IDENTIFICATION OF MATHEMATICAL MODEL COEFFICIENTS IN THE ANALYSIS OF THE HEAT AND MASS TRANSPORT IN WOOD

2000 ◽  
Vol 18 (8) ◽  
pp. 1697-1708 ◽  
Author(s):  
Jerzy Weres ◽  
Wieslaw Olek ◽  
Ryszard Guzenda
Keyword(s):  
Mathematical Model ◽  
Mass Transport ◽  
Heat And Mass Transport

Computer Simulation of the Response of Amperometric Biosensors in Stirred and non Stirred Solution

2003 ◽  
Vol 8 (1) ◽  
pp. 3-18 ◽  
Author(s):  
R. Baronas ◽  
F. Ivanauskas ◽  
J. Kulys
Keyword(s):  
Mathematical Model ◽  
Computer Simulation ◽  
Finite Difference ◽  
Mass Transport ◽  
Enzyme Reaction ◽  
Analyte Concentration ◽  
Amperometric Biosensors ◽  
Finite Difference Technique ◽  
Enzyme Layer ◽  
Biosensor Response

A mathematical model of amperometric biosensors has been developed to simulate the biosensor response in stirred as well as non stirred solution. The model involves three regions: the enzyme layer where enzyme reaction as well as mass transport by diffusion takes place, a diffusion limiting region where only the diffusion takes place, and a convective region, where the analyte concentration is maintained constant. Using computer simulation the influence of the thickness of the enzyme layer as well the diffusion one on the biosensor response was investigated. The computer simulation was carried out using the finite difference technique.

Measurement and Modeling of Latent Heat Release During Freezing of Aqueous Solutions in a Small Container

2000 ◽  
Author(s):  
Ramachandra V. Devireddy ◽  
John C. Bischof ◽  
Perry H. Leo ◽  
John S. Lowengrub
Keyword(s):  
Mass Transport ◽  
Heat Release ◽  
Latent Heat ◽  
Pure Water ◽  
Heat Of Fusion ◽  
Freezing Process ◽  
Latent Heat Release ◽  
Aqueous Systems ◽  
Heat And Mass Transport ◽  
Latent Heat Of Fusion

Abstract The latent heat of fusion, ΔHf of a cryobiological medium (a solute laden aqueous solution) is a crucial parameter in the cryopreservation process. The latent heat has often been approximated by that of pure water (∼ 335 mJ/mg). However, recent calorimetric (DSC - Pyris 1) measurements suggest that the actual magnitude of latent heat of fusion during freezing of solute laden aqueous systems is far less. Fourteen different pre-nucleated solute laden aqueous systems (NaCl-H2O, Phosphate Buffered Saline or PBS, serum free RPMI, cell culture medium, glycerol and Anti Freeze Protein solutions) were found to have significantly lower ΔHf than that of pure water (Devireddy and Bischof, 1998). In the present study additional calorimetric experiments are performed at 1, 5 and 20 °C/min in five representative cryobiological media (isotonic or 1× NaCl-H2O, 10× NaCl-H2O, 1× PBS, 5× PBS and 10× PBS) to determine the kinetics of ice crystallization. The temperature (T) and time (t) dependence of the latent heat release is measured. The experimental data shows that at a fixed temperature, the fraction of heat released at higher cooling rates (5 and 20 °C/min) is lower than at 1 °C/min for all the solutions studied. We then sought a simple model that could predict the experimentally measured behavior and examined the full set of heat and mass transport equations during the freezing process in a DSC sample pan. The model neglects the interaction between the growing ice crystals and is most appropriate during the early stages of the freezing process. An examination of the coefficients in the heat and mass transport equations shows that heat transport occurs much more rapidly than solute transport. Hence, the full model reduces to one in which the temperature profile is constant in space while the solute concentration profile obeys the full time and space dependent diffusion equation. The model reveals the important physical parameters controlling the mass transport at the freezing interface and further elucidates the experimental results, i.e. the temperature and time dependence of the latent heat release.

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