Double-pass Solar Collector Research Articles

Exergy efficiency and sustainability indicators of forced convection mixed mode solar dryer system for drying process

The study investigates the effectiveness of a mixed-mode solar dryer (MSD) featuring two double-pass solar air collectors in series, with a focus on dehydrating cluster figs characterized by high moisture content and rapid deterioration. Exergy analysis is a powerful tool to assess the efficiency and sustainability of drying systems. The study involves experimental data obtained from the drying process under different air mass flow rates (0.018–0.062 kg/s). The solar radiation intensity ranged from 120 W/m2 to 750 W/m2 during these experiments. The solar air collectors and mixed mode dryer exergy efficiency is found to be dependent on solar radiation intensity, showing increased efficiency with higher air mass flow rates due to enhanced heat removal and reduced losses to the surroundings. The findings reveal that the optimal air mass flow rate of 0.062 kg/s yields the highest exergy efficiency in the solar air collectors. The overall exergy efficiency of the mixed-mode solar drying chamber increases with higher air mass flow rates, ranging from 18.8 % to 41.4 %. Improvement potential (IP) analysis indicates that, as the air mass flow rate increases, the potential for reducing exergy losses decreases. The sustainability index (SI), measures the environmental impact, and it ranges from 1.26 to 1.71, with higher values associated with higher exergy efficiency.

Influencing Factors Used for Performance Evaluation of Solar Dryers

Due to the rapid growth in human energy demand, research and development in renewable energy sources have become a top priority. Solar energy, as a renewable energy source, is widely used in the drying industry. This study examines the factors that influence the performance evaluation of solar dryers. The dryer consists of an air collector, a drying chamber, and a chimney. Experiments were conducted at the Solar Energy Laboratory of the Hungarian University of Agriculture and Life Sciences in Hungary (47.59° N, 19.36° E). The drying behaviour of single-pass and double-pass solar dryers was compared under the same environmental conditions. The analysis results indicate that the maximum solar radiation value is 950 W/m2 at 12:00. The maximum temperature difference between the top and bottom channels of the double-pass solar air collector is 9.5 °C. The average humidity in the environment, single-pass, and double-pass drying chambers is 31%, 26.5%, and 24%, respectively. The instantaneous efficiency of the single-pass solar collector reaches a peak of 56%, while the double-pass collector’s instantaneous efficiency peaks at around 60%. The collector performance curves show that the double-pass collector has a more stable performance.

Mathematical modeling and performance evaluations of a wood drying process using photovoltaic thermal and double-pass solar air collectors

This research conducts a novel and complete 4E assessments and introduces an innovative method for examining solar wood drying systems. The software TRNSYS and MATLAB programming are combined to simulate and create a numerical program. This novel combination allows for a thorough examination that goes beyond conventional assessments of wood drying. The aim is to evaluate the effectiveness of a solar wood dryer using two different collectors, a double-pass and a photovoltaic thermal collectors, in terms of four key aspects: energy, exergy, economic, and environmental. Further, the drying process was investigated under various climates in three African cities (Errachidia, Dakar, and Nouakchott). The moisture content of wood was reduced from 74% to 12% in the three cities. Elaborate simulations were performed and the results were confirmed by experimental validation, using methods including Mean Absolute Error, Mean Relative Error, and Root Mean Square Error. The primary findings of this study are the following: In the double-pass dryer, the drying time required in Errachidia, Dakar, and Nouakchott was 139h, 189h, and 170h, respectively. Whereas in the photovoltaic thermal dryer, it needed 192h in Errachidia, 210h in Dakar, and 189h in Nouakchott. Further, using photovoltaic thermal, the dryer exhibited superior exergy efficiency compared to the use of double pass collector. Photovoltaic thermal collector reduces yearly CO2 emissions by an average of 54.87, 66.2, and 44.11 tonnesCO2 in Errachidia, Dakar, and Nouakchott, respectively. In contrast, double pass collector reduces CO2 emissions by an average of 38.49, 57.9, and 38.56 tonnesCO2 in Errachidia, Dakar, and Nouakchott, respectively, throughout the year. Further, the solar dryer, using double pass collector, has a shorter payback time than using photovoltaic thermal collector, indicating a quicker economic return.

Enhancing thermal efficiency of double-pass solar air collectors: A comparative study on the role of V-angled perforated fins

This study investigates the enhancement of thermal efficiency in double-pass solar air collectors (DPSACs) by incorporating V-angled perforated fins. It compares the performance of a finned model (FDPSAC) with a conventional smooth model, aiming to optimize thermal efficiency through improved heat transfer and air distribution. The experiments were conducted under three airflow rates: 0.00864 kg/s (Case I), 0.01143 kg/s (Case II), and 0.01317 kg/s (Case III). The findings indicated that the FDPSAC significantly outperformed the DPSAC, achieving higher outlet temperatures and demonstrating superior heat gain. The daily efficiency for the FDPSAC was 51.6 %, 54.7 %, and 59.2 %, exceeding the DPSAC, which were 49.4 %, 50.5 %, and 53.9 % for cases I, II, and III, respectively. The daily collector efficiency of the FDPSAC improved by approximately 4.45 %, 8.32 %, and 9.83 % relative to the DPSAC for the same case order. The results also showed that the FDPSAC maintained lower temperatures of the absorber plate, suggesting more effective heat dissipation and overall system efficiency. This study highlights the critical role of innovative fin design and optimal airflow management in enhancing solar collector performance. These improvements highlight the potential of the proposed fins to enhance solar air collector efficiency, providing key insights for optimizing thermal systems in sustainable energy.

Investigation of a Photovoltaic–Thermal Solar Dryer System with Double-Pass Solar Air Collectors and Absorber Surfaces Enhanced with Graphene Nanoparticles

As a result of increasing energy demand, seeking eco-friendly and sustainable energy resources increases the interest in renewable energy, specifically solar energy. In this study, a novel photovoltaic–thermal solar dryer system with double-pass solar air collectors and nano-enhanced absorber surface was developed, and its performance was experimentally investigated. Initially, a double-pass solar dryer (DPSD) with an absorber surface of flexible aluminum ducts coated with black matte paint was produced. Then, a double-pass solar dryer (NDPSD) consisting of flexible aluminum ducts coated with graphene and black paint was designed. These two systems were experimentally and simultaneously examined, and parameters such as energy and exergy efficiency, drying rate, and moisture ratio, which are the performance indicators of solar air collectors and the drying process, were analyzed. The sustainability parameters were also considered as a part of the analysis. The mean thermal efficiency of the solar air collectors for DPSD and NDPSD was calculated as 57.23 and 73.36%, respectively, where the airflow rates were measured as 0.024 and 0.017 kg/s. Furthermore, under the same airflow rate conditions, while the mean exergy efficiency of the collector was 27.77% for NDPSD, it was calculated as 16.64% for DPSD. Moreover, exergy efficiencies of the drying chamber varied between 27.35% and 82.20% for NDPSD and between 21.03 and 81.25% for DPSD, under the airflow rates of 0.012–0.016 kg/s conditions, respectively.

A MATLAB simulation-based analytical study of energy, exergy, and cost benefits in jet-impinged protrusion-roughened double pass solar air collector.

This study analyzes the performance and cost-effectiveness of a protrusion-roughened jet-impinged double-pass solar air collector (PRJDPSAC) within a Reynolds number (Re) range of 2500 to 22,500. Examining jet slot parameters, i.e., the jet height ratio (Hjp/Dhd = 0.11-0.44), stream-wise pitch ratio (Xjp/Dhd = 0.44-1.32), and span-wise pitch ratio (Yjp/Dhd = 0.44-1.32), the model demonstrates enhanced energy conversion, minimizes losses, improves efficiency, and brings positive economic impact, making it a promising solution for diverse applications including drying processes, livestock facilities, remote accommodations, and HVAC system pre-heating. The examination incorporates advanced MATLAB simulations to assess energy-exergy performance and cost viability. At lower Re values, both energy ([Formula: see text]) and exergy ([Formula: see text]) efficiencies increase uniformly; however, stabilization and decline occur at higher Re values. The maximum [Formula: see text] for the PRJDPSAC is 4.38% under a temperature rise parameter of 60 × 10-3 Km2/W for obtaining optimum values of Xjp/Dhd = 1.32, Hjp/Dhd = 0.22, and Yjp/Dhd = 1.32, which is 31% higher than that of the smooth double-pass solar air collector (DPSAC). Economic benefits are significant for PRJDPSAC within mair (0.01-0.07kg/s), but above 0.07kg/s, the DPSAC becomes more cost-effective. Integrating simulation and experimental data, the study highlights MATLAB's effectiveness for solar energy system analysis and optimization, reinforcing the practicality of the proposed collector design.

Numerical Analysis Study of a Convective Flow of Nanofluids in a Double-Pass Solar Collector

This paper presents a numerical analysis study of the dynamic and thermal performance of a convective flow of water-copper nanofluids in a double-pass flat solar collector. The flow inside the confined space between the glazing and the insulation is governed by the continuity, momentum, and energy equations. The problem addressed is solved via a CFD ANSYS code using the finite volume method to discretize the equations of the mathematical model. The dynamic and thermal fields are obtained for different values of the volume fraction (φ = 0%, φ = 3%, and φ = 8%). These results are compared with other results mentioned in the literature. The results obtained allowed us to define the influence of these different parameters on the convective nanofluid flow in the solar collector. The increase in the volume fraction further promotes heat transfer. The presence of nanoparticles expects a critical part of the convective heat exchange.

Thermal and Thermo-hydraulic Performance of Finned Double-Pass Solar Air Collector Utilizing Cylindrical Capsules Nano-Enhanced PCM

Double-pass solar air collector with a finned absorber and nano-enhanced PCM in the lower channel is one of the significant and attractive designs proposed to improve the performance. This research paper presents a novel mathematical model of steady-state equilibrium equations created and developed for two air streams: the glass cover, absorber plate, fins, nano-enhanced PCM capsules, and back plate. The influence of various operating parameters on thermal and thermo-hydraulic performance was presented and discussed. The simulations were conducted at air mass flow rates from 0.02 kg/s through 0.06 kg/s and solar irradiance levels ranging from 475 W/m2 to 1000 W/m2. The proposed collector has an optimal energy efficiency of 80%, an exergy efficiency of 18.2% at solar irradiance of 1000 W/m2, and a mass flow rate of 0.06 kg/s. The minimum and maximum improvement potentials for solar irradiance levels of 475–1000 W/m2 at an ambient temperature of 298 K are 163–237 W. The proposed collector's best findings in the current study are 1.0 m in length and a width of roughly 0.3 m for air mass flow rates of 0.02-0.06 kg/s.

Experimental and numerical analysis on the thermal performance of the aluminium absorber

The absorber is a vital part of a solar air collector and has a significant impact on the overall efficiency of a solar air heating unit. The objective of this research is to examine and compare the performance of two distinct aluminium absorbers with and without aluminium fins by using experimental and numerical (computational fluid dynamics – CFD) methods. The studies were conducted in Mandalay, Myanmar, which is located at latitude 21.98° N and longitude 96.1° E, during December 2022. A plate absorber solar air collector (PASAC) and finned absorber solar air collector (FASAC) with the same absorber area of 0.889 m2 are compared in terms of their thermal performance. At a mass flow rate of 0.0389 kg/s, the average thermal efficiency, as computed numerically, is 53.5 % for FASAC, and the experimental results show a thermal efficiency of 54.2 %. Similarly, for PASAC, the numerical computation yields an average thermal efficiency of 44.4 %, while the experimental results indicate a thermal efficiency of 47.3 %. The FASAC outperforms PASAC in terms of thermal performance. The improved thermal performance of the double-pass solar air collectors with aluminium-finned absorbers can be advantageous for employment as a drying process unit.

Mathematical Model of the Thermal Performance of Double-Pass Solar Collector for Solar Energy Application in Sierra Leone

The primary aim of this study was to utilize thermal energy for drying applications on March 21 (day of the year, n = 80) for the climatic weather conditions of Freetown, Sierra Leone. We evaluated the heat absorption of a double-pass solar air collector based on its configuration and exterior input variables before it was designed and mounted at the location of interest. This study considered a steady-state heat transfer using the thermal network procedure for thermodynamic modeling of a double-pass solar collector developed for drying and heating purposes. A mathematical model defining the thermophysical collector properties and many heat transfer coefficients is formed and numerically solved for this purpose. Indeed, this helped us generate the hourly temperature of different heat collector components, which aided in the performance evaluation of the system. The impact of the fluid flowing inside the collector on the temperature of the exit air was analyzed. It was observed that a flow rate of 0.02 kg/s produced an output of 91.72°C. The system's thermal efficiency improves with increased flow rate at various solar radiation intensities. It was observed that the thermal efficiency of the collector increases from 29% to 67% at flow rates of 0.01–0.3 kg/s. Collector lengths of 1.4 and 2.4 m are observed to be economically viable. An increase in the flow rate caused an increase on the efficiency. The hourly outputs for the collector components were represented graphically, and the curve patterns were similar to those of previous studies.

Performance Analysis of a Double Pass Solar Air Thermal Collector with Porous Media Using Lava Rock

This paper investigates double-pass solar air thermal collectors with lava rock as the porous media. The addition of lava rock serves as short-term sensible thermal storage for a solar drying system. It also enhances the convective heat transfer rate to the airflow due to an increased heat transfer area and increased turbulence in the air channel. A mathematical model was developed based on energy balance equations and was numerically solved in MATLAB. The collector’s thermal performance was studied at various levels of solar intensity and at different wind speeds for different design parameters: collector size, air mass flow rate, and lava rock volume. From the study, the optimum efficiencies that were obtained in the range between the intensities of 500 W/m2 and 800 W/m2 were 62% to 64%, respectively, with an optimum flow rate of 0.035 kg/s. The optimum porosity of about 89% was selected for the collector by considering the pressure drop and thermal efficiency. An optimal temperature output range between 41.7 °C and 48.3 °C could be achieved and was suitable for agricultural and food drying applications. Meanwhile, compared to conventional DPSAHs, the average percentage increase in the output temperature of the DPSAH with lava rock was found to be higher by 17.5%.

Parametric study of a solar dryer system for the development and application of solar energy in Sierra Leone

A transient mathematical model has been evaluated to determine the principle of a solar crop dryer for drying vegetables (onion). Considering the meteorological conditions of Freetown (Latitude 8.4840 N, Longitude -13.2300 W), the model was developed to determine air temperatures and other operational parameters of the drying system for a day of March 21st. However, the investigated system had effectively reduced the drying process of onion. The developed double-pass solar air collector system showed a low-temperature output in the morning hours and displayed high-temperature results in the afternoon hours. From 8:00 to 16:00, the solar collector generates fluid output temperatures above 50 0 C, with a peak value of 96 0 C occurred at 12:00. The influence of the mass flow rate on the system's thermal efficiency was investigated. It was noticed that for a certain solar radiation value, an increased in the mass flow rate caused an exponential increased in the solar air collector thermal efficiency. Findings also revealed that an increased in the solar collector length led to a slightly decreased in the outlet air temperatures at a mass flow rate of 0.02 kg/s. The influence of increasing drying air temperatures and air velocity within the drying chamber reduces drying time significantly. The drying time for products dried in the first tray is lesser than for products dried in the subsequent trays, owing to temperature variations. The computation findings were verified to previous studies in the literature and observed to be strongly comparable.

Thermal Performance of a Finned Double-Pass Solar Air Collector Integrated with a Nanoparticle Enhanced-Pcm Tubular Storage System

Thermal Performance of a Finned Double-Pass Solar Air Collector Integrated with a Nanoparticle Enhanced-Pcm Tubular Storage System

Experimental Performance of Solar Air Heaters for Drying Applications

This paper presents the results of an experimental investigation on an indirect active type of solar dryer, using two distinct solar air collector and their impacts on drying agricultural products. The thermal performance of the proposed collectors has been evaluated using the first and second laws of thermodynamics. Experimental observations were done in climatic conditions Gödöllő, Hungary on the 2nd and 9th of October 2017. The experiments were also carried out to dry 2 kg of sliced apples spread over the drying trays. The mas flow rate of air was maintained as 0.038 kg/s and the dryer was operated from 10:00 a.m. to 3:00 p.m. When a double-pass solar air collector's results are compared to a single-pass solar air collector's, it's evident that the double-pass solar air collector produces much more energy and efficiency. The experimental results showed that single-pass and double-pass collectors have daily efficiencies of 42.77% and 56.10%, respectively, with average exergy efficiency values ranging from 31% to 49% for single-pass and 51% to 67% for double-pass. The most significant aspect determining the collectors' thermal efficiency was the temperature rise between the collector outlet and inlet. The average drying efficiencies of the solar dryer for the single and double-pass collectors were evaluated as 12.16% and 16.45%, respectively. The maximum temperature rise for double-pass was determined to be 20 °C, whereas single-pass was found to be 6.5 °C. Furthermore, the highest drying rate was achieved when sliced apples were dried with a double-pass collector mode. It reduced 52% of the water content in the apple in the same amount of time as single-pass drying, compared to 35% in the case of single-pass drying.

Experimental performance of a solar air heater using straight and spiral absorber tubes with thermal energy storage

A flat plate solar air collector is a simple energy conversion system with relatively poor performance due to low heat transfer between air and absorber. Passive heat transfer enhancement methods increase the absorber-side contact area and the localized air turbulence. This research article introduces a dual-purpose copper tube as an extended absorber surface as well as heat storage. The absorber designs are spiral coiled and straight tubes with uniform spacing, filled with glycerol and commercial grade paraffin. Thermal and exergy efficiencies of modified solar air heater configurations are compared with conventional collector with a plain absorber without energy storage. The experimental results show that the double-pass solar collector with a spiral tube with paraffin wax has higher thermal performance than the straight tube and conventional collectors. The spiral coil's thermal and exergy efficiencies with paraffin wax are 29.86% and 1.11%, respectively, at an airflow rate of 0.0076 kg/s with a maximum attained air temperature of 59 °C. The air temperature is maintained for a short time in the heat storage-based absorber even after sunset. Thus, the integration of thermal storage into the solar collector stores the heat for off-sunshine hours and enhances the absorber's energy storage capacity and uniform temperature. The modified absorber surface with heat storage results in better performance without auxiliary power. Further, the enviro-economic study ensures a lower payback period for PCM-integrated spiral tube collectors of about 2.4 years. Such simple and economic absorber designs are beneficial to various solar drying and space heating applications.

Utilizing jet impingement on protrusion/dimple heated plate to improve the performance of double pass solar heat collector

The effect of geometrical parameters of jet impingement on indented protrusion absorber in double-pass solar heat collector (DPSHC) was investigated. For fixed optimum values of protrusion parameters namely arc angle (αp), relative height ratio (ep/Dh), and relative pitch ratio (p/Dh), four different jet height ratios (Hji/Dh) ranging from 0.11 to 0.44 have been used with varying streamwise pitch (Xji/Dh) and spanwise pitch ratio (Yji/Dh). At a constant jet diameter ratio (Dji/Dh), the Reynolds number (Re) of the airflow fluctuated between 2500 and 22500. It has been found that the Hji/Dh plays an important role in the performance of DPSHC and that the maximum value of the Nusselt number (Nudp) = 544 with friction factor (ffdp) = 0.206 was obtained at Xji/Dh=1.32, Hji/Dh=0.22, and Yji/Dh=1.32. The investigation reveals that the thermohydraulic performance (ηdp) of the DPSHC increases as the Re increases from 2500 to 15000 and after that from 15000 to 22500 it starts to decline. The optimum value of ηdp = 3.86 has been found corresponding to Re = 15000, Hji/Dh=0.22, Xji/Dh=1.32, and Yji/Dh=1.32. Nudp and ffdp correlations were developed in terms of jet impingement parameters and the selected range of Re which can be useful for estimating the performance of a DPSHC with the combined technique. The optimum deviation in the Nudp and ffdp values was ±10%, which correlated well with the experimental results.

Experimental investigation of a novel thermal energy storage unit in the heat pump system

In this paper, an experimental study of an innovative latent heat storage unit integrated with the condenser of the heat pump system is presented. Novelty: a heat exchanger has been developed and designed to store the heat released from the condenser of the heat pump using a phase change material. For a sustainable and efficient heating system, it is aimed to use the phase change material in the heat pump system. Latent heat storage unit designed for this purpose has been tested in both air source heat pump and solar assisted heat pump systems. In addition, a new double-pass solar collector has been developed for the solar-assisted heat pump. The average coefficient of performance values varied between 2.19 and 2.34 for air source heat pump system and 2.32–2.77 for solar-assisted heat pump system. With the use of solar energy, the increase of performance of the heat pump was achieved by 15.67%. It was observed that the instantaneous thermal efficiency of double-pass solar collector could reach up to 79.16%. Phase change material in the latent heat storage unit melted and solidified in 180 and 348 min for air source heat pump system, and 150 and 307 min for solar-assisted heat pump system. This result shows that the melting process accelerates under high solar irradiation, and the total melting time decreases.

Performance assessment of solar PV-driven hybrid HDH-RO desalination system integrated with energy recovery units and solar collectors: Theoretical approach

Recently, constructing a high productive desalination unit with low power consumption has been a challenge. Along with that, this study aimed to simulate a new hybrid desalination unit merging two common techniques of high freshwater production: humidification-dehumidification (HDH), and reverse osmosis (RO). For low power consumption, the hybrid HDH-RO unit was powered with a photovoltaic (PV) systems. The system was provided with thermal energy recovery (TER) units, double-pass solar air collectors (SACs), and evacuated tube solar water collectors (SWCs). The TER units were parallel connected to the backside of PV panels for dual function: enhancing the PV conversion performance by cooling and preheating the seawater before entering the SWC. Both SAC and SWC were proposed to improve the evaporation rate inside the humidifier of the HDH unit. For a comprehensive analysis of the HDH-RO system, five coupled theoretical models were derived and solved, which all were validated by previous experimental data from the literature. All results confirmed that the proposed system can be a good choice for producing freshwater with low power consumption. The maximum hourly freshwater production of the new hybrid HDH-RO desalination system varied between 192 and 200 L, with a water recovery ratio ranged between 48 and 49.8%. Also, its specific power consumption (SPC) ranged between 1.22 and 1.24 kWh/m3, with an average saving a range between 14.7 and 65% compared to previous techniques of RO desalination system.

Thermal modeling of air-type double-pass solar collector with PCM-rod embedded in vacuum tube

Based on an evacuated tube collector, we designed an air–type double–pass solar collector with a PCM–rod embedded in a vacuum tube. In this study, the basic parameters of the proposed collector are discussed comprehensively and the spatial layout of each component is illustrated. Simultaneously, a thermal model of the collector has been established to predict the outlet temperature of the collector. The equivalent thermal efficiency of the phase change material is also proposed to explain the change in the thermal efficiency of the collector caused by the PCM. Finally, the thermal performance of the proposed collector was tested and compared with its theoretical value. The results show that the comparison between the simulated and experimentally measured outlet temperatures is in good agreement; the root mean square error and mean bias difference on the outlet temperature are 1.56 K and 1.33 K, respectively. Additionally, even if the irradiation intensity reduces by 39% within 30 min, the outlet temperature decreases by only 7.5 K. The thermal model is also used to analyze the influence of airflow, radiation intensity, ambient temperature and surrounding air speed on the outlet temperature. It was observed that the first three have a greater impact, but the temperature fluctuation is only 0.36% when ambient wind speed is 0.2–2 m/s. In contrast, the heat loss of the collector was evaluated and it was found that the heat loss of the vacuum tube accounted for 0.4%–2.8% of the heat energy of the collector, while the heat loss of the manifold to the ambient accounted for only 0.04%. The phase change material stored 0.247 MJ of heat, of which 0.245 MJ was provided to air, and the conversion rate of heat absorption and release was 99.2%, and the working time of the collector is extended by 8 h. In terms of thermal efficiency, the instantaneous thermal efficiency continued to increase from 13% to 397%, and the equivalent thermal efficiency of the phase change material reached a maximum of 484%.

Design of the double pass solar collector for drying

Solar energy is the free and nearly endless source which can be applied in various fields. Viet Nam locates near the equation and has enormous solar radiation, so this is the good chance for us to harness it. Moreover, Viet Nam is also the agricultural country with the large number of export product. With the large advantage in having enormous solar radiation, we can save up the large amount of energy for drying and other applications. In this paper, the 2 double pass solar collectors which have fins and without fins for drying were designed and simulated by CFD Ansys in some different conditions. The result displays that with the same size, the outlet temperature of the solar collectors with fins is 2 times higher than the without fins one. This temperature can reach 94.6°C with solar radiation 1026.32W/m2, mass flow rate 0.12kg/s and can reach 68.63°C with the same radiation and mass flow rate 0.18kg/s, so it is eligible for agricultural drying.