Mass diffusivity

Mass diffusivity

Mass diffusivity, also known as diffusion coefficient, is a measure of the ability of a substance to diffuse through a medium. It is represented by the symbol D and is defined as the proportionality constant in the Fickian equation, which relates the rate of flow of a substance through an area to the concentration gradient and area. The Péclet number, which is the ratio of convective and diffusive transport, is also dependent on the mass diffusivity.From: The Thermal Human Body [2019], Microfluidic production of mRNA-loaded lipid nanoparticles for vaccine applications [2022]

Basic Thermal Physics: Heat Exchange and Infrared Radiation

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Published in Kurt Ammer, Francis Ring, The Thermal Human Body, 2019

Kurt Ammer, Francis Ring

However, thermal diffusivity must be differentiated from mass diffusivity D, which is the constant of proportionality relating the rate of diffusion of a gas to the gradient of its concentration in another gas, e.g. water vapour in air [4]. If the rate of diffusion of mass is ṁ· [kg·s−1] in a direction specified by a coordinate y [m] and if the concentration over a plane at a given value of y is p [kg·m−3], the rate of flow through an area A is given by the Fickian equation,

Microfluidic production of mRNA-loaded lipid nanoparticles for vaccine applications

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Published in Expert Opinion on Drug Delivery, 2022

Carolina Lopes, Joana Cristóvão, Vânia Silvério, Paulo Roque Lino, Pedro Fonte

The Péclet number, given by Pe = UL/D, where D is the mass diffusivity, indicates ratio between convective and diffusive transport. A small Pe indicates a diffusively dominated flow distribution (poor mixing), while if Pe >100, diffusive mixing plays a secondary role in the transport in comparison with convection (increasingly more efficient mixing).

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Basic Thermal Physics: Heat Exchange and Infrared Radiation

Microfluidic production of mRNA-loaded lipid nanoparticles for vaccine applications