Evacuated Tube Solar Collector Research Articles

Solar-Powered Adsorption-Based Multi-Generation System Working under the Climate Conditions of GCC Countries: Theoretical Investigation

In this study, transient modelling for a solar-powered adsorption-based multi-generation system working under the climatic conditions of the Gulf Cooperation Council (GCC) countries is conducted. Three cities are selected for this study: Sharjah in the United Arab Emirates, Riyadh in Saudi Arabia, and Kuwait City in Kuwait. The system comprises (i) evacuated tube solar collectors (ETCs), (ii) photovoltaic-thermal (PVT) solar collectors, and (iii) a single-stage double-bed silica gel/water-based adsorption chiller for cooling purposes. A MATLAB code is developed and implemented to theoretically investigate the performance of the proposed system. The main findings of this study indicate that among the selected cities, based on the proposed systems and the operating conditions, Riyadh has the highest cooling capacity of 10.4 kW, followed by Kuwait City, then Sharjah. As for the coefficient of performance (COP), Kuwait City demonstrates the highest value of 0.47. The electricity generated by the proposed system in Riyadh, Kuwait City, and Sharjah is 31.65, 31.3, and 30.24 kWh/day, respectively. Furthermore, the theoretical results show that at 18:00, the overall efficiency of the proposed system reaches about 0.64 because of the inclusion of a storage tank and its feeding for the adsorption chiller. This study analyzes the feasibility of using a combination of ETCs and PVT collectors to drive the adsorption chiller system and produce electricity in challenging weather conditions.

Enhancing Thermal Performance of Evacuated Tube Solar Collector using Novel Graphene Oxide Nanofluid

The research article investigates the thermal performance of heat pipe-based evacuated tube solar collector (ETSC) experimentally using graphene oxide (GO) and deionised (DI) water as working fluid with a mass flow rate of 0.5 lit/min, 0.75 lit/min, and 1 lit/min. The different volumetric concentrations of 0.001%, 0.002%, and 0.003% graphene oxide nanofluid samples were prepared in the deionised water. The X-ray diffraction (XRD) was used to determine the structural properties of graphene oxide and the morphology of graphene oxide was studied by scanning electron microscope (SEM). To evaluate the stability of nanofluid samples, the Zeta potential analysis was carried out which showed that prepared nanofluid samples remain stable for up to 30 days. The effect of different nanofluid concentrations on various thermo physical properties of nanofluid was studied and discussed. The thermal performance of ETSC was investigated by considering the effect of volumetric concentrations of nanofluid and mass flow rates. According to the findings, there is a significant increment in temperature difference and energy gain by using nanofluid samples, and the maximum thermal efficiency of ETSC was found to be 37.1% for a volumetric concentration of 0.003% at 1 lit/min mass flow rate as compared to water.

Performance analysis of evacuated tubes with thermosyphon heat pipe solar collector integrated with compound parabolic concentrator under different operating conditions

The present work experimentally evaluated the performance of a solar collector comprised evacuated tube heat pipe (ETHP) coupled with a compound parabolic concentrator at different tilt angles. Therefore, experiments have been conducted in the climate conditions of Tamil Nadu (77.07° E,11.04° N), India, from April 15, 2019, to May 20, 2019. The objective of the work is to explore the effect of a tilting angle on the performance of an evacuated tube solar collector with a thermosyphon attached to the compound parabolic concentrator. The CPC is designed with an aperture width of 343 mm, concentration ratio of 2.32, and aperture angle of 25.4°, improving the solar collector efficiency with the help of MATLAB Programming, which gets Coordinate points based on these coordinate points. CPC Profile is fabricated. The Thermosyphon heat pipe is constructed with a Copper tube having a 19 mm diameter with 40% Acetone charged. The experiments were conducted by varying the tilting angles of the solar collector at 15°, 30°, 45°, and 60° horizontal. The heat resistance and instantaneous efficiency of the solar collector are studied in this study. The result reveals a minimum thermal resistance of 0.02 kW−1, and a maximum efficiency of 78% was recorded at a 45° tilting angle.

Performance of a solar hybrid desalination plant integrated with photovoltaic-thermal collectors for remote regions: Experimental and modeling investigation

Energy and freshwater are the most prioritized needs for any nation nowadays, especially for arid areas. Giving attention to renewable energy sources like solar energy is a must towards a cleaner environment and a world with no need of temporary sources like fossil fuels. Also, a solution to lower the power requirements and costs of desalination hybrid systems should be investigated to overcome the water problem. The present study aims to design and build a novel hybrid desalination plant working with the highest productivity and lowest power consumption. This was done by incorporating a reverse osmosis desalination unit with the conventional solar distiller. The photovoltaic/thermal collectors were utilized to produce electricity as well as a heating unit in addition to the evacuated tube solar collectors, to preheat the hybrid desalination plant feed water. The results presented that the use of photovoltaic/thermal panels and evacuated tube solar collectors as preheating units improved water recovery by 46% and reduced power consumption by 38.34% for the small reverse osmosis unit but the salt rejection decreased by 4%. Cooling the photovoltaic panel increased its electricity production by 24.1% on average. Moreover, the combination of the solar distiller with the reverse osmosis unit on the feed line represents the best configuration which improves the solar distiller’s productivity by 98.32% as compared to separate solar distillers. The cost of freshwater produced is 0.719 $/m3 which is cost competitive compared to previous solar desalination systems.

Annual Performance Evaluation of a Novel Industrial-scale Solar Dryer for Phosphogypsum Waste

Introduction: Solar drying is considered one of the most promising technologies for drying the phosphogypsum “Calcium Sulfate Dehydrate” material as a clean source of energy and saving the environment from its negative impact if it is dried in an open landfill. Method: The dried phosphogypsum (PG) may be recycled and utilized in many useful applications. The presented design of the trapezoidal-shaped greenhouse solar dryer is the preferable solution to perform the drying process in the daytime with solar energy. It may be usable at night, during cloudy and rainy periods, using evacuated tube solar collectors via sensible heat solar thermal energy storage. The system can be operated for 24 hours by solar energy. From theoretical calculations, it was found that the drying time decreased as the gypsum layer in the drying trays decreased due to the improvement of the heat transfer mechanism. The designed solar dryer was studied at various loading capacities depending on the gypsum thickness on the dryer trays. Capacities were 8280 kg, 6624 kg, 4968 kg, 3312 kg, and 1656 kg, corresponding to gypsum thickness of 5 cm, 4 cm, 3 cm, 2 cm, and 1 cm, respectively. The daily collected amount of water and the daily moisture content were estimated with different gypsum thicknesses during all months of the year. Result: It was found that the solar dryer with a capacity of 1,656 kg weight was technically and economically feasible. It was also found that the maximum reduction of moisture content occurred during the summer season, while the minimum values were achieved during winter. Conclusion: With a mass of gypsum equal to 1,656 kg weight, the moisture content of gypsum started to decrease from its initial value (35%) until it reached the final value (10%) in 4 scenarios: the first one, 2 days from April to September, 3 days from March to November, more than 3 days in other months while the minimum moisture content, i.e., 20%, was reported in the first day in June.

Technical and Economic Performance of Four Solar Cooling and Power Co-Generated Systems Integrated With Facades in Chinese Climate Zones

Abstract There has been an increasing interest in solar-driven combined energy supply systems for low-temperate applications, particularly those based on the Organic Rankine Cycle (ORC), Kalina Cycle (KC), or Trilateral Cycle (TLC). However, systems based on these thermodynamic cycles usually employ large area collectors that stand alone or are placed on the roof, without considering integration with the building facade. This research presents a solution to large-scale photothermal utilization integrated with facades for co-generated systems. The current study is the first to conduct performance and economic assessment for four novel solar cooling and power (SCP) co-generated systems driven by evacuated tube solar collectors (ETCs) or semi-transparent photovoltaic (STPV) integrated into the building facades. The suggested systems were simulated using TRNSYS to forecast their performance metrics when used in four Chinese cities with various climate zones. As indicators, a solar fraction (SF) and unit energy cost (UEC) were used to evaluate the technical and financial aspects of each system. The STPV-vapor compression cycle (VCC) system had the highest SF (100%, except Haikou), as well as the lowest UEC (0.211$/kWh on average) among the four cities, according to the results. Among the three solar–thermal co-generation systems, ETC–ORC–VCC had the best performance (SF,37.9%; UEC,0.597$/kWh on average).

Improving the performance of a heat pipe evacuated solar water collector using a magnetic NiFe2O4/water nanofluid

In the recent years, heat pipe evacuated tube solar collectors (HP-ETSCs) are widely utilized due to their easy maintenance and high efficiency. However, increasing the performance of available systems is an important issue that investigated in many studies. The main goal of this study is improving the thermal performance of a HP-ETSC by replacing the working fluid of the system with magnetic nanofluid. In this context, magnetic type NiFe2O4/water nanofluid has been utilized as working fluid in a HP-ETSC to improve the overall performance of the system. Accordingly, NiFe2O4 nanoparticles has been mixed with distilled water at the ratio of 2 wt% in order to obtain magnetic nanofluid. The performance tests have been performed at various water flow rates (0.016 kg/s, 0.033 kg/s, and 0.050 kg/s) using distilled water and NiFe2O4/water magnetic nanofluid. The general outcomes of this work indicated positive results of using NiFe2O4/water magnetic nanofluid on the efficiency of the HP-ETSC. Utilizing NiFe2O4/water nanofluid in the HP-ETSC as working fluid averagely increased the thermal performance as 37.72%, 39.59% and 44.96% at flow rates of 0.016 kg/s, 0.033 kg/s and 0.050 kg/s, respectively. In addition, using NiFe2O4/water magnetic nanofluid in the HP-ETSC averagely increased the exergy efficiency as 60.59%, 55.61%, 59.61% at flow rates of 0.016, 0.033 and 0.050 kg/s, respectively.

Optimization of heat pipe charged with CuO nanofluid using Taguchi technique

Aim of this study is to investigate the influence of various working parameters on the performance of thermosyphon heat pipe, charged with aqueous copper oxide nanofluid. This heat pipe was used as an absorber in twin glass evacuated tube solar collector for heating edible oil stored in an insulated tank. Design of experiments was formulated using minitab™ 19 considering prominent heat pipe working parameters like CuO nanoparticle concentration, CuO nanoparticle size, copper heat pipe diameter, filling ratio, stirring speed and surfactant concentration and their levels through research gaps. Experiments were performed on clear sunny days and impact of parameters on heat pipe solar collector performance was examined using Main effect plot, signal to noise (S/N) ratio and ANOVA. From response table of signal to noise ratio and the ANOVA results, it is concluded that the nanoparticle concentration, nanoparticle size, filling ratio and stirring speed plays important role in heat pipe performance improvement while other parameters like heat pipe diameter and surfactant concentration are less significant. Thus Optimum levels of parameters for best heat pipe solar collector performance were obtained as, nanofluid concentration of 0.3 (% weight), nanoparticle size of 30–50 nm, 8 mm of heat pipe diameter, 45 % of filling ratio, stirring speed of 1200 rotations per minute while preparing nanofluid and surfactant mixing in nanofluid as 0.3 (% volume).

Simple Empirical Relation for an Evacuated-Tube Solar Collector Performance Prediction from Solar Intensity

In this paper, the effect of solar intensity on the heat pipe tip temperature in a heat pipe type—evacuated-tube solar collector (HP-ETSC) was investigated. A simple relation was proposed, relating the solar intensity to the heat pipe tip temperature generated from the experimental data. This simple empirical relation was applied in a set of heat transfer equations derived to predict the heating medium temperature at the manifold outlet of the evacuated-tube solar collector. The calculated results corresponding to two types of heating medium, i.e., palm oil and water, were compared with experimental results from the literature. The results show that the average error was 6.41% for the case of palm oil and 4.66% for the case of water. Based on the case of water as a heating medium fluid, it was found that the flow rate of the heating medium fluid affected the accuracy of prediction, as the percentage error increased with the heating medium flow rate. The maximum percentage error increased from only 1.83% for a water inlet flowing at a Reynolds number of about 2.4 × 103 to 15.23% for a water flow rate at a Reynolds number of about 2.6 × 104. The correction factor was added into the correlation to predict the heat transfer coefficients of heating medium fluids. With this correction factor, the maximum error could be reduced from 11.78% to 7.29% for the palm oil case and from 15.23% to 5.57% for the water case. The average errors corresponding to palm oil and water cases could be reduced to 0.74% and 1.26%, respectively.

Energy, exergy, exergoeconomic and exergoenvironmental analyses of a hybrid renewable energy system with hydrogen fuel cells

In this study, the energy, exergy, exergoeconomic and exergoenvironmental (4E) analyses of a cogeneration system that combines photovoltaic thermal panels (PV/T), evacuated tube solar collectors, an organic Rankine cycle (ORC) and energy storage systems are performed. The cogeneration model is built to meet the load demand of independent houses in remote areas and avoids excessive consumption of traditional energy and environmental pollution. Here, the exergoenvironmental analysis adopts the Eco-indicator-99 method and the all life cycle assessment method is used to calculate the environmental impact of each component. Two comparative studies are conducted to the 4E analyses. The first one compares the comprehensive performance of the battery storage and hydrogen production for energy storage. The results indicate that the cogeneration system using both batteries and hydrogen production for energy storage has the best overall performance. According the exergoeconomic and exergoenvironmental analyses, its environmental impact is 23.6% lower than the cogeneration system using batteries alone and the PV/T can be fully utilized. In addition, the total cost rate is 6.2% lower than the cogeneration system using hydrogen production alone. The second case investigates the effect of adding the evacuated tube solar collectors between the PV/T and ORC on the cogeneration system. The analysis results demonstrate that the evacuated tube solar collectors can increase the heat source temperature of the ORC to increase the power generation of the ORC by 37.14%; however, the total cost rate of the cogeneration system increases by 3.7% and the environmental impact rate increases by 19.8%.

An evacuated tube solar bubble column liquid desiccant regenerator

Liquid desiccant air conditioners (LDAC) are environmentally friendly, require less energy, and can improve air quality. These systems are composed of two main parts: a dehumidifier and a regenerator which are heat and mass exchanger devices that are the main bottlenecks on the overall performance of LDAC systems. Despite their numerous advantages over conventional regenerators, bubble column regenerators have only been studied adiabatically. To address this gap in the literature, an internally heated bubble column regenerator is proposed that is heated with an evacuated tube solar collector while also eliminating the previous issues with corrosion. A prototype was constructed, and the effect of various values of air flow rate, air injection depth, and initial desiccant concentration was studied experimentally in 10 cases (8 modified cases, 2 conventional cases). The results showed that initial concentration has the highest impact on the device’s performance. Increasing air flow rate led to higher water extraction. Air injection depth had no significant impact on the device’s output. In Case 10 (10 L/min air flow rate, 50 cm hose depth, and 30 % initial desiccant concentration), a maximum of 576 g of water was removed from the desiccant. The maximum improvement over the conventional case was 139 % which was achieved in Case 5 (10 L/min air flow rate, 50 cm hose depth, and 35 % initial desiccant concentration). The exergy efficiency for Case 10 was the highest, reaching 8.5 % at the end of the experiment.

Enhanced honey badger optimization of performance analysis of evacuated tube heat pipe solar collector integrated with PCM storage unit

A hybrid method for improving the efficiency of heat pipe evacuated-tube solar-collector (HPETC) is proposed for incorporating the phase-change materials (PCMs) in both off-demand and regular operation. The proposed hybrid approach is called an improved honey badger algorithm (HBA). The crossover and mutation operator improves the honey badger's (HB) foraging habit. The proposed approach aims to generate hot air at various rates of airflow under incident and nonincident solar-radiation situations. The analysis is done on the effects of different energy-storage systems and the position of the heat pipe (HP). In a normal heat-pipe evacuated-tube solar collector, the HP is put within the glass tube that is closer to the upper-surface, and it is held in place through an aluminum fin. However, in the proposed method, the HP is rearranged in the tube's middle. In order to identify the PCM with the highest average-fin temperature, the temperatures of the area-weighted average-fin are measured and compared throughout the glass tubes under typical conditions. For maximizing the thermal-energy carrying capability, the average liquid fraction volume of PCMs is measured for a 24-h flow period. The average liquid-fraction volume of PCMs is continuously observed in stagnation mode till the glass tube reaches the maximal value. The structured mesh patch conforming method is used to invalidate the HPETC system's constituent parts, improving numerical stability and convergence. The proposed method efficiency is 0.43. The proposed method shows high efficiency compared with other existing methods.

Mechanical Analysis Carrired out to a Single Basin Solar Still Integrated with Nano -Composite PCM

In this article, thermal modeling of a single basin solar still coupled with an evacuated tube solar collector under natural circulation mode has been carried out on the basis energy balance equations. The expressions of inner surface of glass cover, outer surface of glass cover, basin liner, and water mass have been derived for the numerical computation. The experiments were conducted under various meteorological conditions for 0.05 m water depth. This experimental setup has been installed at Solar Energy Park, Tamilnadu College of Engineering, Coimbatore, India (Latitude: 11?N; Longitude: 77?E; and an altitude of 409 m above sea level). Observation revealed that there was a considerable increase in the average daily yield of solar still when integrated with an evacuated tube solar collector. For all the cases, the correlation of coefficients (r) between theoretical and experimental values have been verified and they showed good agreement with 0:98 < r < 0:99 and root mean square present deviation of 10:26 < e < 39:7%.

New Evacuated Tube Solar Collector with Parabolic Trough Collector and Helical Coil Heat Exchanger for Usage in Domestic Water Heating

Buildings represent approximately two-thirds of the overall energy needs, mainly due to the growing energy consumption of air conditioning and water heating loads. Hence, it is necessary to minimize energy usage in buildings. Numerous research studies have been carried out on evacuated tube solar collectors, but to our knowledge, no previous study has mentioned the combination of an evacuated tube solar collector with a parabolic trough collector and a helical coil heat exchanger. The objective of this paper is to evaluate the thermal behavior of an innovative evacuated tube solar collector (ETSC) incorporated with a helical coil heat exchanger and equipped with a parabolic trough collector (PTC) used as a domestic water heater. To design the parabolic solar collector, the Parabola Calculator 2.0 software was used, and the Soltrace software was used to determine the optical behavior of a PTC. Moreover, an analytical model was created in order to enhance the performance of the new model of an ETSC by studying the impact of geometric design and functional parameters on the collector’s effectiveness. An assessment of the thermal behavior of the new ETSC was performed. Thus, the proposed analytical model gives the possibility of optimizing ETSCs used as domestic water heaters with lower computational costs. Furthermore, the optimum operational and geometrical parameters of the new ETSC base-helical tube heat exchanger include a higher thermal efficiency of 72%. This finding highlights the potential of the heat exchanger as an excellent component that can be incorporated into ETSCs.

Design and Assessment of the Solar Energy Based Direct Steam Generation Supercritical CO2 Brayton Cycle

The aim of this study is to examine the performance of the supercritical CO2 Brayton cycle (sCO2-BC)with intercooling and reheating for low-temperature solar energy application. The heat required for the sCO2-BC is supplied from an evacuated tube solar collector. Energy and exergy analyses of the solar energy-assisted sCO2-BCwith intercooling and reheating are investigated. In addition, the effects of operating parameters like solar radiation, collector number, compressor, and turbine input pressure on system performance are examined parametrically.According to the findings of the analysis, the net power production is found to be 0.2687 kW. In addition, the solar energy-based sCO2-BC's energy and exergy efficiencies are found to be 3.68% and 3.95%, respectively. Moreover, it has been determined that the sCO2-BC's energy and exergy efficiencies reduce with the increase of solar irradiation, the collector number, and the compressor inlet pressure, while the system's energy and exergy efficiencies rise with the increase of the turbine input pressure.

Development of infrared-assisted hybrid solar dryer for drying pineapple slices: Investigation of drying characteristics, mass transfer parameters, and quality attributes

The research aims to the development and performance evaluation of an infrared-assisted hybrid solar dryer (IR-HSD) for drying pineapple slices. The IR-HSD contains an evacuated tube solar collector, blower assembly, drying chamber, infrared heater, phase change material (PCM) chamber, etc. The study investigates and compares the thermal profiling, drying kinetics, mass transfer parameters and quality attributes of pineapple slices dried using different methods, such as direct drying, phase change material (PCM)-assisted drying, PCM + IR-assisted drying, and sun drying. The average temperatures achieved inside the drying chamber for direct drying and PCM-assisted drying were 60.16 °C and 57.29 °C, respectively, while the temperature reached 60 °C for PCM + IR assisted drying. The average drying rate in PCM + IR drying was higher than in direct and PCM-assisted drying methods. The best-fitting models were the Modified Page model for direct and PCM + IR-assisted drying and the Midilli-Kucuk model for PCM-assisted and sun drying. The higher effective moisture diffusivity for PCM + IR-assisted drying was 2.59 × 10−9 m2/s, followed by direct and PCM-assisted drying. Similarly, the convective mass transfer coefficient obtained was 1.085 × 10−7 m/s, 8.321 × 10−8 m/s, and 1.381 × 10−7 m/s for direct, PCM-assisted, and PCM + IR-assisted drying, respectively. The superior quality attributes such as total flavonoid content (TFC), total phenolic content (TPC), and antioxidant activity were observed in all drying approaches with retention of colour except open sun drying, which decreased significantly. FTIR spectroscopy analysis confirmed the presence of different bioactive, including aromatic compounds, phenols and hydrocarbon functional groups. The infrared-assisted hybrid solar drying of pineapple slices showed a better drying process and quality attributes.

Experimental investigation of a solar evacuated tube collector embedded with a heat pipe using different nanofluids and controlled mechanical exciting pulsations

Numerous studies have been conducted to enhance the thermal performance of evacuated tube solar thermal collectors using various techniques, such as different working fluids, concentrators, and modifications to the absorber design. This work presents a parametric study to improve the thermal performance of a solar-evacuated tube collector embedded with a heat pipe (SETCHP) by utilizing different types of nanofluids and controlled mechanical excitation. The experiment involved six identical SETCHPs operating under the same conditions, with one setup filled with pure acetone as a reference. The second and third setups were filled with (0.5% vol Al2O3)/based acetone and (0.5% vol CuO)/based acetone, respectively. The remaining three setups were modified by imposing controlled mechanical excitation with different frequencies (27–82 Hz) to investigate the effect of vibration on thermal performance. The results demonstrated that the optimal enhancement was achieved with mechanical vibration pulses at 82 Hz, improving efficiency by 91% and 86% with Al2O3/based acetone and CuO/based acetone, respectively. The enhancement percentage of effective heat transfer coefficient (EHTC) and convective heat transfer coefficient (CHTC) varied with solar intensity and vibration, with improvements ranging from 5 to 82% and 3–53%, 26–160% and 5–60%, and 6.5–140% and 6.5–54% for pure acetone, Al2O3, and CuO (0.5% vol) acetone-based nanofluids, respectively.

An investigation of serial connected U-pipe evacuated tube solar collector performance using TiO2/Water nanofluid

U-pipe evacuated solar collector is one of the efficient ways to convert solar energy to heat. In this study, different from the literature, thermal efficiency and pressure drop of a solar collector established with serial connected U-pipe evacuated tubes are investigated. However, a nanofluid has been used in the experimental studies with different concentration ratios. The experimental studies have been performed with water and TiO2/water nanofluid. Thermal efficiency and pressure drop of the collector have been experimentally investigated with different working concentration ratios of the fluid at constant solar radiation rate. Efficiency increased by 14.3% to 22.1% compared to water when using a 2% concentration fluid with decreasing reduced temperature. The highest collector efficiency was 80% approximately with using 2% TiO2 concentrated nanofluid. At the same time, the lowest value was almost 60% with water at 0.033 reduced temperature conditions. Pressure drop of working fluid increased 17.7% with using 2% concentration ratio than water at 40 ℃ average collector temperature. With increasing average collector temperature, pressure drop of working fluid decreased. Similarly, the maximum pumping power was obtained with a 2% concentrated fluid of about 52 W. The results of this study are expected to contribute to filling this deficiency in the literature.

Performance evaluation of an enhanced self-storing evacuated tube solar collector in residential water heating application

Phase change materials (PCMs) offer higher levels energy storage density than conventional hot water tanks commonly used with solar hot water systems. The present study aims at investigating the integration of a selected PCM within the structure of an evacuated tube solar hot water system to create some compact thermal storage capacity. Then conventional solar water heater is compared with this novel PCM-based self-storing design. The results show that the proposed self-storing design can maintain the collector output temperature at around 63 °C after 15 h of not receiving any sunlight. That is whilst the output temperature of the normal collector drops down to ambient temperature in the same period. The obtained energy storage efficiency is 57 % and 75 %, and overall thermal efficiency is 49 % and 72 %, for the normal and the self-storing collectors, respectively. For the small-scale system used in this study, the proposed design helps reduce the size of the hot water storage tank required to supply the hot water demand by 55 %. The study also shows that the same design can even yield better performance at larger scales used in practical applications.

Unsteady-state thermal performance analysis of cascaded packed-bed latent thermal storage in solar heating system

Thermal storage system is crucial to economically and stably utilize solar energy to address its volatility and fluctuation. A cascaded packed-bed latent heat storage system combined with solar evacuated tube collector is constructed in this paper, and the dynamic thermal performances are numerically investigated. The solar evacuated tube collector model is established to simulate the heat transfer fluid (HTF) charging process, which is experimentally verified by comparing the inlet/outlet temperatures. A latent heat storage system in three-stage packed-bed using phase-change materials with different melting temperatures ranging from 311 K to 335 K is modeled by enthalpy-porosity method, which is validated by comparing with the experimental data of literature. Then, the solar thermal storage system is integrated, and the impacts of the mass flow rate of HTF, solar collector area and initial temperature of packed-bed on its dynamic energetic and exergetic performances are analyzed. The results and discussions are analyzed to obtain optimal operation conditions. The increase of mass flow rate by 0.04 kg/s declines the maximum temperature by 9.53%. The initial temperature of packed-bed ranging from 293 K to 300 K achieves higher HTF temperature, heat storage efficiency and charging capacity. The solar collector area is necessarily matched to the phase-change materials to obtain high efficiency and also avoid HTF vaporization.