Collector Outlet Temperature Research Articles

Exploring forced convective solar drying of henna (Lawsonia inermis) and its effect on the biological activities: Comparison with open sun dried product

The first focus of this study is to investigate the design and behavior of locally built solar dryer during processing henna leaves. This was performed through the determination of the most important parameters that effect drying process. Appropriately, it was found that solar radiation has a direct effect on the collector outlet air temperature and consequently the product moisture content. Accordingly, high radiations lead having high air temperature at the drying chamber and consequently, the moisture content will decrease rapidly. Similarly, lower radiations will still lead to decrease of the moisture content, however, the drying rate will be less important than at high radiations. On the other hand, air velocity has an inverse dissipative effect of the energy and its increase leads to the decrease of the outlet temperature of the solar collector. Indeed, the highest outlet temperature from the solar collector was around 32 °C at an air velocity of 2 m/s. At 5.5 m/s, this temperature dropped to around 27 °C. The second objective of this study is to present the effect of different drying methods (i.e. forced convective solar drying and open sun drying) of Lawsonia inermis on the content of secondary metabolites (phenolic and flavonoid compounds) and compare the results with fresh henna samples. The yield of phenolic compounds was determined, and the dry crude extracts were found to be richer than the fresh sample in all of the drying modes used. The best yields are obtained with convective solar dryer and open sun drying samples (28.6 and 13.93%), respectively. The total phenolic and flavonoid contents of convective solar dryer product were 25 and 10% higher than open sun dried samples. Antioxidant tests (DPPH, ABTS, and ferric reducing power) revealed the scavenging and reducing abilities of the extract dried with the solar dryer. The values of antioxidant capacities measured by the three different methods were all consistent, appropriate, and highly correlative for assessing total antioxidant capacities. The solar dryer allows the preservation or even the increase of the antioxidant activity of the tested extracts.

Investigation of thermal performance, drying characteristics and environomical analysis: direct flow evacuated tube solar drying of okra.

A direct flow evacuated tube solar dryer (DF_ETSD), a novel drying system, was used for drying pre-treated okra (Abelmoschus esculentus). The performance of DF_ETSD was analysed by determining thermal profiling, dryer and collector efficiency hourly. The maximum 3-day average ambient temperature, collector outlet temperature and solar radiation were 35.6°C, 66.4°C and 976 W m-2 respectively. The collector efficiency increased as solar radiation increased over time due to a higher temperature difference between the collector outlet and ambient temperature. The maximum collector and dryer efficiency observed were 30.19% and 21.47%, respectively. A pre-treatment of okra was done in hot water at 70, 80 and 90°C for 5min. Okra samples were dried from an initial moisture content of 87.42 ± 1.49% (wb) to a final value of 10.77 ± 1.03% (wb) in 9h. The pre-treatment temperature of 80°C is suitable for maximum drying rate, colour retention and rehydration ratio and minimum water activity, which signifies the longer shelf-life of okra. Midilli and Kucuk model was best fitted (highest R2, lowest χ2 and RMSE) for the control and samples pre-treated at 80°C; however, Verma model was suitably fitted for the sample pre-treated at 70 and 90°C. The payback period of DF_ETSD was found to be 1.27years. Environmental analysis shows the CO2 emission and net CO2 mitigation ranged between 1.24 and 18.65 t and 9.86 and 154.05 t respectively for different selected lifecycles of the dryer. Due to its environmental sustainability and low payback period, the presented drying system is recommended for okra and other fruits and vegetables.

Thermal and dynamic improvement of a double pass solar air heater for drying applications

The low efficiency of solar thermal systems is a drawback that hinders the effective utilization of renewable energy. In this context, a feasibility study was conducted on a double-pass solar air heater designed for solar drying applications. Given that low efficiency often results from inefficient thermal conversion, an optimization of the V-shape absorber was performed by varying the corrugation angle. The CFD method, validated by experimental results, was employed in the current study. The meteorological station located at Mohamed First University in Morocco provided real and unstable weather conditions that were inserted into the software. The results obtained were analyzed and discussed regarding the air domain temperature, collector outlet temperature, collector efficiency, and average drying tray temperature together with its distribution. The findings show that the average air temperature and outlet temperature reach a maximum of 345.53 k and 365.5 k, respectively. For absorber corrugation angles of Φ=100°, a maximum collector efficiency of 86% was achieved. In addition, different mass flow rates (MFRs) ranging from 0.003 to 0.068 kg/s were evaluated in this study. From the results, it was noticed that the optimal MFR varies depending on the products to be dried, with values of 0.028, 0.035, 0.049, and 0.068 kg/s for sweet potato, fig, cauliflower, and orange, respectively.

Drying of the orange slices, and energetic analysis of the drying chamber alimented by a solar air collector for extraction of the water from an orange slice

This study is focused on the extraction of water from sliced oranges through the process of solar drying, while also integrating an energy analysis of the drying chamber, which is powered by a solar air collector for the water extraction process. The experimental investigation encompasses various parameters, including the dimensions of the drying chamber, the solar collector, and the geometry of the orange slices (with a diameter D of 80 mm and thicknesses of ep = 3 mm and 5 mm). The results present the moisture ratio of the orange slices over the drying time and mass flow rate, with three different values (0.019, 0.024, and 0.033 kg/s). Throughout the experiments, the distance between the product support and the drying chamber's heat source was maintained at 140 mm. The report provides an energetic analysis that encompasses the enthalpy of the product, water, vapor, drying chamber, solar collector, and latent heat, all contributing to the control of the drying system. The effects of different mass flow rates (0.019, 0.024, and 0.033 kg/s) on the drying process are also examined in this study, with a focus on the important effects on the moisture ratio and drying velocity. Ultimately, the findings demonstrate that the mass flow rate plays a crucial role in determining the outlet temperature of the solar collector and the inlet temperature of the drying chamber, thereby affecting the kinetics of the drying process and the resulting moisture ratio.

An experimental investigation of the thermal performance of solar collectors utilizing finned aluminum can pipes

An innovative experimental study is presented to improve the performance of solar collectors designed for solar drying systems, focusing on the use of recycled aluminum can waste and the development of the air solar collector. The latter’s absorber is made up of 10 cans with a diameter of 65 mm, a length of 160 mm and a thickness of 0.3 mm, forming a cylindrical finned pipe. Several collector configurations under identical weather conditions, including four collectors with different rows of rods (4, 8, 12–14 rows) and a single collector, were analyzed and compared. The thermal performance of this new collector model was assessed on the basis of solar fluxes and collector inlet and outlet temperatures, collected during the month of September 2021. Experimental results revealed that this collector can increase the outlet temperature of air from 32°C up to 130°C, in the case of a 14-row collector. The study also showed that, at low flow rates, the can-equipped collector achieves an efficiency of 54% for the case of a 14-row collector, compared with 34% for the simple case, representing a 20% improvement over the single case. The study also showed that, at low flow rates, the can-equipped collector achieves higher outlet temperatures.

Integrated photovoltaic-thermal system utilizing front surface water cooling technique: An experimental performance response

In the realm of photovoltaic-thermal (PVT) systems, optimizing operating temperatures for photovoltaic (PV) panels is a challenge. This study introduces a novel solution: a sprayed water PVT system that simultaneously harnesses energy and electricity. The aim is twofold: generate electricity through PV panels and produce hot water via a flat plate collector, using an innovative cooling mechanism. Water sprayed onto the PV panel's surface flows to a collector for storage. With varied flow rates, optimal panel efficiency occurs at a 45⁰ tilt angle, accompanied by lower collector outlet temperatures at higher flow rates. The collector achieves a peak thermal efficiency of 70.6 %, producing hot water at 84.6 °C. Notably, a significant PV panel efficiency enhancement, up to 16.78 %, especially at 1.56 L/min flow rate, is observed. The cooling technique consistently reduces panel temperatures from 45.08 °C to 34.12 °C. A self-cleaning spray mechanism improves efficiency by 2.53 %, resulting in an overall system efficiency of 83.3 %. This research offers an innovative approach to enhance energy generation and electricity in PVT systems, promising sustainable energy optimization.

Coordinated control strategy for concentrated solar power systems considering active defocusing

With an increasing proportion of renewable energy in the energy structure, concentrated solar power plants are required to respond rapidly to automatic generation control (AGC) commands, to ensure the grid stability when connected to the grid. Active defocusing affects the collecting capacity of the collector, which not only serves as a safety protection measure for system operation, but also improves the system load shedding rate and provides the possibility of system participation in the auxiliary service of grid frequency regulation. In this paper, a coordinated control strategy for parabolic through concentrated solar power (PTCSP) system considering active defocusing of collector is proposed. The coordinated controller utilizes four manipulated variables, including mass flow rate of heat transfer oil in the collector, active defocusing angle, mass flow rate of molten salt in the heat storage system, and main steam valve opening, to regulate three output variables, namely, collector outlet temperature, turbine power, and main steam pressure. By integrating the steady-state defocusing angle in the optimization function, the controller can utilize the extra control freedom degree to improve the control effect, and ensure that the final steady-state defocusing angle to be small, which reduces the unnecessary heat collection loss. The proposed control strategy improves the power response rate and also avoids excessive heat transfer oil temperature and main steam pressure. In the simulations featuring two 20% variations in load target value, the root mean square error of the outlet temperature of the collectors is reduced by 0.094, and the heat storage is reduced by 0.99 MWh.

Improvement of the classical artificial neural network simulation model of the parabolic trough solar collector outlet temperature and thermal efficiency using the conformable activation functions

The outlet temperature and the thermal efficiency predictions of the PTSC are essential parameters in the solar thermal power system. Therefore, it is crucial to have a prediction model that can predict its spatiotemporal behavior to the greatest extent possible. For that, the present study provides improved models of the classical ANN model by using ELU, swish, softplus, logsig, and tansig functions through the exponential transfer function to improve the outlet temperature prediction performance and thermal efficiency of PTSC. The PTSC’s outlet temperature simulation showed that the ANN model of topology 6-2-1 with the conformable swish transfer function (cswish) was the best model among nine other studied models, with an R2 and Radj2 of 0.9988, and MAE of 0.0052. The simulation of PTSC’s thermal efficiency proved that the conformable functions logsig, tansig, ELU and the classical ELU function involved in the ANN model for 6-3-1 achieved better results with approximately 95% precision. With the non-integer activation functions, was reduced a neuron in the hidden layer, which leads to the simplicity of the prediction model compared to the use of the classical activation functions. The proposed activation functions do not require high-performance features according to their execution times. Therefore, it could be a good alternative for engineers to apply in other thermal energy systems to make their prediction models more accessible and practical in the control and optimization process.

Performance analysis of a forced indirect cabinet solar dryer for drying figs

In the solar drying process, a lower air velocity is unable to rapidly extract moisture from the products to the outside, while a higher air velocity has a negative effect . To improve the final quality of the dried products, the effect of air inlet velocity (0.1, 0.3, and 0.5 m/s), air outlet position, and inlet size of an indirect solar dryer operating in forced convection was studied . The Computational Fluid Dynamics (CFD) method, validated by experimental results, was used for this investigation while the meteorological data used to define the boundary conditions are exported from the meteorological station. The obtained results show that the average temperature of tray 1 reaches 314, 311.75, and 311 K for the right, middle, and left outlet positions, respectively, with an inlet velocity of 0.1 m/s. In addition, the average collector outlet temperature is higher (329 K) for the 0.05 m inlet size. The trays temperature peaks at 2 pm on the selected day, with an average temperature of 326 and 324 for trays 1 and 2, respectively. Based on the current results, the farmers will have a good insight into the parameters for the realisation of a solar dryer.

Development and assessment of a thermochemical cycle and SOFC-based hydrogen energy system as a potential energy solution for the peak demand in a sustainable community

In this study, an integrated energy system is presented in which hydrogen is produced via the thermochemical cycle. The presented system would provide a potential solution for storing excess electric power in terms of hydrogen generation for a sustainable community. Principles of exergy and energy are utilized to analyze the presented system in terms of exergy and energy efficiencies. The simulation result shows that with the help of the developed system, 0.36 kg/h of hydrogen can be generated, which is utilized via SOFCs to produce and electrify the houses. Additionally, 1000 kW of electric power with 3.6 kW of heating can be supplied via the developed system. With the use of thermochemical cycle considered in the present study, one can produce hydrogen with an energy efficiency of 79.6% and exergy efficiency of 62.9%. Furthermore, to see the impact of different factors on the operation of the developed system, a parametric study is also conducted by changing factors like solar irradiation, the inlet temperature of the molten salt, and the outlet temperature of the solar collector.

An Effective Standalone Solar Air Gap Membrane Distillation Plant for Saline Water Desalination: Mathematical Model, Optimization

Several drinking water production techniques are being established to respond immediately to the growing needs of the population. The system of air gap membrane distillation (AGMD) is the best attractive option for the process of water desalination. This thermal process is characterized by its potential to provide drinking water at low energy costs when combined with solar energy. In this paper, the AGMD brackish water desalination unit potentialities coupled with solar energy were investigated. Ghardaïa of the south region has been considered as the field of our study. Mathematical modeling is investigated by employing MATLAB software to develop the prediction of the permeate flux related to the phenomena of heat and mass transfer. Herein, flat plate solar collectors (SFPC) were exploited as a source for heating saline water through free solar energy conversion. The further model validation of a flat solar collector made it possible for following the instantaneous evolution of the collector outlet temperature depending on the feed water temperature and the flow rate. Furthermore, it is interesting to note that the results prove the possibility to produce water by the solar AGMD process with a maximum permeate flux of 8 kg·m−2·h−1 achieved at 68 °C, a feed temperature. Moreover, gained output ratio (GOR) of the unit of thermal solar desalination was estimated to be about 4.6, which decreases with increasing hot water flow and temperature.

Performance analysis and drying kinetics of beetroot slices dried in an innovative solar dryer without and with thermal storage unit

ABSTRACT An active indirect solar dryer (AISD) has been used to conduct drying experiments of beetroot slices without a thermal storage unit (TSU) (mode-I) and with TSU (mode-II) using paraffin wax as a phase change material. The performance analysis and drying curves of beetroot slices were assessed in both modes and compared. The average drying efficiency and drying rate were enhanced by 48.63% and 41.72% in mode-II compared to mode-I. Two-term exponential and modified Page models were the best models for beetroot slices in mode-I and mode-II, respectively. The specific energy consumption was estimated to be 1.706 and 0.96 kWh/kg, the average moisture diffusivity was 7.11 × 10−9 and 7.22 × 10−9 m2/s, and the mean mass transfer coefficients were 3.56 × 10−3 and 3.64 × 10−3 m/s, respectively. The specific moisture extraction rate was 0.586 and 1.041 kg/kWh and the mean heat transfer coefficient was 4.103 and 4.2 W/m2K, in mode-I and mode-II, respectively. The collector outlet temperature is increased by 2.5 to 10.7°C when the heat is discharged from TSU. In comparison to mode-I, the performance of AISD is superior in mode-II, exhibiting better drying performance due to TSU in the drying section in mode-II.

Drying characteristics and quality analysis of pre-treated turmeric (Curcuma longa) using evacuated tube solar dryer with and without thermal energy storage

Turmeric (Curcuma longa) was dried using evacuated tube solar dryer with and without thermal energy storage to investigate the thermal performance of the dryer, drying characteristics, and quality attributes of pre-treated (control, peeled and cured sample) turmeric slices. Two pre-treatments i.e. curing at 100 °C for 45 min and peeling of fresh turmeric was considered for the study. A comparative study of drying characteristics, mathematical modeling, and quality parameters i.e., colour, total phenolic content, antioxidant scavenging activity, curcumin content was conducted using evacuated solar dryer with phase change material (ETDP) and without PCM (ETD). Average dryer chamber, highest collector outlet and ambient temperatures were 57.8 °C, 77.2 °C, 42.9 °C, and 69.4 °C, 79.4 °C, 42.6 °C for ETDP and ETD respectively. Turmeric samples are dried from initial moisture content of 84.6% (w.b.) to a final moisture content of about 13 to 8.8% (w.b.). Highest drying rate of 17.68 g/gdm-h for cured sample using ETDP while 28.21 g/gdm-h for peeled sample using ETD was observed. Two term model was best fitted for both ETD and ETDP for control and peeled turmeric drying, however Modified Page model was best fitted for cured turmeric. Highest diffusivity of 1.97 × 10-10 m2/s was observed for cured turmeric sample dried using ETD. Cured turmeric sample dried using ETDP retained highest curcumin content: 7.49%, AA:65.92%, TPC:22.38 mg GAE/g and b*:58.63 while cured sample dried using ETD dried fastest.

Experimental and numerical analysis of a grooved hybrid photovoltaic-thermal solar drying system

• CFD analysis of grooved plate, spherical turbulators and baffles in a PVT collector. • Testing of the developed PVT collector in a drying application at two flow rates. • Overall exergy efficiency of PVT system was found in the range of 10.65-11.17%. • Exergy efficiency of drying chamber was attained between the range of 59.16-68.31%. Photovoltaic-thermal (PVT) systems are sustainable applications that allows to produce thermal and electrical energies simultaneously. In this work, a sustainable solar drying system that contains a modified PVT-air collector has been designed, numerically analyzed, manufactured and tested. In the first step of this study, four different PVT collector configurations have been numerically analyzed in order to develop a new hybrid PVT drying system. According to the numerically obtained results, outlet temperature of the PVT collector with grooved absorber, spherical turbulators and baffle configurations was higher than the outlet temperature of the unmodified collector as 15.77%. This promising PVT collector was then fabricated and integrated with a drying chamber. The manufactured hybrid drying system has been tested under various air flow rates. The experimental findings illustrated that the average thermal efficiency and overall exergy efficiency of the PVT collector varied between 61.32-77.49% and 10.65-11.17%, respectively. In addition, mean exergy efficiency of the drying chamber was found in the range of 59.16-68.31%. Average sustainability index values of the collector and the drying chamber was obtained between the ranges of 1.12-1.14 and 3.74-5.82, respectively. Moreover, payback period of the dryer varied between 2.98-3.51 years according to the economic analysis.

Thermodynamic Modeling and Analysis of a Solar and Geothermal-driven Multigeneration System Using TiO2 and SiO2 Nanoparticles

In this study, renewable energy sources including a high-temperature solar parabolic trough collector and geothermal water integrated with a modified Kalina cycle, a combined ORC-EJR cycle, an electrolyzer, an RO desalination unit, and a domestic water heater. SiO2 and TiO2 nanoparticles dissolved in Therminol VP1 are applied as the working fluid of the solar collector. A comparative analysis of introduced working fluids is performed from energy, exergy as well as cost analysis point of view to evaluate their efficiencies. Solar irradiation, ambient temperature, and collector inlet temperature were the parameters investigated to discover their effects on energy and exergy efficiency, solar collector outlet temperature, hydrogen production rate, and freshwater production rate. The highest generated outlet temperature of the solar collector outlet was 693.8 K obtained by Therminol VP1/SiO2 nanofluid. The maximum energy and exergy efficiencies of the proposed system were 36.69 % and 17.76 %, respectively. Moreover, it is found that by increasing the solar collector inlet temperature, the hydrogen production rate decreases while the water production rate increases.

Integration of decentralized solar collectors into a district heating system

• Development of the prototype of the prosumer heat substation with solar collectors. • Experimentally validated TRNSYS model of the prosumer heat substation. • Key factors influencing stability of the feed-in temperature from the solar collectors. • Proposals for DH operators for integration of prosumers with solar collectors. This study focuses on the integration of small capacity prosumers in district heating networks. The challenge for installations with solar collectors lies in the fact that fluctuations in cloud cover and pressure drops in the network are unpredictable. Therefore, it is more difficult to ensure a stable feed-in temperature that meets the technical requirements of the district heating network. For this, an experimental prototype with flat plate and vacuum thermal collectors was developed and the TRNSYS simulation model was created. The model has been validated using data from the test facility. Multiple simulations have been performed to analyse various options for improving the stability of the feed-in temperature. An analysis of the change in the temperature of the heat carrier on sunny and cloudy days in three control modes was carried out. It showed that the temperature fluctuation depends both on weather conditions and "idling" and "rotating" time intervals of the three-way valve. Results of the study show that the cloud cover has a strong influence on the stability of the collector outlet temperature. Fluctuations in the feed-in temperature need to be compensated for by changing the flow rate and different strategies for operating the three-way valve, which become a challenge in real-life conditions with fluctuating differential pressure in the district heating network.

On the thermal performance of evacuated tube solar collector integrated with phase change material

The aim of present work is to analyze a U-type of evacuated tube solar collector in which phase change material (PCM) is employed to store surplus solar energy in daytime and reuse it at nighttime when the solar irradiation vanishes. Both charging and discharging processes are considered and modeled. Two critical points should be considered in designing the proposed collector; the stable requirement outlet temperature of the domestic solar collector during daytime (about 40°C) and assurance of a complete melting/solidification process to reach the maximum energy storage and release. Since the absorbed energy from solar radiation by heat transfer fluid and PCM in both day and nighttime strongly depends on the U-type tube's diameter, three values of which (namely, 6, 8, and 10 mm) are selected to attain the best case. The results show that the case with 6 mm diameter yields a 25% and 13.5% improvement in the liquid fraction and fluid outlet temperature, respectively, at 3:00 PM in the charging process, compared to other cases. Also, this case has achieved a 20% delay in the thermal energy release process and has increased the fluid outlet temperature by 24%, compared to other cases, at 9:00 PM in the discharging process.

Investigation of the thermodynamic analysis of solar Energy-Based multigeneration plant for sustainable multigeneration

Renewable energy-based multigeneration plants are a huge potential to tackle environmental problems and also to the passing of the carbon-free future. The main goal of the present research is to design and examine the combined cycle motivated by solar energy for multigeneration which is power, hydrogen, ammonia, and freshwater generation. The innovative design multigeneration system is made up of a parabolic trough solar collector, a steam Rankine cycle with high and low-pressure turbines, a transcritical Rankine cycle with a carbon-dioxide fluid, a desalination part, a Proton Exchange Membrane electrolysis, and an ammonia reactor. A comprehensive thermodynamic analysis, environmental impact assessment, and exergo-environmental analysis are addressed to determine the performance and carbon dioxide emission reduction of the overall plant. Furthermore, in this planned research, a thorough parametric evaluation is performed to define how the variation of some significant parameters (e.g., ambient temperature, solar radiation, and collector outlet temperature) has an impact on the cycle’s efficiency and useful outputs. The findings of the research analysis indicated that the total net power and hydrogen production capacities are 1654 kW and 0.0025 kgs-1. The irreversibility rate is determined as 7047 kW and the parabolic trough solar collector has the uppermost rate among the components. Furthermore, energetic and exergetic performances of the modeled cycle are computed as 29.04% and 27.43%, respectively. Finally, freshwater and ammonia production rates are determined as 1.182 kgs-1 and 0.004842 kgs-1, respectively.

A Numerical Investigation Into the Flow Development and Heat Transfer Characteristics for Different Tube Geometry Configurations in a Water in Glass Evacuated Tube Solar Water Heater

Abstract This study aims to numerically assess the heat transfer performance of water-in-glass evacuated tube solar water heater (WGET-SWH) for various parameters. It is observed that the natural circulation flowrate, velocity, and temperature distribution are strongly dependent on WGET-SWH geometry and operating conditions. The natural circulation flowrate is found to be increasing with tube length, diameter, inclination angle, and circumferential heat input. However, the heat transfer rate decreases with an increase in aspect ratio. The average Nusselt number increases with an increase in inclination angle till 45 deg and then decreases. Also, the study shows that thermal stratification in reservoir fluid is greatly influenced by circulation flowrate, flow momentum, collector outlet temperature, thermal acceleration, and buoyancy effect.

Comparison of the performance of fixed and two-axis movable solar air heaters with different methods

ABSTRACT Usually, the solar air heater (SAH) is placed in a fixed position based on the tilt angle. This situation adversely affects the thermal performance of the collector, considering the natural motion of the sun. In this experimental study, two SAHs of equal dimensions were designed. A PLC solar tracking system was integrated into one of the SAHs to track the sun in two directions (East-West, North-South). The thermal efficiency values of the SAHs were calculated according to three different mass flow values of the air in the SAH by using the “I” and “II” laws of thermodynamics. It was observed that movable SAH has two times more average heat transfer value, 47.8% more energy efficiency, 2.4 times more exergy efficiency, 20% more coefficient of performance (COP) value, and 23.8% more average collector outlet temperature than fixed SAH. In addition, it was measured that the average irradiance on the absorber plate in the movable SAH is 38% higher than the fixed SAH. After, CFD analysis modeling was carried out for SAH outlet temperature values. The SAH outlet temperature values modeled by CFD analysis were compared with the experimental results. SAH outlet temperature value model was modeled by CFD with less than 1% error value for turbulent flow. As a result of the calculations made with experimental data, it was shown that the PLC tracking feature was an important method to use solar energy more effectively on SAH.