Browsing by Author "Fernando, JAKM"

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item: Thesis-Full-text
Drying kinetics of coir pith and the performance in flash drying
Fernando, JAKM; Amarasinghe, ADUS; Jayasundara, JMMA
Drying and retting can be identified as the most important factors affecting the quality variations in dried coir pith which directly affects the final quality of compressed coir pith products. A pilot scale flash dryer was designed and fabricated to examine the effect of hot air temperature and velocity on the drying behavior of coir pith. Hot air drying was carried out to examine the drying kinetics by allowing the coir pith particles to fluidize and circulate inside the drying chamber. The physico-chemical properties of volume expansion ratio (VE), water retention capacity (WRC), bulk density, pH and electrical conductivity (EC) of compressed coir pith discs were measured. Scanning electron microscopy was used to analyze the microstructures of dried coir pith. The results were compared with the two other drying techniques namely sun drying and oven drying. The effect of time duration for retting and the method of retting the coconut husk were also examined. The optimum temperature for coir pith drying was found to be 140 C. The most suitable range of particle size and the range of moisture content in dried coir pith were identified as 0.5 – 6.3 mm and 12 - 23% (w/w, dry basis) respectively. The VE, WRC, pH and EC of coir pith dried in the flash dryer at the optimum temperature of 140 C was found to be 5.01 ± 0.21, 4.02 ± 0.10 (w/w), 5.95 ± 0.08 and 330 ± 16 μs/cm respectively. These values were comparable with those of the sundried coir pith. Oven drying caused rupturing the cells and case hardening of coir pith. Similar effect was observed with temperatures > 140 C for hot air drying and flash drying. VE and WRC of coco discs were found to increase significantly, pH to change marginally and EC to drop significantly with the increase of retting time. The effective moisture diffusivity was found to increase from 1.18 × 10-8 to 1.37 × 10-8 m2/s with the increase of hot air velocity from 1.4 to 2.5 m/s respectively. Correlation analysis and residual plots were used to determine the adequacy of existing mathematical models for describing the drying behavior of coir pith using hot air. A new mathematical model was proposed and it gave the best correlation between observed and predicted moisture ratio with high value of coefficient of determination (R2) and lower values of root mean square error (RMSE), reduced chi-square (χ2) and mean relative deviation (E %). Wang and Singh model and Linear model were also found to be adequate for accurate prediction of drying behavior of coir pith. Since the experimental setup of this study closely simulated the particle motion and heat and mass transfer in flash drying due to induced fluidization and circulation, the new model has a great potential in designing and modeling of the flash drying of coir pith.
item: Conference-Abstract
Flash drying of coir pith as an alternative to sun drying
Fernando, JAKM; Amarasinghe, ADUS; Jayarathna, WAR; Narayana, M
Flash drying of coir pith as an alternative to sun drying was investigated. 5 kg of Coir pith was flash dried within the temperature range 120 - 160 °C, at 10 °C intervals using gas velocities 26.1 ± 0.2 ms-1 and 32.0 ± 0.15 ms-1 for multiple cycles. The drying efficiency and quality parameters of dried coir pith and coco discs were determined and compared with sun drying. Drying temperature of 140 °C was found to give the best quality coco discs with optimum quality parameters; volume expansion ratio 5.01 ± 0.21, water retention capacity 4.02 ± 0.10 (w/w), pH 5.95 ± 0.08 and electrical conductivity 330 ± 16 μs/cm. These values were comparable with the quality parameters obtained with natural sun drying. The time required for flash drying was only about 12 ± 1 mins whereas time required for sun drying was 9.1 ± 2 hrs. The Microbial count of undried coir pith, 4.23×106 CFU/g, was reduced by 99% and 89% for flash drying and sun drying respectively. Specific moisture extraction rate (SMER) for flash dryer was found to be 0.399 ± 0.012. The results of this study suggests flash drying as a good alternative to sun drying for moisture removal from coir pith.
item:
Influence of pre-processing and coir extraction methods on the physicochemical properties and microbial contamination of coir pith
(2015-06-12) Fernando, JAKM; Amarasinghe, ADUS; Jayasundera, JMMA; ;
Particle size, pH, electrical conductivity, water retention capacity and drying characteristic of coir pith' determine the quality of the final product. These parameters may influence by the time duration for retting, method of crushing and the mode of mechanical extraction. Two types of fiber extraction methods namely Ceylon Drum method and D1 method were examined. Ceylon Drum gave higher percentage of fine particles while D1 method gave higher percentage of medium size particles. Higher fraction of fine particles could be obtained by increasing the retting time. Retting time was significantly lowered by crushing the husk. However, it resulted in lower percentage of fine particles and significantly high percentage of medium particles (more than 75%) suggesting a possible mechanism for obtaining required particle sizes through a combination of crushing and retting. Retting increased the initial moisture content of coir pith but the drying characteristic was not significantly altered as compared to water spraying. Water retention capacity ^(5.75 ± 0.67), volume expansion (5.70± 0.46), pH (5.83 ± 0.19) and electrical conductivity (540 ± 152 W ps/cm) were similar among the sundried coir pith obtained from different pre-processing methods. Initial microbial count was significantly high for retted coir pith but the retained microbial strains