Energy and Exergy Analysis of Drying Process of Lemon Verbena Leaves in a Solar Dryer

Solar dryer dehumidifies the moisture for food preservation using solar radiation. In this paper, performance evaluation of mixed mode solar dryer without storage device by using energy and exergy analysis tool has been presented. Experimental work on proposed design of mixed mode dryer has been carried out at Makurdi, Nigeria. Analysis has been performed by solving the model equation of solar radiation of Makurdi, Nigeria and mathematical model of solar cabinet dryer using Engineering Equation Solver. A solution of mathematical model will give the available useful energy and exergy of solar cabinet dryer. The performance of the system is evaluated by calculating energy utilized in the drying process using experimental data. The analysis highlights the energy losses, irreversibility, exergy losses and exergy destruction at different stages. Performance comparison of solar dryer with storage device and without a storage device is also discussed. It has been concluded that the mixed mode solar dryer with storage material is able to convert 39% of solar energy as the available useful energy of dryer and convert about 13% of useful energy to exergy of the dryer system. While dryer without a storage material converts 42% of solar energy into available useful energy and converts about 17% of available energy to exergy of the dryer. Comparison of both dryers shows that mixed mode dryer without storage material has twice the exergy as compared to the dryer with a storage material.

Thin layer drying kinetics and exergy analysis of turmeric (Curcuma longa) in a mixed mode forced convection solar tunnel dryer

The discrepancies of using open-air sun drying method for drying agricultural produce and to preserve other variety of food items still exists. In the present time, to get rid of all the disadvantages associated with it, many comprehensive design structures of solar food dryer and their modification has been presented and investigated This research paper highlights the energy analysis performed on a latest design of a solar food dryer in which impinging jet mechanism and fins are clubbed together. The enhancement in heat transfer under preferred range of important parameters investigated namely mass flow rate (ṁ), Reynolds’s number, Flow-wise pitch ratio, Fin-spacing ratio etc. It has been observed that this new design of solar food dryer is more efficient and user friendly. The result has been plotted for Reynolds’s number (Re), mass flow rate (ṁ). The findings for this new design of solar food dryer reflect that temperature range of air coming out from outlet section is in the range of (45˚C-55˚C) which is undoubtedly good.

A comprehensive overview on solar grapes drying: Modeling, energy, environmental and economic analysis

In this study, the thin layer drying characteristics in a solar dryer with forced convection and under open sun with natural convection of parsley was investigated, and energy analyses and exergy analyses of the solar drying process of parsley were performed. The drying data were fitted to the 10 different mathematical models. Among the models, the Wang and Singh model for the forced solar drying and the natural open sun drying were found to best explain thin layer‐drying behavior of parsley. Using the first law of thermodynamics, the energy analyses throughout the drying process were estimated. However, exergy analyses during the drying process were determined by applying the second law of thermodynamics. Energy utilization ratio (EUR) values of the drying cabinet varied in the ranges between 8.57–41.56%. The values of exergy inflow and exergy outflow were found to be in the range of 0.263–0.680 kJ/kg and 0.187–0.378 kJ/kg, respectively. The values of exergy loss and exergy efficiency were found to be in the range of 0.0347–0.399 kJ/kg and 35.76–86.79%, respectively. EUR decreased with increasing drying time while exergy efficiency increased. PRACTICAL APPLICATIONSDrying is widely used in a variety of thermal energy applications ranging from food drying to wood drying. Drying can either be done by traditional sun drying or industrially, through the use of solar dryers or hot‐air drying. The solar dryers could be an alternative to the hot‐air drying and open sun drying methods, especially in locations with good sunshine during the harvest season. This study is useful not only for producers of dry parsley, but also for all producers of dry herbs. It may be successfully used in the design, modeling, analysis and performance evaluation of solar and sun drying.

Global demand exists for high-quality fresh produce. Nevertheless, the quality of fresh produce is severely impacted by its perishability due to its high moisture content. Therefore, fresh produces are preserved using artificial dryers (hot-air dryers, catalytic infrared dryers, etc.) driven by electricity or natural fuels. Nonetheless, the exorbitant cost of power has heightened the need for sustainable resources, notably solar energy, for drying. Hence, this article is a review of how solar dryers and solar-assisted dryers have affected the drying kinetics and quality of fresh produce in the last 5 years. The review showed that solar drying modeling technology (thin-layer modeling, computational fluid dynamics, adaptive-network-based fuzzy interference system, artificial neural network) helps examine fresh produce drying characteristics using various simulation tools before developing any procedure. Solar-assisted drying shortens drying times and increases drying rates. Besides, the quality of the dried fresh produce (color, aroma, appearance, rehydration, etc.) should always be considered. Hybrid solar drying produces higher drying rates and product quality than other solar dryers. However, energy analysis needs to be done as several studies have recognized energy efficiency and product quality. In addition, fresh produce must be pre-treated before solar drying to maintain the final product quality. Therefore, future studies should focus on creating other pretreatment techniques to produce the needed chemical and physical changes and enhance mass and heat transfer. Finally, the influence of solar drying on the final products' nutrient retention or loss, functionalities, or sensory characteristics needs further investigation and comparison to other non-solar drying technologies. © 2023 Society of Chemical Industry.

Solar drying is known as the oldest and most common traditional food preservation method. However, if the product is indirectly contacted with the sun light, there is negative effect in the color and nutrient values of the product. Solar dryers have been developed to utilize the heat effect of the sun to solve these problems. It can be used in combination with osmotic dehydration to increase the efficiency of the solar drying process. Osmotic dehydration is applied as a pretreatment technique in the drying process. The pretreatments to be applied before drying have important effects on the quality and operating cost of the product to be dried. In addition, the osmotic dehydration pretreatment enables to shorten the drying time and increase the drying potential. In this study, bananas with high drying temperature and high moisture content were sliced into 3 mm rings, then osmotic dehydration pre-drying was applied, and then they were dried in a solar tray dryer. Sucrose and citric acid solution in 2.5%, 5%, 7.5% and 10% (w/v) concentrations were used for osmotic dehydration treatment. In addition, samples without osmotic dehydration were dried in a solar dryer to determine the effect of pretreatment. The input variables of the drying process are solution concentration (0%, 2.5%, 5%, 7.5% and 10%), type of solution (sucrose solution and citric acid solution), osmotic dehydration time (10, 30, 60 and 90 min) and sun drying time (60, 120, 180, 240 and 300 min). Output variables were chosen as moisture ratio and shrinkage rate. The results clearly showed that both the moisture ratio and the shrinkage ratio have increased due to increased solar dryer time, solution concentration and immerse time. Osmotic dehydration was found to be effective in dried banana rings in the solar tray dryer. Gradient Boosting Machine (GBM) was used to model the drying conditions and the model was successful. The correlation coefficient (R2) values of the GBM model were respectively found as 0.94 and 0.83 for the moisture ratio and the shrinkage ratio.

This paper presents energy and exergy analyses of solar drying of coconuts in a hemispherical solar tunnel drier. Coconuts were dried from an initial moisture content of about 55% (w.b.) to 7% (w.b.) in the solar tunnel drier in 60 hrs whereas the open sun drying process takes 153 hrs for reducing the moisture content to the same level. The drying experiments were conducted at a mass flow rate of 7.25 kg/s with an average air velocity of 0.1 m/s. Using the first law of thermodynamics, energy analysis was carried out to estimate the amount of energy received by the solar tunnel drier and the ratios of energy utilization. However, exergy analysis was accomplished to determine the exergy loss and exergy efficiency by applying the second law of thermodynamics. Energy utilization, energy utilization ratio, exergy inflow and exergy loss in the drier were studied and these values are found to be increased with increasing solar radiation. The exergy inflow and exergy loss in the drier varied between 0.194 kJ/s–8.18 kJ/s and 0.085 kJ/s–5.377 kJ/s respectively. The exergy efficiency of the drier varied between 23.6%–53%.

This study has summarized the energy and exergy analyses of flat plate collector solar dryer. The study involves a fundamental method for the design of the solar collector based on minimum entropy generation number (Ns) and mass flow number (M). The optimal performance parameters of the solar collector were determined using thermodynamic optimization procedure. Black cardamom was dried in the solar dryer at the drying air temperature range of 26–62°C. The amount of useful energy varied between 0.07 and 0.63 kW based on the degree of solar insolation. Subsequently, it was observed that the useful energy accumulated by the solar dryer was sufficient to dry black cardamom samples to 8.2% moisture content from an initial moisture content of 80.6%. The range of energy utilization values inside the cabinet was between 7.53 and 74.61 W for a period of 24 hr. It was observed that the energy utilization ratio (EUR) varied from 22.12–80.73%, 22.62–97.71%, and 14.25–77.81%, respectively, for the three consecutive days. The increase in the inlet air temperature led to an increase in the EUR values. Furthermore, during the drying studies, the exergy efficiency of the drying chamber was ranged from 31.19% to 93.28%, with an average of 72.08%. The developed solar dryer incorporates a free energy source, sustainability, increased drying capacity, and the creation of high‐quality products. This dryer can be promoted as beneficial and sustainable equipment for drying agro products by small and marginal farmers.Practical applicationsFree energy sources and sustainability are the benefits of this solar dryer system. Agricultural producers are considering the use of renewable energy, such as solar energy, in the drying of agricultural goods. The design of the solar collector was based on the minimum entropy generation number. In this study, a dynamic model was provided in which the kinetics of moisture reduction are calculated based on the quantity of solar energy received in the collector and the temperature fluctuation in the collector. The exergy input and exergy loss of the dryer are affected by solar radiation. The quantity of energy received and consumed is included in the energy analysis.

Saffron is the most expensive spice and is highly valuable for non-oil export. Drying process is a critical control point with major effects on chemical and microbiological characteristics, so an appropriate drying method shall meet standard and market requirements as well as cost benefit. Different methods include traditional, freeze, solar, vacuum oven and microwave drying. Solar drying is performed in direct or indirect way. In the 1st way, sunlight is directly exposured with product chamber, while in the later, sun light is stored in solar collectors and then warm air flow is pumped to product chamber. Results by spectroscopy for colour agent (Crocin), odour agent (Saffranal) and flavour agent (Picrocrocin) indicated that solar drying represents high values. Moisture content taken as a key factor of dehydration was detected below permitted standard level. Microbiological profile in solar drying was in compliance with standard and in acceptable level. Optimum drying condition was achieved for 6-6.5 hours in 35-45 o C. Since all microbial safety and chemical quality properties of saffron are preserved in solar drying and also considering energy saving and the resulted cost benefit of this system, it could be introduced as an appropriate drying method in producing rural and collecting sites of saffron.

Chillies are one of the most popular spices consumed in daily cuisine.They contain a high moisture content after harvest.This research aimed to develop the hybrid solar and LPG-powered dryer for drying fresh chillies and to compare the drying time with sun drying and a solar dryer.The results showed that sun drying required 39 hours, the solar dryer used 17 hours and the hybrid solar and LPG-powered dryer used 7 hours to dry the fresh chilies until the remaining moisture was reduced to 30% on a wet basis.A hybrid solar and LPG-powered dryer increased the chilli drying rate by 5 times that of a sun drying process and eliminated problems associated with damage by insects, rain, and contamination.It had a payback period of 18 months.

Predicting solar dryer performance under different environmental conditions or assessing their performance to dry different grains is challenging since repeatable full-scale tests are expensive and time consuming. In the present study, computational fluid dynamics approach was used to model the drying of maize in high-capacity dryers such as greenhouse and solar bubble dryer. The absorption of short-wave radiation and the greenhouse effect in the dryer with incident solar radiation was modelled using a dual-band spectrum. The distribution of airflow, temperature, and absolute humidity was analysed in this study to optimise the drying process of maize. Additionally, these results were also used to quantify the drying rate of both greenhouse and solar bubble dryer. The greenhouse dryer model overpredicted the dryer temperatures by an average of 0.12%, and overpredicted absolute humidity by 0.38 per cent. The average Root-Mean-Square Error (RMSE) of temperature prediction was 1.8 °C, and the average RMSE for absolute humidity was 0.0042 for the greenhouse model. On the other hand, the solar bubble dryer model underpredicted temperatures by 1.7%, and underpredicted humidity values by 0.3 per cent. The mean absolute percentage error for the temperature and absolute humidity prediction of the solar bubble dryer model was 1.69% and 0.28%, respectively. The predicted and observed spatial variation in the temperature was similar for both dryers.

Energy and exergy analyses of solar drying process of pistachio

Production of organic fertilizer from olive mill wastewater by combining solar greenhouse drying and composting

ABSTRACTThis study investigated the thin-layer drying kinetics of salted silver jewfish in a hybrid solar drying system and under open sun. Ten drying models were compared with experimental data of salted silver jewfish drying. A new model was introduced, which is an offset linear logarithmic (offset modified Page model). The fit quality of the models was evaluated using the coefficient of determination (R2), root mean square error (RMSE), and sum of squared absolute error (SSAE). The result showed that Midilli et al. model and new model were comparable with two or three-term exponential drying models. This study also analyzed energy and exergy during solar drying of salted silver jewfish. Energy analysis throughout the solar drying process was estimated on the basis of the first law of thermodynamics, whereas exergy analysis during solar drying was determined on the basis of the second law of thermodynamics. At an average solar radiation of 540 W/m2 and a mass flow rate of 0.0778 kg/sec, the collector efficiency and drying system efficiency were about 41% and 23%, respectively. Specific energy consumption was 2.92 kWh/kg. Moreover, the exergy efficiency during solar drying process ranged from 17% to 44%, with an average value of 31%. The values of improvement potential varied between 106 and 436 W, with an average of 236 W.