•This review presents effect of nanofluids in solar Evacuated Tube Solar Collectors.•Recent studies on this type of solar collector are summarized.•Highest thermal enhancement belongs to heat pipe ...model and SWCNT-based nanofluids.•Nanoparticles concentrations are challenges of using nanofluid in ETSCs.
This review presents impact of nanofluids in solar evacuated tube solar collectors (ETSCs). Recent works on this type of solar collector are summarized. The first part depicts the significance of choosing ETSCs for solar domestic hot water in addition to classification of these collectors and application of each categories. In second part, usage of nanofluids is studied in considered system and through this pervasive review, some issues such as, various kinds of nanofluids, size of nanofluids, volume fraction, and nanofluid application in every kind of ETSCs on the heat transfer augmentation have been analyzed. This state-of-the-art review shows that most of nanofluids in ETSCs are water-based with nanoparticles of TiO2, CuO, and Al2O3. Other types of nanoparticles including CeO2, WO3, Ag, CeO2, GNP, and Cu were less considered up to now. Moreover, 40, 34, and 26% of nanofluids were used with size between 1–25 nm, 25–50 nm, and 50–100 nm, respectively. Furthermore, highest thermal improvement belongs to heat pipe type solar collector with SWCNT-based nanofluids by 93.43% at ṁ = 0.025 kg/s. Besides, nanoparticles concentrations are challenges of using nanofluid in ETSCs. This parameter has marginally affected on performance of ETSCs. So, the optimum amount of this parameter for each type of nanofluids will suggest for future works.
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Novel heat transfer fluids with very low vapor pressure and high thermal stability are highly desirable for both high temperature direct solar collectors and concentrated solar collector. Herein a ...combined analytical and experimental study has been conducted on high temperature direct solar thermal collectors using graphene/ionic liquid nanofluids as the absorbers. A one-dimensional transient heat transfer model has been used to predict the receiver temperature and efficiency with varying parameters such as solar and graphene concentration and receiver height. The results show that the experimental temperature is in good agreement with numerical results under the same conditions. Based on the model, it is shown that the receiver efficiency increases with the solar concentration and receiver height, but decreases with the graphene concentration. The receiver efficiency could be maintained 0.7 under the conditions of 0.0005wt% of graphene in 5cm receiver under 20×1000Wm−2 at 600K. This work provided an important perspective to the graphene/ionic liquid nanofluids for use as a kind of novel heat transfer fluid in direct solar thermal collectors under concentrated solar incident radiation.
•Combined numerical and experimental study on graphene/ionic liquid nanofluid based high temperature receiver.•Effects of solar concentration, graphene concentration, nanofluid height on receiver efficiency were obtained.•Receiver efficiency was beyond 0.7 below 700K.
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Evacuated Tube Solar Collector is a promising type of solar heaters. As an energy storage media, paraffin wax found to has a low thermal conductivity in both charging and discharging processes. In ...this paper, an Evacuated Tube Solar Collector with a helically finned heat pipe experimentally studied. Two collectors used during the tests. The first was the control system, including the conventional fins type. While the second one was the helical fins type. The experiments carried out considering flow rates of 0.165, 0.335, 0.5, and 0.665 L/min. Tap water was used as a heat transfer fluid. The results showed that the helical fins archive better temperature homogeneity in Paraffin along the tube axis than the conventional fins. Under the same flow rate, the maximum temperature difference was found to be 4 °C and 12.25 °C for the helical and the conventional fins systems, respectively. The helical fins found to achieve a daily efficiency enhancement over the conventional one by 15% and 13.6% for the flow rates of 0.5 and 0.665 L/min, respectively. Moreover, the solid to liquid phase change started in the helical fin system after the conventional one by 30–60 min.
•The helical fines are better than the conventional at high flow rates.•The helical fines achieved 0.5–1 h PCM-melting time-delay than the conventional.•The helical fines achieved higher peak temperatures than the conventional type.•The helical fins conduct heat in the solid PCM better than the conventional fins.
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An exergoeconomic assessment of a combined cooling, heating, and power generation system is conducted for summer air conditioning for the school of engineering at Urmia University in Iran. The ...proposed application comprises of parabolic trough solar collectors integrated with an organic Rankine cycle and two single-effect absorption chillers. The novelty of the paper relies on considering the real energy load and solar radiation for the exergoeconomic analysis. Hence, three solar radiation operational modes are simulated, which includes low (solar mode), high (solar and storage mode), and no radiation (storage mode) during the day. The effects of the three vital parameters, including Day numbers, organic Rankine cycle pump inlet temperature, and organic Rankine cycle turbine inlet pressure on several variables are examined. The results illustrated that the highest cooling, heating, and electrical power loads of the building during summer time are 896.9 kW, 228.5 kW, and 1500 kW, respectively. Furthermore, the cost per unit exergy of the generated power for the above-mentioned modes are 11.44 $/GJ, 10.27 $/GJ, and 15.47 $/GJ, respectively. It was concluded that these values decrease by 16.4, 18.4, and 11.9% point as a result of the overall system establishment.
•Exergoeconomic study is performed of a parabolic trough collector-based CCHP system.•Analysis is conducted in summer for the school of engineering at Urmia University.•Study is carried out in three solar radiation operational modes during the day.•On average the cost per unit exergy of system on 160th day of the year is 10.5 $/GJ.•On average the cost rate of system’s products on 160th day of the year is 120.8 $/h.
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Nanofluid-based direct absorption of solar heat results in thermal efficiencies superior to conventional solar thermal technology. In addition, convection of nanofluid can be sustained pump-free in ...the collector. In this article, we study an aqueous magnetic nanofluid capable to establish the photothermal convection in a lab-scale direct absorption solar collector equipped with a solenoid. The nanofluid consisted of 60-nm Fe2O3 particles dispersed in distilled water at concentration in the range 0.5% wt.-2.0% wt. An empirical model of the photothermal convection was developed based on the experiments. The model accounted for magnetic and thermophoretic forces acting within the nanofluid. The nanofluid with up to 2.0% wt. iron oxide nanoparticles obtained the velocity of ∼5 mm/s under the magnetic field of up to 28 mT. This resulted in the maximum thermal efficiency of the collector equal to 65%.
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•Nanofluid-based direct absorption solar collector is studied.•Nanofluid is produced with 0.5% and 2.0% of Fe2O3 nanoparticles.•Magnetic field up to 28 mT is applied to nanofluid.•Photothermal convection is established in the fluid with the velocity of 2-5 mm/s.•Maximum thermal efficiency of the collector is 65%.
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•A novel combined PVT and ST system is developed.•Different kinds of hybrid nanofluids for improving system performance are studied.•The SiC/Gr hybrid nanofluid has the best performance compared to ...others.•In the combined system, ST produces more entropy generation compared to PVT.
Because of the low outflow temperature of the conventional photovoltaic thermal systems and lack of electrical production of the solar thermal collectors, a novel combined system is proposed to solve the two mentioned drawbacks. This novel system is achieved by connecting a photovoltaic thermal unit to a solar thermal collector in series. To increase the overall performance of this novel combined system, different hybrid nanofluids include (1) multiwall carbon nanotube-aluminum oxide (2) multiwall carbon nanotube-silicon carbide (3) graphene-aluminum oxide, and (4) graphene-silicon carbide are compared. The investigation is performed based on the three-dimensional simulation, and the Eulerian-Eulerian model is selected for the simulation of hybrid nanofluids. To estimate the performance of this novel combined system, the first and second laws of thermodynamics are used. Moreover, the share of entropy generation in all components of the system is calculated. The results indicate that the multiwall carbon-silicon carbide hybrid nanofluid with the average electrical and thermal energy efficiency of 13.85% and 56.55%, respectively, has the best performance compared to other fluids. Furthermore, in the combined system, different components of the solar collector produce more entropy generation than the components of the photovoltaic thermal module.
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•Thermodynamic study is performed for a system driven by parabolic trough solar collectors.•A case study for summertime is developed for the school of engineering at Urmia University.•The ...investigation is carried out in low, high, and no solar radiation modes during the day.•Energy efficiency of low, high and no solar radiation modes are 98%, 47.3% and 98%, respectively.•Exergy efficiency of low, high and no solar radiation modes are 17%, 8.3% and 17%, respectively.
A new solar-based, combined cooling, heating, and power system is designed and developed for the school of engineering at Urmia University in Urmia, Iran. The proposed arrangement consists of a solar subsystem with parabolic trough solar collectors, an organic Rankine cycle, two heating processes, and two single-effect absorption chillers. The system is thermodynamically studied for the summer air conditioning requirements, considering genuine energy demand and variable solar radiation in three different operational modes (solar, solar and storage, and storage modes). The influences on the system performance are assessed of varying three main variables including the number of days, organic Rankine cycle pump inlet temperature, and organic Rankine cycle turbine inlet pressure. The results demonstrate that the highest cooling, heating and electrical loads in the summer air conditioning are 896.9 kW, 228.5 kW, and 1500 kW, respectively. The energy load is provided by employing 449–1625 number of PTSCs throughout the year. Furthermore, for summertime the energetic and exergetic analyses reveal that the energy efficiency of the system in the solar mode, solar and storage mode, and storage mode is found to be 98%, 47.3%, and 98%, respectively. Accordingly, the exergy efficiencies were equal to 17%, 8.3%, and 17%.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
•Experimental study of heat dynamic of ASCs in field conditions.•Assessment of two different glazing strategies: with glazing and without glazing.•Evaluate heat dynamic of unglazed and glazed ASC ...when solar irradiation is negligible.•Energy analysis of ASCs with glazing and no glazing.
Exposure to solar irradiation for an extended period during a day causes asphalt pavements can reach to a considerable temperature. Consequently, they can be converted into an affordable solar collector by harvesting thermal energy. In recent years much effort and time have been devoted to improving the thermal performance of solar collectors. To this aim, the glazing strategy is a promising technique. The glass covers results in the reduction of heat loss and protecting the asphalt surface (absorber surface) from the outside environment. Little attention has been given to the glazing strategy in improving the performance of ASCs. The chief aim of the current investigation is a comparative assessment of the performance and heat dynamics of unglazed asphalt solar collectors with glazed asphalt solar collectors under field conditions. The evaluation was carried out using an experimental test-setup composed of an asphalt solar collector with a surface area of 1.2 m2 and a pipe network length of 12 m. Various sensors were utilized to monitor and measure the key parameters such as ambient conditions and working fluid temperature during the experimental runs. The experimental results prove that the glazing strategy is an effective method to improve the performance of ASCs. The constructed glazed ASC increases hot water temperature, meanly around 5 °C, and pavement temperature, meanly around 20 °C, while represents an improvement in the performance, near 10%, compared with the unglazed one.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ
•It is to present comparative and sensitive analysis for PTCs with the MCRT method.•A detailed PTC optical model was developed based on a novel unified MCRT model.•Reference data determined by the ...divergence effect is useful to design a better PTC.•Different PTCs have different levels of sensitivity to different optical errors.•There are no contradictions between accuracy requirements of different parameters.
This paper presents the numerical results of the comparative and sensitive analysis for different parabolic trough solar collector (PTC) systems under different operating conditions, expecting to optimize the PTC system of better comprehensive characteristics and optical performance or to evaluate the accuracy required for future constructions. A more detailed optical model was developed from a previously proposed unified Monte Carlo ray-tracing (MCRT) model. Numerical results were compared with the reference data and good agreements were obtained, proving that the model and the numerical results are reliable. Then the comparative and sensitive analyses for different PTC systems or different geometric parameters under different possible operating conditions were carried out by this detailed optical model. From the numerical results it is revealed that the ideal comprehensive characteristics and optical performance of the PTC systems are very different from some critical points determined by the divergence phenomenon of the non-parallel solar beam, which can also be well explained by the theoretical analysis results. For different operating conditions, the PTC systems of different geometric parameters have different levels of sensitivity to different optical errors, but the optical accuracy requirements from different geometric parameters of the whole PTC system are always consistent.
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In this study, a small scale hybrid solar heating, chilling and power generation system, including parabolic trough solar collector with cavity receiver, a helical screw expander and silica gel–water ...adsorption chiller, etc., was proposed and extensively investigated. The system has the merits of effecting the power generation cycle at lower temperature level with solar energy more efficiently and can provide both thermal energy and power for remote off-grid regions. A case study was carried out to evaluate an annual energy and exergy efficiency of the system under the climate of northwestern region of China. It is found that both the main energy and exergy loss take place at the parabolic trough collector, amount to 36.2% and 70.4%, respectively. Also found is that the studied system can have a higher solar energy conversion efficiency than the conventional solar thermal power generation system alone. The energy efficiency can be increased to 58.0% from 10.2%, and the exergy efficiency can be increased to 15.2% from 12.5%. Moreover, the economical analysis in terms of cost and payback period (PP) has been carried out. The study reveals that the proposed system the PP of the proposed system is about 18 years under present energy price conditions. The sensitivity analysis shows that if the interest rate decreases to 3% or energy price increase by 50%, PP will be less than 10 years.
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