Quality of dried product depends on the temperature and velocity at each position in the dryer.Simultaneous microscopic and macroscopic simulation on Computational Fluid Dynamic(CFD)is a general problem of fixed bed d...Quality of dried product depends on the temperature and velocity at each position in the dryer.Simultaneous microscopic and macroscopic simulation on Computational Fluid Dynamic(CFD)is a general problem of fixed bed dryer consisting of water transportation in porous media and dynamic flow of hot air in the dryer.Simplifying the dryer by assuming the packed bed as porous volume,viscous and inertial resistances(1/α and C_(2))are necessary for calculating the pressure drop and velocity change in the bulk.Comparing theDP/L of the standard packing with experimental results,the porosity and resistance parameters can be estimated.Simulation of unmodified,adding false floor and invest mesh,and insulating the dryer wall are used for validation with previous results.Adding the round holed sieve as false floor and invert mesh can produce better profile but cannot obtain uniform distribution.Air velocity distribution shows similar but the calculating temperature is higher than that from the experiment.By analysis of thermal efficiency of dryer without insulator,the heat loss rates with flue gas and heat flux at wall are in the range 14%-17%and 5.5%-7.3%.Integrating with single fruit or thin layer drying kinetic in the future,the CFD simulation can be used for optimal design of fixed bed dryer.展开更多
Dried longan fruit has become an important export product of Thailand.Knowledge about drying kinetics is essential to optimize the drying process.In this study,drying kinetics of unpeeled longan fruits was investigate...Dried longan fruit has become an important export product of Thailand.Knowledge about drying kinetics is essential to optimize the drying process.In this study,drying kinetics of unpeeled longan fruits was investigated by varying the parameters as follows:air temperature 50~90℃,relative humidity 4%~20%,air velocity 0.2~0.5 m/s,and size of the fruits.The drying curves of longan fruit,dried in a single layer,were strongly affected by the temperature of the drying air and fruit size but less dependent on relative humidity and velocity of the drying air.Eight single-layer drying models were selected from literature to identify suitable ones for fitting moisture ratio curves to data obtained from the drying experiments.Both,the proportional and exponential coefficient of drying time in the‘Page’model could be given in a generalized function for each of the investigated drying parameters.Moreover,the two coefficients could be correlated to all drying parameters simultaneously.This allowed establishing a generalized‘Page’model for estimating drying curves for any value of temperature,fruit size,relative humidity and air velocity within the range of performed experiments.The analysis also revealed an inner correlation between the two‘Page’coefficients,which opens new doors for further research on the application of the‘Page’model for describing drying processes.展开更多
基金This work was financed by Department of Material Science and Engineering and Faculty of Engineering and Industrial Technology,Sipakorn Univesity,THAILAND.
文摘Quality of dried product depends on the temperature and velocity at each position in the dryer.Simultaneous microscopic and macroscopic simulation on Computational Fluid Dynamic(CFD)is a general problem of fixed bed dryer consisting of water transportation in porous media and dynamic flow of hot air in the dryer.Simplifying the dryer by assuming the packed bed as porous volume,viscous and inertial resistances(1/α and C_(2))are necessary for calculating the pressure drop and velocity change in the bulk.Comparing theDP/L of the standard packing with experimental results,the porosity and resistance parameters can be estimated.Simulation of unmodified,adding false floor and invest mesh,and insulating the dryer wall are used for validation with previous results.Adding the round holed sieve as false floor and invert mesh can produce better profile but cannot obtain uniform distribution.Air velocity distribution shows similar but the calculating temperature is higher than that from the experiment.By analysis of thermal efficiency of dryer without insulator,the heat loss rates with flue gas and heat flux at wall are in the range 14%-17%and 5.5%-7.3%.Integrating with single fruit or thin layer drying kinetic in the future,the CFD simulation can be used for optimal design of fixed bed dryer.
基金Deutsche Forschungsgemeinschaft(DFG)within the collaborative research program"Sustainable rural development in mountainous regions of Southeast Asia"(SFB 564)。
文摘Dried longan fruit has become an important export product of Thailand.Knowledge about drying kinetics is essential to optimize the drying process.In this study,drying kinetics of unpeeled longan fruits was investigated by varying the parameters as follows:air temperature 50~90℃,relative humidity 4%~20%,air velocity 0.2~0.5 m/s,and size of the fruits.The drying curves of longan fruit,dried in a single layer,were strongly affected by the temperature of the drying air and fruit size but less dependent on relative humidity and velocity of the drying air.Eight single-layer drying models were selected from literature to identify suitable ones for fitting moisture ratio curves to data obtained from the drying experiments.Both,the proportional and exponential coefficient of drying time in the‘Page’model could be given in a generalized function for each of the investigated drying parameters.Moreover,the two coefficients could be correlated to all drying parameters simultaneously.This allowed establishing a generalized‘Page’model for estimating drying curves for any value of temperature,fruit size,relative humidity and air velocity within the range of performed experiments.The analysis also revealed an inner correlation between the two‘Page’coefficients,which opens new doors for further research on the application of the‘Page’model for describing drying processes.
