,flow rate,and the system pressure.The critical quality decreases with the increase of inlet subcooling and increases with the increase of flow rate.The modified Stelling correlation can accurately predict the experimental PM-CHF value,and the prediction error is within±15%.