BACKGROUND Aqueous-alumina nanofluid was prepared using magnetic stirrer and ultrasonication process. Then, the prepared nanofluid was subjected to flow through the unshielded receiver of the parabolic trough solar collector to investigate the performance of the nanofluid and the effects of the dimensionless parameter were determined. METHODS The experimental work has been divided into two sections. First, the nanofluid was prepared and tested for its morphology, dimensions, and sedimentation using X-Ray Diffraction and Raman shift method. Then, the nanofluids of various concentrations from 0 to 4.0% are used as heat transfer fluid in unshielded type collector. Finally, the effect of the dimensionless parameter on the performance was determined. RESULTS For the whole test period, depending upon the bulk mean temperature, the dimensionless parameters such as Re and Nu varied from 1098 to 4552 & 19.30 to 46.40 for air and 2150 to 7551 & 11.11 to 48.54 for nanofluid. The enhancement of thermal efficiency found for 0% and 4.0% nanoparticle concentrations was 32.84% for the mass flow rate of 0.02 kg/s and 13.26% for the mass flow rate of 0.06 kg/s. CONCLUSION Re and Nu of air depend on air velocity and ambient temperature. Re increased with the mass flow rate and decreased with concentration. Heat loss occurred by convection mode of heat transfer. Heat transfer coefficient and global efficiency increased with increased mass flow rate and volume fraction. The thermal efficiency of both 0% and 4.0% concentrations became equal for increased mass flow rate. It has been proven that at high mass flow rates, the time available to absorb the heat energy from the receiver is insufficient.

中文翻译：

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无量纲参数对去离子水氧化铝纳米流体抛物槽太阳能集热器的影响。

背景技术使用磁力搅拌器和超声处理工艺制备氧化铝纳米流体。然后，使制备的纳米流体流过抛物槽式太阳能集热器的非屏蔽接收器，以研究纳米流体的性能并确定无量纲参数的影响。方法实验工作分为两部分。首先，制备纳米流体，并使用X射线衍射和拉曼位移法测试其形态，尺寸和沉降。然后，将各种浓度为0至4.0％的纳米流体用作非屏蔽型集热器中的传热流体。最后，确定了无量纲参数对性能的影响。结果在整个测试期间，取决于总体平均温度，空气的Re和Nu等无量纲参数从1098到4552，从纳米流体到2150到7551和11.11到48.54，从19.30到46.40。对于0.02kg / s的质量流率，发现0％和4.0％的纳米颗粒浓度的热效率提高为32.84％，对于0.06kg / s的质量流率，为13.26％。结论空气的Re和Nu取决于风速和环境温度。Re随质量流量增加而随浓度降低。热损失是由对流传热方式引起的。传热系数和整体效率随着质量流量和体积分数的增加而增加。对于增加的质量流量，0％和4.0％浓度的热效率变得相等。已经证明，在高质量流量下，