Evacuated Tube Solar Collector Research Articles

The Effect of Using Secondary Reflectors on the Thermal Performance of Solar Collectors with Evacuated Tubes

The aim of this paper is to improve the thermal performance of the evacuated tube solar collectors by using secondary reflectors and covering the collector surface area with an aluminum foil. Adding a secondary reflecting surface in the form of a parabola fixed on the end of the parabolic trough, acts as an additional reflective surface, which increases the input energy to the solar collector and consequently improves the thermal output of the collector. Two solar collectors were manufactured, one with modifications and the other without modifications, which is taken as a reference for the sake of comparison. Four experiments were performed; the first and second experiments reported the influence of adding a horizontal and a vertical secondary reflector on the solar collector efficiency. In the third and fourth experiment the effect of covering the collector surface area with aluminum foil together with a secondary vertical reflector on the heat gained by the bulb is examined. It is found that the average temperature of the heat pipe bulb in case of a secondary reflector installed horizontally is about 2.5% greater than the average temperature of the reference collector, while in case of the secondary reflector installed vertically is 7% greater than the reference collector. Adding the secondary reflecting surface in the vertical position, and covering the surface area of main parabola and the secondary reflector with aluminum foil, has increased the temperature of the heat pipe bulb by 11%. Finally, adding a secondary vertical reflector to the parabolic trough collector and covering both reflectors, i.e. the primary and the secondary reflectors, with aluminum foil improve the heating capability of the solar collector.

Thermodynamics analysis of a lab scale humidification-dehumidification desalination system employing solar energy and fogging approach

Providing essential fresh water for drinking purposes is a crucial task. Most regions worldwide have the brackish or salty bulk water, which is not suitable for drinking. An experimental water desalination system based on the humidification-dehumidification (HDH) technique is provided in this study. Solar energy was used to power the proposed HDH desalination system by employing a photovoltaic solar panel to generate electricity, and an evacuated tube solar collector (ETSC) to heat the feeding water and air. Moreover, the HDH desalination system employed the novel technology of three fogging nozzles, 10 µm each, which showed promising results regarding exergy efficiency and freshwater productivity. A productivity rate of 1.70 kg/hr freshwater was recorded when the mass flow rate ratio of seawater to dry air was 0.857, and it was possible to reach 3.80 kg/hr when the inlet feedwater was heated to 80 °C. The gain-output ratio was achieved at the value of 3.41 for the same mass flow rate ratio of 0.857 and feedwater temperature of 80 °C. The minimum amount of total specific entropy generation (0.256 kJ/ (kg. K)) was obtained at a mass flow rate ratio of 0.857 and feedwater temperature of 60 °C.

Energy, exergy, environmental and economic (4E) analysis of evacuated tube solar collector with helical coils

Energy, exergy, environmental and economic (4E) analysis of evacuated tube solar collector with helical coils

Determination of Cooling Load for a Solar Cooled Building in Khartoum Using a Simulation Method

Cooling load calculations are normally carried out assuming steady state conditions. This is a simple but conservative approach that leads to overestimation of the cooling capacity. For more accurate estimation of cooling loads, one has to take into account the thermal capacity of the walls and internal heat sources, which makes the problem more complicated. In this paper, the unsteady state heat transfer formulation has been used to determine the air conditioning cooling load for a building in Khartoum for a hot summer day. An explicit method was used to calculate the nodal temperatures at each time step of the thermal network. A simulation program was developed to calculate the cooling load at each time step. The building is cooled by absorption cooling system comprised mainly of an evacuated tube solar collector, a lithium bromide –water absorption air conditioner, a storage tank fitted with an auxiliary heater. A mathematical model is built to simulate the absorption cooling system for the solar cooled building and the results showed that the absorption system driven by solar energy from the evacuated tubes solar collector is enough to cover the cooling load demand by the building more than ten hours.

Investigations of performance improvements on the evacuated tube solar collector with and without the incorporation of preheater through various engineering approaches

Solar irradiation is a clean form of energy, and absorption cooling systems powered by solar energy allow for significant energy savings. In the future, the demand for renewable energy may be the most effective way to serve clean energy, especially in Iraq, which has an excellent geographical location. In this research work, the performances of solar collector with and without of preheater have been evaluated. When compared to flat plate collectors at temperatures above 80°C, glass evacuated tube solar collectors provide the combined effects of a highly selective surface coating and vacuum insulation of the absorber element, resulting in a high heat extraction efficiency. Firstly, the Evacuated Vacuum Tube Solar Collector (EVTSC) was tested through experimentation. Secondly, Computational Fluid Dynamics (CFD) approach has been involved in this EVTSC system and thereby the conductive, convective and radiation based heat transfers are computed. Additionally, all possible with inclusive preheater cases are computationally investigated, thereafter the comprehensive report is prepared though validated computational procedures. Finally, the maximum efficiency is observed to be 53% without using a preheater and 61.8% with the usage of the preheater. The increase in efficiency using the preheater is found to be 16.6%.

Numerical Analysis of Evacuated Tube Solar Collector with Heat Pipe Containing an I-section Insert

Numerical Analysis of Evacuated Tube Solar Collector with Heat Pipe Containing an I-section Insert

A novel solar desalination system based on an evacuated tube collective condenser heat pipe solar collector: A thermo-economic and environmental analysis

Solar desalination has captivated consideration to overcome the problem of the scarcity of freshwater, with simple-design, economic, and environment-friendly solutions. This study navigates a novel solar-evacuated glass tube collector integrated with a collective condenser heat pipe system for solar desalination. A newly designed heat pipe array was represented in this work by affixing all the evaporator tube units of the heat pipes to a single condenser unit and was attached to the evacuated tube solar collector. The innovative assembly of the heat pipe provided uniform heating of water and rapid steam generation. The present system acts as a solar collector and as a stand-alone basin for freshwater formation. The performance assessment of the neoteric system was conducted based on half-filled and three-fourth-filled conditions of the water flow pipe kept within the collective condenser heat pipe. The maximum heat pipe temperature recorded during the half-filled state was 156.9°C and 151.48°C in the three-fourth-filled state. The half-filled state of the water flow pipe delivered a total distilled water content of 8,050 ml/day, whereas the three-fourth-filled state delivered 5,925 ml/day of distilled water. The maximum energy and exergy efficiency of the presented system was 19.27% and 3.92%, respectively. The economic minimum unit cost of freshwater by the present system is 4.27 INR, and the payback period is 2.9 years. The present eco-friendly energy system saves 4.25 kWh of electricity and 4.16 × 10−3 tons of CO2 equivalent per year.

Energy analysis of evacuated tube solar collector integrating phase change material in northeast China

Evacuated tube solar collectors (ETSCs) are one of the most popular collector types with regard to solar energy utilization. However, the poor energy performance of ETSCs results in equal timeliness with solar energy. Incorporating phase change material (PCM) into ETSCs is regarded as a novel strategy to alleviate the challenge by means of enhancing their thermal energy storage capacity and improving energy performance. Since thermophysical parameters of PCM have a vital influence on energy performance of ETSCs, the present work aims to identify the effects of density, specific heat capacity, latent heat, thermal conductivity, and melting temperature of PCM on energy performance of ETSCs. The findings exhibit that increasing the density, specific heat capacity and melting temperature of PCM, the peak outlet temperature of heat transfer fluid and effective heat collection of ETSCs containing PCM decreases, while temperature time lag and effective heat collection time increases. Compared with ETSCs containing PCM with density of 425 kg/m3, the effective heat collection time is prolonged up to 44.41 % for the scheme with PCM density of 1700 kg/m3. Utilization of PCM with higher melting temperature is beneficial to enhance energy performance of ETSCs, which the maximum effective heat collection is increased by 4.31 % for ETSCs containing PCM with melting temperature of 333–335 K. However, increasing the values beyond 1700 kg/m3, 1 W/(m·K), 4000 J/(kg·K) and 247,500 J/kg in cold regions of northeast China are not beneficial.

Analysis of a hybrid solar absorption cooling system with thermoelectric generator

In the present work, a hybrid solar/thermoelectric generator (TEG)/absorption cooling system (ACS) is studied. The heat supply to the ACS is produced by an evacuated tube solar collector (ETC). The TEG will use the waste heat from hot parts to produce the electrical demand of the ACS (the pumping and control systems). In this way, the system becomes completely self-sufficient. Different locations of the TEG modules in the system were considered and the effect of various system parameters on the system performance was studied. The results showed that the best location for the TEG modules was between the hot water storage tank and the ambient air. For a temperature at the generator, evaporator, and condenser (= T a b s o r b e r ) equal to 85 °C, 5 °C, and 30 °C respectively, it was found that 184 TEG modules were sufficient to provide the required electrical power with a COP and exergetic efficiency equal to 0.8 and 14.9%, respectively. In addition, it was also shown that the COP of the ACS system with TEG modules is always slightly higher than that without them by about 1.5%. • A thermoelectric generator (TEG) is incorporated into a solar absorption cooling system (ACS). • Two types of TEG, TEG2-126LDT and TGM-199-1.4-0.8, are compared for different positions in the ACS. • Energy and exergy analysis is performed for different operating conditions. • The TGM-199-1.4-0.8 is better for the proposed cycle. • The configuration where the TEG is placed between the hot water storage tank and ambient air temperatures gives the best performance.

Improving the performance of novel evacuated tube solar collector by using nanofluids: experimental study.

The main focus of the work is to determine the performance efficiency of water-%CuO nanofluids and water at varied flow rate of 0.035 lit/sec, 0.045 lit/sec, and 0.065 lit/sec in an evacuated tube collector integrated with an heat exchanger. A heat exchanger made of copper tube connected to a horizontal pipe for collection of heat from a vertical tube, and a vertical copper tube for collection of heat from an evacuated tube collector for solar radiation were used in the investigation. Water showed no absorption, a low thermal capacity when it was not suitable for high thermal application for improvement in performance, the base fluid with colloidal dispersion of %vol CuO nanofluids in the force convection mode. The evacuated tube collector produced the highest efficiency of water -0.3% vol CuO nanofluids at flow rate 0.035 lit/sec compared to 0.1% and 0.2% vol of CuO nanofluids at flow rate of 0.045, 0.065 lit/sec and water. A comparison to the water CuO nanofluids with the highest effective concentration showed a greater increase in thermal efficiency.The performance of theworking fluid performances was examined for parameters like exit temperature, specific heat, thermal conductivity, energy productivity, and efficiency utilizing.

Techno-economic analysis of a solar-powered humidification-dehumidification desalination system under fogging effect

Different techniques are utilized to overcome the problem of freshwater shortage around the world. Humidification-dehumidification technology is among the promising methods, especially when powered by cost-effective solar energy sources or when used in remote desert areas with abundant solar resources. In this study, a solar energy-powered humidification-dehumidification system is assembled and tested. Two solar energy systems are supplying the humidification-dehumidification system with heat and electricity, namely an evacuated tube solar collector and an array of photovoltaic panels, respectively. The studied system utilizes three fogging nozzles, each with a 10-µm diameter, that allow efficient energy conversion. Also, the system was tested under the influence of a single nozzle with a larger diameter for comparison purposes. The fogging technique reduced the power consumption while boosting the total system productivity. The system was able to achieve a maximum gained output ratio of 4.4 at saline water and air temperatures of 80 and 53.44 °C, respectively. The rate of freshwater production ranged between 1.7 and 3.85 L/h. At the highest tested saline water to air ratio, the system with three 10-µm nozzles enhanced the gained output ratio by 23.68 and 67.33 %, compared to the single nozzle configuration with 20 and 30-µm diameter, respectively. An economic evaluation showed a best-averaged price of 0.0543 USD/L of freshwater.

Performance evaluation of using evacuated tubes solar collector, perforated fins, and pebbles in a solar still - experimental study and CO2 mitigation analysis.

The combination of various methods of increasing evaporation rate can highly impact the performance of solar desalination. This investigation aims to find the impact of using evacuated tubes solar collector, perforated fins, and pebbles on the performance enhancement of a solar still. Simultaneously six-evacuated-tube solar collector to raise the evaporation rate of the system, the perforated fins to increase the heat transfer surface between water and absorber, and the immersed pebbles stone in the water to keep the high water temperature at low solar radiation were considered. The hourly and cumulative distillate output (DO) values are presented separately for the daytime and nighttime to provide extensive insight. The results indicate that on a sample day from the six months of experiments, which was in February 2019, the time for DO peak shifts from 1 to 3 p.m. Moreover, the temperature values for MSS experience almost 43 ℃ jumps on the peak and almost 19 ℃ increase on average compared to CSS. Furthermore, the cumulative DO in the daytime reaches from 2.515 to 6.662 L, while during the nighttime, an increase from 0.057 to 0.872 L is observed. Additionally, during the six months, the average DO jumps from 2.88 to 7.03 L, which means a significant enhancement of 144.1%. Moreover, the costs per liter of MSS and CSS are 0.0051 and 0.0056 dollars per liter, respectively. The net amount of CO2 reduction of MSS was improved by about 2.44 times higher than CSS.

A parametric study on the efficiency of a solar evacuated tube collector using phase change materials: A transient simulation

Evacuated solar collectors are renewable systems that provide a considerable quantity of heat during test time. However, this system is unable to provide energy in the absence of sunlight. Thus, this study attempted to numerically study a Solar Evacuated Tube Collector (ETC) performance using phase change materials (PCM). PCM can store considerable thermal energy during the day and release it to the system at night. In order to simulate the ETC-PCM system, an accurate three-dimensional model considering all the layers is designed. In the present numerical investigation, the effect of various properties of the PCM, including enthalpy, melting point, and thermal conductivity, on the outputs of the ETC-PCM system are evaluated separately. Also, the effects of some other factors, such as MWCNT nanoparticles dispersion in the base fluid and working fluid mass flow rate, on the performance of the ETC-PCM system are studied. Furthermore, to evaluate the performance of the system and model the behavior of the PCM during the day, the system is simulated under the weather condition of Hing Kong from sunrise until sunset. According to the results of the simulations, a reduction in PCM melting point from 50 °C to 35 °C can elevate the efficiency of the ETC-PCM device. PCM with a high melting point remains solid during the day. Thus, its effect on the output of the system cannot be revealed. Moreover, it is found that the system using PCM with the latent heat of 160 kJ/kg has the best performance among the studied cases. Besides, it is illustrated that raising the mass flow rate of working fluid and mass fraction of nanoparticles can enhance the system's performance.

Techno-Economic Analysis of dual ejectors solar assisted combined absorption cooling cycle

This paper deals with the Techno-Economic Analysis of dual ejectors –flash tank absorption cooling cycle assisted by solar energy. In this study, the solar system is simulated using the TRNSYS software and a one-dimensional ejector is modeled in EES (Engineering Equation Solver) using NH3/H2O as working fluids. A cooling capacity of 5 kW is considered and a parametric optimization is carried out to select the optimum size of the thermal solar system. The design of the absorption cooling cycle under the Malaysia climate conditions was 5 kW (about 1.5 refrigeration ton) with a solar thermal collector (evacuated tube solar collector of 8.5 m2 sloped at 14° and 0.35 m3 tank size with 0.1 kg s−1 for fluid flow rate). The solar fraction varied between 53.6% in March and 68.6% in February. The payback period and profit gain for the dual ejector cycle, flash –tank with ejector and basic cycle with only ejector are 11 yr, 3192 $; 13.5yr, 1647$; and 16 yr, 874$ respectively. The results also show that the combined dual ejectors-flash tank cycle (Cycle 3) was up to 27% less than of the absorption combined ejector system (Cycle -1), and 10% cheaper than the combined ejector –flash tank absorption system (Cycle -2). Therefore, the economic analysis showed that the absorption system with dual ejectors (Cycle -3) was the preferred option.

Experimental investigation on the thermal appraisal of heat pipe-evacuated tube collector-based water heating system integrated with PCM

There is a great deal of research being done on the performance of solar collectors. Evacuated tube solar collectors are a mature technology that has proved reassuring performance for heat generation. However, low thermal efficiency remains their main challenge. Therefore, research to improve the efficiency of Evacuated Tube of Solar has continued to date based on some new approaches. The present study presented various designs of Evacuated Tube of Solar collector (ETSC) thermally enhanced by the addition of reflectors and thermal storage units with phase change materials and nanoparticles. The proposed models were assessed during different periods and different zones in Tunisia, especially in the Northern and Southern regions. This work established the energy balance of solar thermal systems determined by the input/output method. Assumptions and mathematical relations are presented for the proposed designs. Additionally, measured and regression useful energy as a function of the daily cumulative global solar energy of all ETSC-types was also evaluated. Research gaps in this field are identified and future research trends and directions are recommended.

Adsorption Solar Air Conditioning System for Singapore Climate

The design of an adsorption solar air conditioning system is investigated by using a model with an activated carbon–methanol working pair. This system is analysed with the solar insolation levels and ambient temperatures of Singapore. The proposed design mainly consists of two tubular reactor heat exchangers (TRHEXs) operating out of phase and driven by heat from an evacuated tube solar collector (ETSC). The pair of TRHEXs act as a thermal compressor and contain about 2.275 kg of activated carbon per reactor. The evacuated tube solar collector (ETSC) has better performance and is more cost effective than the flat plate solar collector (FPSC), even though it has a higher cost per unit. On the hottest day of the year, the proposed adsorption system has a maximum cooling power of 2.6 kW and a COP of 0.43 at a maximum driving temperature of 139 °C with a 9.8 m2 ETSC area. The system has a total estimated cost of EUR 10,550 corresponding to about SGD 14,800 with a 7-year payback time. At similar cooling capacities, the adsorption air conditioning system is expected to be more cost effective than the conventional system beyond an expected period of 7 years, with an expected lifetime of 15 to 20 years.

Experimental analysis of Shape-Stabilized PCM applied to a Direct-Absorption evacuated tube solar collector exploiting sodium acetate trihydrate and graphite

A problematic issue with the solar water heaters is the storage tank requirement, which takes considerable space and makes the piping and installation more difficult. This study is the first report on experimentally applying a shape-stabilized PCM to a tankless direct-absorption evacuated tube solar collector to address this challenge and directly store solar energy. The proposed salt hydrate PCM was synthesized at various concentrations of related components and after detecting the optimum compound, it was tested under several cycles to ensure its sustainable heat storage capability. Furthermore, after charging the solar system in the stagnation mode (without water flow), it was discharged at 10, 27, and 40 L per hour (LPH) flow rates. It was revealed that the thermal efficiency in the stagnation mode was improved from 66 % to 82 % using this collector-storage system. In addition, it was concluded that changing the flow rate from 10 to 27 LPH does not considerably reduce the heat gain of collector; however, using the flow rate of 40 LPH plunges the discharge efficiency. Ultimately, cost and carbon footprint analyses of the proposed system were conducted and a payback period of 6 years and annual reduction of 5.4 tons of CO2 emissions were reported.

Modelling single-effect of Lithium Bromide-Water (LiBr–H2O) driven by an evacuated solar tube collector in Ma'an city (Jordan) case study

The refrigeration systems consume a high amount of energy. In Jordan, conventional energy is an expensive option. Thus, this consumption will be significant. In this work, a mathematical model of the Single-Effect Solar Absorption Cooling system (SESAC), utilizing Lithium Bromide-Water (LiBr–H 2 O) as the working fluid, has been developed with evacuated tube collectors. This model has been designed according to the climate in Ma'an, Jordan. The effect of the temperature changing of the cooling system cycle on the coefficient of performance (COP) and the LiBr–H 2 O crystallization has been investigated using MATLAB/Simulink environment. The best temperatures at which the system operates without crystallization were defined. Moreover, the effect of improving the heat exchanger solution on the overall system performance has been investigated. The medium cooling capacity was (120 kW) and it runs by 243.3 m 2 evacuated tube solar collectors. It was found that the generator's temperature is the critical factor that affects the system's performance as a whole. The highest value of COP was 0.74, at a generator temperature of 110 °C without crystallization.

Feasibility of annual dry anaerobic digestion temperature-controlled by solar energy in cold and arid areas.

In cold and arid areas, variations of ambient temperature not only lead to a large amount of heat loss from anaerobic digestion reactors but also greater challenges in the stable production of biogas. Common temperature-controlled methods of biogas production, such as coal combustion, electric heating, biogas combustion and so on, are expensive and high energy-consuming. Openly, solar energy is economical and suitable for stable biogas production. However, no pilot studies have yet shown the feasibility of controlling the temperature of annual biogas production with solar energy in cold and arid areas. This paper first theoretically analyzed the energy balance between evacuated tube solar collectors and anaerobic reactors. Then a biogas production system was developed in Lanzhou City, China, consisting mainly of a 3m3 insulated anaerobic reactor and a solar collector with 30 sticks Φ58×L1800mm evacuated tubes. Annual batch experiments have been carried out to test the feasibility of stable biogas production at a temperature-controlled by solar energy in cold and arid areas. The results show that dry anaerobic digestion with 20% total solid (TS) can start and operate smoothly even under the condition of low solar irradiation for 3-4 consecutive days. The system can run stability by anaerobic digestion at 26±1°C in winter and spring, by mesophilic (37±1°C) and thermophilic (52±1°C) anaerobic digestion in summer and autumn, which implies a highly efficient operation strategy for agricultural and animal husbandry wastes treatment. These theoretical and experimental results provide a scientific basis and engineering reference for the application of biogas production temperature-controlled by solar energy and have important value for the efficient and low-cost anaerobic digestion treatment of agricultural and animal husbandry wastes in cold and arid areas.

Thermal performance of greenhouse heating with loop heat pipe solar collector and ground source heat pump

The hybrid heating system consisting of loop heat pipe solar collector (LHPSC) and ground source heat pump (GSHP) is proposed to control greenhouse temperature in Harbin (the coldest provincial capital of China) in this paper. The combined thermal resistance network and energy balance model is developed to predict transient greenhouse temperature corresponding to the energy supplied by GSHP. The influence of ambient temperature on the thermal performance of greenhouse heating system is analyzed. The results show that the greenhouse temperature fluctuates in the range of 17–24 °C corresponding to the energy of 200 kW intermittently supplied by GSHP, which is reasonable for predicting greenhouse temperature in severely cold regions. As ambient temperature varies from −24 °C to −13 °C, heat loss of maintenance structure, ground, ventilation and water storage tank change in the range of 51.9–73.2 kW, 2.45–3.45 kW, 11.1–15.5 kW and 5.87–6.91 kW, respectively. The maximum thermal efficiency of loop heat pipe solar collector is higher (76.38%) than that of evacuated tube solar collectors (45%–50%), which will be promising for greenhouse heating due to higher thermal efficiency and better environmental adaptability. The results presented in this study will provide further valuable guidelines for designing greenhouse heating system.