Thermal Performance Enhancement in Flat Plate Solar Collector Solar Water Heater: A Review

Enhancing water heater efficiency with aluminum and zinc-coated steel systems for energy solutions

Solar collector plates are integral components for efficient solar heat transfer. While various metallic materials can serve as collector plates, aluminum stands out as a commonly employed choice with thermal conductivity comparable to copper and zinc. The material's thermal conductivity significantly impacts the heat transfer efficiency from sunlight to the collector. Moreover, the surface configuration of the plate is a crucial factor affecting solar heat absorption. This study investigates the utilization of corrugated collector plates made from two materials, aluminum and zinc-coated steel. The solar collector testing phase covers the dry and rainy seasons in Indonesia, thereby providing a comprehensive evaluation in various weather conditions. There are two stages of solar collector testing, namely testing before it is used to heat water and testing to heat water. Radiation data show seasonal variations, with higher radiation observed in the dry season. Evaluation of the performance of the solar collector before being used to heat water resulted in an average efficiency of 41.45 % for aluminum and 33.94 % for zinc-coated steel. Meanwhile, evaluation of the performance of solar collectors used to heat water produces an average efficiency of 20.40 % for aluminum and 10.47 % for zinc-coated steel. Corrugated aluminum solar collectors exhibited promising absorber potential, while zinc-coated steel demonstrated economic viability due to its lower cost compared to aluminum. The research underscores the potential applicability of solar collectors made from both materials throughout different seasons.

An experimental and numerical approach for thermal performance investigation of solar flat plate collector

The present work aims to investigate thermal performance of a solar flat plate collector using water and Cu-MWCNTs nanoparticle-based hybrid nanofluid both experimentally and numerically. X-ray diffraction and FESEM with EDAX mapping were performed to characterize nanoparticles. The experimental setup was developed for thermal performance of FPC varying flow rates (0.5, 1.0, 1.5 LPM), inclination angle (25°, 30°, 35°, 40°, 45°), volume concentration (0%, 0.1%, 0.2%, 0.3%, 0.4%), and intensity (400 W/m2). The 3D numerical model having similar geometry as of actual flat plate collector was modeled using Fluents 15.0. The SST turbulence model was used to capture the chaotic changes in the velocity, temperature, and pressure fields. The experimental findings revealed 79.74% improvement in instantaneous efficiency at 0.4% vol., 1.5 LPM, 45° inclination angle, and 400 W/m2 intensity. The maximum deviation between the experimental and numerically calculated outlet and inlet temperature difference (ΔT) was 3.5% using a hybrid nanofluid. When numerical data are compared, instantaneous efficiency and heat gain both deviate by 2.8% and 2.9% from experimental values. Because of the numerical simulation analysis, it is possible to observe the temperature and flow pattern in flat plate collectors using nanofluids under a set of operating conditions, which would not be possible without the simulation.

Conductive and convective heat transfer augmentation in flat plate solar collector from energy, economic and environmental perspectives - a comprehensive review

The primary objective of the paper is to identify the effective way to enhance the conductive and convective heat transfer of the FPSC. The performance enhancements of different FPSC components such as absorber plate, absorber tube, and heat transfer fluid are reviewed in detail. The influence of absorber plate configurations, material properties, a center-to-center distance of the absorber tube, plate thickness, coatings, and tube geometry have been assessed to increase the conduction heat transfer. Also, the augmentations of convective heat transfer using different nanofluids in FPSC such as Al₂O₃/water, CuO/water, CNT/water, TiO₂/water, SiO₂/water, graphene oxide/water, MgO/water, CeO₂/water, WO₃/water, ZnO/water, and hybrid nanofluids are evaluated in detail. The performance improvements using both conductive and convective (combined) passive technique have been elaborated. The table representation has been used to describe the activities performed in each paper which include FPSC type, passive technique detail, properties of heat transfer fluid, Reynolds number, heat transfer aspects, pumping power, energy, exergy, environmental aspects, and inference. These data will help the researcher to identify existing activities and the potential gap. This review paper also deals with the suggestions for the research work which can be carried out in the direction of heat transfer from solar flat plate collectors.

Evaluation of Multiple Semi-Twisted Tape Inserts in a Heat Exchanger Pipe Using Al2O3 Nanofluid

The hydrothermal performance of multiple semi-twisted tape inserts inside a heat exchanger pipe is numerically examined in three-dimensions. This study aims to find the optimum case for having the highest heat transfer enhancement with the lowest friction factor using nanofluid (Al₂O₃/water). A performance evaluation criterion (PEC) is defined to characterize the performance based on both friction factor and heat transfer. It was found that increasing the number of semi-twisted tapes increases the number of swirl flow streams and leads to an enhancement in the local Nusselt number as well as the friction factor. The average Nusselt number increases from 15.13 to 28.42 and the average friction factor enhances from 0.022 to 0.052 by increasing the number of the semi-twisted tapes from 0 to 4 for the Reynolds number of 1000 for the base fluid. By using four semi-twisted tapes, the average Nusselt number increases from 12.5 to 28.5, while the friction factor reduces from 0.155 to 0.052 when the Reynolds number increases from 250 to 1000 for the base fluid. For the Reynolds number of 1000, the increase in nanofluid concentration from 0 to 3% improves the average Nusselt number and friction factor by 6.41% and 2.29%, respectively. The highest PEC is equal to 1.66 and belongs to the Reynolds number of 750 using four semi-twisted tape inserts with 3% nanoparticles. This work offers instructions to model an advanced design of twisted tape integrated with tubes using multiple semi-twisted tapes, which helps to provide a higher amount of energy demand for solar applications.

Long-Term Performance of Anti-Freeze Protection System of a Solar Thermal System

In a moderate, transitory climate, to prevent freezing of outdoor pipes and collectors in solar thermal systems, anti-freezing fluids are commonly used. There is little experience of using water without any additives as a solar thermal fluid in such a climate. Based on these findings, to fill the knowledge gap this article presents the long-term results of thermal performance and anti-freeze protection of a solar heating system with heat pipe evacuated tube collectors with water as a solar thermal fluid. The operation of this system under real conditions was analysed for five years in southern Poland. The annual value of solar insolation ranged from 839 to almost 1000 kWh/m2. The monthly efficiency of the solar collectors from March to October was usually higher than 25%, and the lowest was between November and January. The anti-freeze protection system consumed annually from 7 to 13% of the heat generated by the collectors in the installation. Supporting the operation of the central heating system in the building during the winter season highly improved the efficiency of the solar collectors. Results show that it is possible to use water without any additives as a solar thermal fluid in a moderate, transitory climate.