Study On Drying Process Of Rice Kernal Based On Glass Transition Theory

A high incidence of open crack formation in rough rice as a heat sensitive material dried at inappropriate temperatures and speeds has great impact on the polished rice rate and edible quality,and therefore its economic value.As a result,the rate of open crack formation was used as a standard for measuring drying techniques in this paper,experiments of constant-temperature hot air drying at different temperatures conditions are conducted and rough rice open crack rate's relationships with cooling duration and moisture content are analyzed.Principles of open crack formation are explored with the help of glass transition theory.Results indicate that a low open crack rate of rough rice fresh out of drying will increase in value as the cooling time lasts before staying stable until cooling time outlasts 24 hours.Open crack rate keeps stable for rough rice with a wet base percentage greater than 18%while increase sharply with a percentage lower than 18%.Open crack rate increments are no greater than 3%when drying temperature stays below or equal to 45 ?.With such results above,further experiment of inconstant-temperature hot air drying on a temperature-dropping basis is conducted.Turning point for temperature being when wet base percentage reaches 18 degrees.Results show that drying parameters are optimal for the 60-45? temperature group with open crack rate is 4%and drying temperature is 295min in this experiment.Experiment of inconstant-temperature hot air drying on a temperature-rising basis is also investigated and compared with that on a temperature-dropping basis.Results show that the temperature-dropping group has an advantage over the temperature-rising group.Vacuum drying experiments at different drying temperature conditions are conducted to show that a increment in open crack rate is no greater than 3%as the temperature stays below or equal to 40 ?.Microwave drying experiments at different power are also conducted to analyze the relationship between open crack rate,microwave power and moisture content.Results show a high open crack rate to microwave drying and that the moisture content value corresponding to the turning point of open crack characteristic curve is positively correlatedto the temperature.Considering the relationships between open crack rate and water content in microwave drying experiment,a combined microwave-hot air drying experiment is also conducted with a result turning out not ideal.For comprehensive comparisons between various drying techniques for rough rice,a natural cooling and drying experiment is also carried out.Drying duration and increased value in open crack rate are set as standards in the paper to conduct various drying experiments and to compare those with turn-out open crack rates increasing by no more than 3%in value.Conclusions:drying techniques in descending order of optimal results are constant-temperature vacuum drying at 40 ? with open crack rate is 4%and drying temperature is 285min,60-45? temperature group of inconstant-temperature hot air drying with open crack rate is 4%and drying temperature is 295min and constant-temperature hot air drying at 45? with open crack rate is 3%and drying temperature is 405min.