Abstract

Flat plate solar collectors are widely utilized for water heating in residential buildings, commercial and industrial applications. The thermal characteristics improvement of the working fluid can dramatically increase solar collector thermal efficiency. The working fluid thermal properties were improved by using nanofluids. Present work aims to study the effect of nano aluminum and titanium oxides addition to the water as a working fluid on solar collector efficiency. Outdoor experiments were carried out according to ASHRAE Standard 86 − 93. Nanoparticles of 25 nm size were used to reduce the agglomeration and increase the dispersion. Nanofluids were prepared at a concentration of 2% by weight and a surfactant was added to improve the stability. The tank outlet temperature was measured at different nanofluid flow rates of 2, 4, and 6 l/m. The maximum increases in tank outlet temperature for Al₂O₃ and TiO₂ were 5 and 7% at a flow rate of 2 l/m, respectively. Al₂O₃ and TiO₂ nanofluid improved the collector efficiencies by 30 and 32% at 2 l/m, respectively. TiO₂ had an increase in collector efficiency about Al₂O₃ at all flow rates. The maximum improvements in thermal conductivity for TiO₂ about Al₂O₃ were 1, 2, and 2.5% at 2, 4, and 6 l/m flow rates. The increases of friction coefficients of the nanofluids were less than 1% at all temperature range. The maximum increase in collector efficiency for Al₂O₃ and TiO₂ were about 22 and 30%, respectively about base fluid. Using Al₂O₃ and TiO₂ nanofluid was recommended to enhance solar collector performance.

摘要

平板太阳能集热器广泛用于住宅建筑、商业和工业应用中的水加热。工作流体的热特性改进可以显着提高太阳能集热器的热效率。通过使用纳米流体改善了工作流体的热性能。目前的工作旨在研究将纳米铝和钛氧化物添加到水中作为工作流体对太阳能集热器效率的影响。根据 ASHRAE 标准 86 - 93 进行户外实验。使用 25 nm 大小的纳米颗粒来减少团聚并增加分散。制备浓度为 2%（重量）的纳米流体，并添加表面活性剂以提高稳定性。在 2、4 和 6 l/m 的不同纳米流体流速下测量罐出口温度。₂ O ₃和TiO ₂在2 l/m 的流速下分别为5%和7%。Al ₂ O ₃和TiO ₂纳米流体在2 l/m 时分别将收集器效率提高了30% 和32%。在所有流速下，TiO ₂对Al ₂ O _{3 的}收集器效率都有提高。在 2、4 和 6 l/m 流速下，TiO ₂对 Al ₂ O _{3 的}热导率的最大改进为_1、2和 2.5%。在所有温度范围内，纳米流体的摩擦系数增加均小于 1%。Al ₂ O 的集电极效率的最大提高₃和 TiO ₂分别约为基液的 22% 和 30%。推荐使用Al ₂ O ₃和TiO ₂纳米流体来提高太阳能集热器的性能。