Comparative analysis of direct‐absorption parabolic‐trough solar collectors considering concentric nanofluid segmentation

Abstract

Summary Nanofluids have been actively used in direct‐absorption solar collectors. In a direct‐absorption parabolic‐trough solar collector (DAPTSC) for medium‐high temperature regime, the nanofluids used to be contained in a transparent glass receiver located at the focal line of a parabolic mirror so that the solar radiation is concentrated to the glass receiver and absorbed volumetrically inside the collector. In order to further increase the thermal efficiency of a DAPTSC, we propose to insert an extra glass tube inside the nanofluid so that the nanofluid is separated into two concentric segmentations (ie, an inner section and an outer section), and apply a nanofluid of lower concentration in the outer section while a nanofluid of a higher concentration in the inner section. The proposed idea is numerically tested on four pairs of DAPTSCs (the variants obtained depending on whether there is a vacuum envelope and whether there is a reflective semicylindrical coating on the receiver). The results show that at the same particle concentration parameter, the DAPTSCs with two concentric segmentations of nanofluids outperform those with one uniform nanofluid for all configurations considered in this work. For a transparent case without an envelope, this efficiency increase is as high as 12.5% point when the inlet temperature is 350 K. In addition, parametric studies are performed for this best configuration to evaluate the effect of absorption coefficient, mass flow rate, collector length, solar irradiance, and convection heat transfer coefficient on the collector performance.

Solar Thermal Conversion of Plasmonic Nanofluids: Fundamentals and Applications

“…For the collector design, an extra glass tube inside was inserted so the nanofluid was separated into two concentric segmentations (i.e., an inner section and an outer section), and a nanofluid of lower concentration was applied in the outer section while a nanofluid of a higher concentration in the inner section. Results showed that at the same NP concentration parameter, the DAPTSCs with two concentric segmentations of nanofluids outperform those with one uniform nanofluid for all considered configurations [104]. Furthermore, the transparent DAPTSC was improved by applying a reflective coating on the upper half of the inner glass tube outer surface such that the optical path length was doubled compared to that of the transparent DAPTSC, allowing a reduction in the absorption coefficient of the nanofluid [105].…”

Multi‐objective assessment of a DAPTC based on 4E analysis: Water‐energy‐environment nexus

“…As a result, outdated systems need to be replaced with newer systems that are more efficient and have higher performance levels. Direct absorption collectors have recently gained consideration due to its higher heat transfer rate and thermal efficiency compared to indirect absorption collectors 6,7 . In these types of collectors, the heat transfer fluid or volumetric absorber directly absorbs solar radiation, and thereby, the irradiative and convective losses in DAPTCs would be reduced 8 .…”

“…Direct absorption collectors have recently gained consideration due to its higher heat transfer rate and thermal efficiency compared to indirect absorption collectors. 6,7 In these types of collectors, the heat transfer fluid or volumetric absorber directly absorbs solar radiation, and thereby, the irradiative and convective losses in DAPTCs would be reduced. 8 According to Khalil et al, 9 DAPTCs enhance thermal efficiency by 19% compared to conventional PTCs.…”

Archives of Electrical Engineering

“…The receiver of the parabolic trough collector is modeled in an engineering equation solver (EES) and with a MATLAB code. Author [7] reported about the direct-absorption parabolic-trough solar collector for the medium to high temperature regime, using a nano-fluid as a heat transfer fluid and evaluated the effect of the mass flow rate, convection heat transfer coefficient, absorption coefficient, and solar irradiance on the collector performance. Author [8] studied the detailed temperature distribution of a PTC receiver using FLUENT software and a MCRT code by considering the heat transfer fluid flow, radiation and conduction heat transfer mechanisms.…”