Forced Convection Solar Dryer Research Articles

Drying of carrot slices in a triple pass solar dryer

An indirect triple pass forced convection solar dryer was developed and its performance was evaluated for drying of carrot slices. The drying experiments were carried out under the meteorological conditions of Coimbatore city in India during the year 2016. The experimental set-up consists of a blower, triple pass packed bed air collector (using sand) with wire mesh absorber plate, and a drying chamber. The air mass flow rate was optimized to 0.062 kg/s. The initial moisture content of the carrot slices was reduced from 87.5% (on wet basis) to the final moisture content of 10% (wet basis) in 6 h duration. The thin layer drying characteristics were analyzed using twelve mathematical models available in open literature. The results showed that the pick-up efficiency of the dryer was varied in the range between 14 and 43% with an average air collector thermal efficiency of 44% during the experimentation. The drying characteristics of carrot slices was predicted with good degree of accuracy using Wang and Singh drying model.

Thin layer drying characteristics of curry leaves (Murraya koenigii) in an indirect solar dryer

In this work, the thin layer drying characteristics of curry leaves (Murraya koenigii) has been studied in an indirect forced convection solar dryer with constant air mass flow rate of 0.0636 kg/s. Twelve thin layer drying models were tested for its suitability to describe the drying characteristics of curry leaves. The dryer has reduced the initial moisture content of curry leaves from 67.3% (wet basis) to the final moisture content of 4.75% (wet basis) in 3.5 hours. The pickup efficiency of indirect solar dryer for drying curry leaves was varied between 4.9% and 23.02%. Based on the statistical parameters, the Modified Henderson and Pabis model and Wang and Singh model were selected for predicting the drying characteristics of curry leaves. The payback period for the solar dryer was evaluated as 8 months, which is found to be much lower when compared with the entire life span of 15 years. The payback evaluation confirms that the solar dryer is economically viable in rural applications.

DETERMINATION OF THIN-LAYER SOLAR DRYING KINETICS OF CASSAVA NOODLES (TAPIOCA)

The aim of this study is to determine the thin-layer drying kinetics of cassava noodles (tapioca) using a solar dryer. To achieve this, an integral type forced convection solar dryer, equipped with rock storage, was developed. Drying kinetics of tapioca were determined using the solar dryer. The treatments in the experiment comprise of air flow velocities (V) of 1.5, 2.5, and 3.5 m/s; and drying layer thicknesses (B) of 0.48 and 0.72 cm. Tapioca samples were dried from an average initial moisture content of 297% (dry basis) to 9.8% (dry basis). Control experiments in the form of open air sun drying of similar quantity of tapioca were also set up and monitored. Graphical plots of moisture content versus drying time, exhibited the characteristic moisture desorption curve, characterized by initial high rate of moisture removal, followed by a slower rate of moisture removal. It was observed from drying rate curves plotted using the drying data, that the drying of the tapioca took place entirely in the falling rate period. The drying rate of the tapioca varied with the different combinations of velocity and drying layer thickness. The drying rate of the tapioca increased with increase in the air flow velocity until velocity of 2.5 m/s; beyond this velocity the drying rate reduced slightly. Also the drying rate of tapioca decreased with increase in drying layer thickness. A maximum drying rate of 39.2%/hr was obtained during the experiment. The maximum system drying efficiency of the dryer was determined as 47.14%, while the maximum dryer pick-up efficiency of 50% was determined during the drying test.

Mathematical modeling and performance analysis of thin layer drying of bitter gourd in sensible storage based indirect solar dryer

Abstract An indirect forced convection solar dryer integrated with porous sensible heat storage medium was developed. The effect of porous thermal storage and mass flow rate of air on the performance of the system for drying bitter gourd was studied. The experimental setup consists of a blower, solar flat plate collector with corrugated absorber plate (2 m 2 ) and a drying chamber. The thermal storage medium (pebble) is placed below the corrugated absorber plate, in the air passage as a porous medium. The experiments have been carried out with various mass flow rates of air and different drying models have been used for explaining the drying behaviour of sliced bitter gourd. The result shows that, (i) the initial moisture content 92% (w.b) of bitter gourd was reduced to 9% (w.b) in 7 h in the proposed drying system, while it was 10 h for open sun drying, (ii) the maximum specific moisture extraction rate was observed as 0.215 kg/kWh at the mass flow rate of 0.0636 kg/s and the corresponding specific energy consumption was 4.44 kWh/kg, (iii) the collector and drying efficiency of the system were 22% and 19% respectively. The two term model and Midilli–Kucuk model are most suitable for indirect solar dryer and open sun drying in terms of statistical parameter respectively. The drying inside sensible heat storage based indirect dryer was more consistent and produced better quality product as compared to open sun drying. Industrial relevance • Every year post harvest losses are increasing rapidly due to the lack of storage facilities. • Solar dryers are the most suitable technology that can be easily availed at low cost and in small scale and it can be used as an income generation option for farmers and women in rural areas. • The role of solar dryers in food processing industries is significant especially in developing countries in the following areas o For preserving fruits and vegetables o Dairy industries o Agricultural crop drying o Timber drying o Industrial waste drying • The utilization of thermal storage medium in the solar dryers is being focused much for the reasons of extending the availability of the system for operation and to achieve better quality of the products.

Performances and improvement potential of solar drying system for palm oil fronds

In this study, an indirect forced convection solar drying system was tested for drying of palm oil fronds. The drying of 100 kg of palm oil fronds via solar drying system reduced the moisture content from 60% (w.b) to 10% (w.b) in 22 h (3 d of drying). During the drying process, the daily mean values of the drying chamber inlet temperature, drying chamber outlet temperature, drying chamber air temperature, and solar radiation ranged from 26 °C to 75 °C, 25 °C–65 °C, 26 °C–67 °C, and 96 W/m2 to 1042 W/m2 respectively, with corresponding average values of 53 °C, 46 °C, 48 °C, and 580 W/m2. At average solar radiation of about 600 W/m2 and air flow rate 0.13 kg/s, the collector, drying system and pick-up efficiencies were found about 31%, 19% and 67% respectively. The specific moisture extraction rate (SMER) was 0.29 kg/kWh. The exergy efficiency varied between 10% and 73%, with an average of 47%. In addition, the improvement potential of solar drying system for palm oil fronds ranged from 8 W to 455 W, with an average of 172 W.

English

In spite of the high global demand for fish which is a major source of animal protein, nearly 10% (13 million tons) of the world’s total fish production is lost through spoilage due to inadequate cold storage and poor marketing/distribution channels. Fish is a highly perishable product that is processed by freezing, canning, salting and drying. About 40% of fish landings in developing countries are preserved through traditional processing methods (smoking, drying and salting) organized at artisanal level. As a result of increased trade and co-operation among neighboring African countries over the past years, processed products from the artisanal sector now form a significant part of the small pelagic fish products traded intra-regionally. Lake Victoria provides about 95% of the total fish landings in Kenya, with Rasrineobola argentea (one of the pelagic species) being the second commercially important fish. It is harvested in very large quantities and is readily available at affordable price and widely used for both domestic and industrial purposes. Open-sun drying is the main preservation method employed by the fish farmers and involves spreading the fish on open ground where it is exposed to contamination, infestation and adverse weather conditions. It is estimated that post harvest losses of between 20 and 50% occur especially during rainy seasons. Although, the landings of R. argentea are higher as compared to other fish species, the value of the catch is often very low due to these huge losses. In an effort to curb these losses, a model of an indirect forced convection solar dryer was developed and tested for thin layer drying of R. argentea fish. The fish, in 10 kg batches were loaded onto the dryer and the moisture content reduced from an initial value of 73% (w. b.) to between 16 and 20% (w. b.) after 11 h of drying at average air flow rate of 0.017 kg/s, where open sun drying took 18 h. The mean efficiencies of collector and drying systems were 9.36 ± 3.95% and 11%, respectively. The drying rate constants of the fish in dryer were found to be: 0.146, 0.206 and 0.148 for the fish in the top, middle and bottom trays, respectively.   Key words: Twin collector, indirect, forced convection, cabinet solar dryer, Rastrineobola argentea fish

Experimental study and simulation of a solar dryer for spearmint leaves (Mentha spicata)

An indirect forced convection solar dryer consisting of an air flat plate collector and a drying cabin was designed and fabricated to investigate its performance under the climate of Algiers. Drying experiments have been performed for spearmint leaves at different air flow rates in order to determine the drying velocity, the characteristic drying curve, the effective diffusion coefficient and the activation energy. A mathematical model based on thermal and mass balances over the component of the solar collector and the cabinet dryer was developed. Simulations are carried out for meteorological data of Algiers (Algeria). We analyse the effect of air mass flow rate, air temperature, products mass, collector area, air recycling rate on the drying time, the solar fraction and the efficiency of the dryer.

Experimental investigation of an indirect-mode forced convection solar dryer for drying thymus and mint

An indirect-mode forced convection solar dryer was designed and fabricated. The thermal performance of the solar dryer under Tanta (latitude, 30° 47′ N and longitude, 31° E) prevailing weather conditions was experimentally investigated. The system consists of a double pass v-corrugated plate solar air heater connected to a drying chamber. A blower was used to force the heated air to the drying chamber. Drying experiments were performed for thymus (initial moisture content 95% on wet basis) and mint (initial moisture content 85% on wet basis) at an initial temperature of 29°C. The final moisture contents for thymus and mint were reached after 34 and 5h, respectively. Fourteen mathematical models of thin layer drying were tested to specify the suitable model for describing the drying behavior of the studied products. It was found that, Midilli and Kucuk model is convenient to describe the thin layer solar drying of mint. However, the Page and modified Page models were found to be the best among others for describing the drying curves of thymus.

An Experimental Study and Analysis on Solar Drying of Bitter Gourd Using an Evacuated Tube Air Collector in Thanjavur, Tamil Nadu, India

The objective of this research work is to design and develop a forced convection solar dryer using evacuated tube air collector and study its performance on bitter gourd in Thanjavur District, Tamilnadu, India. The designed solar dryer consists of a drying chamber, evacuated tube air collector, a blower, and a chimney. Drying parameters, moisture ratio and drying rates, are calculated and their performance is compared with natural sun drying. The results of the present study show that the proposed solar dryer has greater efficiency, and the moisture content of bitter gourd is reduced from 91% to 6.25% in 6 hours as compared to 10 hours in natural sun drying. In this solar dryer, the products are uniformly dried, and the moisture content of the sample is controlled. It is found that the quality of the dried bitter gourd using solar dryer is higher than the natural sun-dried bitter gourd.

Effect of Using Energy Storage Material in an Indirect-mode Forced Convection Solar Dryer on the Drying Characteristics of Grapes

Effect of Using Energy Storage Material in an Indirect-mode Forced Convection Solar Dryer on the Drying Characteristics of Grapes

Experimental Study on Eggplant Drying by an Indirect Solar Dryer and Open Sun Drying

In this article, an indirect forced convection solar dryer is used to study the kinetic drying of eggplant. The effective moisture diffusivity calculated by slop method follows the solar intensity with the maximum value of 1.68 E-09 at 15 PM. Performance of solar dryer is determined by defining the efficiency of collector and an effectiveness factor as the ratio of the drying rate in the indirect solar dryer to the drying rate in the open sun. The collector efficiency and the effectiveness factor vary with the drying time inversely. Results show that the drying rate in the solar dryer is 3.5 g H O. g ds . Hr and is 2 g H O. g ds . Hr for 22 11 11

Design, Analysis and Experimental Evaluation of Photovoltaic Forced Convection Solar Dryer for the Tropics

The photovoltaic (pv) forced convection solar dryer comprises the solar collector, dryer and pv assemblies. It is designed for a continuous operation throughout the day. The direct solar irradiation is utilized during sunshine hours and it automatically switches power supply to the battery during cloud covers and non-insolation periods. The inclusion of a heat reservoir enables heat transfer to continue during this period. In this study, thermal and dryer analyses were done. Experimental investigations were carried out to evaluate the performance of the system by drying plantain chips. The useful power collected was found to be, 391.50W, collector efficiency, 65.6%, dryer efficiency, 39.6%, average drying rate during insolation, 0.0169kg/hr and total drying time was 23 hours. The maximum temperature attained was 55oC. The average drying non insolation period was 0.0112kg/hr. The capital cost is less than $350.

Drying of mint leaves in a solar dryer and under open sun: Modelling, performance analyses

In this study was investigated the thin-layer drying characteristics in solar dryer with forced convection and under open sun with natural convection of mint leaves, and, performed energy analysis and exergy analysis of solar drying process of mint leaves. An indirect forced convection solar dryer consisting of a solar air collector and drying cabinet was used in the experiments. The drying data were fitted to ten the different mathematical models. Among the models, Wang and Singh model for the forced solar drying and the natural sun drying were found to best explain thin-layer drying behaviour of mint leaves. Using the first law of thermodynamics, the energy analysis throughout solar drying process was estimated. However, exergy analysis during solar drying process was determined by applying the second law of thermodynamics. Energy utilization ratio (EUR) values of drying cabinet varied in the ranges between 7.826% and 46.285%. The values of exergetic efficiency were found to be in the range of 34.760–87.717%. The values of improvement potential varied between 0 and 0.017 kJ s −1. Energy utilization ratio and improvement potential decreased with increasing drying time and ambient temperature while exergetic efficiency increased.

Drying of Tomato Using a Solar Dryer with LPG Backup

Drying of Tomato Using a Solar Dryer with LPG Backup

Development of a Photovoltaic Powered Forced Convection Solar Dryer

This solar conversion system incorporates a suction fan powered by a solar PV module. Located at the outlet of the chamber is the d.c suction fan utilised to achieve forced air circulation without the use of external power supply like grid electricity, fossil fuel and battery. Simple thermal energy balance equations and heat transfer equations were employed in the design of the system. The operational efficiency of the collector is 83.2% and mass flow rate 1.58kg/min, the maximum temperature achieved in the chamber was 58oC. The system was used to dry vegetable, hydrophylum. The capital cost is less than $150.

SINGLE-LAYER DRYING BEHAVIOR OF MEXICAN TEA LEAVES (CHENOPODIUM AMBROSIOIDES) IN A CONVECTIVE SOLAR DRYER AND MATHEMATICAL MODELING

Single-layer solar drying experiments were conducted for Mexican tea leaves (Chenopodium ambrosioides) grown in Marrakech. An indirect forced convection solar dryer was used in drying the Mexican tea leaves at different conditions such as ambient air temperature (21° to 35°C), drying air temperature (45° to 60°C) with relative humidity (29 to 53%), airflow rate (0.0277 to 0.0556 m 3/s), and solar radiation (150–920 W/m2). The experimental drying curves showed only a falling rate period. In order to select the suitable form of drying curves, 14 mathematical models were applied to the experimental data and compared according to their statistical parameters. The main factor in controlling the drying rate was found to be the temperature. The drying rate equation was determined empirically from the characteristic drying curve. The diffusion coefficient of the Chenopodium ambrosioides leaves was estimated and varied between 1.0209 × 10−9 and 1.0440 × 10−8 m 2·s−1.The activation energy was found to be 89.1486 kJ·mol−1.

Mathematical modelling of thin layer drying process of long green pepper in solar dryer and under open sun

An experimental study was performed to determine the thin layer drying characteristics in a solar dryer with forced convection and under open sun with natural convection of long green pepper. An indirect forced convection solar dryer consisting of a solar air collector and drying cabinet was used in the experiments. Natural sun drying experiments were conducted for comparison at the same time. The constant rate period is absent from the drying curves. The drying process took place in the falling rate period. The drying data were fitted to 13 different mathematical models. Among the models, the logarithmic model for forced solar drying and the Midilli and Kucuk model for natural sun drying were found best to explain the thin layer drying behaviour of long green peppers. The performance of these models was investigated by comparing the coefficient of determination ( R), reduced chi-square ( χ 2) and root mean square error (RMSE) between the observed and predicted moisture ratios.

05/02599 Contributions of arsenic and chloride from the Kawerau geothermal field to the Tarawera River, New Zealand

In this paper, a comparative study of the drying characteristic of thin layer Ghost Chilli Pepper dried in an indirect-type forced convection solar tunnel dryer and under the open sun is presented. The forced convection solar dryer consists of two double-pass solar air heaters connected in series, a semi-continuous-type tunnel dryer, a shell and tube heat exchanger, and a blower. Nine kg of the ghost chilli pepper was dried in six trays of the dryer, and a sample of 200 g was dried separately in a small tray to measure the moisture removal rate. Simultaneously, another sample of 200 g was dried under the open sun. The moisture content of the chilli samples was reduced from its initial moisture content of 589.6% (db) to the final moisture content of 12% (db) in 123 h and 193 h dried in the solar dryer and under the open sun, respectively. To select the best drying model, eleven thin layer drying models available in literature were fitted to the experimental moisture ratio data. Among these models, Page and Modified Page model for the open sun drying and Midilli and Kucuk model for the solar dryer drying were found to be suitable.

Single layer solar drying behaviour of Citrus aurantium leaves under forced convection

Convective solar drying experiments in thin layers of Citrus aurantium leaves grown in Marrakech, morocco, were conducted. An indirect forced convection solar dryer consisting of a solar air collector, an auxiliary heater, a circulation fan and a drying cabinet is used for the experiments. The air temperature was varied from 50 to 60 °C; the relative humidity from 41% to 53%; and the drying air flow rate from 0.0277 to 0.0833 m3/s. Thirteen statistical models, which are semi-theoretical and/or empirical, were tested for fitting the experimental data. A nonlinear regression analysis using a statistical computer program was used to evaluate the constants of the models. The Midilli–Kucuk drying model was found to be the most suitable for describing the solar drying curves of Citrus aurantium leaves with a correlation coefficient (r) of 0.99998, chi-square (χ2) of 4.664 × 10−6 and MBE of 4.8381 × 10−4.

Mathematical modelling of a thin layer drying of apricots in a solar energized rotary dryer

In this paper we present a mathematical modelling of a thin layer forced solar drying of apricots. An indirect forced convection solar dryer consisting of a solar heater and a rotary column cylindrical drying (RCCD) cabinet was used in the experiments. Air heated by the solar air heater was forced through the apricots by an electrical fan. Moreover, the natural sun drying experiments were conducted for the comparison at the same time. Fourteen different thin layer mathematical drying models were compared according to their coefficients of determination (r,χ2, RMSE) to estimate solar drying curves. The effects of the drying air temperature, velocity and the rotation speed of column on the drying model constants and coefficients were predicted by multiple regressions using a linear type model. Copyright © 2004 John Wiley & Sons, Ltd.