The drying of fibrous and porous-granular materials in a hot airstream

Kirkwood, Kenneth C (1962) The drying of fibrous and porous-granular materials in a hot airstream. PhD thesis, University of Glasgow.

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Before a hot-air drier can be designed to dry a given material the effects of loading of material per unit area of the driers airflow air temperature and humidity on the drying time of the material must be estimated accurately. Since such estimates cannot be made from theoretical caisidorations aloe, the effects of the vario factors on the dying time of a material are usually estimated from the results of a series of drying tests in which each factor in turn in varied while the rest are kept constant This "classical" method of eaperimentation of studying each factor in turn assumes that the effect of each factor acts independently of the other factors. There is howevero no reason why this should be so9 and the magnitude of the effect of a factor estimated by this method may be a fanction of the arbitrary constant values chosen for the other *Mors If ouch interactions between the effects of the various factors are presento the classical experiment cannot detect them and all give estimates of the drying time of a material which will be in error, to a degree depending on the values of the factord chosen and on the magnitude of the intoractions such interactions.could be detected by using a programme of drying tests bawd on the factoxial method of experimentation in which the ofgoot of eeoh factor is valuated over the nap 00 valuesstadied of each of the other factors. As gar as in knovag this method of oupori lavaUtion hau.noli boon wooviono.w applied to 6'41 pvallomo. lt AD employed in the present work to examine the possibility of there being interactions between the effects of loading of materials airflow air temperature and humidity on the drying times of porous-granular9 and fibrous materials in cross-circulation and through-circulation driers. The porous-granular materials studied were inch long inch diameter porous-ceramic granules and to it inch mesh coke; the fibrous material was brewers. spent-grain. The approximate ranges of the various factors studied were Air Temperature 120 to 210P Air Humidity 0.01 to 0.08 lb water/lb dry air Airflow 4 to 13 lb dry air/Ogoft. drier area) (min) Loading of single layer to inch layer (cross-Material circulation drier tests) single layer to 4 inch layer (through-circulation drier tests) A preliminary two-lovol factorial experiment involving sixteen drying tests covering all combinations of the extreme values of the ranges of the various factors was done on each material; the drying behaviour of the material in each drying test was characterized by the constant drying rate did lb water/(lb dry selid)009 the critical moisture content W0 lb water/lb dry solid9 and a Er fin Constant C (the slope of a plot of moisture content W against the logarithm of tha drying time in minutes 0 described by the oquation C log o 0 rt, constant. A fractional three.levol factorial experiment involving twenty-eight to thirty-six additional tests Imo designed to elucidate any eneoto or interactions of 1oadinag aivglovg air temperature and humidity on III We and 0 which appoaro A9 gam mt aw analysis of the values of it,69 W and C obtained in the preliminary sixteen test at to be significant. The third level of each factor studied in this experiment was the median of the factor range. The results of the fractional three-level factorial experiments on the throe materials dried in the cross-circulation and through-circulation driers - involving a total of three hundred drying tests - V are summa: and in Crapo showing the variations in logio -669 We and C with changes in loading airflowo air temperature and humidity. From these graphs the drying times of the various materials in the cress circulation drier could be estimated within 16 of the experimental values and the drying times in the through, ciroulation drier within 10S. Interactions between the effects of the various factors on W Wo and C were found to be small except the interaction between W, the effects of air temperature and humidity on ap oho magnitude of this interaction corresponded with that predicted by the existing theory of the constant drying-rate period. From experience gained in the present imvostigation a 1;oatative design is presented for a small fractional throe-level factorial experiment suitable for obtaining data from which predictions accurate to within 30% may be made of the drying times of porous-vanular and fibrous materials in cross-circulation and through-circulation driers. The experiment involves eleven drying, tests which may be performed using an airstream of atmospheric humidity.

Item Type: Thesis (PhD)
Qualification Level: Doctoral
Additional Information: Adviser: T J Mitchell
Keywords: Thermodynamics
Date of Award: 1962
Depositing User: Enlighten Team
Unique ID: glathesis:1962-73348
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 14 Jun 2019 08:56
Last Modified: 14 Jun 2019 08:56

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