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提出并探讨了导热油基液纳米流体为集热介质的太阳能直接吸收式集热方法用于中温热利用。在室外工况下,采用理论聚光比为5.2的槽式聚光器,对导热油-CuO纳米流体直接吸收式中温集热特性开展了实验测试,并与镀膜真空管集热性能进行了对比分析。实验结果显示,该纳米流体直接吸收式集热器的最大瞬时效率达70%,在150℃以下工况时的集热效率要高于传统镀膜吸收真空集热管;而当集热温度升高至150℃以上,散热明显增大,集热效率降低。通过理论计算结合实验进行热损失分析,发现纳米流体直接吸收式集热过程中最大的热损失项为内管壁对外辐射散热,约占总热损失的55%~70%。
The solar energy direct absorption heat-collecting method based on heat-conducting oil-based liquid nanofluids as heat-collecting medium is proposed and discussed for medium-temperature heat utilization. Under the outdoor condition, the experiment was carried out on the direct absorption characteristics of HTF-CuO nanofluid at mid-temperature by using a slot condenser with a theoretical condensing ratio of 5.2. The performance of the tube was compared with that of the coated vacuum tube . The experimental results show that the maximum instantaneous efficiency of the nanofluid direct absorption collector is up to 70%, and the efficiency of heat collection under operating conditions below 150 ℃ is higher than that of the conventional coating absorption vacuum tube. When the temperature of the collector increases to 150 ℃ above, significantly increased heat dissipation, heat collection efficiency. Through the theoretical calculation and experimental analysis of heat loss, it is found that the largest heat loss term of the nanofluid in direct absorption heat collection is the external radiation heat dissipation of the inner wall, accounting for 55% -70% of the total heat loss.