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In engineering, the mass transfer coefficient is a diffusion rate constant that relates the mass transfer rate, mass transfer area, and concentration change as driving force: [1] = ˙ Where: is the mass transfer coefficient [mol/(s·m 2)/(mol/m 3)], or m/s
The heat transfer coefficient is often calculated from the Nusselt number (a dimensionless number). There are also online calculators available specifically for Heat-transfer fluid applications. Experimental assessment of the heat transfer coefficient poses some challenges especially when small fluxes are to be measured (e.g. < 0.2 W/cm 2). [1] [2]
where ˙ is the heat transferred per unit time, A is the area of the object, h is the heat transfer coefficient, T is the object's surface temperature, and T f is the fluid temperature. [8] The convective heat transfer coefficient is dependent upon the physical properties of the fluid and the physical situation.
D is mass diffusivity (m 2 s −1) h is the convective mass transfer film coefficient (m s −1) Using dimensional analysis, it can also be further defined as a function of the Reynolds and Schmidt numbers: = (,) For example, for a single sphere it can be expressed as [citation needed]:
˙ is the rate of heat transfer out of the body (SI unit: watt), ˙ = is the heat transfer coefficient (assumed independent of T and averaged over the surface) (SI unit: W/(m 2 ⋅K)), is the heat transfer surface area (SI unit: m 2),
h = convection heat transfer coefficient; G = mass flux of the fluid; ρ = density of the fluid; c p = specific heat of the fluid; u = velocity of the fluid; It can also be represented in terms of the fluid's Nusselt, Reynolds, and Prandtl numbers: = where Nu is the Nusselt number;
Where q” is the heat flux, is the thermal conductivity, is the heat transfer coefficient, and the subscripts and compare the surface and bulk values respectively. For mass transfer at an interface, we can equate Fick's law with Newton's law for convection, yielding:
Convective heat transfer, or simply, convection, is the transfer of heat from one place to another by the movement of fluids, a process that is essentially the transfer of heat via mass transfer. The bulk motion of fluid enhances heat transfer in many physical situations, such as between a solid surface and the fluid. [10]