Experimental Investigation of a Solar Bamboo Dryer

ABSTRACT

An experimental investigation was conducted on the performance of a solar box dryer for drying bamboo operating under tropical weather conditions. The dryer is a greenhouse-type designed for multi-crop solar drying. Air circulation was by electrically-operated fan. The results showed that the moisture content of the bamboo could be brought dovn to about 19% from an initial value of nearly 90% in 17 days by operating the dryer over 8 hours each day. under natural drying conditions, the final moisture content reached was only 22%. Although solar drying of bamboo was only marginally faster than natural drying. nonetheless. final moisture content was lower.     

Experimental Investigation of a Solar Bamboo Dryer

An experimental investigation was conducted on the performance of a solar box dryer for drying bamboo operating under tropical weather conditions. The dryer is a greenhouse-type designed for multi-crop solar drying. Air circulation was by electrically-operated fan. The results showed that the moisture content of the bamboo could be brought dovn to about 19% from an initial value of nearly 90% in 17 days by operating the dryer over 8 hours each day. under natural drying conditions, the final moisture content reached was only 22%. Although solar drying of bamboo was only marginally faster than natural drying. nonetheless. final moisture content was lower.     

COMPARISON OF TIMBER DRYING USING SOLAR ENERGY,ELECTRICAL HEATING AND DEHUMIDIFIER.

ABSTRACT

The performance of three different types of dryers for the hot air drying of sawn-limber planks are compared. These were the electric resistance dryer, solar dryer, and the dehumidifier dryer. Whilst the electric and solar dryers depended only upon hot air for drying, the dehumidifier dryer relied on hot dehumidified air. The results of investigations carried out on timber drying employing these three types of dryers in the Engineering Faculty are compiled and compared here in this paper. The results showed that the electric dryer produced the fastest drying lime and lowest moisture content, followed by dehumidifier drying. The solar dryer achieved a lower moisture content and a faster drying rate compared to natural drying, although the difference in drying times was marginal.     

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.     

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 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.     

SIMULATION OF DRYING IN A BATCH LUMBER KILN FROM SINGLE-BOARD TESTS

ABSTRACT

A deterministic model was developed to perform a board-by-board simulation of a forced convective batch lumber kiln. Individual board properties may be input and dryer operating parameters varied. The drying rates are empirical correlations based on single-board laboratory tests. The model incorporates the thermodynamic properties of the wood and gas, as well as mass and energy balances within the lumber stack. It also accounts for differences in heat and mass transfer resulting from position and changing gas properties throughout the dryer. The rate of drying predicted by the model and the final moisture content distribution were verified by weighing boards in a batch kiln before, during, and after drying. The application of the model is illustrated by simulating four common scenarios.     

Drying Kinetics of Tomato Slices in Vacuum Assisted Solar and Open Sun Drying Methods

A lab model vacuum-assisted solar dryer was developed to study the drying kinetics of tomato slices (4, 6, and 8 mm thicknesses) compared with open sun drying under the weather conditions of Montreal, Canada. The drying study showed that the time taken for drying of tomato slices of 4, 6, and 8 mm thicknesses from the initial moisture content of 94.0% to the final moisture content of around 11.5 ± 0.5% (w.b.) was 360, 480, and 600 min in vacuum-assisted solar dryer and 450, 600, and 750 min in open sun drying, respectively. During drying, it was observed that the temperature inside the vacuum chamber was increased to 48°C when the maximum ambient temperature was only 30°C. The quality of tomato slices dried under vacuum-assisted solar dryer was of superior quality in terms of color retention and rehydration ratio. The drying kinetics using thin-layer drying models and the influence of weather parameters such as ambient air temperature, relative humidity, solar insolation, and wind velocity on drying of tomato slices were evaluated.     

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.     

DESIGN AND TESTING OF A COMBINED CONDUCTION-CONVECTION ROTARY PADDY DRYER

ABSTRACT

A rotary drum dryer prototype was designed, fabricated and tested to combine convection drying with conduction heating of paddy to increase moisture reduction rates. Ambient air forced inside the drum counter-flow to the direction of the cascading grains brought about “dryeration” of the hot grains, resulting in cooler grain output and increased moisture reduction rates. Its partial drying capacity doubled that of the benchmark pre-dryer at 5?rpm drum speed and quadrupled at 7?rpm, requiring only a single-pass operation. Tests using freshly harvested and re-wetted paddy showed that partial drying capacity, final moisture content and moisture reduction rate were all significantly affected by counter-flow air velocity, Its overall thermal efficiency was also 50% higher.     

Dehydration of Garlic Slices by Combined Microwave-Vacuum and Air Drying

Abstract

Combination of microwave-vacuum drying and air drying was investigated as a potential mean for drying garlic slices. The sample was dried by microwave-vacuum until the moisture content reached 10% (wet basis), and then by conventional hot-air drying at the temperature of 45°C to final moisture content less than 5% (wet basis). Pungency, color, texture, and rehydration ratio of garlic slices dried by this method were evaluated and compared with those dried by freeze drying and conventional hot-air drying. The comparison showed that the quality of garlic slices dried by the current method was close to that of freeze dried garlic slices and much better than that of conventional hot-air dried ones. The lab microwave-vacuum dryer which the materials to be dried could be rotated in the cavity was developed by the authors.     

PERFORMANCE STUDY OF A RE-CIRCULATING CABINET DRYER USING A HOUSEHOLD DEHUMIDIFIER

ABSTRACT

The performance and operating characteristics of a low temperature re-circulating cabinet dryer using a dehumidifier loop were studied using alfalfa. Chopped alfalfa, initially at 70% moisture content, was dried to 10% moisture content in the dryer. Two dryer setups were used. The dryers in each case had a partitioned cabinet with trays of material on one side and a stack of one or two small household dehumidifiers on the other side. Air was re-circulated through the material from bottom to the top and back through the dehumidifiers. Two drying configurations were tested. In one, the material was left on the trays until drying was complete (batch or fixed tray drying). In the other configuration, the trays were moved from top to bottom, introducing a new tray at the top while removing an old tray from bottom. Drying air temperature ranged from 25 to 45°C. The average air velocity through the material was 0.38 m/s. Alfalfa chops dried in 5 h in the fixed tray drying and in 4 h in the moving tray drying. The specific moisture extraction rate ranged from 0.35 to 1.02 kg/kWh for batch drying and stayed at an average value of 0.50 kg/kWh for continuous/moving tray drying.     

Effect of drying using solar energy and phase change material on kiwifruit properties

Solar energy has great potential as an alternative energy source, but variations in solar radiation require the use of additional energy sources to maintain a continuous drying process. We developed a process for drying kiwifruit using a solar dryer and an energy accumulation system with paraffin wax as phase change material. The final moisture content, total polyphenols, and antioxidant capacity were evaluated and compared with freeze drying. The analyzed experimental factors were kiwi slice thickness and the use or nonuse of fuzzy logic control systems to regulate the air flow through the devices. Critical moisture content, shrinkage, solar panel, and solar energy accumulator efficiencies were calculated. In addition, five empirical models were fitted to the drying curves. The solar panel showed an efficiency between 56 and 76%. The use of the fuzzy logic control system extended the period of available energy, thus prolonging the use of the solar panel and solar energy accumulator and using only 10% of the stored energy; otherwise, without the control system, 43% of the stored energy was used. The highest drying rates were achieved for kiwifruit slices 4?mm thick, using the solar dryer with the control system. The loss of polyphenols and antioxidant capacity were minimal for kiwifruit slices of thickness 8?mm without the control system.     

Modelling and Simulation of a Direct Contact Rotary Dryer

ABSTRACT

A mathematical model able to predict solid and drying gas temperature and moisture content axial profiles along a direct contact rotary dryer was developed. The study was focused on the drying kinetics based on phenomenological models. Two different drying mechanisms in the decreasing drying rate period were tested: proponional to the unbound moisture content and moisture diffusion inside the particle. Experimental data collected in a pilot-scale direct contact rotary dryer was used to validate the model. Soya and fish meals were used as drying material.     

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.     

Optimization of Rubber Wood Drying by Response Surface Method and Multiple Contour Plots

Abstract

By adopting the central-composite experiment design, the response surface methodology was used to optimize operating conditions of rubber wood drying. The independent variables are initial moisture content of rubber wood, and three drying environment parameters namely, temperature, relative humidity, and air velocity. The investigating responses are final moisture content, drying time, and energy consumption. The restriction of the optimization is the designated final moisture content, which is not greater than 16%. The third-order polynomial models with transformed responses were developed from experiment data to generate 3-D response surfaces and contour plots. The analysis of variance (ANOVA) was performed to identify the significant parameters affecting the rubber wood drying. Drying temperature and holding relative humidity are those two influential operating parameters that significantly control the final moisture of rubber wood and affect the drying time and energy. The multiple contour plots of drying responses show that the optimum operating regions are located mainly at high temperature drying zone. The high temperature drying practice can save energy and drying time by 44 and 25% respectively, in comparison to the conventional temperature drying.     

OPTIMUM STRATEGY FOR FLUIDIZED BED PADDY DRYING

Abstract

A feasibility study of paddy drying by fluidization technique was conducted. Operating parameters affecting product quality, drying capacity and energy consumption were investigated. Experimental results showed that drying rate of a paddy kernel was controlled by diffusion. However, drying capacity of a dryer increased with specific air flow rates and drying air temperatures. Energy consumption was reduced when specific air flow rate decreased or when fraction of recycled air increased. Maximum temperature should be limited to 115%C and final moisture content of paddy at 24-25% dry basis if product qualities were maintained. Simulated results obtained from a developed mathematical model indicated that the optimum operating parameters should be as follows : fraction of air recycled of 80%, air velocity of 4.4 m/s, bed thickness of 9.5 cm and specific air flow rate of 0.1 kg/s-kg dry matter. An economic analysis showed that total drying cost was US$ 0.08/kg water evaporated.     

Experimental and Simulated Performances of a Batch-Type Longan Dryer with Air Flow Reversal Using Biomass Burner as a Heat Source

This article presents experimental performance of a batch-type longan dryer using a biomass burner with air flow reversal and also presents modeling of the longan dryer for drying of whole longan. The dryer essentially consists of a biomass burner and a drying bin with an arrangement for periodic air flow reversal. Three drying runs with loading capacity of 2,000, 1,500, and 1,000 kg of whole longan were carried out. There was no significant difference in temperatures in different positions (except inlet and outlet) inside the dryer (p < 0.05) or moisture content inside the dryer (p < 0.05). Whole longan was dried from an initial moisture content of 74% (wb) to a final moisture content of 14% (wb). The drying time of whole longan in the longan dryer was 60, 54, and 48 h for 2,000, 1,500, and 1,000 kg loading, respectively. The quality of dried product was also good in comparison to the high-quality product in markets.

To simulate the performance of the longan dryer for drying of whole longan, a set of partial differential equations was developed and the equations were solved using the finite difference technique. The numerical solution was programmed in Compaq Visual FORTRAN version 6.5 (Compaq Computer Corp., TX). The simulated moisture contents agreed well with the experimental data. This model can be used to provide the design data and it is also essential for optimal dryer design.     

DYNAMIC SIMULATION AND CONTROL OF CONVEYOR-BELT DRYERS

Abstract

The dynamic behavior of conveyor-belt dryers involving externally controlled heat and mass transfer phenomena has been studied via digital simulation. The investigation concerned an industrial dryer used for the moisture removal from wet raisins. The dryer consisted of three drying chambers and a cooling section, all involving the same conveyor belt. For each chamber, perfect temperature control was assumed for the drying air temperature, while its humidity was left uncontrolled. The effect of material temperature and moisture content at the entrance of the dryer and the drying air temperature on material temperature and moisture content at the exit of the dryer and the corresponding drying air humidity, have been explored by step forcing the disturbance and manipulated variables in the non-linear dryer model simulator. Results showed that material moisture content at the exit of the dryer is greatly affected by material moisture content at the entrance as well as by the drying air temperature. Reliable transfer functions for each process module were obtained by fitting several transfer function models on the simulated data using a least-squares approach. It was found that when input material moisture content could be instantly measured, the system responded slowly enough so that excellent control could be achieved for material moisture content at the exit of each chamber. In this case a Pi-feedback cascade temperature controller was used. When a 15 sec delay measuring sensor was introduced, poor performance was observed. A simplified lead-lag feedforward controller, added to the system, in conjunction with the primary Pi-feedback cascade controller, resulted in good control performance of the delay sensor system.