The mass fraction of 0.01 wt% ZnO nanofluid was prepared via the two-step method. The measurement verifies that ZnO nanofluids have better transmission characteristics in the frequency division window range of 400–1200 nm. At the same time, it has good absorption characteristics in ultraviolet and near-infrared bands, which meets the application conditions of the spectral beam-splitting module of the PV/T system. A spectral beam-splitting module of the PV/T system was designed. The simplified physical model was established in ANSYS 14.0. The flow field and convective heat transfer were simulated for different arrangements of the interlayer inlet to obtain a more ideal and uniform temperature distribution to improve the system’s comprehensive efficiency. The results show that the fluid flow in the interlayer under case II is more uniform, and the temperature field distribution is better than other arrangements. Hence, this work could provide a reference for optimising nanofluid flow within a spectral beam-splitting module.

Water-based Zn O nanofluids were prepared via the two-step method, and the influences of dispersant type and mass fraction on the stability and particle size distribution of the nanofluids were investigated. The spectral transmittances of the nanofluids were obtained by a UV-Vis-NIR spectrophotometer. Thermal conductivities of the nanofluids with various mass fractions were measured at different temperatures and a fitted nonlinear correlated equation was established for low-concentration application and compared with existing models. The photothermal conversion performance of the nanofluids was evaluated by theoretical and experimental methods at three optical depths. The results showed that, CTAB as the dispersant provides better physical stability of water-based Zn O nanofluids than SDBS or GA does. Effect of the temperature on the nanofluid thermal conductivity is remarkable with the increase of nanoparticle mass fraction, especially in the range 55°C to 75°C. The maximum thermal conductivity of the studied nanofluids is 0.9488 W/(m·°C) at 75°C, 43.61% higher than that of water. The minimum thermal conductivity of the studied nanofluids is 0.6376 W/(m·°C) at 25°C, 5.16% higher than that of water. The photothermal conversion performance of the nanofluids is quite good with a maximum average absorption efficiency of 0.47, 135% higher than that of water(η=0.2), and the maximum SAR is 527.5 W/g.

A test device for focal-plane energy flux density was designed based on a dual-axis tracking trough concentrator system. The focusing loss caused by the positioning error and tracking error of the receiver was studied through theoretical analysis and experimental testing. Furthermore, the optical loss was quantified by the acquisition factor, and laws of the influence of various errors were revealed. The results show that with the increase in the positioning error, the focal-plane width increases, whereas the focal-plane energy flux density decreases and tends to be uniform. Moreover, the focal-plane center migration and optical loss increase with the increase in the tracking error angle. For the dual-axis tracking trough concentrator system used in this experiment, when the receiver aperture is 50 mm, if the acquisition factor is greater than 90%, the positioning error of receiver is required to be between +/- 1.1% of 455 mm and tracking error angle is required to be less than 0.111 degrees, and the acquisition factor can reach 95%. The acquisition factor is more sensitive to the variation of the tracking error angle. The experimental results arc consistent with the theoretical analysis results, verifying the reliability of the test equipment and methods. The function relation of experiment fitting can effectively guide the engineering application.

Based on the comparison test platform of the dual-axis tracking trough solar system, the effect of the dust accumulation on the photothermal performance of the trough solar energy system is studied through theoretical analysis and experimental tests. The dust reflection factor and correction coefficient of the acquisition factor arc introduced to quantify the effect of dust accumulation on the photothermal performance of the system. The results show that the dust on the condenser has a significant effect on the concentrating characteristic of the focal plane. The uneven distribution of the dust causes more serious scattered radiation. As the amount of dust increases, the energy obtained by the focal plane within a certain size decreases. The energy flux density at the center of the focal plane is reduced, and the receiver with small aperture is more sensitive to the change of energy that can be collected on the focal plane. To ensure the correction coefficient of the acquisition factor of the trough concentrator is greater than 0.90, the dust reflection factor should be less than 4.3%. A prediction model of the effect of dust accumulation on the heat collection performance of the trough solar system is established and verified by the experimental test. The relative error between the predicted value of the model and the experimental value is less than 5.07%, and the good agreement between them is obtained. This prediction method has good universality and can provide theoretical guidance for practical engineering applications.

针对影响双轴跟踪槽式太阳能系统集热效率的多种因素,文章采用量纲分析法建立了集热效率预测模型,构建了包括Re数在内的5个无量纲量.实验测试了不同工况下系统的集热性能,通过多元线性回归对集热效率预测模型进行了求解.研究结果表明:在文章研究范围内,Re对集热效率的影响较大,太阳辐照量、集热管几何参数以及传热工质物性等对集热效率影响相对较小;在集热效率预测模型复测样本范围内,集热效率计算值和实测值之间的最大相对误差不超过15％.文章建立的双轴跟踪槽式太阳能系统集热效率预测模型精度较高,可为槽式太阳能系统的工程设计和优化运行提供理论依据.