Research Of Narrow Annuli Fluid Channel Cooling Heat Transfer Characteristic

Under the condition of different inlet temperature (50℃,60℃,70℃,80℃)and different equivalent diameter (5.96,4.90,3.98,2.90,1.80,0.94mm), using water as working media, the experiments of cooling heat transferin annular channel is studied, and the mechanism of heat transfer and influencefactor are also analyzed; Besides, based on some experimental data, simulatingcalculation is carried out by using CFD software. The results are as follows:As far as the flow state is concerned, the single-phase forced convectionin annular channel can be divided into laminar flow region, transition region,and turbulent flow region in the range of equivalent diameter (1.8mm～5.96mm).The transition region varies with the equivalent diameter changing,when Re number is about 500-2000, the transition region advances with theincrease of annular width; when the equivalent diameter is 0.94mm, onlyturbulent flow region exists in the channel, when the equivalent diameter is1.8～5.96mm, not only turbulent flow region, transition region but also laminarflow region in annular channel have the role of enhancing heat transfer. But theheat transfer would be restrained in the channel with 0.94mm equivalentdiameter.Besides, the influence of inlet hot water temperature on heat transfer ofannular channel is obvious when Re＜1000 and Re＞3000, and under the sameRe number, the heat transfer ability decreases with the increase of inlet hotwater temperature. The effect of equivalent diameter of annular channel onheat transfer is clear at Re＜1000, and with the same Re number, Nu numberdeclines with the annular width reduced. Through the simulating calculation, itis found that the calculation agrees well with the experimental data, and the error is small; the inner diameter of core tube changed have some certain effecton the heat transfer; when the equivalent diameter d=7mm, the heat transferability in turbulent flow region in narrow annular channel can not be enhanced,however the heat transfer ability in laminar flow region and transition regionare still quite obvious.