Tube Collector Research Articles

Heat transfer study of a new hybrid photovoltaic/thermal direct absorption parabolic solar collector by two-phase Buongiorno model.

Solar energy is one of the cleanest sources of renewable energy that is easily accessible in vast geographical areas. As the efficiency of the common solar collectors is very low and is limited by the absorption properties of working fluid, enhancing the thermal performance of these collectors is one of the major challenges of developing parabolic solar thermal power plants. In recent decades, researches revealed that utilizing nanofluid as a novel working fluid has a dramatic effect on the thermophysical and optical properties of the fluid. In this study, the flow and temperature fields of water/magnetite and water/aluminum nanofluids are evaluated by solving the steady form of governing equations including conservation laws of mass, volume fraction transport equation, momentum equation, energy equation, and radiation transfer equation. Moreover, the two-phase Buongiorno model is utilized and Brownian motion, thermophoresis effects, and magnetophoresis movement are taken into account in the nanofluid simulation. The numerical results demonstrate that increasing nanofluid volume fraction and flow rate can increase the thermal performance of the collector tube. It is found that the thermal efficiencies reach maximum values of 151.03% and 158.58% for water/aluminum and water/magnetite nanofluids, respectively. Furthermore, increasing the volume fraction from 0 to 0.3% leads to rise of 24.41% and 21.36% in the maximum temperature of the collector. The effects of different parameters such as nanoparticle volume fraction, flow rate, and nanoparticle kind on the collector thermal and electrical efficiencies, thermal distribution, and entropy production have been studied.

Mathematical model of an innovative double U-tube sun-tracked PTC and its experimental verification

The paper describes in detail an in-house mathematical model, allowing to simulate the operation of an innovative double U-tube sun-tracked Parabolic Trough Collector (PTC). The analysed solar collector is characterized by a modular structure and is designed for low-temperature applications. A double U-tube pipe is used inside the evacuated collector tube, which is the study's main novelty. The energy balance equations are derived for a single U-tube, assuming the uniform flow of the Heat Transfer Fluid (HTF) through all collector U-tubes. The resulting differential equations are solved by approximating the derivatives with appropriate differential schemes. The proposed one-dimensional model with distributed parameters makes it possible to simulate the collector operation under transient conditions. A test stand with the analysed PTC is built to verify the obtained results accuracy and perform an extensive experimental verification. The measured and computed temperature courses of the HTF at the collector outlet are compared for different operation conditions. For all analysed cases, a fully satisfactory agreement between measurement and computational results is obtained. Estimating the accuracy of the developed model results with the measurements, the Root Mean Squared Errors (RMSE) are calculated for three measurement series (for selected days). The obtained RMSE values are 0.375 °C, 0.349 °C, and 0.632 °C for the selected day of January, May, and August, respectively. It proves the high efficiency of the proposed model. The proposed PTC model's main advantage is its simplicity and low computational cost, allowing for its online application.

Flow and mixed convection heat transfer of Hitec salt in multi-sided heating pipes

Molten salt is one of the most commonly used heat storage working fluids in solar thermal power. However, its heat transfer coefficient is low. Optimizing the heat transfer condition could improve the heat transfer performance of molten salts, thereby facilitating convection that enhances heat transfer. In trough and tower solar thermal power generation systems, the heating surface of the molten salt collector tube differs with the different angles of sunlight heating. Numerical simulations on the characteristics of the flow and mixed convection heat transfer of Hitec salt in one-, two-, and three-sided heating conditions in pipes were carried out in this study. The results of mixed convection and heat transfer of molten salt on different multisided heating surfaces showed that the heat accumulated at the heating surfaces and then transferred to the mainstream core region. Under nonuniform heating conditions, the buoyancy effect generated a vortex, which changed the shape of the core area of the mainstream and resulted in the enhancement of the heat transfer ability. Double side heating showed the strongest buoyancy effect. The degree of heat accumulation under three-sided heating was the lowest, and the nonuniformity of the heat transfer process in one-sided heating was the highest.

Performance study of a new smart hybrid parabolic trough collector system integrated with hybrid tubular thermoelectric generator

Advanced parabolic trough systems are the promising technologies for the production of usable heat and electrical power. Here we study the effects of hot water temperature adjustment concept and optical concentrator on the thermal and electrical efficiencies of a new PTC/HTTEG configuration, which comprises parabolic trough concentrator and hybrid tubular thermoelectric generator. The hybrid tubular thermoelectric generator (HTTEG) was integrated within the collector tube, where the hot water is passed between the inner side of the absorber tube and the top surface of the HTTEG. Meanwhile, to create a large temperature difference across the HTTEG sides, a cold water is passed along the inner side of the HTTEG. A low consumption pump was energized using HTTEG power in order to keep the hot water temperature at 95 °C for a long time (temperature adjustment concept). Numerical simulations show that the improvement in performance of the hybrid system highly depends on the adjustment concept and optical concentrator. As the solar concentration ratio increases, the overall efficiency of the hybrid system increases significantly to 76.21% and the amount of hot water reaches to a maximum value of about 846.77 Liter/Day for a concentration of 30 suns. Also, the power generated by the HTTEG and hot water temperature stay stable at 71.37 W and 95 °C, respectively, due to the hot water temperature adjustment effect. To validate the results of numerical model, a new validation method was proposed and discussed. The comparison of results obtained with results of the exact solution indicates a good agreement.

Numerical simulation of a solar collector equipped with a twisted tape and containing a hybrid nanofluid

Increasing demand for energy in the world has made renewable energies so crucial. Solar energy, as the widest and accessible type of renewable energy, is now developed consistently. Solar energy is received and concentrated by equipment made of surficial mirrors. Complete transferring of solar heat flux to the working fluid is a challenge and there have been performed some efforts to enhance the performance of solar heat transfer. Following this goal, the current work numerically investigates heat transfer enhancement in a solar collector exposed to a non-uniform thermal flux. This is fulfilled by considering a hybrid nanofluid in the turbulent collector flow that contains a twisted tape. The effects of Reynold number, the volume fraction of nanoparticles, and wall roughness are detected. It is shown that can be increased up to 23 and 90 percent by rising the volume friction of the hybrid nanofluid and wall roughness of the collector tube, respectively. The pressure distribution in the collector shows a completely different pattern in the part where the wall is heated and the other adiabatic part. This can address an extra force, applying on the twisted tape, which requires consideration.

Impact of Collection Volume and DNA Extraction Method on the Detection of Biomarkers and HPV DNA in First-Void Urine.

The potential of first-void (FV) urine as a non-invasive liquid biopsy for detection of human papillomavirus (HPV) DNA and other biomarkers has been increasingly recognized over the past decade. In this study, we investigated whether the volume of this initial urine stream has an impact on the analytical performance of biomarkers. In parallel, we evaluated different DNA extraction protocols and introduced an internal control in the urine preservative. Twenty-five women, diagnosed with high-risk HPV, provided three home-collected FV urine samples using three FV urine collection devices (Colli-Pee) with collector tubes that differ in volume (4, 10, 20 mL). Each collector tube was prefilled with Urine Conservation Medium spiked with phocine herpesvirus 1 (PhHV-1) DNA as internal control. Five different DNA extraction protocols were compared, followed by PCR for GAPDH and PhHV-1 (qPCR), HPV DNA, and HBB (HPV-Risk Assay), and ACTB (methylation-specific qPCR). Results showed limited effects of collection volume on human and HPV DNA endpoints. In contrast, significant variations in yield for human endpoints were observed for different DNA extraction methods (p < 0.05). Additionally, the potential of PhHV-1 as internal control to monitor FV urine collection, storage, and processing was demonstrated.

Exhaust Noise Reduction by Application of Expanded Collecting System in Pneumatic Tools and Machines

In this paper, we demonstrate how to reduce the noise level of expanded air from pneumatic tools. Instead of a muffler, we propose the expanded collecting system, where the air expands through the pneumatic tube and expansion collector. We have elaborated a mathematical model which illustrates the dynamics of the air flow, as well as the acoustic pressure at the end of the tube. The computational results were compared with experimental data to check the air dynamics and sound pressure. Moreover, the study presents the methodology of noise measurement generated in a pneumatic screwdriver in a quiet back room and on a window-fitting stand in a production hall. In addition, we have performed noise measurements for the pneumatic screwdriver and the pneumatic screwdriver on an industrial scale. These measurements prove the noise reduction of the pneumatic tools when the expanded collecting system is used. When the expanded collecting system was applied to the screwdriver, the measured Sound Pressure Level (SPL) decreased from 87 to 80 dB(A).

Effects of helical absorber tube on the energy and exergy analysis of parabolic solar trough collector – A computational analysis

The aim of the present study is to investigate the thermal performance of parabolic solar trough collector (PTC), LS-2 model, with asmooth and helical absorber tube. Four different cases are analyzed with 0 (smooth), 75, 85, and 95 number of turns of the helical absorber tube of PTC having outer and inner diameter of 70 mm and 66 mm, respectively. The study is conducted in ANSYS Fluent-14 for inlet temperature in the range of 298–308 K and water flow rate of 0.15–0.6 kg/s. Results indicate that an maximum outlet temperature of 392 K is obtained for the absorber tube with 95 turns and at a mass flow rate of 0.15 kg/s. Presence of helical absorber tube increase the net surface area of the absorber and thus the useful heat transfer rate is enhanced by almost 71% for same length of the PTC as that of the smooth absorber based PTC. The overall results indicate that the overall efficiency, thermal efficiency, and exergy efficiency of helical absorber tube based PTC is 3.5%-10%, 4%-10%, and 4%-5% higher than that of the traditional PTC with a smooth absorber tube.

Simulation Study of the Thermal Performance of MSF Desalination Unit Operating by Solar Vacuum Tube Collectors

The Center for Solar Energy Research and Studies (CSERS) has a good experience in operating and evaluating the thermal performance of small scale 5 m3/day Multi-Stage Flushing (MSF) desalination plant connected to solar pond according to the local weather conditions of Tajoura area. However, a new project has been suggested to run the desalination plant with vacuum tubes solar thermal collectors utilizing available technology and experience. In this study an attempt was made to make the best use of readily available components to operate the MSF desalination unit with field of solar thermal collectors. Several configurations of collectors and tank arrangements were designed and examined through the use of simulation software, TRNSYS. The study has shown that the layout-3 (two 500 litre storage tanks each of them connected to 9x5 vacuum tube collectors) gives the best performance with an annual solar fraction over 77% at load temperature of 70 °C with flow rate of 2500 lit/hr, and over 68% at load temperature of 80 °C for working condition of 8 hours daily. The study has also shown that running the desalination plant for 24 hours a day reduces the solar fraction of the solar collector field to 25%

Design and evaluation of flat plate solar collector equipped with nanofluid, rotary tube, and magnetic field inducer in a cold region

Flat plate solar collectors lose a massive part of heat accumulated near the contact region because of the poor thermal characteristics of the working fluid. A new cost-effective design is numerically studied to cover up such deficiency by equipping the flat plate collector with revolutionary tubes and magnetic field inducer to affect Fe3O4/water working nanofluid in the collector tubes. Results substantiate that each of the applied rotary tubes and magnetic field inducer improves the convection mechanism in the tubes by circulating the flow inside the tubes and saves more of available solar energy. Results reveal that 27.8% and 10.44% of lost energy are restored in the solar collector equipped with the magnetic inducer and rotary tubes, respectively. Manipulating the flat plate collector by both rotary tubes and inducer is more influential in comparison with each individual method, and there is an optimal rotational speed in each magnetic field intensity to achieve the best performance. This hybrid technique increases the energetic performance of the plate solar collector from 44.4% to 61.7% which implies that roughly 300 W of the lost energy can be restored in the collector.

Numerical study on heat loss from the surface of solar collector tube filled by oil-NE-PCM/Al2O3 in the presence of the magnetic field

Numerical study on heat loss from the surface of solar collector tube filled by oil-NE-PCM/Al2O3 in the presence of the magnetic field

Geometrical variation in receiver tube of SEGS LS-2 parabolic trough collector (PTC) based on heat flux distribution to improve the thermal performance

Heat flux (HF) distribution around the receiver tube of parabolic trough collectors (PTC) has a crucial effect on their outlet temperature (To) and thermal efficiency (ηth). Since its receiver tube is as a heat exchanger, the higher amounts of ηthcan be achieved by changing the geometry of the receiver tube. In previous researches, the geometrical variations were made in the internal geometry of the receiving tube, such as the use of corrugated paths, the installation of fins, using porous media, using twisted tape, etc. In this work, changes are simultaneously made in the internal and external geometry of the receiving tube, which is for the first time based on the model of HF distribution around the receiver tube. These changes include usVηing and moving the receiver's central plug, and creating concavities on the receiver tube to augment the contact surface of the wall with the internal working fluid. These concavities are created in regions of the tube that have a higher heat transfer to increase the heat transfer rate as a fin. In order to generate various HFs around the receiver tube and consequently create different arrangements of fins, two types of PTCs have been used in this research. To compare the improvement of each case-studies rather than smooth case, two indices of efficiency-based (VfNu) and two-objective evaluation () are defined. Finally the results show that, in view point of Vη index, PTC with three-piece reflector and also with the central plug as well as the big fins can give the optimum results than the other case-studies. On the other hand, considering the index of VfNu, the conventional PTC with E.F = 2/3 and the big fins can give the optimum results.

Research on Thermal Insulation Measures of Power Equipment Condition Monitoring Device in Cold Regions

Outdoor winter temperatures in other northern regions such as Heilongjiang Province are relatively low. As an important equipment of ensuring the safety of transmission lines, the stability of the condition monitoring devices is facing great challenges. In order to ensure that the condition monitoring device can operate reliably in winter, so as to avoid the influence of low temperature in winter on the reliability of the condition monitoring device, in this paper a device is designed that uses solar heat for heat preservation for power equipment condition monitoring device. The device uses an all-glass vacuum solar collector tube to convert solar energy into heat, and realizes instant feedback and control of temperature through a bimetallic temperature sensor. After testing, in winter, the internal temperature of the heat insulation box can be increased by about 30°C compared with the outside, which can effectively improve the winter operating environment of the device.

A Thermal-Hydraulic Model for the Stagnation of Solar Thermal Systems with Flat-Plate Collector Arrays

Stagnation is the transient state of a solar thermal system under high solar irradiation where the useful solar gain is zero. Both flat-plate collectors with selective absorber coatings and vacuum-tube collectors exhibit stagnation temperatures far above the saturation temperature of the glycol-based heat carriers within the range of typical system pressures. Therefore, stagnation is always associated with vaporization and propagation of vapor into the pipes of the solar circuit. It is therefore essential to design the system in such a way that vapor never reaches components that cannot withstand high temperatures. In this article, a thermal-hydraulic model based on the integral form of a two-phase mixture model and a drift-flux correlation is presented. The model is applicable to solar thermal flat-plate collectors with meander-shaped absorber tubes and selective absorber coatings. Experimental data from stagnation experiments on two systems, which are identical except for the optical properties of the absorber coating, allowed comparison with simulations carried out under the same boundary conditions. The absorber of one system features a conventional highly selective coating, while the absorber of the other system features a thermochromic coating, which exhibits a significantly lower stagnation temperature. Comparison of simulation results and experimental data shows good conformity. This model is implemented into an open-source software tool called THD for the thermal-hydraulic dimensioning of solar systems. The latest version of THD, updated by the results of this article, enables planners to achieve cost-optimal design of solar thermal systems and to ensure failsafe operation by predicting the steam range under the initial and boundary conditions of worst-case scenarios.

A review on the application of hybrid nanofluids for parabolic trough collector: Recent progress and outlook

By far, the Parabolic trough collector (PTC) is the most established solar concentrating technology worldwide. This paper draws a comparison among various studies done earlier in the domain to bring forth different models and mediums used to evaluate the effect of nanofluids on thermal parameters for PTC providing an optimum output, resultantly. The study also reveals that by using nanofluid and hybrid nanofluids as heat transfer fluid (HTF) inside the absorber tube of solar collector, the thermal and optical characteristics can be enhanced. Reported papers in literature mention stability, effect on PTC’s performance by implementing various novel designs, collector efficiency enhancement by using various inserts, and selecting proper hybrid nanomaterial into the base fluid. Varied experimental studies report that using hybrid nanofluid results in a more significant enhancement in thermal properties viz-a-viz than the mono fluids. A close look at the results of some of the notable works of the domain explicitly implies that for enhancing the thermal conductivity of nanofluid, metal oxide hybrid nanofluids are more promising than the oxide ones in a rather ‘pecking order’. The study also verges on the proposition that the thermal properties of nanofluid can be accelerated by the usage of hybrid nanofluid instead of mono nanofluid, as a medium, into a more efficient hybrid structure. Conclusively, this review advances the understanding of optimizing alteration parameters for obtaining maximum increase in outcomes and offers substantially adequate understanding for choosing specific techniques to enhance the overall efficiency of PTC, which can be used as a guideline for future trends. • Current and past studies of parabolic trough collectors have been reviewed. • Nanofluid techniques are delineated in performance enhancement. • The implementation of inserts has resulted in Brownian motion enhancement. • The efficiency of the collector using nanofluids is higher than that of the base fluid. • This review provides research gaps for researchers to investigate further.

Flat-Plate Solar Collector Thermal Performance and Optimal Operation Mode by Exergy Analysis and Numerical Simulation

In this paper, the effect of a flat-plate solar collector components exergy destruction rates on the collector performance has been examined. A theoretical model based on energy and exergy balance for glass cover, absorber plate and working fluid resulted in nonlinear ordinary differentials non-autonomous system of equations that was solved numerically. Upon verification of the accuracy of the proposed model with experimental data, the effect of parameters such as solar radiation, mass flow rate, inlet fluid temperature and insulation thickness on the exergy destruction rates and exergy efficiency has been investigated. The model was used to optimize parameters, such as inlet fluid temperature, mass flow rate and number of collector tube. The results reveal that the highest exergy destruction rate occurs in the absorber plate, which is 79.23% of the total exergy destruction rate. Increasing the mass flow rate to 0.0087 kg/s leads to a decrease in the absorber plate exergy destruction rate to a minimum value of 575.74 W/m2 and to an increase in the exergy efficiency to a maximum value of 21.97%. When the inlet fluid temperature increases from 20 to 50 °C, the absorber plate exergy destruction rate reduces from 676.66 to 438.40 W/m2 resulting in a significant increase in the collector exergy efficiency from 6.80 to 37.86%. The optimum operating condition was found to be 37 °C for the inlet fluid temperature, 0.0087 kg/s for mass flow rate and fifteen for the number of tubes.

Development and usability of solar thermal collectors in different fields: An overview

In the present work, solar energy utilizations by different solar systems such as solar water treatment, solar water heating, stem generation for the purpose of electricity generation; solar pumps, etc. have been introduced. Out of these, a focused approach for the solar water heating, solar water distillation by utilizing different solar collectors have been extensively reviewed to identify the generalized usability in that field. The collection of different solar collectors have different capabilities towards the absorption of direct and diffused solar radiations based on its materials, geometry, design, etc. and for that a rigorous observations have been made in the present effort. As the Earth has a solar energy rich surfaces so related technology search in other fields such as mechanical devices such as in mechanical devices, pneumatic suspension cars, thermal devices, pneumatic pumps, etc. is a worthwhile approach with the help of the current study. In the present study, solar thermal collectors such as vacuum tube collectors, flat plate collectors, concentrated reflectors, trough collectors, etc. have been recognized in this study. The parabolic concentrator covers the larger area of solar energy and evacuated tubes efficiently hold the available solar energy. And, polygeneration systems presents better options for the multi-disciplinary utilizations of renewable energy resources. Depending on the targeted approach, a dignified discussion and a concise conclusion have been framed with its futuristic recommendations.

Design, Construction and Performance of a Solar Cloths Drying System

This paper presents the design, construction and performance evaluation of an efficient stand-alone PV- integrated solar clothes drying system for drying applications. The solar clothes drying system was constructed to reduce the reliance on unsustainable electric dryers, which are high electricity-consuming appliances resulting in the emission of large CO2 amounts to the environment. All these developments were geared towards improving the performance and reliability of the alternative sustainable energy systems and help to reduce environmental hazards. After testing different materials for the construction and the evacuated collector tube, the result shows that copper is the best for high performance and efficiency followed by aluminum. But aluminum was used for the casing and a copper tube for the evacuated collector tube. From the performance evaluation test of the hybrid solar clothes drying system, it was observed that The trend of the variation in temperature was a result of the weather condition the solar drying system was able to dry a pair of clothes within 3 hours during the outdoor test and about 3 hours and 45 minutes during the indoor test with a relative humidity of 30%. The economic analysis of the solar drying system was also carried out and the payback period was calculated to be 2.87 years, which was small compared to the life of the hybrid solar drying system.

Performance Enhancement and Improvement of Energy Efficiency in Evacuated Tube Heat Pipe Collector with Nanocomposite: A Review

Solar collector tube is used to combine incident energy and convert it into heat energy. Recently several studies have been done on improving the performance of the solar collector. Solar energy is clean energy and does not create pollution. The sun gives more power than we need. Solar collector consists of an absorber unit which transfers the heat energy of the sun to a working fluid. It is easily seen that solar intensity has more effect on the evacuated tube solar collector. In solar applications like distillation of salty water, heating, drying, air conditioning, and air heating, evacuated tube collector gives higher efficiency than flat plate collector. The evacuated tube solar collector technology gives good performance in bad weather conditions than the conventional system because vacuum inside the glass tube allows it to store higher percentage of heat. The challenge in the production of future generation evacuated tube collector technology is the control and management of operating temperature and heat generation. Heat pipe of solar collector controls operating temperature and prevent overheating that common problem in solar heating application. After chemical treatment, the heat pipe will control the freezing and prevent the evacuated tube. Heat transfer equipment is used to transfer the heat from one fluid to another fluid in many industries. The performance of solar collector with heat pipe depends on various factors such as solar radiation, ambient temperature, and flow conditions. With increasing mass flow rate, the heat transfer coefficient of the nanofluids increases. The use of nanofluids with evacuated tube heat pipe solar collector gives more efficiency and increase the output.

Experimental and CFD analysis of plain and dimples tube at application of solar water heater

Solar based water heater takes on a key role in Energy management. Because of its performance, it is more than electric transformation. It has become the much-demonstrated and built-up tool in a large number of families in India to provide boiling water prerequisites. Solar assisted water heating is a very easy and effective approach to receiving and using the Solar’s energy. It has a conscious position among the energy clients, regardless of its low efficiency. Every progress in the design and experimental of the solar based -powered water heating system would therefore result to reduction of ordinary fuel and costs. The objective of this solar water heater is to enhance the thermal performance throughout the flat plate collector tube. Furthermore, to reduce the heat loss and to improve the heat transfer by modifying the geometric profile of riser tube. To generate the turbulence flow throughout riser tube to get a better heat transfer on the solar system. The modification of geometry is to create dimples inside the riser tube. The dimple is placing a circular type along the riser tube throughout its surface. Finally, the heat transfer is improving by the modifying riser tube. Finally, the experimental result is analysed with CFD software and the results are compared with the experimental solar water heater.