Convection Solar Dryer Research Articles

Exergy and Energy Analysis of Forced Convective Thin-layer Solar Drying of Tiger Nuts (Cyperus esculantus L.)

Aims: To study the exergy and energy analysis for thin-layer solar drying of tiger nuts; and also to determine the drying kinetics for the thin-layer solar drying of tiger nuts. Study Design: Yellow variety of tiger nuts were dried in a forced convection solar dryer to determine the exergy and energy indices. Place and Duration of Study: Federal University of Technology, Owerri, Nigeria between October, 2022 to March, 2023. Methodology: The experiment was conducted at three different air velocities of 1.5, 2.5, and 3.5 m s-1 and two different loads of 70 and 140 g. The tiger nuts were dried from average initial moisture content of 52% (wb) to final moisture content of 10.2% (wb), at an average temperature range of 50.5 to 51.2 ºC. Energy utilization, exergy loss rate, exergy efficiency, improvement potential, and sustainability index were determined. Results: The results of energy utilization, exergy loss rate and improvement potential ranged from 2.1 to 5.09 W, 0.25 to 0.93 W and 0.08 to 0.54 W respectively; however, these values increased with increasing air velocities and loads. The results of exergy efficiency and sustainability index ranged from 41.8 to 68.49% and 1.72 to 3.17 respectively; these values increased with decreasing air velocities and loads. Graphical plots of moisture content with drying time showed that the moisture content of the tiger nuts decreased with increasing drying time. The characteristic nature of the curve is indicative of the fact that there was an initial higher rate of drying, which gradually declined with drying time. The results also showed that the drying rates of the tiger nuts ranged from 6.03 to 8.44 %MC/hr; and these values varied with the different air velocities and loads. Conclusion: The results from this research will serve as a guide in reduction of energy costs for the optimum design of convective dryers.

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.

Assessing mathematical models for the intermittent drying of cocoa (Theobroma cacao L.) beans

Fine flavor cocoa quality is significantly impacted by its postharvest drying process which can be enhanced through mathematical modeling. The objective of this study was to carry out the mathematical modeling of cocoa bean drying kinetics for a greenhouse dryer and considering intermittent drying. In this study, a natural convection solar greenhouse dryer was used to dry cocoa beans with negligible losses to an acceptable moisture content (6.6%) and cotyledon pH (5.25). Models based on Fick’s second law of diffusion, Newton’s model, and Hii, Law and Cloke’s model were developed considering (i) the entire drying period, and (ii) intermittent drying for Fick’s and Newton’s. Effective diffusivities and drying constants increased up to 1.01 ×\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\ imes$$\\end{document} 10–11 m2/s and 0.0165 1/h respectively during drying. Newton’s model slightly outperformed Fick’s model, and the models considering intermittency showed slight improvement over the models for the entire drying period. Considering intermittency when modeling cocoa drying may be useful since a better fit to experimental data resulted, and variation of effective diffusivity and the drying constant was observed over the drying period.

Experimental study of solar drying kinetics and evaluation of activation energy of Eriobotrya japonica fruits

AbstractGiven the seasonal nature and high perishability of Eriobotrya japonica fruits, employing effective preservation techniques like drying is crucial to minimize economic losses and extend the fruit's availability throughout the year. This study rigorously examines the drying kinetics of Eriobotrya japonica fruits using an indirect forced convection solar dryer and highlights the technological advantages of utilizing this dryer over traditional open‐air methods, showing that controlled conditions provide improved drying rates. The research develops the equation for the characteristic drying curve. The Midilli‐Kucuk model was demonstrated to be the most appropriate for describing these kinetics under various conditions, offering a reliable method for predicting drying behavior at untested temperatures. The thermal diffusivity was determined and rises as the temperature increases. The application of the Arrhenius approach enabled the determination of an activation energy of 17.79 kJ/mol, confirming the substantial impact of temperature on the drying process.Practical applicationsThe global challenge of food preservation, especially for perishable fruits like Eriobotrya japonica, requires innovative and efficient solutions to minimize economic losses and ensure the year‐round availability of nutritious produce. Our research demonstrates the technological advantages of using a forced convection solar dryer over traditional methods for drying E. japonica. This system maintains a consistent air temperature, ensuring a stable energy supply, faster, and more uniform drying. A major contribution of this study is the development of the characteristic drying curve equation, which is crucial for optimizing drying parameters and designing an efficient solar dryer specifically for E. japonica. This research not only advances the understanding of the drying kinetics and thermal properties of E. japonica but also provides a foundation for the development of more efficient and sustainable drying technologies. By optimizing the drying process, this study contributes to improving the preservation and quality of loquat fruits, thereby supporting agricultural sustainability and reducing post‐harvest losses. This work is highly relevant to the broader energy community, as it showcases the potential of solar drying technologies in enhancing food preservation while promoting the use of renewable energy sources.

Experimental investigation on a solar dryer assisted with minimum phase change material (PCM) placed on the inner walls of drying chamber

Solar dryers assisted with phase change material (PCM) speed up the drying process by compensating the negating effect of reduced or absence of solar energy under cloudy or non-sunshine hours respectively. The study of the relevant and recent literature indicated that the minimum quantity and proper placement of this PCM have not been explored to take full advantage of using them in solar dryers. Hence in this research work, experimental investigations on banana slice drying were carried out with 4 and 10 numbers of copper tubes filled with 176 and 494 kg of commercial paraffin wax respectively (correspondingly designated as SD-PCM1 and SD-PCM2). The copper tubes were placed in vertical and horizontal orientations on the inner wall of the drying chamber so that the upward movement of air would not disturbed. A comparison of the drying performance of a PCM-based unit with a natural convective solar dryer without PCM (SD) was also presented. As no appreciable differences between the mass loss during drying under SD and SD-PCM1 modes were observed, it was concluded that a mass of PCM greater than 176 g would enhance drying rates. Thus for the same final mass of dried banana slices, the drying time was about 15 and 9 h with SD and SD-PCM2 respectively. As the operating conditions of SD and SD-PCM vary considerably in terms of the thermal energy supplied during the drying process, the concept of a generalized drying curve with dimensionless time was used to study the drying kinetics. A close alignment of experimental data of moisture content ratio with the generalized drying curve under SD and SD-PCM modes indicates similar dryer performance irrespective of the differences in thermal energy supplied. The average exergetic efficiency of SD, SD-PCM1 and SD-PCM2 was 21, 26 and 28 % respectively. The sustainability index and environmental impact factor for SD-PCM2 were 1.41 and 2.5 respectively which was better compared to the respective values of 1.27 and 3.77 in SD mode favoring the use of PCM in solar dryers.

Design and Construction of a Mixed-Mode Natural Convection Solar Dryer for Mango Slices

Fruits like mangoes are produced in large quantities during the peak season, and high postharvest losses occur due to lack of appropriate storage and handling structures. The main goal of this study was to design and construct a mixed-mode natural convection (MMNC) solar dryer for drying of mango slices. The dryer was designed using AutoCAD and constructed with wood and glass using basic woodworking tools and processes. The developed dryer has a direct collector, a vertical collector, and an indirect collector. The drying chamber has two removable frames with 5 shelves each, a total drying area of 2.54 m2 and a capacity of 10 kg of mango slices per batch. The dryer is fitted with caster wheels for easy turning and positioning. Test conducted with 940 g of fresh mango slices resulted in effective drying after 17 hours, from a moisture content of approximately 90% (wb) reduced to 17% (wb). The drying rate was found to be 4.3%/hr. The maximum temperature obtained in the drying chamber was 54.3 ℃ at a maximum ambient temperature of 37.6 ℃. The average temperature-rise in the drying chamber compared to the ambient temperature was 11.5 ℃. The dryer is therefore recommended for use both domestically and by small-scale food processors since it is more hygienic and has proven to be more efficient than open-air sun drying.

Exploring Energy Performance of Taraxacum Leaves Undergoing Hybrid Forced Convection Solar Dryer

Exploring Energy Performance of Taraxacum Leaves Undergoing Hybrid Forced Convection Solar Dryer

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.

Realization and Experimental Study of a Forced Convection Solar Dryer

Post-harvest losses represent a significant cause of food insecurity worldwide. These losses not only affect the availability of food, but they also impact the economic stability of farmers and communities dependent on these crops. Food drying presents itself as a viable solution to reduce these post-harvest losses and ensure greater availability of food for human consumption. It is in this context that our work on the creation of an indirect solar dryer with forced convection, integrating an automatic temperature control system, takes place. This study consisted of creating a prototype and subsequently carrying out drying experiments on onions in order to evaluate the performance of the device. Our experiments took place from October 25 to October 29, 2023 at Joseph KI-ZERBO University. After 8 hours of drying, only 12% of the initial mass of the onions remained. The solar thermal collector presented an efficiency of 62%. And a drying efficiency, estimated at 17% with an average sunshine of 600W/m2.

Modelling Heat and Mass Transfer in High-Capacity Natural Convection Solar Dryers

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.

Natural convective solar dryer powered by stepped fin plate integrated trough array solar air heater for agricultural produce preservations

In this work, heat energy analysis and economic feasibility of natural convection mixed mode solar dryer under three different methods viz., normal flat plate collector solar dryer (NFPSD), step fin plate integrated trough array collector solar dryer (SFPTSD) and SFPTSD with latent heat storage (LHS) are experimentally investigated. The drying time in SFPTSD – LHS (setup 3) to reach its safe moisture content for paddy, wheat, green chilli are 5.5 h, 6 h and 7 h respectively and it is significantly lowered to a maximum of 47 % as compared with NFPSD (setup 1). Also, the average maximum heat efficiency of 62.19 % for collector and 38.32 % for drying cabinet is obtained in setup 3. The specific heat energy consumption is lowered by 20.65 % and specific moisture extraction rate increases to 21.73 % for this proposed setup in comparison with setup 1. The improvement potential is reduced to a substantial margin of 136.5 W and yields an exergetic efficiency increase of 12.38 % than setup 1. An average annual saving increase of 193.08$ with its present value 94.33$ is achieved for setup 3 as compared with setup 1. We recommend this setup can dry edible produce at low cost and affordable to economically weak farming communities.

Energy, Exergy and Economic Analysis of a Mixed-mode Natural Convection Solar Tunnel Dryer for Banana Slices

The energy, exergy and economic analysis of a mixed-mode natural convection solar tunnel dryer for drying banana slices is presented. The collector, drying chamber and chimney energy and exergy are analysed for a load of 3.75 kg of fresh banana slices. Further, the economic analysis in terms of Net Present Value (NPV), Profitability Index (PI), the Payback Period (PB) and the Discounted Payback Period are presented. Drying experiments were done in a period of two days. During the experiment, solar radiation varied from 206.1 W/m2 to 934.5 W/m2; drying chamber temperature varied from 51.7ºC to 81.84ºC while the ambient temperature varied from 21.7ºC to 31.9ºC. The relative humidity ranged from 4.63% to 28.46% for the drying chamber and, 14.9% to 31.8% for the ambient. Under these conditions, the moisture content of the bananas was reduced from 73.89% to 14.27% in seven hours of drying on the first day. Energy and exergy efficiencies ranged from 5.56% to 57.32%, and 0.33% to 2.81%, respectively on Day 1. For Day 2 the energy and exergy efficiencies were from 14.15% to 59.16%, and 0.75% to 3.76%, respectively. For the drying chamber, the efficiency increased gradually in the first two hours to a maximum of 5.36%, corresponding to the period when there was maximum evaporation. The chimney, which is a bare flat plate type without glazing and insulation, lost heat from its surfaces. Nonetheless, it generated enough buoyancy to move air through the dryer. With the solar dryer lifespan of 10 years and the Discounted Payback Period of four years, the project is attractive and worth investing in.

Controlling temperature using proportional integral and derivative control algorithm for hybrid forced convection solar dryer

Drying is one of the crucial processes in agricultural production, especially in grain processing. The drying process can improve grain quality and affect the grain content. However, maintaining the temperature is a challenge in the drying process. Because it can influence the drying performance and produce a low-efficiency reduction of water content, in this study, the hybrid drying system is proposed to improve the performance of the forced convection dryer system. The proposed system used a proportional integral and derivative (PID) control system to obtain the optimal temperature. The proposed system was compared with natural drying and forced convection methods. The experimental result showed that the proposed system performed excellently for three performance evaluations. The average temperature was obtained as the highest of the other methods, with 54.68 °C and 54.55 °C for coffee and cocoa beans. The water content can be reduced by an average of 27.38% and 42.67% for coffee and cocoa beans. Then, the proposed system also had the highest reduction efficiency of water content than the other methods, with 62.71% and 36.94% reductions for coffee and cocoa beans, respectively. The results indicate that the proposed hybrid system performs better than the other methods.

Comprehensive exergy analysis of dandelion root during physical pre-treatment by convective solar drying

Comprehensive exergy analysis of dandelion root during physical pre-treatment by convective solar drying

Comprehensive exergy analysis of dandelion root during physical pretreatment by convective solar drying

Comprehensive exergy analysis of dandelion root during physical pretreatment by convective solar drying

Energy, Exergy and Economic Analysis of a Mixed-mode Natural Convection Solar Tunnel Dryer for Banana Slices

Energy, Exergy and Economic Analysis of a Mixed-mode Natural Convection Solar Tunnel Dryer for Banana Slices

Energy and Exergy Analysis of Forced Convection Solar Drying of Allium Sativum With and With Out Sensible Heat Storage

In this article the energy & exergy analysis of forced convection solar dryer for drying of garlic has been investigated. The exergy parameter, air velocity has been taken to conduct the experiments and its effect on thermal efficiency. Forced draft fans were used in all the two working conditions. During the two conditions, with and without sensible heat storage system, the average air-velocities were 4.5, 9.5 and 11.4 m/s selected as ideal and subsequently its entire effect on thermal efficiency and outlet. The ambient temperatures were between (17-25) °C during the month of October and November. A DC fan is directly connected to the photovoltaic cell in the solar dryer. The thermal energy storage bed was packed with gravels with 1.5 in of thickness up to the surface of flat plate collector, the storage system becomes space-efficient. The average thermal efficiency with sensible heat storage materials was high as compared to system without sensible heat storage. The highest thermal efficiency of 61% was achieved. The maximum collector temperature obtained was 55 °C, with a mean temperature of 42 °C in the drying chamber. The collector’s greatest exergy loss was 30.38 kJ/kg and highest exergy efficiency was 70%.

Use of a forced convection solar dryer for the reduction of post-harvest losses: case of the ‘akikon’ tomato variety in benin (West Africa)

The local variety tomato (Lycopercicum esculentum Mill) named ‘akikon’ is one of the most consumed and widely cultivated fruiting vegetables in Benin Republic. In this work, we designed and built a dryer usable for limiting the frequent losses of the massive produced tomatoes. This paper analyzes the first results, obtained from the different experiments carried out with the developed dryer, in a context of forced convection. The results showed that increasing the temperature from 55 to 70 °C resulted in a shorter drying time decreasing from 1266 to 672 min with a brighter colour of the dried tomatoes for 70 °C. However, the increase of temperature does not affect the smell of the dried tomatoes. After drying, 7 to 8 months were required before we notice a colour change (from red to red-brown) of the dried product , indicating that the storage method still needs to be improved.

Investigation on the performance of a natural convection solar dryer with novel palmitic and sebacic acid eutectic phase change material for thermal energy storage applications

Solar drying has got enormous opportunity in the agricultural sector for hygienic processing of various crops which leads to value addition and high return to farmers. One of the drawbacks associated with solar drying is its usage during non-solar hours. This demerit could be effectively alleviated by integrating latent heat thermal energy storage system based on PCM with the solar dryer and extend its usage beyond sunshine hours. The present study encompasses the development of a novel eutectic phase change material (PCM) consisting of palmitic and sebacic acids (PA-SA) with an individual composition of 80 wt% and 20 wt%, respectively. Using a differential scanning calorimeter, the melting point and enthalpy of fusion of the PA-SA eutectic mixture were determined as 61.10 °C and 161.14 J g−1, respectively. Fourier transform infrared spectroscopy analysis ensured the chemical durability of the fresh eutectic materials and 1000 thermal cycled samples, which proved the suitability of the material for long-term applications. Accelerated thermal cycles up to 1000, and thermal conductivity tests accentuated the superior thermal reliability, and competency of the developed PA-SA PCM. Thermo-gravimetric analysis observed a degradation temperature of 215.13 °C, which is >3 times higher than the operating temperature and hence qualifies the thermal stability test. Corrosion analysis carried out as per ASTM G O1 using three metals such as stainless steel, aluminium and copper revealed the compatibility of using stainless steel as heat exchanger material. Corrosion rates were found to be zero, 0.4015 and 8.6505 mg cm−2 year−1 over 365 cycles respectively for stainless steel, aluminium and copper. Extensive experimental analysis was undertaken to compare the effectiveness of a natural convection solar dryer with and without PA-SA eutectic PCM. The study conducted with 3 kg of eutectic PCM encapsulated in stainless steel cylindrical tubes as heat exchanger elucidated the use of solar with PCM for a duration of four and half hours after sunshine. For solar drying applications, an organic PA-SA eutectic PCM has been developed with a melting range of 61.1 °C and a latent heat of 161.14 J g−1.

Effect of Outlet at the Bottom of the Drying Chamber on the Performance of Natural Convection Solar Dryers

Effect of Outlet at the Bottom of the Drying Chamber on the Performance of Natural Convection Solar Dryers