Convection Solar Dryer Research Articles

New Mathematical Models of Thin Layer Solar Drying of Carrots

Drying behavior of julienne and cylindrical cuts of carrot (var. Danvers) using a solar dryer for both forced and natural convection mode have been undertaken. Sixteen solar drying experiments were carried out in July 2020, which received an average of 11.6 hours of daylight per day. Instant weight change, temperature, relative humidity and solar radiation were monitored, recorded and analysed. Overall uncertainty caused by various instruments, calibration, and reading was calculated. Then, the moisture content of different sliced carrots at different drying airflow and temperatures were converted into moisture ratio and then fitted against drying time. A total of eight mathematical models, including three new models, as well as five mathematical models commonly used in the literature, were compared to find the most fitted solar drying curve based on the coefficient of determination (R2), the Root Mean Square Error (RMSE), and the mean square of the deviations ( . Consequently, for predicting the drying kinetics of carrots in natural convection solar dryer the New Model 1 was found to be the best mathematical model with an R2 = 0.999 for julienne, and 0.9986 for cylindrical cuts. In forced convection drying, the best suitable models were New Model 1 for julienne cuts (R2 = 0.9987) and Diffusion approach for cylindrical cuts (R2 = 0.9994). Finally, it has been observed that the R2 values of New Model 1 and New Model 2 in all cases were greater than 0.99. Since there is a good agreement between theory and experimental data in this study, these developed models can provide a gain in the design of new solar dryers in the industry.

Environmentally viable and economical feasibility analysis of groundnut under natural convection solar dryer

In the present work, the drying of groundnut under the natural convectional solar dryer is carried out. The drying experiment is performed in the meteorological condition of Jabalpur, India (23017′N 79094′ E). The groundnut is dried from 35% (w.b.) initial moisture content to an 8–10% (w.b.) up to a safe moisture content under the solar drying condition. The cost per kg of dried groundnut was estimated ₹ 45.05 (Indian National Rupee) (0.60 US$) for four layers, and 54.34 (0.73 US$) for a single layer respectively, under the solar drying condition. Some key characteristics, such as embodied energy, energy repayment time (EPBT) have been identified to aid in the understanding of the cost analysis of drying systems. Also, evaluate the energy analysis based on CO2 emission in kg per year, CO2 mitigation, and carbon credit earn (CCE) which make solar dryers to be environmentally viable. The cost of the solar dryer can decrease with a diminish the embodied energy and carbon credit trading. This is employed to control pollution by reducing CO2 emissions. The environmental viable to attain a reduction in carbon footprint emission. Payback time for four-layer and single layer drying is obtained to be 0.43 years and 1.74 years, respectively.

Performance evaluation of modified forced convection solar dryer with energy storage unit for drying of elephant apple (Dillenia indica)

AbstractThe development and performance of a modified force convection solar dryer (MFCSD) for drying elephant apple slices have been presented in this research. The MFCSD consists of two solar collectors and a drying chamber of 20 kg drying capacity. The secondary collector is integrated with thermal energy storage unit using a phase change material—paraffin wax. Performance analysis of the MFCSD was studied for drying elephant apple (Dillenia indica) slices. The proposed design enhanced the collector thermal efficiency by 12% as compared to a conventional glass collector. Drying of elephant apple slices in MFCSD will limit exergy losses and increase exergy efficiency. The estimated uncertainty of the collector chamber and the drying unit of the proposed MFCSD were obtained as ±3.3% and ±1.0%. Quality analysis (proximity analysis and textural properties) of the fresh as well as samples dried in open sun drying, tray drying, and MFCSD was carried out. The contents of carbohydrates (47.85 ± 2.66) and protein (21.24 ± 1.68) were high in samples dried in MFCSD when compared to samples dried in other two methods. The ash content of the sample dried in MFCSD was found to be 10.25 ± 0.15%, which was higher than samples dried in tray dryer. The payback period for drying elephant apple in MFCSD is 2.56 years, which is lower than the lifetime period (20 years) of the dryer.Practical ApplicationsA traditional method practiced by small farmers for drying high‐value perishable fruits is conventional open sun drying (OSD). Owing to slow drying rate and excessive heating, products dried under the open sun lose their nutritious and medicinal qualities. The present work details the construction of a low‐cost solar dryer for the drying of elephant apple. The aim of the drying kinetics to develop the architecture aspects of the solar dryer is to refine the drying systems. The results showed that the performance of modified force convection solar dryer (MFCSD) assisted with thermal storage could improve the quality of dried elephant apple slices and reduce drying time in comparison with an OSD method and a tray drying method. MFCSD would be a suitable alternative to the conventional dryers employed commonly in the industries for the drying of high‐valued agricultural products, and it can also be restructured to any size according the requirements.

Investigating performance of a new design of forced convection solar dryer

Drying is a common practice for delaying deterioration, preserving quality, and easier prolonged storage of agricultural products. According to the climatic and geographical conditions of Arsanjan County, Fars, Iran. So far, many studies have been conducted on the design and use of various barriers on absorber plates with the aim of increasing heat exchange and subsequently increasing the efficiency of air heaters and solar dryers. However, the effect of using the metal of the sewing machine bobbin on the performance of these dryers has not been studied yet. Therefore, in this study, for the first time, this metal and also pipes containing PCM (phase change material) were used as a barrier on the absorber plate. The results showed that using bobbin absorber plate and PCM in the dryer improves the average collector efficiency and the average dryer efficiency by 28.5% and 52.1% respectively compared to flat absorber plate without PCM, 26.4% and 36.3% compared to bobbin absorber plate without PCM, and 12.2% and 12.9% compared with flat absorber plate with PCM. Although it took about 4.5 h on average to reach the target moisture content with the dryer, it took about 3 days to achieve the same moisture content when parsley was dried in the shade. After fitting the experimental data with nine drying kinetics models and comparing the results in terms of RMSE and R2, it was found that Midilli model can provide reasonably accurate estimates of the drying curve for drying of parsley in fabricated solar dryer.

Determination of moisture diffusivity and activation energy on fixed bed drying of red pepper (Capsicum annum) on convective solar drying

Moisture diffusivity and activation energy are two important variables in a drying process to understand a certain product's drying behavior. This study aimed to determine the value of effective moisture diffusivity and the activation energy of red pepper in a conventional forced convective drying based on electricity (conventional convective drying/CCD) and forced convective drying based on solar energy (convective solar drying/CSD). The value of effective moisture diffusivity was determined using the equation, which refers to Fick’s second law. The Arrhenius equation determines the activation energy value as a model of the relationship of inverse temperature and the normal logarithmic value of effective moisture diffusivity. The results showed that the values of effective moisture diffusivity of CCD 70 °C were the highest. The regression analysis between the drying layers (X), and effective moisture diffusivity (Y) showed a polynomial pattern with a coefficient determination R2 value of 0.85 (CCD 70 °C), 0.81 (CCD 60 °C), 0.88 (CCD 50 °C), and 0.48 (CSD). (R2) The higher moisture diffusivity values in CCD indicated that the drying systems are more stable than CSD. The drying activation energy calculation showed that the value of CCD's activation energy was 36.36 kJ/mol.K, while the value of CSD's activation energy was 31.28 kJ/mol.K. Those results were consistent with the results of the previous studies.

Comparative study of different drying methods regard to the phenols and flavonoids content of dried Citrus aurantium L. leaves

Objective: To determine the effects of different thermal drying technologies on the total phenol and flavonoid contents (TPC) and total flavonoids (TFC) in sour orange (Citrus aurantium L.) leaves. Design/methodology/approach: Solar drying was carried out in outdoor sunny conditions using two direct solar dryers; one with natural convection, the other with forced convection. The total phenol and flavonoid contents in gallic acid equivalents (GAE) and quercetin (Q), respectively, of ethanolic extracts of C. aurantium were assessed with spectrophotometric techniques. Results: The results demonstrated maximum phenol values for the direct natural convection solar dryer (161.4 mg EAG/g MS) and minimum values for shade drying (61.43 mg EAG/g MS). As for flavonoids, the highest values were obtained in the direct forced convection solar dryer (32.22 ± 1.6 mg EQ/g MS), while the lowest was registered in the open air sun (11.72 mg EQ/g MS). Conclusions: Direct solar dryers are technologies effective for maintaining the phenols and total flavonoids content in dried leaves of C. aurantium.

Techno-economic evaluation of forced convection solar photovoltaic dryer for drying date palm (Phoenix dactylifera L.) fruit

The drying experiment for dehydrating date palm (Phoenix dactylifera L.) fruits was carried out in this dryer (developed by CAZRI, Jodhpur) in the month of June, 2020. During the testing, the maximum average stagnation temperature in the drying chamber was found as 70°C and when loaded with 20 kg date palm it reduced to 64°C, when outside ambient temperature was observed as 39.5°C on a clear day (from 08:00 hr to 18:00 hr). During the drying trial, moisture content of date palm fruits got reduced from 65% (wet basis) to about 26% in 6 days by dryer, whereas in the open sun drying it is taken 8 days. The temperature gradient of the drying chamber got reduced from 6-8°C to 2-3°C in the system provided with pre-heater, which resulted in uniform drying. The effective moisture diffusivity was 4.34  10-9 m2.s-1, and the efficiency of the dryer was 16.1 per cent. The developed hybrid forced convection drying system produced better quality products in shorter time by the efficient use of solar energy. The economic evaluation of the hybrid forced convection solar dryer indicated high value of IRR (57.4 percent) and low value of payback period (2.10 years), suggesting the dryer to be cost efficient. The winnower was used for winnowing the 200-300 kg grains from threshed material in a day in the absence of natural wind. The winnower was also used for separating grains from straw to enhance the utility throughout the year.

Forced Convection Solar Dryer System

Forced Convection Solar Dryer System

Experimental study on drying kinetics for Zingiber Officinale using solar tunnel dryer with thermal energy storage

This research reports an experimental analysis performed using a forced convection solar tunnel dryer integrated with eco-friendly low-cost sensible heat storage material. The experimental setup consists of a single pass air heater and solar tunnel dryer for drying Zingiber Officinale (Ginger). The dryer unit was tested for a two-kilogram ginger load at 12.9165° N, 79.1325° E in the hot air temperature range of 33–74 °C. Performance of drying process for two novel configurations (with sensible heat storage and north wall reflection) and two modes (active and passive) were analyzed. The raw ginger samples initially had a moisture content of 80–82% (w.b.) and were reduced to 9–10% (w.b.) in two successive days. Sensible heat storage found to increase the average temperature of the dryer by 10 °C during the drying process. The results conclude that active drying mode with and without sensible heat storage has the fastest moisture removal rate than passive drying. Amidst the eleven drying models, the models of Midilli – Kucuk and Wang – Singh had best described the kinetics of the product drying. The overall efficiency of the dryer system and specific energy consumption of the ginger was 45% and 5.56 kW-h, respectively for passive mode. The SEM analysis carried out on different micron pore sizes of dried ginger attained uniform moisture removal with a homogeneous surface and a clear fibrous structure.

Experimental Investigation of Forced Convection Solar Dryer with Phase Change Material (PCM)

Solar dryer is an economical way of drying various agricultural products. The limitation of solar drying is that it available only during sunshine hours. An integration of phase change material (PCM) is one of the options to extend drying process after sunshine hours since it store heat in form of latent heat. In this work, an indirect, forced convection, single pass, batch type solar dryer with phase change material (PCM) was designed, constructed and experimentally investigated. Solar collector consists of rectangular pipe type absorber and it works as a PCM chamber. The experiments are carried out on solar dryer test rig under various loads, with PCM and without PCM. The main aim to carry out experiments is that to investigate the feasibility of using a solar dryer with PCM to store the solar energy in form of heat during the daytime, and to release it during the night or cloudy weather. Experiments were conducted to evaluate increments in cycle time, increment in collector’s and dryer’s efficiencies.

Performance studies on mixed-mode forced convection solar cabinet dryer under different air mass flow rates for drying of cluster fig

A Mixed-mode Forced Convection Solar Cabinet Dryer (MFCSCD) is designed for the maximum harnessing of solar radiation. It utilizes the direct heat from solar radiation through glass cover as well as preheated air from two solar air heaters (SAHs) fixed in series having a double pass. The experimental research works were performed in the metrological conditions of Guwahati, India. The drying performance of MFCSCD was analyzed under different air mass flow rates in terms of specific moisture extraction rate (SMER), pickup efficiency, and dryer efficiency for the drying of cluster fig. Further, a thin layer drying kinetics analysis was carried out to find the best suited mathematical model for representing the drying behavior of cluster fig in MFCSCD and open sun drying. Cluster fig dried from moisture content (MC) of 5.67 to 0.08 kg/kg on a dry basis in 7.0, 8.0, 8.5, and 9.5 h at airflow rates of 3.72, 2.76, 1.8, and 1.08 kg/min, respectively, whereas it took 14 h to attain the same moisture level under open sun drying. The experimental results showed higher dryer and pickup efficiencies and SMER at 3.72 kg/min air flow rate. The quality analyses of solar and sun-dried were carried out to estimate the total phenolic content, antioxidant activity, and rehydration ratio.

Energy and Exergy Analysis of an Indirect-Mode Natural Convection Solar Dryer for Maize

The energy and exergy analysis of an indirect-mode natural convection solar dryer for maize grain is presented. Two different sizes of maize grain bed depths of 0.04 m and 0.02 m translating into grain loads of 10 kg and 5 kg respectively, are used in the study to determine their effects on the collector energy and exergy efficiencies and the drying chamber exergy efficiency. Experiments were carried out using an indirect-mode laboratory solar dryer under a solar simulator with a radiation setting of 634.78 W/m2. The analysis gave average collector energy efficiencies of 33.3 % and 46.2 % for the 10 kg and 5 kg loads, respectively, which are higher than the collector exergy efficiencies of 2.4 % and 2.6 % for the 10 kg and 5 kg loads, respectively. The drying chamber exergy efficiencies are 45.2 % and 28.4 % for the 10 kg and 5 kg loads, respectively. In view of this, the 5 kg load is considered to be more efficient at extracting energy from the collector due to higher air flow resulting from its relatively thin grain bed depth of 0.02 m, but less efficient in utilising the extracted energy to evaporate moisture from the grain which has resulted in a lower drying chamber exergy efficiency. Further, the exergy loss in the drying chamber for the 5 kg load is higher than that in the 10 kg load as 72.3 % of the exergy entering the drying chamber is lost through emissions as well as destroyed through internal irreversibility compared to 57.0 % for the 10 kg load. 

Thermodynamic analysis of forced convective solar drying of cocoa with black coated sensible thermal storage material

Thermodynamic analysis of a forced convective solar dryer integrated with black coated sensible (firebrick) thermal storage material (STSM) for cocoa was investigated. The intermittent nature of solar radiation and its consequence on thermal processes such as drying necessitates the introduction of materials for heat supplement to keep the cocoa beans at a raised temperature above the ambient. As a steady flow thermodynamic system, the analysis was carried out based on the first and second laws of thermodynamics to account for the energy involved in the solar drying of cocoa beans. The maximum drying chamber utilization energy during the first and second daytime drying process was 0.739 and 0.724 kJ/kg. The energy utilization (EU) decreased with the increase in time from 12:00 to 18:00 h respectively. Also, the energy utilization ratio (EUR) ranged from 0.190 to 0.577, and 0.222 to 0.931 during the first and second daytime experiments respectively. The collector efficiency varied between 4.2 and 61.2% while the minimum and maximum solar radiation for the two daytimes were 49.6 and 759.6 W/m2 with an average mass flow rate of 0.032 kg/s. The maximum energy efficiencies for the two-day times obtained at 10:00 h were 28.0 and 58.2%. In the drying chamber, the maximum exergy (inflow and loss) for the two-day time drying process was 7.53 and 8.33 kJ/kg, and 4.83 and 8.175 kJ/kg respectively. The exergetic efficiency during the first daytime experiment varied between 1.52 and 65.81%, while it varied between 1.82 and 53.30% during the second daytime. Thus, the results obtained in this study will inform the choice of an appropriate solar dryer design by the relevant stakeholders in the cocoa industry.

CFD Modelling and Simulation of an Indirect Forced Convection Solar Dryer

Solar dryer is a conventional device used for solar drying products. There are several types of solar dryers being employed for drying fruits and vegetables. In this research, the indirect type solar dryer is studied and computational fluid dynamics is employed to simulate the process. Ansys fluent CFD software is used to simulate and obtain dynamic and thermal performance of the dryer at different operating conditions (mass flow rate). The predicted results are validated with the help of experimental results. The average velocity at the exit of the collector was 2.89 m/s for 0.0872 kg/s mass flow rate, while for a mass flow rate of 0.0447 kg/s was 1.36 m/s. The maximum temperature at the collector outlet was 44.6°C and the maximum absorber plate temperature was 69.57°C for a magnitude of 0.0872kg/s mass flow rate. The temperature profiles of the trays are also analysed and the tray closest to the collector is found to have the maximum average temperature. The results also revealed that CFD simulations are a reliable method to predict and design solar dryers.

Experimental study on drying kinetics of ivy gourd using solar dryer

AbstractVegetable preservation through drying technology is an effective method to minimize wastage while satisfying the essential nutrition requirements. It is necessary to expand the existing technologies to preserve seasonal and regional specific vegetables. The present study is intended to find suitable conditions to increase preservation capacity through solar drying. A single slope solar dryer (SSSD) is designed, fabricated and ivy gourd is taken as a vegetable sample. Experiments are carried out in the highest temperature region in South India at 10.925°N latitude, 79.838°E longitude. The safe moisture content of the passive and active mode solar dryer was attained in 9 and 7 hr whereas it took 11 hr in sun drying. During the dehydrating process, the temperature of the system varied from 35 to 71°C. Existing kinetics models are used to optimize the “goodness of fit” and proposed a novel model to suit India's environmental conditions. Exergy analysis and thin layer drying kinetic studies are performed and studied the influence of various parameters in the dehydrating of ivy gourd. The study revealed that the air temperature, RH, global radiation, and airspeed, significantly influence the drying kinetics. However, all the above four drying parameters are interconnected to enhance the drying process and which in turn enhance the drying kinetics process. Obtained results are explained with suitable discussions.Practical ApplicationAlmost 40–50% amount of food items annually are rotten all over the global due to deficiency of proper preservation methods. Solar drying is found as a sustainable approach for food preservation; however, the food items dehydrated under sun dehydrating lose their nutritional, medicinal properties due to slow and nonuniform dehydrating rate. In this article, the newly designed SSSD is developed and a thin‐layer dehydrating mathematical correlation for freshly harvested ivy gourd is conducted. The results showed that forced convection solar drying setup could enhance the product quality of ivy gourd and also decrease the dehydrating time.

Performance Analysis of Red Chilli in a Hybrid Collector with Solar Dryer

This article performed various analysis on Red chilli by hybrid collector with solar dryer (HCSD). This study was carried out forced convection solar dryer which performed better in all aspects such as drying time, moisture removal rate, electrical efficiency, electrical thermal efficiency, thermal efficiency and overall thermal efficiency. In general, solar radiation was provided a sources of generating energy to drive a solar dryer. Hybrid collector has been provided the electrical and thermal energy to run a solar dryer. The solar dryer was tested by drying 12 kg of red chilli in the drying air temperature in the range of 32 0C – 56 0C. The initial moisture content of the red chilli was 71.5 % (weight basis) and was reduced to the final moisture content of 16.2 % (weight basis) in 6 consistent days with clear sunny days. The HCSD was operated between 9 hrs to 16 hrs. Finally, comparative study was also handled for better understanding in HCSD, in which solar dryer drying made better outcome than open sun drying.

Evaluation of Different Designs of Thermal Storage in Solar Drying System.(Dept.M)

A simple, easy built forced convection solar drying system consisting of a solar air heater, drying chamber and thermal storage has been constructed and tested. A new simple pebble bed storage, with special and easy form was designed to be heated with direct solar energy or hot air from the heater or both. The drying system performance was studied under different locations of the storage box with respect to the drying chamber during 24 hours of operation. The performance of the drying system with the best location was studied under different flow rates.

Natural Convection Solar Dryers for Agricultural Products — A Comprehensive Exploration

Objectives: To make review on passive solar dryers and its performance of drying agricultural products. Methods: This article focuses on the development in various categories of passive solar dryers in last six years. The different studies carried out in direct, indirect and mixed mode types of passive dryers for drying agricultural products in the year of 2014 to 2020 have been considered this review. Investigations on forced convection solar dryers have not been included in the current paper. The various experimental setups of solar dryers, specimens used for experimentation, measured output parameters and performance have been illustrated. The changes made in construction of solar dryers for improving the performance have also been reviewed. Findings:The mixed mode passive solar dryer is found to be superior in terms of drying time, better utilization of solar energy and efficiency compared to other passive dryers. Novelty: Several review articles have been published in solar dryers. Nevertheless, no comprehensive reviews have hitherto been published on passive dryers in particular. Hence, our current review article focuses on development in passive dryers and its advancements with emphasis on dryer design features, specimen and measured output parameters. Keywords: Passive solar dryers; Natural convection solar dryers; Direct solar dryers; Indirect solar dryers; Mixed mode solar dryers

Construction and Performance Analysis of a New Natural Convection Solar Dryer for Drying of Tomatoes and Green Chilies

Mechanical drying of farming items is a vitality expending activity in the post-gathering innovation. More prominent accentuation is given to utilizing sun powered vitality sources in this procedure because of the significant expenses and deficiencies of non-renewable energy sources. Therefore, an appropriate technology for drying of agricultural products has been developed and its performance of drying of tomatoes and green chilies was evaluated. A new solar dryer working on natural convection was developed. The point of this investigation is to assess dryer execution under natural convection methods of drying. In natural convection, air mass stream pace of 0.04849 kg/s was acquired. Heated sir stream reached on average drying temperature of 50.5°C in characteristic convection. The outcome acquired from natural convection methods of drying were likewise contrasted with open sun drying. The shading, flavor and time required for drying is good in solar drying when contrasted with sun drying.

Effect of blanching and solar energy-based drying models on the quality of dried shredded apples

This study aimed to find the best technology model to produce high-quality dried shredded apples as the resources of apple tea with the concept of green technology based on solar energy. Apple tea is a beverage product originated from Batu, Malang that is starting to be in high public demand because of its practical, sweet-scented nature and is believed to have a high content of apple antioxidants. This study determined the physical, nutritional, and bioactive changes resulting from the drying process of shredded apples, which were treated by blanching and non-blanching pre-treatment and dried using indirect convective solar drying and open sun drying. Blanched-shredded apples that were dried using an indirect convective solar dryer had the best vitamin C content and lowest mechanical damage, so it is prospective to be developed on a commercial scale as a raw material of apple tea.