Tambula Shaibu, Musademba Downmore, Chihobo Chido H
Department of Fuels and Energy Engineering, Chinhoyi University of Technology, P. Bag 7724, Chinhoyi, Zimbabwe.
Heliyon. 2023 Mar 1;9(3):e14226. doi: 10.1016/j.heliyon.2023.e14226. eCollection 2023 Mar.
The evacuated tube collector (ETC) has gained extensive use in low-temperature applications due to its cheapness and high efficiency. The ETC can be used with a concentrator for medium temperature applications, in the range of 140-200 . However, the heat extraction rate of the absorber tube is a limitation factor, particularly at higher heat flux and high flow rates. The energy gained is not directly proportional to the concentration factor used. This work thus proposes a counter-flow copper absorber for increasing the heat extraction rate and compares its performance to the conventional direct-flow absorber. The designs are both optimized by varying the absorber diameters, and a material property analysis is done. COMSOL Multiphysics is used for the simulations. The performance of the 2 systems is evaluated using a conjugate heat transfer model at flow rate ranges of 0.02-0.2 kg/s and uniform theoretical heat flux of 1000, 2000, and 3000 W/m. Analysis of the results indicates that the counter-flow with 0.01 and 0.02 m inner and outer diameter respectively has 4 times more energy gain than the direct-flow with a 0.01 m diameter. Increasing the heat flux by 2 at 0.02 and 0.2 kg/s flow rate increases the temperature by 1.5 and 1.1 for the counter-flow absorber and 1.2 and 1.04 for the direct-flow absorber. Tripling the heat flux at the same flow rate range increases the temperature by 2 and 1.4 for the counter-flow absorber and 1.5 and 1.07 for the direct-flow absorber. The counter-flow absorber is thus the best choice at higher heat flux and high flow rates which are typically required for industrial heating.
真空管集热器（ETC）因其成本低廉且效率高，已在低温应用中得到广泛使用。ETC可与聚光器配合用于中温应用，温度范围为140 - 200摄氏度。然而，吸收管的热提取率是一个限制因素，特别是在高热通量和高流速情况下。所获得的能量与所使用的聚光系数并非直接成正比。因此，这项工作提出了一种逆流式铜吸收器，以提高热提取率，并将其性能与传统的直流吸收器进行比较。通过改变吸收器直径对两种设计进行了优化，并进行了材料特性分析。使用COMSOL Multiphysics进行模拟。在流速范围为0.02 - 0.2千克/秒以及均匀理论热通量为1000、2000和3000瓦/平方米的条件下，使用共轭传热模型对这两个系统的性能进行了评估。结果分析表明，内径和外径分别为0.01米和0.02米的逆流吸收器所获得的能量比直径为0.01米的直流吸收器多4倍。在流速为0.02千克/秒和0.2千克/秒时，将热通量提高2倍，逆流吸收器的温度分别升高1.5和1.1，直流吸收器的温度分别升高1.2和1.04。在相同流速范围内将热通量提高3倍，逆流吸收器的温度分别升高2和1.4，直流吸收器的温度分别升高1.5和1.07。因此，在工业加热通常所需的高热通量和高流速情况下，逆流吸收器是最佳选择。
