Tube Collector Research Articles

Solar thermal energy performance on mono/trihybrid nanofluid flow through the evacuated thermal collector tube

Solar thermal energy is a versatile and sustainable form of energy. It has vast applications and can be used to reduce fossil fuel consumption. The sun's heat harnesses this renewable energy; therefore, the energy transmission rate plays a significant role here. This article gives the idea of a new geometric design of solar thermal collector tubes for multiple uses and materials to be used on the tube's outer layer to maximize heat absorption. For this purpose, we investigated velocity, temperature, and heat transfer rates due to different nanoparticle (Cu/Al2O3/GO) combinations. We assumed the flow of Newtonian/non-Newtonian nanofluids flowing through the coaxial region of the cylindrical shape solar tubes. Here, water and seawater are considered for the Newtonian case, and sodium alginate is regarded for the non-Newtonian case. The governing equations of the flow are converted into ODEs with the help of similarity variables and solved numerically using the Keller box method. The MATLAB code for the Keller box method has been developed to plot graphical results. The primary outcomes are exhibited through graphs and tables. It is perceived that the temperature and heat transfer rates in Newtonian and non-Newtonian fluids are enhanced due to the trihybrid (Cu + Al2O3+GO) combination. This work can be utilized in an evacuated solar thermal system and gives the idea to develop a sustainable solar thermal system for multipurpose usage.

Effects of geometric and optical irregularities on the flux distribution on an absorber tube of a parabolic trough collector

A parabolic trough collector is the most widely implemented concentrated solar heat collecting device. The performance of the same critically depends on how far the actual optical setup differs from the mathematical ideality. Such a study enables one to quantitatively compare the relative significance of different irregularities and channelize the engineering effort to address the critical ones within a threshold of added cost. The following irregularities are tested in the present work, both individually and simultaneously: absorber tube misalignment, random profile error, narrowed and widened reflector profile, tracking error. A grid and ray independent model as implemented in COMSOL Multiphysics 5.4 is employed. It is duly validated against prior studies. The tested collector parameters are the same as that of SEGS LS2 PTC. It is observed that a tracking error up to 10 mrad causes minimal loss of performance. Misalignment error and narrowing of reflector profile not only cause loss of total heat interception but also produce abnormally high local heat flux which may lead to damage to the absorber tube coating and cover system. Simultaneous occurrence of multiple irregularities can lead to major loss of performance (in the current study ∼50%); hence, calls for intervention and remediation.

ANALYSIS OF THE EFFECTIVENESS OF USING SOLAR SYSTEMS BASED ON PHOTOVOLTAIC MODULES AND SOLAR COLLECTORS FOR ENERGY SUPPLY OF BUDGET FACILITIES

This article analyzes the operation of a solar energy system installed in a higher education institution, consisting of four photovoltaic stations connected to the electrical grid for self-consumption, and a solar hot water system with collectors and a storage tank. The operation of the system was modeled using the RETScreen, T*SOL, and PV*SOL software programs, based on averaged climate data obtained from the "Zhuliany" weather station. The solar system is installed on the south-facing roof of the building and consists of 262 monocrystalline silicon photovoltaic modules of Trina Solar TSM-DE08M (II) type with a power of 370 W, installed at an angle of 30° to the horizon, and 8 Veissmann Vitosol 300-T SP3 vacuum tube collectors with a power of 1.3 kW installed at an angle of 35°. The placement of the solar elements was determined through modeling, considering their dimensions, the features of the roof structure, the placement of ventilation systems, and the shading of the roof surfaces by other elements of the building in Kyiv. As a result of energy modeling, it was determined that the amount of thermal energy obtained is 6.823 MWh/year, and the amount of electrical energy is -109.16 MWh/year, with a total inverter capacity of 95 kW, a traditional fuel replacement coefficient of 50% for the photovoltaic system and 75% for the solar system with collectors, payback periods of 4.3 years for the photovoltaic system, and 13 years for the hot water system when replacing electric boilers and 16 years when obtaining hot water from a district heating network. The reduction in harmful emissions is 45 tons/year of CO2, which is equivalent to 104.3 barrels of crude oil or 19,279 liters of high-octane gasoline or 15.5 tons of recycled waste. Based on the analysis of the data, it is recommended to install such systems in higher education budget institutions to reduce electricity or natural gas consumption and reduce harmful emissions into the environment.

Experimental and simulation on night heat dissipation characteristics and freezing process of evacuated tube solar water heaters

The winter operation of all-glass evacuated tube solar water heaters (ETSWH) often encounters the problem of ice damage. Studying their nighttime heat dissipation and freezing characteristics can further reduce the risk of frost damage during winter use. A numerical model for the nighttime heat dissipation of all-glass evacuated tube collectors is proposed in this study. An enthalpy equation is also introduced to analyze the heat dissipation process and freezing conditions of water inside the ETSWH under lower temperature conditions. Based on this, a nighttime heat loss model for solar vacuum tube collectors, including the effects of radiation and phase change factors, is established and validated through nighttime temperature drop experiments, which can effectively predict the temperature distribution and antifreeze performance of ETSWH during the nighttime heat dissipation process. In addition, the independent effects of the initial temperature of the water inside ETSWH, the thickness of the water tank insulation layer, and the absorptive coating emissivity on the heat dissipation process of ETSWH are studied, and the heat dissipation of ETSWH during winter nights in five different climatic zones in China is simulated. Experimental and simulation results show that under cold and clear winter weather conditions in Luoyang, ice forms in ETSWH during nighttime. The icing first occurs at the bottom of the vacuum tube, and the icing length on the wall and the icing thickness at the bottom can reach 1145 mm and 15 mm, respectively. In severely cold areas and cold regions such as Harbin and Beijing, there is a high risk of frost damage to ETSWH during winter. Keeping the initial working fluid temperature in the heater above 50 °C, ensuring a minimum insulation thickness of 50 mm, and reducing the emissivity of the absorptive coating in the heater to below 0.07 can effectively solve the freezing problem and have significant implications for the promotion and application of all-glass evacuated tube collectors.

5E analysis of a novel designed hot water storage header integrated vacuum tube solar water heater

In this study, 5-E analysis of a heat pipe equipped vacuum tube collector system for residential warm water application has been carried out. The issue of overheating in heat pipes and low thermal efficiency is the major key issues associated with heat pipe vacuum tube collector. This design completely removes the problem of overheating. In addition to this copper fins mounting with condensers of heat pipe enhance the heat transmission rate between the condenser & water stored in a manifold. The results of an experimental investigation reveal that thermal and exergy outputs of the proposed system were obtained almost 63–74% and 4–10% respectively. The average energy gain at the end of the days selected for Run-A, B, and C was calculated to be 7505, 6912, and 6619 kJ respectively, whereas the average exergy gain for corresponding runs was found to be 928, 700, and 401 kJ respectively. In addition to this, the proposed system can provide hot water of approximately 125 L, 76 L, and 52 L in temperatures 50 °C, 55 °C, and 60 °C respectively.Concerning to techno-economic investigation, the per liter cost of warm water generation for the proposed & electric geyser was observed to be 0.15 INR/L & 0.47 INR/L respectively. The levelized energy cost, net present worth, and payback time were found to be 5.48 INR/kWh, 55,819 INR, and 4.12 years respectively. The amount of CO2 mitigation by the developed system was found to be 18.76, 17.28, and 16.54 tCO2/lifetime for Run-A, B & C respectively.

Investigation and optimization of solar collector and geothermal pump hybrid system for cogeneration of heat and power with exergy-economic approach

Abstract To use energy systems based on renewable sources, it is very important to consider backup and hybrid sources because renewable energies are not available all the time; therefore, in this system, a geothermal pump is used to preheat the fluid, then the heated fluid is sent to the vacuum tube collector to reach a higher temperature by absorbing solar-thermal energy, and after absorbing solar energy, it goes to the evaporator to produce superheated steam and finally the superheated fluid moves to the steam turbine to produce energy. After the simulation, thermodynamic analysis along with economic analysis has been done. In the base state, the energy efficiency and exergy of cogeneration were 0.566 and 0.156, respectively; the energy efficiency and electrical exergy were better than 0.057 and 0.065; and the overall output and immutable work values were 50 and 671.1 kW, respectively.

Design and thermodynamic analysis of an innovative parabolic trough photovoltaic/thermal system with film-based beam splitter

This study aims to find a feasible photovoltaic/thermal (PV/T) utilization method based on film-based beam splitting technology. In contrast with previous studies, the main novelty of this paper is proposing the design of an innovative PV/T system using both parabolic trough concentrator (PTC) and film-based beam splitter (FBS). The design approach of the PV/T system is presented. A new FBS used for this PV/T system is designed by using the Needle method, and its average reflectivity and transmissivity are 27.2% and 72.8%. By using Ray Tracing and Computational Fluid Dynamics (CFD) simulation methods, the performance evaluation of the PV/T system is conducted. The evaluation results reveal that when the East-West sun tracking error is 0.2°, the optical efficiencies of the photovoltaic module and the solar thermal collector tube (TCT) can be kept at 95% and 93.9%. Moreover, when the heat transfer fluid (HTF) in the TCT is selected to be the ethylene glycol, the operation analysis results demonstrate that the photoelectric efficiency of the photovoltaic module is 25.4% and the thermal efficiency of the PV/T system is 17.24%. The thermal performance of the system can be improved when the HTF flow velocity is increased properly or when the inlet HTF temperature is decreased. The technical feasibility of the proposed PV/T system can be revealed from the analysis results of this study.

Photo-thermal design and analysis of a novel CPC coupled solar air evacuated tube collector

The conventional evacuated tube solar air collector can’t reach a higher temperature due to poor heat transfer between absorber and air. To maintain a low heat loss at medium temperature and enhance heat transfer, a novel evacuated tube solar air collector coupled with a compound parabolic concentrator is proposed. The matching shape is designed and optimized for the concentrator reflecting surface using non-imaging optics, and by ray tracing, the optical performance is obtained. The corresponding photothermal conversion and heat transfer models are established, and numerical simulation is conducted for thermal performance analysis. The results show that the thermal performance is mainly affected by the air flow rate, the inlet temperature, and the heat source energy density. Compared with the existing single-pass evacuated tube collector, the novel collector has advantages in heat output temperature, thermal efficiency, adaptability to flow rate changes, and potential for series temperature rise under most conditions. When concentrated solar power density is 800–1600 W/m2, the maximum outlet temperature of a novel collecting evacuated tube can reach to a limiting value of 181.17 ℃, representing its thermal insulation performance, while that of the contrast one is 153.25℃. Under normal inlet temperature of 25℃, the maximum output temperature of a single tube of the novel collector is 146.05℃ at a flow rate of 1.02 m3/h, and the maximum thermal efficiency of 59.21% can be achieved at a flow rate of 3.58 m3/h.

Photothermal conversion performance based on optimized design of multi-section compound parabolic concentrator

Solar energy M-CPC (Multi-section Compound Parabolic Concentrator, M-CPC) has the advantages of no tracking and static concentrating, synchronous collection of beam and diffuse radiation, simple structure and easy construction. Therefore, an integrated system based on the optimized design of M-CPC coupled with ECT (All-glass Evacuated Collector Tube, ECT) for solar photothermal conversion is constructed in present research. Moreover, the stability, reliability and applicability of the solar M-CPC system for energy capturing and photothermal conversion are verified by outdoor experiments and numerical calculations. The results show that the average heat collection efficiency of the integrated M-CPC system is 61.0%, the average output temperature of the fluid could reach 350.9K. In addition, the average relative error between the theoretical calculated value and the experimental measured value of fluid temperature rise is 5.1%, which indicates that the M-CPC system has the characteristic of low heat loss in the process of solar radiation utilization. All the above demonstrate that the M-CPC system has appropriate photothermal conversion as well as industrial manufacturing features.

Analysis of Mixed Convection and Free Convection in a Reduced Solar Collector Using a Nanofluid as Heat Transfer Fluid

A three-dimensional investigation of mixed convection which occurs from Al2O3-water nanofluid flow in tube of a reduced solar collector and free convection in air gap situated between cover of solar collector and its absorber was investigated. Heat transmission by conduction in absorber and cover as well as thermal losses to exterior expressed in form of a convective flux have also been taken into account. The different transport equations were solved using CFD-Fluent software which is founded on finite volume method and Boussinesq’s law was introduced to take into account of buoyancy effects. In this investigation, thermal efficiency of solar collector was evaluated and use of nanofluids allows to increase this parameter which is generally low for this kind of thermal systems. Length of thermal regime established in the tube is proposed and this investigation is extended relative to other works developed in this research field. Results obtained gave an idea about the flow structure of the fluid under consideration in a tube of a solar collector and heat transmission mechanisms in air gap and in other elements of the solar collector. These results can facilitate design of this thermal system.

Performance studies of novel all-glass heat pipe evacuated collector tube integrating numerical simulation and experiment method

Metal heat pipe evacuated collector tube (ECT) suffer from cracks in the joint between the glass outer layer and the metal heat pipe due to the large difference in thermal expansion coefficients of glass and metal, resulting in non-industrialization. In this paper, the metal heat pipe is replaced with a glass heat pipe to form an all-glass heat pipe ECT to address the air-tight sealing problem, and a reflective film was added to the lower part of the outer tube to improve energy. According to these results, the thermal stress of 0.279 MPa is well below the bearing range of 40–120 MPa, and the maximum thermal strain of 0.175 mm/mm is also far less than the affordable value of 120 mm/mm, inducting the all-glass structure fully copes with the transient local heating changes. The optical efficiency is increased by 0.17 % by the addition of the reflective film, and yielding an energy output of 87 W and a maximum volume fraction of 4.8 % for liquid–water in the quasi-thermal equilibrium state. At the same time, the evaporation operating speed of the vapor can be increased by improving the solar radiation flux density and reducing thermal losses, and optimizing the multi-level and cross-scale vapor vortices can also improve the convective heat transfer rate, so they are future directions for development. However, there are the limitations of decreasing the thermal conductivity and increases the resistance due to the heat pipe conversion from metal to glass.

A review of different working fluids used in the receiver tube of parabolic trough solar collector

A review of different working fluids used in the receiver tube of parabolic trough solar collector

Experimental Performance and Cost-Effectiveness of a Combined Heating System under Saharan Climate

The solar water heater can be integrated into future residential buildings as the main energy source, which will subsequently reduce the energy cost of water heating. An original configuration for an efficient Domestic Hot Water (DHW) storage tank is developed and experimentally evaluated under Saharan climate. This novel DHW configuration includes a hybrid (solar and electric) energy system with a flat plate solar collector coupled with an electric heater. Additionally, a phase change material (PCM) mixture that is composed of paraffin wax and animal fat with a melting temperature between 35.58 °C and 62.58 °C and latent heat between 180 and 210 kJ/kg is integrated into this novel tank configuration. The experimental results indicated that hot water production by using latent heat storage could be economically attractive. By evaluating the cost of water heating expressed in Algerian dinar per liter (DZD/L), it was found that one liter of hot water may cost around 0.1362 DZD/L (i.e., 0.00096 USD/L) compared to 0.4431 DZD/L for the conventional water heater, an average energy cost savings of 69.26%. On a yearly basis, the average energy cost savings may reach up to 80.25% if optimal tilt for the solar collector is adopted on a monthly basis. The flat plate collector may be vulnerable to convective heat transfer; therefore, other solar collectors, such as vacuum tube collectors, may provide enhanced energy performance.

Predicting the performance of thermal, electrical and overall efficiencies of a nanofluid-based photovoltaic/thermal system using Elman recurrent neural network methodology

In this research, the Elman recurrent neural network methodology is used to develop a relationship to predict the performance of a photovoltaic/thermal device with sheet-and-serpentine tube collector. In this system, PV panels are cooled using the water-magnetite nanofluid. The thermal (ηTH), electrical (ηEL) and overall (ηOV) efficiencies of the PV/T device are utilized as objective functions, and the mass flow rate (m˙) and concentration (φ) of nanofluid are considered as input parameters. The range considered for the m˙ and φ is 20-80 kg/hr and 0-2% respectively. To measure the accuracy of the models developed, the mean absolute percentage error (MAPE), root mean square error (RMSE), and correlation coefficient (R) were used. It was found that the best accuracy is obtained for the ηTH in terms of (Training: R=0.9978 and RMSE=0.2045; Testing: R=0.9973 and RMSE=0.1973) followed by ηOV in terms of (Testing: R=0.9959 and RMSE=0.1797), and ηEL in terms of (Testing: R=0.9825 and RMSE=0.0037), respectively.

An experimental comparative assessment of the energy and exergy efficacy of a ternary nanofluid-based photovoltaic/thermal system equipped with a sheet-and-serpentine tube collector

The usability of water based GO-TiO2-Fe3O4 ternary nanofluid in a photovoltaic/thermal (PV/T) collector from both energy and exergy perspectives is inspected in the present experimental study. The effect of nanoadditive mixing ratio (σ = 1:1:1, 1:2:1, 1:1:2, and 2:1:1), nanofluid mass flow rate (m˙nf = 20, 40, 60 and 80 kg h−1) and nanoparticle volume concentration (φ = 0%, 0.25%, 0.5% and 1%) on the outcomes is investigated. The results revealed that the nanofluid with σ = 1:1:1 has the best performance from both energy and exergy viewpoints. Among the examined cases, the maximum overall energy and exergy efficiencies were 88.23 and 15.36%, respectively, both belonging to the case of σ = 1:1:1, m˙nf = 80 kg h−1, and φ = 1%. Finally, it was found that m˙nf and φ have an escalating effect on both the overall energy and exergy efficiencies.

Analysis on characteristics and operation mode of direct solar collector coupled heat pump drying system

To solve the intermittent problem of solar drying systems, this study proposes a solar vacuum tube collector coupled heat pump drying (HPD) system that can adopt three operating modes as different climatic conditions. The performance of the system under different working modes and drying characteristics was analyzed; moreover, the system was also based on the relationship between energy supply and consumption. The results show that under load conditions, the system runs in the solar drying (SD) mode and the drying chamber temperature can reach >50 °C. In the HPD mode, the average heating power of the system is 11.88 kW, the heating coefficient is 2.26 and the average thermal efficiency of the heat exchanger is 39.3%. In the solar-assisted heat pump drying (SAHPD) mode, the average coefficient of performance of the system is 3.26, compared to HPD model, a 44.2% increase. The heating ratios of the SD, HPD and SAHPD modes were 37.9%, 58.5% and 3.6%, respectively. Furthermore, the Two-term models with R2 value of 0.9986 and RMSE value of 0.01038 was considered the best drying kinetics model for the vacuum tube collector coupled heat pump drying grapes. This study guides the application of SAHPD systems in agricultural products drying.

Performance analysis of parabolic type solar water heater by using copper-dimpled tube with aluminum coating.

A solar water heater has been developed to convert solar radiation into heat for use in residential and commercial settings. The collector makes up the bulk of a solar water heating system. The solar energy is captured by the collector and transferred to the tube that delivers the working fluid, water. In addition to the collector's tube, which carries the working fluid, researchers have focused on the design of the collector's tube. This paper examines the performance of a parabolic plate solar water heater that uses a copper dimpled tube with aluminum-coated tube channels. During the test, the flow rate of base fluid was in the range of 1.0 to 3.0kg/min in steps of 0.5. The performance of the solar water heater was also evaluated and verified using CFD. The test data such as friction factor, Reynolds number, uncertainty analysis, Nusselt number, solar collector efficiency, coefficient of convective heat transfer, linear dimpled tube velocity analysis, achieving maximum energy efficiency and thermal efficiency have been used to generate parametric values for parabolic plate solar water heaters. The results suggest that the best outcomes can be achieved with a mass flow rate of 2.5kg/min and the overall thermal efficiency was raised to 31.85%, which is 11% greater than that of the plain tube with base fluid. At mass flow rates of 2.5kg/min, the pressure drop was found to be 6.24% higher than that of 3.0kg/min. The experimental results were analyzed and compared with the CFD results, and the overall deviation was ± 3.24% which is in the acceptable range.

Thermal and flow performance analysis of a concentrated linear Fresnel solar collector with transverse ribs.

This article deals with the impact of including transverse ribs within the absorber tube of the concentrated linear Fresnel collector (CLFRC) system with a secondary compound parabolic collector (CPC) on thermal and flow performance coefficients. The enhancement rates of heat transfer due to varying governing parameters were compared and analyzed parametrically at Reynolds numbers in the range 5,000-13,000, employing water as the heat transfer fluid. Simulations were performed to solve the governing equations using the finite volume method (FVM) under various boundary conditions. For all Reynolds numbers, the average Nusselt number in the circular tube in the CLFRC system with ribs was found to be larger than that of the plain absorber tube. Also, the inclusion of transverse ribs inside the absorber tube increases the average Nusselt number by approximately 115% at Re = 5,000 and 175% at Re = 13,000. For all Reynolds numbers, the skin friction coefficient of the circular tube with ribs in the CLFRC system is larger than that of the plain absorber tube. The coefficient of surface friction reduces as the Reynolds number increases. The performance assessment criterion was found to vary between 1.8 and 1.9 as the Reynolds number increases.

Effect of various configurations of swirl generator system on the hydrothermal performance of the flat-plate solar collector

This is a numerical study that analysis the heat extraction potential of solar collector tubes by assembling a couple of nozzles at the sealed end of the pipe to make swirl flow. Swirl flow intensifies the turbulence rate which augments heat transfer by ruffling the boundary layer. To this end, several decisive factors including nozzle angle (A: 30°, 45°, 60°, 90°), tube diameter (D: 20 mm, 50 mm), nozzle edge size (N: 6.25, 12.5, 25 mm (for D50) and N: 2.5, 5, 10 mm (for D20)), and mass flow rate (M: 0.1, 0.5, 1 kg/s (for D50) and M: 0.04, 0.2, 0.4 kg/s (for D20)) were considered. Results demonstrated that all of the models of class ''A…/D20/N…/M…“ had higher heat extraction potential but lower friction factor compared with ”A…/D50/N…/M…“. Maximum and minimum values of heat flux extractions are 2113390 W/m2 and 59239 W/m2 that were obtained by ”A60/D20/N2.5/M0.4″ and “A30/D50/N25/M0.1″. The created friction factor by class ”A…/D50/N…/M…“ is higher than class ''A…/D20/N…/M…”. The highest friction factor is 3.51 (''A90/D20/N2.5/M0.04″) and the lowest friction factor is 0.019 (“A30/D20/N2.5/M0.2″). Overall, for all cases, class ”A…/D50/N…/M…“ bear the higher TPF compared with class ”A…/D50/N…/M…“ so that the greatest and lowest values of TPF are 5.09 and 0.49 achieved by ”A30/D50/N6.25/M1″ and “A90/D20/N5/M0.4″, respectively.

Evaluation of efficiency, thermohydraulic performance evaluation criterion, and field synergy principle improvement of the parabolic solar collector containing the hybrid nanofluid using spring turbulators

In this paper, the study and simulation of turbulent flow inside a parabolic solar collector tube equipped with two spring insert samples with two different pitch ratios (P/D = 0.22, 0.44) and a specific cross-section are investigated. Heat transfer and properties of Cu–Fe3O4/Water hybrid nanofluid with volume fractions of φ = 1%, 3%, and 5% for the range of Reynolds numbers of 7000, 9000, and 11000 are selected and investigated using the single-phase method. The tube is used as the adsorbent pipe of a parabolic solar collector to investigate the performance of the parameters such as volume fraction, Nusselt number, pressure drop, parabolic solar collector efficiency, performance evaluation criterion, and field synergy principle. The results show that with decreasing the pitch ratio, Nu and solar collector efficiency increase. The maximum efficiency is 2.53 for a tube with P/D = 0.22 (Re = 7000, φ = 1%). The maximum efficiency is obtained under the same conditions in a tube containing the spring insert with P/D = 0.44 is equal to 2.39. At the same Reynolds numbers, the average of these velocities is significantly higher than a plain tube. Field Synergy Principle is a reliable criterion to investigate the mechanism of heat transfer increase that this coefficient value in the tube equipped with a spring insert is much higher than in a plain tube. This increase indicates the positive performance of the spring insert on the heat transfer rate and solar collector efficiency improvements. Therefore, spring inserts with a lower P/D are more desirable to achieve the highest efficiency of solar collectors as a source of renewable energy.