Heat and mass exchange coefficients

The heat and mass exchange coefficients aH and aH were taken constant in ( 3.50). However, they often depend on local flow circumstances. Their simplified description is given in what follows. 

The heat and mass exchange coefficients are determined as the proportionality coefficients in the Newton laws (1.18) between the heat delivery into the flow Ih, Wt (admixture mass delivery IE, kg/s) and the temperature difference (concentration difference) multiplied by the value of the surface area S o of the whole body. It is known 

The heat and mass transfer coefficients are normally expressed as criterial relations for the thermal and diffusion Nusselt numbers 

The local Reynolds number Re = 2rU/v used in the studies of EPRs varies between 100 and 2 000, so that one often takes n = 1/3, m = 1/2, and C = 0.6. The Prandtl and Schmidt criteria express the properties of interacting substances. For the systems heat in air and water vapour in air , they are Pr = (vp1cp)/A 0.7 and Sc = v/D 0.6 [60], Having transformed these basic empirical relations, Berman [60] suggested a relation for spraying systems aE = 3 U/2r, provided the local velocity U is taken in m/s and the droplet diameter 2r in m. The latter was used in the following performance ofSCSs. 

The transportation of heat and a substance in the air flow is governed by the Fourier and Fick laws (3.55). The thermal conductivity coefficient Dh/(P Cp) and the mass transfer coefficient DE, both possessing the dimension m2/s, determine the intensity 

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