تحليل انرژي و اكسرژي در يك خشك كن خورشيدي بر مبناي نتايج مدل سازي رياضي

چكيده انگليسي :

Energy and Exergy Analysis of a Solar Dryer Based on Mathematical Modeling Samaneh Sami Email s sami@ce iut ac ir 7 03 2011 Department of Chemical Engineering Isfahan University of Technology Isfahan 84156 83111 Iran Degree M Sc Language Farsi Supervisors N Etesami netesami@cc iut ac ir A Rahimi rahimi@eng ui ac ir Abstract In present study the performance of an indirect solar cabinet dryer has been taken into consideration from different aspects For this purpose at the first a dynamic mathematical model was developed to predict the behavior of two main parts of system including the solar collector and the drying chamber For this purpose using conservation law of heat and mass transfer and considering the physical phenomena occurring in a solar dryer the governing equations were derived and solved numerically The predicted results were compared with the two sets of different and valuable experimental data reported in previous researches The comparison between model results and corresponding experimental data shows that the average error in prediction of moisture content of drying solid outlet air temperature of drying chamber and solid temperature was 8 2 8 2 and 6 2 respectively These results reveal that the developed model could be used successfully for performance analysis of a cabinet solar dryer in unsteady state operation conditions Furthermore the effects of some operating parameters on the performance and efficiency of the dryer were investigated The results indicate that for drying purposes the designed air flow rate would be in the range of about 0 0275 0 0385 kg m2s This range of flow rate gives an outlet temperature suitable for most agricultural drying applications because many food materials are sensitive to high temperature Also the corresponding efficiency is considered reasonable in this range In the second part of this study by applying the concepts of energy and exergy analysis a microscopic energy and exergy analysis for an indirect solar cabinet dryer was carried out To this end appropriate energy and exergy models are developed and using the predicted values for temperature and enthalpy of gas stream and the temperature enthalpy and moisture content of the drying solid the energy and exergy efficiencies are estimated and the results were compared to that of the existing experimental data The results show that in spite of high energy efficiency the indirect solar cabinet dryer has relatively low exergy efficiency due to the entropy production from process irreversibilities Results show that the maximum exergy losses are in midday Also the minimums of total exergy efficiency are 32 3 and 47 2 on the first and second days respectively The maximum value for the outlet air temperature was 69 oC In this temperature the maximum outlet exergy and energy of collector are 2 5 kW and 1 12 kW respectively Similarly the effects of some operating parameters including length and surface of the collector and air flow rate were investigated on the destruction and efficiency of the exergy In the last part of the present study a mathematical model based on an economical objective function named relative cost was developed to optimize the solar dryer performance For this purpose all of the structural parameters and operation conditions that can be affecting on the objective function were identified Then the effects of them were verified using logical mathematical relations Results show that the optimum ranges for initial moisture content air mass flux length and surface area of the solar collector are 9 10 d b 0 03 0 045 kg m2 s longer than 2 5 m and 2 5 3 m2 respectively Key words Solar Cabinet Dryer Mathematical Modeling Exergy Analysis Energy Analysis Optimization

سامي، سمانه

تحليل انرژي و اكسرژي در يك خشك كن خورشيدي بر مبناي نتايج مدل سازي رياضي

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