EXPERIMENTAL INVESTIGATION ON SOLAR DRYING OF FISH USING SOLAR TUNNEL DRYER

This paper presents field level performance of the solar tunnel dryer for drying of fish. The dryer consists of a transparent plastic covered flat plate collector and a drying tunnel connected in series to supply hot air directly into the drying tunnel using four d.c. fans, operated by two 40 watt solar modules. This dryer can be used to dry upto 150 kg of fish and three sets of full scale field level drying runs for drying silver jew (Johnius argentatus) fish were conducted in February-March, 1999. The temperature of the drying air at the collector outlet varied from 35.1 ° C to 52.2 ° C during drying. The fish was initially treated with dry salt and stacked for about 16 hours before drying. The salt treated fish was dried to a moisture content of 16.78% (w.b.) from 67% (w.b.) in 5 days of drying in solar tunnel dryer as compared to 5 days of drying in the traditional method for comparable samples to a final moisture content of 32.84%. In addtion, the fish dried in the solar tunnel dryer was completely protected from rain, insects and dust, and the dried fish was a high quality product.     

Solar Drying of Peeled Longan Using a Side Loading Type Solar Tunnel Dryer: Experimental and Simulated Performance

This article presents experimental and simulated results of drying of peeled longan in a side-loading solar tunnel dryer. This new type of solar tunnel dryer consists of a flat-plate solar air heater and a drying unit with a provision for loading and unloading from windows at one side of the dryer. These are connected in series and covered with glass plates. A DC fan driven by a 15-W solar cell module supplies hot air in the drying system. To investigate the experimental performance, five full-scale experimental runs were conducted and 100 kg of peeled longan was dried in each experimental run. The drying air temperature varied from 32 to 76°C. The drying time in the solar tunnel dryer was 16 h to dry peeled longan from an initial moisture content of 84% (w.b.) to a final moisture content of 12% (w.b.), whereas it required 16 h of natural sun drying under similar conditions to reach a moisture content of 40% (w.b.). The quality of solar-dried product was also good in comparison to the high-quality product in markets in terms of color, taste, and flavor. A system of partial differential equations describing heat and moisture transfer during drying of peeled longan in this solar tunnel dryer was developed and this system of nonlinear partial differential equations was solved numerically by the finite difference method. The numerical solution was programmed in Compaq Visual FORTRAN version 6.5. The simulated results agreed well with the experimental data for solar drying. This model can be used to provide the design data and it is essential for optimal design of the dryer.     

Experimental Investigation of a Photovoltaic-Powered Solar Cassava Dryer

This communication describes the design and experimental performance evaluation of a photovoltaic (PV)-powered solar drying system suitable for processing of export-grade cassava developed at the National Centre for Energy Research and Development, University of Nigeria, Nsukka. The drying system, which is capable of handling about 50 kg of fresh crop per batch, comprises an 8.40 m² roof-type solar collector; a drying unit with five trays, each with a cross-sectional area of 0.60 m²; and a PV-powered 90 WAC blower. The experience gained with the solar drying system described here indicates that, in essence, the unit is structurally and functionally operative. The experimental results suggest that, even under unfavorable weather conditions, the unit is able to produce good quality products. Although the active dryer is more expensive than a passive drying system of comparable capacity, it is nonetheless suitable for application in rural, off-grid agricultural settlements in Nigeria.     

THIN LAYER SOLAR DRYING OF SOME VEGETABLES

In this study, a solar cabinet dryer consisting of a solar air heater and a drying cabinet, was used in drying experiments. Pumpkin, green pepper, stuffed pepper, green bean, and onion were dried in thin layers. Three different drying air velocities were applied to the process of drying to determine their effects on drying time. Fresh materials were dried by a natural sun drying method. In order to explain drying curves of these products different moisture ratio models were performed and evaluated based on their determination coefficients (R²). Our results revealed that drying air temperature could increase up to about 46°C. Drying air velocity had an important effect on drying process. Drying time changed between 30.29 and 90.43 hours for different vegetables by the solar drying. This drying time was between 48.59 and 121.81 hours for the natural sun drying. Drying curves could be explained by determined thin layer drying models satisfactorily with very high determination coeffcients.     

Mathematical Modeling of Drying Characteristics of Indian Mackerel (Rastrilliger kangurta) in Solar-Biomass Hybrid Cabinet Dryer

Eight trials were conducted for drying mackerel by a solar biomass hybrid cabinet dryer (S-BHCD) and open sun drying (OSD) at air temperatures of 32.39–57.69°C, relative humidity 23.9–85.8%, and air flow rate of 0.20–0.60 m/s. The solar radiation ranged between 287 and 898 W/m² during the time of experimentation. At nighttime, drying was carried out by combusting biomass. The initial moisture content of the processed mackerel was 72.50±0.44% (w.b.) and was reduced to the final moisture content of 16.67±0.52% (w.b.) in S-BHCD and 16.92±0.54% (w.b.) in OSD. Eleven drying models were used and the coefficients of determination (R ²) and constants were evaluated by nonlinear regression to estimate the drying curves of dried mackerels. The Midilli model was found to more satisfactorily describe the drying process of mackerel in S-BHCD with R ² of 0.9999, χ² of 0.0000374, and RMSE of 0.0057. In the OSD, a two-term drying model satisfactorily described the drying process with R ² of 0.9996, χ² of 0.0000519, and RMSE of 0.0072. The variation of Free Fatty acid (FFA), Peroxide value (PV), Thiobarbituric acid (TBA), Total volatile bases nitrogen (TVB-N), Trimethylamine nitrogen (TMA-N), and histamine contents of dried mackerel by using S-BHCD showed very high corresponding coefficients of determination, where all R ² were greater than 0.90, except TBA value. Bacterial count and mold growth were decreased significantly (P < 0.05). There was no discoloration of the product during 4 months of storage. Contour plots of S-BHCD and OSD dried mackerel also showed that for all sensory attributes examined, panelists preferred fish dried with S-BHCD. The organoleptic analysis showed that the S-BHCD drying methods have a highly significant effect (P < 0.01) on texture and overall acceptability. Biochemical, microbial analysis, and sensory evaluation showed that the product was in prime acceptable form for 4 months of storage at ambient temperature.     

DESIGN FOR LUMBER DRY KILN USING SOLAR/WOOD ENERGY IN TROPICAL LATITUDES

Developing countries with a timber resource that can be manufactured into finished products either for local use or export often lack the capital to build high-cost dry kilns. Many of these countries are in the tropics where solar radiation and ambient temperatures are high. The low-cost solar/wood energy lumber dry kiln described in this report was designed and tested for such countries where solar dry kilns can be built and operated at low cost.

The design is for a 14-m"6,000-fbm capacity kiln having an insulated drying compartment, an external horizontal solar collector, and a furnace room containing a wood burner. Capacities larger or smaller than 6,000 fbm are also possible. This design allows collector and wood burner sizing to match the energy demands of the dryer. The design also incorporates low-cost controls that allow unattended drying when operated as a solar-only dryer. Manual firing is necessary when the wood-burning system is supplying the energy.     

A Novel Design of Crop Dryer for Use in Developing Countries

The dryer is required for drying of grain as well as drying of the processed products in small catchment agro processing centers in the developing world. However, due to varied material characteristics of grain and secondary processed product, two entirely different types of dryers are required. The grain is dried in a recirculatory dryer, whereas processed product is dried in a tray dryer, where it is frequently mixed and trays are also intermittently changed. To avoid the need for two dryers, a novel design of a low-cost hot air dryer was developed where just by changing the trays the dryer can be converted from an LSU grain dryer to a tray-type product dryer. The dryer was tested for drying soybean grain as well as processed soy products like blanched soybean dal and soyflakes. The capacity of the dryer was 100 kg/batch in a tray dryer with each tray accommodating 10 kg of wet material. In case of LSU mode, the capacity of the dryer was 250 kg of grain per batch. The drying time required was 5 h for 250 kg of wet soybean from 24 to 10% moisture content, whereas in a tray dryer 100 kg blanched soybean dal was dried from 60 to 10% in 5 h and 100 kg of soyflakes from 25% moisture content to 10% moisture in 1.75 h. The cost of the dryer is estimated at US$580.00 and it can be fabricated in a moderately equipped workshop in developing countries.     

A Novel Design of Crop Dryer for Use in Developing Countries

The dryer is required for drying of grain as well as drying of the processed products in small catchment agro processing centers in the developing world. However, due to varied material characteristics of grain and secondary processed product, two entirely different types of dryers are required. The grain is dried in a recirculatory dryer, whereas processed product is dried in a tray dryer, where it is frequently mixed and trays are also intermittently changed. To avoid the need for two dryers, a novel design of a low-cost hot air dryer was developed where just by changing the trays the dryer can be converted from an LSU grain dryer to a tray-type product dryer. The dryer was tested for drying soybean grain as well as processed soy products like blanched soybean dal and soyflakes. The capacity of the dryer was 100 kg/batch in a tray dryer with each tray accommodating 10 kg of wet material. In case of LSU mode, the capacity of the dryer was 250 kg of grain per batch. The drying time required was 5 h for 250 kg of wet soybean from 24 to 10% moisture content, whereas in a tray dryer 100 kg blanched soybean dal was dried from 60 to 10% in 5 h and 100 kg of soyflakes from 25% moisture content to 10% moisture in 1.75 h. The cost of the dryer is estimated at US$580.00 and it can be fabricated in a moderately equipped workshop in developing countries.     

Evaluating a Solar Dryer for In-Shell Drying of Split Pistachio Nuts

Abstract

A thin-layer forced air solar dryer was designed to study the feasibility of drying pistachio nuts. The dryer was tested during the 2001 and 2002 drying seasons. The maximum temperature in the solar collector reached 56°C, which was 20°C above the ambient temperature. The required drying time was 36 h. During the first day of drying (0800 to 1700 h) the moisture content dropped to about 21% (wb). The final moisture content of the dried nuts was 6% wb, which was 1% below the recommended storage moisture. The drying constant of the pistachio nuts during solar drying was determined using two mathematical models, a one-term series solution of Fick's diffusion equation and an exponential decaying model. There was no significant difference between the two models (α = 0.05). In general, the quality of solar dried nuts was better than the conventional heated air due to slower drying rates.     

Performance evaluation of parabolic greenhouse-type solar dryer used for drying of cayenne pepper

Abstract

This study examines the performance of a parabolic greenhouse-type solar dryer used for drying of cayenne pepper (Capsicum annuum) in Nan (northern Thailand). The dryer has a base area of 6.0?m × 8.2?m and a height of 3.25?m with the loading capacity of 100–200?kg for fruit or vegetables. It has a parabolic roof structure covered with polycarbonate sheets and is placed on a concrete floor. It is ventilated by three DC fans powered by a 50-Watt solar cell module. The produce is placed on trays with wire mesh base and located on steel supports. Among the advantages of this type of dryer is that the product is protected from rain, dust and insects. The pepper samples consisted of whole pods or cut pods. The drying experiments were carried out in the solar dryer and in an electrical (convective) tray dryer. The study was focusing on drying kinetics and on the effects of the drying treatments on one of the main quality attributes namely the capsaicin content in the dried products.     

Sewage Sludge Solar Drying: Experiences from the First Pilot-Scale Application in Greece

Increasingly strict regulations governing sludge management have raised interest in drying technologies. The feasibility of sewage sludge solar drying was experimentally evaluated in a 66-m² pilot-scale greenhouse plant under typical weather conditions in Greece. The greenhouse was equipped with ventilation fans to maximize the drying process efficiency and a turning drum for efficient sludge mixing. The obtained results proved the applicability and the high performance of the solar drying technology. The time necessary to achieve a dry product with a dry solids content up to 95% ranged between 8 and 31 days, depending on the weather conditions. During drying, sludge organic matter was reduced by 5–21%, and total and fecal coliform content was also decreased up to three orders of magnitude. By taking into consideration the sludge content in heavy metals, the final product can partially or totally replace commercially available inorganic fertilizers in agricultural applications, in accordance with the restrictions imposed by national and European regulations. Based on a preliminary cost analysis concerning the construction of a solar drying facility covering a sum of 80,000 population equivalent (PE), a corresponding capital cost of 24 €/PE is anticipated.     

THIN LAYER SOLAR DRYING OF SOME VEGETABLES

In this study, a solar cabinet dryer consisting of a solar air heater and a drying cabinet, was used in drying experiments. Pumpkin, green pepper, stuffed pepper, green bean, and onion were dried in thin layers. Three different drying air velocities were applied to the process of drying to determine their effects on drying time. Fresh materials were dried by a natural sun drying method. In order to explain drying curves of these products different moisture ratio models were performed and evaluated based on their determination coefficients (R²). Our results revealed that drying air temperature could increase up to about 46°C. Drying air velocity had an important effect on drying process. Drying time changed between 30.29 and 90.43 hours for different vegetables by the solar drying. This drying time was between 48.59 and 121.81 hours for the natural sun drying. Drying curves could be explained by determined thin layer drying models satisfactorily with very high determination coeffcients.     

DESIGN AND CONTINUOUS OPERATION OF A SOLAR CONVECTION DRIER WITH AN AUXILIARY HEATING SYSTEM

A solar drier of the through-draft type (4 trays at 0.5 m² surface area) with natural air convection and an auxiliary gas heating system was constructed. General relationships between the climatic conditions of the ambient air, product load and drying characteristics were established. Test runs with the drier as continuous equipment were carried out over a period of 24 h, using carrot dice as experimental material. Air flow rates through the dryer between 100 and 140 kg/h and overall drying rates between 1.5 and 2 kg/h were reached. The overall energy efficiency coefficient for the hybrid heating system amounted to 27 % as compared to 31 to 37 % for the solar energy heating alone and to 22 to 27 % for gas heating energy alone. A combination of continuous drying in the first stage with subsequent batch-wise finish drying in the same or a supplementary drier seems to be advantageous.     

Drying Of Vanilla Pods Using A Greenhouse Effect Solar Dryer

ABSTRACT

This paper describes the basic design of the GHE solar dryer and evaluates the performance of the dryer when used to dry vanilla pods. From laboratory test results it was indicated that the average drying time for vanilla pods was between 49 to 53, 5 hrs, for the case of heating augmentation using coal briquette stoves. The total amount of coal briquettes used to produce drying air temperature between 33 C to 65 C and RH of about 34% during day time was 61 kg equivalent to 6.1 kW heating rate and the average electric energy usage of 36.5 kWh, respectively. Quality test results indicated that the dried products were of grade IA of the export quality standard with vaniline content of 2.36%.     

Secondary coal recovery from slurry ponds utilizing solar drying

The drying of moist, fine coal waste was experimentally studied using an indoor batch dryer with a constant-radiation heat source. The effect of air velocity and radiation level on the coal drying rate was investigated and an analytical correlation obtained. Outdoor direct solar drying of coal waste was studied in a 3.1 m² dryer. The solar dryer was able to dry coal at a rate of about 14 kg of coal per day per square metre of solar collector area. The simple pay-back period for such a system is between 2.5 to 5 years.     

DESIGN,EXPERIMENTAL AND ECONOMIC EVALUATION OF A COMMERCIAL-TYPE SOLAR DRYER FOR PRODUCTION OF HIGH-QUALITY HAY

Abstract

Design features, development, experimental functional performance and economic evaluation of an energy efficient solar energy dryer for commercial production of high-quality hay and processed forage products are presented. The solar hay dryer consists of an improved solar collector with selective coated aluminum absorber plate and spaced fins, and a drying shed connected to the collector by an insulated duct and having a perforated metal grate floor, swing-away plywood frames and polyethylene curtains for effectively sealing the hay stack, and a crawl space below the floor where a 3-hp in-line centrifugal fan is housed for air circulation by suction. In late August and in early September, 1996, 160 small rectangular bales of alfalfa hay with about 25% bromegrass were successfully dried from 33% initial moisture content to 13%, and from 25% to 11% moisture in 4 and 3 days, respectively, under average weather conditions in Saskatoon, Saskatchewan, Canada. With about 18 m³/min per tonne airflow, 10-15 °C temperature rise above ambit was obtained during peak bright sunshine hours. Relatively high daily average collector Effciency of 76%, high drying effectiveness, drying uniformity, uniform air distribution and tight sealing of the stack were achieved which resulted in an attractive green color of hay, no mold growth on hay, and an overall system drying efficiency of about 79%. Compared to a conventional natural gas drying system or field-drying method, the payback period on extra investment costs recovered through drying cost savings of $3/ t to $6/ t or through over two times higher prices for high-quality hay produced by the solar drying system may be just one or two years, respectively.     

Effect of ambient conditions on drying of herbs in solar greenhouse dryer with integrated heat pump

An even span solar greenhouse dryer was built and applied to dry Java tea (Orthosiphon aristatus) and Sabah snake grass (Clinacanthus nutans Lindau). Findings showed that the solar greenhouse dryer performs satisfactorily during clear weather except at nighttime and rainy day due to product rehydration which is heavily influenced by high relative humidity from ambient air. Integrating of heat pump into the solar greenhouse dryer has successfully reduced the room relative humidity by 10–15%. Also, heat pump has mitigated the product rehydration issue by maintaining room relative humidity at maximum of 65% throughout the drying period. The drying rate of Java tea was improved three to fourfold, i.e., from 0.004–0.008 to 0.018–0.025?g H₂O/g DM min, whereas 10% of drying time was saved for both Java tea leaf and Sabah snake grass leaf with the assistance of heat pump system. Meanwhile, the supply of dry air from the heat pump system with a magnitude of 0.25–0.50?m/s helps in enhancing the drying rate of the herbs as well as minimizing the nonuniformity of drying temperature and relative humidity inside the solar greenhouse dryer.     

Development and Performance Analysis of a New Solar Energy-Assisted Photocatalytic Dryer

A novel patented solar energy-assisted photocatalytic closed-type dryer (SEPCD) was developed to produce dried agro-foods without using chemical additives for antisepsis and/or color retention and to retain higher nutritive value of the fresh produce. The SEPCD was designed to simulate open sun drying with moving dry air and mild temperature. The air temperature in the drying cabinet is maintained at 40-45°C; it is supplied partially by a dehumidification system and partially by a solar energy system. Additionally, the inside of the cabinet was coated with titanium dioxide (TiO₂) to cause a bactericidal effect during the drying process. Results showed that the total mold and bacterial counts for the drying cabinet and dried pineapple slices are significantly reduced in the SEPCD while the dried food quality is also better than that dried by conventional hot air drying.     

A Method for Determination of Porosity Change from Shrinkage Curves of Deformable Materials

The novel low-cost band thermodynamic dryer equipped with a solar collector, a parabolic focusing collector, a heat exchanger, screw fan, and a drying cabinet with a band was designed and tested. The maximum temperature in the solar collector reached 85°C, which was 55°C above the ambient temperature. The required drying time was 4.5 h, much reduced from the traditional solar drying time of 48 h. The final moisture content of the Roselle calyx was 12% w.b., which is the recommended storage moisture content. Measurements of ambient temperature and humidity, air temperature, and relative humidity inside the dryer as well as solids moisture loss-in-weight data are employed as a means to study the performance of the dryer. Solar drying was compared with conventional sun drying and heated air drying, using the following evaluation criteria: drying time, dried Roselle color, texture, taste, and production cost. For evaluation, a model-based Technique for Order Preference by Similarity to Ideal Solution (TOPSIS) methodology was used. After the evaluation, the proposed continuous solar dryer was found to be better than conventional drying and heated air drying due to slower drying rate and better quality of the dried Roselle.     

SOLAR DRYING. FOR REAL APPLICATIONS

The techniques of professional drying can be utilized in solar drying with the view to satisfy the real needs of large agricultural productions and secure product quality and standardization. A solar batch convection dryer designed along this line is presented and its performance for drying fruits and vegetables is discussed together with the techniques used to dry these products.