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

ABSTRACT

An experimental investigation use conducted on the performance of a solar box dryer for drying bamboo operating under tropical rearher conditions. The dryer is a greenhouse-type designed for multi-crap solar drying. Air circulation was by electrically-operated fan. The results shoved that the moisture content of the bamboo could be brought down 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 conditiona. the final moisture content reached was only 12%. Although eolar drying of bamboo vaa only marginally faster than nacural drying. noncrhelesa. final moisture content was lower.     

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.     

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.     

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.     

Dynamic Modeling and a Parametric Study of an Indirect Solar Cabinet Dryer

A dynamic mathematical model for drying of agricultural products in an indirect cabinet solar dryer is presented. This model describes the heat and mass transfer in the drying chamber and also considers the heat transfer and temperature distribution in a solar collector under transient conditions. For this purpose, using conservation laws of heat and mass transfer and considering the physical phenomena occurring in a solar dryer, the governing equations are derived and solved numerically. The model solution provides an effective tool to study the variation of temperature and humidity of the drying air, drying material temperature, and its moisture content on each tray. The predicted results are compared with available experimental data. It is shown that the model can predict the performance of the cabinet solar dryer in unsteady-state operating conditions well. Furthermore, the effect of some operating parameters on the performance and efficiency of dryer is investigated and compared with selected published data.     

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.     

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.     

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.     

SIMULATION OF THE MIXED-MODE NATURAL-CONVECTION SOLAR DRYING OF MAIZE

A mathematical model for mixed mode natural convection solar drying of maize grain is presented. The drying is described by a deep bed procedure that includes conduction within the grain bed. The conduction is due to radiative energy falling on the upper surface of the bed. The results show that temperatures at the top and bottom of the bed are higher than that in the middle resulting in two drying fronts one at the top and the other at the bottom of the bed and moving in opposite directions. This results in more uniform moisture content distribution than in an indirect dryer. The results are verified against experimental data from a prototype mixed mode natural convection maize solar dryer. The laboratory solar dryer was constructed at Newcastle University, U.K. and the experiments carried out under a solar simulator. The agreement between theory and experiment is very good.     

SIMULATION OF THE MIXED-MODE NATURAL-CONVECTION SOLAR DRYING OF MAIZE

A mathematical model for mixed mode natural convection solar drying of maize grain is presented. The drying is described by a deep bed procedure that includes conduction within the grain bed. The conduction is due to radiative energy falling on the upper surface of the bed. The results show that temperatures at the top and bottom of the bed are higher than that in the middle resulting in two drying fronts one at the top and the other at the bottom of the bed and moving in opposite directions. This results in more uniform moisture content distribution than in an indirect dryer. The results are verified against experimental data from a prototype mixed mode natural convection maize solar dryer. The laboratory solar dryer was constructed at Newcastle University, U.K. and the experiments carried out under a solar simulator. The agreement between theory and experiment is very good.     

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.     

Drying characteristics in a jet-spouted bed dryer

A conical jet-spouted bed dryer with inert bodies was used for drying of animal blood plasma. The effects of the operating conditions on the product properties, final moisture content and throughput of the dryer were investigated. A drying rate model using the conventional rate equation, where the overall effective driving force is based on the surface temperature calculated from the unsteady-state heat transfer Fourier equation, was proposed. Satisfactory agreement between calculated and experimental results was obtained.     

Optimization of Drying of Olive Leaves in a Pilot-Scale Heat Pump Dryer

Recently, the interest in olive leaf has increased due to its high phenolic content. It has a high potential for industrial exploitation in food industry and the main process in olive leaf treatment is drying. Drying affects the product quality and is an energy-intensive process, so the use of heat pumps in drying processes that have low operating cost has attracted the attention of the investigators. In this study, response surface methodology was used to optimize operating conditions of drying of olive leaves in a pilot-scale heat pump conveyor dryer. The independent variables were air temperature, air velocity, and process time, and the responses were total phenolic content and antioxidant activity loss, final moisture content, and exergetic efficiency. Optimum operating conditions were found to be temperature of 53.43°C, air velocity of 0.64 m/s, process time of 288.32 min. At this optimum point, total phenolic content loss, total antioxidant activity loss, final moisture content, and exergetic efficiency were found to be 9.77%, 44.25%, 6.0% (w.b.), and 69.55%, respectively.     

The drying kinetics of seeded grape in solar dryer with PCM-based solar integrated collector

This paper presents a novel type of dryer for experimentally evaluating the drying kinetics of seeded grapes. In the developed drying system, it has been particularly included an expanded-surface solar air collector, a solar air collector with phase-change material (PCM) and drying room with swirl element. An expanded-surface solar air collector has been used to achieve high heat transfer and turbulence effect whiles a solar air collector with PCM has been used to perform the drying process even after the sunset. On the other hand, the swirl elements have been located to give the swirl effect to air flow in drying room. These advantages make the proposed novel system a promising dryer in that lower moisture value and less drying time. The drying experiments have been carried out simultaneously both under natural conditions and by the dryer with swirl flow and without swirl flow at three different air velocities. The obtained moisture ratio values have been applied to six different moisture ratio models in the literature. The model having the highest correlation coefficient (R) and the lowest Chi-square (χ²) value has been determined as the most relevant one for each seeded grape drying status.     

Physical Changes in Bamboo (Bambusa phyllostachys) Shoot During Hot Air Drying: Shrinkage, Density, and Porosity

The apparent density of bamboo (Bambusa phyllostachys) shoot was investigated at a moisture content range of 10-92% wet basis by weighing the product in air and determining the buoyancy force in toluene. An analysis of variance (ANOVA) unveiled that moisture content significantly affected apparent density at 95% confidence level. The true density of the bamboo shoot was determined by grinding the dried sample to exclude all internal pores and using density bottles. The experimental data fitted well to a general density equation for fruits and vegetables proposed by Lozano et al. (1983) and to a second order polynomial (SOP) model. The internal porosity generated during drying varied in a nonlinear (quadratic) fashion. Shrinkage at different moisture content levels was measured by evaluating the dimensional changes in bamboo shoot slabs (5.0 × 3.2 × 1.8 cm) by drying in a convection oven and a tray dryer operating at 70°C and 7.2% relative humidity. Shrinkage was affected statistically by decreasing moisture content at 95% confidence level. Shrinkage was compared with available models in literature and found to be oriented based on fiber direction and distinctly different from the isotropic volume change in fruits and vegetables.     

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

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.     

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.     

PAPER DRYING: A STRATEGY FOR HIGHER MACHINE SPEED. II. IMPINGEMENT AIR DRYING FOR HYBRID DRYER SECTIONS

For printing and heavier grades, combining cylinder and impingement air drying into a multiple technique dryer section can enable higher productivity through higher machine speed. The large differences in local moisture content and temperature across the sheet which develop quickly under high intensity impingement drying provide the potential for reducing drying time by sheet reversal between impingement drying cylinders. This advantage was determined experimentally under low intensity impingement drying conditions. Use of the micro-scale based McGill dryer simulator for determining the advantage from sheet reversal between impingement drying cylinders was demonstrated for both laboratory and industrial impingement drying intensities. For completing the drying of 205 g/m² linerboard from 0.3 to 0.5 kg/kg dry under 400°C air jets of Re 20000, drying time is about 30% less with sheet reversal between two impingement drying cylinders than for a single, larger diameter cylinder. This extensively validated dryer simulator enables determining advantageous design specifications and operating conditions for hybrid dryer sections involving combinations of cylinder and impingement air drying, a concept with potential to become common industrial practice.