Passive Solar Dryer Research Articles

Comparison of different solar dryers with and without heat storage for crop drying: A review

AbstractSolar drying systems have proven to be cost‐effective and environmentally friendly for drying various products. An extensive investigation of solar dryers with different designs, applications, and operating principles is conducted. Compared to direct drying, solar drying improves product quality by lowering moisture content without compromising the original product's qualities. Solar dryers are of two types: passive solar dryers and active solar dryers. Passive‐mode solar dryers circulate air through natural convection, whereas active ones circulate air through forced convection. Crop‐affected design characteristics include crop sensitivity, cost and time available to dry the crop, crop moisture content, the level of drying required, and so on. A wide range of research has been carried out on the thermal modeling of the dryer, using different designs. This article also discussed and compared the drying performance of three basic solar dryers: direct solar dryer, dryer with PVT air collection, and phase change materials (PCM). Even though PCM dryers are more expensive and uncommon, their ability to speed up drying at night makes them impactful.

Solar Drying Technology for Agricultural Products: A Review

The application of solar drying technology for fruits, vegetables and other crops is one of the most attractive, cost-effective and eco-friendly. Many types of solar dryers have been designed and developed in different parts of the world, having different degrees of technical performance. There are four types of solar dryers: (1) direct solar dryers, (2) indirect solar dryers, (3) mixed-mode dryers and (4) hybrid solar dryers. A synthesis view of the classification of solar energy dryers is also presented. Two groups of solar energy dryers can be identified: Passive or natural-circulation solar energy dryers and active or forced convection solar energy dryers. This paper is a review of all these types of solar dryers, including aspects of the various designs, details of construction and operational principles. Therefore, the selection of dryers for a particular situation is primarily based on what is available and the types of dryers currently used are widely based on available circumstances. Some recent developments in solar drying technology and the appropriateness of each design type for application by farmers in developing countries are also discussed.

Comparative Study on Performance of Passive and Active Solar Dryer

Performance of solar dryers were tested. In the past, to study the efficiency of solar dryers. A dryer with one drying chamber was built and tested by changing the conditions. In each experiment, the solar irradiance value is different, which can cause the results to be inaccurate. Therefore, in this study, a number of drying chambers are designed according to the number of experimental conditions to be studied during the same period. To reduce factors that will cause discrepancies in the experimental results. The solar dryer with 4 drying chambers was constructed in 1 unit and tested the performance of passive solar dryer (PSD) and active solar dryer (ASD). Air flowrate of ASD varied at 0.03 m3/s (ASD0.03), 0.06 m3/s (ASD0.06) and 0.09 m3/s (ASD0.09). Pork was selected as testing material with initial moisture content of 265% dry basis. Drying rate, solar dryer efficiency and specific energy consumption are criteria to evaluate of solar dryer performance. Result from the experimental was found that the performance of PSD is lowest compared with ASDs. Furthermore, it was revealed that the drying rate of ASD0.06 is higher than that for PSD, ASD0.03 and ASD0.09 by 22% 10% and 8%, respectively. Results from the experimental reveal the ASDs performance are higher than that of PSD. Moreover, it was found that the drying rate of ASD0.06 is higher than that for PSD, ASD0.03 and ASD0.09 by 22% 10% and 8%, respectively. Whereas, specific energy consumption of ASD0.06 is lower than that PSD, ASD0.03 and ASD0.09 by 26%, 11% and 9%, respectively. Finally, it was also found that solar dryer efficiency of PSD, ASD0.03, ASD0.06 and ASD0.09 are 11.68%, 13.34%, 14.89% and 13.73%, respectively.

Performance Evaluation of Indirect Solar Dryer under Passive and Active Modes during Drying Beetroot Slices

In the present work, the drying characteristics of beetroot slabs, thermal and performance characteristics were estimated and analyzed in passive (mode-A) and active (mode-B) indirect solar dryers (ISD). The conventional mode-A dryer was updated with a diverging duct that comprises direct current fans run by photo-voltaic panels to make the mode-B dryer. In mode-B, the drying time of 16.67 and 42.31% is saved compared to mode-A and open sun drying (OSD), respectively, to achieve a final moisture content of 0.057 from 7.7535 kg/kg of dry basis. The Two-term exponential model was observed to be a perfect fit model for beetroot slices in both modes of ISD and OSD, respectively. The improvements in drying rate, dryer and collector efficiencies and specific moisture extraction rate in mode-B over mode-A are found to be 19.97, 19.18, 8.34 and 14.23%, respectively. It is found that mode-B has better thermal and performance properties than mode-A.

Performance evaluation and development of FE modeling for passive greenhouse solar dryer for potato chips drying

AbstractFood losses and hunger around the world are majorly attributed to the lack of diverse food processing technologies and standardized methods. Solar energy is a potential solution for drying agricultural products, but traditional solar drying methods are not yet widely used. This study developed a finite element model using COMSOL Multiphysics to assess the performance of a passive greenhouse dryer for drying food products. The proposed model was used to simulate the drying of potato slices, and the results showed that the dryer was able to reduce the moisture content of the potato slices from 1 to 0.005 in 3 h. The drying efficiency was 20.52%, the relative humidity inside the drying chamber was 25.2%, and the energy and exergy efficiencies were 63.46% and 94.01%, respectively. Overall, the results of this study suggest that the passive greenhouse dryer is a suitable drying method for potato chips. The model developed in this study can be used to further optimize the design of the dryer and to evaluate its performance for other food products.

Development and Performance Evaluation of a Novel Solar Dryer Integrated with Thermal Energy Storage System for Drying of Agricultural Products.

Passive solar dryers play a crucial role in reducing postharvest losses in fruits and vegetables, especially in regions like sub-Saharan Africa with low electrification rates and limited financial resources. However, the intermittent nature of solar energy presents a significant challenge for these dryers. Passive solar dryers integrated with thermal energy storage (TES) can reduce intermittence and improve the drying efficiency. Currently, phase change materials (PCMs) are popular heat storage materials in dryers, and paraffin wax dominates. The main problem with the use of PCMs is that it is necessary to closely constrain the temperature range of the process during charging and discharging. This can be a difficult condition to meet in simple solar dryers due to the variable availability of solar radiation. Instead, solid-phase materials, such as sand and rocks, are often used. Soapstone is one of the natural rocks with good thermal properties, but it has yet to be used as a TES material in solar dryers for drying agricultural products. Therefore, the main objective of the present study was to develop a novel solar dryer integrated with soapstone as a TES material and evaluate its performance. The proximate analysis to examine the quality of dried products using the developed technology was also carried out. The comparative experiments for the developed dryer were conducted in two modes: dryer with TES materials and without TES materials, and the results were compared with open sun drying (OSD) by drying 50 kg of fresh pineapple and carrot at different times. The drying times for pineapples in the dryer with TES, without TES, and OSD were 13, 24, and 52 h, respectively. However, the drying times for carrots in the dryer with TES, without TES, and OSD were 12, 23, and 50 h, respectively. Notably, the dryer integrated with TES materials could supply heat for around 3-4 h after sunset. The thermal efficiency of the dryer, collector efficiency, and storage efficiency of TES materials were calculated and found to be 45, 43, and 74.5%, respectively. Proximate analysis indicated that the dryer integrated with TES materials effectively maintained the quality of the dried products compared to OSD. Solar dryer integrated with soapstone showed great promise as sustainable and efficient solutions for reducing postharvest losses and enhancing food security in resource-constrained regions like sub-Saharan Africa.

Evaluating the environ-economic and exergy-energy impacts of drying carrots in passive and active mode solar dryers

On the basis of exergy-energy and economic-environmental (4E) parameters, passive and active indirect solar dryers (PISD and AISD) were analysed and compared by drying carrot slabs. The PISD dryer was upgraded using fans run by photovoltaic panels those were placed at the gate of a divergent duct to make an AISD setup. Experimentally measured primary parameters were used to evaluate the 4E parameters. Accordingly, AISD had enhancement in collector and drying efficiencies of 19.27 and 11.86% than PISD, respectively. Specific energy consumption (32.2%) and moisture extraction rate (47.17%) were better for AISD than PISD. Both setups were examined for their exergy parameters (mean efficiency, outflow, loss, and inflow). Exergy and environmental stability indicators such as sustainability index, environmental factor, waste exergy and improvement potential were calculated and distinguished for both dryers. AISD dryer gave better CO2 mitigation and carbon credit than PISD. The payback period of energy over 30 years lifespan was 1.33 and 1.78 years, and the economic payback period was 1.02 and 0.622 years, for PISD and AISD respectively. In comparison with PISD, the AISD achieved better in all the evaluated parameters. An uncertainty study was carried out for all the measured and estimated criteria. Results were compared with existing studies.

Exploring the efficacy of natural convection in a cabinet type solar dryer for drying gooseberries: An experimental analysis

A study was conducted to evaluate the efficiency of a cabinet-type solar dryer with naturally convection drying specifically for Indian gooseberries. One notable advantage of utilizing a passive solar dryer is its reliance on natural energy sources, such as solar heat and radiation. By harnessing and utilizing solar energy, the dryer significantly reduces the need for external energy inputs, resulting in lower operational costs and a reduced environmental footprint. This eco-friendly approach contributes to the adoption of sustainable and resource-efficient drying practices. The study involved testing Indian gooseberries in both sliced and unsliced forms within a direct-type passive solar dryer. The aim was to assess their moisture ratio, drying rate, and moisture transport phenomena. Over the drying process, the moisture content of 4.2 kg of Indian gooseberries decreased from an initial moisture content of 78% wet basis (w.b.) to a safe moisture content of 5% w.b. The moisture transport phenomena greatly influenced the shape and size of the drying product, which in turn affected the drying rate. It was observed that sliced gooseberries exhibited a higher effective moisture diffusivity compared to unsliced ones during the drying process. In the solar cabinet dryer, sliced gooseberries dried at a faster rate than unsliced gooseberries. Additionally, the study revealed that the quality of the dried gooseberries produced in the solar dryer surpassed those dried in open sun conditions. In conclusion, passive solar dryer operating at higher temperatures facilitate quicker moisture removal. The findings highlight the potential of utilizing solar dryer for efficient and superior drying of gooseberries, leading to improved product quality.

Analysis and comparison of the performance parameters of passive and active indirect solar dryers with heat storage facility while drying carrot

The performance of passive and active convection indirect solar drying systems provisioned with paraffin wax as heat storage was examined while drying carrot slices. The passive indirect solar dryer (type-I) was made initially, and it was upgraded with solar-powered fans to promote mass flow rate. The new assembly was considered an active setup (type-II). Data collected during experiments were analyzed to determine performance parameters and drying kinetics. There were average improvements of 11.8%, 12.2%, and 20.7% in actual heat supply, activation energy, and specific energy consumption in type-II compared to type-I. The averaged values of collector efficiency of type-I and type-II were 59.7 and 67.8%, and the drying efficiency was 11.1 and 14.2%, respectively, while their respective improvements were 13.6 and 27.93%. It was found that the coefficients of moisture diffusion (De), heat transfer (h), mass transfer (hm), and the rate of specific moisture extraction were increased by 20.83%, 16.9%, 14.52%, and 27.8%, respectively in type-II compared to type-I. A logarithmic correlation was observed for De, h, and hm demonstrating a decrease in moisture content (MC) increased the variables. The MC was diminished from 9.13 to 0.478kg/kg of db in 15h in type-I and 12h in type-II with a 3h saving in drying time with a better drying rate in type-II. The reliability of the results was assessed with uncertainty analysis.

Performance assessment of passive indirect solar dryer comparing without and with heat storage unit by investigating the drying kinetics of carrot

The present study examined the drying kinetics of carrots and the effectiveness of passive indirect solar dryer without (setup-I) and with (setup-II) thermal energy storage (TES). A module containing paraffin wax as a TES unit was incorporated after the test was completed in setup-I to create setup-II. The sample slices were dried in setup-I and setup-II at a drying rate of 0.5 and 0.59 kg/h, respectively. In setup-I, the sample dried from 9.13 to 0.478 dry basis (db) in 16 h, whereas, setup-II took 15 h. The thermal efficiency of the solar heater and actual heat supply for the same were 56.84 & 60.79% and 705.64 & 730.45 W, respectively. Similarly, the average heat and mass transfer coefficients (h and hm) were 6.32 & 7.08 W/m2 K and 0.0055 & 0.0062 m/s, and average effective diffusivity (De) for the same setups were 6.7 × 10−9 and 7.24 × 10−9 m2/s, respectively. Furthermore, the specific energy consumption and specific moisture extraction rate for the same were 3.5 & 0.28 kWh/kg and 0.29 & 3.62 kg/kWh, respectively. Setups I and II had an average drying efficiency of 7.5 and 10.25%, respectively. The activation energy was evaluated for both setups. The De, h and hm were correlated with moisture content for both setups. In addition to helping the drying process to be completed in a day, setup-II performed better in all the evaluated parameters than setup-I. To ensure the reliability of the results, an experimental uncertainty analysis was conducted.

Study of drying parameters of pineapple and performance of indirect solar dryer supported with thermal energy storage: Comparing passive and active modes

In this study, passive and active indirect solar dryers (PISD and AISD) with an energy storage system (paraffin wax) and the drying kinetics of pineapple were investigated. To form AISD, the PISD was restructured by providing solar-powered central processing unit fans. The mass variation and temperature data recorded during the experiments were used to evaluate drying characteristics and parameters. As a result, AISD showed an improvement of 0.089 kW, 4.34 kJ/mol, and 3.5 kWh/kg of actual heat supply, activation energy, and specific energy consumption, respectively, compared to PISD. Similarly, the dryer and collector efficiencies of AISD improved by 25.77 % and 16.52 %, respectively, compared to PISD. For PISD and AISD, the mean specific moisture extraction rate, moisture diffusivity, heat and mass transport coefficients were 3.10 and 3.67 kg/kWh, 5.23 and 5.97 × 10−9 m2/s, 0.00489 and 0.00576 m/s, and 5.6 and 6.47 W/m2K, respectively. After 16 h in PISD and 14 h in AISD, moisture content decreased from 7.91 to 0.417 (db) with an average drying rate of 0.408 and 0.45 kg/h, respectively. Based on the evaluated parameters, AISD performed better than PISD. Uncertainty analysis was performed to check the validity of the results.

Economic evaluation of solar drying process for washed coffee in mixteca region of Oaxaca state, México

Solar drying is an alternative innovation to process where product is exposed to direct sunlight and outdoors and where final quality is not always optimal. Solar dryers are installations that require little capital and low maintenance costs, are easy to build and use any locally available material. Objective of this work was to evaluate economic efficiency of drying process of washed coffee beans using a solar dryer built with regional materials. Study was carried out during 2022 coffee harvest, in a passive semi-parabolic greenhouse solar dryer, with an external cover of 36 m2 as a collector. Results showed a unit cost of $11.29 MXN on average to dry a kilogram of washed coffee and transform it into parchment coffee; the benefit/cost ratio was 1.40 and the investment recovery period was determined in one months, values that make solar drying unit a highly profitable option.

Drying Characteristics and Microbiological Quality Assessment of Solar-Dried Tomato.

Tomato (Lycopersicon esculentum) is an important vegetable used in cooking most local foods in Ghana. At the peak season of harvesting, high loses are incurred because of the absence of tomato processing facilities to store, process, and extend the shelf life of fresh tomatoes. Solar drying has been proven to be a more efficient and low-cost method of enhancing quality and adding value to tomato and other vegetables. However, there are concerns about the functionality and quality of the dried products by consumers due to the methods of drying used. In this study, a passive mixed-mode solar dryer suitable for drying tomato was adapted and used to investigate the dehydration characteristics and microbiological quality of the dried tomato. The efficiency of a passive solar dryer was evaluated and used in the processing of fresh tomato to powder. The processing involved the pretreatment of 6 mm slices of fresh Roma variety of tomato by dipping in potassium metabisulfite solution and ascorbic acid solution. The moisture content, moisture ratio, and dehydration rate of solar-dried tomato were assessed. The 24 h dryer efficiency of 24.2% facilitated the drying process of tomato (final moisture content of 12-14%). Aerobic mesophile counts were lower in solar-dried tomato pretreated with potassium metabisulfite (3.90 CFU/g) compared with sun-dried samples (4.85 CFU/g). Solar-dried tomato powder is safer for consumption compared with open sun-dried tomato samples.

Effect of passive solar drying on food security in rural Mozambique

Achieving food security in Mozambique is critical, since 80% of the population cannot afford an adequate diet. While increasing agricultural production is a necessary effort to address this challenge, inadequate post-harvest treatment leads to storage losses and quality degradation, with repercussions for food security. The use of solar drying is promoted as a solution to provide efficient and reliable access to food preservation that improves the food security situation in rural communities. However, there is a lack of clear evidence on how the use or access to solar drying affects food security. This study identifies the determinants of farmers’ choice to use solar drying and evaluates the effect of a passive solar dryer on food security using survey data from 634 households. We allocated solar dryers to selected communities and all interested individuals belonging to these communities were eligible to use it. Propensity score matching and endogenous switching poisson regression are used to estimate the average effect. The use of solar drying with associated training significantly increases the food security status of participants by increasing household food availability, women’s dietary diversity, and months of adequate household food provision and by decreasing the household food insecurity access scale.

RENEWABLE SOLAR ENERGY SYSTEMS FOR SUSTAINABLE DRYING OF BANANA (MUSA ACUMINATA) PEEL BIOMASS.

Huge amount of banana peel biomass are generated annually which are excellent sources of bioenergy, biofuels and other value-added products. The initial moisture content of banana peel is about 70%, which leads to deterioration and limits the efficiency of conversion processes. Solar energy is abundant, free and renewable, so the solar drying of banana peel was investigated. Drying kinetics of banana peel in passive and active solar dryers were compared with that of direct sunlight. Mathematical and artificial neural network (ANN) modelling methods were applied to describe the rate of drying of the peel. The banana peel dried fastest in the active dryer followed by the passive dryer, then direct sunlight. The peels dried in the falling rate period. The Verma, Midilli-Kucuk and Weibull models best described the peel drying kinetics in direct sunlight, passive and active solar dryers, respectively. Feed-forward multilayer perception ANNs having (4-3-1) network topologies best fitted the drying data. The estimated diffusivities of moisture in the peel were 7.835 × 10-11, 9.59 × 10-11 and 1.952 × 10-10 m2 s-1 during its drying in direct sunlight, passive and active solar dryers, respectively. Renewable solar energy can sustainably remove moisture from banana peel biomass. Keywords: ANN Modelling, Banana peel, drying kinetics, mathematical modelling, solar dryer, thin layer

Uji Eksperimental Efisiensi Panas Alat Pengering Surya Langsung Pasif Berbiaya Murah dengan Variasi Material Penutup Transparan

Indonesia should be able to provide inexpensive solar dryers due to the availability of sunlight all year round throughout the country. This study proposes a passive direct solar dryer as it is the simplest one to construct, with aluminum mesh sheets as a heat-absorbing material, and glass fiber as an insulating material. For the cost-effective transparent cover, this study proposes 0.8 mm clear polycarbonate (PC), 2 mm clear glass, and 2 mm clear acrylic. The experimental test results of the solar dryer model showed that the highest heat efficiency value for polycarbonate (PC) is 16%, whereas the heat efficiency value for glass and acrylic is 10% and 8%, respectively. Through these findings, the construction of solar dryers is simple and low cost by using glass fiber as insulation, aluminum mesh sheets as heat absorbers, and PC instead of thin glass as transparent covers.

Design, realization and comparison of three passive solar dryers. Orange drying application for the Rabat site (Morocco)

This research carried out on drying kinetics and quality of dried orange slices in three indirect solar dryers with natural convection, to compare the thermal performance of solar dryers, a data acquisition system is used to follow the evolution of climatic variables (temperature, relative humidity, solar radiation).The experimental measurements for several days in April and May show the average temperature does not exceed 19.5 °C, while the average internal temperatures are 40 °C for Dry3 (the third solar dryer), 34 °C for Dry1 (the first solar dryer) and 28 °C for Dry2 (the second solar dryer). While the relative humidity of the outdoor environment varies in the interval [60%, 85%]. For the relative humidity into dryers, it is observed that the values are ranging in the intervals [5%, 35%] for Dry3, [5%, 70%] for Dry1, and [32%, 75%] for Dry2. Based on these obtained climatic conditions, drying the orange slices is carried out. It was found that the orange slices lost 72% of their initial mass after 6 days in the Dry3, after 15 days for Dry1 and after 18 days for Dry2.The study'’s main experiments have shown that a special formulated the third solar dryer is most effective through thermal performance and drying duration, in terms of economic costs, the design of the Dry3 with a single compartment is less expensive than conventional two-compartment solar dryers. So, Dry3 is beneficial and encourages its use by the local producer.

Energy-exergy and environ-economic (4E) analysis while drying ivy gourd in a passive indirect solar dryer without and with energy storage system and results comparison

The energy-exergy and environ-economic (4E) analysis was conducted while drying ivy gourd in a natural convection indirect solar dryer (ISD) without and with a thermal energy storage system (TESS). The initial setup was modified with TESS by integrating a rectangular glass box holding polycarbonate tubes filled with paraffin wax. The paraffin wax was selected based on its easy availability in the market, and also the existing studies suggested that it works successfully by shortening the drying time, homogenizing the process and maintaining temperature. Mass loss, air velocity, and temperature data were recorded during experiments in both setups. The average collector and drying efficiencies of ISD were 62.56 and 61.87 (without and with TESS) and 6.62% and 13.13% (without and with TESS), respectively. The specific energy consumptions were 1.549 and 0.253 kWh/kg for without and with TESS, respectively. The exergy parameters for collector and drying cabinet such as average exergy efficiency, loss, outflow, and inflow without and with TESS were estimated. Other exergy parameters such as the ratio of waste exergy, improvement potential, sustainability index and environmental impact factor were estimated and compared for both setups. CO2 mitigation and credit were better with the TESS setup. The energy payback period of the dryer was 1.04 and 1.51 years for without and with TESS setups for a lifespan of 25 years. Comparatively, with TESS setup performed well in all the evaluated parameters.

Performance evaluation of mixed mode passive solar stock fish dryer

The performance evaluation of Mixed-Mode Passive Solar Dryer for drying codfish (Gadusmorhua) was conducted. The dryer is comprised of among other things, materials for sensible heat storage to discharge heat during the off-sunshine period. The drying chamber is integrated with a suction device to aid the convective airflow to avoid reversible reaction during the discharge of accumulated moisture. The solar dryer was evaluated with fresh codfish samples at the initial moisture content of 79% (wet basis). The samples were divided into sets. A set was treated with Moringa Oleifera and the second set with salt solution. The results showed that, for Moringa and salt treatments, the moisture content of the codfish was reduced to 16.03% and 13.33% (wet basis) respectively using the solar dryer while 19.55% and 13.46% respectively under ambient condition in six days. Laboratory tests showed that bacteria and fungi count for Moringa and salt treated codfish under solar dryer were below consumable limits.

Energy, exergy, economic and environmental (4E) analysis of passive and active-modes indirect type solar dryers while drying guava slices

The present study investigated the energy, exergy, economic and environmental (4E) analysis of passive and active mode indirect solar dryers (PMISD and AMISD) while drying guava slices in Warangal, India. The AMISD was developed by attaching a divergent duct with PMISD which consist of DC fans powered by PV panels at the entrance of the collector. The energy analysis revealed that average collector efficiency, drying efficiency and energy utilization ratio were 56.05, 5.42 and 13.27% and 65.37, 6.84 and 10.57% in PMISD and AMISD, respectively. The exergy efficiencies of the collector and drying chamber were 3.74 and 50.92% and, 2.39% and 57.03% in PMISD and AMISD, respectively. The economic analysis revealed that the payback period was noticed to be 2.24 and 1.38 years for PMISD and AMISD, respectively. The energy payback periods of PMISD and AMISD are 1.01 and 1.5 years, respectively. The CO2 emission, CO2 mitigation and maximum carbon credit earned for both the dryers were estimated at a lifetime of 35 years. The 4E analysis concluded that the performance of AMISD is higher compared to PMISD and both ISDs are economically viable and sustainable with a lower impact on the environment.