Surface exchange

Scraped-surface exchangers are particularly suitable for heat transfer with crystalhzation, heat transfer with severe folding of surfaces, heat transfer with solvent extraction, and heat transfer of high-viscosity fluids. They are extensively used in paraffin-wax plants and in petrochemical plants for ciystallization. 

This assumes that the gas-solid exchange kinetics at the interface is rapid. When this process affects the exchange kinetics significantly dieii analysis of concentrations layer by layer in die diffused sample is necessaty. This can be done by the use of SIMS (secondary ion mass spectrometry) and the equation used by Kihier, Steele and co-workers for this diffusion study employs a surface exchange component. 

Lindberg SE, Meyers TP, Taylor GE, Turner RR, Schroeder WH. 1992. Atmosphere/surface exchange of mercury in a forest results of modeling and gradient approaches. J Geophys Res 97 2519-2528. 

The result implies that both oxygen vacancies and electrons are important for the surface exchange process. 

Oxygen Diffusion Coefficient (D ), Oxygen Surface Exchange Coefficient (Ar), and Oxygen Ionic Conductivity (tr,) of LaMn03-Based Oxides Measured by SIMS Technique... 

H2 production from ethanol (as well as methanol) employs these methodologies either as such or after slight modifications, especially in the ATR process, wherein a separate combustion zone is usually not present (Scheme 3). A mixture of ethanol, steam and 02 with an appropriate ethanol steam 02 ratio directly enters on the catalyst bed to produce syngas at higher temperature, around 700 °C.18,22 The authors of this review believe that under the experimental conditions employed, both steam reforming and partial oxidation could occur on the same catalyst surface exchanging heats between them to produce H2 and carbon oxides. The amount of 02 may be different from what is required to achieve the thermally neutral operation. Consequently the reaction has been referred to as an oxidative steam reforming... 

Harriott, P. Chem. Eng. Prog. Symp. Ser. No. 29, 55 (1959) 137-9. Heat transfer in scraped surface exchangers. 

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