Performance Evaluation of a Nanofluid-Based Direct Absorption Solar Collector with Parabolic Trough Concentrator

Abstract

Application of solar collectors for hot water supply, space heating, and cooling plays a significant role in reducing building energy consumption. For conventional solar collectors, solar radiation is absorbed by spectral selective coating on the collectors' tube/plate wall. The poor durability of the coating can lead to an increased manufacturing cost and unreliability for a solar collector operated at a higher temperature. Therefore, a novel nanofluid-based direct absorption solar collector (NDASC) employing uncoated collector tubes has been proposed, and its operating characteristics for medium-temperature solar collection were theoretically and experimentally studied in this paper. CuO/oil nanofluid was prepared and used as working fluid of the NDASC. The heat-transfer mechanism of the NDASC with parabolic trough concentrator was theoretically evaluated and compared with a conventional indirect absorption solar collector (IASC). The theoretical analysis results suggested that the fluid's temperature distribution in the NDASC was much more uniform than that in the IASC, and an enhanced collection efficiency could be achieved for the NDASC operated within a preferred working temperature range. To demonstrate the feasibility of the proposed NDASC, experimental performances of an NDASC and an IASC with the same parabolic trough concentrator were furthermore evaluated and comparatively discussed.

Performance analysis of a direct-absorption parabolic-trough solar collector using plasmonic nanofluids

“…It is also recognized that for using the radiation network approach, the surface is assumed as diffusive and gray. Even though the glass surface is not real diffusive, it is an easy and good approximation by assuming diffusive as also done in other studies [1,42].…”

“…It is seen that the current Ta, inlet temperature T 0 and temperature gain ∆T are all in K, the unit for solar irradiance G T is W/m 2 , and that for volumetric flow rate V in is L/min. The subscripts of 'exp', 'num' and 'cur' indicates the experimental results [46], numerical results [42] and the current simulation results, respectively. The reason that the current thermal efficiency is slightly higher than the experimental data is probably because the current model did not account for the heat loss through the brackets and tube ends.…”

Nanofluids revisited

“…The idea was however revived with the introduction of nanofluids [2,38] by Choi et al Due to the volumetric absorption, temperature maxima can be moved from the outside of a surface absorber into the absorber liquid [137,138] to reduce radiative and convective losses. Numerous articles have been published suggesting different nanoparticles, basefluids and absorber designs for the volumetric solar absorption .…”

Thermal Stability and Performance Testing of Oil-based CuO Nanofluids for Solar Thermal Applications

“…One of the gaps in knowledge stems from the fact that a great deal of nanofluids research focuses on water-based nanofluids for low-temperature (≤100 • C) applications [29][30][31]. However, since a huge demand exists in the medium-temperature range (requiring temperatures just above 100 • C), it is desirable to develop nanofluids, which can use heat transfer oils as their base fluids [32,33]. For these types of nanofluids, only some preliminary "heating" and "heating-cooling-heating" investigations on thermophysical properties have been conducted [4,34].…”