MODELING AND NUMERICAL ANALYSIS OF SINGLE
DROPLET DRYING
DALMAZ, Nesip
M.Sc., Department of Chemical Engineering
Supervisor: Prof. Dr. H. Ö / nder Ö / ZBELGE
Co-Supervisor: Asst. Prof. Dr. Yusuf ULUDAg
August 2005, 120 pages
A new single droplet drying model is developed that can be used as a part of
computational modeling of a typical spray drier. It is aimed to describe the drying
behavior of a single droplet both in constant and falling rate periods using receding
evaporation front approach coupled with the utilization of heat and mass transfer
equations. A special attention is addressed to develop two different numerical
solution methods, namely the Variable Grid Network (VGN) algorithm for constant
rate period and the Variable Time Step (VTS) algorithm for falling rate period, with
the requirement of moving boundary analysis. For the assessment of the validity of
the model, experimental weight and temperature histories of colloidal silica (SiO2),
skimmed milk and sodium sulfate decahydrate (Na2SO4& / #8901 / 10H2O) droplets are
compared with the model predictions. Further, proper choices of the numerical
parameters are sought in order to have successful iteration loops.
The model successfully estimated the weight and temperature histories of colloidal
silica, dried at air temperatures of 101oC and 178oC, and skimmed milk, dried at air
temperatures of 50oC and 90oC, droplets. However, the model failed to predict both
the weight and the temperature histories of Na2SO4& / #8901 / 10H2O droplets dried at air
temperatures of 90oC and 110oC. Using the vapor pressure expression of pure water,
which neglects the non-idealities introduced by solid-liquid interactions, in model
calculations is addressed to be the main reason of the model resulting poor
estimations. However, the developed model gives the flexibility to use a proper
vapor pressure expression without much effort for estimation of the drying history of
droplets having highly soluble solids with strong solid-liquid interactions.
Initial droplet diameters, which were calculated based on the estimations of the
critical droplet weights, were predicted in the range of 1.5-2.0 mm, which are in
good agreement with the experimental measurements.
It is concluded that the study has resulted a new reliable drying model that can be
used to predict the drying histories of different materials.
| Identifer | oai:union.ndltd.org:METU/oai:etd.lib.metu.edu.tr:http://etd.lib.metu.edu.tr/upload/12606487/index.pdf |
| Date | 01 August 2005 |
| Creators | Dalmaz, Nesip |
| Contributors | Ozbelge, H. Onder |
| Publisher | METU |
| Source Sets | Middle East Technical Univ. |
| Language | English |
| Detected Language | English |
| Type | M.S. Thesis |
| Format | text/pdf |
| Rights | To liberate the content for public access |
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